Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Hilcorp Alaska, LLC Production Drilling Support in Cook Inlet, Alaska, 60164-60202 [2024-16112]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 89, Number 142 (Wednesday, July 24, 2024)]
[Notices]
[Pages 60164-60202]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-16112]



[[Page 60163]]

Vol. 89

Wednesday,

No. 142

July 24, 2024

Part III





Department of Commerce





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National Oceanic and Atmospheric Administration





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Takes of Marine Mammals Incidental to Specified Activities; Taking 
Marine Mammals Incidental to Hilcorp Alaska, LLC Production Drilling 
Support in Cook Inlet, Alaska; Notice

Federal Register / Vol. 89 , No. 142 / Wednesday, July 24, 2024 / 
Notices

[[Page 60164]]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XD960]


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to Hilcorp Alaska, LLC Production 
Drilling Support in Cook Inlet, Alaska

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and 
Atmospheric Administration (NOAA), Commerce.

ACTION: Notice; proposed incidental harassment authorization; request 
for comments on proposed authorization and possible renewal.

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SUMMARY: NMFS has received a request from Hilcorp Alaska, LLC (Hilcorp) 
for authorization to take marine mammals incidental to production 
drilling support activities in Cook Inlet, Alaska. Pursuant to the 
Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its 
proposal to issue an incidental harassment authorization (IHA) to 
incidentally take marine mammals during the specified activities. NMFS 
is also requesting comments on a possible one-time, 1-year renewal that 
could be issued under certain circumstances and if all requirements are 
met, as described in Request for Public Comments at the end of this 
notice. NMFS will consider public comments prior to making any final 
decision on the issuance of the requested MMPA authorization and agency 
responses will be summarized in the final notice of our decision.

DATES: Comments and information must be received no later than August 
23, 2024.

ADDRESSES: Comments should be addressed to Jolie Harrison, Chief, 
Permits and Conservation Division, Office of Protected Resources, 
National Marine Fisheries Service and should be submitted via email to 
[email protected]. Electronic copies of the application and 
supporting documents, as well as a list of the references cited in this 
document, may be obtained online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas. In case of problems accessing these documents, please call the 
contact listed below.
    Instructions: NMFS is not responsible for comments sent by any 
other method, to any other address or individual, or received after the 
end of the comment period. Comments, including all attachments, must 
not exceed a 25-megabyte file size. All comments received are a part of 
the public record and will generally be posted online at https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas without change. All personal 
identifying information (e.g., name, address) voluntarily submitted by 
the commenter may be publicly accessible. Do not submit confidential 
business information or otherwise sensitive or protected information.

FOR FURTHER INFORMATION CONTACT: Reny Tyson Moore, Office of Protected 
Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

    The MMPA prohibits the ``take'' of marine mammals, with certain 
exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 
et seq.) direct the Secretary of Commerce (as delegated to NMFS) to 
allow, upon request, the incidental, but not intentional, taking of 
small numbers of marine mammals by U.S. citizens who engage in a 
specified activity (other than commercial fishing) within a specified 
geographical region if certain findings are made and either regulations 
are proposed or, if the taking is limited to harassment, a notice of a 
proposed IHA is provided to the public for review.
    Authorization for incidental takings shall be granted if NMFS finds 
that the taking will have a negligible impact on the species or 
stock(s) and will not have an unmitigable adverse impact on the 
availability of the species or stock(s) for taking for subsistence uses 
(where relevant). Further, NMFS must prescribe the permissible methods 
of taking and other ``means of effecting the least practicable adverse 
impact'' on the affected species or stocks and their habitat, paying 
particular attention to rookeries, mating grounds, and areas of similar 
significance, and on the availability of the species or stocks for 
taking for certain subsistence uses (referred to in shorthand as 
``mitigation''); and requirements pertaining to the monitoring and 
reporting of the takings. The definitions of all applicable MMPA 
statutory terms cited above are included in the relevant sections 
below.

National Environmental Policy Act

    To comply with the National Environmental Policy Act of 1969 (NEPA; 
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A, 
NMFS must review our proposed action (i.e., the issuance of an IHA) 
with respect to potential impacts on the human environment. 
Accordingly, NMFS is preparing an Environmental Assessment (EA) to 
consider the environmental impacts associated with the issuance of the 
proposed IHA. NMFS' draft EA will be made available at https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas at the time of publication of this 
notice. We will review all comments submitted in response to this 
notice prior to concluding our NEPA process or making a final decision 
on the IHA request.

Summary of Request

    On August 2, 2023, NMFS received a request from Hilcorp for an IHA 
to take marine mammals incidental to production drilling support 
activities in Cook Inlet, Alaska. Following NMFS' review of the 
application, Hilcorp submitted revised versions on September 29, 2023, 
December 27, 2023, February 29, 2024, and April 8, 2024. The 
application was deemed adequate and complete on April 12, 2024. 
Hilcorp's request is for take of 12 species of marine mammals, by Level 
B harassment. Neither Hilcorp nor NMFS expect serious injury or 
mortality to result from this activity and, therefore, an IHA is 
appropriate.
    NMFS previously issued an IHA to Hilcorp for similar work (87 FR 
62364, October 1, 2022). Hilcorp complied with all the requirements 
(e.g., mitigation, monitoring, and reporting) of the previous IHA, and 
information regarding their monitoring results may be found in the 
Potential Effects of Specified Activities on Marine Mammals and their 
Habitat section of this notice.

Description of Proposed Activity

Overview

    Hilcorp plans to use three tug boats to tow and hold, and up to 
four tug boats to position, a jack-up rig to support production 
drilling at existing platforms in middle Cook Inlet and Trading Bay, 
Alaska, on 6 non-consecutive days between September 14, 2024, and 
September 13, 2025. Noise produced by tugs under load with a jack-up 
rig may result in take, by Level B harassment, of twelve marine mammal 
species.

Dates and Duration

    The IHA would be effective from September 14, 2024, through 
September 13, 2025. As noted above, Hilcorp proposes to conduct the 
jack-up rig towing, holding, and positioning activities on 6 non-
consecutive days

[[Page 60165]]

during the authorization period. Hilcorp would only conduct tug towing 
rig activities at night if necessary to accommodate a favorable tide.

Specific Geographic Region

    Hilcorp's proposed activities would take place in middle Cook Inlet 
and Trading Bay, Alaska, extending north from Rig Tenders Dock on the 
eastern side of Cook Inlet near Nikiski to an area approximately 32 
kilometers (km) south of Point Possession, west to the Tyonek platform 
in middle Cook Inlet, south to the Dolly Varden platform in Trading 
Bay, and across Cook Inlet to the Rig Tenders Dock. For the purposes of 
this project, lower Cook Inlet refers to waters south of the East and 
West Forelands; middle Cook Inlet refers to waters north of the East 
and West Forelands and south of Threemile River on the west and Point 
Possession on the east; Trading Bay refers to waters from approximately 
the Granite Point Tank Farm on the north to the West Foreland on the 
south; and upper Cook Inlet refers to waters north and east of Beluga 
River on the west and Point Possession on the east. A map of the 
specific area in which Hilcorp plans to operate is provided in figure 1 
below.
BILLING CODE 3510-22-P

[[Page 60166]]

[GRAPHIC] [TIFF OMITTED] TN24JY24.000

BILLING CODE 3510-22-C

Detailed Description of the Specified Activity

    Hilcorp proposes to conduct production drilling activities from 
existing platforms in middle Cook Inlet and Trading Bay between 
September 14, 2024, and September 13, 2025, during which period there 
would be a need for an estimated six days of tug activity. For the 
preceding months (September 2023 to September 2024), Hilcorp is 
operating under an existing IHA (See 87 FR 62364, October 14, 2022). In 
2024, the Spartan 151 jack-up rig (or an equivalent rig) will be 
mobilized for production drilling from the Rig Tenders Dock in Nikiski 
and towed to an existing platform under the aforementioned 2023-2024 
IHA. Tug activities associated with the current IHA request would 
include one demobilization effort of a jack-up rig (Spartan 151 or 
equivalent rig) from an existing platform to Rig Tenders Dock in 
Nikiski, one jack-up rig relocation between existing

[[Page 60167]]

platforms, and one remobilization effort of the jack-up rig from Rig 
Tenders Dock in Nikiski to middle Cook Inlet. A jack-up rig is a type 
of mobile offshore drill unit used in offshore oil and gas drilling 
activities. It is comprised of a buoyant mobile platform or hull with 
moveable legs that are adjusted to raise and lower the hull over the 
surface of the water. Three tugs are needed to safely and effectively 
tow the jack-up rig during moves and to hold it into the correct 
position where it can be temporarily secured to the seafloor. A fourth 
tug may be needed to assist with the positioning of the jack-up rig on 
location.
    Development drilling activities occur from existing platforms 
within Cook Inlet through either well slots or existing wellbores in 
existing platform legs, and no well construction occurs during 
production drilling. All Hilcorp platforms have potential for 
development drilling activities. Drilling activities from platforms 
within Cook Inlet are accomplished by using conventional drilling 
equipment from a variety of rig configurations.
    Some platforms in Cook Inlet have permanent drilling rigs installed 
that operate using power provided by the platform power generation 
systems; other platforms do not have drill rigs, and the use of a 
mobile drill rig is required. Mobile offshore drill rigs may be powered 
by the platform power generation system (if compatible with the 
platform power generation system) or may self-generate power with the 
use of diesel-powered generators.
    While traveling with the jack-up rig during the proposed moves, the 
most common configuration is two tugs positioned side by side 
(approximately 30 to 60 m apart), pulling from the front of the jack-up 
rig, and one tug approximately 200 m behind the front tugs positioned 
behind the jack-up rig, applying tension on the line as needed for 
steering and straightening. While positioning the jack-up rig on a 
platform, the tugs may be fanned out around the jack-up rig to provide 
the finer control of movement necessary to safely position the jack-up 
rig on the platform.
    Upon arrival and readiness to position the rig adjacent to a 
platform, a fourth tug would be on standby to provide assistance. The 
fourth tug would not be expected to extend assistance beyond one hour. 
The horsepower of each of the tugs used during the proposed activities 
may range between 4,000 and 8,000. Specifications of the tugs 
anticipated for use are provided in table 1 below. If these specific 
tugs are not available, the tugs contracted would be of similar size 
and power to those listed in table 1.

       Table 1--Description of Tugs (or Similar) Used for Towing, Holding, and Positioning the Jack-Up Rig
----------------------------------------------------------------------------------------------------------------
               Vessel                          Activity             Length (m)       Width (m)     Gross tonnage
----------------------------------------------------------------------------------------------------------------
Bering Wind........................  Towing, holding, and                     22              10             144
                                      positioning the jack-up
                                      rig.
Stellar Wind.......................  Towing, holding, and                     32              11             160
                                      positioning the jack-up
                                      rig.
Glacial Wind.......................  Towing, holding, and                     37              11             196
                                      positioning the jack-up
                                      rig.
Dr. Hank Kaplan....................  Standby tug used only for                23              11             196
                                      positioning the jack-up
                                      rig, if needed.
----------------------------------------------------------------------------------------------------------------
Note: m = meters.

    The amount of time the tugs are under load transiting, holding, and 
positioning the jack-up rig in Cook Inlet would be tide-dependent. The 
amount of operational effort (i.e., power output) the tugs use for 
transiting would depend on whether the tugs are towing with or against 
the tide and could vary across a tidal cycle as the current increases 
or decreases in speed over time. Hilcorp would make every effort to 
transit with the tide (which requires lower power output) and minimize 
transit against the tide (which requires higher power output).
    A high slack tide would be preferred to position the jack-up rig on 
an existing platform or well site. The relatively slow current and calm 
conditions at a slack tide would enable the tugs to perform the fine 
movements necessary to safely position the jack-up rig within several 
feet of the platform. Additionally, positioning and securing the jack-
up rig at high slack tide rather than low slack tide would allow for 
the legs to be pinned down (jack the legs down onto the sea floor) at 
an adequate height to ensure that the hull of the jack-up rig remains 
above the water level of the subsequent incoming high tide. Because 12 
hours elapse between each high slack tide, tugs are generally under 
load for those 12 hours, even if the towed distance is small, as high 
slack tides are preferred to both attach and detach the jack-up rig 
from the tugs. Once the tugs are on location with the jack-up rig at 
high slack tide (12 hours from the previous departure), there is a 1 to 
2-hour window when the tide is slow enough for the tugs to initiate 
positioning the jack-up rig and pin the legs to the seafloor on 
location. The tugs are estimated to be under load, generally at half-
power conditions or less, for up to 14 hours from the time of departure 
through the initial positioning attempt of the jack-up rig. One 
additional tug may engage during positioning activities to assist with 
fine movements necessary to place the jack-up rig. The fourth tug is 
estimated to engage with the three tugs during a positioning attempt 
for up to 1 hour at half power.
    If the first positioning attempt takes longer than anticipated, the 
increasing current speed would prevent the tugs from safely positioning 
the jack-up rig on location. If the first positioning attempt is not 
successful, the jack-up rig would be pinned down at a nearby location 
and the tugs would be released from the jack-up rig and no longer under 
load. The tugs would remain nearby, generally floating with the 
current. Approximately an hour before the next high slack tide, the 
tugs would re-attach to the jack-up rig and reattempt positioning over 
a period of 2 to 3 hours. Positioning activities would generally be at 
half power. If a second attempt is needed, the tugs would be under load 
holding or positioning the jack-up rig on a second day for up to 5 
hours. Typically, the jack-up rig can be successfully positioned over 
the platform in one or two attempts.
    During a location-to-location transport (e.g., platform-to-
platform), the tugs would transport the jack-up rig traveling with the 
tide in nearly all circumstances except in situations that threaten the 
safety of humans and/or infrastructure integrity. In a north-to-south 
transit, the tugs would tow the jack-up rig with the outgoing tide and 
would typically arrive at their next location to position the jack-up 
rig on the low slack tide, requiring half power or a lower power output 
during the transport. In a south-to-north transit, Hilcorp would prefer 
to pull the jack-up rig from the platform on

[[Page 60168]]

a low slack tide to begin transiting north following the incoming tide. 
This would maximize their control over the jack-up rig and would 
require half power or a lower power output. There may be a situation 
wherein the tugs pulling the jack-up rig begin transiting with the tide 
to their next location, miss the tide window to safely set the jack-up 
rig on the platform or pin it nearby, and so have to transport the 
jack-up rig against the tide to a safe harbor. Tugs may also need to 
transport the jack-up rig against the tide if large pieces of ice or 
extreme wind events threaten the stability of the jack-up rig on the 
platform. All tug towing, holding, or positioning would be done in a 
manner implementing best management practices to preserve water 
quality, and no work would occur around creek mouths or river systems 
leading to prey abundance reductions.
    Although the variability in power output from the tugs can range 
from an estimated 20 percent to 90 percent throughout the hours under 
load with the jack-up rig, as described above, the majority of the 
hours (spent transiting, holding, and positioning) occur at half power 
or less. See the Estimated Take of Marine Mammals section of this 
proposed notice of issuance for more detail on assumptions related to 
power output.
    Proposed mitigation, monitoring, and reporting measures are 
described in detail later in this document (please see Proposed 
Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

    Sections 3 and 4 of the application summarize available information 
regarding status and trends, distribution and habitat preferences, and 
behavior and life history of the potentially affected species. NMFS 
fully considered all of this information, and we refer the reader to 
these descriptions, instead of reprinting the information. Additional 
information regarding population trends and threats may be found in 
NMFS' Stock Assessment Reports (SARs; https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments) and 
more general information about these species (e.g., physical and 
behavioral descriptions) may be found on NMFS' website (https://www.fisheries.noaa.gov/find-species).
    Table 2 lists all species or stocks for which take is expected and 
proposed to be authorized for this activity and summarizes information 
related to the population or stock, including regulatory status under 
the MMPA and Endangered Species Act (ESA) and potential biological 
removal (PBR), where known. PBR is defined by the MMPA as the maximum 
number of animals, not including natural mortalities, that may be 
removed from a marine mammal stock while allowing that stock to reach 
or maintain its optimum sustainable population (as described in NMFS' 
SARs). While no serious injury or mortality is anticipated or proposed 
to be authorized here, PBR and annual serious injury and mortality from 
anthropogenic sources are included here as gross indicators of the 
status of the species or stocks and other threats.
    Marine mammal abundance estimates presented in this document 
represent the total number of individuals that make up a given stock or 
the total number estimated within a particular study or survey area. 
NMFS' stock abundance estimates for most species represent the total 
estimate of individuals within the geographic area, if known, that 
comprises that stock. For some species, this geographic area may extend 
beyond U.S. waters. All managed stocks in this region are assessed in 
NMFS' U.S. 2022 SARs. All values presented in table 2 are the most 
recent available at the time of publication (including from the draft 
2023 SARs) and are available online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

                                            Table 2--Species \1\ Likely Impacted by the Specified Activities
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                                                                                         ESA/MMPA status;    Stock abundance (CV,
             Common name                  Scientific name               Stock             Strategic (Y/N)      Nmin, most recent       PBR     Annual M/
                                                                                                \2\          abundance survey) \3\               SI \4\
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                                                 Order Artiodactyla--Cetacea--Mysticeti (baleen whales)
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Family Eschrichtiidae:
    Gray Whale......................  Eschrichtius robustus..  Eastern N Pacific......  -, -, N             26,960 (0.05, 25,849,         801        131
                                                                                                             2016).
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Family Balaenidae
Family Balaenopteridae (rorquals):
    Fin Whale.......................  Balaenoptera physalus..  Northeast Pacific......  E, D, Y             UND \5\ (UND, UND,            UND        0.6
                                                                                                             2013).
    Humpback Whale..................  Megaptera novaeangliae.  Hawai'i................  -, -, N             11,278 (0.56, 7,265,          127      27.09
                                                                                                             2020).
                                                               Mexico-North Pacific...  T, D, Y             N/A\6\ (N/A, N/A,             UND       0.57
                                                                                                             2006).
                                                               Western North Pacific..  E, D, Y             1,084 (0.088, 1,007,          3.4       5.82
                                                                                                             2006).
    Minke Whale.....................  Balaenoptera             Alaska.................  -, -, N             N/A \7\ (N/A, N/A, N/         UND          0
                                       acutorostrata.                                                        A).
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                                                  Odontoceti (toothed whales, dolphins, and porpoises)
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Family Delphinidae:
    Killer Whale....................  Orcinus orca...........  Eastern North Pacific    -, -, N             1,920 (N/A, 1,920,             19        1.3
                                                                Alaska Resident.                             2019).
                                                               Eastern North Pacific    -, -, N             587 (N/A, 587, 2012)..        5.9        0.8
                                                                Gulf of Alaska,
                                                                Aleutian Islands and
                                                                Bering Sea Transient.
    Pacific White-Sided Dolphin.....  Lagenorhynchus           North Pacific..........  -, -, N             26,880 (N/A, N/A,             UND          0
                                       obliquidens.                                                          1990).
Family Monodontidae (white whales):
    Beluga Whale....................  Delphinapterus leucas..  Cook Inlet.............  E, D, Y             279 \8\ (0.061, 267,         0.53          0
                                                                                                             2018).
Family Phocoenidae (porpoises):

[[Page 60169]]

 
    Dall's Porpoise.................  Phocoenoides dalli.....  Alaska.................  -, -, N             UND \9\ (UND, UND,            UND         37
                                                                                                             2015).
    Harbor Porpoise.................  Phocoena phocoena......  Gulf of Alaska.........  -, -, Y             31,046 (0.21, N/A,            UND         72
                                                                                                             1998).
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                                                               Order Carnivora--Pinnipedia
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Family Otariidae (eared seals and
 sea lions):
    CA Sea Lion.....................  Zalophus californianus.  U.S....................  -, -, N             257,606 (N/A, 233,515,     14,011       >321
                                                                                                             2014).
    Steller Sea Lion................  Eumetopias jubatus.....  Western................  E, D, Y             49,837 \10\ (N/A,             299        267
                                                                                                             49,837, 2020).
Family Phocidae (earless seals):
    Harbor Seal.....................  Phoca vitulina.........  Cook Inlet/Shelikof      -, -, N             28,411 (N/A, 26,907,          807        107
                                                                Strait.                                      2018).
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\1\ Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy
  (https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/; Committee on Taxonomy (2022)).
\2\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed
  under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality
  exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed
  under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\3\ NMFS marine mammal stock assessment reports online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region. CV is coefficient of variation; Nmin is the minimum estimate of stock abundance.
\4\ These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g.,
  commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV
  associated with estimated mortality due to commercial fisheries is presented in some cases.
\5\ The best available abundance estimate for this stock is not considered representative of the entire stock as surveys were limited to a small portion
  of the stock's range. Based upon this estimate and the Nmin, the PBR value is likely negatively biased for the entire stock.
\6\ Abundance estimates are based upon data collected more than 8 years ago and, therefore, current estimates are considered unknown.
\7\ Reliable population estimates are not available for this stock. Please see Friday et al. (2013) and Zerbini et al. (2006) for additional information
  on numbers of minke whales in Alaska.
\8\ On June 15, 2023, NMFS released an updated abundance estimate for endangered CIBWs in Alaska (Goetz et al., 2023). Data collected during NOAA
  Fisheries' 2022 aerial survey suggest that the whale population is stable or may be increasing slightly. Scientists estimated that the population size
  is between 290 and 386, with a median best estimate of 331. In accordance with the MMPA, this population estimate will be incorporated into the CIBW
  SAR, which will be reviewed by an independent panel of experts, the Alaska Scientific Review Group. After this review, the SAR will be made available
  as a draft for public review before being finalized.
\9\ The best available abundance estimate is likely an underestimate for the entire stock because it is based upon a survey that covered only a small
  portion of the stock's range.
\10\ Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys.

    As indicated above, all 12 species (with 15 managed stocks) in 
table 2 temporally and spatially co-occur with the activity to the 
degree that take is reasonably likely to occur. In addition, the 
northern sea otter may be found in Cook Inlet, Alaska. However, 
northern sea otters are managed by the U.S. Fish and Wildlife Service 
and are not considered further in this document.

Gray Whale

    The stock structure for gray whales in the Pacific has been studied 
for a number of years and remains uncertain as of the most recent 
(2022) Pacific SARs (Carretta et al., 2023). Gray whale population 
structure is not determined by simple geography and may be in flux due 
to evolving migratory dynamics (Carretta et al., 2023). Currently, the 
SARs delineate a western North Pacific (WNP) gray whale stock and an 
eastern North Pacific (ENP) stock based on genetic differentiation 
(Carretta et al., 2023). WNP gray whales are not known to feed in or 
travel to upper Cook Inlet (Conant and Lohe, 2023; Weller et al., 
2023). Therefore, we assume that gray whales near the project area are 
members of the ENP stock.
    An Unusual Mortality Event (UME) for gray whales along the West 
Coast and in Alaska occurred from December 17, 2018 through November 9, 
2023. During that time, 146 gray whales stranded off the coast of 
Alaska. The investigative team concluded that the preliminary cause of 
the UME was localized ecosystem changes in the whale's Subarctic and 
Arctic feeding areas that led to changes in food, malnutrition, 
decreased birth rates, and increased mortality (see https://www.fisheries.noaa.gov/national/marine-life-distress/2019-2023-gray-whale-unusual-mortality-event-along-west-coast-and for more 
information).
    Gray whales are infrequent visitors to Cook Inlet, but may be 
seasonally present during spring and fall in the lower inlet (Bureau of 
Ocean Energy Management (BOEM), 2021). Migrating gray whales pass 
through the lower inlet during their spring and fall migrations to and 
from their primary summer feeding areas in the Bering, Chukchi, and 
Beaufort seas (Swartz, 2018; Silber et al., 2021; BOEM, 2021). Several 
surveys and monitoring programs have sighted gray whales in lower Cook 
Inlet (Shelden et al., 2013; Owl Ridge, 2014; Lomac-MacNair et al., 
2013, 2014; Kendall et al., 2015, as cited in Weston and SLR, 2022). 
Gray whales are occasionally seen in mid- and upper Cook Inlet, Alaska, 
but they are not common. During NMFS aerial surveys conducted in June 
1994, 2000, 2001, 2005, and 2009 gray whales were observed in Cook 
Inlet near Port Graham and Elizabeth Island as well as near Kamishak 
Bay, with one gray whale observed as far north as the Beluga River 
(Shelden et al., 2013). Gray whales were also observed offshore of Cape 
Starichkof in 2013 by marine mammal observers monitoring Buccaneer's 
Cosmopolitan drilling project (Owl Ridge, 2014) and in middle Cook 
Inlet in 2014 during the 2014 Apache 2D seismic survey (Lomac-MacNair 
et al., 2015). Several projects performed in Cook Inlet in recent years 
reported no observations of gray whales. These project activities 
included the SAExploration seismic survey in 2015 (Kendall and Cornick, 
2015), the 2018 Cook Inlet Pipeline (CIPL) Extension Project 
(Sitkiewicz et al., 2018), the 2019 Hilcorp seismic survey in lower 
Cook Inlet (Fairweather Science, 2020),

[[Page 60170]]

and Hilcorp's 2023 aerial and rig-based monitoring efforts.
    In 2020, a young male gray whale was stranded in the Twentymile 
River near Girdwood for over a week before swimming back into Turnagain 
Arm. The whale did not survive and was found dead in west Cook Inlet 
later that month (NMFS, 2020). One gray whale was sighted in Knik Arm 
near the Port of Alaska (POA) in Anchorage in upper Cook Inlet in May 
of 2020 during observations conducted during construction of the 
Petroleum and Cement Terminal project (61N Environmental, 2021). The 
sighting occurred less than a week before the reports of the gray whale 
stranding in the Twentymile River and was likely the same animal. In 
2021, one small gray whale was sighted in Knik Arm near Ship Creek, 
south of the POA (61N Environmental, 2022a). Although some sightings 
have been documented in the middle and upper Inlet, the gray whale 
range typically only extends into the lower Cook Inlet region.

Humpback Whale

    The 2022 NMFS Alaska and Pacific SARs described a revised stock 
structure for humpback whales which modifies the previous designated 
stocks to align more closely with the ESA-designated Distinct 
Population Segments (DPSs) (Carretta et al., 2023; Young et al., 2023). 
Specifically, the three previous North Pacific humpback whale stocks 
(Central and Western North Pacific stocks and a CA/OR/WA stock) were 
replaced by five stocks, largely corresponding with the ESA-designated 
DPSs. These include Western North Pacific and Hawaii stocks and a 
Central America/Southern Mexico-California (CA)/Oregon (OR)/Washington 
(WA) stock (which corresponds with the Central America DPS). The 
remaining two stocks, corresponding with the Mexico DPS, are the 
Mainland Mexico-CA/OR/WA and Mexico-North Pacific stocks (Carretta et 
al., 2023; Young et al., 2023). The former stock is expected to occur 
along the west coast from California to southern British Columbia, 
while the latter stock may occur across the Pacific, from northern 
British Columbia through the Gulf of Alaska and Aleutian Islands/Bering 
Sea region to Russia.
    The Hawaii stock consists of one demographically independent 
population (DIP) (Hawaii--Southeast Alaska/Northern British Columbia 
DIP) and the Hawaii--North Pacific unit, which may or may not be 
composed of multiple DIPs (Wade et al., 2021). The DIP and unit are 
managed as a single stock at this time, due to the lack of data 
available to separately assess them and lack of compelling conservation 
benefit to managing them separately (NMFS 2019, 2022c, 2023a). The DIP 
is delineated based on two strong lines of evidence: genetics and 
movement data (Wade et al., 2021). Whales in the Hawaii--Southeast 
Alaska/Northern British Columbia DIP winter off Hawaii and largely 
summer in Southeast Alaska and Northern British Columbia (Wade et al., 
2021). The group of whales that migrate from Russia, western Alaska 
(Bering Sea and Aleutian Islands), and central Alaska (Gulf of Alaska 
excluding Southeast Alaska) to Hawaii have been delineated as the 
Hawaii--North Pacific unit (Wade et al., 2021). There are a small 
number of whales that migrate between Hawaii and southern British 
Columbia/Washington, but current data and analyses do not provide a 
clear understanding of which unit these whales belong to (Wade et al., 
2021; Carretta et al., 2023; Young et al., 2023).
    The Mexico--North Pacific stock is likely composed of multiple 
DIPs, based on movement data (Martien et al., 2021, Wade, 2021, Wade et 
al., 2021). However, because currently available data and analyses are 
not sufficient to delineate or assess DIPs within the unit, it was 
designated as a single stock (NMFS, 2019, 2022d, 2023a). Whales in this 
stock winter off Mexico and the Revillagigedo Archipelago and summer 
primarily in Alaska waters (Martien et al., 2021; Carretta et al., 
2023; Young et al., 2023).
    The Western North Pacific stock consists of two units--the 
Philippines/Okinawa--North Pacific unit and the Marianas/Ogasawara--
North Pacific unit. The units are managed as a single stock at this 
time, due to a lack of data available to separately assess them (NMFS, 
2019, 2022d, 2023a). Recognition of these units is based on movements 
and genetic data (Oleson et al., 2022). Whales in the Philippines/
Okinawa--North Pacific unit winter near the Philippines and in the 
Ryukyu Archipelago and migrate to summer feeding areas primarily off 
the Russian mainland (Oleson et al., 2022). Whales that winter off the 
Mariana Archipelago, Ogasawara, and other areas not yet identified and 
then migrate to summer feeding areas off the Commander Islands, and to 
the Bering Sea and Aleutian Islands comprise the Marianas/Ogasawara--
North Pacific unit.
    The most comprehensive photo-identification data available suggest 
that approximately 89 percent of all humpback whales in the Gulf of 
Alaska are from the Hawaii stock, 11 percent are from the Mexico stock, 
and less than 1 percent are from the Western North Pacific stock (Wade, 
2021). Individuals from different stocks are known to intermix in 
feeding grounds. There is no designated critical habitat for humpback 
whales in or near the Project area (86 FR 21082, April 21, 2021), nor 
does the project overlap with any known biologically important areas.
    Humpback whales are encountered regularly in lower Cook Inlet and 
occasionally in mid-Cook Inlet; sightings are rare in upper Cook Inlet. 
Eighty-three groups containing an estimated 187 humpbacks were sighted 
during the Cook Inlet beluga whale aerial surveys conducted by NMFS 
from 1994 to 2012 (Shelden et al., 2013). Surveys conducted north of 
the forelands have documented small numbers in middle Cook Inlet. 
During the 2014 Apache seismic surveys in Cook Inlet, five groups (six 
individuals) were reported, with three groups north of the forelands on 
the east side of the inlet (Lomac-MacNair et al., 2014). In 2015, 
during the construction of the Furie Operating Alaska, LLC (Furie) 
platform and pipeline, four groups of humpback whales were documented. 
Another group of 6 to 10 unidentified whales, thought to be either 
humpback or gray whales, was sighted approximately 15 km northeast of 
the Julius R. Platform. Large cetaceans were visible near the project 
(i.e., whales or blows were visible) for 2 hours out of the 1,275 hours 
of observation conducted (Jacobs, 2015). During SAExploration's 2015 
seismic program, three humpback whales were observed in Cook Inlet, 
including two near the Forelands and one in lower Cook Inlet (Kendall 
et al., 2015 as cited in Weston and SLR, 2022). Hilcorp did not record 
any sightings of humpback whales from their aerial or rig-based 
monitoring efforts in 2023 (Horsley and Larson, 2023).

Minke Whale

    Two stocks of minke whales occur within U.S. waters: Alaska and 
California/Oregon/Washington (Muto et al., 2022). The Alaskan stock of 
minke whales is considered migratory, as they are speculated to migrate 
seasonally from the Bering and Chukchi Seas in fall to areas of the 
central North Pacific Ocean (Delarue et al., 2013). Although they are 
likely migratory in Alaska, minke whales have been observed off Cape 
Starichkof and Anchor Point year-round (Muto et al., 2017).
    Minke whales are most abundant in the Gulf of Alaska during summer 
and occupy localized feeding areas (Zerbini et al., 2006). During the 
NMFS annual and semiannual surveys of Cook Inlet, minke whales were 
observed near

[[Page 60171]]

Anchor Point in 1998, 1999, 2006, and 2021 (Shelden et al., 2013, 
2015b, 2017, 2022; Shelden and Wade, 2019) and near Ninilchik and the 
middle of lower Cook Inlet in 2021 (Shelden et al., 2022). Minkes were 
sighted southeast of Kalgin Island and near Homer during Apache's 2014 
survey (Lomac-MacNair et al., 2014), and one was observed near Tuxedni 
Bay in 2015 (Kendall et al., 2015, as cited in Weston and SLR, 2022). 
During Hilcorp's seismic survey in lower Cook Inlet in the fall of 
2019, eight minke whales were observed (Fairweather Science, 2020). In 
2018, no minke whales were observed during observations conducted for 
the CIPL project near Tyonek (Sitkiewicz et al., 2018). Minke whales 
were also not recorded during Hilcorp's aerial or rig-based monitoring 
efforts in 2023 (Horsley and Larson, 2023).

Fin Whale

    In U.S. Pacific waters, fin whales are seasonally found in the Gulf 
of Alaska, and Bering Sea and as far north as the northern Chukchi Sea 
(Muto et al., 2021). Several surveys have been conducted to assess the 
distribution and habitat preferences of fin whales within parts of 
their range in the North Pacific. In coastal waters of the Aleutians 
and the Alaska Peninsula, they were found primarily from the Kenai 
Peninsula to the Shumagin Islands, with a higher abundance near the 
Semidi Islands and Kodiak Island (Zerbini et al., 2006). An 
opportunistic survey in the Gulf of Alaska revealed that fin whales 
were concentrated west of Kodiak Island, in Shelikof Strait, and in the 
southern Cook Inlet region, with smaller numbers observed over the 
shelf east of Kodiak to Prince William Sound (Alaska Fisheries Science 
Center [AFSC], 2003). Muto et al. (2021) reported visual sightings and 
acoustic detections in the northeastern Chukchi Sea have been 
increasing, suggesting that the stock may be re-occupying habitat used 
prior to large-scale commercial whaling. Delarue et al. (2013) also 
detected fin whale calls in the northeastern Chukchi Sea from July 
through October in a 3-year acoustic study.
    Fin whales' range extends into lower Cook Inlet; however, their 
sightings are infrequent, and they are mostly spotted near the inlet's 
entrance. Fin whales are usually observed as individuals traveling 
alone, although they are sometimes observed in small groups. Rarely, 
large groups of 50 to 300 fin whales can travel together during 
migrations (NMFS, 2010). Fin whales in Cook Inlet have only been 
observed as individuals or in small groups. From 2000 to 2022, 10 
sightings of 26 estimated individual fin whales in lower Cook Inlet 
were observed during NMFS aerial surveys (Shelden et al., 2013, 2015b, 
2017, 2022; Shelden and Wade, 2019). No fin whales were observed during 
the 2018 Harvest's CIPL Extension Project Acoustic Monitoring Program 
in middle Cook Inlet (Sitkiewicz et al., 2018). In September and 
October 2019, Castellote et al. (2020) detected fin whales acoustically 
in lower Cook Inlet during three-dimensional (3D) seismic surveys, 
which coincided with the Hilcorp lower Cook Inlet seismic survey. 
During this period, 8 sightings of 23 individual fin whales were 
reported, indicating the offshore waters of lower Cook Inlet may be 
more heavily used than previously believed, especially during the fall 
season (Fairweather Science, 2020). Hilcorp did not record any 
sightings of fin whales from their aerial or rig-based monitoring 
efforts in 2023 (Horsley and Larson, 2023).

Beluga Whale

    Five stocks of beluga whales are recognized in Alaska: the Beaufort 
Sea stock, eastern Chukchi Sea stock, eastern Bering Sea stock, Bristol 
Bay stock, and Cook Inlet stock (Young et al., 2023). The Cook Inlet 
stock is geographically and genetically isolated from the other stocks 
(O'Corry-Crowe et al., 1997; Laidre et al., 2000) and resides year-
round in Cook Inlet (Laidre et al., 2000; Castellote et al., 2020). 
Only the Cook Inlet stock inhabits the proposed project area. Cook 
Inlet beluga whales (CIBWs) were designated as depleted under the MMPA 
in 2000 (65 FR 34950, May 31, 2000), and as a DPS and listed as 
endangered under the ESA in October 2008 (73 FR 62919, October 10, 
2008) when the species failed to recover following a moratorium on 
subsistence harvest. Between 2008 and 2018, CIBWs experienced a decline 
of about 2.3 percent per year (Wade et al., 2019). The decline 
overlapped with the northeast Pacific marine heatwave that occurred 
from 2014 to 2016 in the Gulf of Alaska, significantly impacting the 
marine ecosystem (Suryan et al., 2021, as cited in Goetz et al., 2023).
    In June 2023, NMFS released an updated abundance estimate for CIBWs 
in Alaska that incorporates aerial survey data from June 2021 and 2022 
and accounted for visibility bias (Goetz et al., 2023). This report 
estimated that CIBW abundance is between 290 and 386, with a median 
best estimate of 331. Goetz et al. (2023) also present an analysis of 
population trends for the most recent 10-year period (2012-2022). The 
addition of data from the 2021 and 2022 survey years in the analysis 
resulted in a 65.1 percent probability that the CIBW population is now 
increasing at 0.9 percent per year (95 percent prediction interval of -
3 to 5.7 percent). This increase drops slightly to 0.2 percent per year 
(95 percent prediction interval of -1.8 to 2.6 percent) with a 60 
percent probability that the CIBW population is increasing more than 1 
percent per year when data from 2021, which had limited survey coverage 
due to poor weather, are excluded from the analysis. Median group size 
estimates in 2021 and 2022 were 34 and 15, respectively (Goetz et al., 
2023). For management purposes, NMFS has determined that the carrying 
capacity of Cook Inlet is 1,300 CIBWs (65 FR 34590, May 31, 2000) based 
on historical CIBW abundance estimated by Calkins (1989).
    Threats that have the potential to impact this stock and its 
habitat include the following: changes in prey availability due to 
natural environmental variability, ocean acidification, and commercial 
fisheries; climatic changes affecting habitat; predation by killer 
whales; contaminants; noise; ship strikes; waste management; urban 
runoff; construction projects; and physical habitat modifications that 
may occur as Cook Inlet becomes increasingly urbanized (Moore et al., 
2000; Hobbs et al., 2015; NMFS, 2016b). Another source of CIBW 
mortality in Cook Inlet is predation by transient-type (mammal-eating) 
killer whales (NMFS, 2016b; Shelden et al., 2003). No human-caused 
mortality or serious injury of CIBWs through interactions with 
commercial, recreational, and subsistence fisheries, takes by 
subsistence hunters, and or human-caused events (e.g., entanglement in 
marine debris, ship strikes) has been recently documented and 
harvesting of CIBWs has not occurred since 2008 (NMFS, 2008b).
    Recovery Plan. In 2010, a Recovery Team, consisting of a Science 
Panel and Stakeholder Panel, began meeting to develop a Recovery Plan 
for the CIBW. The Final Recovery Plan was published in the Federal 
Register on January 5, 2017 (82 FR 1325). In September 2022, NMFS 
completed the ESA 5-year review for the CIBW DPS and determined that 
the CIBW DPS should remain listed as endangered (NMFS, 2022d).
    In its Recovery Plan (82 FR 1325, January 5, 2017), NMFS identified 
several potential threats to CIBWs, including: (1) high concern: 
catastrophic events (e.g., natural disasters, spills, mass strandings), 
cumulative effects of multiple stressors, and noise; (2) medium 
concern: disease agents (e.g., pathogens, parasites, and harmful algal

[[Page 60172]]

blooms), habitat loss or degradation, reduction in prey, and 
unauthorized take; and (3) low concern: pollution, predation, and 
subsistence harvest. The recovery plan did not treat climate change as 
a distinct threat but rather as a consideration in the threats of high 
and medium concern. Other potential threats most likely to result in 
direct human-caused mortality or serious injury of this stock include 
vessel strikes.
    Critical Habitat. On April 11, 2011, NMFS designated two areas of 
critical habitat for CIBW (76 FR 20179). The designation includes 7,800 
square kilometers (km\2\) of marine and estuarine habitat within Cook 
Inlet, encompassing approximately 1,909 km\2\ in Area 1 and 5,891 km\2\ 
in Area 2 (see figure 1 in 76 FR 20179). Area 1 of the CIBW critical 
habitat encompasses all marine waters of Cook Inlet north of a line 
connecting Point Possession (lat. 61.04[deg] N, long. 150.37[deg] W) 
and the mouth of Three Mile Creek (lat. 61.08.55[deg] N, long. 
151.04.40[deg] W), including waters of the Susitna, Little Susitna, and 
Chickaloon Rivers below mean higher high water (MHHW). From spring 
through fall, Area 1 critical habitat has the highest concentration of 
CIBWs due to its important foraging and calving habitat. Critical 
Habitat Area 2 encompasses some of the fall and winter feeding grounds 
in middle Cook Inlet. This area has a lower concentration of CIBWs in 
spring and summer but is used by CIBWs in fall and winter. More 
information on CIBW critical habitat can be found at https://www.fisheries.noaa.gov/action/critical-habitat-cook-inlet-beluga-whale.
    The designation identified the following Primary Constituent 
Elements, essential features important to the conservation of the CIBW:
    (1) Intertidal and subtidal waters of Cook Inlet with depths of 
less than 9 m mean lower-low water (MLLW) and within 8 km of high- and 
medium-flow anadromous fish streams;
    (2) Primary prey species, including four of the five species of 
Pacific salmon (chum (Oncorhynchus keta), sockeye (Oncorhynchus nerka), 
Chinook (Oncorhynchus tshawytscha), and coho (Oncorhynchus kisutch)), 
Pacific eulachon (Thaleichthys pacificus), Pacific cod (Gadus 
macrocephalus), walleye Pollock (Gadus chalcogrammus), saffron cod 
(Eleginus gracilis), and yellowfin sole (Limanda aspera);
    (3) The absence of toxins or other agents of a type or amount 
harmful to CIBWs;
    (4) Unrestricted passage within or between the critical habitat 
areas; and
    (5) The absence of in-water noise at levels resulting in the 
abandonment of habitat by CIBWs.
    Biologically Important Areas. Wild et al. (2023) delineated a Small 
and Resident Population Biologically Important Area (BIA) in Cook Inlet 
that is active year-round and overlaps Hilcorp's proposed project area. 
The authors assigned the BIA an importance score of 2, an intensity 
score of 2, a data support score of 3, and a boundary certainty score 
of 2 (scores range from 1 to 3, with a higher score representing an 
area of more concentrated or focused use and higher confidence in the 
data supporting the BIA; Harrison et al., 2023). These scores indicate 
that the BIA is of moderate importance and intensity, the authors have 
high confidence that the population is small and resident and in the 
abundance and range estimates of the population, and the boundary 
certainty is medium (see Harrison et al. (2023) for additional 
information about the scoring process used to identify BIAs). The 
boundary of the CIBW BIA is consistent with NMFS' critical habitat 
designation (Wild et al., 2023).
    Ecology. Generally, female beluga whales reach sexual maturity at 9 
to 12 years old, while males reach maturity later (O'Corry-Crowe, 
2009); however, this can vary between populations. For example, in 
Greenland, males in a population of beluga whales were found to reach 
sexual maturity at 6 to 7 years of age and females at 4 to 7 years 
(Heide-Joregensen and Teilmann, 1994). Suydam (2009) estimated that 50 
percent of females were sexually mature at age 8.25 and the average age 
at first birth was 8.27 years for belugas sampled near Point Lay. 
Mating behavior in beluga whales typically occurs between February and 
June, peaking in March (Burns and Seaman, 1986; Suydam, 2009). In the 
Chukchi Sea, the gestation period of beluga whales was determined to be 
14.9 months, with a calving interval of 2 to 3 years and a pregnancy 
rate of 0.41, declining after 25 years of age (Suydam, 2009). Calves 
are born between mid-June and mid-July and typically remain with the 
mother for up to 2 years of age (Suydam, 2009).
    CIBWs feed on a wide variety of prey species, particularly those 
that are seasonally abundant. From late spring through summer, most 
CIBW stomachs sampled contained salmon, which corresponded to the 
timing of fish runs in the area. Anadromous smolt and adult fish 
aggregate at river mouths and adjacent intertidal mudflats (Calkins, 
1989). All five Pacific salmon species (i.e., Chinook, pink 
(Oncorhynchus gorbuscha), coho, sockeye, and chum) spawn in rivers 
throughout Cook Inlet (Moulton, 1997; Moore et al., 2000). Overall, 
Pacific salmon represent the highest percent frequency of occurrence of 
prey species in CIBW stomachs. This suggests that their spring feeding 
in upper Cook Inlet, principally on fat-rich fish such as salmon and 
eulachon, is important to the energetics of these animals (NMFS, 
2016b).
    The nutritional quality of Chinook salmon in particular is 
unparalleled, with an energy content four times greater than that of a 
Coho salmon. It is suggested the decline of the Chinook salmon 
population has left a nutritional void in the diet of the CIBWs that no 
other prey species can fill in terms of quality or quantity (Norman et 
al., 2020, 2022).
    In fall, as anadromous fish runs begin to decline, CIBWs return to 
consume fish species (cod and bottom fish) found in nearshore bays and 
estuaries. Stomach samples from CIBWs are not available for winter 
(December through March), although dive data from CIBWs tagged with 
satellite transmitters suggest that they feed in deeper waters during 
winter (Hobbs et al., 2005), possibly on such prey species as flatfish, 
cod, sculpin, and pollock.
    Distribution in Cook Inlet. The CIBW stock remains within Cook 
Inlet throughout the year, showing only small seasonal shifts in 
distribution (Goetz et al., 2012a; Lammers et al., 2013; Castellotte et 
al., 2015; Shelden et al., 2015a, 2018; Lowry et al., 2019). The 
ecological range of CIBWs has contracted significantly since the 1970s. 
From late spring to fall, nearly the entire population is now found in 
the upper inlet north of the forelands, with a range reduced to 
approximately 39 percent of the size documented in the late 1970s 
(Goetz et al., 2023). The recent annual and semiannual aerial surveys 
(since 2008) found that approximately 83 percent of the population 
inhabits the area between the Beluga River and Little Susitna River 
during the survey period, typically conducted in early June. Some 
aerial survey counts were performed in August, September, and October, 
finding minor differences in the numbers of belugas in the upper inlet 
compared to June, reinforcing the importance of the upper inlet habitat 
area (Young et al., 2023).
    During spring and summer, CIBWs generally aggregate near the warmer 
waters of river mouths along the northern shores of middle and upper 
Cook Inlet where prey availability is high and predator occurrence is 
low (Moore et al., 2000; Shelden and Wade, 2019; McGuire et al., 2020). 
In particular, CIBW groups are seen in the

[[Page 60173]]

Susitna River Delta, the Beluga River and along the shore to the Little 
Susitna River, Knik Arm, and along the shores of Chickaloon Bay. Small 
groups were recorded farther south in Kachemak Bay, Redoubt Bay (Big 
River), and Trading Bay (McArthur River) prior to 1996, but rarely 
thereafter. Since the mid-1990s, most CIBWs (96 to 100 percent) 
aggregate in shallow areas near river mouths in upper Cook Inlet, and 
they are only occasionally sighted in the central or southern portions 
of Cook Inlet during summer (Hobbs et al., 2008). Almost the entire 
population can be found in northern Cook Inlet from late spring through 
the summer and into the fall (Muto et al., 2020), shifting into deeper 
waters in middle Cook Inlet in winter (Hobbs et al., 2008).
    Data from tagged whales (14 tags deployed July 2000 through March 
2003) show that CIBWs use upper Cook Inlet intensively between summer 
and late autumn (Hobbs et al., 2005). CIBWs tagged with satellite 
transmitters continue to use Knik Arm, Turnagain Arm, and Chickaloon 
Bay as late as October, but some range into lower Cook Inlet to 
Chinitna Bay, Tuxedni Bay, and Trading Bay (McArthur River) in fall 
(Hobbs et al., 2005, 2012). From September through November, CIBWs move 
between Knik Arm, Turnagain Arm, and Chickaloon Bay (Hobbs et al., 
2005; Goetz et al., 2012b). By December, CIBWs are distributed 
throughout the upper to mid-inlet. From January into March, they move 
as far south as Kalgin Island and slightly beyond in central offshore 
waters. CIBWs make occasional excursions into Knik Arm and Turnagain 
Arm in February and March in spite of ice cover (Hobbs et al., 2005). 
Although tagged CIBWs move widely around Cook Inlet throughout the 
year, there is no indication of seasonal migration in and out of Cook 
Inlet (Hobbs et al., 2005). Data from NMFS aerial surveys, 
opportunistic sighting reports, and corrected satellite-tagged CIBWs 
confirm that they are more widely dispersed throughout Cook Inlet 
during winter (November-April), with animals found between Kalgin 
Island and Point Possession. Generally fewer observations of CIBWs are 
reported from the Anchorage and Knik Arm area from November through 
April (76 FR 20179, April 11, 2011; Rugh et al., 2000, 2004). Later in 
winter (January into March), belugas were sighted near Kalgin Island 
and in deeper waters offshore. However, even when ice cover exceeds 90 
percent in February and March, belugas travel into Knik Arm and 
Turnagain Arm (Hobbs et al., 2005).
    The NMFS Marine Mammal Lab has conducted long-term passive acoustic 
monitoring demonstrating seasonal shifts in CIBW concentrations 
throughout Cook Inlet. Castellote et al. (2015) conducted long-term 
acoustic monitoring at 13 locations throughout Cook Inlet between 2008 
and 2015: North Eagle Bay, Eagle River Mouth, South Eagle Bay, Six 
Mile, Point MacKenzie, Cairn Point, Fire Island, Little Susitna, Beluga 
River, Trading Bay, Kenai River, Tuxedni Bay, and Homer Spit; the 
former 6 stations being located within Knik Arm. In general, the 
observed seasonal distribution is in accordance with descriptions based 
on aerial surveys and satellite telemetry: CIBW detections are higher 
in the upper inlet during summer, peaking at Little Susitna, Beluga 
River, and Eagle Bay, followed by fewer detections at those locations 
during winter. Higher detections in winter at Trading Bay, Kenai River, 
and Tuxedni Bay suggest a broader CIBW distribution in the lower inlet 
during winter.
    Goetz et al. (2012b) modeled habitat preferences using NMFS' 1994-
2008 June abundance survey data. In large areas, such as the Susitna 
Delta (Beluga to Little Susitna Rivers) and Knik Arm, there was a high 
probability that CIBWs were in larger groups. CIBW presence and 
acoustic foraging behavior also increased closer to rivers with Chinook 
salmon runs, such as the Susitna River (e.g., Castellote et al., 2021). 
Movement has been correlated with the peak discharge of seven major 
rivers emptying into Cook Inlet. Boat-based surveys from 2005 to the 
present (McGuire and Stephens, 2017) and results from passive acoustic 
monitoring across the entire inlet (Castellote et al., 2015) also 
support seasonal patterns observed with other methods. Based on long-
term passive acoustic monitoring, foraging behavior was more prevalent 
during summer, particularly at upper inlet rivers, than during winter. 
The foraging index was highest at Little Susitna, with a peak in July-
August and a secondary peak in May, followed by Beluga River and then 
Eagle Bay; monthly variation in the foraging index indicates CIBWs 
shift their foraging behavior among these three locations from April 
through September. The location of the towing routes are areas of 
predicted low density in the summer months.
    CIBWs are believed to mostly calve in the summer, and breed between 
late spring and early summer (NMFS, 2016b), primarily in upper Cook 
Inlet. The only known observed occurrence of calving occurred on July 
20, 2015, in the Susitna Delta area (T. McGuire, personal 
communication, March 27, 2017). The first neonates encountered during 
each field season from 2005 through 2015 were always seen in the 
Susitna River Delta in July. The photographic identification team's 
documentation of the dates of the first neonate of each year indicate 
that calving begins in mid-late July/early August, generally coinciding 
with the observed timing of annual maximum group size. Probable mating 
behavior of CIBWs was observed in April and May of 2014, in Trading 
Bay. Young CIBWs are nursed for 2 years and may continue to associate 
with their mothers for a considerable time thereafter (Colbeck et al., 
2013). Important calving grounds are thought to be located near the 
river mouths of upper Cook Inlet.9
    During Apache's seismic test program in 2011 along the west coast 
of Redoubt Bay, lower Cook Inlet, a total of 33 CIBWs were sighted 
during the survey (Lomac-MacNair et al., 2013). During Apache's 2012 
seismic program in mid-inlet, a total of 151 groups consisting of an 
estimated 1,463 CIBWs were observed (note individuals were likely 
observed more than once) (Lomac-MacNair et al., 2014). During 
SAExploration's 2015 seismic program, a total of eight groups of 33 
estimated individual CIBWs were visually observed during this time 
period and there were two acoustic detections of CIBWs (Kendall et al., 
2015). During Harvest Alaska's recent CIPL project on the west side of 
Cook Inlet in between Ladd Landing and Tyonek Platform, a total of 143 
CIBW groups (814 individuals) were observed almost daily from May 31 to 
July 11, even though observations spanned from May 9 through September 
15 (Sitkiewicz et al., 2018). There were two CIBW carcasses observed by 
the project vessels in the 2019 Hilcorp lower Cook Inlet seismic survey 
in the fall which were reported to the NMFS Marine Mammal Stranding 
Network (Fairweather Science, 2020). Both carcasses were moderately 
decomposed when they were sighted by the Protected Species Observers 
(PSO). Daily aerial surveys specifically for CIBWs were flown over the 
lower Cook Inlet region, but no beluga whales were observed. In 2023, 
Hilcorp recorded 21 groups of more than 125 beluga whales during aerial 
surveys in middle Cook Inlet, and an additional 21 opportunistic groups 
which included approximately 81 CIBWs (Horsley and Larson, 2023). 
Hilcorp did not record any sightings of CIBWs from their rig-based 
monitoring efforts (Horsley and Larson, 2023)

Killer Whale

    Along the west coast of North America, seasonal and year-round 
occurrence of killer whales has been

[[Page 60174]]

noted along the entire Alaska coast (Braham and Dahlheim, 1982), in 
British Columbia and Washington inland waterways (Bigg et al., 1990), 
and along the outer coasts of Washington, Oregon, and California (Green 
et al., 1992; Barlow 1995, 1997; Forney et al., 1995). Killer whales 
from these areas have been labeled as ``resident,'' ``transient,'' and 
``offshore'' type killer whales (Bigg et al., 1990; Ford et al., 2000; 
Dahlheim et al., 2008) based on aspects of morphology, ecology, 
genetics, and behavior (Ford and Fisher, 1982; Baird and Stacey, 1988; 
Baird et al., 1992; Hoelzel et al., 1998, 2002; Barrett-Lennard, 2000; 
Dahlheim et al., 2008). Based on data regarding association patterns, 
acoustics, movements, and genetic differences, eight killer whale 
stocks are now recognized within the U.S. Pacific, two of which have 
the potential to be found in the proposed project area: the Eastern 
North Pacific Alaska Resident stock and the Gulf of Alaska, Aleutian 
Islands, and the Bering Sea Transient stock. Both stocks occur in lower 
Cook Inlet, but rarely in middle and upper Cook Inlet (Shelden et al., 
2013). While stocks overlap the same geographic area, they maintain 
social and reproductive isolation and feed on different prey species. 
Resident killer whales are primarily fish-eaters, while transients 
primarily hunt and consume marine mammals, such as harbor seals, Dall's 
porpoises, harbor porpoises, beluga whales and sea lions. Killer whales 
are not harvested for subsistence in Alaska. Potential threats most 
likely to result in direct human-caused mortality or serious injury of 
killer whales in this region include oil spills, vessel strikes, and 
interactions with fisheries.
    Killer whales have been sighted near Homer and Port Graham in lower 
Cook Inlet (Shelden et al., 2003, 2022; Rugh et al., 2005). Resident 
killer whales from pods often sighted near Kenai Fjords and Prince 
William Sound have been occasionally photographed in lower Cook Inlet 
(Shelden et al., 2003). The availability of salmon influences when 
resident killer whales are more likely to be sighted in Cook Inlet. 
Killer whales were observed in the Kachemak and English Bay three times 
during aerial surveys conducted between 1993 and 2004 (Rugh et al., 
2005). Passive acoustic monitoring efforts throughout Cook Inlet 
documented killer whales at the Beluga River, Kenai River, and Homer 
Spit, although they were not encountered within Knik Arm (Castellote et 
al., 2016). These detections were likely resident killer whales. 
Transient killer whales likely have not been acoustically detected due 
to their propensity to move quietly through waters to track prey 
(Small, 2010; Lammers et al., 2013). Transient killer whales were 
increasingly reported to feed on belugas in the middle and upper Cook 
Inlet in the 1990s.
    During the 2015 SAExploration seismic program near the North 
Foreland, two killer whales were observed (Kendall et al., 2015, as 
cited in Weston and SLR, 2022). Killer whales were observed in lower 
Cook Inlet in 1994, 1997, 2001, 2005, 2010, 2012, and 2022 during the 
NMFS aerial surveys (Shelden et al., 2013, 2022). Eleven killer whale 
strandings have been reported in Turnagain Arm: 6 in May 1991 and 5 in 
August 1993. During the Hilcorp lower Cook Inlet seismic survey in the 
fall of 2019, 21 killer whales were documented (Fairweather Science, 
2020). Throughout 4 months of observation in 2018 during the CIPL 
project in middle Cook Inlet, no killer whales were observed 
(Sitkiewicz et al., 2018). In September 2021, two killer whales were 
documented in Knik Arm in upper Cook Inlet, near the POA (61N 
Environmental, 2022a). Hilcorp did not record any sightings of killer 
whales from their aerial or rig-based monitoring efforts in 2023 
(Horsley and Larson, 2023).

Pacific White-Sided Dolphin

    The Pacific white-sided dolphin is divided into three stocks within 
U.S. waters. The North Pacific stock includes the coast of Alaska, 
including the project area. Pacific white-sided dolphins are common in 
the Gulf of Alaska's pelagic waters and Alaska's nearshore areas, 
British Columbia, and Washington (Ferrero and Walker, 1996, as cited in 
Muto et al., 2022). They do not typically occur in Cook Inlet, but in 
2019, Castellote et al. (2020) documented short durations of Pacific 
white-sided dolphin presence using passive acoustic recorders near 
Iniskin Bay (6 minutes) and at an offshore mooring located 
approximately midway between Port Graham and Iniskin Bay (51 minutes). 
Detections of vocalizations typically lasted on the order of minutes, 
suggesting the animals did not remain in the area and/or continue 
vocalizing for extended durations. Visual monitoring conducted during 
the same period by marine mammal observers on seismic vessels near the 
offshore recorder did not detect any Pacific white-sided dolphins 
(Fairweather Science, 2020). These observational data, combined with 
anecdotal information, indicate that there is a small potential for 
Pacific white-sided dolphins to occur in the Project area. On May 7, 
2014, Apache Alaska observed three Pacific white-sided dolphins during 
an aerial survey near Kenai. This is one of the only recorded visual 
observations of Pacific white-sided dolphins in Cook Inlet; they have 
not been reported in groups as large as those estimated in other parts 
of Alaska (Muto et al., 2022).

Harbor Porpoise

    In the eastern North Pacific Ocean, harbor porpoise range from 
Point Barrow, along the Alaska coast, and down the west coast of North 
America to Point Conception, California. The 2022 Alaska SARs describe 
a revised stock structure for harbor porpoises (Young et al., 2023). 
Previously, NMFS had designated three stocks of harbor porpoises: the 
Bering Sea stock, the Gulf of Alaska stock, and the Southeast Alaska 
stock (Muto et al., 2022; Zerbini et al., 2022). The 2022 Alaska SARs 
splits the Southeast Alaska stock into three separate stocks, resulting 
in five separate stocks in Alaskan waters for this species. This update 
better aligns harbor porpoise stock structure with genetics, trends in 
abundance, and information regarding discontinuous distribution trends 
(Young et al., 2023). Harbor porpoises found in Cook Inlet are assumed 
to be members of the Gulf of Alaska stock (Young et al., 2023).
    Harbor porpoises occur most frequently in waters less than 100 m 
deep (Hobbs and Waite, 2010) and are common in nearshore areas of the 
Gulf of Alaska, Shelikof Strait, and lower Cook Inlet (Dahlheim et al., 
2000). Harbor porpoises are often observed in lower Cook Inlet in 
Kachemak Bay and from Cape Douglas to the West Foreland (Rugh et al., 
2005). They can be opportunistic foragers but consume primarily 
schooling forage fish (Bowen and Siniff, 1999). Given their shallow 
water distribution, harbor porpoise are vulnerable to physical 
modifications of nearshore habitats resulting from urban and industrial 
development (including waste management and nonpoint source runoff) and 
activities such as construction of docks and other over-water 
structures, filling of shallow areas, dredging, and noise 
(Linnenschmidt et al., 2013). Subsistence users have not reported any 
harvest from the Gulf of Alaska harbor porpoise stock since the early 
1900s (Shelden et al., 2014). Calving occurs from May to August; 
however, this can vary by region. Harbor porpoises are often found 
traveling alone, or in small groups of less than 10 individuals 
(Schmale, 2008).
    Harbor porpoises occur throughout Cook Inlet, with passive acoustic 
detections being more prevalent in

[[Page 60175]]

lower Cook Inlet. Although harbor porpoises have been frequently 
observed during aerial surveys in Cook Inlet (Shelden et al., 2014), 
most sightings are of single animals and are concentrated at Chinitna 
and Tuxedni bays on the west side of lower Cook Inlet (Rugh et al., 
2005), with smaller numbers observed in upper Cook Inlet between April 
and October. The occurrence of larger numbers of porpoise in the lower 
Cook Inlet may be driven by greater availability of preferred prey and 
possibly less competition with CIBWs, as CIBWs move into upper inlet 
waters to forage on Pacific salmon during the summer months (Shelden et 
al., 2014).
    An increase in harbor porpoise sightings in upper Cook Inlet was 
observed over recent decades (e.g., 61N Environmental, 2021, 2022a; 
Shelden et al., 2014). Small numbers of harbor porpoises have been 
consistently reported in upper Cook Inlet between April and October 
(Prevel-Ramos et al., 2008). The overall increase in the number of 
harbor porpoise sightings in upper Cook Inlet is unknown, although it 
may be an artifact of increased studies and marine mammal monitoring 
programs in upper Cook Inlet. It is also possible that the contraction 
in the CIBW's range has opened up previously occupied CIBW range to 
harbor porpoises (Shelden et al., 2014).
    During Apache's 2012 seismic program in middle Cook Inlet, 137 
groups of harbor porpoises comprising 190 individuals were documented 
between May and August (Lomac-MacNair et al., 2013). In June 2012, 
Shelden et al. (2015b) documented 65 groups of 129 individual harbor 
porpoises during an aerial survey, none of which were in upper Cook 
Inlet. Kendall et al. (2015, as cited in Weston and SLR, 2022) 
documented 52 groups comprising 65 individuals north of the Forelands 
during SAExploration's 2015 seismic survey. Shelden et al. (2017, 2019, 
and 2022) also conducted aerial surveys in June and July over Cook 
Inlet in 2016, 2018, 2021, and 2022 and recorded 65 individuals. 
Observations occurred in middle and lower Cook Inlet with a majority in 
Kachemak Bay. There were two sightings of three harbor porpoises 
observed during the 2019 Hilcorp lower Cook Inlet seismic survey in the 
fall (Fairweather Science, 2020). A total of 29 groups (44 individuals) 
were observed north of the Forelands from May to September during the 
CIPL Extension Project (Sitkiewicz et al., 2018). During jack-up rig 
moves in 2021, a PSO observed two individual harbor porpoises in middle 
Cook Inlet: one in July and one in October. Four monitoring events were 
conducted at the POA in Anchorage between April 2020 and August 2022, 
during which 42 groups of harbor porpoises comprising 50 individual 
porpoises were documented over 285 days of observation (61N 
Environmental 2021, 2022a, 2022b, and 2022c). One harbor porpoise was 
observed during Hilcorp's boat-based monitoring efforts in June 2023 
(Horsley and Larson, 2023).

Dall's Porpoise

    Dall's porpoises are found throughout the North Pacific, from 
southern Japan to southern California north to the Bering Sea. All 
Dall's porpoises in Alaska are of the Alaska stock. This species can be 
found in offshore, inshore, and nearshore habitat. The Dall's porpoise 
range in Alaska includes lower Cook Inlet, but very few sightings have 
been reported in upper Cook Inlet. Observations have been documented 
near Kachemak Bay and Anchor Point (Owl Ridge, 2014; BOEM, 2015). 
Shelden et al. (2013) and Rugh et al. (2005) collated data from aerial 
surveys conducted between 1994 and 2012 and documented 9 sightings of 
25 individuals in the lower Cook Inlet during June and/or July 1997, 
1999, and 2000. No Dall's porpoise were observed on subsequent surveys 
in June and/or July 2014, 2016, 2018, 2021, and 2022 (Shelden et al., 
2015b, 2017, and 2022; Shelden and Wade, 2019). During Apache's 2014 
seismic survey, two groups of three Dall's porpoises were observed in 
Upper and middle Cook Inlet (Lomac-MacNair et al., 2014). In August 
2015, one Dall's porpoise was reported in the mid-inlet north of 
Nikiski in middle Cook Inlet during SAExploration's seismic program 
(Kendall et al., 2015 as cited in Weston and SLR, 2022). During aerial 
surveys in Cook Inlet, they were observed in Iniskin Bay, Barren 
Island, Elizabeth Island, and Kamishak Bay (Shelden et al., 2013). No 
Dall's porpoises were observed during the 2018 CIPL Extension Project 
Acoustic Monitoring Program in middle Cook Inlet (Sitkiewicz et al., 
2018); however, 30 individuals in 10 groups were sighted during a lower 
Cook Inlet seismic project in the fall 2019 (Fairweather Science, 
2020). Hilcorp recorded three sightings of Dall's porpoises in 2021 and 
one sighting of a Dall's porpoise in 2023 from their rig-based 
monitoring efforts in the project area (Korsmo et al., 2022; Horsley 
and Larson, 2023). This higher number of sightings suggests Dall's 
porpoise may use portions of middle Cook Inlet in greater numbers than 
previously expected but would still be considered infrequent in middle 
and upper Cook Inlet.

Steller Sea Lion

    Two DPSs of Steller sea lion occur in Alaska: the western DPS and 
the eastern DPS. The western DPS includes animals that occur west of 
Cape Suckling, Alaska, and therefore includes individuals within the 
Project area. The western DPS was listed under the ESA as threatened in 
1990 (55 FR 49204, November 26, 1990), and its continued population 
decline resulted in a change in listing status to endangered in 1997 
(62 FR 24345, May 5, 1997). Since 2000, studies indicate that the 
population east of Samalga Pass (i.e., east of the Aleutian Islands) 
has increased and is potentially stable (Young et al., 2023).
    There is uncertainty regarding threats currently impeding the 
recovery of Steller sea lions, particularly in the Aleutian Islands. 
Many factors have been suggested as causes of the steep decline in 
abundance of western Steller sea lions observed in the 1980s, including 
competitive effects of fishing, environmental change, disease, 
contaminants, killer whale predation, incidental take, and illegal and 
legal shooting (Atkinson et al., 2008; NMFS, 2008a). A number of 
management actions have been implemented since 1990 to promote the 
recovery of the Western U.S. stock of Steller sea lions, including 5.6-
km (3-nautical mile) no-entry zones around rookeries, prohibition of 
shooting at or near sea lions, and regulation of fisheries for sea lion 
prey species (e.g., walleye pollock, Pacific cod, and Atka mackerel 
(Pleurogrammus monopterygius)) (Sinclair et al., 2013; Tollit et al., 
2017). Additionally, potentially deleterious events, such as harmful 
algal blooms (Lefebvre et al., 2016) and disease transmission across 
the Arctic (VanWormer et al., 2019) that have been associated with 
warming waters, could lead to potentially negative population-level 
impacts on Steller sea lions.
    NMFS designated critical habitat for Steller sea lions on August 
27, 1993 (58 FR 45269), including portions of the southern reaches of 
lower Cook Inlet. The critical habitat designation for the Western DPS 
of was determined to include a 37-km (20-nautical mile) buffer around 
all major haul-outs and rookeries, and associated terrestrial, 
atmospheric, and aquatic zones, plus three large offshore foraging 
areas, none of which occurs in the project area. There is no designated 
critical habitat for Steller sea lions in the mid- or upper inlet, nor 
are there any known BIAs for Steller sea lions within the project area. 
Rookeries and haul out sites in lower

[[Page 60176]]

Cook Inlet include those near the mouth of the inlet, which are 
approximately 56 km or more south of the closest action area.
    Steller sea lions are opportunistic predators, feeding primarily on 
a wide variety of seasonally abundant fishes and cephalopods, including 
Pacific herring (Clupea pallasi), walleye pollock, capelin (Mallotus 
villosus), Pacific sand lance (Ammodytes hexapterus), Pacific cod, 
salmon (Oncorhynchus spp.), and squid (Teuthida spp.); (Jefferson et 
al., 2008; Wynne et al., 2011). Steller sea lions do not generally eat 
every day, but tend to forage every 1-2 days and return to haulouts to 
rest between foraging trips (Merrick and Loughlin, 1997; Rehberg et 
al., 2009). Steller sea lions feed largely on walleye pollock, salmon, 
and arrowtooth flounder during the summer, and walleye pollock and 
Pacific cod during the winter (Sinclair and Zeppelin, 2002).
    Most Steller sea lions in Cook Inlet occur south of Anchor Point on 
the east side of lower Cook Inlet, with concentrations near haulout 
sites at Shaw Island and Elizabeth Island and by Chinitna Bay and 
Iniskin Bay on the west side (Rugh et al., 2005). Steller sea lions are 
rarely seen in upper Cook Inlet (Nemeth et al., 2007). About 3,600 sea 
lions use haulout sites in the lower Cook Inlet area (Sweeney et al., 
2017), with additional individuals venturing into the area to forage.
    Several surveys and monitoring programs have documented Steller sea 
lions throughout Cook Inlet, including in upper Cook Inlet in 2012 
(Lomac-MacNair et al., 2013), near Cape Starichkof in 2013 (Owl Ridge, 
2014), in middle and lower Cook Inlet in 2015 (Kendall et al., 2015, as 
cited in Weston and SLR, 2022), in middle Cook Inlet in 2018 
(Sitkiewicz et al., 2018), in lower Cook Inlet in 2019 (Fairweather 
Science, 2020), and near the POA in Anchorage in 2020, 2021, and 2022 
(61N Environmental, 2021, 2022a, 2022b, and 2022c). During NMFS Cook 
Inlet beluga whale aerial surveys from 2000 to 2016, 39 sightings of 
769 estimated individual Steller sea lions in lower Cook Inlet were 
recorded (Shelden et al., 2017). Sightings of large congregations of 
Steller sea lions during NMFS aerial surveys occurred outside the 
specific geographic region, on land in the mouth of Cook Inlet (e.g., 
Elizabeth and Shaw Islands). In 2012, during Apache's 3D Seismic 
surveys, three sightings of approximately four individuals in upper 
Cook Inlet were recorded (Lomac-MacNair et al., 2013). PSOs associated 
with Buccaneer's drilling project off Cape Starichkof observed seven 
Steller sea lions in summer 2013 (Owl Ridge, 2014), and another four 
Steller sea lions were observed in 2015 in Cook Inlet during 
SAExploration's 3D Seismic Program. Of the three 2015 sightings, one 
sighting occurred between the West and East Forelands, one occurred 
near Nikiski, and one occurred northeast of the North Foreland in the 
center of Cook Inlet (Kendall and Cornick, 2015). Five sightings of 
five Steller sea lions were recorded during Hilcorp's lower Cook Inlet 
seismic survey in the fall of 2019 (Fairweather Science, 2020). 
Additionally, one sighting of two individuals occurred during the CIPL 
Extension Project in 2018 in middle Cook Inlet (Sitkiewicz et al., 
2018). At the end of July 2022, while conducting a waterfowl survey an 
estimated 25 Steller sea lions were observed hauled-out at low tide in 
the Lewis River, on the west side of Cook Inlet. (K. Lindberg, personal 
communication, August 15, 2022). Steller sea lions have also been 
reported near the POA in Anchorage in 2020, 2021, and 2022 (61N 2021, 
2022a, 2022b, and 2022c). Hilcorp did not record any sightings of 
Steller sea lions from their aerial or rig-based monitoring efforts in 
2023 (Horsley and Larson, 2023).

Harbor Seal

    Harbor seals inhabit waters all along the western coast of the 
United States, British Columbia, and north through Alaska waters to the 
Pribilof Islands and Cape Newenham. NMFS currently identifies 12 stocks 
of harbor seals in Alaska based largely on genetic structure (Young et 
al., 2023). Harbor seals in the proposed project area are members of 
the Cook Inlet/Shelikof stock, which ranges from the southwest tip of 
Unimak Island east along the southern coast of the Alaska Peninsula to 
Elizabeth Island off the southwest tip of the Kenai Peninsula, 
including Cook Inlet, Knik Arm, and Turnagain Arm. Distribution of the 
Cook Inlet/Shelikof stock extends from Unimak Island, in the Aleutian 
Islands archipelago, north through all of upper and lower Cook Inlet 
(Young et al., 2023).
    Harbor seals inhabit the coastal and estuarine waters of Cook Inlet 
and are observed in both upper and lower Cook Inlet throughout most of 
the year (Boveng et al., 2012; Shelden et al., 2013). High-density 
areas include Kachemak Bay, Iniskin Bay, Iliamna Bay, Kamishak Bay, 
Cape Douglas, and Shelikof Strait. Up to a few hundred seals seasonally 
occur in middle and upper Cook Inlet (Rugh et al. 2005), with the 
highest concentrations found near the Susitna River and other 
tributaries within upper Cook Inlet during eulachon and salmon runs 
(Nemeth et al., 2007; Boveng et al., 2012), but most remain south of 
the forelands (Boveng et al., 2012).
    Harbor seals haul out on rocks, reefs, beaches, and drifting 
glacial ice (Young et al., 2023). Their movements are influenced by 
tides, weather, season, food availability, and reproduction, as well as 
individual sex and age class (Lowry et al., 2001; Small et al., 2003; 
Boveng et al., 2012). The results of past and recent satellite tagging 
studies in Southeast Alaska, Prince William Sound, Kodiak Island, and 
Cook Inlet are also consistent with the conclusion that harbor seals 
are non-migratory (Lowry et al., 2001; Small et al., 2003; Boveng et 
al., 2012). However, some long-distance movements of tagged animals in 
Alaska have been recorded (Pitcher and McAllister, 1981; Lowry et al., 
2001; Small et al., 2003; Womble, 2012; Womble and Gende, 2013). Strong 
fidelity of individuals for haulout sites during the breeding season 
has been documented in several populations (H[auml]rk[ouml]nen and 
Harding, 2001), including in Cook Inlet (Pitcher and McAllister, 1981; 
Small et al., 2005; Boveng et al., 2012; Womble, 2012; Womble and 
Gende, 2013). Harbor seals usually give birth to a single pup between 
May and mid-July; birthing locations are dispersed over several haulout 
sites and not confined to major rookeries (Klinkhart et al., 2008). 
More than 200 haulout sites are documented in lower Cook Inlet 
(Montgomery et al., 2007) and 18 in middle and upper Cook Inlet (London 
et al., 2015). Of the 18 in middle and upper Cook Inlet, nine are 
considered ``key haulout'' locations where aggregations of 50 or more 
harbor seals have been documented. Seven key haulouts are in the 
Susitna River delta, and two are near the Chickaloon River.
    Recent research on satellite-tagged harbor seals observed several 
movement patterns within Cook Inlet (Boveng et al., 2012), including a 
strong seasonal pattern of more coastal and restricted spatial use 
during the spring and summer (breeding, pupping, molting) and more 
wide-ranging movements within and outside of Cook Inlet during the 
winter months, with some seals ranging as far as Shumagin Islands. 
During summer months, movements and distribution were mostly confined 
to the west side of Cook Inlet and Kachemak Bay, and seals captured in 
lower Cook Inlet generally exhibited site fidelity by remaining south 
of the Forelands in lower Cook Inlet after release (Boveng et al., 
2012). In the fall, a portion of the harbor seals appeared to move out 
of Cook Inlet and into Shelikof Strait, northern Kodiak Island, and

[[Page 60177]]

coastal habitats of the Alaska Peninsula. The western coast of Cook 
Inlet had higher usage by harbor seals than eastern coast habitats, and 
seals captured in lower Cook Inlet generally exhibited site fidelity by 
remaining south of the Forelands in lower Cook Inlet after release 
(south of Nikiski; Boveng et al., 2012).
    Harbor seals have been sighted in Cook Inlet during every year of 
the aerial surveys conducted by NMFS and during all recent mitigation 
and monitoring programs in lower, middle, and upper Cook Inlet (61N 
Environmental, 2021, 2022a, 2022b, and 2022c; Fairweather Science, 
2020; Kendall et al., 2015 as cited in Weston and SLR, 2022; Lomac-
MacNair et al., 2013, 2014; Sitkiewicz et al., 2018). In addition, 
Hilcorp recorded one sighting of a harbor seal in 2021 and three 
sightings of harbor seals in 2023 from their aerial and rig-based 
monitoring efforts in the project area (Korsmo et al. 2022; Horsley and 
Larson, 2023).

California Sea Lion

    California sea lions live along the Pacific coastline spanning an 
area from central Mexico to Southeast Alaska and typically breed on 
islands located in southern California, western Baja California, and 
the Gulf of California (Carretta et al., 2020). Five genetically 
distinct geographic populations are known to exist: Pacific Temperate, 
Pacific Subtropical, Southern Gulf of California, Central Gulf of 
California, and Northern Gulf of California (Schramm et al., 2009).
    Few observations of California sea lions have been reported in 
Alaska and most observations have been limited to solitary individuals, 
typically males that are known to migrate long distances. Occasionally, 
California sea lions can be found in small groups of two or more and 
are usually associated with Steller sea lions at their haul outs and 
rookeries (Maniscalco et al., 2004). The few California sea lions 
observed in Alaska typically do not travel further north than Southeast 
Alaska. They are often associated with Steller sea lion haulouts and 
rookeries (Maniscalco et al., 2004). Sightings in Cook Inlet are rare, 
with two documented during the Apache 2012 seismic survey (Lomac-
MacNair et al., 2013) and anecdotal sightings in Kachemak Bay. None 
were sighted during the 2019 Hilcorp lower Cook Inlet seismic survey 
(Fairweather Science, 2020), the CIPL project in 2018 (Sitkiewicz et 
al., 2018), or the 2023 Hilcorp aerial or rig-based monitoring efforts 
(Horsley and Larson, 2023).

Marine Mammal Hearing

    Hearing is the most important sensory modality for marine mammals 
underwater, and exposure to anthropogenic sound can have deleterious 
effects. To appropriately assess the potential effects of exposure to 
sound, it is necessary to understand the frequency ranges marine 
mammals are able to hear. Not all marine mammal species have equal 
hearing capabilities (e.g., Richardson et al., 1995; Wartzok and 
Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al. 
(2007, 2019) recommended that marine mammals be divided into hearing 
groups based on directly measured (behavioral or auditory evoked 
potential techniques) or estimated hearing ranges (behavioral response 
data, anatomical modeling, etc.). Subsequently, NMFS (2018) described 
generalized hearing ranges for these marine mammal hearing groups. 
Generalized hearing ranges were chosen based on the approximately 65 
decibel (dB) threshold from the normalized composite audiograms, with 
the exception for lower limits for low-frequency cetaceans where the 
lower bound was deemed to be biologically implausible and the lower 
bound from Southall et al. (2007) retained. Marine mammal hearing 
groups and their associated hearing ranges are provided in table 3. 
Specific to this action, gray whales, fin whales, minke whales, and 
humpback whales are considered low-frequency (LF) cetaceans, beluga 
whales, pacific white-sided dolphins, and killer whales are considered 
mid-frequency (MF) cetaceans, harbor porpoises and Dall's porpoises are 
considered high-frequency (HF) cetaceans, Steller sea lions and 
California sea lions are otariid pinnipeds (OW), and harbor seals are 
phocid pinnipeds (PW).

                  Table 3--Marine Mammal Hearing Groups
                              [NMFS, 2018]
------------------------------------------------------------------------
               Hearing group                 Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen         7 Hz to 35 kHz.
 whales).
Mid-frequency (MF) cetaceans (dolphins,      150 Hz to 160 kHz.
 toothed whales, beaked whales, bottlenose
 whales).
High-frequency (HF) cetaceans (true          275 Hz to 160 kHz.
 porpoises, Kogia, river dolphins,
 Cephalorhynchid, Lagenorhynchus cruciger &
 L. australis).
Phocid pinnipeds (PW) (underwater) (true     50 Hz to 86 kHz.
 seals).
Otariid pinnipeds (OW) (underwater) (sea     60 Hz to 39 kHz.
 lions and fur seals).
------------------------------------------------------------------------
* Represents the generalized hearing range for the entire group as a
  composite (i.e., all species within the group), where individual
  species' hearing ranges are typically not as broad. Generalized
  hearing range chosen based on ~65 dB threshold from normalized
  composite audiogram, with the exception for lower limits for LF
  cetaceans (Southall et al., 2007) and PW pinniped (approximation).

    The pinniped functional hearing group was modified from Southall et 
al. (2007) on the basis of data indicating that phocid species have 
consistently demonstrated an extended frequency range of hearing 
compared to otariids, especially in the higher frequency range 
(Hemil[auml] et al., 2006; Kastelein et al., 2009; Reichmuth and Holt, 
2013). This division between phocid and otariid pinnipeds is now 
reflected in the updated hearing groups proposed in Southall et al. 
(2019).
    For more detail concerning these groups and associated frequency 
ranges, please see NMFS (2018) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their 
Habitat

    This section provides a discussion of the ways in which components 
of the specified activity may impact marine mammals and their habitat. 
The Estimated Take of Marine Mammals section later in this document 
includes a quantitative analysis of the number of individuals that are 
expected to be taken by this activity. The Negligible Impact Analysis 
and Determination section considers the content of this section, the 
Estimated Take of Marine Mammals section, and the Proposed Mitigation 
section, to draw conclusions regarding the likely impacts of these 
activities on the reproductive success or survivorship of individuals 
and whether those impacts are reasonably expected to, or reasonably 
likely to, adversely affect the

[[Page 60178]]

species or stock through effects on annual rates of recruitment or 
survival.
    Effects on marine mammals during the specified activity are 
expected to potentially occur from three to four tugs towing, holding, 
and or positioning a jack-up rig. Underwater noise from Hilcorp's 
proposed activities have the potential to result in Level B harassment 
of marine mammals in the action area.

Background on Sound

    This section contains a brief technical background on sound, on the 
characteristics of certain sound types, and on metrics used relevant to 
the specified activity and to a discussion of the potential effects of 
the specified activity on marine mammals found later in this document. 
For general information on sound and its interaction with the marine 
environment, please see: Erbe and Thomas (2022); Au and Hastings 
(2008); Richardson et al. (1995); Urick (1983); as well as the 
Discovery of Sound in the Sea website at https://dosits.org/.
    Sound is a vibration that travels as an acoustic wave through a 
medium such as a gas, liquid or solid. Sound waves alternately compress 
and decompress the medium as the wave travels. In water, sound waves 
radiate in a manner similar to ripples on the surface of a pond and may 
be either directed in a beam (narrow beam or directional sources) or 
sound may radiate in all directions (omnidirectional sources), as is 
the case for sound produced by tugs under load with a jack-up rig 
considered here. The compressions and decompressions associated with 
sound waves are detected as changes in pressure by marine mammals and 
human-made sound receptors such as hydrophones.
    Sound travels more efficiently in water than almost any other form 
of energy, making the use of sound as a primary sensory modality ideal 
for inhabitants of the aquatic environment. In seawater, sound travels 
at roughly 1,500 meters per second (m/s). In air, sound waves travel 
much more slowly at about 340 m/s. However, the speed of sound in water 
can vary by a small amount based on characteristics of the transmission 
medium such as temperature and salinity.
    The basic characteristics of a sound wave are frequency, 
wavelength, velocity, and amplitude. Frequency is the number of 
pressure waves that pass by a reference point per unit of time and is 
measured in hertz (Hz) or cycles per second. Wavelength is the distance 
between two peaks or corresponding points of a sound wave (length of 
one cycle). Higher frequency sounds have shorter wavelengths than lower 
frequency sounds, and typically attenuate (decrease) more rapidly with 
distance, except in certain cases in shallower water. The amplitude of 
a sound pressure wave is related to the subjective ``loudness'' of a 
sound and is typically expressed in dB, which are a relative unit of 
measurement that is used to express the ratio of one value of a power 
or pressure to another. A sound pressure level (SPL) in dB is described 
as the ratio between a measured pressure and a reference pressure, and 
is a logarithmic unit that accounts for large variations in amplitude; 
therefore, a relatively small change in dB corresponds to large changes 
in sound pressure. For example, a 10-dB increase is a 10-fold increase 
in acoustic power. A 20-dB increase is then a 100-fold increase in 
power and a 30-dB increase is a 1000-fold increase in power. However, a 
10-fold increase in acoustic power does not mean that the sound is 
perceived as being 10 times louder. The dB is a relative unit comparing 
two pressures; therefore, a reference pressure must always be 
indicated. For underwater sound, this is 1 microPascal ([mu]Pa). For 
in-air sound, the reference pressure is 20 microPascal ([mu]Pa). The 
amplitude of a sound can be presented in various ways; however, NMFS 
typically considers three metrics: sound exposure level (SEL), root-
mean-square (RMS) SPL, and peak SPL (defined below). The source level 
represents the SPL referenced at a standard distance from the source, 
typically 1 m (Richardson et al., 1995; American National Standards 
Institute (ANSI), 2013), while the received level is the SPL at the 
receiver's position. For tugging activities, the SPL is typically 
referenced at 1 m.
    SEL (represented as dB referenced to 1 micropascal squared second 
(re 1 [mu]Pa\2\-s)) represents the total energy in a stated frequency 
band over a stated time interval or event, and considers both intensity 
and duration of exposure. SEL can also be a cumulative metric; it can 
be accumulated over a single pulse (i.e., during activities such as 
impact pile driving) or calculated over periods containing multiple 
pulses (SELcum). Cumulative SEL (SELcum) 
represents the total energy accumulated by a receiver over a defined 
time window or during an event. The SEL metric is useful because it 
allows sound exposures of different durations to be related to one 
another in terms of total acoustic energy. The duration of a sound 
event and the number of pulses, however, should be specified as there 
is no accepted standard duration over which the summation of energy is 
measured.
    RMS SPL is equal to 10 times the logarithm (base 10) of the ratio 
of the mean-square sound pressure to the specified reference value, and 
given in units of dB (International Organization for Standardization 
(ISO), 2017). RMS is calculated by squaring all of the sound 
amplitudes, averaging the squares, and then taking the square root of 
the average (Urick, 1983). RMS accounts for both positive and negative 
values; squaring the pressures makes all values positive so that they 
may be accounted for in the summation of pressure levels (Hastings and 
Popper, 2005). This measurement is often used in the context of 
discussing behavioral effects, in part because behavioral effects, 
which often result from auditory cues, may be better expressed through 
averaged units than by peak SPL. For impulsive sounds, RMS is 
calculated by the portion of the waveform containing 90 percent of the 
sound energy from the impulsive event (Madsen, 2005).
    Peak SPL (also referred to as zero-to-peak sound pressure or 0-pk) 
is the maximum instantaneous sound pressure measurable in the water, 
which can arise from a positive or negative sound pressure, during a 
specified time, for a specific frequency range at a specified distance 
from the source, and is represented in the same units as the RMS sound 
pressure (ISO, 2017). Along with SEL, this metric is used in evaluating 
the potential for permanent threshold shift (PTS) and temporary 
threshold shift (TTS) associated with impulsive sound sources.
    Sounds are also characterized by their temporal components. 
Continuous sounds are those whose sound pressure level remains above 
that of the ambient or background sound with negligibly small 
fluctuations in level (ANSI, 2005) while intermittent sounds are 
defined as sounds with interrupted levels of low or no sound (National 
Institute for Occupational Safety and Health (NIOSH), 1998). A key 
distinction between continuous and intermittent sound sources is that 
intermittent sounds have a more regular (predictable) pattern of bursts 
of sounds and silent periods (i.e., duty cycle), which continuous 
sounds do not. Tugs under load are considered sources of continuous 
sound.
    Sounds may be either impulsive or non-impulsive (defined below). 
The distinction between these two sound types is important because they 
have differing potential to cause physical effects, particularly with 
regard to noise-induced hearing loss (e.g., Ward, 1997 in Southall et 
al., 2007). Please see

[[Page 60179]]

NMFS (2018) and Southall et al. (2007, 2019) for an in-depth discussion 
of these concepts.
    Impulsive sound sources (e.g., explosions, gunshots, sonic booms, 
seismic airgun shots, impact pile driving) produce signals that are 
brief (typically considered to be less than 1 second), broadband, 
atonal transients (ANSI, 1986, 2005; NIOSH, 1998) and occur either as 
isolated events or repeated in some succession. Impulsive sounds are 
all characterized by a relatively rapid rise from ambient pressure to a 
maximal pressure value followed by a rapid decay period that may 
include a period of diminishing, oscillating maximal and minimal 
pressures, and generally have an increased capacity to induce physical 
injury as compared with sounds that lack these features. Impulsive 
sounds are intermittent in nature. The duration of such sounds, as 
received at a distance, can be greatly extended in a highly reverberant 
environment.
    Non-impulsive sounds can be tonal, narrowband, or broadband, brief 
or prolonged, and may be either continuous or non-continuous (ANSI, 
1995; NIOSH, 1998). Some of these non-impulsive sounds can be transient 
signals of short duration but without the essential properties of 
impulses (e.g., rapid rise time). Examples of non-impulsive sounds 
include those produced by vessels (including tugs under load), 
aircraft, machinery operations such as drilling or dredging, vibratory 
pile driving, and active sonar systems.
    Even in the absence of sound from the specified activity, the 
underwater environment is characterized by sounds from both natural and 
anthropogenic sound sources. Ambient sound is defined as a composite of 
naturally-occurring (i.e., non-anthropogenic) sound from many sources 
both near and far (ANSI, 1995). Background sound is similar, but 
includes all sounds, including anthropogenic sounds, minus the sound 
produced by the proposed activities (NMFS, 2012, 2016a). The sound 
level of a region is defined by the total acoustical energy being 
generated by known and unknown sources. These sources may include 
physical (e.g., wind and waves, earthquakes, ice, atmospheric sound), 
biological (e.g., sounds produced by marine mammals, fish, and 
invertebrates), and anthropogenic (e.g., vessels, dredging, 
construction) sound.
    A number of sources contribute to background and ambient sound, 
including wind and waves, which are a main source of naturally 
occurring ambient sound for frequencies between 200 Hz and 50 kilohertz 
(kHz) (Mitson, 1995). In general, background and ambient sound levels 
tend to increase with increasing wind speed and wave height. 
Precipitation can become an important component of total sound at 
frequencies above 500 Hz, and possibly down to 100 Hz during quiet 
times. Marine mammals can contribute significantly to background and 
ambient sound levels, as can some fish and snapping shrimp. The 
frequency band for biological contributions is from approximately 12 Hz 
to over 100 kHz. Sources of background sound related to human activity 
include transportation (surface vessels), dredging and construction, 
oil and gas drilling and production, geophysical surveys, sonar, and 
explosions. Vessel noise typically dominates the total background sound 
for frequencies between 20 and 300 Hz. In general, the frequencies of 
many anthropogenic sounds, particularly those produced by construction 
activities, are below 1 kHz (Richardson et al., 1995). When sounds at 
frequencies greater than 1 kHz are produced, they generally attenuate 
relatively rapidly (Richardson et al., 1995), particularly above 20 kHz 
due to propagation losses and absorption (Urick, 1983).
    Transmission loss (TL) defines the degree to which underwater sound 
has spread in space and lost energy after having moved through the 
environment and reached a receiver. It is defined as the reduction in a 
specified level between two specified points that are within an 
underwater acoustic field (ISO, 2017). Careful consideration of 
transmission loss and appropriate propagation modeling is a crucial 
step in determining the impacts of underwater sound, as it helps to 
define the ranges (isopleths) to which impacts are expected and depends 
significantly on local environmental parameters such as seabed type, 
water depth (bathymetry), and the local speed of sound. Geometric 
spreading laws are powerful tools which provide a simple means of 
estimating TL, based on the shape of the sound wave front in the water 
column. For a sound source that is equally loud in all directions and 
in deep water, the sound field takes the form of a sphere, as the sound 
extends in every direction uniformly. In this case, the intensity of 
the sound is spread across the surface of the sphere, and thus we can 
relate intensity loss to the square of the range (as area = 4*pi*r\2\). 
When expressing logarithmically in dB as TL, we find that TL = 
20*Log10(range), this situation is known as spherical 
spreading. In shallow water, the sea surface and seafloor will bound 
the shape of the sound, leading to a more cylindrical shape, as the top 
and bottom of the sphere is truncated by the largely reflective 
boundaries. This situation is termed cylindrical spreading, and is 
given by TL = 10*Log10(range) (Urick, 1983). An intermediate 
scenario may be defined by the equation TL = 
15*Log10(range), and is referred to as practical spreading. 
Though these geometric spreading laws do not capture many often 
important details (scattering, absorption, etc.), they offer a 
reasonable and simple approximation of how sound decreases in intensity 
as it is transmitted. Cook Inlet is a particularly complex acoustic 
environment with strong currents, large tides, variable sea floor and 
generally changing conditions.
    The sum of the various natural and anthropogenic sound sources at 
any given location and time depends not only on the source levels, but 
also on the propagation of sound through the environment. Sound 
propagation is dependent on the spatially and temporally varying 
properties of the water column and sea floor, and is frequency-
dependent. As a result of the dependence on a large number of varying 
factors, background and ambient sound levels can be expected to vary 
widely over both coarse and fine spatial and temporal scales. Sound 
levels at a given frequency and location can vary by 10 to 20 dB from 
day to day (Richardson et al., 1995). The result is that, depending on 
the source type and its intensity, sound from a specified activity may 
be a negligible addition to the local environment or could form a 
distinctive signal that may affect marine mammals.

Description of Sound Sources for the Specified Activities

    In-water activities associated with the project that have the 
potential to incidentally take marine mammals through exposure to sound 
would be tugs towing, holding, and positioning the jack-up rig. Unlike 
discrete noise sources with known potential to harass marine mammals 
(e.g., pile driving, seismic surveys), both the noise sources and 
impacts from the tugs towing the jack-up rig are less well documented. 
Sound energy associated with the specified activity is produced by 
vessel propeller cavitation. Bow thrusters would be occasionally used 
for a short duration (20 to 30 seconds) to either push or pull a vessel 
in or away from a dock or platform. Other sound sources include onboard 
diesel generators and sound from the main engine, but both are 
subordinate to the thruster and main

[[Page 60180]]

propeller blade rate harmonics (Gray and Greeley, 1980). The various 
scenarios that may occur during this project include tugs in a 
stationary mode positioning the drill rig and pulling the jack-up rig 
at nearly full power against strong tides. Our assessments of the 
likelihood for harassment of marine mammals incidental to Hilcorp's tug 
activities specified here are conservative in light of the general 
Level B harassment exposure thresholds, the fact that NMFS is still in 
the process of developing analyses of the impact that non-quantitative 
contextual factors have on the likelihood of Level B harassment 
occurring, and the nature and duration of the particular tug activities 
analyzed here.

Acoustic Impacts

    The introduction of anthropogenic noise into the aquatic 
environment from tugs under load is the primary means by which marine 
mammals may be harassed from Hilcorp's specified activity. In general, 
animals exposed to natural or anthropogenic sound may experience 
physical and psychological effects, ranging in magnitude from none to 
severe (Southall et al., 2007, 2019). Exposure to anthropogenic noise 
has the potential to result in auditory threshold shifts and behavioral 
reactions (e.g., avoidance, temporary cessation of foraging and 
vocalizing, changes in dive behavior). It can also lead to non-
observable physiological responses, such as an increase in stress 
hormones. Additional noise in a marine mammal's habitat can mask 
acoustic cues used by marine mammals to carry out daily functions, such 
as communication and predator and prey detection. The effects of noise 
on marine mammals are dependent on several factors, including but not 
limited to sound type (e.g., impulsive vs. non-impulsive), the species, 
age and sex class (e.g., adult male vs. mom with calf), duration of 
exposure, the distance between the vessel and the animal, received 
levels, behavior at time of exposure, and previous history with 
exposure (Wartzok et al., 2004; Southall et al., 2007). Here we discuss 
physical auditory effects (threshold shifts) followed by behavioral 
effects and potential impacts on habitat.
    NMFS defines a noise-induced threshold shift (TS) as a change, 
usually an increase, in the threshold of audibility at a specified 
frequency or portion of an individual's hearing range above a 
previously established reference level (NMFS, 2018). The amount of 
threshold shift is customarily expressed in dB. A TS can be permanent 
or temporary. As described in NMFS (2018) there are numerous factors to 
consider when examining the consequence of TS, including but not 
limited to the signal temporal pattern (e.g., impulsive or non-
impulsive), likelihood an individual would be exposed for a long enough 
duration or to a high enough level to induce a TS, the magnitude of the 
TS, time to recovery (seconds to minutes or hours to days), the 
frequency range of the exposure (i.e., spectral content), the hearing 
frequency range of the exposed species relative to the signal's 
frequency spectrum (i.e., how animal uses sound within the frequency 
band of the signal; e.g., Kastelein et al., 2014), and the overlap 
between the animal and the source (e.g., spatial, temporal, and 
spectral).
    Permanent Threshold Shift (PTS). NMFS defines PTS as a permanent, 
irreversible increase in the threshold of audibility at a specified 
frequency or portion of an individual's hearing range above a 
previously established reference level (NMFS, 2018). PTS does not 
generally affect more than a limited frequency range, and an animal 
that has incurred PTS has incurred some level of hearing loss at the 
relevant frequencies; typically animals with PTS are not functionally 
deaf (Au and Hastings, 2008; Finneran, 2016). Available data from 
humans and other terrestrial mammals indicate that a 40-dB threshold 
shift approximates PTS onset (see Ward et al., 1958, 1959; Ward 1960; 
Kryter et al., 1966; Miller, 1974; Ahroon et al., 1996; Henderson et 
al., 2008). PTS levels for marine mammals are estimates, as with the 
exception of a single study unintentionally inducing PTS in a harbor 
seal (Kastak et al., 2008), there are no empirical data measuring PTS 
in marine mammals largely due to the fact that, for ethical reasons, 
experiments involving anthropogenic noise exposure at levels inducing 
PTS are not typically pursued or authorized (NMFS, 2018).
    Temporary Threshold Shift (TTS). TTS is a temporary, reversible 
increase in the threshold of audibility at a specified frequency or 
portion of an individual's hearing range above a previously established 
reference level (NMFS, 2018). Based on data from marine mammal TTS 
measurements (see Southall et al., 2007, 2019), a TTS of 6 dB is 
considered the minimum threshold shift clearly larger than any day-to-
day or session-to-session variation in a subject's normal hearing 
ability (Finneran et al., 2000, 2002; Schlundt et al., 2000). As 
described in Finneran (2015), marine mammal studies have shown the 
amount of TTS increases with SELcum in an accelerating 
fashion: at low exposures with lower SELcum, the amount of 
TTS is typically small and the growth curves have shallow slopes. At 
exposures with higher SELcum, the growth curves become 
steeper and approach linear relationships with the noise SEL.
    Depending on the degree (elevation of threshold in dB), duration 
(i.e., recovery time), and frequency range of TTS, and the context in 
which it is experienced, TTS can have effects on marine mammals ranging 
from discountable to serious (similar to those discussed in auditory 
masking, below). For example, a marine mammal may be able to readily 
compensate for a brief, relatively small amount of TTS in a non-
critical frequency range that takes place during a time when the animal 
is traveling through the open ocean, where ambient noise is lower and 
there are not as many competing sounds present. Alternatively, a larger 
amount and longer duration of TTS sustained during time when 
communication is critical for successful mother/calf interactions could 
have more serious impacts. We note that reduced hearing sensitivity as 
a simple function of aging has been observed in marine mammals, as well 
as humans and other taxa (Southall et al., 2007), so we can infer that 
strategies exist for coping with this condition to some degree, though 
likely not without cost.
    Many studies have examined noise-induced hearing loss in marine 
mammals (see Finneran (2015) and Southall et al. (2019) for summaries). 
TTS is the mildest form of hearing impairment that can occur during 
exposure to sound (Kryter, 2013). While experiencing TTS, the hearing 
threshold rises, and a sound must be at a higher level in order to be 
heard. In terrestrial and marine mammals, TTS can last from minutes or 
hours to days (in cases of strong TTS). In many cases, hearing 
sensitivity recovers rapidly after exposure to the sound ends. For 
cetaceans, published data on the onset of TTS are limited to captive 
bottlenose dolphin (Tursiops truncatus), beluga whale, harbor porpoise, 
and Yangtze finless porpoise (Neophocoena asiaeorientalis) (Southall et 
al., 2019). For pinnipeds in water, measurements of TTS are limited to 
harbor seals, elephant seals (Mirounga angustirostris), bearded seals 
(Erignathus barbatus) and California sea lions (Kastak et al., 1999, 
2007; Kastelein et al., 2019b, 2019c, 2021, 2022a, 2022b; Reichmuth et 
al., 2019; Sills et al., 2020). TTS was not observed in spotted (Phoca 
largha) and ringed (Pusa hispida) seals exposed to single airgun 
impulse sounds at levels

[[Page 60181]]

matching previous predictions of TTS onset (Reichmuth et al., 2016). 
These studies examine hearing thresholds measured in marine mammals 
before and after exposure to intense or long-duration sound exposures. 
The difference between the pre-exposure and post-exposure thresholds 
can be used to determine the amount of threshold shift at various post-
exposure times.
    The amount and onset of TTS depends on the exposure frequency. 
Sounds below the region of best sensitivity for a species or hearing 
group are less hazardous than those near the region of best sensitivity 
(Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure 
levels are higher compared to those in the region of best sensitivity 
(i.e., a low frequency noise would need to be louder to cause TTS onset 
when TTS exposure level is higher), as shown for harbor porpoises and 
harbor seals (Kastelein et al., 2019a, 2019c). Note that in general, 
harbor seals and harbor porpoises have a lower TTS onset than other 
measured pinniped or cetacean species (Finneran, 2015). In addition, 
TTS can accumulate across multiple exposures, but the resulting TTS 
will be less than the TTS from a single, continuous exposure with the 
same SEL (Mooney et al., 2009; Finneran et al., 2010; Kastelein et al., 
2014, 2015). This means that TTS predictions based on the total, 
cumulative SEL will overestimate the amount of TTS from intermittent 
exposures, such as sonars and impulsive sources. Nachtigall et al. 
(2018) describe measurements of hearing sensitivity of multiple 
odontocete species (bottlenose dolphin, harbor porpoise, beluga, and 
false killer whale (Pseudorca crassidens)) when a relatively loud sound 
was preceded by a warning sound. These captive animals were shown to 
reduce hearing sensitivity when warned of an impending intense sound. 
Based on these experimental observations of captive animals, the 
authors suggest that wild animals may dampen their hearing during 
prolonged exposures or if conditioned to anticipate intense sounds. 
Another study showed that echolocating animals (including odontocetes) 
might have anatomical specializations that might allow for conditioned 
hearing reduction and filtering of low-frequency ambient noise, 
including increased stiffness and control of middle ear structures and 
placement of inner ear structures (Ketten et al., 2021). Data available 
on noise-induced hearing loss for mysticetes are currently lacking 
(NMFS, 2018). Additionally, the existing marine mammal TTS data come 
from a limited number of individuals within these species.
    Relationships between TTS and PTS thresholds have not been studied 
in marine mammals, and there is no PTS data for cetaceans, but such 
relationships are assumed to be similar to those in humans and other 
terrestrial mammals. PTS typically occurs at exposure levels at least 
several decibels above that inducing mild TTS (e.g., a 40-dB threshold 
shift approximates PTS onset (Kryter et al., 1966; Miller, 1974), while 
a 6-dB threshold shift approximates TTS onset (Southall et al., 2007, 
2019). Based on data from terrestrial mammals, a precautionary 
assumption is that the PTS thresholds for impulsive sounds are at least 
6 dB higher than the TTS threshold on a peak-pressure basis and PTS 
cumulative sound exposure level thresholds are 15 to 20 dB higher than 
TTS cumulative sound exposure level thresholds (Southall et al., 2007, 
2019). Given the higher level of sound or longer exposure duration 
necessary to cause PTS as compared with TTS, it is considerably less 
likely that PTS could occur. Given the nature of tugging, a transient 
activity, and the fact that many marine mammals are likely moving 
through the project areas and not remaining for extended periods of 
time, the potential for threshold shift is low.
    Non-acoustic Stressors. HiIlcorp's proposed activities on marine 
mammals could also involve non-acoustic stressors. Potential non-
acoustic stressors could result from the physical presence of the 
equipment (e.g., tug configuration) and personnel; however, given there 
are no known pinniped haul-out sites in the vicinity of the project 
site, visual and other non-acoustic stressors would be limited, and any 
impacts to marine mammals are expected to primarily be acoustic in 
nature.
    Behavioral Harassment. Exposure to noise also has the potential to 
behaviorally disturb marine mammals to a level that rises to the 
definition of Level B harassment under the MMPA. Behavioral disturbance 
may include a variety of effects, including subtle changes in behavior 
(e.g., minor or brief avoidance of an area or changes in 
vocalizations), more conspicuous changes in similar behavioral 
activities, and more sustained and/or potentially severe reactions, 
such as displacement from or abandonment of high-quality habitat. 
Behavioral responses may include changing durations of surfacing and 
dives, changing direction and/or speed; reducing/increasing vocal 
activities; changing/cessation of certain behavioral activities (such 
as socializing or feeding); eliciting a visible startle response or 
aggressive behavior (such as tail/fin slapping or jaw clapping); and 
avoidance of areas where sound sources are located (Erbe et al., 2019). 
In addition, pinnipeds may increase their haul out time, possibly to 
avoid in-water disturbance (Thorson and Reyff, 2006).
    Behavioral responses to sound are highly variable and context-
specific and any reactions depend on numerous intrinsic and extrinsic 
factors (e.g., species, state of maturity, experience, current 
activity, reproductive state, auditory sensitivity, time of day), as 
well as the interplay between factors (e.g., Richardson et al., 1995; 
Wartzok et al., 2004; Southall et al., 2007, 2019; Weilgart, 2007; 
Archer et al., 2010; Erbe et al. 2019). Behavioral reactions can vary 
not only among individuals but also within an individual, depending on 
previous experience with a sound source, context, and numerous other 
factors (Ellison et al., 2012), and can vary depending on 
characteristics associated with the sound source (e.g., whether it is 
moving or stationary, number of sources, distance from the source). For 
example, animals that are resting may show greater behavioral change in 
response to disturbing sound levels than animals that are highly 
motivated to remain in an area for feeding (Richardson et al., 1995; 
Wartzok et al., 2004; National Research Council (NRC), 2005). In 
general, pinnipeds seem more tolerant of, or at least habituate more 
quickly to, potentially disturbing underwater sound than do cetaceans, 
and generally seem to be less responsive to exposure to industrial 
sound than most cetaceans. Please see appendices B and C of Southall et 
al. (2007) and Gomez et al. (2016) for reviews of studies involving 
marine mammal behavioral responses to sound.
    Habituation can occur when an animal's response to a stimulus wanes 
with repeated exposure, usually in the absence of unpleasant associated 
events (Wartzok et al., 2004). Animals are most likely to habituate to 
sounds that are predictable and unvarying. It is important to note that 
habituation is appropriately considered as a ``progressive reduction in 
response to stimuli that are perceived as neither aversive nor 
beneficial,'' rather than as, more generally, moderation in response to 
human disturbance (Bejder et al., 2009). The opposite process is 
sensitization, when an unpleasant experience leads to subsequent 
responses, often in the form of avoidance, at a lower level of 
exposure.

[[Page 60182]]

    Available studies show wide variation in response to underwater 
sound; therefore, it is difficult to predict specifically how any given 
sound in a particular instance might affect marine mammals perceiving 
the signal (e.g., Erbe et al. 2019). If a marine mammal does react 
briefly to an underwater sound by changing its behavior or moving a 
small distance, the impacts of the change are unlikely to be 
significant to the individual, let alone the stock or population. If a 
sound source displaces marine mammals from an important feeding or 
breeding area for a prolonged period, impacts on individuals and 
populations could be significant (e.g., Lusseau and Bejder, 2007; 
Weilgart, 2007; NRC, 2005). However, there are broad categories of 
potential response, which we describe in greater detail here, that 
include alteration of dive behavior, alteration of foraging behavior, 
effects to breathing, interference with or alteration of vocalization, 
avoidance, and flight.
    Changes in dive behavior can vary widely and may consist of 
increased or decreased dive times and surface intervals as well as 
changes in the rates of ascent and descent during a dive (e.g., Frankel 
and Clark, 2000; Costa et al., 2003; Ng and Leung, 2003; Nowacek et 
al., 2004; Goldbogen et al., 2013a, 2013b, Blair et al., 2016). 
Variations in dive behavior may reflect interruptions in biologically 
significant activities (e.g., foraging) or they may be of little 
biological significance. The impact of an alteration to dive behavior 
resulting from an acoustic exposure depends on what the animal is doing 
at the time of the exposure and the type and magnitude of the response.
    Disruption of feeding behavior from anthropogenic sound exposure is 
usually inferred by observed displacement from known foraging areas, 
the appearance of secondary indicators (e.g., bubble nets or sediment 
plumes), or changes in dive behavior. Acoustic and movement bio-logging 
tools also have been used in some cases to infer responses to 
anthropogenic noise. For example, Blair et al. (2016) reported 
significant effects on humpback whale foraging behavior in Stellwagen 
Bank in response to ship noise including slower descent rates, and 
fewer side-rolling events per dive with increasing ship nose. In 
addition, Wisniewska et al. (2018) reported that tagged harbor 
porpoises demonstrated fewer prey capture attempts when encountering 
occasional high-noise levels resulting from vessel noise as well as 
more vigorous fluking, interrupted foraging, and cessation of 
echolocation signals observed in response to some high-noise vessel 
passes. As for other types of behavioral response, the frequency, 
duration, and temporal pattern of signal presentation, as well as 
differences in species sensitivity, are likely contributing factors to 
differences in response in any given circumstance (e.g., Croll et al., 
2001; Nowacek et al., 2004; Madsen et al., 2006; Yazvenko et al., 
2007).
    Variations in respiration naturally vary with different behaviors 
and alterations to breathing rate as a function of acoustic exposure 
can be expected to co-occur with other behavioral reactions, such as a 
flight response or an alteration in diving. However, respiration rates 
in and of themselves may be representative of annoyance or an acute 
stress response. Various studies have shown that respiration rates may 
either be unaffected or could increase, depending on the species and 
signal characteristics, again highlighting the importance in 
understanding species differences in the tolerance of underwater noise 
when determining the potential for impacts resulting from anthropogenic 
sound exposure (e.g., Kastelein et al., 2001, 2005, 2006; Gailey et 
al., 2007).
    Avoidance is the displacement of an individual from an area or 
migration path as a result of the presence of a sound or other 
stressors, and is one of the most obvious manifestations of disturbance 
in marine mammals (Richardson et al., 1995). For example, gray whales 
are known to change direction--deflecting from customary migratory 
paths--in order to avoid noise from seismic surveys (Malme et al., 
1984). Harbor porpoises, Atlantic white-sided dolphins (Lagenorhynchus 
actusus), and minke whales have demonstrated avoidance in response to 
vessels during line transect surveys (Palka and Hammond, 2001). In 
addition, beluga whales in the St. Lawrence Estuary in Canada have been 
reported to increase levels of avoidance with increased boat presence 
by way of increased dive durations and swim speeds, decreased surfacing 
intervals, and by bunching together into groups (Blane and Jaakson, 
1994). Avoidance may be short-term, with animals returning to the area 
once the noise has ceased (e.g., Bowles et al., 1994; Goold, 1996; 
Stone et al., 2000; Morton and Symonds, 2002; Gailey et al., 2007). 
Longer-term displacement is possible, however, which may lead to 
changes in abundance or distribution patterns of the affected species 
in the affected region if habituation to the presence of the sound does 
not occur (e.g., Blackwell et al., 2004; Bejder et al., 2006; Teilmann 
et al., 2006).
    A flight response is a dramatic change in normal movement to a 
directed and rapid movement away from the perceived location of a sound 
source. The flight response differs from other avoidance responses in 
the intensity of the response (e.g., directed movement, rate of 
travel). Relatively little information on flight responses of marine 
mammals to anthropogenic signals exist, although observations of flight 
responses to the presence of predators have occurred (Connor and 
Heithaus, 1996; Bowers et al., 2018). The result of a flight response 
could range from brief, temporary exertion and displacement from the 
area where the signal provokes flight to, in extreme cases, marine 
mammal strandings (England et al., 2001). However, it should be noted 
that response to a perceived predator does not necessarily invoke 
flight (Ford and Reeves, 2008), and whether individuals are solitary or 
in groups may influence the response.
    Behavioral disturbance can also impact marine mammals in more 
subtle ways. Increased vigilance may result in costs related to 
diversion of focus and attention (i.e., when a response consists of 
increased vigilance, it may come at the cost of decreased attention to 
other critical behaviors such as foraging or resting). These effects 
have generally not been demonstrated for marine mammals, but studies 
involving fishes and terrestrial animals have shown that increased 
vigilance may substantially reduce feeding rates (e.g., Beauchamp and 
Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In 
addition, chronic disturbance can cause population declines through 
reduction of fitness (e.g., decline in body condition) and subsequent 
reduction in reproductive success, survival, or both (e.g., Harrington 
and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, 
Ridgway et al. (2006) reported that increased vigilance in bottlenose 
dolphins exposed to sound over a 5-day period did not cause any sleep 
deprivation or stress effects.
    Many animals perform vital functions, such as feeding, resting, 
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption 
of such functions resulting from reactions to stressors such as sound 
exposure are more likely to be significant if they last more than one 
diel cycle or recur on subsequent days (Southall et al., 2007). 
Consequently, a behavioral response lasting less than 1 day and not 
recurring on subsequent days is not considered particularly severe 
unless it could directly affect reproduction or survival (Southall et 
al., 2007). Note that there is a difference between multi-day

[[Page 60183]]

substantive (i.e., meaningful) behavioral reactions and multi-day 
anthropogenic activities. For example, just because an activity lasts 
for multiple days does not necessarily mean that individual animals are 
either exposed to activity-related stressors for multiple days or, 
further, exposed in a manner resulting in sustained multi-day 
substantive behavioral responses.
    Stress responses. An animal's perception of a threat may be 
sufficient to trigger stress responses consisting of some combination 
of behavioral responses, autonomic nervous system responses, 
neuroendocrine responses, or immune responses (e.g., Selye, 1950; 
Moberg, 2000). In many cases, an animal's first and sometimes most 
economical (in terms of energetic costs) response is behavioral 
avoidance of the potential stressor. Autonomic nervous system responses 
to stress typically involve changes in heart rate, blood pressure, and 
gastrointestinal activity. These responses have a relatively short 
duration and may or may not have a significant long-term effect on an 
animal's fitness.
    Neuroendocrine stress responses often involve the hypothalamus-
pituitary-adrenal system. Virtually all neuroendocrine functions that 
are affected by stress--including immune competence, reproduction, 
metabolism, and behavior--are regulated by pituitary hormones. Stress-
induced changes in the secretion of pituitary hormones have been 
implicated in failed reproduction, altered metabolism, reduced immune 
competence, and behavioral disturbance (e.g., Moberg, 1987; Blecha, 
2000). Increases in the circulation of glucocorticoids are also equated 
with stress (Romano et al., 2004).
    The primary distinction between stress (which is adaptive and does 
not normally place an animal at risk) and ``distress'' is the cost of 
the response. During a stress response, an animal uses glycogen stores 
that can be quickly replenished once the stress is alleviated. In such 
circumstances, the cost of the stress response would not pose serious 
fitness consequences. However, when an animal does not have sufficient 
energy reserves to satisfy the energetic costs of a stress response, 
energy resources must be diverted from other functions. This state of 
distress will last until the animal replenishes its energetic reserves 
sufficient to restore normal function.
    Relationships between these physiological mechanisms, animal 
behavior, and the costs of stress responses are well-studied through 
controlled experiments and for both laboratory and free-ranging animals 
(e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003; 
Krausman et al., 2004; Lankford et al., 2005). Stress responses due to 
exposure to anthropogenic sounds or other stressors and their effects 
on marine mammals have also been reviewed (Fair and Becker, 2000; 
Romano et al., 2002b) and, more rarely, studied in wild populations 
(e.g., Romano et al., 2002a). For example, Rolland et al. (2012) found 
that noise reduction from reduced ship traffic in the Bay of Fundy was 
associated with decreased stress in North Atlantic right whales. In 
addition, Lemos et al. (2022) observed a correlation between higher 
levels of fecal glucocorticoid metabolite concentrations (indicative of 
a stress response) and vessel traffic in gray whales. These and other 
studies lead to a reasonable expectation that some marine mammals will 
experience physiological stress responses upon exposure to acoustic 
stressors and that it is possible that some of these would be 
classified as ``distress.'' In addition, any animal experiencing TTS 
would likely also experience stress responses (NRC, 2005), however 
distress is an unlikely result of this project based on observations of 
marine mammals during previous, similar construction projects.
    Norman (2011) reviewed environmental and anthropogenic stressors 
for CIBWs. Lyamin et al. (2011) determined that the heart rate of a 
beluga whale increases in response to noise, depending on the frequency 
and intensity. Acceleration of heart rate in the beluga whale is the 
first component of the ``acoustic startle response.'' Romano et al. 
(2004) demonstrated that captive beluga whales exposed to high-level 
impulsive sounds (i.e., seismic airgun and/or single pure tones up to 
201 dB RMS) resembling sonar pings showed increased stress hormone 
levels of norepinephrine, epinephrine, and dopamine when TTS was 
reached. Thomas et al. (1990) exposed beluga whales to playbacks of an 
oil-drilling platform in operation (``Sedco 708,'' 40 Hz-20 kHz; source 
level 153 dB). Ambient SPL at ambient conditions in the pool before 
playbacks was 106 dB and 134 to 137 dB RMS during playbacks at the 
monitoring hydrophone across the pool. All cell and platelet counts and 
21 different blood chemicals, including epinephrine and norepinephrine, 
were within normal limits throughout baseline and playback periods, and 
stress response hormone levels did not increase immediately after 
playbacks. The difference between the Romano et al. (2004) and Thomas 
et al. (1990) studies could be the differences in the type of sound 
(seismic airgun and/or tone versus oil drilling), the intensity and 
duration of the sound, the individual's response, and the surrounding 
circumstances of the individual's environment. The sounds in the Thomas 
et al. (1990) study would be more similar to those anticipated by 
Hilcorp's tugs under load with a jack-up rig; therefore, no more than 
short-term, low-hormone stress responses, if any, of CIBWs or other 
marine mammals are expected as a result of exposure to noise during 
tugs under load with a jack-up rig during Hilcorp's planned activities.
    Auditory Masking. Since many marine mammals rely on sound to find 
prey, moderate social interactions, and facilitate mating (Tyack, 
2008), noise from anthropogenic sound sources can interfere with these 
functions, but only if the noise spectrum overlaps with the hearing 
sensitivity of the receiving marine mammal (Southall et al., 2007; 
Clark et al., 2009; Hatch et al., 2012). Chronic exposure to excessive, 
though not high-intensity, noise could cause masking at particular 
frequencies for marine mammals that utilize sound for vital biological 
functions (Clark et al., 2009). Acoustic masking is when other noises 
such as from human sources interfere with an animal's ability to 
detect, recognize, or discriminate between acoustic signals of interest 
(e.g., those used for intraspecific communication and social 
interactions, prey detection, predator avoidance, navigation) 
(Richardson et al., 1995; Erbe et al., 2016). Therefore, under certain 
circumstances, marine mammals whose acoustical sensors or environment 
are being severely masked could also be impaired from maximizing their 
performance fitness for survival and reproduction. The ability of a 
noise source to mask biologically important sounds depends on the 
characteristics of both the noise source and the signal of interest 
(e.g., signal-to-noise ratio, temporal variability, direction), in 
relation to each other and to an animal's hearing abilities (e.g., 
sensitivity, frequency range, critical ratios, frequency 
discrimination, directional discrimination, age or TTS hearing loss), 
and existing ambient noise and propagation conditions (Hotchkin and 
Parks, 2013).
    Marine mammals vocalize for different purposes and across multiple 
modes, such as whistling, echolocation click production, calling, and 
singing. Changes in vocalization behavior in response to anthropogenic 
noise can occur for any of these modes and may result from a need to 
compete with an increase in background noise or may reflect increased 
vigilance or a startle

[[Page 60184]]

response. For example, in the presence of potentially masking signals, 
humpback whales and killer whales have been observed to increase the 
length of their songs (Miller et al., 2000; Fristrup et al., 2003) or 
vocalizations (Foote et al., 2004), respectively, while North Atlantic 
right whales (Eubalaena glacialis) have been observed to shift the 
frequency content of their calls upward while reducing the rate of 
calling in areas of increased anthropogenic noise (Parks et al., 2007). 
Fin whales have also been documented lowering the bandwidth, peak 
frequency, and center frequency of their vocalizations under increased 
levels of background noise from large vessels (Castellote et al. 2012). 
Other alterations to communication signals have also been observed. For 
example, gray whales, in response to playback experiments exposing them 
to vessel noise, have been observed increasing their vocalization rate 
and producing louder signals at times of increased outboard engine 
noise (Dahlheim and Castellote, 2016). Alternatively, in some cases, 
animals may cease sound production during production of aversive 
signals (Bowles et al., 1994; Wisniewska et al., 2018).
    Under certain circumstances, marine mammals experiencing 
significant masking could also be impaired from maximizing their 
performance fitness in survival and reproduction. Therefore, when the 
coincident (masking) sound is human-made, it may be considered 
harassment when disrupting or altering critical behaviors. It is 
important to distinguish TTS and PTS, which persist after the sound 
exposure, from masking, which occurs during the sound exposure. Because 
masking (without resulting in TS) is not associated with abnormal 
physiological function, it is not considered a physiological effect, 
but rather a potential behavioral effect (though not necessarily one 
that would be associated with harassment).
    The frequency range of the potentially masking sound is important 
in determining any potential behavioral impacts. For example, low-
frequency signals may have less effect on high-frequency echolocation 
sounds produced by odontocetes but are more likely to affect detection 
of mysticete communication calls and other potentially important 
natural sounds such as those produced by surf and some prey species. 
The masking of communication signals by anthropogenic noise may be 
considered as a reduction in the communication space of animals (e.g., 
Clark et al., 2009) and may result in energetic or other costs as 
animals change their vocalization behavior (e.g., Miller et al., 2000; 
Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2010; Holt 
et al., 2009). Masking can be reduced in situations where the signal 
and noise come from different directions (Richardson et al., 1995), 
through amplitude modulation of the signal, or through other 
compensatory behaviors (Hotchkin and Parks, 2013).
    Marine mammals at or near the proposed project site may be exposed 
to anthropogenic noise which may be a source of masking. Vocalization 
changes may result from a need to compete with an increase in 
background noise and include increasing the source level, modifying the 
frequency, increasing the call repetition rate of vocalizations, or 
ceasing to vocalize in the presence of increased noise (Hotchkin and 
Parks, 2013). For example, in response to vessel noise, CIBWs may shift 
the frequency of their echolocation clicks and communication signals, 
reduce their overall calling rates, and or increase the emission of 
certain call signals to prevent masking by anthropogenic noise (Lesage 
et al. 1999; Tyack, 2000; Eickmeier and Vallarta, 2022).
    Masking occurs in the frequency band that the animals utilize, and 
is more likely to occur in the presence of broadband, relatively 
continuous noise sources such as tugging. Since noises generated from 
tugs towing and positioning are mostly concentrated at low frequency 
ranges, with a small concentration in high frequencies as well, these 
activities likely have less effect on mid-frequency echolocation sounds 
by odontocetes (toothed whales) such as CIBWs. However, lower frequency 
noises are more likely to affect detection of communication calls and 
other potentially important natural sounds such as surf and prey noise. 
Low-frequency noise may also affect communication signals when they 
occur near the frequency band for noise and thus reduce the 
communication space of animals (e.g., Clark et al., 2009) and cause 
increased stress levels (e.g., Holt et al., 2009). Unlike TS, masking, 
which can occur over large temporal and spatial scales, can potentially 
affect the species at population, community, or even ecosystem levels, 
in addition to individual levels. Masking affects both senders and 
receivers of the signals, and at higher levels for longer durations, 
could have long-term chronic effects on marine mammal species and 
populations. However, the noise generated by the tugs will not be 
concentrated in one location or for more than 5 hours per positioning 
attempt, and up to two positioning attempts at the same site. Thus, 
while Hilcorp's activities may mask some acoustic signals that are 
relevant to the daily behavior of marine mammals, the short-term 
duration and limited areas affected make it very unlikely that the 
fitness of individual marine mammals would be impacted.
    In consideration of the range of potential effects (PTS to 
behavioral disturbance), we consider the potential exposure scenarios 
and context in which species would be exposed to tugs under load with a 
jack-up rig during Hilcorp's planned activities. CIBWs may be present 
in low numbers during the work; therefore, some individuals may be 
reasonably expected to be exposed to elevated sound levels However, 
CIBWs are expected to be transiting through the area, given this work 
is proposed primarily in middle Cook Inlet (as described in the 
Description of Marine Mammals in the Area of Specified Activities 
section), thereby limiting exposure duration, as CIBWs in the area are 
expected to be headed to or from the concentrated foraging areas 
farther north near the Beluga River, Susitna Delta, and Knik and 
Turnigan Arms. Similarly, humpback whales, fin whales, minke whales, 
gray whales, killer whales, California sea lion, and Steller sea lions 
are not expected to remain in the area of the tugs. Dall's porpoise, 
harbor porpoise, and harbor seal have been sighted with more regularity 
than many other species during oil and gas activities in Cook Inlet but 
due to the transitory nature of these species, they are unlikely to 
remain close to a tug under load for the full duration of the noise-
producing activity. In fact, during Hilcorp's jack-up rig-based 
monitoring efforts in 2023, only one Dall's porpoise, two harbor seals, 
and one harbor porpoise were observed across four different sightings, 
and observations only lasted 1 to 5 minutes (Horsley and Larson, 2023). 
Because of this and the relatively low-level sources, the likelihood of 
PTS and TTS over the course of the tug activities is discountable. 
Harbor seals may linger or haul-out in the area but they are not known 
to do so in any large number or for extended periods of time (there are 
no known major haul-outs or rookeries coinciding with the anticipated 
transit routes). Here we find there is small potential for TTS over the 
course of tug activities but again, PTS is not likely due to the nature 
of tugging. Potential for PTS and TTS due to pile driving is discussed 
further in the Estimated Take section.
    Given most marine mammals are likely transiting through the area, 
exposure is expected to be brief but the

[[Page 60185]]

actual presence of the tug and jack-up rig may result in animals 
shifting pathways around the work site (e.g., avoidance), increasing 
speed or dive times, changing their group formations, or altering their 
acoustic signals. The likelihood of no more than a short-term, 
localized disturbance response is supported by data from Hilcorp's 
previous jack-up rig-based monitoring efforts in 2023, which reported 
no observable reactions to the towing activities outside of two harbor 
seals diving. Further other data indicate CIBWs and other marine 
mammals regularly pass by industrialized areas such as the POA (61N 
Environmental, 2021, 2022a, 2022b, 2022c; Easley-Appleyard and Leonard, 
2022); therefore, we do not expect abandonment of their transiting 
route or other disruptions of their behavioral patterns. We also 
anticipate some animals may respond with such mild reactions to the 
project that the response would not be detectable. For example, during 
low levels of tug power output (e.g., while tugs may be operating at 
low power because of favorable conditions), the animals may be able to 
hear the work but any resulting reactions, if any, are not expected to 
rise to the level of take.
    While in some cases marine mammals have exhibited little to no 
obviously detectable response to certain common or routine 
industrialized activity (Cornick et al., 2011; Horley and Larson, 
2023), it is possible some animals may at times be exposed to received 
levels of sound above the Level B harassment threshold. This potential 
exposure in combination with the nature of the tug and jack-up rig 
configuration (e.g., difficult to maneuver, potential need to operate 
at night) means it is possible that take by Level B harassment could 
occur over the total estimated period of activities; therefore, NMFS in 
response to Hilcorp's IHA application proposes to authorize take by 
Level B harassment from Hilcorp's use of tugs towing a jack-up rig for 
both positioning and straight-line tug activities.

Potential Effects on Marine Mammal Habitat

    Hilcorp's proposed activities could have localized, temporary 
impacts on marine mammal habitat, including prey, by increasing in-
water sound pressure levels. Increased noise levels may affect acoustic 
habitat and adversely affect marine mammal prey in the vicinity of the 
project areas (see discussion below). Elevated levels of underwater 
noise would ensonify the project areas where both fishes and mammals 
occur and could affect foraging success. Additionally, marine mammals 
may avoid the area during rig towing, holding, and or positioning; 
however, displacement due to noise is expected to be temporary and is 
not expected to result in long-term effects to the individuals or 
populations.
    The total area likely impacted by Hilcorp's activities is 
relatively small compared to the available habitat in Cook Inlet. 
Avoidance by potential prey (i.e., fish) of the immediate area due to 
increased noise is possible. The duration of fish and marine mammal 
avoidance of this area after tugging stops is unknown, but a rapid 
return to normal recruitment, distribution, and behavior is 
anticipated. Any behavioral avoidance by fish or marine mammals of the 
disturbed area would still leave significantly large areas of fish and 
marine mammal foraging habitat in the nearby vicinity. Increased 
turbidity near the seafloor is not anticipated
    Potential Effects on Prey. Sound may affect marine mammals through 
impacts on the abundance, behavior, or distribution of prey species 
(e.g., crustaceans, cephalopods, fishes, zooplankton). Marine mammal 
prey varies by species, season, and location and, for some, is not well 
documented. Studies regarding the effects of noise on known marine 
mammal prey are described here.
    Fishes utilize the soundscape and components of sound in their 
environment to perform important functions such as foraging, predator 
avoidance, mating, and spawning (e.g., Zelick et al., 1999; Fay, 2009). 
Depending on their hearing anatomy and peripheral sensory structures, 
which vary among species, fishes hear sounds using pressure and 
particle motion sensitivity capabilities and detect the motion of 
surrounding water (Fay et al., 2008). The potential effects of noise on 
fishes depends on the overlapping frequency range, distance from the 
sound source, water depth of exposure, and species-specific hearing 
sensitivity, anatomy, and physiology. Reactions also depend on the 
physiological state of the fish, past exposures, motivation (e.g., 
feeding, spawning, migration), and other environmental factors.
    Fish react to sounds that are especially strong and/or intermittent 
low-frequency sounds, and behavioral responses such as flight or 
avoidance are the most likely effects. Short duration, sharp sounds can 
cause overt or subtle changes in fish behavior and local distribution. 
SPLs of sufficient strength have been known to cause injury to fishes 
and fish mortality (summarized in Popper et al., 2014). However, in 
most fish species, hair cells in the ear continuously regenerate and 
loss of auditory function likely is restored when damaged cells are 
replaced with new cells. Halvorsen et al. (2012) showed that a TTS of 4 
to 6 dB was recoverable within 24 hours for one species. Impacts would 
be most severe when the individual fish is close to the source and when 
the duration of exposure is long. Injury caused by barotrauma can range 
from slight to severe and can cause death, and is most likely for fish 
with swim bladders.
    Fish have been observed to react when engine and propeller sounds 
exceed a certain level (Olsen et al., 1983; Ona, 1988; Ona and Godo, 
1990). Avoidance reactions have been observed in fish, including cod 
and herring, when vessel sound levels were 110 to 130 dB re 1 [mu]Pa 
rms (Nakken, 1992; Olsen, 1979; Ona and Godo, 1990; Ona and Toresen, 
1988). Vessel sound source levels in the audible range for fish are 
typically 150 to 170 dB re 1 [mu]Pa per Hz (Richardson et al., 1995). 
The tugs used during the specified activity could be expected to 
produce levels in this range when in transit. Based upon the reports in 
the literature and the predicted sound levels from these vessels, some 
temporary avoidance by fish in the immediate area may occur. Overall, 
no more than negligible impacts on fish are expected as a result of the 
specified activity.
    Zooplankton is a food source for several marine mammal species, as 
well as a food source for fish that are then preyed upon by marine 
mammals. Population effects on zooplankton could have indirect effects 
on marine mammals. Data are limited on the effects of underwater sound 
on zooplankton species, particularly sound from ship traffic and 
construction (Erbe et al., 2019). Popper and Hastings (2009) reviewed 
information on the effects of human-generated sound and concluded that 
no substantive data are available on whether the sound levels from pile 
driving, seismic activity, or any human-made sound would have 
physiological effects on invertebrates. Any such effects would be 
limited to the area very near (1 to 5 m) the sound source and would 
result in no population effects because of the relatively small area 
affected at any one time and the reproductive strategy of most 
zooplankton species (short generation, high fecundity, and very high 
natural mortality). No adverse impact on zooplankton populations is 
expected to occur from the specified activity due in part to large 
reproductive capacities and naturally high levels of predation and 
mortality of these populations. Any

[[Page 60186]]

mortalities or impacts that might occur would be negligible.
    In summary, given the relatively small areas being affected, as 
well as the temporary and mostly transitory nature of the tugging, any 
adverse effects from Hilcorp's activities on any prey habitat or prey 
populations are expected to be minor and temporary. The most likely 
impact to fishes at the project site would be temporary avoidance of 
the area. Any behavioral avoidance by fish of the disturbed area would 
still leave significantly large areas of fish and marine mammal 
foraging habitat in the nearby vicinity. Thus, we preliminarily 
conclude that impacts of the specified activities are not likely to 
have more than short-term adverse effects on any prey habitat or 
populations of prey species. Further, any impacts to marine mammal 
habitat are not expected to result in significant or long-term 
consequences for individual marine mammals, or to contribute to adverse 
impacts on their populations.

Estimated Take of Marine Mammals

    This section provides an estimate of the number of incidental takes 
proposed for authorization through the IHA, which will inform NMFS' 
consideration of ``small numbers,'' the negligible impact 
determinations, and impacts on subsistence uses.
    Harassment is the only type of take expected to result from these 
activities. Except with respect to certain activities not pertinent 
here, section 3(18) of the MMPA defines ``harassment'' as any act of 
pursuit, torment, or annoyance, which (i) has the potential to injure a 
marine mammal or marine mammal stock in the wild (Level A harassment); 
or (ii) has the potential to disturb a marine mammal or marine mammal 
stock in the wild by causing disruption of behavioral patterns, 
including, but not limited to, migration, breathing, nursing, breeding, 
feeding, or sheltering (Level B harassment).
    Authorized takes would be by Level B harassment only, in the form 
of behavioral reactions and or TTS for individual marine mammals 
resulting from exposure to Hilcorp's acoustic sources (i.e., tugs 
towing, holding, and positioning). Based on the nature of the activity, 
Level A harassment is neither anticipated nor proposed to be 
authorized.
    As described previously, no serious injury or mortality is 
anticipated or proposed to be authorized for this activity. Below we 
describe how the proposed take numbers are estimated.
    For acoustic impacts, generally speaking, we estimate take by 
considering: (1) acoustic thresholds above which NMFS believes the best 
available science indicates marine mammals will be behaviorally 
harassed or incur some degree of permanent hearing impairment; (2) the 
area or volume of water that will be ensonified above these levels in a 
day; (3) the density or occurrence of marine mammals within these 
ensonified areas; and, (4) the number of days of activities. We note 
that while these factors can contribute to a basic calculation to 
provide an initial prediction of potential takes, additional 
information that can qualitatively inform take estimates is also 
sometimes available (e.g., previous monitoring results or average group 
size). Below, we describe the factors considered here in more detail 
and present the proposed take estimates.

Acoustic Thresholds

    NMFS recommends the use of acoustic thresholds that identify the 
received level of underwater sound above which exposed marine mammals 
would be reasonably expected to be behaviorally harassed (equated to 
Level B harassment) or to incur PTS of some degree (equated to Level A 
harassment).
    Level B Harassment--Though significantly driven by received level, 
the onset of behavioral disturbance from anthropogenic noise exposure 
is also informed to varying degrees by other factors related to the 
source or exposure context (e.g., frequency, predictability, duty 
cycle, duration of the exposure, signal-to-noise ratio, distance to the 
source), the environment (e.g., bathymetry, other noises in the area, 
predators in the area), and the receiving animals (hearing, motivation, 
experience, demography, life stage, depth) and can be difficult to 
predict (e.g., Richardson et al., 1995; Southall et al. 2007, 2021, 
Ellison et al. 2012). Based on what the available science indicates and 
the practical need to use a threshold based on a metric that is both 
predictable and measurable for most activities, NMFS typically uses a 
generalized acoustic threshold based on received level to estimate the 
onset of behavioral harassment (i.e., Level B harassment). NMFS 
generally predicts that marine mammals are likely to be behaviorally 
disturbed in a manner considered to be Level B harassment when exposed 
to underwater anthropogenic noise above root-mean-squared pressure 
received levels (RMS SPL) of 120 dB (referenced to 1 micropascal (re 1 
[mu]Pa)) for continuous (e.g., tugging, vibratory pile driving, 
drilling) and above RMS SPL 160 dB re 1 [mu]Pa for non-explosive 
impulsive (e.g., seismic airguns) or intermittent (e.g., scientific 
sonar) sources. Generally speaking, Level B harassment take estimates 
based on these thresholds are expected to include any likely takes by 
TTS as, in most cases, the likelihood of TTS occurs at distances from 
the source smaller than those at which behavioral harassment is likely. 
TTS of a sufficient degree can manifest as behavioral harassment, as 
reduced hearing sensitivity and the potential reduced opportunities to 
detect important signals (conspecific communication, predators, prey) 
may result in changes in behavior patterns that would not otherwise 
occur.
    Hilcorp's proposed activity includes the use of continuous sources 
(tugs towing, holding, and positioning a jack-up rig), and therefore 
the RMS SPL threshold of 120 is applicable.
    Level A harassment--NMFS' Technical Guidance for Assessing the 
Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) 
(Technical Guidance, 2018) identifies dual criteria to assess auditory 
injury (Level A harassment) to five different marine mammal groups 
(based on hearing sensitivity) as a result of exposure to noise from 
two different types of sources (impulsive or non-impulsive). Hilcorp's 
proposed activity includes the use of non-impulsive sources (i.e., tugs 
towing, holding, and positioning a jack-up rig).
    These thresholds are provided in table 4 below. The references, 
analysis, and methodology used in the development of the thresholds are 
described in NMFS' 2018 Technical Guidance, which may be accessed at: 
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

                     Table 4--Thresholds Identifying the Onset of Permanent Threshold Shift
----------------------------------------------------------------------------------------------------------------
                                                     PTS onset acoustic thresholds * (received level)
             Hearing group              ------------------------------------------------------------------------
                                                  Impulsive                         Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans...........  Cell 1: Lpk,flat: 219 dB;   Cell 2: LE,LF,24h: 199 dB.
                                          LE,LF,24h: 183 dB.

[[Page 60187]]

 
Mid-Frequency (MF) Cetaceans...........  Cell 3: Lpk,flat: 230 dB;   Cell 4: LE,MF,24h: 198 dB.
                                          LE,MF,24h: 185 dB.
High-Frequency (HF) Cetaceans..........  Cell 5: Lpk,flat: 202 dB;   Cell 6: LE,HF,24h: 173 dB.
                                          LE,HF,24h: 155 dB.
Phocid Pinnipeds (PW) (Underwater).....  Cell 7: Lpk,flat: 218 dB;   Cell 8: LE,PW,24h: 201 dB.
                                          LE,PW,24h: 185 dB.
Otariid Pinnipeds (OW) (Underwater)....  Cell 9: Lpk,flat: 232 dB;   Cell 10: LE,OW,24h: 219 dB.
                                          LE,OW,24h: 203 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for
  calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level
  thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure (Lpk) has a reference value of 1 [micro]Pa, and cumulative sound exposure level (LE)
  has a reference value of 1[micro]Pa\2\s. In this table, thresholds are abbreviated to reflect American
  National Standards Institute standards (ANSI, 2013). However, peak sound pressure is defined by ANSI as
  incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript
  ``flat'' is being included to indicate peak sound pressure should be flat weighted or unweighted within the
  generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates
  the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds)
  and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could
  be exceeded in a multitude of ways (i.e., varying exposure levels and durations, duty cycle). When possible,
  it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be
  exceeded.

Ensonified Area

    Here, we describe operational and environmental parameters of the 
activity that are used in estimating the area ensonified above the 
acoustic thresholds, including source levels and transmission loss 
coefficient.
    The sound field in the project area is the existing background 
noise plus additional noise resulting from tugs under load with a jack-
up rig. Marine mammals are expected to be affected via sound generated 
by the primary components of the project (i.e., tugs towing, holding, 
and positioning a jack-up rig). Calculation of the area ensonified by 
the proposed action is dependent on the background sound levels at the 
project site, the source levels of the proposed activities, and the 
estimated transmission loss coefficients for the proposed activities at 
the site. These factors are addressed below.
    Sound Source Levels of Proposed Activities. The project includes 3 
to 4 tugs under load with a jack-up rig. Hilcorp conducted a literature 
review of underwater sound emissions of tugs under various loading 
efforts. The sound source levels for tugs of various horsepower (2,000 
to 8,200) under load can range from approximately 164 dB RMS to 202 dB 
RMS. This range largely relates to the level of operational effort, 
with full power output and higher speeds generating more propeller 
cavitation and hence greater sound source levels than lower power 
output and lower speeds. Tugs under tow produce higher source levels 
than tugs transiting with no load because of the higher power output 
necessary to pull the load. The amount of power the tugs expend while 
operating is the best predictor of relative sound source level. Several 
factors would determine the duration that the tugboats are towing the 
jack-up rig, including the origin and destination of the towing route 
(e.g., Rig Tenders Dock, an existing platform) and the tidal 
conditions. The power output would be variable and influenced by the 
prevailing wind direction and velocity, the current velocity, and the 
tidal stage. To the extent feasible, transport would be timed with the 
tide to minimize towing duration and power output.
    Hilcorp's literature review identified no existing data on sound 
source levels of tugs towing jack-up rigs. Accordingly, for this 
analysis, Hilcorp considered data from tug-under-load activities, 
including berthing and towing activities. Austin and Warner (2013) 
measured 167 dB RMS for tug towing barge activity in Cook Inlet. 
Blackwell and Greene (2002) reported berthing activities in the POA 
with a source level of 179 dB RMS. Laurinolli et al. (2005) measured a 
source level of 200 dB RMS for anchor towing activities by a tugboat in 
the Strait of Juan de Fuca, WA. The Roberts Bank Terminal 2 study 
(2014) repeated measurements of the same tug operating under different 
speeds and loading conditions. Broadband measurements from this study 
ranged from approximately 162 dB RMS up to 200 dB RMS.
    The rig manager for Hilcorp, who is experienced with towing jack-up 
rigs in Cook Inlet, described operational conditions wherein the tugs 
generally operate at half power or less for the majority of the time 
they are under load (pers. Comm., Durham, 2021). Transits with the tide 
(lower power output) are preferred for safety reasons, and effort is 
made to reduce or eliminate traveling against the tide (higher power 
output). The Roberts Bank Terminal 2 study (2014) allowed for a 
comparison of source levels from the same vessel (Seaspan Resolution 
tug) at half power versus full power. Seaspan Resolution's half-power 
(i.e., 50 percent) berthing scenario had a sound source level of 180 dB 
RMS. In addition, the Roberts Bank Terminal 2 Study (2014) reported a 
mean tug source level of 179.3 dB RMS from 650 tug transits under 
varying load and speed conditions.
    The 50 percent (or less) power output scenario occurs during the 
vast majority of tug towing jack-up rig activity, as described in the 
Detailed Description of the Specific Activity section. Therefore, based 
on Hilcorp's literature review, a source level of 180 dB RMS was found 
to be an appropriate proxy source level for a single tug under load 
based on the Roberts Bank Terminal 2 study. If all three tugs were 
operating simultaneously at 180 dB RMS, the overall source emission 
levels would be expected to increase by approximately 5 dB when 
logarithmically adding the sources (i.e., to 185 dB RMS). To further 
support this level as an appropriate proxy, a sound source verification 
(SSV) study performed by JASCO Applied Sciences (JASCO) in Cook Inlet 
in October 2021 (Lawrence et al., 2022) measured the sound source level 
from three tugs pulling a jack-up rig in Cook Inlet at various power 
outputs. Lawrence et al. (2022) reported a source level of 167.3 dB RMS 
for the 20 percent-power scenario and a source level of 205.9 dB RMS 
for the 85 percent-power scenario. Assuming a linear scaling of tug 
power, a source level of 185 dB RMS was calculated as a single point 
source level for three tugs operating at 50 percent power output. 
Because the 2021 Cook Inlet SSV measurements by JASCO represent the 
most recent best available data, and because multiple tugs may be 
operating simultaneously, the analyses presented below use a mean tug 
sound source level scenario of 185 dB RMS to calculate the Level B 
harassment estimates for three tugs operating at 50

[[Page 60188]]

percent power output. In practice, the load condition of the three tugs 
is unlikely to be identical at all times, so sound emissions would be 
dominated by the single tug in the group that is working hardest at any 
point in time.
    Further modeling was done to account for one additional tug working 
for one hour at 50 percent power during jack-up rig positioning, a 
stationary activity. This is equivalent in terms of acoustic energy to 
three tugs operating at 180.0 dB RMS (each of them) for 4 hours, joined 
by a fourth tug for 1 hour, increasing the source level to 186.0 dB RMS 
only during the 1-hour period (the logarithmic sum of four tugs working 
together at 180.0 dB RMS). An SEL of 185.1 dB was used to account for 
the cumulative sound exposure when calculating Level A harassment by 
adding a 4th tug operating at 50 percent power for 20 percent of the 5-
hour period. This is equivalent in terms of acoustic energy to 3 tugs 
operating at 185.0 dB for 4 hours, joined by a fourth tug for 1 hour, 
increasing the source level to 186.0 dB only during the 1-hour period. 
The use of the 20 percent duty cycle was a computational requirement 
and, although equal in terms of overall energy and determination of 
impacts, should not be confused with the actual instantaneous SPL (see 
section 6.2.1.1 of Hilcorp's application for additional computational 
details).
    In summary, Hilcorp has proposed to use a source level of 185.0 dB 
RMS to calculate the stationary Level B harassment isopleth where three 
tugs were under load for 4 hours with a 50 percent power output and a 
source level of 186.0 dB RMS to calculate the stationary Level B 
harassment isopleth where four tugs were under load for 1 hour with a 
50 percent power output. Further, Hilcorp has proposed to use a source 
level of 185.1 dB SEL to calculate the stationary Level A harassment 
isopleths where three tugs were underload for 4 hours and then one tug 
joined for 1 additional hour. Lastly, Hilcorp proposed to use the 185.0 
dB RMS level to model the mobile Level A harassment isopleths for three 
tugs under load with a 50 percent power output. NMFS concurs that 
Hilcorp's proposed source levels are appropriate.
    Underwater Sound Propagation Modeling. Hilcorp contracted SLR 
Consulting to model the extent of the Level A and Level B harassment 
isopleths for tugs under load with a jack-up rig during their proposed 
activities. Cook Inlet is a particularly complex acoustic environment 
with strong currents, large tides, variable sea floor and generally 
changing conditions. Accordingly, Hilcorp applied a more detailed 
propagation model than the ``practical spreading loss'' approach that 
uses a factor of 15. The objective of a more detailed propagation 
calculation is to improve the representation of the influence of some 
environmental variables, in particular, by accounting for bathymetry 
and specific sound source locations and frequency-dependent propagation 
effects.
    Modeling was conducted using the dBSea software package. The fluid 
parabolic equation modeling algorithm was used with 5 Pad[eacute] terms 
to calculate the TL between the source and the receiver at low 
frequencies (\1/3\-octave bands, 31.5 Hz up to 1 kHz). For higher 
frequencies (1 kHz up to 8 kHz) the ray tracing model was used with 
1,000 reflections for each ray. Sound sources were assumed to be 
omnidirectional and modeled as points. The received sound levels for 
the project were calculated as follows: (1) One-third octave source 
spectral levels were obtained via reference spectral curves with 
subsequent corrections based on their corresponding overall source 
levels; (2) TL was modeled at one-third octave band central frequencies 
along 100 radial paths at regular increments around each source 
location, out to the maximum range of the bathymetry data set or until 
constrained by land; (3) The bathymetry variation of the vertical plane 
along each modeling path was obtained via interpolation of the 
bathymetry dataset which has 83 m grid resolution; (4) The one-third 
octave source levels and transmission loss were combined to obtain the 
received levels as a function of range, depth, and frequency; and (5) 
The overall received levels were calculated at a 1-m depth resolution 
along each propagation path by summing all frequency band spectral 
levels.
    Model Inputs. Bathymetry data used in the model was collected from 
the NOAA National Centers for Environmental Information (AFSC, 2019). 
Using NOAA's temperature and salinity data, sound speed profiles were 
computed for depths from 0 to 100 m for May, July, and October to 
capture the range of possible sound speed depending on the time of year 
Hilcorp's work could be conducted. These sound speed profiles were 
compiled using the Mackenzie Equation (1981) and are presented in table 
8 of Hilcorp's application (available at https://www.fisheries.noaa.gov/action/incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0). Geoacoustic 
parameters were also incorporated into the model. The parameters were 
based on substrate type and their relation to depth. These parameters 
are presented in table 9 of Hilcorp's application (available at https://www.fisheries.noaa.gov/action/incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0).
    Detailed broadband sound transmission loss modeling in dBSea used 
the source level of 185 dB RMS calculated in one-third octave band 
levels (31.5 Hz to 64,000 Hz) for frequency dependent solutions. The 
frequencies associated with tug sound sources occur within the hearing 
range of marine mammals in Cook Inlet. Received levels for each hearing 
marine mammal group based on one-third octave auditory weighting 
functions were also calculated and integrated into the modeling 
scenarios of dBSea. For modeling the distances to relevant PTS 
thresholds, a weighting factor adjustment was not used; instead, the 
data on the spectrum associated with their source was used and 
incorporated the full auditory weighting function for each marine 
mammal hearing group.
    The tugs towing the jack-up rig represent a mobile sound source, 
and tugs holding and positioning the jack-up rig on a platform are more 
akin to a stationary sound source. In addition, three tugs would be 
used for towing (mobile) and holding and positioning (stationary) and 
up to four tugs could be used for positioning (stationary). 
Consequently, sound TL modeling was undertaken for the various 
stationary and mobile scenarios for three and four tugs to generate 
Level A and Level B harassment threshold distances.
    For acoustic modeling purposes of the stationary Level A harassment 
thresholds, two locations representative of where tugs will be 
stationary while they position the jack-up rig were selected in middle 
Cook Inlet near the Tyonek platform and in lower Trading Bay where the 
production platforms are located. To account for the mobile scenarios, 
the acoustic model generated Levels A and Level B harassment distances 
along a representative route from the Rig Tenders dock in Nikiski to 
the Tyonek platform, the northernmost platform in Cook Inlet 
(representing middle Cook Inlet), as well as from the Tyonek Platform 
to the Dolly Varden platform in lower Trading Bay, then from the Dolly 
Varden platform back to the Rig Tenders Dock in Nikiski. Note that this 
route is representative of a typical route the tugs may take; the 
specific route is not yet known, as the order in which platforms will 
be drilled with the jack-up rig is not yet known. These results were 
used to calculate Level A and Level B harassment exposure estimates 
from mobile tugs

[[Page 60189]]

towing a jack-up rig. The Level B harassment results were also used to 
calculate Level B harassment exposure estimates from stationary tugs 
holding or positioning a jack-up rig, as the mobile route encompassed 
the stationary modeling points. The locations represent a range of 
water depths from 18 to 77 m found throughout the project area.
    For mobile Level B harassment and stationary Level B harassment 
with three tugs, the average distance to the 120 dB RMS threshold was 
based on the assessment of 100 radials at 25 locations across seasons 
(May, July, and October) and represents the average Level B harassment 
zone for each season and location (table 5). The result is a mobile and 
stationary Level B harassment zone of 3,850 m when three tugs are used 
(table 5). For stationary Level B harassment with four tugs, the 
average distance to the 120 dB RMS threshold was based on 100 radials 
at two locations, one in Trading Bay and one in middle Cook Inlet, 
across seasons (May, July, and October) and represents the average 
Level B harassment zone for each season and location. The result is a 
stationary Level B harassment zone of 4,453 m when four tugs are in use 
(table 6). NMFS concurs that 3,850 m and 4,453 m are appropriate 
estimates for the extent of the Level B harassment zones for Hilcorp's 
towing, holding, and positioning activities when using three and four 
tugs, respectively.

   Table 5--Average Distances to the Level B Harassment Threshold (120 dB) for Three Tugs Towing (Mobile) and
                                Holding and Positioning for 4 Hours (Stationary)
----------------------------------------------------------------------------------------------------------------
                                                     Average distance to 120 dB threshold (m)         Season
                                                 ------------------------------------------------     average
                    Location                                                                        distance to
                                                        May            July           October     threshold  (m)
----------------------------------------------------------------------------------------------------------------
M1..............................................           4,215           3,911           4,352           4,159
M2..............................................           3,946           3,841           4,350           4,046
M3..............................................           4,156           3,971           4,458           4,195
M4..............................................           4,040           3,844           4,364           4,083
M5..............................................           4,053           3,676           4,304           4,011
M6..............................................           3,716           3,445           3,554           3,572
M7..............................................           2,947           2,753           2,898           2,866
M8..............................................           3,270           3,008           3,247           3,175
M9..............................................           3,567           3,359           3,727           3,551
M10.............................................           3,600           3,487           3,691           3,593
M11.............................................           3,746           3,579           4,214           3,846
M12.............................................           3,815           3,600           3,995           3,803
M13.............................................           4,010           3,831           4,338           4,060
M14.............................................           3,837           3,647           4,217           3,900
M15.............................................           3,966           3,798           4,455           4,073
M16.............................................           3,873           3,676           4,504           4,018
M18.............................................           5,562           3,893           4,626           4,694
M20.............................................           5,044           3,692           4,320           4,352
M22.............................................           4,717           3,553           4,067           4,112
M24.............................................           4,456           3,384           4,182           4,007
M25.............................................           3,842           3,686           4,218           3,915
M26.............................................           3,690           3,400           3,801           3,630
M27.............................................           3,707           3,497           3,711           3,638
M28.............................................           3,546           3,271           3,480           3,432
M29.............................................           3,618           3,279           3,646           3,514
                                                 ---------------------------------------------------------------
    Average.....................................           3,958           3,563           4,029           3,850
----------------------------------------------------------------------------------------------------------------


 Table 6--Average Distances to the Level B Harassment Threshold (120 dB) for Four Tugs Positioning (Stationary)
                                                   for 1 Hour
----------------------------------------------------------------------------------------------------------------
                                                      Average distance to Level B harassment          Season
                                                                   threshold (m)                      average
                    Location                     ------------------------------------------------   distance to
                                                        May            July           October     threshold  (m)
----------------------------------------------------------------------------------------------------------------
Trading Bay.....................................           4,610           3,850           4,810           4,423
Middle CI.......................................           4,820           4,130           4,500           4,483
                                                 ---------------------------------------------------------------
    Average.....................................           4,715           3,990           4,655           4,453
----------------------------------------------------------------------------------------------------------------

    The average Level A harassment distances for the stationary, four 
tug scenario were calculated assuming a SEL of 185.1 dB for a 5-hour 
exposure duration (table 7). For the mobile, three tug scenario, the 
average Level A harassment distances were calculated assuming a SEL of 
185.0 dB with an 18-second exposure period (table 8). This 18-second 
exposure was derived using the standard TL equation (Source Level-TL = 
Received Level) for determining threshold distance (R [m]), where TL = 
15Log10. In this case, the equation was 185.0 dB-15Log10 = 173 dB. 
Solving for threshold distance (R) yields a distance of approximately 6 
m, which was then used as the preliminary

[[Page 60190]]

ensonified radius to determine the duration of time it would take for 
the ensonified area of the sound source traveling at a speed of 2.06 m/
s (4 knots) to pass a marine mammal. The duration (twice the radius 
divided by speed of the source) that the ensonified area of a single 
tug would take to pass a marine mammal under these conditions is 6 
seconds. An 18-second exposure was used in the model to reflect the 
time it would take for three ensonified areas (from three consecutive 
individual tugs) to pass a single point that represents a marine mammal 
(6 seconds + 6 seconds + 6 seconds = 18 seconds).

           Table 7--Average Distances to the Level A Harassment Thresholds for Four Stationary Tugs Under Load With a Jack-Up Rig for 5 Hours
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                            Average distance (m) to Level A harassment threshold by functional hearing
                                                                                                               group
                 Location                              Season            -------------------------------------------------------------------------------
                                                                                LF              MF              HF              PW            OW \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Trading Bay...............................  May.........................             107              77             792              64  ..............
Trading Bay...............................  July........................             132              80             758              66  ..............
Trading Bay...............................  October.....................             105              75             784              79  ..............
Middle Cook Inlet.........................  May.........................              86              85             712              78  ..............
Middle Cook Inlet.........................  July........................              95              89             718              80  ..............
Middle Cook Inlet.........................  October.....................              82              86             730              80  ..............
Average...................................  ............................             102              82             749              75               0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ The Level A harassment distances are smaller than the footprint of the tugs.


                            Table 8--Average Distances to the Level A Harassment Thresholds for Three Mobile Tugs Under Load
                                                With a Jack-Up Rig Assuming a 18-Second Exposure Duration
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               Average distance (m) to Level A threshold by functional hearing group
                 Location                              Season            -------------------------------------------------------------------------------
                                                                              LF \1\          MF \1\            HF            PW \1\          OW \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
M2........................................  May.........................  ..............  ..............              10  ..............  ..............
M2........................................  July........................  ..............  ..............               5  ..............  ..............
M2........................................  October.....................  ..............  ..............              10  ..............  ..............
M11.......................................  May.........................  ..............  ..............              10  ..............  ..............
M11.......................................  July........................  ..............  ..............               5  ..............  ..............
M11.......................................  October.....................  ..............  ..............              10  ..............  ..............
M22.......................................  May.........................  ..............  ..............              10  ..............  ..............
M22.......................................  July........................  ..............  ..............               5  ..............  ..............
M22.......................................  October.....................  ..............  ..............              10  ..............  ..............
                                           -------------------------------------------------------------------------------------------------------------
    Average...............................  ............................               0               0               8               0               0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ The Level A harassment distances are smaller than the footprint of the tugs.

    Tugs are anticipated to be towing the jack-up rig between platforms 
and considered a mobile sound source for 6 hours in a single day per 
jack-up rig move. Tugs are anticipated to be towing the jack-up rig and 
considered a mobile source during demobilization and mobilization to/
from Rig Tenders Dock in Nikiski for 9 hours. One jack-up rig move 
between platforms is planned during the IHA period. Tugs are 
anticipated to be holding or positioning the jack-up rig at the 
platforms or Rig Tenders Dock during demobilization and mobilization 
and are considered a stationary sound source for 5 hours in the first 
day and 5 hours in the second day if a second attempt to pin the jack-
up rig is required. A second attempt was built into the exposure 
estimate for each pinning event; three total pinning events are 
anticipated during the IHA period for production drilling.
    The ensonified area for a location-to-location transport for 
production drilling represents a rig move between two production 
platforms in middle Cook Inlet and/or Trading Bay and includes 6 mobile 
hours over an average distance of 16.77 km in a single day and 5 
stationary hours on the first day and 5 stationary hours on a second 
day. The 5 stationary hours are further broken into 4 hours with three 
tugs under load and 1 hour with four tugs under load. One location-to-
location jack-up rig move is planned for the IHA period.
    The ensonified area for production drilling demobilization and 
mobilization represents a rig move from a production platform in middle 
Cook Inlet to Rig Tenders Dock in Nikiski and reverse for mobilization 
and includes 9 mobile hours over a distance of up to 64.34 km in a 
single day and 5 stationary hours on the first day and 5 stationary 
hours on a second day, which are further broken into the same three 
tugs working for 4 hours and four tugs working for 1 hour as mentioned 
above. A summary of the estimated Level A and Level B harassment 
distances and areas for the various tugging scenarios if provided in 
table 9.

[[Page 60191]]



 Table 9--Average Distances and Areas to the Estimated Level A and Bevel B Harassment Thresholds for the Various
                                                Tugging Scenarios
----------------------------------------------------------------------------------------------------------------
                                        Level A harassment distance (m)/area (km\2\)                Level B
                             -----------------------------------------------------------------     harassment
          Activity                                                                             distance (m)/area
                                   LF           MF           HF           PW           OW           (km\2\)
----------------------------------------------------------------------------------------------------------------
                                           Demobilization/Mobilization
----------------------------------------------------------------------------------------------------------------
3 Tugs Towing a Jack-Up Rig--         \1\          \1\       8/1.07          \1\          \1\       3,850/541.96
 Mobile.....................
3 Tugs Towing a Jack-Up Rig--    102/0.03      82/0.02     749/1.76      75/0.02          \1\        3,850/46.56
 Stationary for up to 4
 hours......................
4 Tugs Towing a Jack-Up Rig--    102/0.03      82/0.02     749/1.76      75/0.02          \1\        4,453/62.30
 Stationary for up to 1 hour
----------------------------------------------------------------------------------------------------------------
                                              Location-to-Location
----------------------------------------------------------------------------------------------------------------
3 Tugs Towing a Jack-Up Rig--         \1\          \1\       8/0.28          \1\          \1\        3,850/175.6
 Mobile.....................
3 Tugs Towing a Jack-Up Rig--    102/0.03      82/0.02     749/1.76      75/0.02          \1\        3,850/46.56
 Stationary for up to 4
 hours......................
4 Tugs Towing a Jack-Up Rig--    102/0.03      82/0.02     749/1.76      75/0.02          \1\        4,453/62.30
 Stationary for up to 1 hour
----------------------------------------------------------------------------------------------------------------
\1\ The Level A harassment distances are smaller than the footprint of the tugs.

Marine Mammal Occurrence

    In this section we provide information about the occurrence of 
marine mammals, including density or other relevant information which 
will inform the take calculations.
    Densities for marine mammals in Cook Inlet were derived from NMFS' 
Marine Mammal Laboratory (MML) aerial surveys, typically flown in June, 
from 2000 to 2022 (Rugh et al., 2005; Shelden et al., 2013, 2015b, 
2017, 2019, 2022; Goetz, et al. 2023). While the surveys are 
concentrated for a few days in summer annually, which may skew 
densities for seasonally present species, they represent the best 
available long-term dataset of marine mammal sightings available in 
Cook Inlet. Density was calculated by summing the total number of 
animals observed and dividing the number sighted by the area surveyed. 
The total number of animals observed accounts for both lower and upper 
Cook Inlet. There are no density estimates available for California sea 
lions and Pacific white-sided dolphins in Cook Inlet, as they were so 
infrequently sighted. Average densities across survey years are 
presented in table 10.

   Table 10--Average Densities of Marine Mammal Species in Cook Inlet
------------------------------------------------------------------------
                                                            Density
                       Species                          (individuals per
                                                             km\2\)
------------------------------------------------------------------------
Humpback whale.......................................            0.00185
Minke whale..........................................            0.00004
Gray whale...........................................            0.00007
Fin whale............................................            0.00028
Killer whale.........................................            0.00061
Beluga whale (MML--Entire Cook Inlet)................            0.07166
Beluga whale (MML--Middle Cook Inlet)................            0.00658
Beluga whale (MML--Lower Cook Inlet).................            0.00003
Beluga whale (Goetz--North Cook Inlet)...............            0.00166
Beluga whale (Goetz--Lower Cook Inlet)...............            0.00000
Beluga whale (Goetz--Trading Bay)....................            0.01505
Dall's porpoise......................................            0.00014
Harbor porpoise......................................            0.00380
Pacific white-sided dolphin..........................             N/A\1\
Harbor seal..........................................            0.26819
Steller sea lion.....................................            0.00669
California sea lion..................................            N/A \1\
------------------------------------------------------------------------
\1\ Density estimates are not available in Cook Inlet for this species.

    For CIBWs, two densities were considered as a comparison of 
available data. The first source considered was directly from the MML 
aerial surveys, as described above. Sighting data collected during 
aerial surveys was collected and then several correction factors were 
applied to address perception, availability, and proximity bias. These 
corrected sightings totals were then divided by the total area covered 
during the survey to arrive at a density value. Densities were derived 
for the entirety of Cook Inlet as well as for middle and lower Cook 
Inlet. Densities across all three regions are low and there is a known 
effect of seasonality on the distribution of the whales. Thus, 
densities derived directly from surveys flown in the summer might 
underestimate the density of CIBWs in lower Cook Inlet at other ice-
free times of the year.
    The other mechanism for arriving at CIBW density considered here is 
the Goetz et al. (2012a) habitat-based model. This model is derived 
from sightings and incorporates depth soundings, coastal substrate 
type, environmental sensitivity index, anthropogenic disturbance, and 
anadromous fish streams to predict densities throughout Cook Inlet. The 
output of this model is a density map of Cook Inlet, which predicts 
spatially explicit density estimates for CIBW. Using the resulting grid 
densities, average densities were calculated for two regions applicable 
to Hilcorp's operations (table 10). The densities applicable to the 
area of activity (i.e., the North Cook Inlet Unit density for middle 
Cook Inlet activities

[[Page 60192]]

and the Trading Bay density for activities in Trading Bay) are provided 
in table 10 above and were carried forward to the exposure estimates as 
they were deemed to likely be the most representative estimates 
available. Likewise, when a range is given, the higher end of the range 
was used out of caution to calculate exposure estimates (i.e., Trading 
Bay in the Goetz model has a range of 0.004453 to 0.015053; 0.015053 
was used for the exposure estimates).

Take Estimation

    Here we describe how the information provided above is synthesized 
to produce a quantitative estimate of the take that is reasonably 
likely to occur and proposed for authorization.
    As described above, Hilcorp's tug towing rig activity considers a 
total of three rig moves across 6 days (one 2-day location-to-location 
jack-up rig move, one 2-day demobilization effort, and one 2-day 
mobilization effort). For the location-to-location move, Hilcorp 
assumed 6 hours of mobile (towing) and 5 hours of stationary (holding 
and positioning) activities on the first day, and 5 hours of the 
stationary activity (4 hours with three tugs and 1 hour with four tugs) 
on the second day to account for two positioning attempts (across 2 
days). For the demobilization and mobilization efforts, Hilcorp assumed 
9 hours of mobile and 5 hours of stationary (4 hours with three tugs 
and 1 hour with four tugs) activities on the first day, and 5 hours of 
stationary (4 hours with three tugs and 1 hour with four tugs) 
activities on the second day (across 2 days for each effort, for a 
total of 4 days of tugs under load with a jack-up rigs).
    Take by Level A harassment was estimated by multiplying the 
ensonified Level A harassment areas per tugging activity scenario for 
each functional hearing group (table 9) by the estimated marine mammal 
densities (table 10) to get an estimate of exposures per day. This 
value was then multiplied by the number of days per move and the number 
of moves of that type of activity scenario. The estimated exposures by 
activity scenario were then summed to result in a number of exposures 
for all tug towing rig activity. Based on this analysis, only Dall's 
porpoise, harbor porpoise, and harbor seals had estimated take by Level 
A harassment that were greater than zero: 0.001, 0.018, and 0.006, 
respectively. Given these small estimates, NMFS does not propose to 
authorize take by Level A harassment related to Hilcorp's tugging 
activity. For mobile tugging, the distances to the PTS thresholds for 
HF cetaceans and phocids are smaller than the overall size of the tug 
and rig configuration (i.e., 8 m and 0 m, respectively), making it 
unlikely an animal would remain close enough to the tug engines to 
incur PTS. For stationary positioning of the jack up rig, the PTS 
isopleths for both the 3-tug and 4-tug scenarios are up to 749 m for HF 
cetaceans and up to 102 m for all other species, but calculated on the 
assumption that an animal would remain within several hundred meters of 
the jack-up rig for the full 5 hours of noise-producing activity. Given 
the location of the activity is not in an area known to be essential 
habitat for any marine mammal species with extreme site fidelity over 
the course of 2 days, in addition to the mobile nature of marine 
mammals, the occurrence of PTS is unlikely and thus not proposed to be 
authorized for any species.
    The ensonified Level B harassment areas calculated per activity 
scenario (three tug stationary, four tug stationary, and three tug 
mobile for the location-to-location move and the demobilization and 
mobilization efforts) for a single day (see table 9) were multiplied by 
marine mammal densities to get an estimate of exposures per day. This 
was then multiplied by the number of days per move and the number of 
moves of that type of activity scenario to arrive at the number of 
estimated exposures per activity type. These exposures by activity 
scenario were then summed to result in a number of exposures per year 
for all Hilcorp's proposed tug under load activities (table 11). As 
exposure estimates were calculated based on specific potential rig 
moves or well locations, the density value for CIBWs that was carried 
through the estimate was the higher density value for that particular 
location (table 10). There are no estimated exposures based on this 
method of calculation for California sea lions and pacific white-sided 
dolphins because the assumed density of these species in the project 
area is 0.00 animals per km\2\. Table 11 also indicates the number of 
takes, by Level B harassment, proposed to be authorized. For species 
where the total calculated take by Level B harassment is less than the 
estimated group size for that species, NMFS adjusted the take proposed 
for authorization to the anticipated group size. Explanations for 
species for which take proposed for authorization is greater than the 
calculated take are included below.

           Table 11--Amount of Estimated and Proposed Take by Level B Harassment, by Species and Stock for Hilcorp's Tug Towing, Holding, and Positioning of a Jack-Up Rig Activities
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               Location-to-location                         Demobilization/mobilization                Total
                                                                 ------------------------------------------------------------------------------------------------ estimated take   Proposed Take
                            Scenario                                               3 Stationary    4 Stationary                    3 Stationary    4 Stationary     by level B      by Level B
                                                                   3 Mobile Tugs       Tugs            Tugs        3 Mobile Tugs       Tugs            Tugs         harassment      Harassment
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Level B Harassment Area (km\2\).................................          175.67           46.56           62.30          541.96           46.56           62.30
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
Species                                                                                        Estimated Take by Level B Harassment
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale..................................................           0.324           0.029           0.010           2.001           0.057           0.019           2.440               3
Minke whale.....................................................           0.005           0.000           0.000           0.031           0.001           0.000           0.037               3
Gray whale......................................................           0.012           0.001           0.000           0.072           0.002           0.001           0.088               3
Fin whale.......................................................           0.048           0.004           0.001           0.299           0.009           0.003           0.364               2
Killer whale....................................................           0.108           0.009           0.003           0.663           0.019           0.006           0.808              10
Beluga whale....................................................           1.900           0.168           0.056           7.133           0.204           0.068           9.529              15
Dall's porpoise.................................................           0.024           0.002           0.001           0.148           0.004           0.001           0.180               6
Harbor porpoise.................................................           0.667           0.059           0.020           4.117           0.118           0.039           5.020              12
Pacific white-sided dolphin.....................................           0.000           0.000           0.000           0.000           0.000           0.000           0.000               3
Harbor seal.....................................................          47.112           4.163           1.392         290.699           8.325           2.785         354.476             355
Steller sea lion................................................           1.175           0.104           0.035           7.253           0.208           0.069           8.844               9
California sea lion.............................................           0.000           0.000           0.000           0.000           0.000           0.000           0.000               2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------


[[Page 60193]]

    During annual aerial surveys conducted in Cook Inlet from 2000 to 
2016, humpback group sizes ranged from one to 12 individuals, with most 
groups comprised of 1 to 3 individuals (Shelden et al., 2013). Three 
humpback whales were observed in Cook Inlet during SAExploration's 
seismic study in 2015: two near the Forelands and one in Kachemak Bay 
(Kendall and Cornick, 2015). In total, 14 sightings of 38 humpback 
whales (ranging in group size from 1 to 14) were recorded in the 2019 
Hilcorp lower Cook Inlet seismic survey in the fall (Fairweather 
Science, 2020). Two sightings totaling three individual humpback whales 
were recorded near Ladd Landing north of the Forelands on the recent 
Harvest Alaska CIPL Extension Project (Sitkiewicz et al., 2018). Based 
on documented observations from the CIPL Extension Project, which is 
the data closest to the specific geographic region, NMFS is proposing 
to authorize, three takes by Level B harassment for humpback whales, 
which is slightly greater than the take estimated using the methods 
described above (0.2440 takes by Level B harassment, table 11).
    Minke whales usually travel in groups of two to three individuals 
(NMFS, 2023b). During Cook Inlet-wide aerial surveys conducted from 
1993 to 2004, minke whales were encountered three times (1998, 1999, 
and 2006), all were observed off Anchor Point (Shelden et al., 2013, 
2015b, and 2017). Several minke whales were recorded off Cape 
Starichkof in early summer 2013 during exploratory drilling (Owl Ridge, 
2014), suggesting this location is regularly used by minke whales year-
round. During Apache's 2014 survey, a total of two minke whale groups 
(three individuals) were observed. One sighting occurred southeast of 
Kalgin Island while the other sighting occurred near Homer (Lomac-
MacNair et al., 2014). SAExploration noted one minke whale near Tuxedni 
Bay in 2015 (Kendall and Cornick, 2015). Eight sightings of eight minke 
whales were recorded in the 2019 Hilcorp lower Cook Inlet seismic 
survey (Fairweather Science, 2020). Based on these observations of 
group size and consistency of sightings in Cook Inlet, NMFS is 
proposing to authorize three takes by Level B harassment for minke 
whales (table 11). This is higher than the exposure estimate (i.e., 
0.037, table 11) to allow for the potential occurrence of a group, or 
several individuals, during the project period.
    During Apache's 2012 seismic program, nine sightings of a total of 
nine gray whales were observed in June and July (Lomac-MacNair et al., 
2013). In 2014, one gray whale was observed during Apache's seismic 
program (Lomac-MacNair et al., 2014) and in 2015, no gray whales were 
observed during SAExploration's seismic survey (Kendall and Cornick, 
2015). No gray whales were observed during the 2018 CIPL Extension 
Project (Sitkiewicz et al., 2018) or during the 2019 Hilcorp seismic 
survey in lower Cook Inlet (Fairweather Science, 2020). The greatest 
densities of gray whales in Cook Inlet occur from November through 
January and March through May; the former are southbound, the latter 
are northbound (Ferguson et al., 2015). Based on this information, NMFS 
is proposing to authorize three takes by Level B harassment for gray 
whales. This is higher than the exposure estimate (i.e., 0.088, table 
11) to allow for the potential occurrence of a group, or several 
individuals, particularly during the fall shoulder season during the 
higher density periods mentioned above.
    Fin whales most often travel alone, although they are sometimes 
seen in groups of two to seven individuals. During migration they may 
be in groups of 50 to 300 individuals (NMFS, 2010). During the NMFS 
aerial surveys in Cook Inlet from 2000 to 2018, 10 sightings of 26 
estimated individual fin whales were recorded in lower Cook Inlet 
(Shelden et al., 2013, 2015b, and 2017; Shelden and Wade, 2019). Wild 
et al. (2023) identified areas south of the mouth of Cook Inlet as a 
fin whale feeding BIA from June to September with an importance score 
of 1 and an intensity score of 1 (see Harrison et al. 2023 for more 
details regarding BIA scoring). As such, the potential for fin whales 
to occupy waters adjacent to the BIA during that time period and near 
the specified area may be higher. Acoustic detections of fin whales 
were recorded during passive acoustic monitoring in the fall of 2019 
(Castellote et al., 2020) Additionally, during seismic surveys 
conducted in 2019 by Hilcorp in lower Cook Inlet, 8 sightings of 23 fin 
whales were recorded in groups ranging in size from 1 to 15 individuals 
(Fairweather Science, 2020). The higher number of sightings in a single 
year relative to the multi-year NMFS aerial surveys flown earlier in 
season each year suggests fin whales may be present in greater numbers 
in the fall. Given the possible presence of fin whales in the project 
area, NMFS proposes to authorize two takes by Level B harassment for 
fin whales during tugs Hilcorp's planned activities.
    Killer whale pods typically consist of a few to 20 or more animals 
(NMFS, 2023c). During seismic surveys conducted in 2019 by Hilcorp in 
lower Cook Inlet, 21 killer whales were observed. Although also 
observed as single individuals, killer whales were recorded during this 
survey in groups ranging in size from two to five individuals 
(Fairweather Science, 2020). One killer whale group of two individuals 
was observed during the 2015 SAExploration seismic program near the 
North Foreland (Kendall and Cornick, 2015). Based on recent documented 
sightings, observed group sizes, and the established presence of killer 
whales in Cook Inlet, NMFS is proposing to authorize 10 takes by Level 
B harassment for killer whales. This would facilitate two sightings 
with a group size of five individuals, which represents the upper end 
of recorded group size in recent surveys conducted in Cook Inlet.
    The total estimated take for CIWB was calculated to be 9.529 
individuals based on recorded densities and estimated durations that 
tugs would be under load with a jack-up rig (table 11). The 2018 MML 
aerial survey (Shelden and Wade, 2019) reported a median beluga group 
size estimate of approximately 11 whales, although estimated group 
sizes were highly variable (ranging from 2 to 147 whales) as was the 
case in previous survey years (Boyd et al., 2019). The median group 
size during 2021 and 2022 MML aerial surveys was 34 and 15, 
respectively, with variability between 1 and 174 between the years 
(Goetz et al., 2023). Additionally, vessel-based surveys in 2019 found 
CIBW groups in the Susitna River Delta (roughly 24 km north of the 
Tyonek Platform) that ranged from 5 to 200 animals (McGuire et al., 
2022). Based on these observations, NMFS proposes to increase the 
estimated take calculated above and authorize 15 takes by Level B 
harassment for CIBWs to account for 1 group of 15 individuals, the 
lower end of the 2022 median group size, or 2 observations of smaller-
sized groups. While large groups of CIBWs have been seen in the Susitna 
River Delta region, they are not expected near Hilcorp's specified 
activity because groups of this size have not been observed or 
documented outside river deltas in upper Cook Inlet; however, smaller 
groups (i.e., around the 2022 median group size) could be traveling 
through to access the Susitna River Delta and other nearby coastal 
locations.
    Dall's porpoises are usually found in groups averaging between 2 
and 12 individuals (NMFS, 2023d). During seismic surveys conducted in 
2019 by Hilcorp in lower Cook Inlet, Dall's porpoises were recorded in 
groups ranging from two to seven individuals (Fairweather Science, 
2020). The 2012

[[Page 60194]]

Apache survey recorded two groups of three individual Dall's porpoises 
(Lomac-MacNair et al., 2014). NMFS proposes to authorize six takes by 
Level B harassment for Dall's porpoises. This is greater than the 
estimated exposure estimate for this species (0.180, table 11), but 
would allow for at least one group at the higher end of documented 
group size or a combination of small groups plus individuals.
    Harbor porpoises are most often seen in groups of two to three 
(NMFS, 2023e); however, based on observations during project-based 
marine mammal monitoring, they can also occur in larger group sizes. 
Shelden et al. (2014) compiled historical sightings of harbor porpoises 
from lower to upper Cook Inlet that spanned from a few animals to 92 
individuals. The 2018 CIPL Extension Project that occurred in middle 
Cook Inlet reported 29 sightings of 44 individuals (Sitkiewicz et al., 
2018). NMFS proposes to authorize 12 takes by Level B harassment for 
harbor porpoises to allow for multiple group sightings during the 
specified activity. This authorization is greater than the exposure 
estimate calculated (5.020, table 11) but would account for the 
possibility of a couple sightings of small groups of harbor porpoises 
during Hilcorp's 6 days of tugging activity.
    Recent data specific to Pacific white-sided dolphins within Cook 
Inlet is lacking, and the calculated exposure estimate is zero based on 
the paucity of sightings of this species in this region (table 11). 
However, Pacific-white sided dolphins have been observed in Cook Inlet. 
During an aerial survey in May 2014, Apache observed three Pacific 
white-sided dolphins near Kenai. No large groups of Pacific white-sided 
dolphins have been reported within Cook Inlet, although acoustic 
detections of several Pacific white-sided dolphins were recorded near 
Iniskin Bay during Hilcorp's 3D seismic survey in 2020. Prior to this, 
only one other survey in the last 20 years noted the presence of 
Pacific white-sided dolphins (three animals) within Cook Inlet. As a 
result of the dearth of current data on this species, an accurate 
density for Pacific white-sided dolphins in the specific project region 
has not been generated. However, based on the possibility of this 
species in the project area, NMFS proposes to authorize three takes by 
Level B harassment for Pacific white-sided dolphins, the maximum number 
of Pacific white-sided dolphins that have been recorded in the somewhat 
recent past are present in Cook Inlet. This is consistent with NMFS' 
IHA for Hilcorp's previous tugging activities (87 FR 62364, October 14, 
2022).
    Harbor seals are often solitary in water but can haul out in groups 
of a few to thousands (Alaska Department of Fish and Game (ADF&G), 
2022). Given their presence in the study region, NMFS proposes to 
authorize 355 takes by Level B harassment for harbor seals, which is 
commensurate with the calculated exposure estimate based on harbor seal 
densities and Hilcorp's estimated durations for tugs under load with a 
jack-up rig (table 11).
    Steller sea lions tend to forage individually or in small groups 
(Fiscus and Baines, 1966) but have been documented feeding in larger 
groups when schooling fish were present (Gende et al., 2001). Steller 
sea lions have been observed during marine mammal surveys conducted in 
Cook Inlet. In 2012, during Apache's 3D Seismic survey, three sightings 
of approximately four individuals in upper Cook Inlet were reported 
(Lomac-MacNair et al., 2013). Marine mammal observers associated with 
Buccaneer's drilling project off Cape Starichkof observed seven Steller 
sea lions during the summer of 2013 (Owl Ridge, 2014). During 
SAExploration's 3D Seismic Program in 2015, four Steller sea lions were 
observed in Cook Inlet. One sighting occurred between the West and East 
Forelands, one occurred near Nikiski, and one occurred northeast of the 
North Foreland in the center of Cook Inlet (Kendall and Cornick, 2015). 
During NMFS Cook Inlet beluga whale aerial surveys from 2000 to 2016, 
39 sightings of 769 estimated individual Steller sea lions in lower 
Cook Inlet were reported (Shelden et al., 2017). During a waterfowl 
survey in upper Cook Inlet, an observer documented an estimated 25 
Steller sea lions hauled-out at low tide in the Lewis River on the west 
side of Cook Inlet (K. Lindberg, pers. comm., August 15, 2022). Hilcorp 
reported one sighting of two Steller sea lions while conducting 
pipeline work in upper Cook Inlet (Sitkiewicz et al., 2018). 
Commensurate with exposure estimates shown in table 11, NMFS is 
proposing to authorize nine takes by Level B harassment for Steller sea 
lions.
    While California sea lions are uncommon in the specific geographic 
region, two were seen during the 2012 Apache seismic survey in Cook 
Inlet (Lomac-MacNair et al., 2013). California sea lions in Alaska are 
typically alone but may be seen in small groups usually associated with 
Steller sea lions at their haul outs and rookeries (Maniscalco et al., 
2004). Despite the estimated exposure estimate being zero due to the 
lack of sightings during aerial surveys, NMFS proposes to authorize two 
takes by Level B harassment for California sea lions to account for the 
potential to see up to two animals over the course of the season. This 
is consistent with NMFS authorization for Hilcorp's previous tugging 
activities (87 FR 62364, October 14, 2022).

Proposed Mitigation

    In order to issue an IHA under section 101(a)(5)(D) of the MMPA, 
NMFS must set forth the permissible methods of taking pursuant to the 
activity, and other means of effecting the least practicable impact on 
the species or stock and its habitat, paying particular attention to 
rookeries, mating grounds, and areas of similar significance, and on 
the availability of the species or stock for taking for certain 
subsistence uses. NMFS regulations require applicants for incidental 
take authorizations to include information about the availability and 
feasibility (economic and technological) of equipment, methods, and 
manner of conducting the activity or other means of effecting the least 
practicable adverse impact upon the affected species or stocks, and 
their habitat (50 CFR 216.104(a)(11)).
    In evaluating how mitigation may or may not be appropriate to 
ensure the least practicable adverse impact on species or stocks and 
their habitat, as well as subsistence uses where applicable, NMFS 
considers two primary factors:
    (1) The manner in which, and the degree to which, the successful 
implementation of the measure(s) is expected to reduce impacts to 
marine mammals, marine mammal species or stocks, and their habitat, as 
well as subsistence uses. This considers the nature of the potential 
adverse impact being mitigated (likelihood, scope, range). It further 
considers the likelihood that the measure will be effective if 
implemented (probability of accomplishing the mitigating result if 
implemented as planned), the likelihood of effective implementation 
(probability implemented as planned); and
    (2) The practicability of the measures for applicant 
implementation, which may consider such things as cost and impact on 
operations.
    There is a discountable potential for marine mammals to incur PTS 
from the project, as source levels are relatively low, non-impulsive, 
and animals would have to remain at very close distances for multiple 
hours to accumulate acoustic energy at levels that could damage 
hearing. Therefore, we do not believe there is reasonable potential for 
Level A harassment and we are not proposing to authorize it. However, 
Hilcorp will implement a number of

[[Page 60195]]

mitigation measures designed to reduce the potential for and severity 
of Level B harassment and minimize the impacts of the project.
    The tugs towing a jack-up rig are not able to shut down while 
transiting, holding, or positioning the rig. Hilcorp would maneuver the 
tugs towing the jack-up rig such that they maintain a consistent speed 
(approximately 4 knots [7 km/hr]) and avoid multiple changes of speed 
and direction to make the course of the vessels as predictable as 
possible to marine mammals in the surrounding environment, 
characteristics that are expected to be associated with a lower 
likelihood of disturbance.
    During activities involving tugs under load with a jack-up rig, 
Hilcorp would implement a clearance zone of 1,500 m centered around the 
jack-up rig for non-CIBW species and a clearance zone that extends as 
far as PSOs can feasibly observe for CIBWs. The 1,500 m proposed 
clearance zone is consistent with previous authorizations for tugging 
activities (87 FR 62364, October 14, 2022), and was determined to be 
appropriate as it is approximately twice as large as largest Level A 
harassment zone (table 10) and is a reasonable distance within which 
cryptic species (e.g., porpoises, pinnipeds) could be observed. The 
larger clearance zone for CIBWs is a new measure aimed to further 
minimize any potential impacts from tugs under load with a jack-up rig 
on this species.
    Hilcorp would employ two NMFS-approved PSOs to conduct marine 
mammal monitoring to a distance out to the greatest extent possible for 
all mobile and stationary tugging activity. Prior to new commencing 
activities during daylight hours or if there is a 30-minute lapse in 
operational activities, the PSOs would observe the clearance zones 
described above for 30 minutes (i.e., pre-clearance monitoring) 
(transitioning from towing to positioning without shutting down would 
not be considered commencing a new operational activity). If no marine 
mammals are observed within the relevant clearance zone during this 
pre-clearance monitoring period, tugs may commence their towing, 
positioning, or holding of a jack-up rig. If a non-CIBW marine 
mammal(s) is observed within the relevant clearance zone during the 
pre-clearance monitoring period towing, positioning, or holding of a 
jack-up rig would be delayed, unless the delay interferes with the 
safety of working conditions. Operations would not commence until the 
PSO(s) observe that the non-CIBW animal(s) is outside of and on a path 
away from the clearance zone, or 30 minutes have elapsed without 
observing the non-CIBW marine mammal. If a CIBW(s) is observed within 
the relevant clearance zone during those 30 minutes, operations may not 
commence until the CIBW(s) is no longer detected at any range and 30 
minutes have elapsed without any observations of CIBWs. Once the PSOs 
have determined one of those conditions are met, operations may 
commence. PSOs would also conduct monitoring for marine mammals through 
30 minutes post-completion of any tugging activity each day, and after 
each stoppage of 30 minutes or greater.
    During nighttime hours or low/no-light conditions, night-vision 
devices (NVDs) shown to be effective at detecting marine mammals in 
low-light conditions (e.g., Portable Visual Search-7 model, or similar) 
would be provided to PSOs to aid in their monitoring of marine mammals. 
Every effort would be made to observe that the relevant clearance zone 
is free of marine mammals by using night-vision devices and or the 
naked eye, however it may not always be possible to see and clear the 
entire clearance zones prior to nighttime transport. Prior to 
commencing new operational activities during nighttime hours or if 
there is a 30-minute lapse in operational activities in low/no-light 
conditions, the PSOs would observe out to the greatest extent feasible 
while using NVDs for 30 minutes (i.e., pre-clearance monitoring); if no 
marine mammals are observed during this pre-clearance monitoring 
period, tugs may commence towing, positioning, or holding a jack-up 
rig. If a marine mammal(s) is observed during the pre-clearance 
monitoring period, tugs towing, positioning, or holding a jack-up rig 
would be delayed, unless the delay interferes with the safety of 
working conditions. Operations would not commence until the PSO(s) 
observe that: (1) the animal(s) is outside of the observable area; or 
(2) 30 minutes have elapsed. Once the PSOs have determined one of those 
conditions are met, operations may commence.
    Hilcorp would operate with the tide, resulting in a low power 
output from the tugs towing the jack-up rig, unless human safety or 
equipment integrity are at risk. Due to the nature of tidal cycles in 
Cook Inlet, it is possible that the most favorable tide for the towing 
operation would occur during nighttime hours. Hilcorp would operate the 
tugs towing the jack-up rigs at night if the nighttime operations 
result in a lower power output from the tugs by operating with a 
favorable tide.
    Out of concern for potential disturbance to CIBWs in sensitive and 
essential habitat, Hilcorp would maintain a distance of 2.4 km from the 
MLLW line of the Susitna River Delta (Beluga River to the Little 
Susitna River) between April 15 and November 15. The dates of 
applicability of this exclusion area have been expanded based on new 
available science, including visual surveys and acoustic studies, which 
indicate that substantial numbers of CIBWs continue to occur in the 
Susitna Delta area through at least mid-November (M. Castellote, pers. 
comm., T. McGuire, pers. comm.). In addition, Hilcorp would coordinate 
with local Tribes as described in its Stakeholder Engagement Plan (see 
Appendix C in Hilcorp's application), notify the communities of any 
changes in the operation, and take action to avoid or mitigate impacts 
to subsistence harvests.
    For transportation of a jack-up rig to or from the Tyonek platform, 
in addition to the two PSOs stationed on the rig during towing, one 
additional PSO would be stationed on the Tyonek platform to monitor for 
marine mammals. The PSO would be on-watch for at least 1 hour before 
tugs are expected to arrive (scheduled to approach the Level B 
harassment threshold).
    Based on our evaluation of Hilcorp's proposed measures, NMFS has 
preliminarily determined that the proposed mitigation measures provide 
the means of effecting the least practicable impact on the affected 
species or stocks and their habitat, paying particular attention to 
rookeries, mating grounds, and areas of similar significance, and on 
the availability of such species or stock for subsistence uses.

Proposed Monitoring and Reporting

    In order to issue an IHA for an activity, section 101(a)(5)(D) of 
the MMPA states that NMFS must set forth requirements pertaining to the 
monitoring and reporting of such taking. The MMPA implementing 
regulations at 50 CFR 216.104(a)(13) indicate that requests for 
authorizations must include the suggested means of accomplishing the 
necessary monitoring and reporting that will result in increased 
knowledge of the species and of the level of taking or impacts on 
populations of marine mammals that are expected to be present while 
conducting the activities. Effective reporting is critical both to 
compliance as well as ensuring that the most value is obtained from the 
required monitoring.
    Monitoring and reporting requirements prescribed by NMFS should 
contribute to improved

[[Page 60196]]

understanding of one or more of the following:
     Occurrence of marine mammal species or stocks in the area 
in which take is anticipated (e.g., presence, abundance, distribution, 
density);
     Nature, scope, or context of likely marine mammal exposure 
to potential stressors/impacts (individual or cumulative, acute or 
chronic), through better understanding of: (1) action or environment 
(e.g., source characterization, propagation, ambient noise); (2) 
affected species (e.g., life history, dive patterns); (3) co-occurrence 
of marine mammal species with the activity; or (4) biological or 
behavioral context of exposure (e.g., age, calving or feeding areas);
     Individual marine mammal responses (behavioral or 
physiological) to acoustic stressors (acute, chronic, or cumulative), 
other stressors, or cumulative impacts from multiple stressors;
     How anticipated responses to stressors impact either: (1) 
long-term fitness and survival of individual marine mammals; or (2) 
populations, species, or stocks;
     Effects on marine mammal habitat (e.g., marine mammal prey 
species, acoustic habitat, or other important physical components of 
marine mammal habitat); and
     Mitigation and monitoring effectiveness.
    Hilcorp would abide by all monitoring and reporting measures 
contained within the IHA, if issued, and their Marine Mammal Monitoring 
and Mitigation Plan (see appendix D of Hilcorp's application). A 
summary of those measures and additional requirements proposed by NMFS 
is provided below.
    A minimum of two NMFS-approved PSOs must be stationed on the tug or 
jack-up rig for monitoring purposes for the entirety of jack-up rig 
towing, holding, and positioning operations. PSOs would be independent 
of the activity contractor (for example, employed by a subcontractor) 
and have no other assigned tasks during monitoring periods. At least 
one PSO would have prior experience performing the duties of a PSO 
during an activity pursuant to a NMFS-issued Incidental Take 
Authorization or Letter of Concurrence. Other PSOs may substitute other 
relevant experience (including relevant Alaska Native traditional 
knowledge), education (degree in biological science or related field), 
or training for prior experience performing the duties of a PSO.
    PSOs would also have the following additional qualifications:
    (a) The ability to conduct field observations and collect data 
according to assigned protocols;
    (b) Experience or training in the field identification of marine 
mammals, including the identification of behaviors;
    (c) Sufficient training, orientation, or experience with the 
tugging operation to provide for personal safety during observations;
    (d) Sufficient writing skills to record required information 
including but not limited to the number and species of marine mammals 
observed; dates and times when tugs were under load with the jack-up 
rig; dates, times, and reason for implementation of mitigation (or why 
mitigation was not implemented when required); and marine mammal 
behavior; and
    (e) The ability to communicate orally, by radio or in person, with 
project personnel to provide real-time information on marine mammals 
observed in the area as necessary.
    PSOs would be positioned aboard the tug or the jack-up-rig at the 
best practical vantage points that are determined to be safe, ideally 
an elevated stable platform from which a single PSO would have an 
unobstructed 360-degree view of the water or a total 360-degree view 
between all PSOs on-watch. Generally, one PSO would be on the port side 
and one PSO would be on the starboard side. Additionally, when towing 
the jack-up rig to the Tyonek platform, an additional PSO would be 
stationed on the Tyonek platform 1 hour before tugs are expected to 
arrive (i.e., scheduled to approach the Level B threshold) to monitor 
for marine mammals out to the maximum extent possible. PSOs may use a 
combination of equipment to scan the monitoring area and to verify the 
required monitoring distance from the project site, including the naked 
eye, 7 by 50 binoculars, and NMFS approved NVDs for low light and 
nighttime operations. PSOs would be in communication with all vessel 
captains via VHF radio and/or cell phones at all times and alert vessel 
captains to all marine mammal sightings relative to the vessel 
location.
    Hilcorp would submit interim monthly reports for all months in 
which tug towing, holding, or positioning of the jack-up rig occurs. 
Monthly reports would be due 14 days after the conclusion of each 
calendar month, and would include a summary of marine mammal species 
and behavioral observations, delays, and tugging activities completed 
(i.e., tugs towing, holding, or positioning the jack-up rig). They also 
must include an assessment of the amount of tugging remaining to be 
completed, in addition to the number of CIBWs observed within estimated 
harassment zones to date.
    A draft final summary marine mammal monitoring report would be 
submitted to NMFS within 90 days after the completion of the tug towing 
jack-up rig activities for the year or 60 calendar days prior to the 
requested issuance of any subsequent IHA for similar activity at the 
same location, whichever comes first. The draft summary report would 
include an overall description of all work completed, a narrative 
regarding marine mammal sightings, and associated marine mammal 
observation data sheets (data must be submitted electronically in a 
format that can be queried such as a spreadsheet or database). 
Specifically, the summary report would include:
     Date and time that monitored activity begins or ends;
     Activities occurring during each observation period, 
including (a) the type of activity (towing, holding, positioning), (b) 
the total duration of each type of activity, (c) the number of attempts 
required for positioning, (d) when nighttime operations were required, 
and (e) whether towing against the tide was required;
     PSO locations during marine mammal monitoring;
     Environmental conditions during monitoring periods (at the 
beginning and end of the PSO shift and whenever conditions change 
significantly), including Beaufort sea state, tidal state, and any 
other relevant weather conditions including cloud cover, fog, sun 
glare, overall visibility to the horizon, and estimated observable 
distance;
     Upon observation of a marine mammal, the following 
information:
    [cir] Name of PSO who sighted the animal(s) and PSO location and 
activity at time of sighting;
    [cir] Time of sighting;
    [cir] Identification of the animal(s) (e.g., genus/species, lowest 
possible taxonomic level, or unidentified), PSO confidence in 
identification, and the composition of the group if there is a mix of 
species;
    [cir] Distance and location of each observed marine mammal relative 
to the tug boats for each sighting;
    [cir] Estimated number of animals (min/max/best estimate);
    [cir] Estimated number of animals by cohort (adults, juveniles, 
neonates, group composition, etc.);
    [cir] Animal's closest point of approach and estimated time spent 
within the harassment zone;
    [cir] Description of any marine mammal behavioral observations 
(e.g., observed

[[Page 60197]]

behaviors such as feeding or traveling), including an assessment of 
behavioral responses thought to have resulted from the activity (e.g., 
no response or changes in behavioral state such as ceasing feeding, 
changing direction, flushing, or breaching);
     Number of marine mammals detected within the harassment 
zones, by species; and
     Detailed information about implementation of any 
mitigation (e.g., delays), a description of specific actions that 
ensued, and resulting changes in behavior of the animal(s), if any.
    If no comments are received from NMFS within 30 days, the draft 
summary report would constitute the final report. If comments are 
received, a final report addressing NMFS comments must be submitted 
within 30 days after receipt of comments.
    In the event that personnel involved in Hilcorp's tugging 
activities discover an injured or dead marine mammal, Hilcorp would 
report the incident to the Office of Protected Resources, NMFS 
([email protected], [email protected]), and to 
the Alaska Regional Stranding Coordinator as soon as feasible. If the 
death or injury was clearly caused by the specified activity, Hilcorp 
would immediately cease the specified activities until NMFS is able to 
review the circumstances of the incident and determine what, if any, 
additional measures are appropriate to ensure compliance with the IHA. 
Hilcorp would not resume their activities until notified by NMFS. The 
report would include the following information:
     Time, date, and location (latitude and longitude) of the 
first discovery (and updated location information if known and 
applicable);
     Species identification (if known) or description of the 
animal(s) involved;
     Condition of the animal(s) (including carcass condition if 
the animal is dead);
     Observed behaviors of the animal(s), if alive;
     If available, photographs or video footage of the 
animal(s); and
     General circumstances under which the animal was 
discovered.

Negligible Impact Analysis and Determination

    NMFS has defined negligible impact as an impact resulting from the 
specified activity that cannot be reasonably expected to, and is not 
reasonably likely to, adversely affect the species or stock through 
effects on annual rates of recruitment or survival (50 CFR 216.103). A 
negligible impact finding is based on the lack of likely adverse 
effects on annual rates of recruitment or survival (i.e., population-
level effects). An estimate of the number of takes alone is not enough 
information on which to base an impact determination. In addition to 
considering estimates of the number of marine mammals that might be 
``taken'' through harassment, NMFS considers other factors, such as the 
likely nature of any impacts or responses (e.g., intensity, duration), 
the context of any impacts or responses (e.g., critical reproductive 
time or location, foraging impacts affecting energetics), as well as 
effects on habitat, and the likely effectiveness of the mitigation. We 
also assess the number, intensity, and context of estimated takes by 
evaluating this information relative to population status. Consistent 
with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, 
September 29, 1989), the impacts from other past and ongoing 
anthropogenic activities are incorporated into this analysis via their 
impacts on the baseline (e.g., as reflected in the regulatory status of 
the species, population size and growth rate where known, ongoing 
sources of human-caused mortality, or ambient noise levels).
    To avoid repetition, the discussion of our analysis applies to all 
the species listed in table 11, except CIBWs, given that many of the 
anticipated effects of this project on different marine mammal stocks 
are expected to be relatively similar in nature. For CIBWs, there are 
meaningful differences in anticipated individual responses to 
activities, impact of expected take on the population, or impacts on 
habitat; therefore, we provide a separate independent detailed analysis 
for CIBWs following the analysis for other species for which we propose 
take authorization.
    NMFS has identified several key factors which may be employed to 
assess the level of analysis necessary to conclude whether potential 
impacts associated with a specified activity should be considered 
negligible. These include (but are not limited to) the type and 
magnitude of taking, the amount and importance of the available habitat 
for the species or stock that is affected, the duration of the 
anticipated effect on the individuals, and the status of the species or 
stock. The potential effects of the specified activity on humpback 
whales, minke whales, gray whales, fin whales, killer whales, Dall's 
porpoises, harbor porpoises, Pacific white-sided dolphins, Steller sea 
lions, harbor seals, and California sea lions are discussed below. 
These factors also apply to CIBWs; however, an additional analysis for 
CIBWs is provided in a separate sub-section below.
    Tugs under load with the jack-up rig, as outlined previously, have 
the potential to disturb or displace marine mammals. Specifically, the 
specified activities may result in take, in the form of Level B 
harassment, from underwater sounds generated by tugs towing, holding, 
and positioning a jack-up rig. Potential takes could occur if marine 
mammals are present in zones ensonified above the thresholds for Level 
B harassment, identified above, while activities are underway.
    Hilcorp's planned activities and associated impacts would occur 
within a limited, confined area of the affected species or stocks' 
range over a total of 6 days between September 14, 2024, and September 
13, 2025. The intensity and duration of take by Level B harassment 
would be minimized through use of mitigation measures described herein. 
Further the amount of take proposed to be authorized is small when 
compared to stock abundance (see tables 2 and 11). In addition, NMFS 
does not anticipate that serious injury or mortality would occur as a 
result of Hilcorp's planned activity given the nature of the activity, 
even in the absence of required mitigation.
    Exposures to elevated sound levels produced during tugs under load 
with the jack-up rig may cause behavioral disturbance of some 
individuals within the vicinity of the sound source. Behavioral 
responses of marine mammals to tugs under load with the jack-up rig are 
expected to be mild, short term, and temporary. Effects on individuals 
that are taken by Level B harassment, as enumerated in the Estimated 
Take section, on the basis of reports in the literature as well as 
monitoring from other similar activities conducted by Hilcorp (Horsley 
and Larson, 2023), would likely be limited to behavioral response such 
as increased swimming speeds, changing in directions of travel and 
diving and surfacing behaviors, increased respiration rates, or 
decreased foraging (if such activity were occurring) (Ridgway et al., 
1997; Nowacek et al., 2007; Thorson and Reyff, 2006; Kendall and 
Cornick, 2015; Goldbogen et al., 2013b; Blair et al., 2016; Wisniewska 
et al., 2018; Piwetz et al., 2021). Marine mammals within the Level B 
harassment zones may not show any visual cues they are disturbed by 
activities or they could become alert, avoid the area, leave the area, 
or have other mild responses that are not observable such as increased 
stress levels (e.g., Rolland et al. 2012; Bejder et al., 2006; Rako et 
al., 2013; Pirotta et

[[Page 60198]]

al., 2015; P[eacute]rez-Jorge et al., 2016). They may also exhibit 
increased vocalization rates (e.g., Dahlheim, 1987; Dahlheim and 
Castellote, 2016), louder vocalizations (e.g., Frankel and Gabriele, 
2017; Fournet et al., 2018), alterations in the spectral features of 
vocalizations (e.g., Castellote et al., 2012), or a cessation of 
communication signals (e.g., Tsujii et al., 2018). However, as 
described in the Potential Effects of Specified Activities on Marine 
Mammals and Their Habitat section, marine mammals observed near 
Hilcorp's planned activities have shown little to no observable 
reactions to tugs under load with a jack-up rig (Horsley and Larson, 
2023).
    Tugs pulling, holding, and positioning a jack-up rig are slow-
moving as compared to typical recreational and commercial vessel 
traffic. Assuming an animal was stationary, exposure from the moving 
tug configuration (which comprises most of the tug activity being 
considered) would be on the order of minutes in any particular 
location. The slow, predictable, and generally straight path of this 
activity is expected to further lessen the likelihood that sound 
exposures at the expected levels would result in the harassment of 
marine mammals. Also, this slow transit along a predictable path is 
planned in an area of routine vessel traffic where many large vessels 
move in slow straight-line paths, and some individuals are expected to 
be habituated to these sorts of sounds. While it is possible that 
animals may swim around the project area, avoiding closer approaches to 
the boats, we do not expect them to abandon any intended path. Further, 
most animals present in the region would likely be transiting through 
the area; therefore, any potential exposure is expected to be brief. 
Based on the characteristics of the sound source and the other 
activities regularly encountered in the area, it is unlikely Hilcorp's 
plannedactivities would be of a duration or intensity expected to 
result in impacts on reproduction or survival.
    Further, most of the species present in the region would only be 
present temporarily based on seasonal patterns or during transit 
between other habitats. These temporarily present species would be 
exposed to even shorter periods of noise-generating activity, further 
decreasing the impacts. Most likely, individual animals would simply 
move away from the sound source and be temporarily displaced from the 
area. Takes may also occur during important feeding times. The project 
area though represents a small portion of available foraging habitat 
and impacts on marine mammal feeding for all species should be minimal.
    We anticipate that any potential reactions and behavioral changes 
are expected to subside quickly when the exposures cease and, 
therefore, we do not expect long-term adverse consequences from 
Hilcorp's proposed activities for individuals of any species. The 
intensity of Level B harassment events would be minimized through use 
of mitigation measures described herein, which were not quantitatively 
factored into the take estimates. Hilcorp would use PSOs to monitor for 
marine mammals before commencing any tugging activity, which would 
minimize the potential for marine mammals to be present within Level B 
harassment zones when tugs are under load. Further, given the absence 
of any major rookeries or areas of known biological significance for 
marine mammals (e.g., foraging hot spots) within the estimated 
harassment zones (other than critical habitat and a BIA for CIBWs as 
described below), we assume that potential takes by Level B harassment 
would have an inconsequential short-term effect on individuals and 
would not result in population-level impacts.
    Theoretically, repeated, sequential exposure to elevated noise from 
tugs under load with a jack-up rig over a long duration could result in 
more severe impacts to individuals that could affect a population (via 
sustained or repeated disruption of important behaviors such as 
feeding, resting, traveling, and socializing; Southall et al., 2007). 
Alternatively, marine mammals exposed to repetitious sounds may become 
habituated, desensitized, or tolerant after initial exposure to these 
sounds (reviewed by Richardson et al., 1995; Southall et al., 2007). 
Cook Inlet is a regional hub of marine transportation, and is used by 
various classes of vessels, including containerships, bulk cargo 
freighters, tankers, commercial and sport-fishing vessels, and 
recreational vessels. Off-shore vessels, tug vessels, and tour boats 
represent 86 percent of the total operating days for vessels in Cook 
Inlet (BOEM, 2016). Given that marine mammals still frequent and use 
Cook Inlet despite being exposed to anthropogenic sounds such as those 
produced by tug boats and other vessels across many years, these severe 
population level impacts resulting from the additional noise produced 
by tugs under load with a jack-up rig are not anticipated. The absence 
of any pinniped haulouts or other known home-ranges in the planned 
action area further decreases the likelihood of severe population level 
impacts.
    Hilcorp's tugs under load with a jack-up rig are also not expected 
to have significant adverse effects on any marine mammal habitat as no 
physical impacts to habitat are anticipated to results from the 
specified activities and any impacts to marine mammal habitat (i.e., 
elevated sound levels) would be temporary. In addition to being 
temporary and short in overall duration, the acoustic footprint of the 
proposed activity is small relative to the overall distribution of the 
animals in the area and their use of the area. Additionally, the 
habitat within the estimated acoustic footprint is not known to be 
heavily used by marine mammals.
    Impacts to marine mammal prey species are also expected to be minor 
and temporary and to have, at most, short-term effects on foraging of 
individual marine mammals, and likely no effect on the populations of 
marine mammals as a whole. Overall, as described above, the area 
anticipated to be impacted by Hilcorp's planned activities is very 
small compared to the available surrounding habitat, and does not 
include habitat of particular importance. The most likely impact to 
prey would be temporary behavioral avoidance of the immediate area. 
When tugs are under load with the jack-up rig, it is expected that some 
fish would temporarily leave the area of disturbance (e.g., Nakken, 
1992; Olsen, 1979; Ona and Godo, 1990; Ona and Toresen, 1988), thus 
impacting marine mammals' foraging opportunities in a limited portion 
of their foraging range. But, because of the relatively small area of 
the habitat that may be affected, and lack of any foraging habitat of 
particular importance, the impacts to marine mammal habitat are not 
expected to cause significant or long-term negative consequences.
    Finally, Hilcorp will minimize potential exposure of marine mammals 
to elevated noise levels by delaying tugs being under load with the 
jack-up rig if marine mammals are observed during the pre-clearance 
monitoring period. Hilcorp would also implement vessel maneuvering 
measures to reduce the likelihood of disturbing marine mammals during 
any periods when marine mammals may be present near the vessels. 
Lastly, Hilcorp would also reduce the impact of their activity by 
conducting tugging operations with favorable tides whenever feasible.
    In summary and as described above, the following factors (with 
additional analyses for CIBWs included below) primarily support our 
preliminary determinations that the impacts resulting from the 
activities described for this proposed IHA are not expected

[[Page 60199]]

to adversely affect the species or stocks through effects on annual 
rates of recruitment or survival:
     No takes by mortality, serious injury, or Level A 
harassment are anticipated or proposed to be authorized;
     Exposure would likely be brief given the short duration of 
the specified activity and the transiting behavior of marine mammals in 
the action area;
     Marine mammal densities are low in the project area; 
therefore, there will not be substantial numbers of marine mammals 
exposed to the noise from the project compared to the affected 
population sizes;
     Take would not occur in places and/or times where take 
would be more likely to accrue to impacts on reproduction or survival, 
such as within ESA-designated or proposed critical habitat, BIAs (other 
than for CIBWs as described below), or other habitats critical to 
recruitment or survival (e.g., rookery);
     The project area represents a very small portion of the 
available foraging area for all potentially impacted marine mammal 
species;
     Take would only occur within middle Cook Inlet and Trading 
Bay--a limited, confined area of any given stock's home range;
     Monitoring reports from previous projects where tugs were 
under load with a jack-up rig in Cook Inlet have documented little to 
no observable effect on individuals of the same species impacted by the 
specified activities;
     The required mitigation measures (i.e., pre-clearance 
monitoring, vessel maneuver) are expected to be effective in reducing 
the effects of the specified activity by minimizing the numbers of 
marine mammals exposed to sound and the intensity of the exposures; and
     The intensity of anticipated takes by Level B harassment 
is low for all stocks consisting of, at worst, temporary modifications 
in behavior, and would not be of a duration or intensity expected to 
result in impacts on reproduction or survival.
    Cook Inlet Beluga Whales. For CIBWs, we further discuss our 
negligible impact findings in addition to the findings discussed above 
for all species in the context of potential impacts to this endangered 
stock based on our evaluation of the take proposed to be authorized 
(table 11).
    All tug towing, holding, or positioning would be done in a manner 
implementing best management practices to preserve water quality, and 
no work would occur around creek mouths or river systems leading to 
prey abundance reductions. In addition, no physical structures would 
restrict passage, though impacts to the acoustic habitat are relevant 
and discussed here. While the specified activity would occur within 
CIBW Critical Habitat Area 2, and the CIBW small and resident BIA, 
monitoring data from Hilcorp's activities suggest that the presence of 
tugs under load with a jack-up rig do not discourage CIBWs from 
transiting throughout Cook Inlet and between critical habitat areas and 
that the whales do not abandon critical habitat areas (Horsley and 
Larson, 2023). In addition, large numbers of CIBWs have continued to 
use Cook Inlet and pass through the area, likely traveling to critical 
foraging grounds found in upper Cook Inlet, while noise-producing 
anthropogenic activities, including vessel use, have taken place during 
the past 2 decades (e.g., Shelden et al., 2013, 2015b, 2017, 2022; 
Shelden and Wade, 2019; Geotz et al., 2023). These findings are not 
surprising as food is a strong motivation for marine mammals. As 
described in Forney et al. (2017), animals typically favor particular 
areas because of their importance for survival (e.g., feeding or 
breeding), and leaving may have significant costs to fitness (reduced 
foraging success, increased predation risk, increased exposure to other 
anthropogenic threats). Consequently, animals may be highly motivated 
to maintain foraging behavior in historical foraging areas despite 
negative impacts (e.g., Rolland et al., 2012).
    Generation of sound may result in avoidance behaviors that would be 
limited in time and space relative to the larger availability of 
important habitat areas in Cook Inlet; however, the area ensonified by 
sound from the specified activity is anticipated to be small compared 
to the overall available critical habitat for CIBWs to feed and travel. 
Therefore, the specified activity would not create a barrier to 
movement through or within important areas. We anticipate that 
disturbance to CIBWs would manifest in the same manner as other marine 
mammals described above (i.e., increased swimming speeds, changes in 
the direction of travel and dive behaviors, increased respiration 
rates, decreased foraging (if such activity were occurring), or 
alterations to communication signals). We do not believe exposure to 
elevated noise levels during transit past tugging activity would have 
adverse effects on individuals' fitness for reproduction or survival.
    Although data demonstrate that CIBWs are not abandoning the planned 
project area during anthropogenic activities, results of an expert 
elicitation (EE) at a 2016 workshop, which predicted the impacts of 
noise on CIBW survival and reproduction given lost foraging 
opportunities, helped to inform our assessment of impacts on this 
stock. The 2016 EE workshop used conceptual models of an interim 
population consequences of disturbance (PCoD) for marine mammals (NRC, 
2005; New et al., 2014; Tollit et al., 2016) to help in understanding 
how noise-related stressors might affect vital rates (survival, birth 
rate and growth) for CIBW (King et al., 2015). NMFS (2016b) suggests 
that the main direct effects of noise on CIBWs are likely to be through 
masking of vocalizations used for communication and prey location and 
habitat degradation. The 2016 workshop on CIBWs was specifically 
designed to provide regulators with a tool to help understand whether 
chronic and acute anthropogenic noise from various sources and projects 
are likely to be limiting recovery of the CIBW population. The full 
report can be found at https://www.smruconsulting.com/publications/ 
with a summary of the expert elicitation portion of the workshop below.
    For each of the noise effect mechanisms chosen for EE, the experts 
provided a set of parameters and values that determined the forms of a 
relationship between the number of days of disturbance a female CIBW 
experiences in a particular period and the effect of that disturbance 
on her energy reserves. Examples included the number of days of 
disturbance during the period April, May, and June that would be 
predicted to reduce the energy reserves of a pregnant CIBW to such a 
level that she is certain to terminate the pregnancy or abandon the 
calf soon after birth, the number of days of disturbance in the period 
April-September required to reduce the energy reserves of a lactating 
CIBW to a level where she is certain to abandon her calf, and the 
number of days of disturbance where a female fails to gain sufficient 
energy by the end of summer to maintain themselves and their calves 
during the subsequent winter. Overall, median values ranged from 16 to 
69 days of disturbance depending on the question. However, for this 
elicitation, a ``day of disturbance'' was defined as any day on which 
an animal loses the ability to forage for at least one tidal cycle 
(i.e., it forgoes 50-100 percent of its energy intake on that day). The 
day of disturbance considered in the context of the report is notably 
more severe than the Level B harassment expected to result from these 
activities, which as described is expected to be comprised 
predominantly of temporary

[[Page 60200]]

modifications in the behavior of individual CIBWs (e.g., faster swim 
speeds, longer dives, decreased sighting durations, alterations in 
communication). Also, NMFS proposes to authorize 15 instances of takes, 
with the instances representing disturbance events within a day--this 
means that either 15 different individual CIBWs are disturbed on no 
more than 1 day each, or some lesser number of individuals may be 
disturbed on more than 1 day, but with the product of individuals and 
days not exceeding 15. Given the overall anticipated take, and the 
short duration of the specified activities (i.e., 6 days), it is 
unlikely that any one CIBW will be disturbed on more than a couple 
days. Lastly, even if a CIBW was exposed every day of Hilcorp's planned 
activities, these activities are only planned for 6 days, and thus do 
not fall into the expected range of days of disturbance expected to 
elicit an effect on energy reserves as determined by the experts as 
described above (i.e., 16 to 19 days). Further, Hilcorp has proposed 
mitigation measures specific to CIBWs whereby they would not begin 
towing, holding, or positioning of the jack-up rig should a CIBW be 
observed at any distance. While Level B harassment (behavioral 
disturbance) would be authorized, this measure, along with other 
mitigation measures described herein, would limit the severity of the 
effects of that Level B harassment to behavioral changes such as 
increased swim speeds, changes in diving and surfacing behaviors, and 
alterations to communication signals, not the loss of foraging 
capabilities. Finally, take by mortality, serious injury, or Level A 
harassment of CIBWs is not anticipated or proposed to be authorized.
    In summary and as described above, the additional following factors 
primarily support our preliminary determination that the impacts 
resulting from this activity are not expected to adversely affect the 
CIBWs through effects on annual rates of recruitment or survival:
     The area of exposure would be limited to habitat primarily 
used for transiting, and not areas known to be of particular importance 
for feeding or reproduction;
     The activities are not expected to result in CIBWs 
abandoning critical habitat nor are they expected to restrict passage 
of CIBWs within or between critical habitat areas; and
     Any disturbance to CIBWs is expected to be limited to 
temporary modifications in behavior, and would not be of a duration or 
intensity expected to result in impacts on reproduction or survival.
    Based on the analysis contained herein of the likely effects of the 
specified activity on marine mammals and their habitat, and taking into 
consideration the implementation of the proposed monitoring and 
mitigation measures, NMFS preliminarily finds that the total marine 
mammal take from the proposed activity will have a negligible impact on 
all affected marine mammal species or stocks.

Small Numbers

    As noted previously, only take of small numbers of marine mammals 
may be authorized under sections 101(a)(5)(A) and (D) of the MMPA for 
specified activities other than military readiness activities. The MMPA 
does not define small numbers and so, in practice, where estimated 
numbers are available, NMFS compares the number of individuals taken to 
the most appropriate estimation of abundance of the relevant species or 
stock in our determination of whether an authorization is limited to 
small numbers of marine mammals. When the predicted number of 
individuals to be taken is fewer than one-third of the species or stock 
abundance, the take is considered to be of small numbers (86 FR 5322, 
January 19, 2021). Additionally, other qualitative factors may be 
considered in the analysis, such as the temporal or spatial scale of 
the activities.
    For all stocks whose abundance estimate is known, the amount of 
taking is less than one-third of the best available population 
abundance estimate (in fact it is less than 2 percent for all stocks, 
except for CIBWs whose proposed take is 5.38 percent of the stock; 
table 12). The number of animals proposed for authorization to be taken 
from these stocks therefore, would be considered small relative to the 
relevant stocks abundances even if each estimated take occurred to a 
new individual.

                   Table 12--Proposed Take To Be Authorized as a Percentage of Stock Abundance
----------------------------------------------------------------------------------------------------------------
                                     Proposed total
                                     amount of take                                  Abundance      Percent of
              Species                     to be                 Stock                 (Nbest)          stock
                                       authorized
----------------------------------------------------------------------------------------------------------------
Humpback whale.....................               3  Hawaii (Hawaii DPS)........          11,278            0.03
                                                     Mexico-North Pacific                \1\ N/A             N/A
                                                      (Mexico DPS).
                                                     Western North Pacific......           1,084            0.28
Minke whale........................               3  Alaska.....................         \2\ N/A             N/A
Gray whale.........................               3  Eastern Pacific............          26,960            0.01
Fin whale..........................               2  Northeast Pacific..........         \3\ UND             N/A
Killer whale.......................              10  Eastern North Pacific                 1,920            0.52
                                                      Alaska Resident.
                                                     Eastern North Pacific Gulf              587             1.7
                                                      of Alaska, Aleutian
                                                      Islands, and Bering Sea
                                                      Transient.
Beluga whale.......................              15  Cook Inlet.................         \4\ 279            5.38
Dall's porpoise....................               6  Alaska.....................         \5\ UND             N/A
Harbor porpoise....................              12  Gulf of Alaska.............          31,046            0.04
Pacific white-sided dolphin........               3  North Pacific..............          26,880            0.01
Harbor seal........................             365  Cook Inlet/Shelikof........          28,411            1.29
Steller sea lion...................               9  Western U.S................      \6\ 49,932            0.02
California sea lion................               2  U.S........................         257,606           <0.01
----------------------------------------------------------------------------------------------------------------
\1\ Abundance estimates are based upon data collected more than 8 years ago and, therefore, current estimates
  are considered unknown.
\2\ Reliable population estimates are not available for this stock. Please see Friday et al. (2013) and Zerbini
  et al. (2006) for additional information on numbers of minke whales in Alaska.
\3\ The best available abundance estimate for this stock is not considered representative of the entire stock as
  surveys were limited to a small portion of the stock's range.

[[Page 60201]]

 
\4\ On June 15, 2023, NMFS released an updated abundance estimate for endangered CIBWs in Alaska (Goetz et al.,
  2023). Data collected during NOAA Fisheries' 2022 aerial survey suggest that the whale population is stable or
  may be increasing slightly. Scientists estimated that the population size is between 290 and 386, with a
  median best estimate of 331. In accordance with the MMPA, this population estimate will be incorporated into
  the CIBW SAR, which will be reviewed by an independent panel of experts, the Alaska Scientific Review Group.
  After this review, the SAR will be made available as a draft for public review before being finalized. When
  the number of instances of takes is compared to this median abundance, the percent of the stock proposed for
  authorization is 4.53%.
\5\ The best available abundance estimate is likely an underestimate for the entire stock because it is based
  upon a survey that covered only a small portion of the stock's range.
\6\ Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys.

    Abundance estimates for the Mexico-North Pacific stock of humpback 
whales are based upon data collected more than 8 years ago and, 
therefore, current estimates are considered unknown (Young et al., 
2023). The most recent minimum population estimates (NMIN) 
for this population include an estimate of 2,241 individuals between 
2003 and 2006 (Martinez-Aguilar, 2011) and 766 individuals between 2004 
and 2006 (Wade, 2021). NMFS' Guidelines for Assessing Marine Mammal 
Stocks suggest that the NMIN estimate of the stock should be 
adjusted to account for potential abundance changes that may have 
occurred since the last survey and provide reasonable assurance that 
the stock size is at least as large as the estimate (NMFS, 2023a). The 
abundance trend for this stock is unclear; therefore, there is no basis 
for adjusting these estimates (Young et al., 2023). Assuming the 
population has been stable, the 4 takes of this stock proposed for 
authorization represents small numbers of this stock (0.18 percent of 
the stock assuming a NMIN of 2,241 individuals and 0.52 
percent of the stock assuming an NMIN of 766 individuals).
    A lack of an accepted stock abundance value for the Alaska stock of 
minke whale did not allow for the calculation of an expected percentage 
of the population that would be affected. The most relevant estimate of 
partial stock abundance is 1,233 minke whales in coastal waters of the 
Alaska Peninsula and Aleutian Islands (Zerbini et al., 2006). Given 
three proposed takes by Level B harassment for the stock, comparison to 
the best estimate of stock abundance shows, at most, less than 1 
percent of the stock would be expected to be impacted.
    There is no stock-wide abundance estimate for Northeast Pacific fin 
whales. However, Young et al. (2022) estimate the minimum stock size 
for the areas surveyed is 2,554. Given two proposed takes by Level B 
harassment for the stock, comparison to the minimum population estimate 
shows, at most, less than 1 percent of the stock would be expected to 
be impacted.
    The Alaska stock of Dall's porpoise has no official NMFS abundance 
estimate for this area, as the most recent estimate is greater than 8 
years old. As described in the 2022 Alaska SAR (Young et al., 2023) the 
minimum population estimate is assumed to correspond to the point 
estimate of the 2015 vessel-based abundance computed by Rone et al. 
(2017) in the Gulf of Alaska (N = 13,110; CV = 0.22). Given six 
authorized takes by Level B harassment for the stock, comparison to the 
minimum population estimate shows, at most, less than 1 percent of the 
stock would be expected to be impacted.
    Based on the analysis contained herein of the proposed activity 
(including the proposed mitigation and monitoring measures) and the 
anticipated take of marine mammals, NMFS preliminarily finds that small 
numbers of marine mammals would be taken relative to the population 
size of the affected species or stocks.

Unmitigable Adverse Impact Analysis and Determination

    In order to issue an IHA, NMFS must find that the specified 
activity will not have an ``unmitigable adverse impact'' on the 
subsistence uses of the affected marine mammal species or stocks by 
Alaskan Natives. NMFS has defined ``unmitigable adverse impact'' in 50 
CFR 216.103 as an impact resulting from the specified activity: (1) 
That is likely to reduce the availability of the species to a level 
insufficient for a harvest to meet subsistence needs by: (i) Causing 
the marine mammals to abandon or avoid hunting areas; (ii) Directly 
displacing subsistence users; or (iii) Placing physical barriers 
between the marine mammals and the subsistence hunters; and (2) That 
cannot be sufficiently mitigated by other measures to increase the 
availability of marine mammals to allow subsistence needs to be met.
    Hilcorp's towing, holding, and positioning of the jack-up rig would 
occur offshore and north of Kenai and the Village of Salmatof. The last 
ADF&G subsistence survey conducted in Kenai was in 1998 (Fall et al., 
2000). In the greater Kenai area, an estimated 13 harbor seals and no 
sea lions were harvested in 1988 by an estimated 10 households. In the 
Kenai area, estimated harbor seal harvest has ranged between 13 (1998) 
and 35 (1997) animals. In 1996, two sea lions and six harbor seals were 
harvested. No sea otters have been reported harvested in Kenai. ADF&G 
Community Subsistence Information System harvest data are not available 
for Salamatof, so Hilcorp assumes the subsistence harvest patterns are 
similar to other communities along the road system on the southern 
Kenai Peninsula, namely Kenai.
    Tugs towing, holding, or positioning a jack-up rig on the Tyonek 
platform in the North Cook Inlet Unit in middle Cook Inlet would occur 
approximately 10 km from the Native Village of Tyonek. Tyonek, on the 
western side of middle Cook Inlet, has a subsistence harvest area that 
extends south from the Susitna River to Tuxedni Bay (Stanek et al., 
2007). Moose and salmon are the most important subsistence resources 
measured by harvested weight (Stanek, 1994). In Tyonek, harbor seals 
were harvested between June and September by 6 percent of the 
households (Jones et al., 2015). Seals were harvested in several areas, 
encompassing an area stretching 32 km along the Cook Inlet coastline 
from the McArthur Flats north to the Beluga River. Seals were searched 
for or harvested in the Trading Bay areas as well as from the beach 
adjacent to Tyonek (Jones et al., 2015).
    The only non-ESA-listed marine mammal available for subsistence 
harvest in Cook Inlet is the harbor seal (Wolfe et al., 2009). The 
listed Steller sea lions are occasionally taken in lower Cook Inlet, 
but at a low level (Wolfe et al. 2009) (e.g., 33 harbor seals were 
harvested in Tyonek between 1983 and 2013). Seal hunting occurs 
opportunistically among Alaska Natives who may be fishing or traveling 
in upper Cook Inlet near the mouths of the Susitna River, Beluga River, 
and Little Susitna River. Hilcorp's tug towing jack-up rig activities 
may overlap with subsistence hunting of seals. However, these 
activities typically occur along the shoreline or very close to shore 
near river mouths, whereas most of Hilcorps's tugging is in the middle 
of the Inlet and rarely near the shoreline or river mouths.
    Any harassment to marine mammal stocks if it were to occur would be 
limited to minor behavioral changes (e.g., increased swim speeds, 
changes in dive behaviors and communication signals, temporary 
avoidance near the tugs) and is anticipated to be short-term,

[[Page 60202]]

mild, and not result in any abandonment or behaviors that would make 
the animals unavailable to Alaska Natives.
    To further minimize any potential effects of their action on 
subsistence activities, Hilcorp has outlined their communication plan 
for engaging with subsistence users in their Stakeholder Engagement 
Plan (appendix C of Hilcorp's application). This includes using 
traditional/subsistence knowledge to inform planning for the activity. 
Hilcorp would be required to abide by this plan and update the plan 
accordingly.
    Based on the description of the specified activity, the measures 
described to minimize adverse effects on the availability of marine 
mammals for subsistence purposes, and the proposed mitigation and 
monitoring measures, NMFS has preliminarily determined that there will 
not be an unmitigable adverse impact on subsistence uses from the POA's 
proposed activities.

Endangered Species Act

    Section 7(a)(2) of the Endangered Species Act of 1973 (ESA; 16 
U.S.C. 1531 et seq.) requires that each Federal agency insure that any 
action it authorizes, funds, or carries out is not likely to jeopardize 
the continued existence of any endangered or threatened species or 
result in the destruction or adverse modification of designated 
critical habitat. To ensure ESA compliance for the issuance of IHAs, 
NMFS consults internally whenever we propose to authorize take for 
endangered or threatened species, in this case with the NMFS Alaska 
Regional Office (AKRO).
    NMFS is proposing to authorize take of fin whale, humpback whale 
(Mexico DPS and Western North Pacific DPS), fin whale (Northeastern 
Pacific stock), beluga whale (Cook Inlet), and Steller sea lion 
(Western DPS), which are listed under the ESA. The Permits and 
Conservation Division has requested initiation of section 7 
consultation with NMFS AKRO for the issuance of this IHA. NMFS will 
conclude the ESA consultation prior to reaching a determination 
regarding the proposed issuance of the authorization.

Proposed Authorization

    As a result of these preliminary determinations, NMFS proposes to 
an IHA to Hilcorp for the use of tugs to tow, hold, and position a 
jack-up rig in support of their oil and gas activities in Cook Inlet, 
Alaska from September 14, 2024 through September 13, 2025, provided the 
previously mentioned mitigation, monitoring, and reporting requirements 
are incorporated. Drafts of the proposed IHA can be found at: https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act.

Request for Public Comments

    We request comment on our analyses, the proposed authorization, and 
any other aspect of this notice of proposed IHA and the draft EA for 
the proposed tugging activities. We also request comment on the 
potential renewal of this proposed IHA as described in the paragraph 
below. Please include with your comments any supporting data or 
literature citations to help inform decisions on the proposed IHA or a 
subsequent renewal IHA.
    On a case-by-case basis, NMFS may issue a one-time, 1-year renewal 
IHA following notice to the public providing an additional 15 days for 
public comments when (1) up to another year of identical or nearly 
identical activities as described in the Description of Proposed 
Activity section of this notice is planned or (2) the activities as 
described in the Description of Proposed Activity section of this 
notice would not be completed by the time the IHA expires and a renewal 
would allow for completion of the activities beyond that described in 
the Dates and Duration section of this notice, provided all of the 
following conditions are met:
     A request for renewal is received no later than 60 days 
prior to the needed renewal IHA effective date (recognizing that the 
renewal IHA expiration date cannot extend beyond 1 year from expiration 
of the initial IHA).
     The request for renewal must include the following:
    (1) An explanation that the activities to be conducted under the 
requested renewal IHA are identical to the activities analyzed under 
the initial IHA, are a subset of the activities, or include changes so 
minor (e.g., reduction in pile size) that the changes do not affect the 
previous analyses, mitigation and monitoring requirements, or take 
estimates (with the exception of reducing the type or amount of take).
    (2) A preliminary monitoring report showing the results of the 
required monitoring to date and an explanation showing that the 
monitoring results do not indicate impacts of a scale or nature not 
previously analyzed or authorized.
     Upon review of the request for renewal, the status of the 
affected species or stocks, and any other pertinent information, NMFS 
determines that there are no more than minor changes in the activities, 
the mitigation and monitoring measures will remain the same and 
appropriate, and the findings in the initial IHA remain valid.

    Dated: July 17, 2024.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2024-16112 Filed 7-23-24; 8:45 am]
BILLING CODE 3510-22-P