Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Hydaburg Seaplane Base Refurbishment Project in Hydaburg, Alaska, 45774-45805 [2023-14939]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 88, Number 135 (Monday, July 17, 2023)]
[Notices]
[Pages 45774-45805]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-14939]



[[Page 45773]]

Vol. 88

Monday,

No. 135

July 17, 2023

Part IV





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 the Hydaburg Seaplane Base Refurbishment 
Project in Hydaburg, Alaska; Notice

Federal Register / Vol. 88 , No. 135 / Monday, July 17, 2023 / 
Notices

[[Page 45774]]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XD052]


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to the Hydaburg Seaplane Base 
Refurbishment Project in Hydaburg, 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 the Alaska Department of 
Transportation and Public Facilities (DOT&PF) for authorization to take 
marine mammals incidental to the Hydaburg Seaplane Base Refurbishment 
Project in Hydaburg, 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 
16, 2023.

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-construction-activities. 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-construction-activities 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 mitigation, 
monitoring and reporting of the takings are set forth. 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.
    This action is consistent with categories of activities identified 
in Categorical Exclusion B4 (IHAs with no anticipated serious injury or 
mortality) of the Companion Manual for NAO 216-6A, which do not 
individually or cumulatively have the potential for significant impacts 
on the quality of the human environment and for which we have not 
identified any extraordinary circumstances that would preclude this 
categorical exclusion. Accordingly, NMFS has preliminarily determined 
that the issuance of the proposed IHA qualifies to be categorically 
excluded from further NEPA review.
    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 June 28, 2022, NMFS received a request from DOT&PF for an IHA to 
take marine mammals incidental to the Hydaburg Seaplane Base 
Refurbishment Project in Hydaburg, Alaska. Following NMFS' review of 
the application, and multiple discussions between DOT&PF and NMFS, 
DOT&PF submitted responses to NMFS questions on December 15, 2022 and a 
revised application on February 22, 2023. The application was deemed 
adequate and complete on March 13, 2023. DOT&PF's request is for take 
of nine species of marine mammals by Level B harassment and, for a 
subset of these species (i.e., harbor seal (Phoca vitulina), northern 
elephant seal (Mirounga angustirostris), harbor porpoise (Phocoena 
phocoena), Dall's porpoise (Phocoenoides dalli), humpback whale 
(Megaptera novaeangliae), and minke whale (Balaenoptera 
acutorostrata)), Level A harassment. Neither DOT&PF nor NMFS expect 
serious injury or mortality to result from this activity and, 
therefore, an IHA is appropriate.

Description of Proposed Activity

Overview

    DOT&PF, in cooperation with the Federal Aviation Administration, is 
proposing maintenance improvements to the existing Hydaburg Seaplane 
Base as part of the Hydaburg Seaplane Base Refurbishment Project. The 
existing facility has experienced deterioration in recent years, and 
DOT&PF has conducted several repair projects. The facility is near the 
end of its useful life,

[[Page 45775]]

and replacement of the existing float structures is required to 
continue safe operation in the future. The in-water portion of the 
project would include the removal of five existing steel piles and 
installation of eight permanent steel piles to support replacement of 
the floating dock structure. Up to 10 temporary steel piles would be 
installed to support permanent pile installation and would be removed 
following completion of permanent pile installation. Proposed 
activities included as part of the project with potential to affect 
marine mammals include vibratory removal, down-the-hole (DTH) 
installation, and vibratory and impact installation of steel pipe 
piles.

Dates and Duration

    The proposed IHA would be effective from September 15, 2023, 
through September 14, 2024. Construction of the proposed project is 
anticipated to occur over approximately 2 months beginning in early 
fall 2023. Pile installation and removal will be intermittent during 
this period, depending on weather, construction and mechanical delays, 
protected species shutdowns, and other potential delays and logistical 
constraints. Pile installation will occur intermittently during the 
work period for durations of minutes to hours at a time. Pile 
installation and removal will occur over 26 nonconsecutive days within 
the 2-month construction window. DOT&PF plans to conduct all work 
during daylight hours.

Specific Geographic Region

    The project site is located in the City of Hydaburg, on Prince of 
Wales Island, approximately 76 kilometers (km) west of Ketchikan, in 
southeast Alaska. The Hydaburg Seaplane Base is located at the south 
end of Hydaburg, attached to the Hydaburg city dock on the north shore 
of the Sukkwan Strait (Figure 1).
    Hydaburg is located along the Sukkwan Strait on the southwest side 
of Prince of Wales Island. A series of passes and straits lead to the 
open Pacific Ocean; however, Hydaburg is tucked in a relatively calm 
and secluded area. Sukkwan Strait is generally characterized by 
semidiurnal tides with mean tidal ranges of around 5 meters (m). 
Freshwater inputs to Sukkwan Strait include multiple anadromous 
streams: Hydaburg River, Saltery Creek, and two streams originating 
from unnamed lakes. The bathymetry of the bay is variable depending on 
location and proximity to shore, islands, or rocks. Depths approach 76 
m within Sukkwan Strait and up to 37 m in South Pass.
    Ongoing vessel activities near Hydaburg, as well as land-based 
industrial and commercial activities, result in elevated in-air and 
underwater acoustic conditions in the project area that likely increase 
with proximity to the project site. Background sound levels likely vary 
seasonally, with elevated levels during summer when the commercial and 
fishing industries are at their peaks. Hydaburg has no cruise ship or 
ferry facilities, so only commercial and fishing vessels visit Hydaburg 
regularly (Miller et al., 2019).
BILLING CODE 3510-22-P

[[Page 45776]]

[GRAPHIC] [TIFF OMITTED] TN17JY23.000

BILLING CODE 3510-22-C
Figure 1--Location of Seaplane Base in Hydaburg, Alaska

[[Page 45777]]

Detailed Description of the Specified Activity

    The DOT&PF proposed project would involve the removal of five 
existing cantilever steel pipe piles (16-inch (40.64-centimeter (cm)) 
diameter) that support the existing multiple-float structure. The 
multiple-float timber structure, which covers 372 square m (m\2\), 
would also be removed. A new 446-m\2\ single-float timber structure 
would be installed in the same general location. Four 24-inch (60.96-
cm) and four 20-inch (50.80-cm) permanent steel pipe piles would be 
installed vertically to act as restraints for the new seaplane float. 
Up to 10 temporary 24-inch (60.96 cm) steel pipe piles would be 
installed to support pile installation and would be removed following 
completion of construction. Rock sockets and tension anchors would be 
required on all 24-inch (60.96 cm) piles and two 20-inch (50.80 cm) 
piles. Rock sockets would also be potentially required on five of the 
temporary piles. See Table 1 for a summary of the numbers and types of 
piles to be installed and removed, as well as the estimated durations 
of each activity.

                                                                      Table 1--Summary of Piles To Be Installed and Removed
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                                                                                                                                               Tension
                                                                                                                              Rock socket     anchor DTH      Total       Typical
                                                                                Number of   Number of    Impact   Vibratory     DTH pile         pile      duration of  production     Days of
                      Pile diameter and type                        Number of     rock       tension    strikes    duration  Installation,  installation,    activity     rate in   installation
                                                                      piles      sockets     anchors    per pile   per pile   duration per   duration per   per pile,    piles per   or removal
                                                                                                                  (minutes)  pile, minutes  pile, minutes     hours         day
                                                                                                                                (range)        (range)                    (range)
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                                                                                        Pile Installation
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24'' Steel Plumb Piles (Permanent)...............................           4           4           4         50         15   240 (60-480)   120 (60-240)         6.75   0.5 (0-1)             8
20'' Steel Plumb Piles (Permanent)...............................           4           2           2         50         15   240 (60-480)   120 (60-240)    \1\ 0.75/   0.5 (0-1)             8
                                                                                                                                                                  6.75
24'' Steel Piles (Temporary).....................................          10           5         N/A        N/A         15   240 (60-480)            N/A         4.25  2.5 (1-10)             4
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                                                                                          Pile Removal
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16'' Steel Cantilevered Piles....................................           5         N/A         N/A        N/A         30            N/A            N/A          0.5   2.5 (2-4)             2
24'' Steel Piles (Temporary).....................................          10         N/A         N/A        N/A         30            N/A            N/A          0.5   2.5 (2-4)             2
                                                                  ------------------------------------------------------------------------------------------------------------------------------
    Totals.......................................................          23          11           6        N/A        N/A            N/A            N/A          N/A         N/A            26
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\1\ Two of the 20-inch plumb piles will include vibratory and impact installation in addition to rock sockets and tension anchors, estimated at 6.75 hours duration total, and two will only use
  vibratory and impact, estimated at 0.75 hours duration total.

    DTH pile installation would involve drilling rock sockets into the 
bedrock to support installation of piles. A rock socket is a pile 
inserted into a drilled hole in the underlying bedrock after the pile 
has been driven through the overlying softer sediments to refusal by 
vibratory or impact methods. The pile is advanced farther into the 
drilled hole to properly secure the bottom portion of the pile into the 
rock. The depth of the rock socket varies, but up to 6 m may be 
required for this project. The diameter of the rock socket is slightly 
larger than the pile being driven. Rock sockets are constructed using a 
DTH device that consists of a drill bit that drills through the bedrock 
using both rotary and percussion mechanisms. This breaks up the rock to 
allow removal of the fragments and insertion of the pile. The pile is 
advanced at the same time that drilling occurs. Drill cuttings are 
expelled from the top of the pile using compressed air. It is estimated 
that drilling rock sockets into the bedrock may take on average 4 hours 
per pile.
    Tension anchors would be installed in six of the permanent piles 
(four 24-inch (60.96-cm) and two 20-inch (50.80-cm) piles). Tension 
anchors are installed within piles that are drilled into the bedrock 
below the elevation of the pile tip after the pile has been driven 
through the sediment layer to refusal. A 6- or 8-inch (15.24- or 20.32-
cm) diameter steel pipe casing would be inserted inside the larger 
diameter production pile. A rock drill would be inserted into the 
casing, and a 6- to 8-inch (15.24- to 20.32-cm) diameter hole would be 
drilled into bedrock with rotary and percussion drilling methods. The 
drilling work is contained within the steel pile casing and the steel 
pipe pile. The typical depth of the drilled tension anchor hole varies, 
but 6-9 m is common. Rock fragments would be removed through the top of 
the casing with compressed air. A steel rod would then be grouted into 
the drilled hole and affixed to the top of the pile. The purpose of a 
tension anchor is to secure the pile to the bedrock to withstand uplift 
forces. It is estimated that tension anchor installation will take 
about 1-4 hours per pile. Hereafter, DTH pile installation refers to 
both rock socket drilling and tension anchor installation unless 
specified. See Figure 1-3 in the DOT&PF's application for a schematic 
of DTH pile installation and tension anchor techniques.
    Pile removal would be conducted using a vibratory hammer. Pile 
installation would be conducted using both a vibratory and an impact 
hammer and DTH pile installation methods. Piles would be advanced to 
refusal using a vibratory hammer. After DTH pile installation, the 
final approximately 3 m of driving would be conducted using an impact 
hammer so that the structural capacity of the pile embedment could be 
verified. The pile installation methods used would depend on sediment 
depth and conditions at each pile location. Pile installation and 
removal would occur in waters approximately 6-7 m in depth.
    Actual numbers and sizes of piles, installation times, numbers of 
impact strikes, and other design and construction details and methods 
may vary slightly from the estimates outlined in this document. The 
DOT&PF does not anticipate that the project will change such that 
potential impacts on marine mammals will change or vary from those 
described here.
    Proposed mitigation, monitoring, and reporting measures are 
described in detail later in this document (please see Proposed 
Mitigation and Proposed Monitoring and Reporting).

[[Page 45778]]

Description of Marine Mammals in the Area of Specified Activities

    Sections 3 and 4 of the DOT&PF's 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, referenced here, instead of 
reprinting the information. Additional information regarding population 
trends and threats may be found in NMFS' Stock Assessment Reports 
(SARs; 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 expected to occur, 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 stocks managed under the MMPA in this region 
are assessed in NMFS' U.S. Alaska and Pacific SARs (e.g., Carretta, et 
al., 2022; Muto et al., 2022). All values presented in Table 2 are the 
most recent available at the time of publication (including from the 
draft 2022 SARs, Young et al., 2022) and are available online at: 
www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments).

                                            Table 2--Species \4\ Likely Impacted by the Specified Activities
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                                                                                                              Stock abundance (CV,
            Common name                  Scientific name              Stock             ESA/MMPA status;       Nmin, most recent       PBR     Annual M/
                                                                                      strategic  (Y/N) \1\   abundance survey) \2\               SI \3\
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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).
Family Balaenopteridae (rorquals):
    Humpback Whale.................  Megaptera novaeangliae  Central N Pacific.....  -, -, Y                 10,103 (0.3, 7,891,          3.4       4.46
                                                                                                              2006).
    Minke Whale....................  Balaenoptera            Alaska................  -, -, N                 N/A (N/A, N/A, N/A)..        UND          0
                                      acutorostrata.
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                                                  Odontoceti (toothed whales, dolphins, and porpoises)
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Family Physeteridae:
    Sperm Whale....................  Physeter macrocephalus  N Pacific.............  E, D, Y                 UND (UND, UND, 2015).        UND        3.5
Family Delphinidae:
    Killer Whale...................  Orcinus orca..........  Eastern North Pacific   -, -, N                 1,920 (N/A, 1,920,            19        1.3
                                                              Alaska Resident.                                2019).
    Killer Whale...................  Orcinus orca..........  Eastern Northern        -, -, N                 302 (N/A, 302, 2018).        2.2        0.2
                                                              Pacific Northern
                                                              Resident.
    Killer Whale...................  Orcinus orca..........  West Coast Transient..  -, -, N                 349 (N/A, 349, 2018).        3.5        0.4
    Pacific White-Sided Dolphin....  Lagenorhynchus          N Pacific.............  -, -, N                 26,880 (N/A, N/A,            UND          0
                                      obliquidens.                                                            1990).
Family Phocoenidae (porpoises):
    Dall's Porpoise................  Phocoenoides dalli....  Alaska................  -, -, N                 UND (UND, UND, 2015).        UND         37
    Harbor Porpoise................  Phocoena..............  Southeast Alaska......  -, -, Y                 UND (UND, UND, 2019).        UND         34
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                                                               Order Carnivora--Pinnipedia
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Family Otariidae (eared seals and
 sea lions):
    Steller Sea Lion...............  Eumetopias jubatus....  Eastern...............  -, -, N                 43,201 (N/A, 43,201,       2,592        112
                                                                                                              2017).
Family Phocidae (earless seals):
    Harbor Seal....................  Phoca vitulina........  Dixon/Cape Decision...  -, -, N                 23,478 (N/A, 21,453,         644         69
                                                                                                              2015).
    Northern Elephant Seal.........  Mirounga                CA Breeding...........  -, -, N                 187,386 (N/A, 85,369,      5,122       13.7
                                      angustirostris.                                                         2013).
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\1\ 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.
\2\ 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. In some cases, CV is not applicable (N/A)
\3\ 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 human caused mortality and serious injury (M/SI) often cannot be determined precisely and is in some cases
  presented as a minimum value or range.
\4\ 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)).


[[Page 45779]]

    On January 24, 2023, NMFS published the draft 2022 SARs (https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region). The Alaska and Pacific SARs include a 
proposed update to the humpback whale stock structure and the Alaska 
SAR includes a proposed update to the Southeast Alaska harbor porpoise 
stock structure. These new structures, if finalized, would modify the 
MMPA-designated humpback stocks to align more closely with the ESA-
designated distinct population segments (DPSs), and for harbor porpoise 
to align with genetics, trends in abundance, and discontinuous 
distribution NMFS has proposed as supporting the delineation of two 
demographically independent populations. Please refer to the draft 2022 
Alaska and Pacific SARs for additional information.
    NMFS Office of Protected Resources, Permits and Conservation 
Division has generally considered peer-reviewed data in draft SARs 
(relative to data provided in the most recent final SARs), when 
available, as the best available science, and has done so here for all 
species and stocks, with the exception of the new proposal to revise 
humpback whale and harbor porpoise stock structure. Given that the 
proposed changes to the stock structures involve application of NMFS' 
Guidance for Assessing Marine Mammals Stocks and could be revised 
following consideration of public comments, it is more appropriate to 
conduct our analysis in this proposed authorization based on the status 
quo stock structure identified in the most recent final SARs for those 
species (Carretta et al., 2022; Muto et al., 2022).
    All species that could potentially occur in the proposed survey 
areas are included in Table 2 of the IHA application. While gray whale 
and sperm whale have occurred in northern Southeast Alaska in recent 
years, they are highly unlikely to occur in the proposed project area. 
The temporal and/or spatial occurrence of these species is such that 
take is not expected to occur, and they are not discussed further. The 
remaining 9 species (with 11 managed stocks) in Table 2 temporally and 
spatially co-occur with the activity to the degree that take is 
reasonably likely to occur, and we have proposed authorizing it.

Steller Sea Lion

    Steller sea lions are found throughout the northern Pacific Ocean, 
including coastal and inland waters from Russia (Kuril Islands and the 
Sea of Okhotsk), east to Alaska, and south to central California 
(A[ntilde]o Nuevo Island). Steller sea lions were listed as threatened 
range-wide under the ESA on November 26, 1990 (55 FR 49204); they were 
subsequently partitioned into the western and eastern DPSs (and MMPA 
stocks) in 1997 (62 FR 24345, May 5, 1997). The eastern DPS remained 
classified as threatened (62 FR 24345) until it was delisted in 
November 2013, while the western DPS (those individuals west of 
144[deg] W longitude or Cape Suckling, Alaska) was upgraded to 
endangered status following separation of the DPSs, and it remains 
endangered today. There is regular movement of both DPSs across this 
144[deg] W longitude boundary (Jemison et al., 2013), however, due to 
the distance from this DPS boundary, it is likely that only eastern DPS 
Steller sea lions are present in the project area. Therefore, animals 
potentially affected by the project are assumed to be part of the 
eastern DPS.
    Steller sea lions are opportunistic predators, feeding primarily on 
a wide variety of fishes and cephalopods, including Pacific herring 
(Clupea pallasi), walleye pollock (Gadus chalcogramma), capelin 
(Mallotus villosus), Pacific sand lance (Ammodytes hexapterus), Pacific 
cod (Gadus macrocephalus), 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 are not common in the project area and systematic 
counts or surveys have not been completed in the area directly 
surrounding Hydaburg. The nearest documented haulout is Point Islet 
(Point Rock), about 13 km southeast of Hydaburg (see Figure 4-1 in the 
DOT&PF's application). No Steller sea lions were present during aerial 
surveys over Point Islet that occurred during 2013, 2015, or 2017 
(Fritz et al., 2016b; Sweeney et al., 2017), and it was not surveyed in 
2019 (Sweeney et al., 2019). Anecdotal evidence provided by local 
residents indicates that Steller sea lions are rare and do not occur 
regularly near the project area. However, Steller sea lion presence 
could be higher during the late summer and early fall salmon runs.

Harbor Seal

    Harbor seals range from Baja California north along the west coasts 
of California, Oregon, Washington, British Columbia, and Southeast 
Alaska; west through the Gulf of Alaska, Prince William Sound, and the 
Aleutian Islands; and north in the Bering Sea to Cape Newenham and the 
Pribilof Islands. In 2010, harbor seals in Alaska were partitioned into 
12 separate stocks based largely on genetic structure (Allen and 
Angliss, 2010). Harbor seals present near Hydaburg are recognized as 
part of the Dixon/Cape Decision stock.
    Harbor seals haul out on rocks, reefs, beaches, and drifting 
glacial ice, and feed in marine, estuarine, and occasionally fresh 
waters (Muto et al., 2022). Harbor seals generally are non-migratory, 
with local movements associated with such factors as tides, weather, 
season, food availability, and reproduction (Scheffer and Slipp, 1944; 
Fisher 1952; Bigg, 1969, 1981; Hastings et al., 2004). 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 (Swain et al., 1996; 
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).
    Harbor seals usually give birth to a single pup between May and 
mid-July. Birthing locations are often dispersed over several haulout 
sites and not confined to major rookeries (Klinkhart et al., 2008). 
Strong fidelity of individuals for haul-out sites during the breeding 
season though have been documented in several populations 
(H[auml]rk[ouml]nen and Harding, 2001), including some regions in 
Alaska such as Kodiak Island, Prince William Sound, Glacier Bay/Icy 
Strait, and Cook Inlet (Pitcher and McAllister, 1981; Small et al., 
2005; Boveng et al., 2012; Womble, 2012; Womble and Gende, 2013).
    Harbor seals forage on fish and invertebrates (Orr et al., 2004) 
including capelin, eulachon (Thaleichthys pacificus), cod, pollock, 
flatfish, shrimp, octopus, and squid (Wynne, 2012). They are 
opportunistic feeders that forage in marine, estuarine, and 
occasionally freshwater habitat, adjusting their foraging behavior to 
take advantage of prey that are locally and seasonally abundant (Payne 
and Selzer, 1989). Depending on prey availability, research has 
demonstrated that harbor seals conduct both shallow and deep dives 
while foraging (Tollit et al., 1997).
    Harbor seals are commonly sighted in the waters of the inside 
passages throughout Southeast Alaska. Surveys have been rarely carried 
out on Dixon/Cape Decision, with the last surveys taking place between 
2007 to 2011 and 2015. The NMFS Alaska Fisheries

[[Page 45780]]

Science Center identifies two ``key'' haulouts, or haulouts that have 
had 50 or more harbor seals documented during surveys, in Sukkwan 
Strait and four additional ``not key'' haulouts, those with fewer than 
50 harbor seals documented during surveys, near the proposed project 
area (see Figure 4-2 in the DOT&PF's application) (NOAA, 2021). NMFS 
aerial survey data indicate that as few as 0 to as many as 157 harbor 
seals were sighted near the project area during surveys between 2003 
and 2011 (Areas BD28 and BD30; NOAA, 2022). However, local residents 
report that only a few (two to four) harbor seals are regularly 
observed near Hydaburg. These individuals are generally observed near 
the small boat harbor outside of the proposed project area and during 
peak salmon runs in late summer and early fall. Harbor seals are known 
to be curious and may approach novel activity, so it is possible that 
some may enter the proposed project area during pile installation and 
removal.

Northern Elephant Seal

    Northern elephant seals are wide-ranging throughout the North 
Pacific, spending as much as 80 percent of their time at sea (Hindell 
and Perrin, 2009). Populations of northern elephant seals in the U.S. 
and Mexico have recovered after being nearly hunted to extinction 
(Stewart et al., 1994). Northern elephant seals underwent a severe 
population bottleneck and loss of genetic diversity when the population 
was reduced to an estimated 10-30 individuals (Hoelzel et al., 2002). 
Since 1998, northern elephant seals have been undergoing a large 
population increase, estimated at 3.1 percent annually (Lowry et al., 
2020). There are two demographically isolated breeding populations: the 
California breeding population and the Baja California population. No 
international agreements exist for the joint management of this species 
by the U.S. and Mexico. The California breeding population is 
considered to be a separate stock. Any northern elephant seals observed 
near Hydaburg would be considered part of the California breeding 
stock.
    Spatial segregation in foraging areas between males and females is 
evident from satellite tag data (Le Beouf et al., 2000). Males migrate 
to the Gulf of Alaska and western Aleutian Islands along the 
continental shelf to feed on benthic prey, while females migrate to 
pelagic areas in the Gulf of Alaska and the central North Pacific to 
feed on pelagic prey (Le Beouf et al., 2000). Elephant seals spend a 
majority of their time at sea (average of 74.7 days during post 
breeding migration and an average of 218.5 days during the post-molting 
migration; Robinson et al., 2012). Although northern elephant seals are 
known to visit the Gulf of Alaska to feed on benthic prey, they rarely 
occur on the beaches of Alaska.
    Northern elephant seals breed and give birth in California and Baja 
Mexico, primarily on offshore islands (Stewart et al., 1994, from 
December to March (Stewart and Huber, 1993)) before dispersing widely 
across the North Pacific (Le Boeuf et al., 2000). Although movement and 
genetic exchange continues between rookeries, most elephant seals 
return to natal rookeries when they start breeding (Huber et al., 
1991). Gestation in elephant seals lasts 11 months, with births taking 
place onshore when seals are at the breeding colony (Stewart et al., 
1994).
    There is a low probability that northern elephant seals would occur 
in the proposed project area. Northern elephant seals generally feed 
along the continental shelf break (Le Boeuf et al., 2000) and are not 
expected to spend time in shallow areas like the Sukkwan Strait. No 
sightings of elephant seals have been documented near Hydaburg; 
however, protected species observers (PSOs) at a DOT&PF project site in 
Ketchikan (located approximately 76 km east of Hydaburg) reported 
sightings of a northern elephant seal on multiple days (C. Gentemann, 
personal communication, April 8, 2022). Additional sightings of 
northern elephant seals around the state concurrent to the Ketchikan 
sighting were reported in Seward, King Cove, and Kodiak (L. Davis, 
personal communication, April 14, 2022). Given the recent increase in 
sightings, including sightings in Southeast Alaska, it is assumed that 
a few northern elephant seals could be present in Hydaburg during 
construction of the proposed project.

Harbor Porpoise

    In the eastern North Pacific Ocean, the harbor porpoise ranges from 
Point Barrow, along the Alaska coast, and down the west coast of North 
America to Point Conception, California. In Alaska, harbor porpoises 
are currently divided into three stocks, based primarily on geography: 
the Bering Sea stock, the Southeast Alaska stock, and the Gulf of 
Alaska stock. Harbor porpoises near Hydaburg are currently recognized 
as members of the Southeast Alaska stock. The Southeast Alaska stock 
ranges from Cape Suckling to the Canada boundary (Muto et al., 2022).
    Harbor porpoises primarily frequent coastal waters in southeast 
Alaska (Dahlheim et al., 2009) and occur most frequently in waters less 
than 100 m deep (Hobbs and Waite, 2010). Harbor porpoises forage in 
waters less than 200 m deep on small pelagic schooling fishes such as 
herring, cod, pollock, octopus, smelt, and bottom-dwelling fish, 
occasionally feeding on squid and crustaceans (Bj[oslash]rge and 
Tolley, 2009; Wynne et al., 2011).
    Calving occurs from May to August; however, this can vary by 
region. Harbor porpoises are often found traveling alone, or in small 
groups less than 10 individuals (Schmale, 2008). According to aerial 
surveys of harbor porpoise abundance in southeast Alaska conducted in 
1991-1993, mean group size was calculated to be 1.2 animals (Dahlheim 
et al., 2000).
    Studies of harbor porpoises reported no evidence of seasonal 
changes in distribution for the inland waters of southeast Alaska 
(Dahlheim et al., 2009). Their small overall size, lack of a visible 
blow, low dorsal fins and overall low profile, and short surfacing time 
make them difficult to observe (Dahlheim et al., 2015), likely reducing 
identification and reporting of this species, and these estimates 
therefore may be low.
    Although there have been no systematic studies or observations of 
harbor porpoises specific to Hydaburg or Sukkwan Strait, there is 
potential for them to occur in the proposed project area. Abundance 
data for harbor porpoises in southeast Alaska were collected during 18 
seasonal surveys spanning 22 years, from 1991 to 2012 (Dahlheim et al., 
2015). During that study, a total of 81 harbor porpoises were observed 
in the southern inland waters of southeast Alaska; however, the survey 
terminated 80 km southeast of Hydaburg and did not include Sukkwan 
Strait as part of the survey. There does not appear to be any seasonal 
variation in harbor porpoise density in the inland waters of southeast 
Alaska (Dahlheim et al., 2015). Harbor porpoises have not been reported 
by local residents.

Dall's Porpoise

    Dall's porpoises are found throughout the North Pacific, from 
southern Japan to southern California and north to the Bering Sea. All 
Dall's porpoises in Alaska are members of the Alaska stock, and those 
off California, Oregon, and Washington are part of a separate stock. 
Dall's porpoises can be found in offshore, inshore, and nearshore 
habitat, but they are most commonly found in waters deeper than 183 m 
(Dahlheim et al., 2009; Jefferson, 2009).
    Common prey of Dall's porpoise include a variety of small, 
schooling fishes (such as herrings and mackerels)

[[Page 45781]]

and cephalopods. Dall's porpoises may migrate between inshore and 
offshore areas and make latitudinal movements or short seasonal 
migrations, but these movements are generally not consistent 
(Jefferson, 2009).
    Dall's porpoises generally occur in groups of 2 to 20 individuals 
but have also been recorded in groups numbering in the hundreds. The 
mean group size in southeast Alaska is estimated at approximately three 
individuals (Dahlheim et al., 2009; Jefferson, 2019). However, Dall's 
porpoises are reported to typically occur in groups of 10-15 animals 
near Ketchikan Alaska, which is located approximately 76 km east of 
Hydaburg, with an estimated maximum group size of 20 animals (Freitag 
2017, 83 FR 37473, August 1, 2018).
    No systematic studies of Dall's porpoise abundance or distribution 
have occurred in Sukkwan Strait; however, Dall's porpoises have been 
observed in Cordova Bay 30 km south of Hydaburg during a summer 2011 
survey (Jefferson et al., 2019). Despite generalized water depth 
preferences, Dall's porpoises may occur in shallow waters. Moran et al. 
(2018) recently mapped Dall's porpoise distributions in bays, shallow 
water, and nearshore areas of Prince William Sound, habitats not 
typically utilized by this species. If Dall's porpoises occur in the 
proposed project area, they will likely be present in March or April, 
given the strong seasonal patterns observed in nearby areas of 
southeast Alaska (Dahlheim et al., 2009). No local residents have 
described seeing Dall's porpoises within Sukkwan Strait.

Pacific White-Sided Dolphin

    Pacific white-sided dolphins are a pelagic species inhabiting 
temperate waters of the North Pacific Ocean and along the coasts of 
California, Oregon, Washington, and Alaska (Muto et al., 2022). Despite 
their distribution mostly in deep, offshore waters, they may also be 
found over the continental shelf and in nearshore waters, including 
inland waters of southeast Alaska (Ferrero and Walker, 1996). Pacific 
white-sided dolphins are managed as two distinct stocks: the 
California/Oregon/Washington stock and the North Pacific stock (north 
of 45[deg] N, including Alaska). Pacific white-sided dolphins present 
near the project area are recognized as being members of the North 
Pacific stock, which ranges from Canada into Alaska (Muto et al., 
2022).
    Pacific white-sided dolphins prey on squid and small schooling fish 
such as capelin, sardines, and herring (Morton, 2006). They are known 
to work in groups to herd schools of fish and can dive underwater for 
up to 6 minutes to feed (Morton, 2006). Group sizes have been reported 
to range from 40 to over 1,000 animals, but groups of between 10 and 
100 individuals (Stacey and Baird, 1991) occur most commonly. Seasonal 
movements of Pacific white-sided dolphins are not well understood, but 
there is evidence of both north-south seasonal movement (Leatherwood et 
al., 1984) and inshore-offshore seasonal movement (Stacey and Baird, 
1991).
    Pacific white-sided dolphins do not generally occur in the shallow, 
inland waterways of southeast Alaska. Scientific studies and data are 
lacking relative to the presence or abundance of Pacific white-sided 
dolphins in or near Sukkwan Strait. When Pacific white-sided dolphins 
have been observed, sighting rates were highest in spring and decreased 
throughout summer and fall (Dahlheim et al., 2009).
    Most observations of Pacific white-sided dolphins occur off the 
outer coast or in inland waterways near entrances to the open ocean. 
According to Muto et al. (2022), aerial surveys in 1997 sighted one 
group of 164 Pacific white-sided dolphins in Dixon Entrance to the 
southeast of Hydaburg. These observational data, combined with 
anecdotal information, indicate that there is a small potential for 
Pacific white-sided dolphins to occur in the proposed project area. 
NMFS previously estimated that a group of up to 92 individuals (median 
between 20 and 164 individuals) could be present at Metlakatla, Alaska 
(86 FR 43190, August 6, 2021), which is located approximately 80 km 
east of Hydaburg.

Killer Whale

    Killer whales have been observed in all the world's oceans, but the 
highest densities occur in colder and more productive waters found at 
high latitudes (NMFS, 2016a). Killer whales occur along the entire 
Alaska coast, in British Columbia and Washington inland waterways, and 
along the outer coasts of Washington, Oregon, and California (NMFS, 
2016a).
    Based on data regarding association patterns, acoustics, movements, 
and genetic differences, eight killer whale stocks are now recognized 
within the Pacific U.S. exclusive economic zone. Only individuals from 
the Eastern North Pacific Alaska Resident stock (Alaska Resident 
stock), Eastern North Pacific Northern Resident stock (Northern 
Resident stock), and West Coast Transient stock may occur in the 
proposed project area (Muto et al., 2022).
    There are three distinct ecotypes, or forms, of killer whales 
recognized: resident, transient, and offshore. The three ecotypes 
differ morphologically, ecologically, behaviorally, and genetically. 
Surveys between 1991 and 2007 encountered resident killer whales during 
all seasons throughout southeast Alaska. Both residents and transients 
were common in a variety of habitats and all major waterways, including 
protected bays and inlets. There does not appear to be strong seasonal 
variation in abundance or distribution of killer whales, but there was 
substantial variability between years during this study (Dahlheim et 
al., 2009). Spatial distribution has been shown to vary among the 
different ecotypes, with resident and, to a lesser extent, transient 
killer whales more commonly observed along the continental shelf, and 
offshore killer whales more commonly observed in pelagic waters (Rice 
et al., 2021).
    Transient killer whales hunt and feed primarily on marine mammals, 
while residents forage primarily on fish. Transient killer whales feed 
primarily on harbor seals, Dall's porpoises, harbor porpoises, and sea 
lions. Resident killer whale populations in the eastern North Pacific 
feed mainly on salmonids, showing a strong preference for Chinook 
salmon (NMFS, 2016a).
    Transient killer whales are often found in long-term stable social 
units (pods) of 1 to 16 whales. Average pod sizes in southeast Alaska 
were six in spring, five in summer, and four in fall (Dahlheim et al., 
2009). Pod sizes of transient whales are generally smaller than those 
of resident social groups. Resident killer whales occur in pods ranging 
from 7 to 70 whales that are seen in association with one another more 
than 50 percent of the time (Dahlheim et al., 2009; NMFS 2016b). In 
southeast Alaska, resident killer whale mean pod size was approximately 
21.5 in spring, 32.3 in summer, and 19.3 in fall (Dahlheim et al., 
2009).
    No systematic studies of killer whales have been conducted in or 
around Sukkwan Strait. Dahlheim et al. (2009) observed transient killer 
whales within Lynn Canal, Icy Strait, Stephens Passage, Frederick 
Sound, and upper Chatham Strait. Anecdotal local information suggests 
that killer whales are rarely seen near the Hydaburg area, but a pod 
may be seen occasionally every few months.

Humpback Whale

    Humpback whales are found throughout southeast Alaska in a variety 
of marine environments, including open ocean, nearshore waters, and 
areas with strong tidal currents (Dahlheim et al., 2009). Most humpback 
whales are migratory and spend winters in the

[[Page 45782]]

breeding grounds off either Hawaii or Mexico. Humpback whales generally 
arrive in southeast Alaska in March and return to their wintering 
grounds in November. Some humpback whales depart late or arrive early 
to feeding grounds, and therefore the species occurs in southeast 
Alaska year-round (Straley, 1990; Straley et al., 2018). Current 
threats to humpback whales include vessel strikes, spills, climate 
change, and commercial fishing operations (Muto et al., 2022).
    Humpback whales worldwide were designated as ``endangered'' under 
the Endangered Species Conservation Act in 1970 and had been listed as 
a species under the ESA since its inception in 1973. On September 8, 
2016, NMFS published a final decision that changed the status of 
humpback whales under the ESA (81 FR 62259), effective on October 11, 
2016. The decision recognized the existence of 14 DPSs based on 
distinct breeding areas in tropical and temperate waters. Five of the 
14 DPSs were classified under the ESA (4 endangered and 1 threatened), 
while the other 9 DPSs were delisted. Humpback whales found in the 
project area are predominantly members of the Hawaii DPS, which is not 
listed under the ESA. However, based on a comprehensive photo-
identification study, members of the Mexico DPS, which is listed as 
threatened, are known to occur in southeast Alaska. Members of 
different DPSs are known to intermix on feeding grounds; therefore, all 
waters off the coast of Alaska should be considered to potentially have 
ESA-listed humpback whales. Approximately 2 percent of all humpback 
whales encountered in southeast Alaska and northern British Columbia 
are expected to be members of the Mexico DPS, while all others are 
expected to be members of the Hawaii DPS (Wade et al., 2021).
    The DPSs of humpback whales that were identified through the ESA 
listing process do not necessarily equate to the existing MMPA stocks. 
The stock delineations of humpback whales under the MMPA are currently 
under review. Until this review is complete, NMFS considers humpback 
whales in southeast Alaska to be part of the Central North Pacific 
stock, with a status of endangered under the ESA and designations of 
strategic and depleted under the MMPA (Muto et al., 2022).
    Southeast Alaska is considered a biologically important area (BIA) 
for feeding humpback whales between May and September (Wild et al., 
2023), though not currently designated as critical habitat (86 FR 
21082, April 21, 2021). Most humpback whales migrate to other regions 
during winter to breed, but over-wintering (non-breeding) humpback 
whales have been noted and may be increasingly common and attributable 
to staggered migration (Straley, 1990, Straley et al., 2018). It is 
thought that those humpbacks that remain in southeast Alaska do so in 
response to the availability of winter schools of fish prey, which 
primarily includes overwintering herring (Straley et al., 2018). In 
Alaska, humpback whales filter feed on tiny crustaceans, plankton, and 
small fish such as walleye pollock, Pacific sand lance, herring (Clupea 
pallasii), eulachon (Thaleichthys pacificus), and capelin (Witteveen et 
al., 2012). It is common to observe groups of humpback whales 
cooperatively bubble feeding. Group sizes in southeast Alaska generally 
range from one to four individuals (Dahlheim et al., 2009).
    No systematic studies have documented humpback whale abundance near 
Hydaburg. Anecdotal information from local residents suggests that 
humpback whales' utilization of the area is intermittent year-round. 
Their abundance, distribution, and occurrence are dependent on and 
fluctuate with fish prey. Local residents estimate that one to two 
humpback whales may be present in the Sukkwan Strait on a weekly basis. 
Elsewhere in southeast Alaska, marine mammal monitoring for projects in 
Tongass Narrows, Ketchikan, Alaska, indicate that humpback whales are 
present in that area most regularly from May through October (DOT&PF, 
2021; 2022) and may occur in lower numbers in winter, which we would 
expect to be the case for Hydaburg.

Minke Whale

    Minke whales are found throughout the northern hemisphere in polar, 
temperate, and tropical waters (Jefferson et al., 2008). The population 
status of minke whales is considered stable throughout most of their 
range. Historically, commercial whaling reduced the population size of 
this species, but given their small size, they were never a primary 
target of whaling and did not experience severe population declines as 
did larger cetaceans.
    The International Whaling Commission has identified three minke 
whale stocks in the North Pacific: one near the Sea of Japan, a second 
in the rest of the western Pacific, and a third, less concentrated, 
stock throughout the eastern Pacific. NMFS further splits this third 
stock between Alaska whales and resident whales of California, Oregon, 
and Washington (Muto et al., 2022). Minke whales in southeast Alaska 
are part of the Alaska stock (Muto et al., 2022). Minke whales are 
found in all Alaskan waters. There are no population estimates for 
minke whales in southeast Alaska. Surveys in southeast Alaska have 
consistently identified individuals throughout inland waters in low 
numbers (Dahlheim et al., 2009).
    In Alaska, the minke whale diet consists primarily of euphausiids 
and walleye pollock. Minke whales are generally found in shallow, 
coastal waters within 200 m of shore (Zerbini et al., 2006) and are 
almost always solitary or in small groups of two to three. Rarely, 
loose aggregations of up to 400 animals have been associated with 
feeding areas in Arctic latitudes. In Alaska, seasonal movements are 
associated with feeding areas that are generally located at the edge of 
the pack ice (NMFS, 2014).
    There are no known occurrences of minke whales within the project 
area. Dedicated surveys for cetaceans in southeast Alaska found that 
minke whales were scattered throughout inland waters from Glacier Bay 
and Icy Strait to Clarence Strait, with small concentrations near the 
entrance of Glacier Bay (Dahlheim et al., 2009). All sightings were of 
single minke whales, except for a single sighting of multiple minke 
whales. Surveys took place in spring, summer, and fall, and minke 
whales were present in low numbers in all seasons and years. NMFS is 
not aware of information on the winter occurrence of minke whales in 
southeast Alaska.
    Anecdotal observations suggest that minke whales are not seen near 
Hydaburg and so are expected to occur rarely in the project area. 
However, NMFS has previously estimated that a group of up to three 
individuals could be present at nearby Metlakatla, Alaska over 4 months 
(86 FR 43190, August 6, 2021). Since their ranges extend into the 
project area and they have been observed in southeast Alaska, including 
in Clarence Strait (Dahlheim et al., 2009), it is possible the species 
could occur near the project area.

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 or hear over the same frequency range (e.g., 
Richardson et al., 1995; Wartzok and Ketten, 1999; Au and Hastings,

[[Page 45783]]

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.). Note that no direct measurements of hearing ability 
have been successfully completed for mysticetes (i.e., low-frequency 
cetaceans). 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.

                  Table 3--Marine Mammal Hearing Groups
                              [NMFS, 2018]
------------------------------------------------------------------------
                                                   Generalized  hearing
                  Hearing group                           range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen whales)....  7 Hz to 35 kHz.
Mid-frequency (MF) cetaceans (dolphins, toothed   150 Hz to 160 kHz.
 whales, beaked whales, bottlenose whales).
High-frequency (HF) cetaceans (true porpoises,    275 Hz to 160 kHz.
 Kogia, river dolphins, Cephalorhynchid,
 Lagenorhynchus cruciger & L. australis).
Phocid pinnipeds (PW) (underwater) (true seals).  50 Hz to 86 kHz.
Otariid pinnipeds (OW) (underwater) (sea lions    60 Hz to 39 kHz.
 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 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 et al., 2013).
    For more detail concerning these groups and associated generalized 
hearing 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 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 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 species or stock through effects on annual rates of 
recruitment or survival.
    Acoustic effects on marine mammals during the specified activity 
are expected to potentially occur from impact pile installation, 
vibratory pile installation, and DTH systems. The effects of underwater 
noise from the DOT&PF's proposed activities have the potential to 
result in Level B harassment of marine mammals in the action area, and, 
for some species as a result of certain activities, Level A harassment

Background on Sound

    This section contains a brief technical background on sound, on the 
characteristics of certain sound types, and on metrics used in this 
proposal in as much as the information is 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, e.g., Erbe and Thomas (2022); Au and Hastings (2008); 
Richardson et al. (1995); Urick (1983) as well as the Discovery of 
Sound in the Sea (DOSITS) 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 the construction 
activities 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 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

[[Page 45784]]

increase in power and a 30-dB increase is a 1,000-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 from 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 pile driving activities, the 
SPL is typically referenced at 10 m.
    SEL (represented as dB referenced to 1 micropascal squared per 
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. The per-pulse SEL (e.g., single 
strike or single shot SEL) is calculated over the time window 
containing the entire pulse (i.e., 100 percent of the acoustic energy). 
SEL can also be a cumulative metric; it can be accumulated over a 
single pulse (for pile driving this is the same as single-strike SEL, 
above; SELss), 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 10 times the logarithm (base 10) of the ratio of the 
mean-square sound pressure to the specified reference value, in dB 
(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 (International 
Organization for Standardization (ISO), 2017) at a specified distance 
from the source, and is represented in the same units as the RMS sound 
pressure. Along with SEL, this metric is used in evaluating the 
potential for PTS (permanent threshold shift) and TTS (temporary 
threshold shift) associated with impulsive sound sources.
    Sounds are also characterized by their temporal component. 
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.
    Sounds can 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 NMFS et al. (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 one second), broadband, 
atonal transients (ANSI, 1986; NIOSH, 1998; ANSI 2005) 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, 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 typically loud due to 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 sounds 
produced by the proposed activity (NMFS, 2012; NOAA, 2016b). 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.

[[Page 45785]]

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, 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 by the ISO 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), for the case of 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 two geometric 
spreading laws defined above 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. In the absence of measured data indicating the level of 
transmission loss at a given site for a specific activity, NMFS 
recommends practical spreading (i.e., 15*Log10(range)) to 
model acoustic propagation for construction activities in most 
nearshore environments.
    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 10-20 dB from day 
to day (Richardson et al., 1995). The result is that, depending on the 
source type and its intensity, sound from the specified activity may be 
a negligible addition to the local environment or could form a 
distinctive signal that may affect marine mammals.
    Ongoing marine vessel traffic, seaplane traffic and associated 
activities throughout the Sukkwan Strait area, as well as land-based 
industrial and commercial activities, result in elevated in-air and 
underwater sound conditions in the project area that increase with 
proximity to the project site. Sound levels likely vary seasonally, 
with elevated levels during summer, when the commercial and fishing 
industries are at their peaks.

Description of Sound Sources for the Specified Activities

    In-water construction activities associated with the project would 
include impact pile installation, vibratory pile installation and 
removal, and DTH installation. Impact hammers operate by repeatedly 
dropping and/or pushing a heavy piston onto a pile to drive the pile 
into the substrate. Sound generated by impact hammers is characterized 
by rapid rise times and high peak levels, a potentially injurious 
combination (Hastings and Popper, 2005). Vibratory hammers install 
piles by vibrating them and allowing the weight of the hammer to push 
them into the sediment. Vibratory hammers typically produce less sound 
(i.e., lower levels) than impact hammers. Peak SPLs may be 180 dB or 
greater, but are generally 10 to 20 dB lower than SPLs generated during 
impact pile driving of the same-sized pile (Oestman et al., 2009). The 
rise time is slower, reducing the probability and severity of injury, 
and the sound energy is distributed over a greater amount of time 
(Nedwell and Edwards, 2002; Carlson et al., 2005).
    DTH systems would also be used during the proposed construction to 
install rock sockets and tension anchors. A DTH hammer is essentially a 
drill bit that drills through the bedrock using a rotating function 
like a normal drill, in concert with a hammering mechanism operated by 
a pneumatic (or sometimes hydraulic) component integrated into the DTH 
hammer to increase speed of progress through the substrate (i.e., it is 
similar to a ``hammer drill'' hand tool). The sounds produced by the 
DTH methods contain both a continuous non-impulsive component from the 
drilling action and an impulsive component from the hammering effect. 
Therefore, NMFS treats DTH systems as both impulsive and continuous, 
non-impulsive sound source types simultaneously.
    The likely or possible impacts of the DOT&PF's proposed activities 
on marine mammals could involve both non-acoustic and acoustic 
stressors. Potential non-acoustic stressors could result from the 
physical presence of the equipment and personnel; however, given there 
are no known pinniped haul-out sites in the vicinity of the proposed 
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.

Acoustic Impacts

    The introduction of anthropogenic noise into the aquatic 
environment from pile driving or drilling is the primary means by which 
marine mammals may be harassed from the DOT&PF'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). In general, exposure 
to pile driving or drilling 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). Exposure to anthropogenic noise can also lead to non-
observable physiological responses, such 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 pile 
driving or drilling 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

[[Page 45786]]

between the pile 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 (2018a), 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 
and vocalization 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). When considering auditory effects for the DOT&PF's proposed 
activities, vibratory pile driving is considered a non-impulsive 
source, while impact pile driving is treated as an impulsive source. 
DTH systems are considered to have both non-impulsive and impulsive 
components.
    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 (Richardson et al., 1995; Au and Hastings, 2008). 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 criteria 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 
various ethical reasons, experiments involving anthropogenic noise 
exposure at levels inducing PTS are not typically pursued or authorized 
(NMFS, 2018).
    Temporary Threshold Shift (TTS)--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 cetacean 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 (Schlundt et 
al., 2000; Finneran et al., 2000, 2002). 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 (Delphinapterus 
leucas), 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, 
bearded seals (Erignathus barbatus), and California sea lions (Zalophus 
californianus) (Kastak et al., 1999; 2007; Kastelein et al., 2019b; 
2019c; Reichmuth et al., 2019; Sills et al., 2020; Kastelein et al., 
2021; 2022a; 2022b). 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 at low frequencies, well below the region of best sensitivity 
for a species or hearing group, are less hazardous than those at higher 
frequencies, 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; Kastelein et al., 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

[[Page 45787]]

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 (a 40-dB threshold shift approximates PTS onset; 
e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB 
threshold shift approximates TTS onset; e.g., Southall et al., 2007). 
Based on data from terrestrial mammals, a precautionary assumption is 
that the PTS thresholds for impulsive sounds (such as impact pile 
driving pulses as received close to the source) 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). 
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.
    Behavioral Harassment--Exposure to noise from pile driving and 
drilling also has the potential to behaviorally disturb marine mammals 
to a level that rises to the definition of harassment under the MMPA. 
Generally speaking, NMFS considers a behavioral disturbance that rises 
to the level of harassment under the MMPA a non-minor response--in 
other words, not every response qualifies as behavioral disturbance, 
and for responses that do, those of a higher level, or accrued across a 
longer duration, have the potential to affect foraging, reproduction, 
or survival. 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. Disturbance may result in 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); avoidance of areas where sound sources are located. 
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; Weilgart, 2007; Archer et al., 2010, Southall et al., 2021). 
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). 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.
    As noted above, behavioral state may affect the type of response. 
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; National Research Council (NRC), 2003; Wartzok et al., 2004). 
Controlled experiments with captive marine mammals have showed 
pronounced behavioral reactions, including avoidance of loud sound 
sources (Ridgway et al., 1997; Finneran et al., 2003). Observed 
responses of wild marine mammals to loud pulsed sound sources 
(typically seismic airguns or acoustic harassment devices) have been 
varied but often consist of avoidance behavior or other behavioral 
changes suggesting discomfort (Morton and Symonds, 2002; see also 
Richardson et al., 1995; Nowacek et al., 2007).
    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. 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. However, 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,b). 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

[[Page 45788]]

the time of the exposure and the type and magnitude of the response.
    Disruption of feeding behavior can be difficult to correlate with 
anthropogenic sound exposure, so it 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. 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). A determination of whether foraging disruptions incur fitness 
consequences would require information on or estimates of the energetic 
requirements of the affected individuals and the relationship between 
prey availability, foraging effort and success, and the life history 
stage of the animal.
    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).
    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 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 or vocalizations, 
respectively (Miller et al., 2000; Fristrup et al., 2003; Foote et al., 
2004), while 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). In some cases, animals may cease sound production during 
production of aversive signals (Bowles et al., 1994).
    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). 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, 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 
substantive 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

[[Page 45789]]

(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. 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, 2003), however 
distress is an unlikely result of this project based on observations of 
marine mammals during previous, similar construction projects.
    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 or vocal ranges of the 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 in 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.
    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.
    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 (Houser, 2014). Masking can be tested directly 
in captive species (e.g., Erbe, 2008), but in wild populations it must 
be either modeled or inferred from evidence of masking compensation. 
There are few studies addressing real-world masking sounds likely to be 
experienced by marine mammals in the wild (e.g., Branstetter et al., 
2013).
    Marine mammals near the proposed project site are exposed to 
anthropogenic noise which may lead to some habituation, but is also 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).
    Masking is more likely to occur in the presence of broadband, 
relatively continuous noise sources. Energy distribution of pile 
driving covers a broad frequency spectrum, and sound from pile driving 
would be within the audible range of pinnipeds and cetaceans present in 
the proposed action area. While some construction during the DOT&PF'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 survival would be affected.
    Airborne Acoustic Effects--Pinnipeds that occur near the project 
site could be exposed to airborne sounds associated with construction 
activities that have the potential to cause behavioral harassment, 
depending on their distance from these activities. Airborne noise would 
primarily be an issue for pinnipeds that are swimming or hauled out 
near the project site within the range of noise levels elevated above 
airborne acoustic criteria. Although pinnipeds are known to haul-out 
regularly on man-made objects, incidents of take resulting solely from 
airborne sound are unlikely due to the sheltered proximity between the 
proposed project area and the known haulout sites (the closest known 
pinniped haulout is for harbor seals, which is located 4.5 km (2.8 mi) 
southeast of the proposed project site, but blocked by a land shadow). 
Cetaceans are not expected to be exposed to airborne sounds that would 
result in harassment as defined under the MMPA.

[[Page 45790]]

    We recognize that pinnipeds in the water could be exposed to 
airborne sound that may result in behavioral harassment when looking 
with their heads above water. Most likely, airborne sound would cause 
behavioral responses similar to those discussed above in relation to 
underwater sound. For instance, anthropogenic sound could cause hauled-
out pinnipeds to exhibit changes in their normal behavior, such as 
reduction in vocalizations, or cause them to temporarily abandon the 
area and move further from the source. However, these animals would 
previously have been ``taken'' because of exposure to underwater sound 
above the behavioral harassment thresholds, which are in all cases 
larger than those associated with airborne sound. Thus, the behavioral 
harassment of these animals is already accounted for in these estimates 
of potential take. Therefore, we do not believe that authorization of 
incidental take resulting from airborne sound for pinnipeds is 
warranted, and airborne sound is not discussed further here.

Potential Effects on Marine Mammal Habitat

    The proposed project will occur within the same footprint as 
existing marine infrastructure. The nearshore and intertidal habitat 
where the proposed project will occur is an area of relatively high 
marine vessel traffic. Most marine mammals do not generally use the 
area within the footprint of the project area. Temporary, intermittent, 
and short-term habitat alteration may result from increased noise 
levels within the Level A and Level B harassment zones. Effects on 
marine mammals will be limited to temporary displacement from pile 
installation and removal noise, and effects on prey species will be 
similarly limited in time and space.
    Water Quality--Temporary and localized reduction in water quality 
will occur as a result of in-water construction activities. Most of 
this effect will occur during the installation and removal of piles and 
bedrock removal when bottom sediments are disturbed. The installation 
and removal of piles and bedrock removal will disturb bottom sediments 
and may cause a temporary increase in suspended sediment in the project 
area. During pile extraction, sediment attached to the pile moves 
vertically through the water column until gravitational forces cause it 
to slough off under its own weight. The small resulting sediment plume 
is expected to settle out of the water column within a few hours. 
Studies of the effects of turbid water on fish (marine mammal prey) 
suggest that concentrations of suspended sediment can reach thousands 
of milligrams per liter before an acute toxic reaction is expected 
(Burton, 1993).
    Impacts to water quality from DTH hammers are expected to be 
similar to those described for pile driving. Impacts to water quality 
would be localized and temporary and would have negligible impacts on 
marine mammal habitat. Effects to turbidity and sedimentation are 
expected to be short-term, minor, and localized. Since the currents are 
strong in the area, following the completion of sediment-disturbing 
activities, suspended sediments in the water column should dissipate 
and quickly return to background levels in all construction scenarios. 
Turbidity within the water column has the potential to reduce the level 
of oxygen in the water and irritate the gills of prey fish species in 
the proposed project area. However, turbidity plumes associated with 
the project would be temporary and localized, and fish in the proposed 
project area would be able to move away from and avoid the areas where 
plumes may occur. Therefore, it is expected that the impacts on prey 
fish species from turbidity, and therefore on marine mammals, would be 
minimal and temporary. In general, the area likely impacted by the 
proposed construction activities is relatively small compared to the 
available marine mammal habitat in southeast Alaska.
    Potential Effects on Prey--Sound may affect marine mammals through 
impacts on the abundance, behavior, or distribution of prey species 
(e.g., crustaceans, cephalopods, fish, 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.
    Fish 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 and Mann, 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. Key impacts to fishes may include 
behavioral responses, hearing damage, barotrauma (pressure-related 
injuries), and mortality.
    Fish react to sounds that are especially strong and/or intermittent 
low-frequency sounds. Short duration, sharp sounds can cause overt or 
subtle changes in fish behavior and local distribution. The reaction of 
fish to noise depends on the physiological state of the fish, past 
exposures, motivation (e.g., feeding, spawning, migration), and other 
environmental factors. Hastings and Popper (2005) identified several 
studies that suggest fish may relocate to avoid certain areas of sound 
energy. Additional studies have documented effects of pile driving on 
fishes; several are based on studies in support of large, multiyear 
bridge construction projects (e.g., Scholik and Yan, 2001, 2002; Popper 
and Hastings, 2009). Several studies have demonstrated that impulse 
sounds might affect the distribution and behavior of some fishes, 
potentially impacting foraging opportunities or increasing energetic 
costs (e.g., Fewtrell and McCauley, 2012; Pearson et al., 1992; Skalski 
et al., 1992; Santulli et al., 1999; Paxton et al., 2017). However, 
some studies have shown no or slight reaction to impulse sounds (e.g., 
Pe[ntilde]a et al., 2013; Wardle et al., 2001; Jorgenson and Gyselman, 
2009; Cott et al., 2012). More commonly, though, the impacts of noise 
on fishes are temporary.
    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. (2012a) showed that a TTS of 
4-6 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. Barotrauma injuries have been documented during 
controlled exposure to impact pile driving (Halvorsen et al., 2012b; 
Casper et al., 2013).
    Essential fish habitat (EFH) has been designated in the proposed 
project area for all five species of salmon (i.e., chum salmon, pink 
salmon, coho salmon, sockeye salmon, and Chinook salmon; NMFS 2017), 
which are common prey of marine mammals. Many creeks flowing into 
Sukkwan Strait and nearby areas are known to contain salmonids, 
including three primary creeks: Hydaburg River, Natzuhini River, and 
Saltery Creek (Giefer and Blossom

[[Page 45791]]

2020); however, adverse effects on EFH in this area are not expected.
    Fish populations in the proposed project area that serve as marine 
mammal prey could be temporarily affected by noise from pile 
installation and removal. The frequency range in which fish generally 
perceive underwater sounds is 50 to 2,000 Hz, with peak sensitivities 
below 800 Hz (Popper and Hastings, 2009). Fish behavior or distribution 
may change, especially with strong and/or intermittent sounds that 
could harm fish. High underwater SPLs have been documented to alter 
behavior, cause hearing loss, and injure or kill individual fish by 
causing serious internal injury (Hastings and Popper, 2005).
    The greatest potential impact to fishes during construction would 
occur during impact pile driving and DTH excavation. In-water 
construction activities would only occur during daylight hours allowing 
fish to forage and transit the project area in the evening. Vibratory 
pile driving would possibly elicit behavioral reactions from fishes 
such as temporary avoidance of the area but is unlikely to cause 
injuries to fishes or have persistent effects on local fish 
populations. In general, impacts on marine mammal prey species are 
expected to be minor, localized, and temporary.

In-Water Construction Effects on Potential Foraging Habitat

    The proposed activities would not result in permanent impacts to 
habitats used directly by marine mammals. The total seafloor area 
affected by pile installation and removal is a very small area compared 
to the vast foraging area available to marine mammals outside this 
project area. Construction would have minimal permanent and temporary 
impacts on benthic invertebrate species, a marine mammal prey source. 
In addition, although southeast Alaska in its entirety is listed as a 
BIA for humpback whales (Wild et al., 2023), the proposed project area 
does not contain particularly high-value habitat and is not unusually 
important for this species or any of the other species potentially 
impacted by the DOT&PF's proposed activities. Therefore, impacts of the 
project are not likely to have adverse effects on marine mammal 
foraging habitat in the proposed project area.
    The area impacted by the proposed project is relatively small 
compared to the available habitat just outside the project area, and 
there are no areas of particular importance that would be impacted by 
this project. 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. As described in the preceding, 
the potential for the DOT&PF's construction to affect the availability 
of prey to marine mammals or to meaningfully impact the quality of 
physical or acoustic habitat is considered to be insignificant.

Estimated Take

    This section provides an estimate of the number of incidental takes 
proposed for authorization through this IHA, which will inform both 
NMFS' consideration of ``small numbers,'' and the negligible impact 
determinations.
    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 primarily be by Level B harassment, as use 
of the acoustic source (i.e., vibratory pile driving, impact pile 
driving, and DTH systems) has the potential to result in disruption of 
behavioral patterns for individual marine mammals. There is also some 
potential for auditory (Level A harassment) to result, primarily for 
mysticetes and high frequency species and phocids because predicted 
auditory injury zones are larger than for mid-frequency species and 
otariids. Auditory injury is unlikely to occur for mid-frequency 
species or otariids. The proposed mitigation and monitoring measures 
are expected to minimize the severity of the taking to the extent 
practicable. 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., 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. NMFS generally predicts that marine mammals are 
likely to be behaviorally harassed 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 re 1 [mu]Pa 
for continuous (e.g., 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 behavioral 
harassment thresholds are expected to include any likely takes by TTS 
as, in most cases, the likelihood of TTS occurs at distances from the 
source less than those at which behavioral harassment is likely. TTS of 
a sufficient degree can manifest as behavioral harassment, as reduced 
hearing sensitivity and the

[[Page 45792]]

potential reduced opportunities to detect important signals 
(conspecific communication, predators, prey) may result in changes in 
behavior patterns that would not otherwise occur.
    The DOT&PF's proposed activity includes the use of continuous 
(vibratory pile driving) and intermittent (impact pile driving) 
sources, and therefore the RMS SPL thresholds of 120 and 160 dB re 1 
[mu]Pa are applicable. DTH systems have both continuous, non-impulsive, 
and impulsive components as discussed in the Description of Sound 
Sources section above. When evaluating Level B harassment, NMFS 
recommends treating DTH as a continuous source and applying the RMS SPL 
thresholds of 120 dB re 1 [mu]Pa.
    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). The 
DOT&PF's proposed construction includes the use of impulsive (impact 
pile driving) and non-impulsive (vibratory pile driving) sources. As 
described above, DTH includes both impulsive and non-impulsive 
characteristics. When evaluating Level A harassment, NMFS recommends 
treating DTH as an impulsive source.
    The thresholds used to identify the onset of PTS are provided in 
Table 4. The references, analysis, and methodology used in the 
development of the thresholds are described in NMFS' 2018 Technical 
Guidance, which may be accessed at: 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.
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 NMFS' 2018 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 construction noise from the proposed project. 
Marine mammals are expected to be affected via sound generated by the 
primary components of the project (i.e., impact pile installation, 
vibratory pile installation, vibratory pile removal, and DTH).
    Sound Source Levels of Proposed Activities--The intensity of pile 
driving sounds is greatly influenced by factors such as the type of 
piles (material and diameter), hammer type, and the physical 
environment (e.g., sediment type) in which the activity takes place. 
The DOT&PF evaluated SPL and TL measurements available for certain pile 
types and sizes from similar activities elsewhere in Alaska or outside 
of Alaska and relied on relevant sound source verification studies to 
determine appropriate proxy levels for their proposed activities. 
Recently proposed and issued IHAs from southeast Alaska were also 
reviewed to identify the most appropriate SPLs and TL coefficients for 
use in this application. NMFS agrees that the SPL values and TL 
coefficients that the DOT&PF proposed for vibratory installation and 
removal and impact installation of 16-inch (40.64 cm), 20-inch (50.80 
cm), and 24-inch (60.96 cm) steel piles are appropriate proxy levels 
for their proposed construction activities (see Table 5 for proposed 
proxy levels). However, NMFS finds that DOT&PF's proposed SPL values 
for 8-inch (20.32 cm) tension anchors and TL coefficients for all DTH 
activities (described in further detail below) are not consistent with 
what NMFS assesses to be the best available science, and instead 
proposes for use SPLs and TL coefficients for DTH consistent with NMFS' 
recommendations for analyses of noise from DTH systems (https://media.fisheries.noaa.gov/2022-11/PUBLIC%20DTH%20Basic%20Guidance_November%202022.pdf) (NMFS, 2022). NMFS 
specifically requests comments on its proposed SPL values and TL 
coefficients for DTH systems, assessment that these values are more 
appropriate than those proposed by DOT&PF, as well as on its DTH 
recommendations generally. Note that the values in Table 5 represent 
SPL referenced at a distance of 10 m from the source.

[[Page 45793]]



Table 5--Summary of Unattenuated In-Water Pile Driving Proxy Levels (at 10 m) and Transmission Loss Coefficients
----------------------------------------------------------------------------------------------------------------
                                                                                 SELss (dB re 1
                                 Installation     Peak SPL (dB   RMS SPL (dB re   [micro]Pa\2\      Reference
          Pile type                 method            re 1        1 [micro]Pa)        sec)           (levels)
                                                   [micro]Pa)
----------------------------------------------------------------------------------------------------------------
16-inch steel piles..........  Vibratory hammer              NA             158              NA  CALTRANS
                                                                                                  (2020).
20-inch steel piles..........  Vibratory hammer              NA             161              NA  Navy (2015).
24-inch steel piles..........  Vibratory hammer              NA             161              NA  Navy (2015).
20-inch steel piles..........  Impact hammer...             208             187             176  CALTRANS
                                                                                                  (2020).
24-inch steel piles..........  Impact hammer...             208             193             178  CALTRANS
                                                                                                  (2020).
8-inch tension anchors.......  DTH system......         \2\ 170             156         \2\ 144  Reyff and
                                                                                                  Heyvaert
                                                                                                  (2019); Reyff
                                                                                                  (2020).
20-inch rock sockets.........  DTH system......             184             167             159  Heyvaert and
                                                                                                  Reyff (2021).
24-inch rock sockets.........  DTH system......             184             167             159  Heyvaert and
                                                                                                  Reyff (2021).
----------------------------------------------------------------------------------------------------------------
Notes: NMFS conservatively assumes that noise levels during vibratory pile removal are the same as those during
  installation for the same type and size pile; all SPLs are unattenuated and represent the SPL referenced at a
  distance of 10 m from the source; NA = Not applicable; dB re 1 [micro]Pa = decibels (dB) referenced to a
  pressure of 1 micropascal.

    NMFS recommends that DTH system installation be treated as a 
continuous sound source for Level B behavioral harassment calculations 
and as an impulsive source for Level A harassment calculations (NMFS, 
2022) given these systems produce noise including characteristics of 
both source types (described above in the Description of Sound Sources 
section). The DOT&PF reviewed projects that were most similar to the 
specified activity in terms of drilling activities, type and size of 
piles installed, method of pile installation, and substrate conditions. 
Data from DTH system installation of 24-inch (60.96-cm) piles in 
Tenakee Springs, Alaska, indicate a continuous RMS SPL of 167 dB, an 
impulsive peak SPL of 184 dB, and a SELss level of 159 dB 
(all at 10 m) (Heyvaert and Reyff, 2021). Therefore, DOT&PF proposed 
these levels as proxy values for DTH system installation of 20- and 24-
inch (50.80- and 60.96-cm) rock sockets during the proposed activities. 
NMFS concurs that these levels are appropriate proxy levels for the 
installation of rock sockets via DTH systems for the proposed project 
(Table 5).
    TL coefficient data from Denes et al. (2016) and Heyvaert and Reyff 
(2021) indicate that sounds from 24-inch (60.96-cm) drilling rock 
sockets in Kodiak and Tenakee Springs, Alaska, decay at rates ranging 
from 18.9*log10(R) to 20.3*log10(R), where R 
indicates range from the subject pile, for RMS SPLs, respectively. 
Therefore, Reyff (2022) recommends in Appendix C of the DOT&PF's 
application that sounds from DTH activities are characteristic of a 
point source and proposed a TL coefficient of 19.0 be used as a proxy 
for 20- and 24-inch (50.80- and 60.96-cm) rock socket installation in 
Hydaburg (Denes et al., 2016; Heyvaert and Reyff, 2021). While there is 
evidence that TL coefficients can be high during DTH activities (e.g., 
Denes et al., 2016; Reyff, 2020; Heyvaert and Reyff, 2021), TL 
coefficient measurements reported from DTH activities are highly 
variable and in some cases have been reported to be lower, and more 
representative of practical spreading models (i.e., 
15*log10(R)). For example, recent rock socket measurements 
from Tongass Narrows in Ketchikan, Alaska, located approximately 76 km 
east of Hydaburg, Alaska, reported TL coefficients of 14.1 for 
SELss, 14.3 for RMS SPL, and 14.8 for Peak SPL measurements 
of 24-inch (60.96-cm) open-end steel piles for ranges recorded out to 
80-95 m (Miner, 2023). Other rock socket measurements from Skagway, 
Alaska, reported TL coefficients of 13.3 for SELss and 13.8 
for Peak SPL measurements of 42-inch (106.68-cm) steel piles for ranges 
recorded out to 1,400 m from the pile (Reyff, 2020). Further, the TL 
measurements reported by Denes et al. (2016) and Heyvaert and Reyff 
(2021) in Kodiak and Tenakee Springs, Alaska, were also high for impact 
and vibratory pile driving. For example, in Tenakee Springs, TL 
coefficients for impact pile driving of 18-inch (45.75-cm) steel 
battered piles, 24-inch (60.96-cm) steel vertical piles, and 30-inch 
(76.20-cm) steel battered and vertical piles ranged from 18.8 to 19.1 
for SELss, 19.6 to 20.1 for RMS SPL, and 18.9 to 20.0 for 
Peak SPL measurements recorded out to 1,100 m (Heyvaert and Reyff, 
2021). The TL coefficients reported for impact pile driving and 
vibratory pile driving of 24-inch (60.96-cm) piles in Kodiak, when 
considering monitoring ranges out to 1,125 m, were 20.3 and 21.9 for 
RMS SPL, respectively (Denes et al., 2016). Therefore, the TL 
coefficients reported by these two studies, and used by Reyff (2022) 
and the DOT&PF to support a proxy TL coefficient of 19.0, may not be 
representative of TL coefficients in other locations in southeast 
Alaska or potentially at those same locations under different 
conditions. In addition, all of the acoustic measurements (i.e., for 
vibratory, impact, and DTH pile driving) from Kodiak were missing 
energy on the recordings between 50-300 Hz due to the shallow 
bathymetry in the region (which did not support propagation of low 
frequencies), making their data less suitable for use as proxy data as 
they did not include the full range of frequencies produced by the 
construction activities (Denes et al., 2016).
    As described in the Description of Sound Sources section, sound 
propagation, and thus TL, through an environment can be complicated and 
depend on a multitude of factors (e.g., seabed type, bathymetry, and 
the local sound speed profiles, characteristics of the sound itself), 
which can vary temporally and spatially. Many of these factors that 
affect sound propagation and TL are thus site- and time-specific. For 
coastal activities, such as pile driving, if area-specific information 
on propagation/transmission loss is not available, NMFS generally 
recommends practical spreading (TL=15 * log10(R)) (e.g., 
Stadler and Woodbury, 2009; CALTRANS, 2015; NMFS, 2020). There are no 
site specific TL data available for the drilling of rock sockets in 
Hydaburg, Alaska. Therefore, at this time, NMFS has preliminarily 
determined that DOT&PF's proposed TL coefficient of 19.0 for the 
installation of rock sockets during their proposed project is 
inappropriate, and instead proposes a default TL coefficient of 15.0 be 
used for these activities. This is consistent with the recommendations 
outlined in NMFS (2020) and NMFS (2022).
    Underwater noise from tension anchor construction is typically 
lower than noise produced by other DTH activities. During tension 
anchor

[[Page 45794]]

construction, the casing used during drilling is inside a larger-
diameter pile, reducing noise levels. In addition, anchor holes are 
substantially smaller in diameter and deeper than rock sockets, and 
therefore, result in much lower sound (Reyff and Heyvaert, 2019). The 
DOT&PF and NMFS agree that a continuous RMS SPL of 156 dB (at 10 m) 
(Reyff and Heyvaert, 2019) is the most appropriate proxy level to use 
for the installation of 8-inch (20.32-cm) tension anchors at this time. 
However, DOT&PF proposed that 8-inch (20.32-cm) tension anchors should 
be considered as a solely non-impulsive, continuous sound source when 
calculating Level A and Level B behavioral harassment rather than as 
having both impulsive (Level A) and continuous (Level B behavioral 
harassment) components as recommended by NMFS (2022). DOT&PF based this 
argument on the finding that Heyvaert and Reyff (2021) could not 
classify the tension anchor installation as impulsive for the purposes 
of Level A harassment zone calculations because the impulse sound level 
was generally not much louder than the continuous sound level. However, 
there is evidence that DTH piling and DTH drilling contains impulsive 
components (i.e., pulsed sounds) (Guan et al., 2022), including from 
Heyvaert and Reyff (2021) who reported that sounds from tension rock 
anchor installation had impulsive characteristics, but that the noise 
from these pulses were not distinctly higher than the constant drilling 
sounds. It is important to account for these impulsive characteristics 
since they have a greater potential to cause noise-induced hearing loss 
compared to non-impulsive sounds. Thus, there does not appear to be 
enough evidence to indicate that 8-inch (20.32-cm) rock tension anchor 
piles have no impulsive components. Therefore, as the data suggest is 
appropriate, NMFS proposes impulsive SELss values of 144 dB 
and 170 dB peak SPL (Reyff, 2020), respectively (at 10 m), for the DTH 
system installation of 8-inch (20.32-cm) tension anchors during the 
proposed activity.
    DOT&PF propose a TL coefficient of 19.0 for 8-inch (20.32-cm) 
tension anchors based on the measurements from Skagway, Alaska (Reyff 
and Heyvaert, 2019; Reyff, 2020) and Tenakee Springs, Alaska (Heyvaert 
and Reyff, 2021) as recommended in Reyff (2022) in Appendix C of the 
DOT&PF's application. These are the only two hydroacoustic studies both 
the DOT&PF and NMFS are aware of that have involved the installation of 
tension anchors. Reyff and Heyvaert (2019) and Reyff (2020) (which 
provides an update to Reyff and Heyvaert, 2019) reported a TL 
coefficient of 24.2 for RMS SPL values recorded from 36 to 110 m from 
the pile of 8-inch (20.32-cm) rock tension anchors in Skagway, Alaska. 
Heyvaert and Reyff (2021) reported a TL coefficient of 19.2 for RMS SPL 
values recorded from 9 to 900 m of 8-inch (20.32-cm) rock anchor 
casings installed within 24-inch (60.96-cm) diameter vertical piles and 
17.0 for RMS SPL values recorded from 10 to 110 m of 8-inch (20.32-cm) 
rock anchor casings installed within 18-inch (45.75 cm) diameter 
battered piles in Tenakee Springs, Alaska.
    As discussed above, TL measurements from this particular study in 
Tenakee Springs appear to be higher in general for all pile driving 
activities (vibratory and impact pile driving and DTH systems) and thus 
may not be representative of TL coefficients recorded elsewhere in 
southeast Alaska or under different circumstances at Tenakee Springs. 
For the Skagway dataset, sound level measurements were only made out to 
110 m, and therefore it is unknown if the resulting TL coefficient is 
representative at greater distances. While there is data to suggest 
that TL coefficients from the installation of tension anchors may 
typically be higher than 15*log10(R) (e.g., Reyff and 
Heyvaert, 2019; Reyff, 2020; Heyvaert and Reyff, 2021), these data are 
based on measurements of only a few piles and they were obtained from 
study sites located over 320 km away from Hydaburg, Alaska. Thus, given 
the lack of site specific TL measurements for the installation of 
tension anchors in Hydaburg, at this time, NMFS does not agree with the 
DOT&PF's proposed TL coefficient of 19.0 for the DTH installation of 
rock tension anchor piles and instead proposes a default TL coefficient 
of 15.0, which is consistent with recommendations outlined in NMFS 
(2020) and NMFS (2022).
    Estimated Harassment Isopleths--All Level B harassment isopleths 
are reported in Table 7 considering RMS SPLs and the default TL 
coefficient. Land forms (including causeways, breakwaters, islands, and 
other land masses) impede the transmission of underwater sound and 
create shadows behind them where sound from construction is not 
audible. At Hydaburg, Level B harassment isopleths from the proposed 
project will be blocked by Sukkwan Island, Spook Island, Mushroom 
Island, and the coastline along Prince of Wales Island both southeast 
and northwest of the project site. The maximum distance that a 
harassment isopleth can extend due to these land masses is 5,162 m.
    The ensonified area associated with Level A harassment is 
technically challenging to predict due to the need to account for a 
duration component. Therefore, NMFS developed an optional User 
Spreadsheet tool to accompany the Technical Guidance (2018) that can be 
used to relatively simply predict an isopleth distance for use in 
conjunction with marine mammal density or occurrence to help predict 
potential takes. We note that because of some of the assumptions 
included in the methods underlying this optional tool, we anticipate 
that the resulting isopleth estimates are typically going to be 
overestimates of some degree, which may result in an overestimate of 
potential take by Level A harassment. However, this optional tool 
offers the best way to estimate isopleth distances when more 
sophisticated modeling methods are not available or practical. For 
stationary sources (such as from impact pile driving, vibratory pile 
driving, and DTH), the optional User Spreadsheet tool predicts the 
distance at which, if a marine mammal remained at that distance for the 
duration of the activity, it would be expected to incur PTS. Inputs 
used in the optional User Spreadsheet tool are reported in Table 6 and 
the resulting estimated isopleths are reported in Table 7. (Please see 
Table 6-5 in the DOT&PF's application for harassment isopleths 
calculated using the DTH TL coefficients and source levels for 8-in 
(20.32-cm) tension anchors proposed therein).

[[Page 45795]]



                                                                              Table 6--NMFS User Spreadsheet Inputs
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                              Vibratory pile driving                                        Impact pile driving                             DTH
                                 ---------------------------------------------------------------------------------------------------------------------------------------------------------------
                                     16-inch steel       20-inch steel              24-inch steel piles              20-inch steel       24-inch steel      20- and 24-inch     8-inch tension
                                         piles               piles       ----------------------------------------        piles               piles            rock socket           anchor
                                 ----------------------------------------                                        -------------------------------------------------------------------------------
                                                         Installation/       Installation           Removal
                                        Removal             removal                                                  Installation        Installation        Installation        Installation
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Spreadsheet Tab Used............  A.1) Non-Impul,     A.1) Non-Impul,     A.1) Non-Impul,     A.1) Non-Impul,     E.1) Impact pile    E.1) Impact pile    E.2) DTH Systems..  A.1) DTH Systems.
                                   Stat, Cont.         Stat, Cont.         Stat, Cont.         Stat, Cont.         driving.            driving.
Source Level (SPL)..............  158 dB RMS........  161 dB RMS........  161 dB RMS........  161 dB RMS........  176 dB SEL........  178 dB SEL........  159 dB RMS........  144 dB RMS.
Transmission Loss Coefficient...  15................  15................  15................  15................  15................  15................  15................  15.
Weighting Factor Adjustment       2.5...............  2.5...............  2.5...............  2.5...............  2.................  2.................  2.................  2.
 (kHz).
Time to install/remove single     30................  15/30 \1\.........  15/30 \1\.........  30................  ..................  ..................  60-480 \2\........  60-240.\2\
 pile (minutes).
Number of strikes per pile......  ..................  ..................  ..................  ..................  50................  50................  15................  15.
Piles per day...................  2.................  2/10 \1\..........  2/10 \1\..........  2.................  1/2 \1\...........  1/2 \1\...........  1.................  1.
Distance of sound pressure level  10................  10................  10................  10................  10................  10................  10................  10.
 measurement (m).
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ A maximum scenario was calculated for this activity.
\2\ A range of scenarios was calculated for this activity.


   Table 7--Distances to Level A Harassment, by Hearing Group, and Distances and Areas of Level B Harassment Thresholds per Pile Type and Pile Driving
                                                                         Method
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                          Level A harassment distance (m)        Level B       Level B
                                                                                     ----------------------------------------  harassment    harassment
            Activity                  Pile size       Minutes (min) or    Piles per                                           distance (m)  area (km\2\)
                                                      strikes per pile       day        LF      MF      HF      PW      OW     all hearing   all hearing
                                                                                                                                 groups        groups
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vibratory Installation.........  20- and 24-inch...  15 min............            2       5       1       7       3       1     \3\ 5,412      \4\ 4.34
                                                     30 \1\ min........       \1\ 10      20       2      30      13       1
Vibratory Removal..............  16-inch...........  30 min............            2       5       1       7       3       1         3,415          3.90
                                 24-inch...........  30 min............            2       7       1      11       5       1     \3\ 5,412      \4\ 4.34
Impact Installation............  20-inch...........  50 strikes........            1      47       2      56      25       2         1,585          2.14
                                                     50 \1\ strikes....        \1\ 2      74       3      88      40       3
                                 24-inch...........  50 strikes........            1      63       3      75      34       3           631          0.65
                                                     50 \1\ strikes....        \1\ 2     100       4     119      54       4
DTH (Rock Socket) \2\..........  20- and 24-inch...  60 min............            1     359      13     427     192      14    \3\ 13,594      \4\ 4.34
                                                     120 min...........            1     569      21     678     305      23
                                                     180 min...........            1     746      27     888     399      29
                                                     240 min...........            1     903      33   1,076     484      36
                                                     300 min...........            1   1,048      38   1,249     561      41
                                                     360 min...........            1   1,184      43   1,410     634      47
                                                     420 min...........            1   1,312      47   1,563     702      52
                                                     480 min...........            1   1,434      51   1,708     768      56
DTH (Tension Anchor) \2\.......  8-inch............  60 min............            1      36       2      43      20       2         2,512          3.07
                                                     120 min...........            1      57       2      68      31       3
                                                     180 min...........            1      75       3      89      40       3
                                                     240 min...........            1      91       4     108       4       4
                                                     300 min...........            1     105       4     125      57       5
                                                     360 min...........            1     119       5     141      64       5
                                                     420 min...........            1     132       5     157      71       6
                                                     480 min...........            1     144       6     171      77       6
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ A maximum scenario was calculated for this activity.
\2\ A range of scenarios was calculated for this activity.
\3\ Harassment distances would be truncated where appropriate to account for land masses, to a maximum distance of 5,162 m.
\4\ Harassment areas are truncated where appropriate to account for land masses, to a maximum area of 4.34 km\2\.

Marine Mammal Occurrence and Take Estimation

    In this section we provide information about the occurrence of 
marine mammals, including density or other relevant information that 
will inform the take calculations. We also describe how this 
information is synthesized to produce a quantitative estimate of the 
take that is reasonably likely to occur and proposed for authorization. 
Although construction is currently planned to begin in fall 2023, 
unexpected delays associated with construction can occur. To account 
for this uncertainty, the following exposure estimates assume that 
construction would occur during the periods of peak abundance for those 
species for which abundance varies seasonally.
    Due to the differences in the DTH analysis between the DOT&PF's 
application and this notice, estimated Level B harassment isopleths for 
DTH activities are larger than those calculated by the DOT&PF (Tables 
6-4 and 6-5 in the DOT&PF's application versus Table 7 in this notice). 
However, because Level B harassment isopleths are truncated by local 
land masses, the maximum estimated areas of ensonification for Level B 
harassment are equivalent. Therefore, no adjustment is needed to 
estimates of total take.

Steller Sea Lion

    No density or abundance numbers exist for Steller sea lions in the 
proposed action area, and they are not known to regularly occur near 
Hydaburg. However, in context of a lack of local data, the DOT&PF

[[Page 45796]]

conservatively estimated that during peak salmon runs, 6 groups of 10 
individuals could be exposed to project-related underwater noise each 
week during pile installation and removal activities, for a total of 
240 exposures (4 weeks * 60 sea lions per week = 240 total exposures).
    DOT&PF's largest estimated Level A harassment zone for Steller sea 
lions was 39 m (see Tables 6-4 and 6-5 in the DOT&PF's application). 
Based on this assumption, the DOT&PF assumed that it would be unlikely 
for a Steller sea lion to approach that closely and remain unobserved 
for a period of time long enough to incur PTS. While the harassment 
isopleths estimated herein are larger than those proposed by the DOT&PF 
(see Table 7), the largest Level A harassment zone for Steller sea 
lions is still only 59 m. Due to the small Level A harassment zones 
(Table 7) and the implementation of shutdown zones, which will be 
larger than Level A harassment zones (described below in the Proposed 
Mitigation section), NMFS concurs with the DOT&PFs assessment that take 
by Level A harassment is not anticipated for Steller sea lions. 
Therefore, NMFS proposes to authorize all 240 estimated exposures as 
takes by Level B harassment. Takes by Level A harassment for Steller 
sea lions are not proposed to be authorized.

Harbor Seal

    Up to six known harbor seal haulouts are located near the proposed 
project area; however, they are all located outside of the estimated 
harassment zones, with the closest haulout located just over 4.5 km 
(2.8 mi) southeast of the proposed project site, but blocked by a land 
shadow (see Figure 4-2 in the DOT&PF's application). Within the project 
area, harbor seals remain relatively rare as described by local 
residents. The DOT&PF conservatively estimated that up to 8 harbor 
seals could be within estimated harassment zones each day during pile 
installation and removal activities, for a total of 208 exposures (26 
days * 8 seals per day = 208 total exposures).
    DOT&PF's largest estimated Level A harassment zone for harbor seals 
was 308 m (see Tables 6-4 and 6-5 in the DOT&PF's application). While 
there are no known harbor seal haulouts located within this distance, 
it is possible that harbor seals may approach and enter within this 
distance for sufficient duration to incur PTS. DOT&PF estimated that up 
to 12 harbor seals per week could occur within the Level A harassment 
zones. Based on this analysis, and the DOT&PF's proposal to implement a 
shutdown zone larger than the largest Level A harassment zone (i.e., 
310 m, see Table 6-5 in the DOT&PF's application), the DOT&PF requested 
that 48 takes by Level A harassment (12 exposures per week * 4 weeks of 
pile installation = 48 exposures) and 160 takes by Level B harassment 
(208 total exposures minus 48 takes by Level A harassment) be proposed 
for authorization.
    The largest Level A harassment zone for harbor seals, as estimated 
by NMFS, is 768 m. While there are still no known harbor seal haulouts 
within this distance, the likelihood of harbor seals occurring within 
the Level A harassment zones for sufficient duration to incur PTS 
increases. Further, the largest practicable shutdown zone that the 
DOT&PF states it can implement for harbor seals is 400 m (described 
below in the Proposed Mitigation section), which is smaller than the 
Level A harassment zones estimated to result from 240 or more minutes 
of 20- and 24-inch (50.8- and 60.96-cm) DTH rock socket installation. 
To account for this difference, NMFS proposes to authorize additional 
takes by Level A harassment, as compared with the DOT&PF's request. 
Additional takes were determined by calculating the ratio of the 
largest Level A harassment area for 20- and 24-inch (50.8- and 60.96-
cm) DTH activities (i.e., 0.89 km\2\ for a Level A harassment distance 
of 768 m) minus the area of the proposed shutdown zone for harbor seals 
(i.e., 0.27 km\2\ for a shutdown zone distance of 400 m) to the area of 
the Level B harassment isopleth (4.34 km\2\ for a Level B harassment 
distance of 5,162 m) (i.e., (0.89 km\2\-0.27 km\2\)/4.34 km\2\ = 0.14). 
We then multiplied this ratio by the total number of estimated harbor 
seal exposures to determine additional take by Level A harassment 
(i.e., 0.14 * 208 exposures = 29.12 takes, rounded up to 30 takes). The 
total proposed take by Level A harassment was then calculated as the 
take originally proposed and requested by the DOT&PF plus the 
additional take calculated by NMFS (i.e., 48 + 30), for a total of 78 
takes by Level A harassment. Takes by Level B harassment were 
calculated as the number of estimated harbor seal exposures minus the 
proposed amount of take by Level A harassment (i.e., 208-78). 
Therefore, NMFS proposes to authorize 78 takes by Level A harassment 
and 130 takes by Level B harassment for harbor seals, for a total of 
208 takes.

Northern Elephant Seal

    Northern elephant seal abundance throughout coastal southeast 
Alaska is low, and anecdotal reports have not included northern 
elephant seals near the proposed project area. However, northern 
elephant seals have been observed elsewhere in southeast Alaska; 
therefore, this species could occur near the proposed project area. To 
account for this possibility, the DOT&PF estimated that one northern 
elephant seal could be within estimated harassment zones each week 
during pile installation and removal activities, for a total of four 
exposures (4 weeks * 1 northern elephant seal each week = 4 total 
exposures).
    DOT&PF's largest estimated Level A harassment zone for northern 
elephant seals was 308 m (see Tables 6-4 and 6-5 in the DOT&PF's 
application). The DOT&PF assumed that northern elephant seals would be 
unlikely to approach this distance without detection while underwater 
activities are underway, and therefore did not request that takes by 
Level A harassment be authorized for northern elephant seals. However, 
the harassment isopleths for DTH activities estimated by NMFS are much 
larger. In addition, the largest practical shutdown zone the DOT&PF 
states it can implement for northern elephant seals (400 m) (described 
below in the Proposed Mitigation section) is smaller than the Level A 
harassment isopleths that result from 240 or minutes more of 20- and 
24-inch (50.8- and 60.96-cm) DTH rock socket installation. To account 
for this difference, NMFS followed the same method as described above 
for harbor seals to calculate take by Level A harassment to propose for 
northern elephant seals. This was achieved by calculating the ratio of 
the largest Level A harassment area for 20- and 24-inch (50.8- and 
60.96-cm) DTH activities (i.e., 0.89 km\2\ for a Level A harassment 
distance of 768 m) minus the area of the proposed shutdown zone for 
elephant seals (i.e., 0.27 km\2\ for a shutdown zone distance of 400 m) 
to the area of the Level B harassment isopleth (4.34 km\2\ for a Level 
B harassment distance of 5,162 m) (i.e., (0.89 km\2\-0.27 km\2\)/4.34 
km\2\ = 0.14), and by multiplying this ratio by the total number of 
estimated northern elephant seal exposures (i.e., 0.14 * 4 exposures = 
0.56 takes, rounded up to 1 take by Level A harassment). Takes by Level 
B harassment were calculated as the number of estimated northern 
elephant exposures minus the proposed amount of take by Level A 
harassment to be authorized (i.e., 4-1). Therefore, NMFS proposes to 
authorize one take by Level A harassment and three takes by Level B 
harassment for northern elephant seals, for a total of four takes.

[[Page 45797]]

Harbor Porpoise

    There have been no systematic studies or observations of harbor 
porpoises specific to Hydaburg or Sukkwan Strait, and sightings of 
harbor porpoises have not been described in this region by local 
residents. As such, there is limited potential for them to occur in the 
proposed project area, but they could occur in low numbers as 
individuals have been observed in southern inland waters of southeast 
Alaska. Therefore, the DOT&PF estimated that up to two harbor porpoises 
could be within estimated harassment zones each day during pile 
installation and removal activities, for a total of 52 exposures (26 
days * 2 porpoises per day = 52 exposures).
    Harbor porpoises are small, lack a visible blow, have low dorsal 
fins, an overall low profile, and a short surfacing time, making them 
difficult to observe (Dahlheim et al., 2015). These characteristics 
likely reduce the identification and reporting of this species. For 
these reasons, the DOT&PF requested that a small number of takes by 
Level A harassment be authorized for harbor porpoises. Based off of a 
maximum Level A harassment isopleth distance of 579 m for harbor 
porpoises estimated by the DOT&PF, the DOT&PF assumed that one pair of 
harbor porpoises may enter the Level A harassment zone every 7 days of 
in-water construction. Therefore, the DOT&PF requested that NMFS 
propose to authorize eight takes by Level A harassment for harbor 
porpoise for the proposed construction activities (4 weeks * 2 harbor 
porpoise per week = 8 takes by Level A harassment).
    The maximum Level A harassment isopleth estimated by NMFS for 
harbor porpoises is 1,708 m, 2.9 times larger than the isopleth 
estimated by the DOT&PF (580 m). The largest practicable shutdown zone 
that the DOT&PF states it can implement for harbor porpoises is 500 m 
(described below in the Proposed Mitigation section), which is smaller 
than the Level A harassment isopleths estimated to result from 120 or 
more minutes of 20- and 24-inch (50.8- and 60.96-cm) DTH rock socket 
installation. To account for this difference and the increased 
possibility of harbor porpoises occurring outside of the shutdown zone 
and in the Level A harassment zone long enough to incur PTS, NMFS 
proposes to authorize additional takes by Level A harassment, as 
compared with the DOT&PF's request. Additional takes were determined by 
calculating the ratio of the largest Level A harassment area for 20- 
and 24-inch (50.8- and 60.96-cm) DTH activities (i.e., 2.25 km\2\ for a 
Level A harassment distance of 1,708 m minus the area of the proposed 
shutdown zone for harbor porpoises (i.e., 0.42 km\2\ for a shutdown 
zone distance of 500 m) to the area of the Level B harassment isopleth 
(4.34 km\2\ for a Level B harassment distance of 5,162 m) (i.e., (2.25 
km\2\-0.42 km\2\)/4.34 km\2\ = 0.42). We then multiplied this ratio by 
the total number of estimated harbor porpoise exposures to determine 
additional take by Level A harassment (i.e., 0.42 * 8 exposures = 3.36 
takes, rounded up to 4 takes). The total proposed take by Level A 
harassment was then calculated as the take originally proposed and 
requested by the DOT&PF plus the additional take calculated by NMFS to 
account for the larger Level A harassment zones estimated by NMFS to 
result from DTH activities (i.e., 8 + 4), for a total of 12 takes by 
Level A harassment. Takes by Level B harassment were calculated as the 
number of estimated harbor porpoise exposures minus the proposed amount 
of take by Level A harassment (i.e., 52-12). Therefore, NMFS proposes 
to authorize 12 takes by Level A harassment and 40 takes by Level B 
harassment for harbor seals, for a total of 52 takes.

Dall's Porpoise

    Dall's porpoises are not expected to occur in Sukkwan Strait 
because the shallow water habitat of the bay is atypical of areas where 
Dall's porpoises usually occur. However, recent research indicates that 
Dall's porpoises may opportunistically exploit nearshore habitats where 
predators, such as killer whales, are absent. Therefore, the DOT&PF 
anticipates that one large Dall's porpoise pod (15 individuals) could 
be within the estimated harassment zones during in-water construction, 
for a total of 15 possible exposures.
    DOT&PF's largest estimated Level A harassment zone for Dall's 
porpoise was 579 m. Dall's porpoises typically appear in larger groups 
and exhibit behaviors that make them more visible and thus easier to 
observe at distance. Based on this assumption, the DOT&PF did not 
request any takes by Level A harassment for this species. However, 
similar to harbor porpoises, the maximum Level A harassment zone 
estimated by NMFS (1,708 m) is 2.9 times larger than the zone estimated 
by the DOT&PF. The largest practicable shutdown zone that the DOT&PF 
states it can implement for Dall's porpoises during this project is 500 
m (described below in the Proposed Mitigation section), which is 
smaller than the Level A harassment zones estimated by NMFS to result 
from 120 or more minutes of 20- and 24-inch (50.8- and 60.96-cm) DTH 
rock socket installation. To account for this difference and the 
increased possibility of Dall's porpoises occurring outside of the 
shutdown zone and in the Level A harassment zones for sufficient 
duration to incur PTS, NMFS proposes to add additional takes by Level A 
harassment, as compared with the DOT&PF's request. Because Dall's 
porpoises typically occur in groups, NMFS proposes to authorize 15 
takes (i.e., one large pod) by Level A harassment in addition to the 15 
takes by Level B harassment that the DOT&PF requested, for a total of 
30 takes. This would help to ensure that the DOT&PF have enough takes 
to account for the possibility of one large pod occurring in either the 
Level A or the Level B harassment zone.

Pacific White-Sided Dolphin

    Pacific white-sided dolphins do not generally occur in the shallow, 
inland waterways of southeast Alaska. There are no records of this 
species occurring in Sukkwan Strait, and it is uncommon for individuals 
to occur in the proposed project area. However, recent fluctuations in 
distribution and abundance decrease the certainty in this prediction. 
Therefore, the DOT&PF conservatively estimated that one large group (92 
individuals) of Pacific white-sided dolphins could be within estimated 
harassment zones during the proposed in-water construction.
    DOT&PF's largest estimated Level A harassment zone for Pacific 
white-sided dolphins was 37 m (see Tables 6-4 and 6-5 in the DOT&PF's 
application). Given the large group size and more conspicuous nature of 
Pacific white-sided dolphins, the DOT&PF did not request any takes by 
Level A harassment for this species as it would be unlikely they would 
approach this distance for sufficient duration to incur PTS. The 
largest Level A harassment zone estimated by NMFS for Pacific white 
sided dolphins is still only 51 m. Due to the small Level A harassment 
zones (Table 7) and the implementation of shutdown zones, which will be 
larger than Level A harassment zones (described below in the Proposed 
Mitigation section), NMFS concurs with the DOT&PFs assessment that take 
by Level A harassment is not anticipated for Pacific white-sided 
dolphins. Therefore, NMFS proposes to authorize all 92 estimated 
exposures as takes by Level B harassment. Takes by Level A harassment 
for Pacific white-sided dolphins are not proposed to be authorized.

[[Page 45798]]

Killer Whale

    Killer whales are observed infrequently throughout Sukkwan Strait, 
and their presence near Hydaburg is unlikely. However, anecdotal local 
information suggests that a pod may be seen in the proposed project 
area every few months. Therefore, the DOT&PF estimate that one killer 
whale pod of up to 15 individuals may be within estimated harassment 
zones once during the proposed pile installation and removal activities 
(15 total exposures).
    DOT&PF's largest estimated Level A harassment zone for killer 
whales was 37 m (see Tables 6-4 and 6-5 in the DOT&PF's application). 
Because killer whales are unlikely to enter Sukkwan Strait and are 
relatively conspicuous, the DOT&OF did not request any takes by Level A 
harassment for this species as it would be unlikely they would approach 
this distance for sufficient duration to incur PTS. The largest Level A 
harassment zone for killer whales estimated by NMFS is still only 51 m 
(Table 7). Due to the small Level A harassment zones (Table 7) and the 
implementation of shutdown zones, which will be larger than Level A 
harassment zones (described below in the Proposed Mitigation section), 
NMFS concurs with the DOT&PFs assessment that take by Level A 
harassment is not anticipated for killer whales. Therefore, NMFS 
proposes to authorize all 15 estimated exposures as takes by Level B 
harassment. Takes by Level A harassment for killer whales are not 
proposed to be authorized.

Humpback Whale

    Use of Sukkwan Strait by humpback whales is common but intermittent 
and dependent on the presence of prey fish. Based on anecdotal evidence 
from local residents, the DOT&PF predicts that four groups of two 
whales, up to eight individuals per week, may be within estimated 
harassment zones each week during the 4 weeks of the proposed pile 
installation and removal activities, for a total of 32 exposures (8 per 
week * 4 weeks = 32 total exposures). Wade (2021) estimated that 
approximately 2.4 percent of humpback whales in southeast Alaska are 
members of the Mexico DPS, while all others are members of the Hawaii 
DPS. Therefore, the DOT&PF estimates that 1 of the exposures (32 whales 
* 0.024 = 0.77 rounded up to 1) would be of Mexico DPS individuals and 
31 exposures would be of Hawaii DPS individuals.
    DOT&PF's largest estimated Level A harassment zone for humpback 
whales was 504 m (see Tables 6-4 and 6-5 in the DOT&PF's application). 
However, due to the long duration of DTH piling that is anticipated, 
and the potential for humpback whales to enter the Level A harassment 
zones from around obstructions or landforms near the proposed project 
area, the DOT&PF requested that NMFS propose to authorize 4 takes by 
Level A harassment (equivalent to two groups of two individuals) of 
humpback whales. Due to the small percentage of humpback whales that 
may belong to the Mexico DPS in southeast Alaska, the DOT&PF assumes 
that all takes by Level A harassment will be attributed to Hawaii DPS 
whales.
    The largest Level A harassment zone for humpback whales, as 
estimated by NMFS, is 1,435 m (Table 7). The largest practicable 
shutdown zone that the DOT&PF states it can implement for humpback 
whales during this project is 1,000 m (described below in the Proposed 
Mitigation section), which is smaller than the Level A harassment zones 
estimated by NMFS to result from 300 or more minutes of 20- and 24-inch 
(50.8- and 60.96-cm) DTH rock socket installation. To account for this 
difference and the increased possibility of humpback whales occurring 
outside of the shutdown zone and in the Level A harassment zone long 
enough to incur PTS, NMFS proposes to add additional takes by Level A 
harassment, compared with the DOT&PF's request.
    NMFS calculated additional takes by Level A harassment by 
determining the ratio of the largest Level A harassment area for 20- 
and 24-inch (50.8- and 60.96-cm) DTH activities (i.e., 2.01 km\2\ for a 
Level A harassment distance of 1,435 m) minus the area of the proposed 
shutdown zone for humpback whales (i.e., 1.34 km\2\ for a shutdown zone 
distance of 1,000 m) to the area of the Level B harassment isopleth 
(4.34 km\2\ for a Level B harassment distance of 5,162 m) (i.e., (2.01 
km\2\-1.34 km\2\)/4.34 km\2\ = 0.15). We then multiplied this ratio by 
the total number of estimated humpback whales exposures to determine 
additional take by Level A harassment (i.e., 0.15 * 32 exposures = 4.80 
takes, rounded up to 5 takes). The total proposed take by Level A 
harassment was then calculated as the take originally proposed and 
requested by the DOT&PF plus the additional take calculated by NMFS to 
account for the larger Level A harassment zones estimated to result 
from DTH activities (i.e., 4 + 5), for a total of 9 takes by Level A 
harassment. Takes by Level B harassment were calculated as the number 
of estimated humpback whale exposures minus the proposed amount of take 
by Level A harassment (i.e., 32-9). Therefore, NMFS proposes to 
authorize 9 takes by Level A harassment and 23 takes by Level B 
harassment for humpback whales, for a total of 32 takes. Given that 
approximately 2.4 percent of humpback whales in southeast Alaska are 
members of the Mexico DPS, NMFS assumes that one of the proposed take 
by Level B harassment may be attributed to a humpback whale from the 
Mexico DPS (32 * 2.4 percent = 0.77, rounded up to 1 take). All other 
takes by Level B harassment and all takes by Level A harassment (i.e., 
31) are assumed to be attributed to humpback whales from the Hawaii 
DPS.

Minke Whale

    Minke whale abundance throughout southeast Alaska is low, and 
anecdotal reports have not included minke whales near the proposed 
project area. However, minke whales are distributed throughout a wide 
variety of habitats and have been observed elsewhere in southeast 
Alaska; therefore, this species could occur near the proposed project 
area. NMFS has previously estimated that three individual minke whales 
could occur near Metlakatla every 4 months during a similar activity 
(86 FR 43190, August 6, 2021). Therefore, DOT&PF conservatively 
estimated that up to three minke whales may be exposed to project-
related underwater noise during the proposed pile installation and 
removal activities.
    DOT&PF's largest estimated Level A harassment zone for minke whales 
was 504 m (see Tables 6-4 and 6-5 in the DOT&PF's application). Due to 
the low likelihood of minke whale occurrence near the proposed project 
site, the DOT&PF did not request any takes by Level A harassment for 
this species. However, the maximum Level A harassment isopleth 
estimated by NMFS for minke whales is 1,435 m. The largest practicable 
shutdown zone that the DOT&PF states it can implement for minke whales 
during this project is 1,000 m (described below in the Proposed 
Mitigation section), which is smaller than the Level A harassment 
isopleths estimated by NMFS to result from 300 or more minutes of 20- 
and 24-inch (50.8- and 60.96-cm) DTH rock socket installation. To 
account for this difference and the increased possibility of minke 
whales occurring outside of the shutdown zone and within the Level A 
harassment zone long enough to incur PTS, NMFS proposes to add takes by 
Level A harassment, compared with the DOT&PF's request.
    NMFS calculated takes by Level A harassment by determining the 
ratio of the largest Level A harassment area for 20- and 24-inch (50.8- 
and 60.69-cm)

[[Page 45799]]

DTH activities (i.e., 2.01 km\2\ for a Level A harassment distance of 
1,435 m) minus the area of the proposed shutdown zone for minke whales 
(i.e., 1.34 km\2\ for a shutdown zone distance of 1,000 m) to the area 
of the Level B harassment isopleth (4.34 km\2\) for a Level B 
harassment distance of 5,162 m) (i.e., (2.01 km\2\-1.34 km\2\)/4.34 
km\2\ = 0.15). We then multiplied this ratio by the total number of 
estimated minke whales exposures to determine take by Level A 
harassment (i.e., 0.15 * 3 exposures = 0.45 takes, rounded up to 1 take 
by Level A harassment). Takes by Level B harassment were calculated as 
the number of estimated minke whale exposures minus the proposed amount 
of take by Level A harassment (i.e., 3-1). Therefore, NMFS proposes to 
authorize one take by Level A harassment and two takes by Level B 
harassment for minke whales, for a total of three takes.
    In summary, the total amount of Level A harassment and Level B 
harassment authorized for each marine mammal stock is presented in 
Table 8.

            Table 8--Amount of Take as a Percentage of Stock Abundance, by Stock and Harassment Type
----------------------------------------------------------------------------------------------------------------
                                                                         Authorized take
               Species                     Stock or DPS      ---------------------------------------  Percent of
                                                                Level A      Level B       Total        stock
----------------------------------------------------------------------------------------------------------------
Steller sea lion....................  Eastern...............            0          240          240         0.56
Harbor seals........................  Dixon/Cape Decision...           78          130          208         0.89
Northern elephant seals.............  CA Breeding...........            1            3            4        <0.01
Harbor porpoises....................  Southeast Alaska......           12           40           52     \1\ 0.47
Dall's porpoises....................  Alaska................           15           15           30     \2\ 0.23
Pacific white-sided dolphins........  N Pacific.............            0           92           92         0.34
Killer whales.......................  Eastern North Pacific             0           15           15     \3\ 0.78
                                       Alaska Resident.
                                      Eastern Northern                                                  \3\ 4.97
                                       Pacific Northern
                                       Resident.
                                      West Coast Transient..                                            \3\ 4.30
Humpback whales.....................  Central N Pacific.....            9           23           32         0.32
Minke whales........................  Alaska................            1            2            3  ...........
----------------------------------------------------------------------------------------------------------------
\1\ NMFS does not have an official abundance estimate for this stock; therefore, this percentage is based off of
  the most recent abundance estimate for this stock (11,146; Hobbs and Waite, 2010).
\2\ NMFS does not have an official abundance estimate for this stock; therefore, this percentage is based off of
  the minimum population estimate for this stock (13,110; Muto et al., 2022).
\3\ NMFS conservatively assumes that all 15 takes occur to each stock.

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 (latter not applicable for this action). 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. 
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.
    The DOT&PF must employ the following standard mitigation measures, 
as included in the proposed IHA:
     Ensure that construction supervisors and crews, the 
monitoring team and relevant DOT&PF staff are trained prior to the 
start of all pile driving and DTH activity, so that responsibilities, 
communication procedures, monitoring protocols, and operational 
procedures are clearly understood. New personnel joining during the 
project must be trained prior to commencing work;
     Avoid direct physical interaction with marine mammals 
during construction activity. If a marine mammal comes within 10 m of 
such activity, operations shall cease. Should a marine mammal come 
within 10 m of a vessel in transit, the boat operator would reduce 
vessel speed to the minimum level required to maintain steerage and 
safe working conditions. If human safety is at risk, the in-water 
activity will be allowed to continue until it is safe to stop;
     Employ PSOs and establish monitoring locations as 
described in Section 5 of the IHA. The DOT&PF must monitor the project 
area to the maximum extent possible based on the required number of 
PSOs, required monitoring locations, and environmental conditions. For 
all pile driving and DTH activities at least two PSOs must be used;
     For all pile driving/removal activities, a minimum 30 m 
shutdown zone must be established. The purpose of a shutdown zone is 
generally to define an area within which shutdown of activity would 
occur upon sighting of a marine mammal (or in anticipation of an animal 
entering the defined area). Shutdown zones will vary based on the type 
of driving/removal activity type and by marine mammal hearing group 
(see Table 9). Here, shutdown zones are larger than or equivalent to 
the calculated Level A harassment isopleths shown in Table 7, except 
when indicated due to practicability and effectiveness concerns. These 
concerns include the limited viewpoints available

[[Page 45800]]

to station PSOs along Sukkwan Strait, the presence of landmasses that 
may obstruct viewpoints, and decreased effectiveness in sighting marine 
mammals at increased distances. Further, shutdown zones at greater 
distances than proposed in Table 9 would likely result in the DOT&PFs 
activities being shut down more frequently than is practicable for them 
to maintain their project schedule. Note the shutdown zones for DTH 
activity proposed in this notice differ from those proposed by the 
DOT&PF (see Table 6-5 of their application) based on the increased 
Level A harassment isopleth estimates resulting from NMFS' analysis 
(see detailed discussion in the Estimated Take section);

                                               Table 9--Proposed Shutdown Zones During Project Activities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                Shutdown zone (m)
            Activity                   Pile size         Minutes (min) or    Piles per  ----------------------------------------------------------------
                                                         strikes per pile       day           LF           MF           HF           PW           OW
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vibratory Installation..........  20- and 24-inch....  <=30 min...........         <=10           30           30           30           30           30
Vibratory Removal...............  16- and 24-inch....  30 min.............            2           30           30           30           30           30
Impact Installation.............  20-inch............  50 strikes.........            1           50           30           60           30           30
                                                       50 strikes.........            2           80           30           90       \1\ 40           30
                                  24-inch............  50 strikes.........            1           70           30           80           40           30
                                                       50 strikes.........            2      \1\ 100           30          120           60           30
DTH (Rock Socket)...............  20- and 24-inch....  60 min.............            1          360           30          430          200           30
                                                       120 min............            1          570           30      \2\ 500          310           30
                                                       180 min............            1          750           30      \2\ 500          400           30
                                                       240 min............            1        1,000           40      \2\ 500      \2\ 400           40
                                                       300 min............            1    \2\ 1,000           40      \2\ 500      \2\ 400           50
                                                       360 min............            1    \2\ 1,000           50      \2\ 500      \2\ 400           50
                                                       420 min............            1    \2\ 1,000           50      \2\ 500      \2\ 400           60
                                                       480 min............            1    \2\ 1,000           60      \2\ 500      \2\ 400           60
DTH (Tension Anchor)............  8-inch.............  60 min.............            1           40           30           50           30           30
                                                       120 min............            1           60           30           70           40           30
                                                       180 min............            1           80           30           90       \1\ 40           30
                                                       240 min............            1          100           30          110           30           30
                                                       300 min............            1          110           30          130           60           30
                                                       360 min............            1          120           30          150           70           30
                                                       420 min............            1          140           30          160           80           30
                                                       480 min............            1          150           30          180           80           30
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ The proposed shutdown zone is equivalent to the Level A harassment distance.
\2\ The proposed shutdown is smaller than the Level A harassment distance.

     DOT&PF anticipates that the maximum number of piles to be 
installed and or the daily duration of pile driving or DTH use may vary 
significantly, with large differences in maximum zone sizes possible 
depending on the work planned for a given day (Table 7). Given this 
uncertainty, DOT&PF will utilize a tiered system to identify and 
monitor the appropriate Level A harassment zones and shutdown zones on 
a daily basis, based on the maximum expected number of piles to be 
installed (impact or vibratory pile driving) or the maximum expected 
DTH duration for each day. At the start of each work day, DOT&PF will 
determine the maximum scenario for that day (according to the defined 
duration intervals in Tables 7 and 9), which will determine the 
appropriate Level A harassment isopleth and associated shutdown zone 
for that day. This Level A harassment zone (Table 7) and associated 
shutdown zone (Table 9) must be observed by PSO(s) for the entire work 
day, regardless of whether DOT&PF ultimately meets the anticipated 
scenario parameters for that day;
     Marine mammals observed anywhere within visual range of 
the PSO will be tracked relative to construction activities. If a 
marine mammal is observed entering or within the shutdown zones 
indicated in Table 9, pile driving or DTH activities must be delayed or 
halted. If pile driving or DTH activities are delayed or halted due to 
the presence of a marine mammal, the activity may not commence or 
resume until either the animal has voluntarily exited and been visually 
confirmed beyond the shutdown zone (Table 9) or 15 minutes have passed 
without re-detection of the animal;
     Monitoring must take place from 30 minutes prior to 
initiation of pile driving (i.e., pre-clearance monitoring) through 30 
minutes post-completion of pile driving or DTH activity;
     Pre-start clearance monitoring must be conducted during 
periods of visibility sufficient for the lead PSO to determine that the 
shutdown zones indicated in Table 9 are clear of marine mammals. Pile 
driving may commence following 30 minutes of observation when the 
determination is made that the shutdown zones are clear of marine 
mammals;
     The DOT&PF must use soft start techniques when impact pile 
driving. Soft start requires contractors to provide an initial set of 
three strikes at reduced energy, followed by a 30-second waiting 
period, then two subsequent reduced energy strike sets. A soft start 
must be implemented at the start of each day's impact pile driving and 
at any time following cessation of impact pile driving for a period of 
30 minutes or longer. Soft starts will not be used for vibratory pile 
installation and removal or for DTH activities. PSOs shall begin 
observing for marine mammals 30 minutes before ``soft start'' or in-
water pile installation or removal begins;
     Pile driving activity must be halted upon observation of 
either a species for which incidental take is not authorized or a 
species for which incidental take has been authorized but the 
authorized number of takes has been met, entering or within the 
harassment zone;
    Based on our evaluation of the applicant's proposed measures, as 
well as other measures considered by NMFS, 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, 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

[[Page 45801]]

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 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.

Visual Monitoring

    Monitoring must be conducted by qualified, NMFS-approved PSOs, in 
accordance with the following:
     PSOs must be independent of the activity contractor (e.g., 
employed by a subcontractor) and have no other assigned tasks during 
monitoring periods. At least one PSO must have prior experience 
performing the duties of a PSO during construction activity pursuant to 
a NMFS-issued IHA or Letter of Concurrence. Other PSOs may substitute 
other relevant experience, education (degree in biological science or 
related field), or training for prior experience performing the duties 
of a. PSOs must be approved by NMFS prior to beginning any activity 
subject to these IHAs;
     DOT&PF must employ at least two PSOs during all pile 
driving and DTH activities. A minimum of one PSO must be assigned to 
the active pile driving or DTH location to monitor for marine mammals 
and implement shutdown/delay procedures when applicable by calling for 
the shutdown to the hammer operator. At least one additional PSO is 
also required, and should be placed at the best practical vantage 
point(s) to ensure that the shutdown zones are fully monitored and as 
much as the Level B harassment zones are monitored as practicable; 
though the observation points may vary depending on the construction 
activity and location of the piles;
     Where a team of three or more PSOs is required, a lead 
observer or monitoring coordinator must be designated. The lead 
observer must have prior experience performing the duties of a PSO 
during construction activity pursuant to a NMFS-issued incidental take 
authorization;
     PSOs would use a hand-held GPS device, rangefinder, or 
reticle binoculars to verify the required monitoring distance from the 
project site;
     PSOs must record all observations of marine mammals, 
regardless of distance from the pile being driven. PSOs shall document 
any behavioral reactions in concert with distance from piles being 
driven or removed;
     PSOs must have the following additional qualifications:
     Ability to conduct field observations and collect data 
according to assigned protocols;
     Experience or training in the field identification of 
marine mammals, including the identification of behaviors;
     Sufficient training, orientation, or experience with the 
construction operation to provide for personal safety during 
observations;
     Writing skills sufficient to record required information 
including but not limited to the number and species of marine mammals 
observed; dates and times when in-water construction activities were 
conducted; dates, times, and reason for implementation of mitigation 
(or why mitigation was not implemented when required); and marine 
mammal behavior; and
     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.

Reporting

    A draft marine mammal monitoring report would be submitted to NMFS 
within 90 days after the completion of pile driving and DTH activities, 
or 60 days prior to a requested date of issuance of any future IHAs for 
projects at the same location, whichever comes first. The reports would 
include an overall description of work completed, a narrative regarding 
marine mammal sightings, and associated PSO data sheets. Specifically, 
the reports must include:
     Dates and times (begin and end) of all marine mammal 
monitoring;
     Construction activities occurring during each daily 
observation period, including the number and type of piles driven or 
removed and by what method (i.e., impact, vibratory, or DTH) and the 
total equipment duration for vibratory installation, removal and DTH 
for each pile or total number of strikes for each pile (impact 
driving);
     PSO locations during marine mammal monitoring;
     Environmental conditions during monitoring periods (at 
beginning and end of PSO shift and whenever conditions change 
significantly), including Beaufort sea state and any other relevant 
weather conditions including cloud cover, fog, sun glare, and overall 
visibility to the horizon, and estimated observable distance;
     Upon observation of a marine mammal, the following 
information: name of PSO who sighted the animal(s) and PSO location and 
activity at time of sighting; time of sighting; 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; distance and bearing of each 
marine mammal observed relative to the pile being driven for each 
sighting (if pile driving was occurring at time of sighting); estimated 
number of animals (minimum, maximum, and best estimate); estimated 
number of animals by cohort (adults, juveniles, neonates, group 
composition, sex class, etc.); animal's closest point of approach and 
estimated time spent within the harassment zone; description of any 
marine mammal behavioral observations (e.g., observed behaviors such as 
feeding or traveling), including an assessment of behavioral responses 
thought to have resulted from the activity (e.g., no

[[Page 45802]]

response or changes in behavioral state such as ceasing feeding, 
changing direction, flushing, or breaching);
     Number of marine mammals detected within the harassment 
zones and shutdown zones, by species;
     Detailed information about any implementation of any 
mitigation triggered (e.g., shutdowns and 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 
final reports would constitute the final reports. If comments are 
received, a final report addressing NMFS comments must be submitted 
within 30 days after receipt of comments.

Reporting Injured or Dead Marine Mammals

    In the event that personnel involved in the construction activities 
discover an injured or dead marine mammal, the IHA-holder must 
immediately cease the specified activities and report the incident to 
the Office of Protected Resources, NMFS 
([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, the DOT&PF must 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 terms of the 
IHAs. The DOT&PF must not resume their activities until notified by 
NMFS. The report must 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 majority of our analysis applies to all 
the species listed in Table 2, given that many of the anticipated 
effects of the DOT&PFs construction activities on different marine 
mammal stocks are expected to be relatively similar in nature. Where 
there are meaningful differences between species or stocks, or groups 
of species, in anticipated individual responses to activities, impact 
of expected take on the population due to differences in population 
status, or impacts on habitat, they are described independently in the 
analysis below.
    Pile driving and DTH activities associated with the project, 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 and, for some species Level A 
harassment, from underwater sounds generated by pile driving and DTH 
systems. Potential takes could occur if marine mammals are present in 
zones ensonified above the thresholds for Level B harassment or Level A 
harassment, identified above, while activities are underway.
    The DOT&PF's proposed activities and associated impacts will occur 
within a limited, confined area of the stocks' range. The work would 
occur in the vicinity of the seaplane dock immediately adjacent to 
Hydaburg and sound from the proposed activities would be blocked by 
Sukkwan Island, Spook Island, Mushroom Island, and the coastline along 
Prince of Wales Island both southeast and northwest of the proposed 
project site (see Figure 1-2 in the DOT&PF's application) to a maximum 
distance of 5,162 m and area of 4.34 km\2\. The intensity and duration 
of take by Level A harassment and Level B harassment will be minimized 
through use of mitigation measures described herein. Further the amount 
of take authorized is small when compared to stock abundance. In 
addition, NMFS does not anticipate that serious injury or mortality 
will occur as a result of the DOT&PF's planned activity given the 
nature of the activity, even in the absence of required mitigation.
    Exposures to elevated sound levels produced during pile driving and 
DTH may cause behavioral disturbance of some individuals. Behavioral 
responses of marine mammals to pile driving, pile removal, and DTH 
systems at the proposed project site 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, will likely be limited to reactions such as increased 
swimming speeds, increased surfacing time, or decreased foraging (if 
such activity were occurring) (e.g., Thorson and Reyff, 2006). 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 display other mild responses that are not 
observable such as changes in vocalization patterns or increased haul 
out time (Thorson and Reyff, 2006). Additionally, some of the species 
present in the region will only be present temporarily based on 
seasonal patterns or during transit between other habitats. These 
temporarily present species will be exposed to even smaller periods of 
noise-generating activity, further decreasing the impacts. Most likely, 
individual animals will simply move away from the sound source and be 
temporarily displaced from the area, although even this reaction has 
been observed primarily only in association with impact pile driving. 
Because DOT&PF's activities could occur during any season, takes may 
occur during important feeding times. The project area though 
represents a small portion of available foraging habitat and impacts

[[Page 45803]]

on marine mammal feeding for all species should be minimal.
    The activities analyzed here are similar to numerous other 
construction activities conducted along southeastern Alaska (e.g., 86 
FR 43190, August 6, 2021; 87 FR 15387, March 18, 2022), which have 
taken place with no known long-term adverse consequences from 
behavioral harassment. These reactions and behavioral changes are 
expected to subside quickly when the exposures cease and, therefore, no 
such long-term adverse consequences should be expected (e.g., Graham et 
al., 2017). The intensity of Level B harassment events will be 
minimized through use of mitigation measures described herein, which 
were not quantitatively factored into the take estimates. The DOT&PF 
will use at least two PSOs stationed strategically to increase 
detectability of marine mammals during in-water pile driving and DTH 
activities, enabling a high rate of success in implementation of 
shutdowns to avoid or minimize injury for most species. Further, given 
the absence of any major rookeries and haulouts within the estimated 
harassment zones, 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.
    As stated in the mitigation section, DOT&PF will implement shutdown 
zones that equal or exceed many of the Level A harassment isopleths 
shown in Table 8. Take by Level A harassment is proposed for 
authorization for some species (harbor seals, northern elephant seals, 
harbor porpoises, Dall's porpoises, humpback whales, and minke whales) 
to account for the potential that an animal could enter and remain 
within the Level A harassment zone for a duration long enough to incur 
PTS. Any take by Level A harassment is expected to arise from, at most, 
a small degree of PTS because animals would need to be exposed to 
higher levels and/or longer duration than are expected to occur here in 
order to incur any more than a small degree of PTS.
    Due to the levels and durations of likely exposure, animals that 
experience PTS will likely only receive slight PTS, i.e., minor 
degradation of hearing capabilities within regions of hearing that 
align most completely with the frequency range of the energy produced 
by DOT&PF's proposed in-water construction activities (i.e., the low-
frequency region below 2 kHz), not severe hearing impairment or 
impairment in the reigns of greatest hearing sensitivity. If hearing 
impairment does occur, it is most likely that the affected animal will 
lose a few dBs in its hearing sensitivity, which in most cases is not 
likely to meaningfully affect its ability to forage and communicate 
with conspecifics. There are no data to suggest that a single instance 
in which an animal accrues PTS (or TTS) and is subject to behavioral 
disturbance would result in impacts to reproduction or survival. If PTS 
were to occur, it would be at a lower level likely to accrue to a 
relatively small portion of the population by being a stationary 
activity in one particular location. Additionally, and as noted 
previously, some subset of the individuals that are behaviorally 
harassed could also simultaneously incur some small degree of TTS for a 
short duration of time. Because of the small degree anticipated, 
though, any PTS or TTS potentially incurred here is not expected to 
adversely impact individual fitness, let alone annual rates of 
recruitment or survival.
    Theoretically, repeated, sequential exposure to pile driving noise 
over a long duration could result in more severe impacts to individuals 
that could affect a population. However, the limited number of non-
consecutive pile driving days for this project and the absence of any 
pinniped haulouts or other known cetacean residency patterns in the 
proposed action area means that these types of impacts are not 
anticipated.
    For all species except humpback whales, there are no known BIAs 
near the project zone that will be impacted by DOT&PF's planned 
activities. For humpback whales, the whole of southeast Alaska is a 
seasonal feeding BIA from May through September (Wild et al., 2023), 
however, Sukkwan Strait is a small passageway and represents a very 
small portion of the total available habitat. Also, while southeast 
Alaska is considered an important area for feeding humpback during this 
time, it is not currently designated as critical habitat for humpback 
whales (86 FR 21082, April 21, 2021).
    The project is also not expected to have significant adverse 
effects on any marine mammal habitat. The project activities will not 
modify existing marine mammal habitat since the project will occur 
within the same footprint as existing marine infrastructure. Impacts to 
the immediate substrate are anticipated, but these would be limited to 
minor, temporary suspension of sediments, which could impact water 
quality and visibility for a short amount of time but which would not 
be expected to have any effects on individual marine mammals.
    In addition, impacts to marine mammal prey species are 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, the area impacted by 
the project is very small compared to the available surrounding 
habitat, and does not include habitat of particular importance. The 
most likely impact to prey will be temporary behavioral avoidance of 
the immediate area. During construction activities, it is expected that 
some fish and marine mammals would temporarily leave the area of 
disturbance, thus impacting marine mammals' foraging opportunities in a 
limited portion of the foraging range. But, because of the relatively 
small area of the habitat that may be affected, and lack of any habitat 
of particular importance, the impacts to marine mammal habitat are not 
expected to cause significant or long-term negative consequences.
    In summary and as described above, the following factors primarily 
support our preliminary determination that the impacts resulting from 
this activity are not expected to adversely affect any of the species 
or stocks through effects on annual rates of recruitment or survival:
     No serious injury or mortality is anticipated or 
authorized;
     Level A harassment proposed for authorization is expected 
to be of a lower degree that would not impact the fitness of any 
animals;
     Anticipated incidents of Level B harassment consist of, at 
worst, temporary modifications in behavior;
     The required mitigation measures (i.e., soft starts, 
shutdown zones) are expected to be effective in reducing the effects of 
the specified activity by minimizing the numbers of marine mammals 
exposed to injurious levels of sound, and by ensuring that any take by 
Level A harassment is, at most, a small degree of PTS;
     The intensity of anticipated takes by Level B harassment 
is low for all stocks and will not be of a duration or intensity 
expected to result in impacts on reproduction or survival;
     Minimal impacts to marine mammal habitat/prey are 
expected;
     The only known area of specific biological importance 
covers a broad area of southeast Alaska for humpback whales, and the 
project area is a very small portion of that BIA. No other known areas 
of particular biological importance to any of the affected species or 
stocks are impacted by the activity, including ESA-designated critical 
habitat;
     The project area represents a very small portion of the 
available foraging area for all potentially impacted marine

[[Page 45804]]

mammal species and stocks and anticipated habitat impacts are minor; 
and
     Monitoring reports from similar work in southeast Alaska 
have documented little to no effect on individuals of the same species 
impacted by the specified activities.
    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 small numbers of incidental take may be 
authorized under section 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. Additionally, other 
qualitative factors may be considered in the analysis, such as the 
temporal or spatial scale of the activities.
    The maximum annual amount of take NMFS proposes to authorize for 
five marine mammal stocks is below one-third of the estimated stock 
abundance for all species (in fact, take of individuals is less than 
five percent of the abundance of all affected stocks, see Table 8). The 
number of animals proposed for authorization to be taken from these 
stocks would be considered small relative to the relevant stock's 
abundances even if each estimated take occurred to a new individual. 
Some individuals may return multiple times in a day, but PSOs would 
count them as separate individuals if they cannot be individually 
identified.
    The Alaska stock of Dall's porpoise has no official NMFS abundance 
estimate for this area, as the most recent estimate is greater than 
eight years old. Abundance estimates for Dall's porpoise in inland 
waters of southeast Alaska were calculated from 19 line-transect vessel 
surveys from 1991 to 2012 (Jefferson et al., 2019). Abundance across 
the whole period was estimated at 5,381 (CV = 0.25), 2,680 (CV = 0.20), 
and 1,637 (CV = 0.23) in the spring, summer, and fall, respectively 
(Jefferson et al., 2019). The minimum population estimate 
(NMIN) for the entire Alaska stock is assumed to correspond 
to the point estimate of a 2015 vessel-based abundance computed by Rone 
et al. (2017) in the Gulf of Alaska (N = 13,110; CV = 0.22) (Muto et 
al., 2022); however, the study area of this survey corresponds to a 
small fraction of the range of the stock and, thus it is reasonable to 
assume that the stock size is equal to or greater than that estimate 
(Muto et al., 2022). Therefore, the 22 takes of this stock proposed for 
authorization clearly represent small numbers of this stock.
    Likewise, the Southeast Alaska stock of harbor porpoise has no 
official NMFS abundance estimate as the most recent estimate is greater 
than 8 years old. Aerial surveys of this stock were conducted in June 
and July 1997 and resulted in an abundance estimate of 11,146 harbor 
porpoise in the coastal and inland waters of southeast Alaska (Hobbs 
and Waite, 2010). The minimum population estimate for this stock is 
1,057 individuals; however, this estimate represents some portion of 
the total number of animals in the stock and is not corrected for 
animals missed on the survey track line for which the estimate is 
based. Therefore, this estimate is negatively biased (Muto et al, 
2022). Regardless, the 52 takes of this stock proposed for 
authorization represent small numbers of this stock.
    There is no current or historical estimate of the Alaska minke 
whale stock, but minke whale abundance has been estimated to be over 
1,000 whales in portions of Alaska (Muto et al., 2022) so the 3 takes 
proposed for authorization represent small numbers of this stock. 
Additionally, the range of the Alaska stock of minke whales is 
extensive, stretching from the Canadian Pacific coast to the Chukchi 
Sea, and DOT&PF's project area impacts a small portion of this range. 
Therefore, the three takes of minke whale proposed for authorization is 
small relative to estimated survey abundance, even if each proposed 
take occurred to a new individual.
    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.
    Alaska Natives have traditionally harvested subsistence resources 
in southeast Alaska for many hundreds of years, particularly large 
terrestrial mammals, marine mammals, salmon, and other fish (Alaska 
Department of Fish and Game (ADF&G), 1997). Harbor seals and sea otters 
are reported to be the marine mammal species most regularly harvested 
for subsistence in the waters surrounding Hydaburg (NOAA, 2013). An 
estimated 14.4 harbor seals were harvested by Hydaburg residents every 
year from 2000 through 2008 (ADF&G, 2009a, 2009b). Hunting usually 
occurs in the late fall and winter (ADF&G, 2009a). The ADF&G has not 
recorded harvest of cetaceans from Hydaburg (ADF&G, 2022). There are no 
subsistence activities near the proposed project that target humpback 
whales, and subsistence hunters rarely target Steller sea lions near 
the proposed project area.
    Approximately 93 percent of Hydaburg residents identified as Alaska 
Native (Sill and Koster, 2017) in 2012. Nearly half of all households 
harvested wild resources in 2012, with nearly all Hydaburg households 
using salmon, non-salmon fish, marine invertebrates, and vegetation 
(Sill and Koster, 2017). Only six percent of Hydaburg households 
participated in the hunting, use, or receiving of harbor seals in 2012, 
whereas up to eight percent used sea otters (Sill and Koster, 2017). 
Based on data from 2012, marine mammals account for approximately one 
percent (1,666 pounds or 756 kg) of all subsistence harvest in Hydaburg 
(Sill and Koster, 2017).
    All proposed pile driving and DTH activities will take place in the 
vicinity of seaplane dock immediately adjacent

[[Page 45805]]

to Hydaburg where subsistence activities do not generally occur. The 
proposed project will not have an adverse impact on the availability of 
marine mammals for subsistence use at locations farther away. Some 
minor, short-term disturbance of the harbor seals or sea otters could 
occur, but this is not likely to have any measurable effect on 
subsistence harvest activities in the region. No changes to 
availability of subsistence resources will result from the specified 
activities. Additionally, DOT&PF is working with Haida Elders on the 
project to raise awareness and collaborate on the project within the 
local community.
    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 
DOT&PF's proposed activities.

Endangered Species Act

    Section 7(a)(2) of the 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 NMFS' Alaska Regional Office (AKRO).
    NMFS is proposing to authorize take of the Central North Pacific 
stock of humpback whales, of which a portion belong to the Mexico DPS 
of humpback whales, which are ESA-listed. The Permits and Conservation 
Division has requested initiation of section 7 consultation with the 
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 
issue an IHA to the DOT&PF for conducting pile driving and DTH 
activities during of the Hydaburg Seaplane Base Refurbishment Project 
in Hydaburg, Alaska beginning in September 2023, provided the 
previously mentioned mitigation, monitoring, and reporting requirements 
are incorporated. A draft of the proposed IHA can be found at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities.

Request for Public Comments

    We request comment on our analyses, the proposed authorization, and 
any other aspect of this notice of proposed IHA for the proposed 
construction 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 request for this 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 
Activities section of this notice is planned, or (2) the activities as 
described in the Description of Proposed Activities 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); 
and
    (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 10, 2023.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2023-14939 Filed 7-14-23; 8:45 am]
BILLING CODE 3510-22-P