Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Geophysical Surveys of the Guerrero Gap in the Eastern Tropical Pacific, 1992-2025 [2022-00455]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 87, Number 8 (Wednesday, January 12, 2022)]
[Notices]
[Pages 1992-2025]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-00455]



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Vol. 87

Wednesday,

No. 8

January 12, 2022

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 Geophysical Surveys of the Guerrero Gap in 
the Eastern Tropical Pacific; Notice

Federal Register / Vol. 87 , No. 8 / Wednesday, January 12, 2022 / 
Notices

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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XB628]


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to Geophysical Surveys of the Guerrero 
Gap in the Eastern Tropical Pacific

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 Lamont-Doherty Earth 
Observatory (L-DEO) for authorization to take marine mammals incidental 
to geophysical surveys of the Guerrero Gap off the coast of Mexico in 
the Eastern Tropical Pacific. 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, one-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 February 
11, 2022.

ADDRESSES: Comments should be addressed to Jolie Harrison, Chief, 
Permits and Conservation Division, Office of Protected Resources, 
National Marine Fisheries Service submitted via email to 
[email protected].
    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 
www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act 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: Amy Fowler, Office of Protected 
Resources, NMFS, (301) 427-8401. 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/permit/incidental-take-authorizations-under-marine-mammal-protection-act. In case of problems accessing these 
documents, please call the contact listed above.

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 incidental harassment authorization 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.
    Accordingly, NMFS plans to adopt the National Science Foundation's 
(NSF's) Environmental Assessment (EA), provided our independent 
evaluation of the document finds that it includes adequate information 
analyzing the effects on the human environment of issuing the IHA. The 
NSF's EA is available at https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act.
    We will review all comments submitted in response to this notice 
prior to concluding our NEPA process or making a final decision on the 
IHA request.

Summary of Request

    On August 21, 2021, NMFS received a request from L-DEO for an IHA 
to take marine mammals incidental to geophysical surveys of the 
Guerrero Gap off the coast of Mexico in the Eastern Tropical Pacific 
(ETP). The application was deemed adequate and complete on December 14, 
2021. L-DEO's request is for take of a small number of 30 species of 
marine mammals by Level B harassment and, for two of those species, by 
Level A harassment. Neither L-DEO nor NMFS expects serious injury or 
mortality to result from this activity and, therefore, an IHA is 
appropriate.

Description of Proposed Activity

Overview

    Researchers from L-DEO, University of Texas Institute of Geophysics 
(UTIG), and Northern Arizona University (NAU), with funding from the 
NSF, and in collaboration with researchers from the National Autonomous 
University of Mexico (Universidad Nacional Autonoma de Mexico or UNAM) 
and Kyoto University, propose to conduct high-energy seismic surveys 
from the research vessel (R/V) Marcus G. Langseth (Langseth) in and 
around the Guerrero Gap off western Mexico, in the ETP. The proposed 
study would use two-dimensional (2-D) seismic surveying to quantify 
incoming plate hydration and examine the role of fluids on megathrust 
slip behavior in and around the Guerrero Gap of the Middle America 
Trench. This is one of the best-known examples in the world of along-
strike variations in slip behavior of the plate boundary. L-DEO 
proposes to conduct two different methods of seismic acquisition, 
multi-channel seismic (MCS) using a hydrophone streamer and refraction 
surveys using ocean bottom seismometers (OBSs). The

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surveys would use a 36-airgun towed array with a total discharge volume 
of ~6600 cubic inches (in\3\) as an acoustic source, acquiring return 
signals using both a towed streamer as well as OBSs. The majority of 
the proposed 2-D seismic surveys would occur within the Exclusive 
Economic Zone (EEZ) of Mexico, including territorial seas, and a small 
portion would occur in International Waters.

Dates and Duration

    The proposed research cruise would be expected to last for 48 days, 
including approximately 20 days of seismic survey operations, 3 days of 
transit to and from the survey area, 19 days for equipment deployment/
recovery, and 6 days of contingency time for poor weather, etc. The R/V 
Langseth would likely leave out of and return to port in Manzanillo, 
Mexico, during spring 2022. The proposed IHA would be valid from March 
1, 2022 through February 28, 2023.

Specific Geographic Region

    The proposed surveys would occur within the area of approximately 
14-18.5[deg]N and approximately 99-105[deg]W. Representative survey 
tracklines are shown in Figure 1. Some deviation in actual track lines, 
including the order of survey operations, could be necessary for 
reasons such as science drivers, poor data quality, inclement weather, 
or mechanical issues with the research vessel and/or equipment. The 
majority of the proposed surveys would occur within the EEZ of Mexico, 
including territorial seas, and a small portion would occur in 
International Waters. The surveys would occur in waters up to 5,560 
meters (m) deep. Most of the survey effort (94 percent) would occur in 
deep water (>1000 m), and 6 percent would occur in intermediate water 
(100-1000 m deep); no effort would occur in shallow water (<100 m 
deep). A total of 3,600 kilometers (km) of transect lines would be 
surveyed (2,230 km of 2-D MCS reflection data and 1,370 km of OBS 
refraction data).
    Approximately 6 percent of the total survey effort would occur in 
Mexican territorial waters. Note that the MMPA does not apply in 
Mexican territorial waters. L-DEO is subject only to Mexican law in 
conducting that portion of the survey. However, NMFS has calculated the 
expected level of incidental take in the entire activity area 
(including Mexican territorial waters) as part of the analysis 
supporting our determination under the MMPA that the activity will have 
a negligible impact on the affected species (see Estimated Take and 
Negligible Impact Analysis and Determination).
BILLING CODE 3510-22-P
[GRAPHIC] [TIFF OMITTED] TN12JA22.027


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BILLING CODE 3510-22-C

Detailed Description of Specific Activity

    The procedures to be used for the proposed marine geophysical 
surveys would be similar to those used during previous surveys by L-DEO 
that received incidental take authorizations from NMFS (e.g., 85 FR 
55645; September 9, 2020, 84 FR 35073; July 22, 2019) and would use 
conventional seismic methodology. The survey would involve one source 
vessel, R/V Langseth, which would tow a 36-airgun array with a 
discharge volume of ~6600 in\3\ at a depth of 12 m. The array consists 
of 36 elements, including 20 Bolt 1500LL airguns with volumes of 180 to 
360 in\3\ and 16 Bolt 1900LLX airguns with volumes of 40 to 120 in\3\. 
The airgun array configuration is illustrated in Figure 2-11 of NSF and 
the U.S. Geological Survey's (USGS's) Programmatic Environmental Impact 
Statement (PEIS; NSF-USGS, 2011). (The PEIS is available online at: 
www.nsf.gov/geo/oce/envcomp/usgs-nsf-marine-seismic-research/nsf-usgs-final-eis-oeis-with-appendices.pdf).
    The proposed surveys consist of eight MCS lines, of which six are 
coincident OBS refraction lines that are located perpendicular to the 
margin; these six lines would therefore be acquired twice. 
Approximately 62 percent of the total survey effort would be MCS 
surveys, with the remaining 38 percent using OBSs. There could be 
additional seismic survey operations associated with turns, airgun 
testing, and repeat coverage of any areas where initial data quality is 
sub-standard, and 25 percent has been added to the assumed survey line-
kms to account for this potential. NMFS considers this a conservative 
approach to estimating potential acoustic exposures.
    The vessel speed during seismic survey operations would be ~4.1 
knots (~7.6 km/hour) during MCS reflection surveys and 5 knots (~9.3 
km/hour) during OBS refraction surveys. The airguns would fire at a 
shot interval of 50 m (approximately 24 seconds) during MCS surveys 
with the hydrophone streamer and at a 400-m (155 seconds) interval 
during refraction surveys to OBSs. The receiving system would consist 
of a 15-km long hydrophone streamer and short-period OBSs. As the 
airgun arrays are towed along the survey lines, the OBSs would receive 
and store the returning acoustic signals internally for later analysis, 
and the hydrophone streamer would transfer the data to the on-board 
processing system.
    The seismometers would consist of 33 OBSs, which would be deployed 
at a total of 124 sites. The instruments would be deployed by R/V 
Langseth and spaced 10 or 12 km apart. Following refraction shooting of 
one line, short-period instruments on that line would be recovered, 
serviced, and redeployed on a subsequent refraction line while MCS data 
are acquired. The OBSs have a height and diameter of approximately 1 m 
and an anchor weighing roughly 80 kilograms (kg). OBS sample rate would 
be set at 200 hertz (Hz). All OBSs would be recovered by the end of the 
survey.
    To retrieve OBSs, an acoustic release transponder (pinger) is used 
to interrogate the instrument at a frequency of 8-11 kilohertz (kHz), 
and a response is received at a frequency of 11.5-13 kHz. The burn-wire 
release assembly is then activated, and the instrument is released to 
float to the surface from the anchor which is not retrieved. Take of 
marine mammals is not expected to occur incidental to L-DEO's use of 
OBSs.
    In addition to the operations of the airgun array, a multibeam 
echosounder (MBES), a sub-bottom profiler (SBP), and an Acoustic 
Doppler Current Profiler (ADCP) would be operated from R/V Langseth 
continuously during the seismic surveys, but not during transit to and 
from the survey area. Take of marine mammals is not expected to occur 
incidental to use of the MBES, SBP, or ADCP as, due to these sources' 
characteristics (e.g., narrow downward-directed beam), marine mammals 
would experience no more than one or two brief ping exposures from 
them, if any exposure were to occur. Accordingly, the use of MBES, SBP, 
and ADCP are not analyzed further in this document.
    Proposed mitigation, monitoring, and reporting measures are 
described in detail later in this document (please see Proposed 
Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

    Sections 3 and 4 of the application summarize available information 
regarding status and trends, distribution and habitat preferences, and 
behavior and life history, of the potentially affected species. Brief 
discussions of some species and stocks is presented below. For all 
other species, we refer the reader to the descriptions in L-DEO's IHA 
application, incorporated here by reference, instead of reprinting the 
information. Additional information regarding population trends and 
threats may be found in NMFS's Stock Assessment Reports (SARs; https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments) and more general information about these species 
(e.g., physical and behavioral descriptions) may be found on NMFS's 
website (https://www.fisheries.noaa.gov/find-species).
    Table 1 lists all species or stocks for which take is expected and 
proposed to be authorized for this action, 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. For taxonomy, we follow Committee on 
Taxonomy (2021). 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's SARs). While no 
serious injury or mortality is anticipated or proposed for 
authorization here, PBR and annual serious injury and mortality from 
anthropogenic sources are included here as gross indicators of the 
status of the species 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's stock abundance estimates for most species represent the total 
estimate of individuals within the geographic area, if known, that 
comprises that stock. For some species, this geographic area may extend 
beyond U.S. waters. All managed stocks in this region are assessed in 
NMFS's U.S. Pacific SARs. All values presented in Table 1 are the most 
recent available at the time of publication and are available in the 
2020 SARs (Carretta et al., 2021) and draft 2021 SARs (available online 
at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports). Where available, 
abundance and status information is also presented for marine mammals 
in the Pacific waters of Mexico and/or the greater ETP region. Table 1 
denotes the status of species and stocks under the U.S. MMPA and ESA. 
We note also that the Guadalupe fur seal is classified as ``En peligro 
de extinci[oacute]n'' (in danger of extinction) under the Norma Oficial 
Mexicana NOM-059-SEMARNAT-2010 and all other marine mammal species 
listed in Table 1, with the exception of Longman's beaked whales and 
Deraniyagala's beaked whales, are listed as ``Sujetas a 
protecci[oacute]n especial'' (subject to special protection).

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                                                                   Table 1--Marine Mammals That Could Occur in the Survey Area
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                                                                                                     Stock abundance (CV,
            Common name                Scientific name           Stock         ESA/MMPA  status;      Nmin, most recent             PBR           Annual M/SI\3\   ETP abundance  Mexico Pacific
                                                                              strategic (Y/N) \1\   abundance survey) \2\                                               \4\        abundance \5\
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                                                              Order Cetartiodactyla--Cetacea--Superfamily Mysticeti (baleen whales)
                                                                                Family Balaenopteridae (rorquals)
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Humpback Whale....................  Megaptera              Central N         -, -, Y..............  10,103 (0.3, 7,890,    83...................              26           2,566  ..............
                                     novaeangliae.          Pacific                                  2006).
Minke whale.......................  Balaenoptera           N/A               -, -, N..............  N/A..................  N/A..................             N/A             115  ..............
                                     acutorostrata.
Bryde's whale.....................  Balaenoptera edeni...  Eastern Tropical  -, -, N..............  Unknown (Unknown,      Undetermined.........         Unknown          10,411             649
                                                            Pacific                                  Unknown, N/A).
Sei whale.........................  Balaenoptera borealis  Eastern N         E, D, Y..............  519 (0.4, 374, 2014).  0.75.................           >=0.2               0  ..............
                                                            Pacific
Fin whale.........................  Balaenoptera physalus  N/A               E, D, Y..............  N/A..................  N/A..................             N/A             574             145
Blue whale........................  Balaenoptera musculus  Eastern N         E, D, Y..............  1,898 (0.085, 1,767,   4.1..................          >=19.4           1,415             773
                                                            Pacific                                  2018).
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                                                                Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
                                                                                       Family Physeteridae
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Sperm whale.......................  Physeter               N/A               E, D, Y..............  N/A..................  N/A..................             N/A           4,145            2810
                                     macrocephalus.
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                                                                                         Family Kogiidae
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Dwarf Sperm Whale.................  Kogia sima...........  N/A               N/A..................  N/A..................  N/A..................             N/A      \6\ 11,200  ..............
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                                                                                Family Ziphiidae (beaked whales)
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Cuvier's Beaked Whale.............  Ziphius cavirostris..  N/A               -, -, N..............  N/A..................  N/A..................             N/A      \7\ 20,000      \8\ 68,828
Longman's beaked whale............  Indopacetus pacificus  N/A               -, -, N..............  N/A..................  N/A..................             N/A           1,007  ..............
Blainville's beaked whale.........  Mesoplodon             N/A               -, -, N..............  N/A..................  N/A..................             N/A      \9\ 25,300      \8\ 68,828
                                     densirostris.
Ginkgo-toothed beaked whale.......  M. ginkgodens........  N/A               -, -, N..............  N/A..................  N/A..................             N/A      \9\ 25,300      \8\ 68,828
Deraniyagala's beaked whale.......  M. hotaula...........  N/A               -, -, N..............  N/A..................  N/A..................             N/A      \9\ 25,300      \8\ 68,828
Pygmy beaked whale................  M. peruvianus........  N/A               -, -, N..............  N/A..................  N/A..................             N/A      \9\ 25,300      \8\ 68,828
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                                                                                       Family Delphinidae
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Risso's dolphin...................  Grampus griseus......  N/A               -, -, N..............  N/A..................  N/A..................             N/A         110,457          24,084
Rough-toothed dolphin.............  Steno bredanensis....  N/A               -, -, N..............  N/A..................  N/A..................             N/A         107,663          37,511
Common bottlenose dolphin.........  Tursiops truncatus...  N/A               -, -, N..............  N/A..................  N/A..................             N/A         335,834          61,536
Pantropical spotted dolphin.......  Stenella attenuata...  N/A\10\           -, D, N..............  N/A..................  N/A..................             N/A  \11\ 1,297,091         146,296
Spinner dolphin...................  Stenella longirostris  N/A \10\          -, D, N..............  N/A..................  N/A..................             N/A  \11\ 2,075,871         186,906
Striped dolphin...................  Stenella coeruleoalba  N/A               -, -, N..............  N/A..................  N/A..................             N/A         964,362         128,867
Short-beaked common dolphin.......  Delphinus delphis....  N/A               -, -, N..............  N/A..................  N/A..................             N/A       3,127,203          283196
Fraser's dolphin..................  Lagenodelphis hosei..  N/A               -, -, N..............  N/A..................  N/A..................             N/A     \7\ 289,300  ..............
Short-finned pilot whale..........  Globicephala           N/A               -, -, N..............  N/A..................  N/A..................             N/A    \12\ 589,315           3,348
                                     macrorhynchus.
Killer whale......................  Orcinus orca.........  N/A               -, -, N..............  N/A..................  N/A..................             N/A       \7\ 8,500             852
False killer whale................  Pseudorca crassidens.  N/A               -, -, N..............  N/A..................  N/A..................             N/A      \7\ 39,800
Pygmy killer whale................  Feresa attenuata.....  N/A               -, -, N..............  N/A..................  N/A..................             N/A      \7\ 38,900  ..............
Melon-headed whale................  Peponocephala electra  N/A               -, -, N..............  N/A..................  N/A..................             N/A      \7\ 45,400  ..............
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                                                                             Order Carnivora--Superfamily Pinnipedia
                                                                          Family Otariidae (eared seals and sea lions)
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Guadalupe fur seal................  Arctocephalus          Mexico            T, D, Y..............  34,187 (N/A, 31,019,   1062.................           >=3.8  ..............  ..............
                                     townsendi.                                                      2013).

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California sea lion...............  Zalophus               U.S.              -, -, N..............  257,606 (N/A,233,515,  14011................            >320         105,000  ..............
                                     californianus.                                                  2014).
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\1\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted
  under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under
  the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\2\ NMFS marine mammal stock assessment reports online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports . CV is coefficient of
  variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable.
\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 M/SI
  often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some
  cases.
\4\ From NMFS (2015b) unless otherwise noted.
\5\ Pacific Mexico excluding the Gulf of California (from Gerrodette and Palacios (1996) unless otherwise noted).
\6\ Estimate for ETP is mostly for K. sima but may also include some K. breviceps (Wade and Gerrodette 1993).
\7\ Wade and Gerrodette 1993.
\8\ Abundance for all ziphiids.
\9\ This estimate for the ETP includes all species of the genus Mesoplodon.
\10\ Several stocks of these species, while not classified as such in the U.S. SARs, are considered depleted due to historical interactions with tuna fisheries in the area. Please see below
  for a discussion of these stocks.
\11\ Includes abundance of several stocks added together.
\12\ Based on surveys in 2000 (Gerrodette and Forcada 2002).

    As indicated above, all 30 species (with six managed stocks) in 
Table 1 temporally and spatially co-occur with the activity to the 
degree that take is reasonably likely to occur, and we have proposed 
authorizing it. As the planned survey lines are outside of the U.S. 
EEZ, they do not directly overlap with the defined ranges for most U.S. 
managed stocks (Carretta et al., 2021). For some species (e.g., Bryde's 
whale, Guadalupe fur seal; see Table 1), animals encountered during the 
surveys could be from a defined stock under the MMPA but most marine 
mammals in the survey area do not belong to any defined stock. Species 
that could potentially occur in the proposed research area but are not 
likely to be encountered due to the rarity of their occurrence (i.e., 
are considered extralimital or rare visitors to the coastal waters of 
Mexico in the Eastern Tropical Pacific) are described briefly but 
omitted from further analysis. These generally include species that do 
not normally occur in the area but for which there are one or more 
occurrence records that are considered beyond the normal range of the 
species. These species include the gray whale (Eschrichtius robustus), 
Hubbs' beaked whale (Mesoplodon carlhubbsi), Stejneger's beaked whale 
(M. stejnegeri), Perrin's beaked whale (M. perrini), Baird's beaked 
whale (Berardius bairdii), pygmy sperm whale (Kogia breviceps), long-
finned pilot whale (Globicephala melas), Dall's porpoise (Phocoenoides 
dalli), Pacific white-sided dolphin (Lagenorhynchus obliquidens), and 
northern right whale dolphin (Lissodelphis borealis), which all 
generally occur well north of the proposed survey area (e.g, north of 
the Baja peninsula). Five additional pinniped species are known to 
occur in the ETP but are considered extralimital in the proposed survey 
area: The Gal[aacute]pagos sea lion (Zalophus wollebaeki), 
Gal[aacute]pagos fur seal (Arctocephalus galapagoensis), South American 
fur seal (A. australis), and the South American sea lion (Otaria 
flavescens), which all occur south of the survey area, and the northern 
elephant seal (Mirounga angustirostris) which is found north of the 
survey area.
    Prior to 2016, humpback whales were listed under the ESA as an 
endangered species worldwide. Following a 2015 global status review 
(Bettridge et al., 2015), NMFS delineated 14 distinct population 
segments (DPSs) with different listing statuses (81 FR 62259; September 
8, 2016) pursuant to the ESA. The DPSs that occur in U.S. waters do not 
necessarily equate to the existing stocks designated under the MMPA and 
shown in Table 1. The threatened Mexico DPS and endangered Central 
America DPS may occur within the proposed survey area. However, due to 
the expected timing of the proposed survey (spring), most humpbacks 
from the Mexico DPS will have begun their migration north toward the 
feeding grounds off of the U.S. west coast and are likely to be outside 
of the survey area. Humpbacks from the Central America DPS will likely 
be migrating northward through the survey area at the time of the 
proposed survey. Therefore, we assume that most humpback whales taken 
by the proposed survey activities will be from the Central America DPS.
    The pantropical spotted dolphin is one of the most abundant 
cetaceans and is distributed worldwide in tropical and some subtropical 
waters, between ~40[deg]N and 40[deg]S (Jefferson et al., 2015). In the 
ETP, this species ranges from 25[deg] N off the Baja California 
Peninsula to 17[deg] S, off southern Peru (Perrin and Hohn, 1994). 
There are two forms of pantropical spotted dolphin (Perrin 2018a): 
Coastal (Stenella attenuata graffmani) and offshore (S. a. attenuata), 
both of which could occur within the proposed survey area. Along the 
coast of Latin America, the coastal form typically occurs within 20 km 
from shore (Urb[aacute]n 2008 in Heckel et al., 2020). There are 
currently three recognized stocks of spotted dolphins in the ETP: The 
coastal stock and two offshore stocks--the northeast and the west/south 
stocks (Wade and Gerrodette 1993; Leslie et al., 2019). Much of what is 
known about the pantropical spotted dolphin in the ETP is related to 
the historical tuna purse-seine fishery in that area (Perrin and Hohn 
1994). There was an overall stock decline of spotted dolphins from 
1960-1980 because of the fishery (Allen 1985). In 1979, the population 
size of spotted dolphins in the ETP was estimated at 2.9-3.3 million 
(Allen 1985). For 1986-1990, Wade and Gerrodette (1993) reported an 
estimate of 2.1 million. Gerrodette and Forcada (2005) noted that the 
population of offshore northeastern spotted dolphins had not yet 
recovered from the earlier population declines; possible reasons for 
the lack of growth were attributed to unreported bycatch, effects of 
fishing activity on survival and reproduction, and long-term changes in 
the ecosystem. The abundance estimate for 2006 was ~857,884 
northeastern offshore spotted

[[Page 1997]]

dolphins, and 439,208 western-southern offshore spotted dolphins; the 
coastal subspecies was estimated at 278,155 and was less affected by 
fishing activities (Gerrodette et al., 2008). In 2004, the mortality 
rate in the tuna fishery was estimated at 0.03 percent (Bayliff 2004). 
Perrin (2018a) noted that for the last few years, hundreds of spotted 
dolphins have been taken in the fishery. Currently, there are ~640,000 
northeastern offshore spotted dolphins inhabiting the ETP (Perrin 
2018a). This stock is still considered depleted and may be slow to 
recover due to continued chase and encirclement by the tuna fishery, 
which may in turn affect reproductive rates (Cramer et al., 2008; 
Kellar et al., 2013). The northeastern offshore and coastal stocks of 
pantropical spotted dolphins are likely to be encountered during the 
proposed surveys.
    The spinner dolphin is pantropical in distribution, including 
oceanic tropical and sub-tropical waters between 40[deg] N and 40[deg] 
S (Jefferson et al., 2015). It is generally considered a pelagic 
species, but it can also be found in coastal waters (Perrin 2018b). In 
the ETP, three types of spinner dolphins have been identified and two 
of those are recognized as subspecies: The eastern spinner dolphin 
(Stenella longirostris orientalis), considered an offshore species, the 
Central American spinner (S.l. centroamericana; also known as the Costa 
Rican spinner), considered a coastal species occurring from southern 
Mexico to Costa Rica (Perrin 1990; Dizon et al., 1991), and the 
`whitebelly' spinner which is thought to be a hybrid of the eastern 
spinner and Gray's spinner (S.l. longirostris). Gray's spinner dolphin 
is not expected to occur within the proposed study area. Although there 
is a great deal of overlap between the ranges of eastern and whitebelly 
spinner dolphins, the eastern form generally occurs in the northeastern 
portion of the ETP, whereas the whitebelly spinner occurs in the 
southern portion of the ETP, ranging farther offshore (Wade and 
Gerrodette 1993; Reilly and Fiedler 1994). Reilly and Fiedler (1994) 
noted that eastern spinners are associated with waters that have high 
surface temperatures and chlorophyll and shallow thermoclines, whereas 
whitebelly spinners are associated with cooler surface temperatures, 
lower chlorophyll levels, and deeper thermoclines. The eastern spinner 
dolphins are the most likely to occur in the proposed survey area (see 
Ferguson and Barlow 2001; Heckel et al., 2020), as this subspecies 
occurs in the ETP, east of 145[deg] W, between 24[deg] N off the Baja 
California Peninsula and 10[deg] S off Peru (Perrin 1990). Wade and 
Gerrodette (1993) reported an abundance estimate of 1.7 million, and 
Gerrodette et al. (2005) estimated the abundance at 1.1 million for 
2003. Gerrodette and Forcada (2005) noted that the population of 
eastern spinner dolphins had not yet recovered from the earlier 
population declines due to the tuna fishery. The population estimate 
for eastern spinner dolphins in 2003 was 612,662 (Gerrodette et al., 
2005). In 2000, the whitebelly dolphin was estimated to number 801,000 
in the ETP (Gerrodette et al., 2005). Bayliff (2004) noted a spinner 
dolphin mortality rate in the tuna fishery of 0.03 percent for 2004. 
Possible reasons why the population has not recovered include under-
reported bycatch, effects of fishing activity on survival and 
reproduction, and long-term changes in the ecosystem (Gerrodette and 
Forcada, 2005). The continued chase and encirclement by the tuna 
fishery may be affecting the reproductive rates of the eastern spinner 
dolphin (Cramer et al., 2008).
    The common dolphin is found in oceanic and nearshore waters of 
tropical and warm temperate oceans around the world, ranging from 
~60[deg] N to ~50[deg] S (Jefferson et al., 2015). There are two 
subspecies of common dolphins that occur in the eastern Pacific Ocean, 
the short-beaked form (Delphinus delphis delphis) and the long-beaked 
form (D. delphis bairdii). The long-beaked form generally prefers 
shallower water (Perrin 2018c), typically occurring within 180 km from 
shore (Jefferson et al., 2015). The short-beaked form occurs along the 
entire coast of Mexico and has been sighted near the proposed survey 
area off Nayarit, Michoac[aacute]n, and Guerrero; the long-beaked form 
occurs off the Baja California Peninsula and the Gulf of California 
(Heckel et al., 2020). The southern limit of the long-beaked form 
appears to be 22[deg] N (Urb[aacute]n 2008), and no sightings in 
Mexican waters have been made to the south of that. Thus, only the 
short-beaked form is expected to occur within the study area.

Unusual Mortality Events (UME)

    A UME is defined under the MMPA as ``a stranding that is 
unexpected; involves a significant die-off of any marine mammal 
population; and demands immediate response.'' For more information on 
UMEs, please visit: www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-unusual-mortality-events.
    Increased strandings of Guadalupe fur seals have occurred along the 
entire coast of California. Guadalupe fur seal strandings began in 
January 2015 and were eight times higher than the historical average. 
Strandings have continued since 2015 and have remained well above 
average through 2019. Strandings are seasonal and generally peak in 
April through June of each year. Strandings in Oregon and Washington 
became elevated starting in 2019 and have continued to present. 
Strandings in these two states in 2019 are five times higher than the 
historical average. As of December 2021, a total of 724 Guadalupe fur 
seals have stranded and are considered part of the UME (542 in 
California and 182 in Oregon and Washington). Stranded Guadalupe fur 
seals are mostly weaned pups and juveniles (1-2 years old). The 
majority of stranded animals showed signs of malnutrition with 
secondary bacterial and parasitic infections. For more information, 
please visit https://www.fisheries.noaa.gov/national/marine-life-distress/2015-2021-guadalupe-fur-seal-unusual-mortality-event-california.

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. Current data indicate that not all marine 
mammal species have equal hearing capabilities (e.g., Richardson et 
al., 1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect 
this, Southall et al. (2007) recommended that marine mammals be divided 
into functional hearing groups based on directly measured or estimated 
hearing ranges on the basis of available behavioral response data, 
audiograms derived using auditory evoked potential techniques, 
anatomical modeling, and other data. 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 2.

[[Page 1998]]



                  Table 2--Marine Mammal Hearing Groups
                              [NMFS, 2018]
------------------------------------------------------------------------
               Hearing group                 Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen         7 Hz to 35 kHz.
 whales).
Mid-frequency (MF) cetaceans (dolphins,      150 Hz to 160 kHz.
 toothed whales, beaked whales, bottlenose
 whales).
High-frequency (HF) cetaceans (true          275 Hz to 160 kHz.
 porpoises, Kogia, river dolphins,
 cephalorhynchid, Lagenorhynchus cruciger &
 L. australis).
Phocid pinnipeds (PW) (underwater) (true     50 Hz to 86 kHz.
 seals).
Otariid pinnipeds (OW) (underwater) (sea     60 Hz to 39 kHz.
 lions and fur seals).
------------------------------------------------------------------------
* Represents the generalized hearing range for the entire group as a
  composite (i.e., all species within the group), where individual
  species' hearing ranges are typically not as broad. Generalized
  hearing range chosen based on ~65 dB threshold from normalized
  composite audiogram, with the exception for lower limits for LF
  cetaceans (Southall et al. 2007) and PW pinniped (approximation).

    The pinniped functional hearing group was modified from Southall et 
al. (2007) on the basis of data indicating that phocid species have 
consistently demonstrated an extended frequency range of hearing 
compared to otariids, especially in the higher frequency range 
(Hemil[auml] et al., 2006; Kastelein et al., 2009; Reichmuth and Holt, 
2013).
    For more detail concerning these groups and associated frequency 
ranges, please see NMFS (2018) for a review of available information. 
30 marine mammal species (28 cetacean and two pinniped (both otariid) 
species) have the reasonable potential to co-occur with the proposed 
survey activities. Please refer to Table 1. Of the cetacean species 
that may be present, six are classified as low-frequency cetaceans 
(i.e., all mysticete species), 20 are classified as mid-frequency 
cetaceans (i.e., all delphinid and ziphiid species and the sperm 
whale), and two are classified as high-frequency cetaceans (i.e., 
harbor porpoise and Kogia spp.).

Potential Effects of Specified Activities on Marine Mammals and Their 
Habitat

    This section includes a summary and discussion of the ways that 
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 how those 
impacts on individuals are likely to impact marine mammal species or 
stocks.

Description of Active Acoustic Sound Sources

    This section contains a brief technical background on sound, the 
characteristics of certain sound types, and on metrics used in this 
proposal inasmuch 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.
    Sound travels in waves, the basic components of which 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, except in certain cases in shallower water. Amplitude is the 
height of the sound pressure wave or the ``loudness'' of a sound and is 
typically described using the relative unit of the dB. A sound pressure 
level (SPL) in dB is described as the ratio between a measured pressure 
and a reference pressure (for underwater sound, this is 1 microPascal 
([mu]Pa)) 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. The source level (SL) represents the 
SPL referenced at a distance of 1 m from the source (referenced to 1 
[mu]Pa) while the received level is the SPL at the listener's position 
(referenced to 1 [mu]Pa).
    Root mean square (rms) is the quadratic mean sound pressure over 
the duration of an impulse. Root mean square is calculated by squaring 
all of the sound amplitudes, averaging the squares, and then taking the 
square root of the average (Urick, 1983). Root mean square 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 pressures.
    Sound exposure level (SEL; represented as dB re 1 [mu]Pa\2\-s) 
represents the total energy contained within a pulse and considers both 
intensity and duration of exposure. Peak sound pressure (also referred 
to as zero-to-peak sound pressure or 0-p) is the maximum instantaneous 
sound pressure measurable in the water at a specified distance from the 
source and is represented in the same units as the rms sound pressure. 
Another common metric is peak-to-peak sound pressure (pk-pk), which is 
the algebraic difference between the peak positive and peak negative 
sound pressures. Peak-to-peak pressure is typically approximately 6 dB 
higher than peak pressure (Southall et al., 2007).
    When underwater objects vibrate or activity occurs, sound-pressure 
waves are created. These waves alternately compress and decompress the 
water as the sound wave travels. Underwater sound waves radiate in a 
manner similar to ripples on the surface of a pond and may be either 
directed in a beam or beams or may radiate in all directions 
(omnidirectional sources), as is the case for pulses produced by the 
airgun arrays considered here. The compressions and decompressions 
associated with sound waves are detected as changes in pressure by 
aquatic life and man-made sound receptors such as hydrophones.
    Even in the absence of sound from the specified activity, the 
underwater environment is typically loud due to ambient sound. Ambient 
sound is defined as environmental background sound levels lacking a 
single source or point (Richardson et al., 1995), and 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.,

[[Page 1999]]

sounds produced by marine mammals, fish, and invertebrates), and 
anthropogenic (e.g., vessels, dredging, construction) sound. A number 
of sources contribute to ambient sound, including the following 
(Richardson et al., 1995):
     Wind and waves: The complex interactions between wind and 
water surface, including processes such as breaking waves and wave-
induced bubble oscillations and cavitation, are a main source of 
naturally occurring ambient sound for frequencies between 200 Hz and 50 
kHz (Mitson, 1995). In general, ambient sound levels tend to increase 
with increasing wind speed and wave height. Surf sound becomes 
important near shore, with measurements collected at a distance of 8.5 
km from shore showing an increase of 10 dB in the 100 to 700 Hz band 
during heavy surf conditions;
     Precipitation: Sound from rain and hail impacting the 
water surface can become an important component of total sound at 
frequencies above 500 Hz, and possibly down to 100 Hz during quiet 
times;
     Biological: Marine mammals can contribute significantly to 
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; and
     Anthropogenic: Sources of ambient sound related to human 
activity include transportation (surface vessels), dredging and 
construction, oil and gas drilling and production, seismic surveys, 
sonar, explosions, and ocean acoustic studies. Vessel noise typically 
dominates the total ambient sound for frequencies between 20 and 300 
Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz 
and, if higher frequency sound levels are created, they attenuate 
rapidly. Sound from identifiable anthropogenic sources other than the 
activity of interest (e.g., a passing vessel) is sometimes termed 
background sound, as opposed to ambient sound.
    The sum of the various natural and anthropogenic sound sources at 
any given location and time--which comprise ``ambient'' or 
``background'' sound--depends not only on the source levels (as 
determined by current weather conditions and levels of biological and 
human activity) but also on the ability of sound to propagate through 
the environment. In turn, 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, 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 a given 
activity may be a negligible addition to the local environment or could 
form a distinctive signal that may affect marine mammals. Details of 
source types are described in the following text.
    Sounds are often considered to fall into one of two general types: 
Pulsed and non-pulsed (defined in the following). The distinction 
between these two sound types is important because they have differing 
potential to cause physical effects, particularly with regard to 
hearing (e.g., Ward, 1997 in Southall et al., 2007). Please see 
Southall et al. (2007) for an in-depth discussion of these concepts.
    Pulsed sound sources (e.g., airguns, explosions, gunshots, sonic 
booms, impact pile driving) produce signals that are brief (typically 
considered to be less than one second), broadband, atonal transients 
(ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur 
either as isolated events or repeated in some succession. Pulsed 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.
    Non-pulsed 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-pulsed sounds can be transient signals 
of short duration but without the essential properties of pulses (e.g., 
rapid rise time). Examples of non-pulsed sounds include those produced 
by vessels, aircraft, machinery operations such as drilling or 
dredging, vibratory pile driving, and active sonar systems (such as 
those used by the U.S. Navy). The duration of such sounds, as received 
at a distance, can be greatly extended in a highly reverberant 
environment.
    Airgun arrays produce pulsed signals with energy in a frequency 
range from about 10-2,000 Hz, with most energy radiated at frequencies 
below 200 Hz. The amplitude of the acoustic wave emitted from the 
source is equal in all directions (i.e., omnidirectional), but airgun 
arrays do possess some directionality due to different phase delays 
between guns in different directions. Airgun arrays are typically tuned 
to maximize functionality for data acquisition purposes, meaning that 
sound transmitted in horizontal directions and at higher frequencies is 
minimized to the extent possible.

Acoustic Effects

    Here, we discuss the effects of active acoustic sources on marine 
mammals.
    Potential Effects of Underwater Sound--Please refer to the 
information given previously (``Description of Active Acoustic Sound 
Sources'') regarding sound, characteristics of sound types, and metrics 
used in this document. Note that, in the following discussion, we refer 
in many cases to a review article concerning studies of noise-induced 
hearing loss conducted from 1996-2015 (i.e., Finneran, 2015). For 
study-specific citations, please see that work. Anthropogenic sounds 
cover a broad range of frequencies and sound levels and can have a 
range of highly variable impacts on marine life, from none or minor to 
potentially severe responses, depending on received levels, duration of 
exposure, behavioral context, and various other factors. The potential 
effects of underwater sound from active acoustic sources can 
potentially result in one or more of the following: Temporary or 
permanent hearing impairment, non-auditory physical or physiological 
effects, behavioral disturbance, stress, and masking (Richardson et 
al., 1995; Gordon et al., 2004; Nowacek et al., 2007; Southall et al., 
2007; G[ouml]tz et al., 2009). The degree of effect is intrinsically 
related to the signal characteristics, received level, distance from 
the source, and duration of the sound exposure. In general, sudden, 
high level sounds can cause hearing loss, as can longer exposures to 
lower level sounds. Temporary or permanent loss of hearing will occur 
almost exclusively for noise within an animal's hearing range. We first 
describe specific manifestations of acoustic effects before providing 
discussion specific to the use of airgun arrays.
    Richardson et al. (1995) described zones of increasing intensity of 
effect that might be expected to occur, in relation to distance from a 
source and assuming that the signal is within an animal's hearing 
range. First is the area within which the acoustic signal would be 
audible (potentially perceived) to the animal, but not strong enough to 
elicit any overt behavioral or physiological response. The next zone 
corresponds with the area where the signal is audible to the animal and 
of sufficient intensity

[[Page 2000]]

to elicit behavioral or physiological responsiveness. Third is a zone 
within which, for signals of high intensity, the received level is 
sufficient to potentially cause discomfort or tissue damage to auditory 
or other systems. Overlaying these zones to a certain extent is the 
area within which masking (i.e., when a sound interferes with or masks 
the ability of an animal to detect a signal of interest that is above 
the absolute hearing threshold) may occur; the masking zone may be 
highly variable in size.
    We describe the more severe effects of certain non-auditory 
physical or physiological effects only briefly as we do not expect that 
use of airgun arrays are reasonably likely to result in such effects 
(see below for further discussion). Potential effects from impulsive 
sound sources can range in severity from effects such as behavioral 
disturbance or tactile perception to physical discomfort, slight injury 
of the internal organs and the auditory system, or mortality (Yelverton 
et al., 1973). Non-auditory physiological effects or injuries that 
theoretically might occur in marine mammals exposed to high level 
underwater sound or as a secondary effect of extreme behavioral 
reactions (e.g., change in dive profile as a result of an avoidance 
reaction) caused by exposure to sound include neurological effects, 
bubble formation, resonance effects, and other types of organ or tissue 
damage (Cox et al., 2006; Southall et al., 2007; Zimmer and Tyack, 
2007; Tal et al., 2015). The survey activities considered here do not 
involve the use of devices such as explosives or mid-frequency tactical 
sonar that are associated with these types of effects.
    Threshold Shift--Marine mammals exposed to high-intensity sound, or 
to lower-intensity sound for prolonged periods, can experience hearing 
threshold shift (TS), which is the loss of hearing sensitivity at 
certain frequency ranges (Finneran, 2015). TS can be permanent (PTS), 
in which case the loss of hearing sensitivity is not fully recoverable, 
or temporary (TTS), in which case the animal's hearing threshold would 
recover over time (Southall et al., 2007). Repeated sound exposure that 
leads to TTS could cause PTS. In severe cases of PTS, there can be 
total or partial deafness, while in most cases the animal has an 
impaired ability to hear sounds in specific frequency ranges (Kryter, 
1985).
    When PTS occurs, there is physical damage to the sound receptors in 
the ear (i.e., tissue damage), whereas TTS represents primarily tissue 
fatigue and is reversible (Southall et al., 2007). In addition, other 
investigators have suggested that TTS is within the normal bounds of 
physiological variability and tolerance and does not represent physical 
injury (e.g., Ward, 1997). Therefore, NMFS does not consider TTS to 
constitute auditory injury.
    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 dBs 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 impulse sounds (such as airgun 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.
    For mid-frequency cetaceans in particular, potential protective 
mechanisms may help limit onset of TTS or prevent onset of PTS. Such 
mechanisms include dampening of hearing, auditory adaptation, or 
behavioral amelioration (e.g., Nachtigall and Supin, 2013; Miller et 
al., 2012; Finneran et al., 2015; Popov et al., 2016).
    TTS is the mildest form of hearing impairment that can occur during 
exposure to sound (Kryter, 1985). 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. Few data 
on sound levels and durations necessary to elicit mild TTS have been 
obtained for marine mammals.
    Marine mammal hearing plays a critical role in communication with 
conspecifics, and interpretation of environmental cues for purposes 
such as predator avoidance and prey capture. 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. 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 occurs during a time 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.
    Finneran et al. (2015) measured hearing thresholds in three captive 
bottlenose dolphins before and after exposure to ten pulses produced by 
a seismic airgun in order to study TTS induced after exposure to 
multiple pulses. Exposures began at relatively low levels and gradually 
increased over a period of several months, with the highest exposures 
at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from 
193-195 dB. No substantial TTS was observed. In addition, behavioral 
reactions were observed that indicated that animals can learn behaviors 
that effectively mitigate noise exposures (although exposure patterns 
must be learned, which is less likely in wild animals than for the 
captive animals considered in this study). The authors note that the 
failure to induce more significant auditory effects likely due to the 
intermittent nature of exposure, the relatively low peak pressure 
produced by the acoustic source, and the low-frequency energy in airgun 
pulses as compared with the frequency range of best sensitivity for 
dolphins and other mid-frequency cetaceans.
    Currently, TTS data only exist for four species of cetaceans 
(bottlenose dolphin, beluga whale (Delphinapterus leucas), harbor 
porpoise (Phocoena phocoena), and Yangtze finless porpoise (Neophocaena 
asiaeorientalis)) exposed to a limited number of sound sources (i.e., 
mostly tones and octave-band noise) in laboratory settings (Finneran, 
2015). In general, harbor porpoises have a lower TTS onset than other 
measured cetacean species (Finneran, 2015). Additionally, the existing 
marine mammal TTS data come from a limited number of individuals within 
these species. There are no data available on noise-induced hearing 
loss for mysticetes.
    Critical questions remain regarding the rate of TTS growth and 
recovery after exposure to intermittent noise and the effects of single 
and multiple pulses. Data at present are also insufficient to construct 
generalized models for recovery and determine the time necessary to 
treat subsequent exposures as independent events. More

[[Page 2001]]

information is needed on the relationship between auditory evoked 
potential and behavioral measures of TTS for various stimuli. For 
summaries of data on TTS in marine mammals or for further discussion of 
TTS onset thresholds, please see Southall et al. (2007, 2019), Finneran 
and Jenkins (2012), Finneran (2015), and NMFS (2018).
    Behavioral Effects--Behavioral disturbance may include a variety of 
effects, including subtle changes in behavior (e.g., minor or brief 
avoidance of an area or changes in vocalizations), more conspicuous 
changes in similar behavioral activities, and more sustained and/or 
potentially severe reactions, such as displacement from or abandonment 
of high-quality habitat. Behavioral responses 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., 2003; Southall et al., 2007, 
2019; Weilgart, 2007; Archer et al., 2010). 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). 
Please see Appendices B-C of Southall et al. (2007) for a review 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., 2003). 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, 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; NRC, 2003; Wartzok et al., 2003). Controlled experiments with 
captive marine mammals have showed pronounced behavioral reactions, 
including avoidance of loud sound sources (Ridgway et al., 1997). 
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). However, many 
delphinids approach acoustic source vessels with no apparent discomfort 
or obvious behavioral change (e.g., Barkaszi et al., 2012; Barkaszi and 
Kelly, 2018).
    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; 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 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.
    Of note for one of the species that occur in the survey area, 
visual tracking, passive acoustic monitoring, and movement recording 
tags were used to quantify sperm whale behavior prior to, during, and 
following exposure to airgun arrays at received levels in the range 
140-160 dB at distances of 7-13 km, following a phase-in of sound 
intensity and full array exposures at 1-13 km (Madsen et al., 2006; 
Miller et al., 2009). Sperm whales did not exhibit horizontal avoidance 
behavior at the surface. However, foraging behavior may have been 
affected. The sperm whales exhibited 19 percent less vocal (buzz) rate 
during full exposure relative to post exposure, and the whale that was 
approached most closely had an extended resting period and did not 
resume foraging until the airguns had ceased firing. The remaining 
whales continued to execute foraging dives throughout exposure; 
however, swimming movements during foraging dives were 6 percent lower 
during exposure than control periods (Miller et al., 2009). These data 
raise concerns that seismic surveys may impact foraging behavior in 
sperm whales, although more data are required to understand whether the 
differences were due to exposure or natural variation in sperm whale 
behavior (Miller et al., 2009).
    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

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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, 2016).
    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 amplitude of 
calls (Miller et al., 2000; Fristrup et al., 2003; Foote et al., 2004; 
Holt et al., 2012), while right whales 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).
    Cerchio et al. (2014) used passive acoustic monitoring to document 
the presence of singing humpback whales off the coast of northern 
Angola and to opportunistically test for the effect of seismic survey 
activity on the number of singing whales. Two recording units were 
deployed between March and December 2008 in the offshore environment; 
numbers of singers were counted every hour. Generalized Additive Mixed 
Models were used to assess the effect of survey day (seasonality), hour 
(diel variation), moon phase, and received levels of noise (measured 
from a single pulse during each 10 minute sampled period) on singer 
number. The number of singers significantly decreased with increasing 
received level of noise, suggesting that humpback whale breeding 
activity was disrupted to some extent by the survey activity.
    Castellote et al. (2012) reported acoustic and behavioral changes 
by fin whales in response to shipping and airgun noise. Acoustic 
features of fin whale song notes recorded in the Mediterranean Sea and 
northeast Atlantic Ocean were compared for areas with different 
shipping noise levels and traffic intensities and during a seismic 
airgun survey. During the first 72 hours of the survey, a steady 
decrease in song received levels and bearings to singers indicated that 
whales moved away from the acoustic source and out of the study area. 
This displacement persisted for a time period well beyond the 10-day 
duration of seismic airgun activity, providing evidence that fin whales 
may avoid an area for an extended period in the presence of increased 
noise. The authors hypothesize that fin whale acoustic communication is 
modified to compensate for increased background noise and that a 
sensitization process may play a role in the observed temporary 
displacement.
    Seismic pulses at average received levels of 131 dB re 1 [mu]Pa\2\-
s caused blue whales to increase call production (Di Iorio and Clark, 
2010). In contrast, McDonald et al. (1995) tracked a blue whale with 
seafloor seismometers and reported that it stopped vocalizing and 
changed its travel direction at a range of 10 km from the acoustic 
source vessel (estimated received level 143 dB pk-pk). Blackwell et al. 
(2013) found that bowhead whale call rates dropped significantly at 
onset of airgun use at sites with a median distance of 41-45 km from 
the survey. Blackwell et al. (2015) expanded this analysis to show that 
whales actually increased calling rates as soon as airgun signals were 
detectable before ultimately decreasing calling rates at higher 
received levels (i.e., 10-minute SELcum of ~127 dB). Overall, these 
results suggest that bowhead whales may adjust their vocal output in an 
effort to compensate for noise before ceasing vocalization effort and 
ultimately deflecting from the acoustic source (Blackwell et al., 2013, 
2015). These studies demonstrate that even low levels of noise received 
far from the source can induce changes in vocalization and/or behavior 
for mysticetes.
    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). Humpback whales showed avoidance behavior in the presence of an 
active seismic array during observational studies and controlled 
exposure experiments in western Australia (McCauley et al., 2000). 
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., Bejder et al., 2006; Teilmann et al., 2006).
    Forney et al. (2017) detail the potential effects of noise on 
marine mammal populations with high site fidelity, including 
displacement and auditory masking, noting that a lack of observed 
response does not imply absence of fitness costs and that apparent 
tolerance of disturbance may have population-level impacts that are 
less obvious and difficult to document. Forney et al. (2017) state 
that, for these animals, remaining in a disturbed area may reflect a 
lack of alternatives rather than a lack of effects. The authors discuss 
several case studies, including western Pacific gray whales, which are 
a small population of mysticetes believed to be adversely affected by 
oil and gas development off Sakhalin Island, Russia (Weller et al., 
2002; Reeves et al., 2005). Western gray whales display a high degree 
of interannual site fidelity to the area for foraging purposes, and 
observations in the area during airgun surveys has shown the potential 
for harm caused by displacement from such an important area (Weller et 
al., 2006; Johnson et al., 2007). Forney et al. (2017) also discuss 
beaked whales, noting that anthropogenic effects in areas where they 
are resident could cause severe biological consequences, in part 
because displacement may adversely affect foraging rates, reproduction, 
or health, while an overriding instinct to remain could lead to more 
severe acute effects.
    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). 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 
(Evans and 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

[[Page 2003]]

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 fish 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 five-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 one 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.
    Stone (2015) reported data from at-sea observations during 1,196 
seismic surveys from 1994 to 2010. When large arrays of airguns 
(considered to be 500 in\3\ or more) were firing, lateral displacement, 
more localized avoidance, or other changes in behavior were evident for 
most odontocetes. However, significant responses to large arrays were 
found only for the minke whale and fin whale. Behavioral responses 
observed included changes in swimming or surfacing behavior, with 
indications that cetaceans remained near the water surface at these 
times. Cetaceans were recorded as feeding less often when large arrays 
were active. Behavioral observations of gray whales during a seismic 
survey monitored whale movements and respirations pre-, during, and 
post-seismic survey (Gailey et al., 2016). Behavioral state and water 
depth were the best `natural' predictors of whale movements and 
respiration and, after considering natural variation, none of the 
response variables were significantly associated with seismic survey or 
vessel sounds.
    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., Seyle, 1950; 
Moberg, 2000). In many cases, an animal's first and sometimes most 
economical (in terms of energetic costs) response is behavioral 
avoidance of the potential stressor. Autonomic nervous system responses 
to stress typically involve changes in heart rate, blood pressure, and 
gastrointestinal activity. These responses have a relatively short 
duration and may or may not have a significant long-term effect on an 
animal's fitness.
    Neuroendocrine stress responses often involve the hypothalamus-
pituitary-adrenal system. Virtually all neuroendocrine functions that 
are affected by stress--including immune competence, reproduction, 
metabolism, and behavior--are regulated by pituitary hormones. Stress-
induced changes in the secretion of pituitary hormones have been 
implicated in failed reproduction, altered metabolism, reduced immune 
competence, and behavioral disturbance (e.g., Moberg, 1987; Blecha, 
2000). Increases in the circulation of glucocorticoids are also equated 
with stress (Romano et al., 2004).
    The primary distinction between stress (which is adaptive and does 
not normally place an animal at risk) and ``distress'' is the cost of 
the response. During a stress response, an animal uses glycogen stores 
that can be quickly replenished once the stress is alleviated. In such 
circumstances, the cost of the stress response would not pose serious 
fitness consequences. However, when an animal does not have sufficient 
energy reserves to satisfy the energetic costs of a stress response, 
energy resources must be diverted from other functions. This state of 
distress will last until the animal replenishes its energetic reserves 
sufficiently 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).
    Auditory Masking--Sound can disrupt behavior through masking, or 
interfering 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). Masking occurs when the receipt of a sound is interfered with by 
another coincident sound at similar frequencies and at similar or 
higher intensity, and may occur whether the sound is natural (e.g., 
snapping shrimp, wind, waves, precipitation) or anthropogenic (e.g., 
shipping, sonar, seismic exploration) in origin. 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 man-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

[[Page 2004]]

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, 2009; 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 and Moore, 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).
    Masking affects both senders and receivers of acoustic signals and 
can potentially have long-term chronic effects on marine mammals at the 
population level as well as at the individual level. Low-frequency 
ambient sound levels have increased by as much as 20 dB (more than 
three times in terms of SPL) in the world's ocean from pre-industrial 
periods, with most of the increase from distant commercial shipping 
(Hildebrand, 2009). All anthropogenic sound sources, but especially 
chronic and lower-frequency signals (e.g., from vessel traffic), 
contribute to elevated ambient sound levels, thus intensifying masking.
    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited, although there are few specific data on this. Because of 
the intermittent nature and low duty cycle of seismic pulses, animals 
can emit and receive sounds in the relatively quiet intervals between 
pulses. However, in exceptional situations, reverberation occurs for 
much or all of the interval between pulses (e.g., Simard et al. 2005; 
Clark and Gagnon 2006), which could mask calls. Situations with 
prolonged strong reverberation are infrequent. However, it is common 
for reverberation to cause some lesser degree of elevation of the 
background level between airgun pulses (e.g., Gedamke 2011; Guerra et 
al. 2011, 2016; Klinck et al. 2012; Guan et al. 2015), and this weaker 
reverberation presumably reduces the detection range of calls and other 
natural sounds to some degree. Guerra et al. (2016) reported that 
ambient noise levels between seismic pulses were elevated as a result 
of reverberation at ranges of 50 km from the seismic source. Based on 
measurements in deep water of the Southern Ocean, Gedamke (2011) 
estimated that the slight elevation of background levels during 
intervals between pulses reduced blue and fin whale communication space 
by as much as 36-51 percent when a seismic survey was operating 450-
2,800 km away. Based on preliminary modeling, Wittekind et al. (2016) 
reported that airgun sounds could reduce the communication range of 
blue and fin whales 2000 km from the seismic source. Nieukirk et al. 
(2012) and Blackwell et al. (2013) noted the potential for masking 
effects from seismic surveys on large whales.
    Some baleen and toothed whales are known to continue calling in the 
presence of seismic pulses, and their calls usually can be heard 
between the pulses (e.g., Nieukirk et al. 2012; Thode et al. 2012; 
Br[ouml]ker et al. 2013; Sciacca et al. 2016). As noted above, Cerchio 
et al. (2014) suggested that the breeding display of humpback whales 
off Angola could be disrupted by seismic sounds, as singing activity 
declined with increasing received levels. In addition, some cetaceans 
are known to change their calling rates, shift their peak frequencies, 
or otherwise modify their vocal behavior in response to airgun sounds 
(e.g., Di Iorio and Clark 2010; Castellote et al. 2012; Blackwell et 
al. 2013, 2015). The hearing systems of baleen whales are undoubtedly 
more sensitive to low-frequency sounds than are the ears of the small 
odontocetes that have been studied directly (e.g., MacGillivray et al. 
2014). The sounds important to small odontocetes are predominantly at 
much higher frequencies than are the dominant components of airgun 
sounds, thus limiting the potential for masking. In general, masking 
effects of seismic pulses are expected to be minor, given the normally 
intermittent nature of seismic pulses.

Vessel Noise

    Vessel noise from the Langseth could affect marine animals in the 
proposed survey areas. Houghton et al. (2015) proposed that vessel 
speed is the most important predictor of received noise levels, and 
Putland et al. (2017) also reported reduced sound levels with decreased 
vessel speed. Sounds produced by large vessels generally dominate 
ambient noise at frequencies from 20 to 300 Hz (Richardson et al. 
1995). However, some energy is also produced at higher frequencies 
(Hermannsen et al. 2014); low levels of high-frequency sound from 
vessels has been shown to elicit responses in harbor porpoise (Dyndo et 
al. 2015). Increased levels of ship noise have been shown to affect 
foraging by porpoise (Teilmann et al. 2015; Wisniewska et al. 2018); 
Wisniewska et al. (2018) suggest that a decrease in foraging success 
could have long-term fitness consequences.
    Ship noise, through masking, can reduce the effective communication 
distance of a marine mammal if the frequency of the sound source is 
close to that used by the animal, and if the sound is present for a 
significant fraction of time (e.g., Richardson et al. 1995; Clark et 
al. 2009; Jensen et al. 2009; Gervaise et al. 2012; Hatch et al. 2012; 
Rice et al. 2014; Dunlop 2015; Erbe et al. 2015; Jones et al. 2017; 
Putland et al. 2017). In addition to the frequency and duration of the 
masking sound, the strength, temporal pattern, and location of the 
introduced sound also play a role in the extent of the masking 
(Branstetter et al. 2013, 2016; Finneran and Branstetter 2013; Sills et 
al. 2017). Branstetter et al. (2013) reported that time-domain metrics 
are also important in describing and predicting masking. In order to 
compensate for increased ambient noise, some cetaceans are known to 
increase the source levels of their calls in the presence of elevated 
noise levels from shipping, shift their peak frequencies, or otherwise 
change their vocal behavior (e.g., Parks et al. 2016a,b; Bittencourt et 
al. 2016; Dahlheim and Castellote 2016; Gospi[cacute] and Picciulin 
2016; Gridley et al. 2016; Heiler et al. 2016; Martins et al. 2016; 
O'Brien et al. 2016; Tenessen and Parks 2016). Holt et al. (2015) 
reported that changes in vocal modifications can have increased 
energetic costs for individual marine mammals. A negative correlation 
between the presence of some cetacean species and the number of vessels 
in an area has been demonstrated by several studies (e.g., Campana et 
al. 2015; Culloch et al. 2016).

[[Page 2005]]

    Baleen whales are thought to be more sensitive to sound at these 
low frequencies than are toothed whales (e.g., MacGillivray et al. 
2014), possibly causing localized avoidance of the proposed survey area 
during seismic operations. Reactions of gray and humpback whales to 
vessels have been studied, and there is limited information available 
about the reactions of right whales and rorquals (e.g., fin, blue, 
minke, humpback, sei, and Bryde's whales). Reactions of humpback whales 
to boats are variable, ranging from approach to avoidance (Payne 1978; 
Salden 1993). Baker et al. (1982, 1983) and Baker and Herman (1989) 
found humpbacks often move away when vessels are within several 
kilometers. Humpbacks seem less likely to react overtly when actively 
feeding than when resting or engaged in other activities (Krieger and 
Wing 1984, 1986). Increased levels of ship noise have been shown to 
affect foraging by humpback whales (Blair et al. 2016). Fin whale 
sightings in the western Mediterranean were negatively correlated with 
the number of vessels in the area (Campana et al. 2015). Minke whales 
have shown slight displacement in response to construction-related 
vessel traffic (Anderwald et al. 2013).
    Many odontocetes show considerable tolerance of vessel traffic, 
although they sometimes react at long distances if confined by ice or 
shallow water, if previously harassed by vessels, or have had little or 
no recent exposure to ships (Richardson et al. 1995). Dolphins of many 
species tolerate and sometimes approach vessels (e.g., Anderwald et al. 
2013). Some dolphin species approach moving vessels to ride the bow or 
stern waves (Williams et al. 1992). Pirotta et al. (2015) noted that 
the physical presence of vessels, not just ship noise, disturbed the 
foraging activity of bottlenose dolphins. Sightings of striped dolphin, 
Risso's dolphin, sperm whale, and Cuvier's beaked whale in the western 
Mediterranean were negatively correlated with the number of vessels in 
the area (Campana et al. 2015).
    There are few data on the behavioral reactions of beaked whales to 
vessel noise, though they seem to avoid approaching vessels (e.g., 
W[uuml]rsig et al. 1998) or dive for an extended period when approached 
by a vessel (e.g., Kasuya 1986). Based on a single observation, Aguilar 
Soto et al. (2006) suggest foraging efficiency of Cuvier's beaked 
whales may be reduced by close approach of vessels.
    Sounds emitted by the Langseth are low frequency and continuous, 
but would be widely dispersed in both space and time. Vessel traffic 
associated with the proposed survey is of low density compared to 
traffic associated with commercial shipping, industry support vessels, 
or commercial fishing vessels, and would therefore be expected to 
represent an insignificant incremental increase in the total amount of 
anthropogenic sound input to the marine environment, and the effects of 
vessel noise described above are not expected to occur as a result of 
this survey. In summary, project vessel sounds would not be at levels 
expected to cause anything more than possible localized and temporary 
behavioral changes in marine mammals, and would not be expected to 
result in significant negative effects on individuals or at the 
population level. In addition, in all oceans of the world, large vessel 
traffic is currently so prevalent that it is commonly considered a 
usual source of ambient sound (NSF-USGS 2011).

Ship Strike

    Vessel collisions with marine mammals, or ship strikes, can result 
in death or serious injury of the animal. Wounds resulting from ship 
strike may include massive trauma, hemorrhaging, broken bones, or 
propeller lacerations (Knowlton and Kraus, 2001). An animal at the 
surface may be struck directly by a vessel, a surfacing animal may hit 
the bottom of a vessel, or an animal just below the surface may be cut 
by a vessel's propeller. Superficial strikes may not kill or result in 
the death of the animal. These interactions are typically associated 
with large whales (e.g., fin whales), which are occasionally found 
draped across the bulbous bow of large commercial ships upon arrival in 
port. Although smaller cetaceans are more maneuverable in relation to 
large vessels than are large whales, they may also be susceptible to 
strike. The severity of injuries typically depends on the size and 
speed of the vessel, with the probability of death or serious injury 
increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist 
et al., 2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013). 
Impact forces increase with speed, as does the probability of a strike 
at a given distance (Silber et al., 2010; Gende et al., 2011).
    Pace and Silber (2005) also found that the probability of death or 
serious injury increased rapidly with increasing vessel speed. 
Specifically, the predicted probability of serious injury or death 
resulting from a strike increased from 45 to 75 percent as vessel speed 
increased from 10 to 14 knots, and exceeded 90 percent at 17 knots. 
Higher speeds during collisions result in greater force of impact, but 
higher speeds also appear to increase the chance of severe injuries or 
death through increased likelihood of collision by pulling whales 
toward the vessel (Clyne, 1999; Knowlton et al., 1995). In a separate 
study, Vanderlaan and Taggart (2007) analyzed the probability of lethal 
mortality of large whales at a given speed, showing that the greatest 
rate of change in the probability of a lethal injury to a large whale 
as a function of vessel speed occurs between 8.6 and 15 knots. The 
chances of a lethal injury decline from approximately 80 percent at 15 
knots to approximately 20 percent at 8.6 knots. At speeds below 11.8 
knots, the chances of lethal injury drop below 50 percent, while the 
probability asymptotically increases toward 100 percent above 15 knots.
    The vessel speed during seismic survey operations would be 
approximately 4.1 knots (7.6 km/h) during MCS reflection surveys and 5 
knots (9.3 km/h) during OBS refraction surveys. At this speed, both the 
possibility of striking a marine mammal and the possibility of a strike 
resulting in serious injury or mortality are so low as to be 
discountable. At average transit speed, the probability of serious 
injury or mortality resulting from a strike is less than 50 percent. 
However, the likelihood of a strike actually happening is again low. 
Ship strikes, as analyzed in the studies cited above, generally involve 
commercial shipping, which is much more common in both space and time 
than is geophysical survey activity. Commercial shipping vessels are 
also generally much larger than typical geophysical survey vessels 
(e.g., up to 360 m long cargo vessels compared to the 71-m R/V 
Langseth). Jensen and Silber (2004) summarized ship strikes of large 
whales worldwide from 1975-2003 and found that most collisions occurred 
in the open ocean and involved large vessels (e.g., commercial shipping 
vessels). No such incidents were reported for geophysical survey 
vessels during that time period.
    It is possible for ship strikes to occur while traveling at slow 
speeds. For example, a hydrographic survey vessel traveling at low 
speed (5.5 knots) while conducting mapping surveys off the central 
California coast struck and killed a blue whale in 2009. The State of 
California determined that the whale had suddenly and unexpectedly 
surfaced beneath the hull, with the result that the propeller severed 
the whale's vertebrae, and that this was an unavoidable event. This 
strike represents the only such incident in approximately 540,000 hours 
of similar coastal mapping activity (p = 1.9 x 10-\6\; 95 
percent CI = 0-5.5 x 10-\6\; NMFS, 2013b). In addition, a 
research vessel

[[Page 2006]]

reported a fatal strike in 2011 of a dolphin in the Atlantic, 
demonstrating that it is possible for strikes involving smaller 
cetaceans to occur. In that case, the incident report indicated that an 
animal apparently was struck by the vessel's propeller as it was 
intentionally swimming near the vessel. While indicative of the type of 
unusual events that cannot be ruled out, neither of these instances 
represents a circumstance that would be considered reasonably 
foreseeable or that would be considered preventable.
    Although the likelihood of the vessel striking a marine mammal is 
low, we require a robust ship strike avoidance protocol (see Proposed 
Mitigation), which we believe eliminates any foreseeable risk of ship 
strike during transit. We anticipate that vessel collisions involving a 
seismic data acquisition vessel towing gear, while not impossible, 
represent unlikely, unpredictable events for which there are no 
preventive measures. Given the required mitigation measures, the 
relatively slow speed of the vessel towing gear, the presence of bridge 
crew watching for obstacles at all times (including marine mammals), 
and the presence of marine mammal observers, we believe that the 
possibility of ship strike is discountable and, further, that were a 
strike of a large whale to occur, it would be unlikely to result in 
serious injury or mortality. No incidental take resulting from ship 
strike is anticipated, and this potential effect of the specified 
activity will not be discussed further in the following analysis.
    Stranding--When a living or dead marine mammal swims or floats onto 
shore and becomes ``beached'' or incapable of returning to sea, the 
event is a ``stranding'' (Geraci et al., 1999; Perrin and Geraci, 2002; 
Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a 
stranding under the MMPA is that ``(A) a marine mammal is dead and is 
(i) on a beach or shore of the United States; or (ii) in waters under 
the jurisdiction of the United States (including any navigable waters); 
or (B) a marine mammal is alive and is (i) on a beach or shore of the 
United States and is unable to return to the water; (ii) on a beach or 
shore of the United States and, although able to return to the water, 
is in need of apparent medical attention; or (iii) in the waters under 
the jurisdiction of the United States (including any navigable waters), 
but is unable to return to its natural habitat under its own power or 
without assistance.''
    Marine mammals strand for a variety of reasons, such as infectious 
agents, biotoxicosis, starvation, fishery interaction, ship strike, 
unusual oceanographic or weather events, sound exposure, or 
combinations of these stressors sustained concurrently or in series. 
However, the cause or causes of most strandings are unknown (Geraci et 
al., 1976; Eaton, 1979; Odell et al., 1980; Best, 1982). Numerous 
studies suggest that the physiology, behavior, habitat relationships, 
age, or condition of cetaceans may cause them to strand or might pre-
dispose them to strand when exposed to another phenomenon. These 
suggestions are consistent with the conclusions of numerous other 
studies that have demonstrated that combinations of dissimilar 
stressors commonly combine to kill an animal or dramatically reduce its 
fitness, even though one exposure without the other does not produce 
the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; 
Fair and Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a; 
2005b, Romero, 2004; Sih et al., 2004).
    There is no conclusive evidence that exposure to airgun noise 
results in behaviorally-mediated forms of injury. Behaviorally-mediated 
injury (i.e., mass stranding events) has been primarily associated with 
beaked whales exposed to mid-frequency active (MFA) naval sonar. 
Tactical sonar and the alerting stimulus used in Nowacek et al. (2004) 
are very different from the noise produced by airguns. One should 
therefore not expect the same reaction to airgun noise as to these 
other sources. As explained below, military MFA sonar is very different 
from airguns, and one should not assume that airguns will cause the 
same effects as MFA sonar (including strandings).
    To understand why Navy MFA sonar affects beaked whales differently 
than airguns do, it is important to note the distinction between 
behavioral sensitivity and susceptibility to auditory injury. To 
understand the potential for auditory injury in a particular marine 
mammal species in relation to a given acoustic signal, the frequency 
range the species is able to hear is critical, as well as the species' 
auditory sensitivity to frequencies within that range. Current data 
indicate that not all marine mammal species have equal hearing 
capabilities across all frequencies and, therefore, species are grouped 
into hearing groups with generalized hearing ranges assigned on the 
basis of available data (Southall et al., 2007, 2019). Hearing ranges 
as well as auditory sensitivity/susceptibility to frequencies within 
those ranges vary across the different groups. For example, in terms of 
hearing range, the high-frequency cetaceans (e.g., Kogia spp.) have a 
generalized hearing range of frequencies between 275 Hz and 160 kHz, 
while mid-frequency cetaceans--such as dolphins and beaked whales--have 
a generalized hearing range between 150 Hz to 160 kHz. Regarding 
auditory susceptibility within the hearing range, while mid-frequency 
cetaceans and high-frequency cetaceans have roughly similar hearing 
ranges, the high-frequency group is much more susceptible to noise-
induced hearing loss during sound exposure, i.e., these species have 
lower thresholds for these effects than other hearing groups (NMFS, 
2018). Referring to a species as behaviorally sensitive to noise simply 
means that an animal of that species is more likely to respond to lower 
received levels of sound than an animal of another species that is 
considered less behaviorally sensitive. So, while dolphin species and 
beaked whale species--both in the mid-frequency cetacean hearing 
group--are assumed to (generally) hear the same sounds equally well and 
be equally susceptible to noise-induced hearing loss (auditory injury), 
the best available information indicates that a beaked whale is more 
likely to behaviorally respond to that sound at a lower received level 
compared to an animal from other mid-frequency cetacean species that 
are less behaviorally sensitive. This distinction is important because, 
while beaked whales are more likely to respond behaviorally to sounds 
than are many other species (even at lower levels), they cannot hear 
the predominant, lower frequency sounds from seismic airguns as well as 
sounds that have more energy at frequencies that beaked whales can hear 
better (such as military MFA sonar).
    Navy MFA sonar affects beaked whales differently than airguns do 
because it produces energy at different frequencies than airguns. Mid-
frequency cetacean hearing is generically thought to be best between 
8.8 to 110 kHz, i.e., these cutoff values define the range above and 
below which a species in the group is assumed to have declining 
auditory sensitivity, until reaching frequencies that cannot be heard 
(NMFS, 2018). However, beaked whale hearing is likely best within a 
higher, narrower range (20-80 kHz, with best sensitivity around 40 
kHz), based on a few measurements of hearing in stranded beaked whales 
(Cook et al., 2006; Finneran et al., 2009; Pacini et al., 2011) and 
several studies of acoustic signals produced by beaked whales (e.g., 
Frantzis et al., 2002; Johnson et al., 2004, 2006; Zimmer et al., 
2005). While precaution requires that the full range of

[[Page 2007]]

audibility be considered when assessing risks associated with noise 
exposure (Southall et al., 2007, 2019), animals typically produce sound 
at frequencies where they hear best. More recently, Southall et al. 
(2019) suggested that certain species amongst the historical mid-
frequency hearing group (beaked whales, sperm whales, and killer 
whales) are likely more sensitive to lower frequencies within the 
group's generalized hearing range than are other species within the 
group and state that the data for beaked whales suggest sensitivity to 
approximately 5 kHz. However, this information is consistent with the 
general conclusion that beaked whales (and other mid-frequency 
cetaceans) are relatively insensitive to the frequencies where most 
energy of an airgun signal is found. Military MFA sonar is typically 
considered to operate in the frequency range of approximately 3-14 kHz 
(D'Amico et al., 2009), i.e., outside the range of likely best hearing 
for beaked whales but within or close to the lower bounds, whereas most 
energy in an airgun signal is radiated at much lower frequencies, below 
500 Hz (Dragoset, 1990).
    It is important to distinguish between energy (loudness, measured 
in dB) and frequency (pitch, measured in Hz). In considering the 
potential impacts of mid-frequency components of airgun noise (1-10 
kHz, where beaked whales can be expected to hear) on marine mammal 
hearing, one needs to account for the energy associated with these 
higher frequencies and determine what energy is truly ``significant.'' 
Although there is mid-frequency energy associated with airgun noise (as 
expected from a broadband source), airgun sound is predominantly below 
1 kHz (Breitzke et al., 2008; Tashmukhambetov et al., 2008; Tolstoy et 
al., 2009). As stated by Richardson et al. (1995), ``[. . .] most 
emitted [seismic airgun] energy is at 10-120 Hz, but the pulses contain 
some energy up to 500-1,000 Hz.'' Tolstoy et al. (2009) conducted 
empirical measurements, demonstrating that sound energy levels 
associated with airguns were at least 20 dB lower at 1 kHz (considered 
``mid-frequency'') compared to higher energy levels associated with 
lower frequencies (below 300 Hz) (``all but a small fraction of the 
total energy being concentrated in the 10-300 Hz range'' [Tolstoy et 
al., 2009]), and at higher frequencies (e.g., 2.6-4 kHz), power might 
be less than 10 percent of the peak power at 10 Hz (Yoder, 2002). 
Energy levels measured by Tolstoy et al. (2009) were even lower at 
frequencies above 1 kHz. In addition, as sound propagates away from the 
source, it tends to lose higher-frequency components faster than low-
frequency components (i.e., low-frequency sounds typically propagate 
longer distances than high-frequency sounds) (Diebold et al., 2010). 
Although higher-frequency components of airgun signals have been 
recorded, it is typically in surface-ducting conditions (e.g., DeRuiter 
et al., 2006; Madsen et al., 2006) or in shallow water, where there are 
advantageous propagation conditions for the higher frequency (but low-
energy) components of the airgun signal (Hermannsen et al., 2015). This 
should not be of concern because the likely behavioral reactions of 
beaked whales that can result in acute physical injury would result 
from noise exposure at depth (because of the potentially greater 
consequences of severe behavioral reactions). In summary, the frequency 
content of airgun signals is such that beaked whales will not be able 
to hear the signals well (compared to MFA sonar), especially at depth 
where we expect the consequences of noise exposure could be more 
severe.
    Aside from frequency content, there are other significant 
differences between MFA sonar signals and the sounds produced by 
airguns that minimize the risk of severe behavioral reactions that 
could lead to strandings or deaths at sea, e.g., significantly longer 
signal duration, horizontal sound direction, typical fast and 
unpredictable source movement. All of these characteristics of MFA 
sonar tend towards greater potential to cause severe behavioral or 
physiological reactions in exposed beaked whales that may contribute to 
stranding. Although both sources are powerful, MFA sonar contains 
significantly greater energy in the mid-frequency range, where beaked 
whales hear better. Short-duration, high energy pulses--such as those 
produced by airguns--have greater potential to cause damage to auditory 
structures (though this is unlikely for mid-frequency cetaceans, as 
explained later in this document), but it is longer duration signals 
that have been implicated in the vast majority of beaked whale 
strandings. Faster, less predictable movements in combination with 
multiple source vessels are more likely to elicit a severe, potentially 
anti-predator response. Of additional interest in assessing the 
divergent characteristics of MFA sonar and airgun signals and their 
relative potential to cause stranding events or deaths at sea is the 
similarity between the MFA sonar signals and stereotyped calls of 
beaked whales' primary predator: The killer whale (Zimmer and Tyack, 
2007). Although generic disturbance stimuli--as airgun noise may be 
considered in this case for beaked whales--may also trigger 
antipredator responses, stronger responses should generally be expected 
when perceived risk is greater, as when the stimulus is confused for a 
known predator (Frid and Dill, 2002). In addition, because the source 
of the perceived predator (i.e., what is actually a MFA sonar signal) 
will likely be closer to the whales (because attenuation limits the 
range of detection of mid-frequencies) and moving faster (because it 
will be on faster-moving vessels), any antipredator response would be 
more likely to be severe (with greater perceived predation risk, an 
animal is more likely to disregard the cost of the response; Frid and 
Dill, 2002). Indeed, when analyzing movements of a beaked whale exposed 
to playback of killer whale predation calls, Allen et al. (2014) found 
that the whale engaged in a prolonged, directed avoidance response, 
suggesting a behavioral reaction that could pose a risk factor for 
stranding. Overall, these significant differences between sound from 
MFA sonar and the mid-frequency sound component from airguns and the 
likelihood that MFA sonar signals will be interpreted in error as a 
predator are critical to understanding the likely risk of behaviorally-
mediated injury due to seismic surveys.
    The available scientific literature also provides a useful contrast 
between airgun noise and MFA sonar regarding the likely risk of 
behaviorally-mediated injury. There is strong evidence for the 
association of beaked whale stranding events with MFA sonar use, and 
particularly detailed accounting of several events is available (e.g., 
a 2000 Bahamas stranding event for which investigators concluded that 
MFA sonar use was responsible; Evans and England, 2001). D'Amico et al. 
(2009) reviewed 126 beaked whale mass stranding events over the period 
from 1950 (i.e., from the development of modern MFA sonar systems) 
through 2004. Of these, there were two events where detailed 
information was available on both the timing and location of the 
stranding and the concurrent nearby naval activity, including 
verification of active MFA sonar usage, with no evidence for an 
alternative cause of stranding. An additional ten events were at 
minimum spatially and temporally coincident with naval activity likely 
to have included MFA sonar use and, despite incomplete knowledge of 
timing and location of the stranding or the naval activity in some 
cases, there was no evidence for an alternative cause of

[[Page 2008]]

stranding. The U.S. Navy has publicly stated agreement that five such 
events since 1996 were associated in time and space with MFA sonar use, 
either by the U.S. Navy alone or in joint training exercises with the 
North Atlantic Treaty Organization. The U.S. Navy additionally noted 
that, as of 2017, a 2014 beaked whale stranding event in Crete 
coincident with naval exercises was under review and had not yet been 
determined to be linked to sonar activities (U.S. Navy, 2017). 
Separately, the International Council for the Exploration of the Sea 
reported in 2005 that, worldwide, there have been about 50 known 
strandings, consisting mostly of beaked whales, with a potential causal 
link to MFA sonar (ICES, 2005). In contrast, very few such associations 
have been made to seismic surveys, despite widespread use of airguns as 
a geophysical sound source in numerous locations around the world.
    A more recent review of possible stranding associations with 
seismic surveys (Castellote and Llorens, 2016) states plainly that, 
``[s]peculation concerning possible links between seismic survey noise 
and cetacean strandings is available for a dozen events but without 
convincing causal evidence.'' The authors' ``exhaustive'' search of 
available information found 10 events worth further investigation via a 
ranking system representing a rough metric of the relative level of 
confidence offered by the data for inferences about the possible role 
of the seismic survey in a given stranding event. Only three of these 
events involved beaked whales. Whereas D'Amico et al. (2009) used a 1-5 
ranking system, in which ``1'' represented the most robust evidence 
connecting the event to MFA sonar use, Castellote and Llorens (2016) 
used a 1-6 ranking system, in which ``6'' represented the most robust 
evidence connecting the event to the seismic survey. As described 
above, D'Amico et al. (2009) found that two events were ranked ``1'' 
and ten events were ranked ``2'' (i.e., 12 beaked whale stranding 
events were found to be associated with MFA sonar use). In contrast, 
Castellote and Llorens (2016) found that none of the three beaked whale 
stranding events achieved their highest ranks of 5 or 6. Of the 10 
total events, none achieved the highest rank of 6. Two events were 
ranked as 5: One stranding in Peru involving dolphins and porpoises and 
a 2008 stranding in Madagascar. This latter ranking can only broadly be 
associated with the survey itself, as opposed to use of seismic 
airguns. An exhaustive investigation of this stranding event, which did 
not involve beaked whales, concluded that use of a high-frequency 
mapping system (12-kHz multibeam echosounder) was the most plausible 
and likely initial behavioral trigger of the event, which was likely 
exacerbated by several site- and situation-specific secondary factors. 
The review panel found that seismic airguns were used after the initial 
strandings and animals entering a lagoon system, that airgun use 
clearly had no role as an initial trigger, and that there was no 
evidence that airgun use dissuaded animals from leaving (Southall et 
al., 2013).
    However, one of these stranding events, involving two Cuvier's 
beaked whales, was contemporaneous with and reasonably associated 
spatially with a 2002 seismic survey in the Gulf of California 
conducted by L-DEO, as was the case for the 2007 Gulf of Cadiz seismic 
survey discussed by Castellote and Llorens (also involving two Cuvier's 
beaked whales). However, neither event was considered a ``true atypical 
mass stranding'' (according to Frantzis [1998]) as used in the analysis 
of Castellote and Llorens (2016). While we agree with the authors that 
this lack of evidence should not be considered conclusive, it is clear 
that there is very little evidence that seismic surveys should be 
considered as posing a significant risk of acute harm to beaked whales 
or other mid-frequency cetaceans. We have considered the potential for 
the proposed surveys to result in marine mammal stranding and have 
concluded that, based on the best available information, stranding is 
not expected to occur.
    Entanglement--Entanglements occur when marine mammals become 
wrapped around cables, lines, nets, or other objects suspended in the 
water column. During seismic survey operations, numerous cables, lines, 
and other objects primarily associated with the airgun array and 
hydrophone streamers will be towed behind the Langseth near the water`s 
surface. However, we are not aware of any cases of entanglement of 
mysticetes in seismic survey equipment. No incidents of entanglement of 
marine mammals with seismic survey gear have been documented in over 
54,000 nmi (100,000 km) of previous NSF-funded seismic surveys when 
observers were aboard (e.g., Smultea and Holst 2003; Haley and Koski 
2004; Holst 2004; Smultea et al., 2004; Holst et al., 2005; Haley and 
Ireland 2006; SIO and NSF 2006; Hauser et al., 2008; Holst and Smultea 
2008). Although entanglement with the streamer is theoretically 
possible, it has not been documented during tens of thousands of miles 
of NSF-sponsored seismic cruises or, to our knowledge, during hundreds 
of thousands of miles of industrial seismic cruises. Entanglement in 
OBSs and ocean bottom nodes (OBNs) is also not expected to occur. There 
are a relative few deployed devices, and no interaction between marine 
mammals and any such device has been recorded during prior NSF surveys 
using the devices. There are no meaningful entanglement risks posed by 
the proposed survey, and entanglement risks are not discussed further 
in this document.

Anticipated Effects on Marine Mammal Habitat

    Physical Disturbance--Sources of seafloor disturbance related to 
geophysical surveys that may impact marine mammal habitat include 
placement of anchors, nodes, cables, sensors, or other equipment on or 
in the seafloor for various activities. Equipment deployed on the 
seafloor has the potential to cause direct physical damage and could 
affect bottom-associated fish resources.
    Placement of OBSs on the seafloor could damage areas of hard bottom 
where direct contact with the seafloor occurs and could crush epifauna 
(organisms that live on the seafloor or surface of other organisms). 
Damage to unknown or unseen hard bottom could occur, but because of the 
small area covered by most bottom-founded equipment and the patchy 
distribution of hard bottom habitat, contact with unknown hard bottom 
is expected to be rare and impacts minor. Seafloor disturbance in areas 
of soft bottom can cause loss of small patches of epifauna and infauna 
due to burial or crushing, and bottom-feeding fishes could be 
temporarily displaced from feeding areas. Overall, any effects of 
physical damage to habitat are expected to be minor and temporary.
    Effects to Prey--Marine mammal prey varies by species, season, and 
location and, for some, is not well documented. Fish react to sounds 
which are especially strong and/or intermittent low-frequency sounds, 
and behavioral responses such as flight or avoidance are the most 
likely effects. However, the reaction of fish to airguns depends on the 
physiological state of the fish, past exposures, motivation (e.g., 
feeding, spawning, migration), and other environmental factors. Several 
studies have demonstrated that airgun 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.,

[[Page 2009]]

1992; Skalski et al., 1992; Santulli et al., 1999; Paxton et al., 
2017), though the bulk of studies indicate no or slight reaction to 
noise (e.g., Miller and Cripps, 2013; Dalen and Knutsen, 1987; Pena et 
al., 2013; Chapman and Hawkins, 1969; Wardle et al., 2001; Sara et al., 
2007; Jorgenson and Gyselman, 2009; Blaxter et al., 1981; Cott et al., 
2012; Boeger et al., 2006), and that, most commonly, while there are 
likely to be impacts to fish as a result of noise from nearby airguns, 
such effects will be temporary. For example, investigators reported 
significant, short-term declines in commercial fishing catch rate of 
gadid fishes during and for up to 5 days after seismic survey 
operations, but the catch rate subsequently returned to normal (Engas 
et al., 1996; Engas and Lokkeborg, 2002). Other studies have reported 
similar findings (Hassel et al., 2004). Skalski et al. (1992) also 
found a reduction in catch rates--for rockfish (Sebastes spp.) in 
response to controlled airgun exposure--but suggested that the 
mechanism underlying the decline was not dispersal but rather decreased 
responsiveness to baited hooks associated with an alarm behavioral 
response. A companion study showed that alarm and startle responses 
were not sustained following the removal of the sound source (Pearson 
et al., 1992). Therefore, Skalski et al. (1992) suggested that the 
effects on fish abundance may be transitory, primarily occurring during 
the sound exposure itself. In some cases, effects on catch rates are 
variable within a study, which may be more broadly representative of 
temporary displacement of fish in response to airgun noise (i.e., catch 
rates may increase in some locations and decrease in others) than any 
long-term damage to the fish themselves (Streever et al., 2016).
    SPLs of sufficient strength have been known to cause injury to fish 
and fish mortality and, in some studies, fish auditory systems have 
been damaged by airgun noise (McCauley et al., 2003; Popper et al., 
2005; Song et al., 2008). 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. (2012b. (2012) 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--both of which are conditions unlikely to occur for 
this survey that is necessarily transient in any given location and 
likely result in brief, infrequent noise exposure to prey species in 
any given area. For this survey, the sound source is constantly moving, 
and most fish would likely avoid the sound source prior to receiving 
sound of sufficient intensity to cause physiological or anatomical 
damage. In addition, ramp-up may allow certain fish species the 
opportunity to move further away from the sound source.
    A recent comprehensive review (Carroll et al., 2017) found that 
results are mixed as to the effects of airgun noise on the prey of 
marine mammals. While some studies suggest a change in prey 
distribution and/or a reduction in prey abundance following the use of 
seismic airguns, others suggest no effects or even positive effects in 
prey abundance. As one specific example, Paxton et al. (2017), which 
describes findings related to the effects of a 2014 seismic survey on a 
reef off of North Carolina, showed a 78 percent decrease in observed 
nighttime abundance for certain species. It is important to note that 
the evening hours during which the decline in fish habitat use was 
recorded (via video recording) occurred on the same day that the 
seismic survey passed, and no subsequent data is presented to support 
an inference that the response was long-lasting. Additionally, given 
that the finding is based on video images, the lack of recorded fish 
presence does not support a conclusion that the fish actually moved 
away from the site or suffered any serious impairment. In summary, this 
particular study corroborates prior studies indicating that a startle 
response or short-term displacement should be expected.
    Available data suggest that cephalopods are capable of sensing the 
particle motion of sounds and detect low frequencies up to 1-1.5 kHz, 
depending on the species, and so are likely to detect airgun noise 
(Kaifu et al., 2008; Hu et al., 2009; Mooney et al., 2010; Samson et 
al., 2014). Auditory injuries (lesions occurring on the statocyst 
sensory hair cells) have been reported upon controlled exposure to low-
frequency sounds, suggesting that cephalopods are particularly 
sensitive to low-frequency sound (Andre et al., 2011; Sole et al., 
2013). Behavioral responses, such as inking and jetting, have also been 
reported upon exposure to low-frequency sound (McCauley et al., 2000b; 
Samson et al., 2014). Similar to fish, however, the transient nature of 
the survey leads to an expectation that effects will be largely limited 
to behavioral reactions and would occur as a result of brief, 
infrequent exposures.
    With regard to potential impacts on zooplankton, McCauley et al. 
(2017) found that exposure to airgun noise resulted in significant 
depletion for more than half the taxa present and that there were two 
to three times more dead zooplankton after airgun exposure compared 
with controls for all taxa, within 1 km of the airguns. However, the 
authors also stated that in order to have significant impacts on r-
selected species (i.e., those with high growth rates and that produce 
many offspring) such as plankton, the spatial or temporal scale of 
impact must be large in comparison with the ecosystem concerned, and it 
is possible that the findings reflect avoidance by zooplankton rather 
than mortality (McCauley et al., 2017). In addition, the results of 
this study are inconsistent with a large body of research that 
generally finds limited spatial and temporal impacts to zooplankton as 
a result of exposure to airgun noise (e.g., Dalen and Knutsen, 1987; 
Payne, 2004; Stanley et al., 2011). Most prior research on this topic, 
which has focused on relatively small spatial scales, has showed 
minimal effects (e.g., Kostyuchenko, 1973; Booman et al., 1996; 
S[aelig]tre and Ona, 1996; Pearson et al., 1994; Bolle et al., 2012).
    A modeling exercise was conducted as a follow-up to the McCauley et 
al. (2017) study (as recommended by McCauley et al.), in order to 
assess the potential for impacts on ocean ecosystem dynamics and 
zooplankton population dynamics (Richardson et al., 2017). Richardson 
et al. (2017) found that for copepods with a short life cycle in a 
high-energy environment, a full-scale airgun survey would impact 
copepod abundance up to three days following the end of the survey, 
suggesting that effects such as those found by McCauley et al. (2017) 
would not be expected to be detectable downstream of the survey areas, 
either spatially or temporally.
    Notably, a more recent study produced results inconsistent with 
those of McCauley et al. (2017). Researchers conducted a field and 
laboratory study to assess if exposure to airgun noise affects 
mortality, predator escape response, or gene expression of the copepod 
Calanus finmarchicus (Fields et al., 2019). Immediate mortality of 
copepods was significantly higher, relative to controls, at distances 
of 5 m or less from the airguns. Mortality one week after the airgun 
blast was significantly higher in the copepods placed 10 m from the 
airgun but was not significantly different from the controls at a 
distance of 20 m from the airgun. The increase in mortality, relative 
to controls, did not exceed 30 percent at any distance from the airgun. 
Moreover,

[[Page 2010]]

the authors caution that even this higher mortality in the immediate 
vicinity of the airguns may be more pronounced than what would be 
observed in free-swimming animals due to increased flow speed of fluid 
inside bags containing the experimental animals. There were no 
sublethal effects on the escape performance or the sensory threshold 
needed to initiate an escape response at any of the distances from the 
airgun that were tested. Whereas McCauley et al. (2017) reported an SEL 
of 156 dB at a range of 509-658 m, with zooplankton mortality observed 
at that range, Fields et al. (2019) reported an SEL of 186 dB at a 
range of 25 m, with no reported mortality at that distance. Regardless, 
if we assume a worst-case likelihood of severe impacts to zooplankton 
within approximately 1 km of the acoustic source, the brief time to 
regeneration of the potentially affected zooplankton populations does 
not lead us to expect any meaningful follow-on effects to the prey base 
for marine mammals.
    A 2017 review article concluded that, while laboratory results 
provide scientific evidence for high-intensity and low-frequency sound-
induced physical trauma and other negative effects on some fish and 
invertebrates, the sound exposure scenarios in some cases are not 
realistic to those encountered by marine organisms during routine 
seismic survey operations (Carroll et al., 2017). The review finds that 
there has been no evidence of reduced catch or abundance following 
seismic activities for invertebrates, and that there is conflicting 
evidence for fish with catch observed to increase, decrease, or remain 
the same. Further, where there is evidence for decreased catch rates in 
response to airgun noise, these findings provide no information about 
the underlying biological cause of catch rate reduction (Carroll et 
al., 2017).
    In summary, impacts of the specified activity on marine mammal prey 
species will likely be limited to behavioral responses, the majority of 
prey species will be capable of moving out of the area during the 
survey, a rapid return to normal recruitment, distribution, and 
behavior for prey species is anticipated, and, overall, impacts to prey 
species will be minor and temporary. Prey species exposed to sound 
might move away from the sound source, experience TTS, experience 
masking of biologically relevant sounds, or show no obvious direct 
effects. Mortality from decompression injuries is possible in close 
proximity to a sound, but only limited data on mortality in response to 
airgun noise exposure are available (Hawkins et al., 2014). The most 
likely impacts for most prey species in the survey area would be 
temporary avoidance of the area. The proposed survey would move through 
an area relatively quickly, limiting exposure to multiple impulsive 
sounds. In all cases, sound levels would return to ambient once the 
survey moves out of the area or ends and the noise source is shut down 
and, when exposure to sound ends, behavioral and/or physiological 
responses are expected to end relatively quickly (McCauley et al., 
2000b). The duration of fish avoidance of a given area after survey 
effort stops is unknown, but a rapid return to normal recruitment, 
distribution, and behavior is anticipated. While the potential for 
disruption of spawning aggregations or schools of important prey 
species can be meaningful on a local scale, the mobile and temporary 
nature of this survey and the likelihood of temporary avoidance 
behavior suggest that impacts would be minor.
    Acoustic Habitat--Acoustic habitat is the soundscape--which 
encompasses all of the sound present in a particular location and time, 
as a whole--when considered from the perspective of the animals 
experiencing it. Animals produce sound for, or listen for sounds 
produced by, conspecifics (communication during feeding, mating, and 
other social activities), other animals (finding prey or avoiding 
predators), and the physical environment (finding suitable habitats, 
navigating). Together, sounds made by animals and the geophysical 
environment (e.g., produced by earthquakes, lightning, wind, rain, 
waves) make up the natural contributions to the total acoustics of a 
place. These acoustic conditions, termed acoustic habitat, are one 
attribute of an animal's total habitat.
    Soundscapes are also defined by, and acoustic habitat influenced 
by, the total contribution of anthropogenic sound. This may include 
incidental emissions from sources such as vessel traffic, or may be 
intentionally introduced to the marine environment for data acquisition 
purposes (as in the use of airgun arrays). Anthropogenic noise varies 
widely in its frequency content, duration, and loudness and these 
characteristics greatly influence the potential habitat-mediated 
effects to marine mammals (please see also the previous discussion on 
masking under ``Acoustic Effects''), which may range from local effects 
for brief periods of time to chronic effects over large areas and for 
long durations. Depending on the extent of effects to habitat, animals 
may alter their communications signals (thereby potentially expending 
additional energy) or miss acoustic cues (either conspecific or 
adventitious). For more detail on these concepts see, e.g., Barber et 
al., 2010; Pijanowski et al., 2011; Francis and Barber, 2013; Lillis et 
al., 2014.
    Problems arising from a failure to detect cues are more likely to 
occur when noise stimuli are chronic and overlap with biologically 
relevant cues used for communication, orientation, and predator/prey 
detection (Francis and Barber, 2013). Although the signals emitted by 
seismic airgun arrays are generally low frequency, they would also 
likely be of short duration and transient in any given area due to the 
nature of these surveys. As described previously, exploratory surveys 
such as these cover a large area but would be transient rather than 
focused in a given location over time and therefore would not be 
considered chronic in any given location.
    Based on the information discussed herein, we conclude that impacts 
of the specified activity are not likely to have more than short-term 
adverse effects on any prey habitat or populations of prey species. 
Further, any impacts to marine mammal habitat are not expected to 
result in significant or long-term consequences for individual marine 
mammals, or to contribute to adverse impacts on their populations.

Estimated Take

    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 
analysis and determination.
    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 seismic airguns has the potential to result in disruption of 
behavioral patterns for individual marine mammals. There is also some 
potential for auditory injury (Level A harassment) for mysticetes and 
high frequency cetaceans (i.e.,

[[Page 2011]]

porpoises, Kogia spp.). The proposed mitigation and monitoring measures 
are expected to minimize the severity of such taking to the extent 
practicable.
    As noted previously, no serious injury or mortality is anticipated 
or proposed to be authorized for this activity. Below we describe how 
the take is estimated.
    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 basic 
factors can contribute to a basic calculation to provide an initial 
prediction of 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 
estimate.

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 for non-explosive sources--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 (e.g., frequency, predictability, 
duty cycle), the environment (e.g., bathymetry), and the receiving 
animals (hearing, motivation, experience, demography, behavioral 
context) and can be difficult to predict (Southall et al., 2007, 
Ellison et al., 2012). Based on what the available science indicates 
and the practical need to use a threshold based on a factor that is 
both predictable and measurable for most activities, NMFS uses a 
generalized acoustic threshold based on received level to estimate the 
onset of behavioral harassment. NMFS predicts that marine mammals are 
likely to be behaviorally harassed in a manner we consider Level B 
harassment when exposed to underwater anthropogenic noise above 
received levels of 120 dB re 1 [mu]Pa (rms) for continuous (e.g., 
vibratory pile-driving, drilling) and above 160 dB re 1 [mu]Pa (rms) 
for non-explosive impulsive (e.g., seismic airguns) or intermittent 
(e.g., scientific sonar) sources. L-DEO's proposed activity includes 
the use of impulsive seismic sources. Therefore, the 160 dB re 1 [mu]Pa 
(rms) threshold is applicable for analysis of Level B harassment.
    Level A harassment for non-explosive sources--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). L-DEO's proposed seismic survey includes 
the use of impulsive (seismic airguns) sources.
    These thresholds are provided in the table below. The references, 
analysis, and methodology used in the development of the thresholds are 
described in NMFS 2018 Technical Guidance, which may be accessed at 
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

                     Table 3--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 this Technical Guidance. Hence, the subscript
  ``flat'' is being included to indicate peak sound pressure should be flat weighted or unweighted within the
  generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates
  the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds)
  and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could
  be exceeded in a multitude of ways (i.e., varying exposure levels and durations, duty cycle). When possible,
  it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be
  exceeded.

Ensonified Area

    Here, we describe operational and environmental parameters of the 
activity that will feed into identifying the area ensonified above the 
acoustic thresholds, which include source levels and transmission loss 
coefficient.
    The proposed 2-D survey would acquire data using the 36-airgun 
array with a total discharge of 6,600 in\3\ at a maximum tow depth of 
12 m. L-DEO model results are used to determine the 160-dBrms radius 
for the 36-airgun array in deep water (>1,000 m) down to a maximum 
water depth of 2,000 m. Received sound levels were predicted by L-DEO's 
model (Diebold et al., 2010) which uses ray tracing for the direct wave 
traveling from the array to the receiver and its associated source 
ghost (reflection at the air-water interface in the vicinity of the 
array), in a constant-velocity half-space (infinite homogeneous ocean 
layer, unbounded by a seafloor). In addition, propagation measurements 
of pulses from the 36-airgun array at a tow depth of 6 m have been 
reported in deep water (approximately 1,600 m), intermediate water 
depth on the slope (approximately 600-1,100 m), and shallow water 
(approximately 50 m) in the Gulf of Mexico in 2007-2008 (Tolstoy et al. 
2009; Diebold et al. 2010).

[[Page 2012]]

    For deep and intermediate-water cases, the field measurements 
cannot be used readily to derive Level A and Level B harassment 
isopleths, as at those sites the calibration hydrophone was located at 
a roughly constant depth of 350-500 m, which may not intersect all the 
SPL isopleths at their widest point from the sea surface down to the 
maximum relevant water depth for marine mammals of ~2,000 m. At short 
ranges, where the direct arrivals dominate and the effects of seafloor 
interactions are minimal, the data recorded at the deep and slope sites 
are suitable for comparison with modeled levels at the depth of the 
calibration hydrophone. At longer ranges, the comparison with the 
model--constructed from the maximum SPL through the entire water column 
at varying distances from the airgun array--is the most relevant.
    In deep and intermediate-water depths, comparisons at short ranges 
between sound levels for direct arrivals recorded by the calibration 
hydrophone and model results for the same array tow depth are in good 
agreement (Fig. 12 and 14 in Appendix H of NSF-USGS, 2011). 
Consequently, isopleths falling within this domain can be predicted 
reliably by the L-DEO model, although they may be imperfectly sampled 
by measurements recorded at a single depth. At greater distances, the 
calibration data show that seafloor-reflected and sub-seafloor-
refracted arrivals dominate, whereas the direct arrivals become weak 
and/or incoherent. Aside from local topography effects, the region 
around the critical distance is where the observed levels rise closest 
to the model curve. However, the observed sound levels are found to 
fall almost entirely below the model curve. Thus, analysis of the Gulf 
of Mexico calibration measurements demonstrates that although simple, 
the L-DEO model is a robust tool for conservatively estimating 
isopleths.
    For deep water (>1,000 m), L-DEO used the deep-water radii obtained 
from model results down to a maximum water depth of 2,000 m. The radii 
for intermediate water depths (100-1,000 m) were derived from the deep-
water ones by applying a correction factor (multiplication) of 1.5, 
such that observed levels at very near offsets fall below the corrected 
mitigation curve (See Fig. 16 in Appendix H of NSF-USGS, 2011).
    L-DEO's modeling methodology is described in greater detail in 
their IHA application. The estimated distances to the Level B 
harassment isopleths for the array are shown in Table 4. Please note 
that no survey effort will occur in waters <100 m deep. The estimated 
isopleth distance specific to shallow water depths are provided for 
reference only.

         Table 4--Predicted Radial Distances to Isopleths Corresponding to Level B Harassment Threshold
----------------------------------------------------------------------------------------------------------------
                                                                                                      Level B
                        Source and volume                          Tow depth (m)    Water depth     harassment
                                                                                        (m)          zone (m)
----------------------------------------------------------------------------------------------------------------
36 airgun array; 6,600 in\3\....................................              12          >1,000       \1\ 6,733
                                                                                       100-1,000      \2\ 10,100
                                                                                        \3\ <100      \4\ 25,494
----------------------------------------------------------------------------------------------------------------
\1\ Distance based on L-DEO model results.
\2\ Distance is based on L-DEO model results with a 1.5 x correction factor between deep and intermediate water
  depths.
\3\ No survey effort will occur in waters <100 m deep.
\4\ Distance is based on empirically derived measurements in the Gulf of Mexico (GoM) with scaling applied to
  account for differences in tow depth.

    Predicted distances to Level A harassment isopleths, which vary 
based on marine mammal hearing groups, were calculated based on 
modeling performed by L-DEO using the NUCLEUS source modeling software 
program and the NMFS User Spreadsheet, described below. The acoustic 
thresholds for impulsive sounds (e.g., airguns) contained in the 
Technical Guidance were presented as dual metric acoustic thresholds 
using both SELcum and peak sound pressure metrics (NMFS 
2018). As dual metrics, NMFS considers onset of PTS (Level A 
harassment) to have occurred when either one of the two metrics is 
exceeded (i.e., metric resulting in the largest isopleth). The 
SELcum metric considers both level and duration of exposure, 
as well as auditory weighting functions by marine mammal hearing group. 
In recognition of the fact that the requirement to calculate Level A 
harassment ensonified areas could be more technically challenging to 
predict due to the duration component and the use of weighting 
functions in the new SELcum thresholds, NMFS developed an 
optional User Spreadsheet that includes tools to help predict a simple 
isopleth that can be used in conjunction with marine mammal density or 
occurrence to facilitate the estimation of take numbers.
    The values for SELcum and peak SPL for the Langseth 
airgun arrays were derived from calculating the modified far-field 
signature. The far-field signature is often used as a theoretical 
representation of the source level. To compute the far-field signature, 
the source level is estimated at a large distance below the array 
(e.g., 9 km), and this level is back projected mathematically to a 
notional distance of 1 m from the array's geometrical center. However, 
when the source is an array of multiple airguns separated in space, the 
source level from the theoretical far-field signature is not 
necessarily the best measurement of the source level that is physically 
achieved at the source (Tolstoy et al., 2009). Near the source (at 
short ranges, distances <1 km), the pulses of sound pressure from each 
individual airgun in the source array do not stack constructively, as 
they do for the theoretical far-field signature. The pulses from the 
different airguns spread out in time such that the source levels 
observed or modeled are the result of the summation of pulses from a 
few airguns, not the full array (Tolstoy et al., 2009). At larger 
distances, away from the source array center, sound pressure of all the 
airguns in the array stack coherently, but not within one time sample, 
resulting in smaller source levels (a few dB) than the source level 
derived from the far-field signature. Because the far-field signature 
does not take into account the large array effect near the source and 
is calculated as a point source, the modified far-field signature is a 
more appropriate measure of the sound source level for distributed 
sound sources, such as airgun arrays. L-DEO used the acoustic modeling 
methodology as used for estimating Level B harassment distances with a 
small grid step of 1 m in both the inline and depth directions. The 
propagation modeling takes into account all airgun

[[Page 2013]]

interactions at short distances from the source, including interactions 
between subarrays, which are modeled using the NUCLEUS software to 
estimate the notional signature and MATLAB software to calculate the 
pressure signal at each mesh point of a grid.
    In order to more realistically incorporate the Technical Guidance's 
weighting functions over the seismic array's full acoustic band, 
unweighted spectrum data for the Langseth's airgun array (modeled in 1 
Hz bands) was used to make adjustments (dB) to the unweighted spectrum 
levels, by frequency, according to the weighting functions for each 
relevant marine mammal hearing group. These adjusted/weighted spectrum 
levels were then converted to pressures ([mu]Pa) in order to integrate 
them over the entire broadband spectrum, resulting in broadband 
weighted source levels by hearing group that could be directly 
incorporated within the User Spreadsheet (i.e., to override the 
Spreadsheet's more simple weighting factor adjustment). Using the User 
Spreadsheet's ``safe distance'' methodology for mobile sources 
(described by Sivle et al., 2014) with the hearing group-specific 
weighted source levels, and inputs assuming spherical spreading 
propagation and information specific to the planned survey (i.e., the 
2.2 m/s source velocity and (worst-case) 50-m shot interval, equivalent 
to a repetition rate of 23.1 seconds), potential radial distances to 
auditory injury zones were then calculated for SELcum 
thresholds.
    Inputs to the User Spreadsheets in the form of estimated source 
levels are shown in Appendix A of L-DEO's application. User 
Spreadsheets used by L-DEO to estimate distances to Level A harassment 
isopleths for the airgun arrays are also provided in Appendix A of the 
application. Outputs from the User Spreadsheets in the form of 
estimated distances to Level A harassment isopleths for the survey are 
shown in Table 5. As described above, NMFS considers onset of PTS 
(Level A harassment) to have occurred when either one of the dual 
metrics (SELcum and Peak SPLflat) is exceeded 
(i.e., metric resulting in the largest isopleth). L-DEO proposes to 
conduct two different methods of seismic acquisition, MCS using a 
hydrophone streamer (approximately 62 percent of the total survey 
effort) and refraction surveys using OBSs (approximately 38 percent of 
the total survey effort). The airguns would fire at a shot interval of 
50 m (repetition rate of 23 seconds) during MCS surveys and at a 400-m 
interval (repetition rate of 155 seconds) during refraction surveys to 
OBSs. The distances presented in Table 5 were calculated using the MCS 
survey inputs as using the 50-m shot interval provides more 
conservative distances than the 400-m shot interval.

        Table 5--Modeled Radial Distances (m) to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
                                                                    Level A harassment zone (m)
       Source (volume)             Threshold     ---------------------------------------------------------------
                                                   LF cetaceans    MF cetaceans    HF cetaceans      Otariids
----------------------------------------------------------------------------------------------------------------
36-airgun array (6,600        SELcum............           320.2               0             1.0               0
 in\3\).
                              Peak..............             8.9            13.9           268.3            10.6
----------------------------------------------------------------------------------------------------------------

    Note that because of some of the assumptions included in the 
methods used (e.g., stationary receiver with no vertical or horizontal 
movement in response to the acoustic source), isopleths produced may be 
overestimates to some degree, which will ultimately result in some 
degree of overestimation of Level A harassment. However, these tools 
offer the best way to predict appropriate isopleths when more 
sophisticated modeling methods are not available, and NMFS continues to 
develop ways to quantitatively refine these tools and will 
qualitatively address the output where appropriate. For mobile sources, 
such as the proposed seismic survey, the User Spreadsheet predicts the 
closest distance at which a stationary animal would not incur PTS if 
the sound source traveled by the animal in a straight line at a 
constant speed.
    Auditory injury is unlikely to occur for mid-frequency cetaceans 
and otariid pinnipeds, given very small modeled zones of injury for 
those species (all estimated zones less than 15 m for mid-frequency 
cetaceans and otariid pinnipeds), in context of distributed source 
dynamics. The source level of the array is a theoretical definition 
assuming a point source and measurement in the far-field of the source 
(MacGillivray, 2006). As described by Caldwell and Dragoset (2000), an 
array is not a point source, but one that spans a small area. In the 
far-field, individual elements in arrays will effectively work as one 
source because individual pressure peaks will have coalesced into one 
relatively broad pulse. The array can then be considered a ``point 
source.'' For distances within the near-field, i.e., approximately 2-3 
times the array dimensions, pressure peaks from individual elements do 
not arrive simultaneously because the observation point is not 
equidistant from each element. The effect is destructive interference 
of the outputs of each element, so that peak pressures in the near-
field will be significantly lower than the output of the largest 
individual element. Here, the relevant peak isopleth distances would in 
all cases be expected to be within the near-field of the array where 
the definition of source level breaks down. Therefore, actual locations 
within this distance of the array center where the sound level exceeds 
the relevant peak SPL thresholds would not necessarily exist. In 
general, Caldwell and Dragoset (2000) suggest that the near-field for 
airgun arrays is considered to extend out to approximately 250 m.
    In order to provide quantitative support for this theoretical 
argument, we calculated expected maximum distances at which the near-
field would transition to the far-field (Table 5). For a specific array 
one can estimate the distance at which the near-field transitions to 
the far-field by:
[GRAPHIC] [TIFF OMITTED] TN12JA22.028

with the condition that D >> [lambda], and where D is the distance, 
L is the longest dimension of the array, and [lambda] is the 
wavelength of the signal (Lurton, 2002).

    Given that [lambda] can be defined by:
    [GRAPHIC] [TIFF OMITTED] TN12JA22.029
    
where f is the frequency of the sound signal and v is the speed of 
the sound in the medium of interest, one can rewrite the equation 
for D as:
[GRAPHIC] [TIFF OMITTED] TN12JA22.030

and calculate D directly given a particular frequency and known speed

[[Page 2014]]

of sound (here assumed to be 1,500 meters per second in water, although 
this varies with environmental conditions).
    To determine the closest distance to the arrays at which the source 
level predictions in Table 5 are valid (i.e., maximum extent of the 
near-field), we calculated D based on an assumed frequency of 1 kHz. A 
frequency of 1 kHz is commonly used in near-field/far-field 
calculations for airgun arrays (Zykov and Carr, 2014; MacGillivray, 
2006; NSF and USGS, 2011), and based on representative airgun spectrum 
data and field measurements of an airgun array used on the Langseth, 
nearly all (greater than 95 percent) of the energy from airgun arrays 
is below 1 kHz (Tolstoy et al., 2009). Thus, using 1 kHz as the upper 
cut-off for calculating the maximum extent of the near-field should 
reasonably represent the near-field extent in field conditions.
    If the largest distance to the peak sound pressure level threshold 
was equal to or less than the longest dimension of the array (i.e., 
under the array), or within the near-field, then received levels that 
meet or exceed the threshold in most cases are not expected to occur. 
This is because within the near-field and within the dimensions of the 
array, the source levels specified in Appendix A of L-DEO's application 
are overestimated and not applicable. In fact, until one reaches a 
distance of approximately three or four times the near-field distance 
the average intensity of sound at any given distance from the array is 
still less than that based on calculations that assume a directional 
point source (Lurton, 2002). The 6,600-in\3\ airgun array planned for 
use during the proposed survey has an approximate diagonal of 28.8 m, 
resulting in a near-field distance of 138.7 m at 1 kHz (NSF and USGS, 
2011). Field measurements of this array indicate that the source 
behaves like multiple discrete sources, rather than a directional point 
source, beginning at approximately 400 m (deep site) to 1 km (shallow 
site) from the center of the array (Tolstoy et al., 2009), distances 
that are actually greater than four times the calculated 140-m near-
field distance. Within these distances, the recorded received levels 
were always lower than would be predicted based on calculations that 
assume a directional point source, and increasingly so as one moves 
closer towards the array (Tolstoy et al., 2009). Given this, relying on 
the calculated distance (138.7 m) as the distance at which we expect to 
be in the near-field is a conservative approach since even beyond this 
distance the acoustic modeling still overestimates the actual received 
level. Within the near-field, in order to explicitly evaluate the 
likelihood of exceeding any particular acoustic threshold, one would 
need to consider the exact position of the animal, its relationship to 
individual array elements, and how the individual acoustic sources 
propagate and their acoustic fields interact. Given that within the 
near-field and dimensions of the array source levels would be below 
those assumed here, we believe exceedance of the peak pressure 
threshold would only be possible under highly unlikely circumstances.
    In consideration of the received sound levels in the near-field as 
described above, we expect the potential for Level A harassment of mid-
frequency cetaceans, otariid pinnipeds, and phocid pinnipeds to be de 
minimis, even before the likely moderating effects of aversion and/or 
other compensatory behaviors (e.g., Nachtigall et al., 2018) are 
considered. We do not believe that Level A harassment is a likely 
outcome for any mid-frequency cetacean, otariid pinniped, or phocid 
pinniped and do not propose to authorize any Level A harassment for 
these species.

Marine Mammal Occurrence

    In this section we provide the information about the presence, 
density, or group dynamics of marine mammals that will inform the take 
calculations.
    L-DEO used habitat-based stratified marine mammal densities for 
summer for the ETP when available (Barlow et al., 2009), and densities 
for the ETP from NMFS (2015b) for all other species (Table 6). Barlow 
et al. (2009) used data from 16 NMFS Southwest Fisheries Science Center 
(SWFSC) ship-based cetacean and ecosystem assessment surveys between 
1986 and 2006 to develop habitat models to predict density for 15 
cetacean species in the ETP. Model predictions were then used in 
standard line-transect formulae to estimate density for each transect 
segment for each survey year. Predicted densities for each year were 
smoothed with geospatial methods to obtain a continuous grid of density 
estimates for the surveyed area in the ETP. These annual grids were 
then averaged to obtain a composite grid that represents our best 
estimates of cetacean density over the past 20 years in the ETP. The 
models developed by Barlow et al. (2009) have been incorporated into a 
web-based GIS software system developed by Duke University's Strategic 
Environmental Research and Development Program. The habitat-based 
density models consist of 100 km x 100 km grid cells. Densities in the 
grid cells that overlapped the survey area were averaged for each of 
the three water depth categories (shallow, intermediate, deep).
    The NMFS SWFSC also developed density estimates for species in the 
ETP that may be affected by their own fisheries research activities 
(NMFS 2015b). These estimates were derived from abundance estimates 
using ship-based surveys of marine mammals in the ETP, as reported by 
Gerrodette et al. (2008). While the SWFSC developed volumetric density 
estimates (animals/km\3\) to account for typical dive depth of each 
species (0-200 m and >200 m), L-DEO used the area density (animals/
km\2\) to represent expected density across all water depth strata.
    For the sei whale, for which NMFS (2015b) reported a density of 
zero, L-DEO used the spring density for Baja from U.S. Navy (2017b). No 
regional density estimates are available for Guadalupe fur seals in the 
ETP; therefore, NMFS (2015b) used the density of Guadalupe fur seals in 
the California Current Ecosystem (CCE) as a proxy. However, as the 
survey area is south of the typical range of Guadalupe fur seals (Ortiz 
et al., 2019), the density from the CCE is likely an overestimate. In 
the survey area, Guadalupe fur seals are extremely unlikely to occur in 
waters over the continental shelf under 2,000 m (T. Norris, pers. 
comm.). NMFS has therefore assumed that the density of Guadalupe fur 
seals in water depths under 2,000 m is zero animals per square km, and 
have retained the CCE density estimate for waters over 2,000 m deep 
(Table 6).

[[Page 2015]]



                   Table 6--Estimated Densities of Marine Mammals in the Proposed Survey Area
----------------------------------------------------------------------------------------------------------------
                                                                         Density (#/km\2\) in survey area
                                                                 -----------------------------------------------
                             Species                                               Intermediate
                                                                   Shallow water    water (100-     Deep water
                                                                     (<100 m)        1,000 m)       (>1,000 m)
----------------------------------------------------------------------------------------------------------------
Humpback whale..................................................     \1\ 0.00013     \1\ 0.00013     \1\ 0.00013
Minke whale.....................................................     \1\ 0.00001     \1\ 0.00001     \1\ 0.00001
Bryde's whale...................................................    \2\ 0.000486    \2\ 0.000489    \2\ 0.000451
Fin whale.......................................................     \1\ 0.00003     \1\ 0.00003     \1\ 0.00003
Sei whale.......................................................     \3\ 0.00005     \3\ 0.00005     \3\ 0.00005
Blue whale......................................................     \2\ 0.00010     \2\ 0.00009     \2\ 0.00008
Sperm whale.....................................................     \1\ 0.00019     \1\ 0.00019     \1\ 0.00019
Cuvier's beaked whale...........................................     \2\ 0.00105     \2\ 0.00106     \2\ 0.00107
Longman's beaked whale..........................................     \1\ 0.00004     \1\ 0.00004     \1\ 0.00004
Mesoplodon spp \4\..............................................     \2\ 0.00032     \2\ 0.00033     \2\ 0.00036
Risso's dolphin.................................................     \1\ 0.00517     \1\ 0.00517     \1\ 0.00517
Rough-toothed dolphin...........................................     \2\ 0.00880     \2\ 0.00891     \2\ 0.00945
Common bottlenose dolphin.......................................     \2\ 0.04809     \2\ 0.04502     \2\ 0.03557
Pantropical spotted dolphin.....................................     \1\ 0.12263     \1\ 0.12263     \1\ 0.12263
Spinner dolphin (whitebelly)....................................     \2\ 0.00148     \2\ 0.00155     \2\ 0.00193
Spinner dolphin (eastern).......................................     \2\ 0.13182     \2\ 0.12989     \2\ 0.12791
Striped dolphin.................................................     \2\ 0.02800     \2\ 0.02890     \2\ 0.03516
Short-beaked common dolphin.....................................     \2\ 0.04934     \2\ 0.04881     \2\ 0.04435
Fraser's dolphin................................................     \1\ 0.01355     \1\ 0.01355     \1\ 0.01355
Short-finned pilot whale \5\....................................     \2\ 0.00346     \2\ 0.00344     \2\ 0.00382
Killer whale....................................................      \1\ 0.0004      \1\ 0.0004      \1\ 0.0004
False killer whale..............................................     \1\ 0.00186     \1\ 0.00186     \1\ 0.00186
Pygmy killer whale..............................................     \1\ 0.00183     \1\ 0.00183     \1\ 0.00183
Melon-headed whale..............................................     \1\ 0.00213     \1\ 0.00213     \1\ 0.00213
Kogia spp.......................................................     \1\ 0.00053     \1\ 0.00053     \1\ 0.00053
Guadalupe fur seal..............................................               0         \1\ \6\     \1\ 0.00741
                                                                                         0.00741
California sea lion.............................................     \1\ 0.16262     \1\ 0.16262           \7\ 0
----------------------------------------------------------------------------------------------------------------
\1\ Density in greater ETP (NMFS 2015b).
\2\ Density in proposed survey area (Barlow et al., 2009).
\3\ Density for Baja (U.S. Navy 2017b).
\4\ Density for Mesoplodon species guild (Blainville's beaked whale, Gingko-toothed beaked whale, Deraniyagala's
  beaked whale, and pygmy beaked whale).
\5\ Density for Globicephala species guild.
\6\ Density is assumed to be zero in waters <2,000 m.
\7\ Density is assumed to be zero in deep water (>1,000 m).

Take Calculation and Estimation

    Here we describe how the information provided above is brought 
together to produce a quantitative take estimate.
    In order to estimate the number of marine mammals predicted to be 
exposed to sound levels that would result in Level A or Level B 
harassment, radial distances from the airgun array to predicted 
isopleths corresponding to the Level A harassment and Level B 
harassment thresholds are calculated, as described above. Those radial 
distances are then used to calculate the area(s) around the airgun 
array predicted to be ensonified to sound levels that exceed the Level 
A and Level B harassment thresholds. L-DEO identified specific seismic 
survey trackline(s) that could be surveyed on one day of research; in 
this case, a representative 182-km MCS line and a 222-km long OBS line 
were chosen. The distances to the 160-dB Level B harassment threshold 
and PTS (Level A harassment) thresholds (based on L-DEO model results) 
were used to draw a buffer around every transect line in GIS to 
determine the daily ensonified area in each depth category. The 
ensonified areas were then multiplied by the number of survey days (7 
days for OBS survey effort; 13 days for MCS survey effort) increased by 
25 percent. As noted previously, L-DEO has added 25 percent in the form 
of operational days, which is equivalent to adding 25 percent to the 
proposed line kilometers to be surveyed. This accounts for the 
possibility that additional operational days are required, but likely 
results in an overestimate of actual exposures. For additional details 
regarding calculations of ensonified area, please see Appendix D of L-
DEO's application. L-DEO's estimated incidents of exposure above Level 
A and Level B harassment criteria are presented in Table 7.
    As previously noted, NMFS does not have authority under the MMPA 
within the territorial seas of foreign nations (from 0-12 nmi (22.2 km) 
from shore), as the MMPA does not apply in those waters, and therefore 
does not authorize incidental take that may occur as a result of 
activities occurring within territorial waters. However, NMFS has still 
calculated the estimated level of incidental take in the entire 
activity area (including Mexican territorial waters) as part of the 
analysis supporting our determination under the MMPA that the activity 
will have a negligible impact on the affected species. The total 
estimated take in U.S. and Mexican waters is presented in Table 8 (see 
Negligible Impact Analysis and Determination).
    L-DEO generally assumed that their estimates of marine mammal 
exposures above harassment thresholds to equate to take and requested 
authorization of those takes. Those estimates in turn form the basis 
for our proposed take authorization numbers. For the species for which 
NMFS does not expect there to be a reasonable potential for take by 
Level A harassment to occur, i.e., mid-frequency cetaceans and all 
pinnipeds, we have added L-DEO's estimated exposures above Level A 
harassment thresholds (and requests for take by Level A harassment) to 
their estimated exposures above the Level B harassment threshold to 
produce a total number of incidents of take by Level B harassment

[[Page 2016]]

that is proposed for authorization. Estimated exposures and proposed 
take numbers for authorization are shown in Table 7.

                          Table 7--Estimated and Proposed Take by Level A and Level B Harassment, and Percentage of Population
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                             Estimated       Estimated    Proposed takes  Proposed takes                     Regional
                 Species                  takes by Level  takes by Level    by Level B      by Level A    Total proposed    population      Percent of
                                           B harassment    A harassment     harassment      harassment         take            size         population
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale..........................               8               0               8               0               8       \a\ 2,566            0.31
Minke whale.............................               1               0           \b\ 2               0           \b\ 2             115            1.74
Bryde's whale...........................              27               1              27               1              28         \a\ 649            4.31
Fin whale...............................               2               0               2               0               2         \a\ 145            1.38
Sei whale...............................               3               0               3               0               3      \c\ 29,600            0.01
Blue whale..............................               5               0               5               0               5             773            0.65
Sperm whale.............................              12               0              12               0              12           2,810            0.43
Cuvier's beaked whale...................              69               0              69               0              69      \c\ 20,000            0.35
Longman's beaked whale..................               3               0               3               0               3       \c\ 1,007            0.30
Mesoplodon spp..........................              23               0              23               0              23      \c\ 25,300            0.09
Risso's dolphin.........................             327               1             328               0             328      \a\ 24,084            1.36
Rough-toothed dolphin...................             596               1             597               0             597      \a\ 37,511            1.59
Common bottlenose dolphin...............           2,268               6            2274               0            2274      \a\ 61,536            3.70
Pantropical spotted dolphin.............           7,973              15            7988               0            7988     \a\ 146,296            5.46
Spinner dolphin (whitebelly)............             121               0             121               0             121     \a\ 186,906            0.06
Spinner dolphin (eastern)...............           8,173              16           8,189               0            8189     \a\ 186,906            4.38
Striped dolphin.........................           2,209               3            2212               0            2212     \a\ 128,867            1.72
Short-beaked common dolphin.............           2,812               6            2818               0            2818     \a\ 283,196            1.00
Fraser's dolphin........................             856               2             858               0             858     \c\ 289,300            0.30
Short-finned pilot whale................             244               0             244               0             244       \a\ 3,348            7.29
Killer whale............................              25               0              25               0              25         \a\ 852            2.93
False killer whale......................             118               0             118               0             118      \c\ 39,600            0.30
Pygmy killer whale......................             116               0             116               0             116      \c\ 38,900            0.30
Melon-headed whale......................             135               0             135               0             135      \c\ 45,400            0.30
Kogia spp...............................              33               1              33               1              34  \c\ \d\ 11,200            0.30
Guadalupe fur seal......................             415               1             416               0             416      \c\ 34,187            1.22
California sea lion.....................             349              16             365               0             365     \c\ 105,000            0.35
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Estimated population in Pacific waters of Mexico (Gerrodette and Palacios (1996)).
\b\ Proposed take increased to maximum group size.
\c\ Population in ETP or wider Pacific (NMFS 2015b).
\d\ Population of Kogia species guild.

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, we 
carefully consider 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) and 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, impact on 
operations, and, in the case of a military readiness activity, 
personnel safety, practicality of implementation, and impact on the 
effectiveness of the military readiness activity.
    In order to satisfy the MMPA's least practicable adverse impact 
standard, NMFS has evaluated a suite of basic mitigation protocols for 
seismic surveys that are required regardless of the status of a stock. 
Additional or enhanced protections may be required for species whose 
stocks are in particularly poor health and/or are subject to some 
significant additional stressor that lessens that stock's ability to 
weather the effects of the specified activities without worsening its 
status. We reviewed seismic mitigation protocols required or 
recommended elsewhere

[[Page 2017]]

(e.g., HESS, 1999; DOC, 2013; IBAMA, 2018; Kyhn et al., 2011; JNCC, 
2017; DEWHA, 2008; BOEM, 2016; DFO, 2008; GHFS, 2015; MMOA, 2016; 
Nowacek et al., 2013; Nowacek and Southall, 2016), recommendations 
received during public comment periods for previous actions, and the 
available scientific literature. We also considered recommendations 
given in a number of review articles (e.g., Weir and Dolman, 2007; 
Compton et al., 2008; Parsons et al., 2009; Wright and Cosentino, 2015; 
Stone, 2015b). This exhaustive review and consideration of public 
comments regarding previous, similar activities has led to development 
of the protocols included here.

Vessel-Based Visual Mitigation Monitoring

    Visual monitoring requires the use of trained observers (herein 
referred to as visual protected species observers (PSOs)) to scan the 
ocean surface for the presence of marine mammals. The area to be 
scanned visually includes primarily the exclusion zone (EZ), within 
which observation of certain marine mammals requires shutdown of the 
acoustic source, but also a buffer zone and, to the extent possible 
depending on conditions, the surrounding waters. The buffer zone means 
an area beyond the EZ to be monitored for the presence of marine 
mammals that may enter the EZ. During pre-start clearance monitoring 
(i.e., before ramp-up begins), the buffer zone also acts as an 
extension of the EZ in that observations of marine mammals within the 
buffer zone would also prevent airgun operations from beginning (i.e., 
ramp-up). The buffer zone encompasses the area at and below the sea 
surface from the edge of the 0-500 m EZ, out to a radius of 1,000 m 
from the edges of the airgun array (500-1,000 m). This 1,000-m zone (EZ 
plus buffer) represents the pre-start clearance zone. Visual monitoring 
of the EZ and adjacent waters is intended to establish and, when visual 
conditions allow, maintain zones around the sound source that are clear 
of marine mammals, thereby reducing or eliminating the potential for 
injury and minimizing the potential for more severe behavioral 
reactions for animals occurring closer to the vessel. Visual monitoring 
of the buffer zone is intended to (1) provide additional protection to 
marine mammals that may be in the vicinity of the vessel during pre-
start clearance, and (2) during airgun use, aid in establishing and 
maintaining the EZ by alerting the visual observer and crew of marine 
mammals that are outside of, but may approach and enter, the EZ.
    L-DEO must use dedicated, trained, NMFS-approved PSOs. The PSOs 
must have no tasks other than to conduct observational effort, record 
observational data, and communicate with and instruct relevant vessel 
crew with regard to the presence of marine mammals and mitigation 
requirements. PSO resumes shall be provided to NMFS for approval.
    At least one of the visual and two of the acoustic PSOs (discussed 
below) aboard the vessel must have a minimum of 90 days at-sea 
experience working in those roles, respectively, with no more than 18 
months elapsed since the conclusion of the at-sea experience. One 
visual PSO with such experience shall be designated as the lead for the 
entire protected species observation team. The lead PSO shall serve as 
primary point of contact for the vessel operator and ensure all PSO 
requirements per the IHA are met. To the maximum extent practicable, 
the experienced PSOs should be scheduled to be on duty with those PSOs 
with appropriate training but who have not yet gained relevant 
experience.
    During survey operations (e.g., any day on which use of the 
acoustic source is planned to occur, and whenever the acoustic source 
is in the water, whether activated or not), a minimum of two visual 
PSOs must be on duty and conducting visual observations at all times 
during daylight hours (i.e., from 30 minutes prior to sunrise through 
30 minutes following sunset). Visual monitoring of the pre-start 
clearance zone must begin no less than 30 minutes prior to ramp-up, and 
monitoring must continue until one hour after use of the acoustic 
source ceases or until 30 minutes past sunset. Visual PSOs shall 
coordinate to ensure 360[deg] visual coverage around the vessel from 
the most appropriate observation posts, and shall conduct visual 
observations using binoculars and the naked eye while free from 
distractions and in a consistent, systematic, and diligent manner.
    PSOs shall establish and monitor the exclusion and buffer zones. 
These zones shall be based upon the radial distance from the edges of 
the acoustic source (rather than being based on the center of the array 
or around the vessel itself). During use of the acoustic source (i.e., 
anytime airguns are active, including ramp-up), detections of marine 
mammals within the buffer zone (but outside the EZ) shall be 
communicated to the operator to prepare for the potential shutdown of 
the acoustic source. Visual PSOs will immediately communicate all 
observations to the on duty acoustic PSO(s), including any 
determination by the PSO regarding species identification, distance, 
and bearing and the degree of confidence in the determination. Any 
observations of marine mammals by crew members shall be relayed to the 
PSO team. During good conditions (e.g., daylight hours; Beaufort sea 
state (BSS) 3 or less), visual PSOs shall conduct observations when the 
acoustic source is not operating for comparison of sighting rates and 
behavior with and without use of the acoustic source and between 
acquisition periods, to the maximum extent practicable.
    Visual PSOs may be on watch for a maximum of 4 consecutive hours 
followed by a break of at least one hour between watches and may 
conduct a maximum of 12 hours of observation per 24-hour period. 
Combined observational duties (visual and acoustic but not at same 
time) may not exceed 12 hours per 24-hour period for any individual 
PSO.

Passive Acoustic Monitoring

    Acoustic monitoring means the use of trained personnel (sometimes 
referred to as passive acoustic monitoring (PAM) operators, herein 
referred to as acoustic PSOs) to operate PAM equipment to acoustically 
detect the presence of marine mammals. Acoustic monitoring involves 
acoustically detecting marine mammals regardless of distance from the 
source, as localization of animals may not always be possible. Acoustic 
monitoring is intended to further support visual monitoring (during 
daylight hours) in maintaining an EZ around the sound source that is 
clear of marine mammals. In cases where visual monitoring is not 
effective (e.g., due to weather, nighttime), acoustic monitoring may be 
used to allow certain activities to occur, as further detailed below.
    PAM would take place in addition to the visual monitoring program. 
Visual monitoring typically is not effective during periods of poor 
visibility or at night, and even with good visibility, is unable to 
detect marine mammals when they are below the surface or beyond visual 
range. Acoustic monitoring can be used in addition to visual 
observations to improve detection, identification, and localization of 
cetaceans. The acoustic monitoring would serve to alert visual PSOs (if 
on duty) when vocalizing cetaceans are detected. It is only useful when 
marine mammals vocalize, but it can be effective either by day or by 
night, and does not depend on good visibility. It would be monitored in 
real time so that the visual observers can be advised when cetaceans 
are detected.
    The R/V Langseth will use a towed PAM system, which must be 
monitored

[[Page 2018]]

by at a minimum one on duty acoustic PSO beginning at least 30 minutes 
prior to ramp-up and at all times during use of the acoustic source. 
Acoustic PSOs may be on watch for a maximum of 4 consecutive hours 
followed by a break of at least one hour between watches and may 
conduct a maximum of 12 hours of observation per 24-hour period. 
Combined observational duties (acoustic and visual but not at same 
time) may not exceed 12 hours per 24-hour period for any individual 
PSO.
    Survey activity may continue for 30 minutes when the PAM system 
malfunctions or is damaged, while the PAM operator diagnoses the issue. 
If the diagnosis indicates that the PAM system must be repaired to 
solve the problem, operations may continue for an additional 5 hours 
without acoustic monitoring during daylight hours only under the 
following conditions:
     Sea state is less than or equal to BSS 4;
     No marine mammals (excluding delphinids) detected solely 
by PAM in the applicable EZ in the previous 2 hours;
     NMFS is notified via email as soon as practicable with the 
time and location in which operations began occurring without an active 
PAM system; and
     Operations with an active acoustic source, but without an 
operating PAM system, do not exceed a cumulative total of 5 hours in 
any 24-hour period.

Establishment of Exclusion and Pre-Start Clearance Zones

    An EZ is a defined area within which occurrence of a marine mammal 
triggers mitigation action intended to reduce the potential for certain 
outcomes, e.g., auditory injury, disruption of critical behaviors. The 
PSOs would establish a minimum EZ with a 500-m radius. The 500-m EZ 
would be based on radial distance from the edge of the airgun array 
(rather than being based on the center of the array or around the 
vessel itself). With certain exceptions (described below), if a marine 
mammal appears within or enters this zone, the acoustic source would be 
shut down.
    The pre-start clearance zone is defined as the area that must be 
clear of marine mammals prior to beginning ramp-up of the acoustic 
source, and includes the EZ plus the buffer zone. Detections of marine 
mammals within the pre-start clearance zone would prevent airgun 
operations from beginning (i.e., ramp-up).
    The 500-m EZ is intended to be precautionary in the sense that it 
would be expected to contain sound exceeding the injury criteria for 
all cetacean hearing groups, (based on the dual criteria of 
SELcum and peak SPL), while also providing a consistent, 
reasonably observable zone within which PSOs would typically be able to 
conduct effective observational effort. Additionally, a 500-m EZ is 
expected to minimize the likelihood that marine mammals will be exposed 
to levels likely to result in more severe behavioral responses. 
Although significantly greater distances may be observed from an 
elevated platform under good conditions, we believe that 500 m is 
likely regularly attainable for PSOs using the naked eye during typical 
conditions. The pre-start clearance zone simply represents the addition 
of a buffer to the EZ, doubling the EZ size during pre-clearance.
    An extended EZ of 1,500 m must be enforced for all beaked whales 
and Kogia species. No buffer of this extended EZ is required.

Pre-Start Clearance and Ramp-Up

    Ramp-up (sometimes referred to as ``soft start'') means the gradual 
and systematic increase of emitted sound levels from an airgun array. 
Ramp-up begins by first activating a single airgun of the smallest 
volume, followed by doubling the number of active elements in stages 
until the full complement of an array's airguns are active. Each stage 
should be approximately the same duration, and the total duration 
should not be less than approximately 20 minutes. The intent of pre-
start clearance observation (30 minutes) is to ensure no protected 
species are observed within the pre-clearance zone (or extended EZ, for 
beaked whales and Kogia spp.) prior to the beginning of ramp-up. During 
pre-start clearance period is the only time observations of marine 
mammals in the buffer zone would prevent operations (i.e., the 
beginning of ramp-up). The intent of ramp-up is to warn marine mammals 
of pending seismic survey operations and to allow sufficient time for 
those animals to leave the immediate vicinity. A ramp-up procedure, 
involving a step-wise increase in the number of airguns firing and 
total array volume until all operational airguns are activated and the 
full volume is achieved, is required at all times as part of the 
activation of the acoustic source. All operators must adhere to the 
following pre-start clearance and ramp-up requirements:
     The operator must notify a designated PSO of the planned 
start of ramp-up as agreed upon with the lead PSO; the notification 
time should not be less than 60 minutes prior to the planned ramp-up in 
order to allow the PSOs time to monitor the pre-start clearance zone 
(and extended EZ) for 30 minutes prior to the initiation of ramp-up 
(pre-start clearance);
     Ramp-ups shall be scheduled so as to minimize the time 
spent with the source activated prior to reaching the designated run-
in;
     One of the PSOs conducting pre-start clearance 
observations must be notified again immediately prior to initiating 
ramp-up procedures and the operator must receive confirmation from the 
PSO to proceed;
     Ramp-up may not be initiated if any marine mammal is 
within the applicable exclusion or buffer zone. If a marine mammal is 
observed within the pre-start clearance zone (or extended EZ, for 
beaked whales and Kogia species) during the 30 minute pre-start 
clearance period, ramp-up may not begin until the animal(s) has been 
observed exiting the zones or until an additional time period has 
elapsed with no further sightings (15 minutes for small odontocetes and 
pinnipeds, and 30 minutes for all mysticetes and all other odontocetes, 
including sperm whales, beaked whales, and large delphinids, such as 
killer whales);
     Ramp-up shall begin by activating a single airgun of the 
smallest volume in the array and shall continue in stages by doubling 
the number of active elements at the commencement of each stage, with 
each stage of approximately the same duration. Duration shall not be 
less than 20 minutes. The operator must provide information to the PSO 
documenting that appropriate procedures were followed;
     PSOs must monitor the pre-start clearance zone (and 
extended EZ) during ramp-up, and ramp-up must cease and the source must 
be shut down upon detection of a marine mammal within the applicable 
zone. Once ramp-up has begun, detections of marine mammals within the 
buffer zone do not require shutdown, but such observation shall be 
communicated to the operator to prepare for the potential shutdown;
     Ramp-up may occur at times of poor visibility, including 
nighttime, if appropriate acoustic monitoring has occurred with no 
detections in the 30 minutes prior to beginning ramp-up. Acoustic 
source activation may only occur at times of poor visibility where 
operational planning cannot reasonably avoid such circumstances;
     If the acoustic source is shut down for brief periods 
(i.e., less than 30 minutes) for reasons other than that described for 
shutdown (e.g., mechanical difficulty), it may be activated again 
without ramp-up if PSOs have maintained constant visual and/or acoustic 
observation and no visual or

[[Page 2019]]

acoustic detections of marine mammals have occurred within the 
applicable EZ. For any longer shutdown, pre-start clearance observation 
and ramp-up are required. For any shutdown at night or in periods of 
poor visibility (e.g., BSS 4 or greater), ramp-up is required, but if 
the shutdown period was brief and constant observation was maintained, 
pre-start clearance watch of 30 minutes is not required; and
     Testing of the acoustic source involving all elements 
requires ramp-up. Testing limited to individual source elements or 
strings does not require ramp-up but does require pre-start clearance 
of 30 min.

Shutdown

    The shutdown of an airgun array requires the immediate de-
activation of all individual airgun elements of the array. Any PSO on 
duty will have the authority to delay the start of survey operations or 
to call for shutdown of the acoustic source if a marine mammal is 
detected within the applicable EZ. The operator must also establish and 
maintain clear lines of communication directly between PSOs on duty and 
crew controlling the acoustic source to ensure that shutdown commands 
are conveyed swiftly while allowing PSOs to maintain watch. When both 
visual and acoustic PSOs are on duty, all detections will be 
immediately communicated to the remainder of the on-duty PSO team for 
potential verification of visual observations by the acoustic PSO or of 
acoustic detections by visual PSOs. When the airgun array is active 
(i.e., anytime one or more airguns is active, including during ramp-up) 
and (1) a marine mammal appears within or enters the applicable EZ and/
or (2) a marine mammal (other than delphinids, see below) is detected 
acoustically and localized within the applicable EZ, the acoustic 
source will be shut down. When shutdown is called for by a PSO, the 
acoustic source will be immediately deactivated and any dispute 
resolved only following deactivation. Additionally, shutdown will occur 
whenever PAM alone (without visual sighting), confirms presence of 
marine mammal(s) in the EZ. If the acoustic PSO cannot confirm presence 
within the EZ, visual PSOs will be notified but shutdown is not 
required.
    Following a shutdown, airgun activity would not resume until the 
marine mammal has cleared the EZ. The animal would be considered to 
have cleared the EZ if it is visually observed to have departed the EZ 
(i.e., animal is not required to fully exit the buffer zone where 
applicable), or it has not been seen within the EZ for 15 minutes for 
small odontocetes and pinnipeds, or 30 minutes for all mysticetes and 
all other odontocetes, including sperm whales, beaked whales, Kogia 
species, and large delphinids, such as killer whales.
    The shutdown requirement is waived for small dolphins if an 
individual is detected within the EZ. As defined here, the small 
dolphin group is intended to encompass those members of the Family 
Delphinidae most likely to voluntarily approach the source vessel for 
purposes of interacting with the vessel and/or airgun array (e.g., bow 
riding). This exception to the shutdown requirement applies solely to 
specific genera of small dolphins (Delphinus, Lagenodelphis, 
Lissodelphis, Stenella, Steno, and Tursiops).
    We include this small dolphin exception because shutdown 
requirements for small dolphins under all circumstances represent 
practicability concerns without likely commensurate benefits for the 
animals in question. Small dolphins are generally the most commonly 
observed marine mammals in the specific geographic region and would 
typically be the only marine mammals likely to intentionally approach 
the vessel. As described above, auditory injury is extremely unlikely 
to occur for mid-frequency cetaceans (e.g., delphinids), as this group 
is relatively insensitive to sound produced at the predominant 
frequencies in an airgun pulse while also having a relatively high 
threshold for the onset of auditory injury (i.e., permanent threshold 
shift).
    A large body of anecdotal evidence indicates that small dolphins 
commonly approach vessels and/or towed arrays during active sound 
production for purposes of bow riding, with no apparent effect observed 
in those delphinoids (e.g., Barkaszi et al., 2012, Barkaszi and Kelly, 
2018). The potential for increased shutdowns resulting from such a 
measure would require the Langseth to revisit the missed track line to 
reacquire data, resulting in an overall increase in the total sound 
energy input to the marine environment and an increase in the total 
duration over which the survey is active in a given area. Although 
other mid-frequency hearing specialists (e.g., large delphinids) are no 
more likely to incur auditory injury than are small dolphins, they are 
much less likely to approach vessels. Therefore, retaining a shutdown 
requirement for large delphinids would not have similar impacts in 
terms of either practicability for the applicant or corollary increase 
in sound energy output and time on the water. We do anticipate some 
benefit for a shutdown requirement for large delphinids in that it 
simplifies somewhat the total range of decision-making for PSOs and may 
preclude any potential for physiological effects other than to the 
auditory system as well as some more severe behavioral reactions for 
any such animals in close proximity to the Langseth.
    Visual PSOs shall use best professional judgment in making the 
decision to call for a shutdown if there is uncertainty regarding 
identification (i.e., whether the observed marine mammal(s) belongs to 
one of the delphinid genera for which shutdown is waived or one of the 
species with a larger EZ).
    L-DEO must implement shutdown if a marine mammal species for which 
take was not authorized, or a species for which authorization was 
granted but the takes have been met, approaches the Level A or Level B 
harassment zones. L-DEO must also implement shutdown if any large whale 
(defined as a sperm whale or any mysticete species) with a calf 
(defined as an animal less than two-thirds the body size of an adult 
observed to be in close association with an adult) and/or an 
aggregation of six or more large whales are observed at any distance.

Vessel Strike Avoidance

    Vessel operators and crews must maintain a vigilant watch for all 
protected species and slow down, stop their vessel, or alter course, as 
appropriate and regardless of vessel size, to avoid striking any marine 
mammal. A visual observer aboard the vessel must monitor a vessel 
strike avoidance zone around the vessel (distances stated below). 
Visual observers monitoring the vessel strike avoidance zone may be 
third-party observers (i.e., PSOs) or crew members, but crew members 
responsible for these duties must be provided sufficient training to 
(1) distinguish marine mammals from other phenomena and (2) broadly to 
identify a marine mammal as a whale or other marine mammal.
    Vessel speeds must be reduced to 10 knots or less when mother/calf 
pairs, pods, or large assemblages of cetaceans are observed near a 
vessel.
    All vessels must maintain a minimum separation distance of 100 m 
from sperm whales and all other baleen whales.
    All vessels must, to the maximum extent practicable, attempt to 
maintain a minimum separation distance of 50 m from all other marine 
mammals, with an understanding that at times this may not be possible 
(e.g., for animals that approach the vessel).

[[Page 2020]]

    When marine mammals are sighted while a vessel is underway, the 
vessel shall take action as necessary to avoid violating the relevant 
separation distance (e.g., attempt to remain parallel to the animal's 
course, avoid excessive speed or abrupt changes in direction until the 
animal has left the area). If marine mammals are sighted within the 
relevant separation distance, the vessel must reduce speed and shift 
the engine to neutral, not engaging the engines until animals are clear 
of the area. This does not apply to any vessel towing gear or any 
vessel that is navigationally constrained.
    These requirements do not apply in any case where compliance would 
create an imminent and serious threat to a person or vessel or to the 
extent that a vessel is restricted in its ability to maneuver and, 
because of the restriction, cannot comply.
    We have carefully evaluated the suite of mitigation measures 
described here and considered a range of other measures in the context 
of ensuring that we prescribe the means of effecting the least 
practicable adverse impact on the affected marine mammal species and 
stocks and their habitat. Based on our evaluation of the proposed 
measures, as well as other measures considered by NMFS described above, 
NMFS has preliminarily determined that the mitigation measures provide 
the means of effecting the least practicable impact on the affected 
species or stocks and their habitat, paying particular attention to 
rookeries, mating grounds, and areas of similar significance.

Mitigation Measures in Mexican Waters

    As stated previously, NMFS cannot authorize the incidental take of 
marine mammals in the territorial seas of foreign nations, as the MMPA 
does not apply in those waters. L-DEO is required to adhere to the 
mitigation measures described above while operating within the Mexican 
EEZ and International Waters. The requirements do not apply within 
Mexican territorial waters. Mexico may prescribe mitigation measures 
that would apply to survey operations within the Mexican EEZ and 
territorial waters but NMFS is currently unaware of any specific 
potential requirements. While operating within the Mexican EEZ but 
outside Mexican territorial waters, if mitigation requirements 
prescribed by NMFS differ from the requirements established under 
Mexican law, L-DEO would adhere to the most protective measure. For 
operations in Mexican territorial waters, L-DEO would implement 
measures required under Mexican law (if any). If information regarding 
measures required under Mexican law becomes available prior to NMFS' 
final decision on this request for IHA, NMFS will consider it as 
appropriate in making its negligible impact determination.

Proposed Monitoring and Reporting

    In order to issue an IHA for an activity, section 101(a)(5)(D) of 
the MMPA states that NMFS must set forth requirements pertaining to the 
monitoring and reporting of such taking. The MMPA implementing 
regulations at 50 CFR 216.104(a)(13) indicate that requests for 
authorizations must include the suggested means of accomplishing the 
necessary monitoring and reporting that will result in increased 
knowledge of the species and of the level of taking or impacts on 
populations of marine mammals that are expected to be present in the 
proposed action area. 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 action; 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.

Vessel-Based Visual Monitoring

    As described above, PSO observations would take place during 
daytime airgun operations. During seismic survey operations, at least 
five visual PSOs would be based aboard the Langseth. Two visual PSOs 
would be on duty at all time during daytime hours. Monitoring shall be 
conducted in accordance with the following requirements:
     The operator shall provide PSOs with bigeye binoculars 
(e.g., 25 x 150; 2.7 view angle; individual ocular focus; height 
control) of appropriate quality (i.e., Fujinon or equivalent) solely 
for PSO use. These shall be pedestal-mounted on the deck at the most 
appropriate vantage point that provides for optimal sea surface 
observation, PSO safety, and safe operation of the vessel; and
     The operator will work with the selected third-party 
observer provider to ensure PSOs have all equipment (including backup 
equipment) needed to adequately perform necessary tasks, including 
accurate determination of distance and bearing to observed marine 
mammals.
    PSOs must have the following requirements and qualifications:
     PSOs shall be independent, dedicated, trained visual and 
acoustic PSOs and must be employed by a third-party observer provider;
     PSOs shall have no tasks other than to conduct 
observational effort (visual or acoustic), collect data, and 
communicate with and instruct relevant vessel crew with regard to the 
presence of protected species and mitigation requirements (including 
brief alerts regarding maritime hazards);
     PSOs shall have successfully completed an approved PSO 
training course appropriate for their designated task (visual or 
acoustic). Acoustic PSOs are required to complete specialized training 
for operating PAM systems and are encouraged to have familiarity with 
the vessel with which they will be working;
     PSOs can act as acoustic or visual observers (but not at 
the same time) as long as they demonstrate that their training and 
experience are sufficient to perform the task at hand;
     NMFS must review and approve PSO resumes accompanied by a 
relevant training course information packet that includes the name and 
qualifications (i.e., experience, training completed, or educational 
background) of the instructor(s), the course outline or syllabus, and 
course reference material as well as a document stating successful 
completion of the course;

[[Page 2021]]

     PSOs must successfully complete relevant training, 
including completion of all required coursework and passing (80 percent 
or greater) a written and/or oral examination developed for the 
training program;
     PSOs must have successfully attained a bachelor's degree 
from an accredited college or university with a major in one of the 
natural sciences, a minimum of 30 semester hours or equivalent in the 
biological sciences, and at least one undergraduate course in math or 
statistics; and
     The educational requirements may be waived if the PSO has 
acquired the relevant skills through alternate experience. Requests for 
such a waiver shall be submitted to NMFS and must include written 
justification. Requests shall be granted or denied (with justification) 
by NMFS within 1 week of receipt of submitted information. Alternate 
experience that may be considered includes, but is not limited to (1) 
secondary education and/or experience comparable to PSO duties; (2) 
previous work experience conducting academic, commercial, or 
government-sponsored protected species surveys; or (3) previous work 
experience as a PSO; the PSO should demonstrate good standing and 
consistently good performance of PSO duties.
    For data collection purposes, PSOs shall use standardized data 
collection forms, whether hard copy or electronic. PSOs shall record 
detailed information about any implementation of mitigation 
requirements, including the distance of animals to the acoustic source 
and description of specific actions that ensued, the behavior of the 
animal(s), any observed changes in behavior before and after 
implementation of mitigation, and if shutdown was implemented, the 
length of time before any subsequent ramp-up of the acoustic source. If 
required mitigation was not implemented, PSOs should record a 
description of the circumstances. At a minimum, the following 
information must be recorded:
     Vessel names (source vessel and other vessels associated 
with survey) and call signs;
     PSO names and affiliations;
     Dates of departures and returns to port with port name;
     Date and participants of PSO briefings;
     Dates and times (Greenwich Mean Time) of survey effort and 
times corresponding with PSO effort;
     Vessel location (latitude/longitude) when survey effort 
began and ended and vessel location at beginning and end of visual PSO 
duty shifts;
     Vessel heading and speed at beginning and end of visual 
PSO duty shifts and upon any line change;
     Environmental conditions while on visual survey (at 
beginning and end of PSO shift and whenever conditions changed 
significantly), including BSS and any other relevant weather conditions 
including cloud cover, fog, sun glare, and overall visibility to the 
horizon;
     Factors that may have contributed to impaired observations 
during each PSO shift change or as needed as environmental conditions 
changed (e.g., vessel traffic, equipment malfunctions); and
     Survey activity information, such as acoustic source power 
output while in operation, number and volume of airguns operating in 
the array, tow depth of the array, and any other notes of significance 
(i.e., pre-start clearance, ramp-up, shutdown, testing, shooting, ramp-
up completion, end of operations, streamers, etc.).
    The following information should be recorded upon visual 
observation of any protected species:
     Watch status (sighting made by PSO on/off effort, 
opportunistic, crew, alternate vessel/platform);
     PSO who sighted the animal;
     Time of sighting;
     Vessel location at time of sighting;
     Water depth;
     Direction of vessel's travel (compass direction);
     Direction of animal's travel relative to the vessel;
     Pace of the animal;
     Estimated distance to the animal and its heading relative 
to vessel at initial sighting;
     Identification of the animal (e.g., genus/species, lowest 
possible taxonomic level, or unidentified) and the composition of the 
group if there is a mix of species;
     Estimated number of animals (high/low/best);
     Estimated number of animals by cohort (adults, yearlings, 
juveniles, calves, group composition, etc.);
     Description (as many distinguishing features as possible 
of each individual seen, including length, shape, color, pattern, scars 
or markings, shape and size of dorsal fin, shape of head, and blow 
characteristics);
     Detailed behavior observations (e.g., number of blows/
breaths, number of surfaces, breaching, spyhopping, diving, feeding, 
traveling; as explicit and detailed as possible; note any observed 
changes in behavior);
     Animal's closest point of approach (CPA) and/or closest 
distance from any element of the acoustic source;
     Platform activity at time of sighting (e.g., deploying, 
recovering, testing, shooting, data acquisition, other); and
     Description of any actions implemented in response to the 
sighting (e.g., delays, shutdown, ramp-up) and time and location of the 
action.
    If a marine mammal is detected while using the PAM system, the 
following information should be recorded:
     An acoustic encounter identification number, and whether 
the detection was linked with a visual sighting;
     Date and time when first and last heard;
     Types and nature of sounds heard (e.g., clicks, whistles, 
creaks, burst pulses, continuous, sporadic, strength of signal); and
     Any additional information recorded such as water depth of 
the hydrophone array, bearing of the animal to the vessel (if 
determinable), species or taxonomic group (if determinable), 
spectrogram screenshot, and any other notable information.

Reporting

    A report would be submitted to NMFS within 90 days after the end of 
the cruise. The report would summarize the dates and locations of 
seismic survey operations, and all marine mammal sightings (dates, 
times, locations, activities, associated seismic survey activities), 
and provide full documentation of methods, results, and interpretation 
pertaining to all monitoring.
    The draft report shall also include geo-referenced time-stamped 
vessel tracklines for all time periods during which airguns were 
operating. Tracklines should include points recording any change in 
airgun status (e.g., when the airguns began operating, when they were 
turned off, or when they changed from full array to single gun or vice 
versa). GIS files shall be provided in ESRI shapefile format and 
include the UTC date and time, latitude in decimal degrees, and 
longitude in decimal degrees. All coordinates shall be referenced to 
the WGS84 geographic coordinate system. In addition to the report, all 
raw observational data shall be made available to NMFS. The report must 
summarize the data collected as described above and in the IHA. A final 
report must be submitted within 30 days following resolution of any 
comments on the draft report.

Reporting Injured or Dead Marine Mammals

    Discovery of injured or dead marine mammals--In the event that 
personnel involved in survey activities covered by

[[Page 2022]]

the authorization discover an injured or dead marine mammal, the L-DEO 
shall report the incident to the Office of Protected Resources (OPR), 
NMFS and to the NMFS West Coast Regional Stranding Coordinator as soon 
as feasible. The report must include the following information:
     Time, date, and location (latitude/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.
    Vessel strike--In the event of a ship strike of a marine mammal by 
any vessel involved in the activities covered by the authorization, L-
DEO shall report the incident to OPR, NMFS and to the NMFS West Coast 
Regional Stranding Coordinator as soon as feasible. The report must 
include the following information:
     Time, date, and location (latitude/longitude) of the 
incident;
     Vessel's speed during and leading up to the incident;
     Vessel's course/heading and what operations were being 
conducted (if applicable);
     Status of all sound sources in use;
     Description of avoidance measures/requirements that were 
in place at the time of the strike and what additional measure were 
taken, if any, to avoid strike;
     Environmental conditions (e.g., wind speed and direction, 
Beaufort sea state, cloud cover, visibility) immediately preceding the 
strike;
     Species identification (if known) or description of the 
animal(s) involved;
     Estimated size and length of the animal that was struck;
     Description of the behavior of the animal immediately 
preceding and following the strike;
     If available, description of the presence and behavior of 
any other marine mammals present immediately preceding the strike;
     Estimated fate of the animal (e.g., dead, injured but 
alive, injured and moving, blood or tissue observed in the water, 
status unknown, disappeared); and
     To the extent practicable, photographs or video footage of 
the animal(s).

Actions To Minimize Additional Harm to Live-Stranded (or Milling) 
Marine Mammals

    In the event of a live stranding (or near-shore atypical milling) 
event within 50 km of the survey operations, where the NMFS stranding 
network is engaged in herding or other interventions to return animals 
to the water, the Director of OPR, NMFS (or designee) will advise L-DEO 
of the need to implement shutdown for all active acoustic sources 
operating within 50 km of the stranding. Procedures related to 
shutdowns for live stranding or milling marine mammals include the 
following:
     If at any time, the marine mammal(s) die or are 
euthanized, or if herding/intervention efforts are stopped, the 
Director of OPR, NMFS (or designee) will advise L-DEO that the shutdown 
around the animals' location is no longer needed.
     Otherwise, shutdown procedures will remain in effect until 
the Director of OPR, NMFS (or designee) determines and advises L-DEO 
that all live animals involved have left the area (either of their own 
volition or following an intervention).
     If further observations of the marine mammals indicate the 
potential for re-stranding, additional coordination with L-DEO will be 
required to determine what measures are necessary to minimize that 
likelihood (e.g., extending the shutdown or moving operations farther 
away) and to implement those measures as appropriate.
    Additional Information Requests--If NMFS determines that the 
circumstances of any marine mammal stranding found in the vicinity of 
the activity suggest investigation of the association with survey 
activities is warranted, and an investigation into the stranding is 
being pursued, NMFS will submit a written request to L-DEO indicating 
that the following initial available information must be provided as 
soon as possible, but no later than 7 business days after the request 
for information:
     Status of all sound source use in the 48 hours preceding 
the estimated time of stranding and within 50 km of the discovery/
notification of the stranding by NMFS; and
     If available, description of the behavior of any marine 
mammal(s) observed preceding (i.e., within 48 hours and 50 km) and 
immediately after the discovery of the stranding.
    In the event that the investigation is still inconclusive, the 
investigation of the association of the survey activities is still 
warranted, and the investigation is still being pursued, NMFS may 
provide additional information requests, in writing, regarding the 
nature and location of survey operations prior to the time period 
above.

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 responses (e.g., intensity, duration), the context 
of any responses (e.g., critical reproductive time or location, 
migration), 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's 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 environmental 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, our analysis applies to all species listed in 
Table 1, given that NMFS expects the anticipated effects of the planned 
geophysical survey to be 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, NMFS has identified species-specific factors to inform the 
analysis.
    As described above, we propose to authorize only the takes 
estimated to occur outside of Mexican territorial waters (Table 7); 
however, for the purposes of our negligible impact analysis and 
determination, we consider the total number of takes that are

[[Page 2023]]

anticipated to occur as a result of the entire survey (including the 
portion of the survey that would occur within the Mexican territorial 
waters (approximately 6 percent of the survey) (Table 8).

                                           Table 8--Total Estimated Take Including Mexican Territorial Waters
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                              Level B         Level A
                                                            harassment      harassment        Level B         Level A
                                                            (excluding      (excluding      harassment      harassment     Total Level B   Total Level A
                         Species                              Mexican         Mexican        (Mexican        (Mexican       harassment      harassment
                                                            territorial     territorial     territorial     territorial
                                                              waters)         waters)         waters)         waters)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale..........................................               8               0               1               0               9               0
Minke whale.............................................               2               0               0               0               2               0
Bryde's whale...........................................              27               1               2               0              29               1
Fin whale...............................................               2               0               0               0               2               0
Sei whale...............................................               3               0               0               0               3               0
Blue whale..............................................               5               0               0               0               5               0
Sperm whale.............................................              12               0               1               0              13               0
Cuvier's beaked whale...................................              69               0              69               0             138               0
Longman's beaked whale..................................               3               0               0               0               3               0
Mesoplodon spp..........................................              23               0               1               0              24               0
Risso's dolphin.........................................             328               0              22               0             350               0
Rough-toothed dolphin...................................             597               0              38               0             635               0
Common bottlenose dolphin...............................           2,274               0             196               0           2,470               0
Pantropical spotted dolphin.............................           7,988               0             519               0           8,507               0
Spinner dolphin (whitebelly)............................             121               0               7               0             128               0
Spinner dolphin (eastern)...............................           8,189               0             557               0           8,746               0
Striped dolphin.........................................           2,212               0             122               0           2,334               0
Short-beaked common dolphin.............................           2,818               0             209               0           3,027               0
Fraser's dolphin........................................             858               0              58               0             916               0
Short-finned pilot whale................................             244               0              15               0             259               0
Killer whale............................................              25               0               2               0              27               0
False killer whale......................................             118               0               8               0             126               0
Pygmy killer whale......................................             116               0               8               0             124               0
Melon-headed whale......................................             135               0               9               0             144               0
Kogia spp...............................................              33               1               2               0              35               1
Guadalupe fur seal......................................             416               0               1               0             417               0
California sea lion.....................................             365               0             693               0           1,058               0
--------------------------------------------------------------------------------------------------------------------------------------------------------

    NMFS does not anticipate that serious injury or mortality would 
occur as a result of L-DEO's planned survey, even in the absence of 
mitigation, and none are proposed for authorization. Non-auditory 
physical effects, stranding, and vessel strike are also not expected to 
occur.
    We are proposing to authorize a limited number of instances of 
Level A harassment of two species (Bryde's whale and dwarf sperm 
whales, which are members of the low- and high-frequency cetacean 
hearing groups, respectively) in the form of PTS, and Level B 
harassment only of the remaining marine mammal species. We believe that 
any PTS incurred in marine mammals as a result of the planned activity 
would be in the form of only a small degree of PTS, not total deafness, 
because of the constant movement of both the R/V Langseth and of the 
marine mammals in the project areas, as well as the fact that the 
vessel is not expected to remain in any one area in which individual 
marine mammals would be expected to concentrate for an extended period 
of time. Additionally, L-DEO would shut down the airgun array if marine 
mammals approach within 500 m (with the exception of specific genera of 
dolphins, see Proposed Mitigation), further reducing the expected 
duration and intensity of sound, and therefore the likelihood of marine 
mammals incurring PTS. Since the duration of exposure to loud sounds 
will be relatively short it would be unlikely to affect the fitness of 
any individuals. Also, as described above, we expect that marine 
mammals would likely move away from a sound source that represents an 
aversive stimulus, especially at levels that would be expected to 
result in PTS, given sufficient notice of the R/V Langseth's approach 
due to the vessel's relatively low speed when conducting seismic 
surveys. Accordingly, we expect that the majority of takes would be in 
the form of short-term Level B behavioral harassment in the form of 
temporary avoidance of the area or decreased foraging (if such activity 
were occurring), reactions that are considered to be of low severity 
and with no lasting biological consequences (e.g., Southall et al., 
2007, Ellison et al., 2012).
    Marine mammal habitat may be impacted by elevated sound levels, but 
these impacts would be temporary. Prey species are mobile and are 
broadly distributed throughout the project areas; therefore, marine 
mammals that may be temporarily displaced during survey activities are 
expected to be able to resume foraging once they have moved away from 
areas with disturbing levels of underwater noise. Because of the 
relatively short duration (up to 24 days) and temporary nature of the 
disturbance, the availability of similar habitat and resources in the 
surrounding area, the impacts to marine mammals and the food sources 
that they utilize are not expected to cause significant or long-term 
consequences for individual marine mammals or their populations.
    Yazvenko et al. (2007) reported no apparent changes in the 
frequency of feeding activity in Western gray whales exposed to airgun 
sounds in their feeding grounds near Sakhalin Island. Goldbogen et al. 
(2013) found blue whales feeding on highly concentrated prey in shallow 
depths were less likely to respond and cease foraging than whales 
feeding on deep, dispersed prey when exposed to simulated sonar 
sources, suggesting that the benefits of feeding for humpbacks foraging 
on high-density prey may outweigh perceived

[[Page 2024]]

harm from the acoustic stimulus, such as the seismic survey (Southall 
et al., 2016). Additionally, L-DEO will shut down the airgun array upon 
observation of an aggregation of six or more large whales, which would 
reduce impacts to cooperatively foraging animals. For all habitats, no 
physical impacts to habitat are anticipated from seismic activities. 
While SPLs of sufficient strength have been known to cause injury to 
fish and fish and invertebrate mortality, in feeding habitats, the most 
likely impact to prey species from survey activities would be temporary 
avoidance of the affected area and any injury or mortality of prey 
species would be localized around the survey and not of a degree that 
would adversely impact marine mammal foraging. The duration of fish 
avoidance of a given area after survey effort stops is unknown, but a 
rapid return to normal recruitment, distribution and behavior is 
expected. Given the short operational seismic time near or traversing 
specific habitat areas, as well as the ability of cetaceans and prey 
species to move away from acoustic sources, NMFS expects that there 
would be, at worst, minimal impacts to animals and habitat within these 
areas. The proposed survey tracklines do not overlap with any 
designated critical habitat for ESA-listed species or areas of known 
importance for any species.

Negligible Impact Conclusions

    The proposed survey would be of short duration (up to 25 days of 
seismic operations), and the acoustic ``footprint'' of the proposed 
survey would be small relative to the ranges of the marine mammals that 
would potentially be affected. Sound levels would increase in the 
marine environment in a relatively small area surrounding the vessel 
compared to the range of the marine mammals within the proposed survey 
area. Short term exposures to survey operations are not likely to 
significantly disrupt marine mammal behavior, and the potential for 
longer-term avoidance of important areas is limited.
    The proposed mitigation measures are expected to reduce the number 
of takes by Level A harassment (in the form of PTS) by allowing for 
detection of marine mammals in the vicinity of the vessel by visual and 
acoustic observers. The proposed mitigation measures are also expected 
to minimize the severity of any potential behavioral disturbance (Level 
B harassment) via shutdowns of the airgun array. Based on previous 
monitoring reports for substantially similar activities that have been 
previously authorized by NMFS (available at https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities), we expect that the 
proposed mitigation will be effective in preventing, at least to some 
extent, potential PTS in marine mammals that may otherwise occur in the 
absence of the proposed mitigation (although all authorized PTS has 
been accounted for in this analysis).
    NMFS concludes that exposures to marine mammal species and stocks 
due to L-DEO's proposed seismic survey activities would result in only 
short-term (temporary and short in duration) effects to individuals 
exposed, over relatively small areas of the affected animals' ranges. 
Animals may temporarily avoid the immediate area, but are not expected 
to permanently abandon the area. Major shifts in habitat use, 
distribution, or foraging success are not expected. NMFS does not 
anticipate the proposed take estimates to impact annual rates of 
recruitment or survival.
    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 the species or stock 
through effects on annual rates of recruitment or survival:
     No serious injury or mortality is anticipated or proposed 
to be authorized, even absent mitigation;
     The proposed activity is temporary and of relatively short 
duration (up to 25 days);
     The anticipated impacts of the proposed activity on marine 
mammals would primarily be temporary behavioral changes due to 
avoidance of the area around the survey vessel;
     The number of instances of potential PTS that may occur 
are expected to be very small in number. Instances of potential PTS 
that are incurred in marine mammals are expected to be of a low level, 
due to constant movement of the vessel and of the marine mammals in the 
area, and the nature of the survey design (not concentrated in areas of 
high marine mammal concentration);
     The availability of alternate areas of similar habitat 
value for marine mammals to temporarily vacate the survey area during 
the proposed survey to avoid exposure to sounds from the activity;
     The potential adverse effects on fish or invertebrate 
species that serve as prey species for marine mammals from the proposed 
survey would be temporary and spatially limited, and impacts to marine 
mammal foraging would be minimal; and
     The proposed mitigation measures, including visual and 
acoustic monitoring and shutdowns are expected to minimize potential 
impacts to marine mammals (both amount and severity).
    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 mitigation and 
monitoring 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 above, only small numbers of incidental take may be 
authorized under sections 101(a)(5)(A) and (D) of the MMPA for 
specified activities other than military readiness activities. The MMPA 
does not define small numbers and so, in practice, where estimated 
numbers are available, NMFS compares the number of individuals taken to 
the most appropriate estimation of abundance of the relevant species or 
stock in our determination of whether an authorization is limited to 
small numbers of marine mammals. When the predicted number of 
individuals to be taken is fewer than one third of the species or stock 
abundance, the take is considered to be of small numbers. Additionally, 
other qualitative factors may be considered in the analysis, such as 
the temporal or spatial scale of the activities.
    The amount of take NMFS proposes to authorize is below one third of 
the estimated population abundance of all species (Gerrodette and 
Palacios 1996); NMFS 2015b). In fact, take of individuals is less than 
8 percent of the abundance of any affected population.
    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 will be taken relative to the population size 
of the affected species or stocks.

Unmitigable Adverse Impact Analysis and Determination

    There are no relevant subsistence uses of the affected marine 
mammal stocks or species implicated by this action. Therefore, NMFS has 
determined that the total taking of affected species or stocks would 
not have an unmitigable adverse impact on the availability of such 
species or stocks for taking for subsistence purposes.

[[Page 2025]]

Endangered Species Act

    Section 7(a)(2) of the Endangered Species Act of 1973 (ESA: 16 
U.S.C. 1531 et seq.) requires that each Federal agency insure that any 
action it authorizes, funds, or carries out is not likely to jeopardize 
the continued existence of any endangered or threatened species or 
result in the destruction or adverse modification of designated 
critical habitat. To ensure ESA compliance for the issuance of IHAs, 
NMFS consults internally whenever we propose to authorize take for 
endangered or threatened species.
    NMFS is proposing to authorize take of blue whales, fin whales, sei 
whales, sperm whales, Mexico DPS humpback whales, Central America DPS 
humpback whales, and Guadalupe fur seals, which are listed under the 
ESA. The NMFS OPR Permits and Conservation Division has requested 
initiation of Section 7 consultation with the NMFS OPR ESA Interagency 
Cooperation Division 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 L-DEO for conducting marine geophysical surveys in the 
ETP, beginning in spring 2022, 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/permit/incidental-take-authorizations-under-marine-mammal-protection-act.

Request for Public Comments

    We request comment on our analyses, the proposed authorization, and 
any other aspect of this notice of proposed IHA for the proposed 
geophysical surveys. We also request at this time 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, one-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:
    (1) 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 one year from expiration of 
the initial IHA);
    (2) The request for renewal must include the following:
     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
     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.
    (3) 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: January 7, 2022.
Catherine Marzin,
Acting Director, Office of Protected Resources, National Marine 
Fisheries Service.
[FR Doc. 2022-00455 Filed 1-7-22; 4:15 pm]
BILLING CODE 3510-22-P