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Notice2025-07613

Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey Off Western Mexico in the Eastern Tropical Pacific Ocean

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Published

May 5, 2025

Issuing agencies

Commerce DepartmentNational Oceanic and Atmospheric Administration

Abstract

NMFS has received a request from the Lamont-Doherty Earth Observatory (L-DEO) for authorization to take marine mammals incidental to a marine geophysical survey off Western Mexico in the Eastern Tropical Pacific Ocean (ETP). Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an incidental harassment authorization (IHA) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-time, 1-year renewal that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorization and agency responses will be summarized in the final notice of our decision.

Full Text

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[Federal Register Volume 90, Number 85 (Monday, May 5, 2025)]
[Notices]
[Pages 19090-19119]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-07613]

[[Page 19089]]

Vol. 90

Monday,

No. 85

May 5, 2025

Part II

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 a Marine Geophysical Survey Off Western
Mexico in the Eastern Tropical Pacific Ocean; Notice

Federal Register / Vol. 90 , No. 85 / Monday, May 5, 2025 / Notices

[[Page 19090]]

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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XE764]

Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to a Marine Geophysical Survey Off
Western Mexico in the Eastern Tropical Pacific Ocean

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 a marine geophysical survey off Western Mexico in the Eastern
Tropical Pacific Ocean (ETP). Pursuant to the Marine Mammal Protection
Act (MMPA), NMFS is requesting comments on its proposal to issue an
incidental harassment authorization (IHA) to incidentally take marine
mammals during the specified activities. NMFS is also requesting
comments on a possible one-time, 1-year renewal that could be issued
under certain circumstances and if all requirements are met, as
described in Request for Public Comments at the end of this notice.
NMFS will consider public comments prior to making any final decision
on the issuance of the requested MMPA authorization and agency
responses will be summarized in the final notice of our decision.

DATES: Comments and information must be received no later than June 4,
2025.

ADDRESSES: Comments should be addressed to Jolie Harrison, Chief,
Permits and Conservation Division, Office of Protected Resources,
National Marine Fisheries Service and should be submitted via email to
<a href="/cdn-cgi/l/email-protection#abe2fffb85c3cad9c7cac8c3ced9ebc5c4caca85ccc4dd">[email&#160;protected]</a>. 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: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities">https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities</a>. In case of problems accessing these
documents, please call the contact listed below.
Instructions: NMFS is not responsible for comments sent by any
other method, to any other address or individual, or received after the
end of the comment period. Comments, including all attachments, must
not exceed a 25-megabyte file size. All comments received are a part of
the public record and will generally be posted online at <a href="https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act">https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act</a> 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: Jenna Harlacher, Office of Protected
Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

The MMPA prohibits the ``take'' of marine mammals, with certain
exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361
et seq.) direct the Secretary of Commerce (as delegated to NMFS) to
allow, upon request, the incidental, but not intentional, taking of
small numbers of marine mammals by U.S. citizens who engage in a
specified activity (other than commercial fishing) within a specified
geographical region if certain findings are made and either regulations
are proposed or, if the taking is limited to harassment, a notice of a
proposed IHA is provided to the public for review.
Authorization for incidental takings shall be granted if NMFS finds
that the taking will have a negligible impact on the species or
stock(s) and will not have an unmitigable adverse impact on the
availability of the species or stock(s) for taking for subsistence uses
(where relevant). Further, NMFS must prescribe the permissible methods
of taking and other ``means of effecting the least practicable adverse
impact'' on the affected species or stocks and their habitat, paying
particular attention to rookeries, mating grounds, and areas of similar
significance, and on the availability of the species or stocks for
taking for certain subsistence uses (referred to in shorthand as
``mitigation''); and requirements pertaining to the monitoring and
reporting of the takings. The definitions of all applicable MMPA
statutory terms used above are included in the relevant sections below
and can be found in section 3 of the MMPA (16 U.S.C. 1362) and NMFS
regulations at 50 CFR 216.103.

National Environmental Policy Act

To comply with the National Environmental Policy Act of 1969 (NEPA;
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A,
NMFS must review our proposed action (i.e., the issuance of an IHA)
with respect to potential impacts on the human environment.
This action is consistent with categories of activities identified
in Categorical Exclusion B4 (IHAs with no anticipated serious injury or
mortality) of the Companion Manual for NAO 216-6A, which do not
individually or cumulatively have the potential for significant impacts
on the quality of the human environment and for which we have not
identified any extraordinary circumstances that would preclude this
categorical exclusion. Accordingly, NMFS has preliminarily determined
that the issuance of the proposed IHA qualifies to be categorically
excluded from further NEPA review.

Summary of Request

On November 14, 2024, NMFS received a request from the L-DEO for an
IHA to take marine mammals incidental to a marine geophysical survey
off Western Mexico in the ETP. After sending initial questions to the
applicant, L-DEO deferred the IHA request due to vessel clearance
issues. On January 29, 2025 L-DEO alerted us that they received
clearance but their proposed survey dates had changed. With revised
dates, NMFS continued processing the application and it was deemed
adequate and complete on March 4, 2025. L-DEO's request is for take of
29 species of marine mammals, by Level B harassment only. Neither L-DEO
nor NMFS expect serious injury or mortality to result from this
activity and, therefore, an IHA is appropriate.

Description of Proposed Activity

Overview

Researchers from the New Mexico Institute of Mining and Technology
(NMT) and University of New Mexico (UNM), with funding from the
National Science Foundation (NSF), and in collaboration with Centro de
Investigaci[oacute]n Cient[iacute]fica y de Educaci[oacute]n Superior
de Ensenada (CICESE), propose to conduct a low-energy marine seismic
survey, using airguns as the acoustic source, and heat probe
measurements, conducted from the research vessel (R/V) Marcus G.
Langseth (Langseth), which is owned and operated by L-DEO. The proposed
survey would occur off Western Mexico in the ETP from approximately
November 2025 to December 2025. The proposed survey would occur within
the Mexican exclusive economic zone (EEZ) but outside of territorial
waters, in

[[Page 19091]]

water depths ranging from approximately 1,000 to 5,300 meters (m). To
complete this 2-dimensional (2-D) survey, the Langseth would tow a
cluster of two 45 cubic inch (in\3\, 737 cubic centimeters (cc))
generator injector (GI) airguns with a total discharge volume of 90
in\3\ (~1,475 cc) at a depth of 3 m. The airgun array receiver would
consist of a 3-5 kilometer (km) long solid-state hydrophone streamer.
The airguns would fire at a shot interval of 6.25-12.5 m. Approximately
1,258 kilometers (km) of seismic acquisition is planned. Airgun arrays
would introduce underwater sound that may result in take of marine
mammals.
The purpose of the proposed survey is to obtain information on the
sediment distribution and geologic structure of the Cocos plate and
margin wedge, which is necessary for constraining the thermal structure
of the subduction zone offshore southern Mexico. The main goal of the
proposed seismic surveys is to acquire 2-D seismic reflection data, in
conjunction with densely spaced heat probe measurements, to quantify
the effects of fluid circulation in oceanic crust on temperatures in
the southern Mexico subduction zone.

Dates and Duration

The Langseth is proposed to leave out of port in Manzanilla,
Mexico, on November 18, 2025, and return to port in Manzanilla, Mexico,
on December 15, 2025, after the survey is completed. The survey is
expected to last 24 days, which includes approximately 7 days of
seismic operations, 14 days of heat probe measurements, and 3 days of
transit.

Specific Geographic Region

The proposed survey would occur within approximately ~15.5-17[deg]
N and 99.5-102[deg] W, off the Pacific coast of Mexico within the EEZ
of Mexico, in water depths ranging from approximately 1,000 to 5,300 m.
The region where the survey is proposed to occur is depicted in figure
1. Representative survey tracklines are shown; however, some deviation
in actual tracklines, 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. Therefore, for the proposed survey, the tracklines could
occur anywhere within the coordinates noted above. The Langseth would
likely leave out of and return to port in Manzanilla, Mexico
(approximately 420 km north of the survey area).
BILLING CODE 3510-22-P
[GRAPHIC] [TIFF OMITTED] TN05MY25.000

BILLING CODE 3510-22-C

[[Page 19092]]

Detailed Description of the Specified Activity

The procedures to be used for the proposed survey would be similar
to those used during previous seismic surveys conducted by L-DEO and
would use conventional seismic methodology. The survey would involve
one source vessel, Langseth, which is owned and operated by L-DEO.
During the low-energy 2D seismic survey, Langseth would tow two GI
airguns with a total discharge volume of 90 in\3\. The two inline
airguns would be spaced 2.46 m apart. The airgun array configurations
are illustrated in figure 2-14 of NSF and the U.S. Geological Survey's
(USGS) Programmatic Environmental Impact Statement (PEIS; NSF-USGS,
2011). (The PEIS is available online at: <a href="https://www.nsf.gov/geo/oce/envcomp/usgs-nsf-marine-seismic-research/nsf-usgs-final-eis-oeis_3june2011.pdf">https://www.nsf.gov/geo/oce/envcomp/usgs-nsf-marine-seismic-research/nsf-usgs-final-eis-oeis_3june2011.pdf</a>). The receiving system would consist of a 3-5 km
long solid-state hydrophone streamer. As the airgun arrays are towed
along the survey lines, the hydrophone streamer would transfer the data
to the on-board processing system. Approximately 1,258 km of seismic
acquisition are planned. The survey would take place in water depths
ranging from approximately 1,000 to 5,300 m.
Heat flow data would be acquired with a heat flow probe that takes
the temperature of the sediments like a thermometer. Heat probe
measurements are made by lowering the probe through the water column
and letting it plunge ~3.5 m into the sediment. Measurements consist of
two parts--thermal gradient and conductivity--and would be made every
~500-1,000 m. At each measurement site the probe is left in the
seafloor for ~15 minutes. After the measurement is taken, the probe is
pulled out of the sediment and raised ~200 m above the seafloor, the
ship then moves position along the transect, and the process is
repeated (referred to as ``pogo'' mode). During heat flow probe
operations, a 12-kilohertz (kHz) bottom-finding pinger would be
employed, and an acoustic release would be used once during an initial
calibration of the heat probe activities.
The heat flow probe would be equipped with an ultra-short baseline
(USBL) transducer acoustic positioning system (or pinger) to allow it
to ``talk'' with the research vessel. The pole-mounted USBL transducer
pings once per second to the receiver to locate the heat flow probe
location and vice versa. The reflected pings are picked up by a Knudsen
Chirp 3260 sub-bottom profiler (SBP). While on station for heat flow
measurements, the MBES would be turned off.
In addition to the operations of the airgun array and the heat flow
probe, the ocean floor would be mapped with the Kongsberg EM 122
multibeam echosounder (MBES), and a SBP. A Teledyne RDI 75 kHz Ocean
Surveyor acoustic doppler current profiler (ADCP) would be used to
measure water current velocities. Take of marine mammals is not
expected to occur incidental to use of the MBES, SBP, ADCP, and heat
flow probe operations whether or not the airguns are operating
simultaneously with the other sources. Given their characteristics
(e.g., narrow downward-directed beam), marine mammals would experience
no more than one or two brief ping exposures, if any exposure were to
occur. NMFS does not expect that the use of these sources is likely to
cause take of marine mammals.
Proposed mitigation, monitoring, and reporting measures are
described in detail later in this document (please see Proposed
Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

Sections 3 and 4 of the application summarize available information
regarding status and trends, distribution and habitat preferences, and
behavior and life history of the potentially affected species. NMFS
fully considered all of this information, and we refer the reader to
these descriptions, instead of reprinting the information. Additional
information about these species (e.g., physical and behavioral
descriptions) may be found on NMFS' website (<a href="https://www.fisheries.noaa.gov/find-species">https://www.fisheries.noaa.gov/find-species</a>). NMFS refers the reader to the
aforementioned source for general information regarding the species
listed in table 1.
Table 1 lists all species or stocks for which take is expected and
proposed to be authorized for this activity and summarizes information
related to the population or stock, including regulatory status under
the MMPA and Endangered Species Act (ESA) and potential biological
removal (PBR), where known. PBR is defined by the MMPA as the maximum
number of animals, not including natural mortalities, that may be
removed from a marine mammal stock while allowing that stock to reach
or maintain its optimum sustainable population (as described in NMFS'
stock assessment reports (SARs)). While no serious injury or mortality
is anticipated or proposed to be authorized here, PBR and annual
serious injury and mortality (M/SI) from anthropogenic sources are
included here as gross indicators of the status of the species or
stocks and other threats.
Marine mammal abundance estimates presented in this document
represent the total number of individuals that make up a given stock or
the total number estimated within a particular study or survey area.
NMFS'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
draft 2024 SARs (available online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports">https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports</a>). 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).

[[Page 19093]]

Table 1--Species Likely Impacted by the Specified Activities
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Stock abundance
ESA/MMPA (CV, Nmin, ETP Mexico
Common name Scientific name Stock status; most recent PBR Annual M/ abundance Pacific
strategic abundance SI \3\ \4\ abundance
(Y/N) \1\ survey) \2\ \5\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Order Artiodactyla--Cetacea--Mysticeti (baleen whales)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Balaenopteridae
(rorquals):
Humpback Whale........... Megaptera Central America/ E, D, Y 1,496 (0.2, 3.5.............. 14.9 2,566 ...........
novaeangliae. Southern Mexico- 1,284, 2021).
California-
Oregon-
Washington.
Minke whale.............. Balaenoptera N/A............. -, -, N N/A............. N/A.............. N/A 115 ...........
acutorostrata.
Bryde's whale............ Balaenoptera Eastern Tropical -, -, N Unknown Undetermined..... Unknown 10,411 649
edeni. Pacific. (Unknown,
Unknown, N/A).
Sei whale................ Balaenoptera Eastern N E, D, Y 519 (0.4, 374, 0.75............. >=0.2 0 ...........
borealis. Pacific. 2014).
Fin whale................ Balaenoptera N/A............. E, D, Y N/A............. N/A.............. N/A 574 145
physalus.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Odontoceti (toothed whales, dolphins, and porpoises)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Physeteridae:
Sperm whale.............. Physeter N/A............. E, D, Y N/A............. N/A.............. N/A 4,145 2,810
macrocephalus.
Family Kogiidae:
Dwarf Sperm Whale........ Kogia sima...... N/A............. N/A N/A............. N/A.............. N/A \6\ 11,200 ...........
Pygmy Sperm Whale........ Kogia breviceps. N/A............. -, -, N N/A............. N/A.............. N/A \6\ 11,200 ...........
Family Ziphiidae (beaked
whales):
Cuvier's Beaked Whale.... Ziphius N/A............. -, -, N N/A............. N/A.............. N/A \7\ 20,000 \8\ 68,828
cavirostris.
Longman's beaked whale... Indopacetus N/A............. -, -, N N/A............. N/A.............. N/A 1,007 ...........
pacificus.
Blainville's beaked whale Mesoplodon N/A............. -, -, N N/A............. N/A.............. N/A \9\ 25,300 \8\ 68,828
densirostris.
Ginkgo-toothed beaked M. ginkgodens... N/A............. -, -, N N/A............. N/A.............. N/A \9\ 25,300 \8\ 68,828
whale.
Deraniyagala's beaked M. hotaula...... N/A............. -, -, N N/A............. N/A.............. N/A \9\ 25,300 \8\ 68,828
whale.
Pygmy beaked whale....... M. peruvianus... N/A............. -, -, N N/A............. N/A.............. N/A \9\ 25,300 \8\ 68,828
Family Delphinidae:
Risso's dolphin.......... Grampus griseus. N/A............. -, -, N N/A............. N/A.............. N/A 110,457 24,084
Rough-toothed dolphin.... Steno N/A............. -, -, N N/A............. N/A.............. N/A 107,663 37,511
bredanensis.
Common bottlenose dolphin Tursiops N/A............. -, -, N N/A............. N/A.............. N/A 335,834 61,536
truncatus.
Pantropical spotted Stenella N/A............. -, D, N N/A............. N/A.............. N/A \10\ 146,296
dolphin. attenuata. 1,297,091
Spinner dolphin.......... Stenella N/A............. -, D, N N/A............. N/A.............. N/A \10\ 186,906
longirostris. 2,075,871
Striped dolphin.......... Stenella N/A............. -, -, N N/A............. N/A.............. N/A 964,362 128,867
coeruleoalba.
Short-beaked common Delphinus N/A............. -, -, N N/A............. N/A.............. N/A 3,127,203 283,196
dolphin. delphis.
Fraser's dolphin......... Lagenodelphis N/A............. -, -, N N/A............. N/A.............. N/A \7\ 289,300 ...........
hosei.
Short-finned pilot whale. Globicephala N/A............. -, -, N N/A............. N/A.............. N/A \11\ 3,348
macrorhynchus. 589,315
Killer whale............. Orcinus orca.... N/A............. -, -, N N/A............. N/A.............. N/A \7\ 8,500 852
False killer whale....... Pseudorca N/A............. -, -, N N/A............. N/A.............. N/A \7\ 39,800 ...........
crassidens.
Pygmy killer whale....... Feresa attenuata N/A............. -, -, N N/A............. N/A.............. N/A \7\ 38,900 ...........
Melon-headed whale....... Peponocephala N/A............. -, -, N N/A............. N/A.............. N/A \7\ 45,400 ...........
electra.
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Order Carnivora--Pinnipedia
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Family Otariidae (eared seals
and sea lions):
Guadalupe fur seal....... Arctocephalus Mexico.......... T, D, Y 63,850 (N/A, 1,959............ >=10.0 ........... ...........
townsendi. 57,199, 2013).

[[Page 19094]]

California sea lion...... Zalophus U.S............. -, -, N 257,606 (N/A, 14,011........... >321 105,000 ...........
californianus. 233,515, 2014).
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\1\ ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or
designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or
which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is
automatically designated under the MMPA as depleted and as a strategic stock.
\2\ NMFS marine mammal stock assessment reports online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports</a>. 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\ Includes abundance of several stocks added together.
\11\ Based on surveys in 2000 (Gerrodette and Forcada 2002).

As indicated above, all 29 species in table 1 temporally and
spatially co-occur with the activity to the degree that take is
reasonably likely to occur. 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., 2024). 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.
Some species could potentially occur in the proposed survey area
but are not likely to be encountered due to the rarity of their
occurrence. These species include the North Pacific right whale
(Eubalaena japonica), blue whale (Balaenoptera musculus), 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), vaquita (Phocoena
sinus), harbor porpoise (Phocoena phocoena), Dall's porpoise
(Phocoenoides dalli), Pacific white-sided dolphin (Lagenorhynchus
obliquidens), and northern right whale dolphin (Lissodelphis borealis),
which all generally occur well outside or 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.
In addition to what is included in sections 3 and 4 of the IHA
application, and NMFS' website, further detail informing the regional
occurrence for select species of particular or unique vulnerability
(i.e., information regarding ESA listed or MMPA depleted species) is
provided below.

Humpback Whale

The Central America distinct population segment (DPS) equates to
the Central America/Southern Mexico-CA/OR/WA stock designated under the
MMPA and shown in table 1. The endangered Central America DPS may occur
within the proposed survey area, based on the timing of the proposed
survey (November-December). Humpbacks from the Central America DPS
could be migrating through the survey area at the time of the proposed
survey.
Whales in the Central America/Southern Mexico-CA/OR/WA stock winter
off the coasts of Nicaragua, Honduras, El Salvador, Guatemala, Panama,
Costa Rica, and southern Mexico including the states of Oaxaca and
Guerrero, with some animals ranging even farther north (Taylor et al.
2021); they summer off California, Oregon, and Washington (Calambokidis
et al. 2000).
Nine sightings were made during surveys off the Pacific coast of
Mexico in November 2019 (Oedekoven et al. 2021). The central coast of
Oaxaca is thought to be a migratory corridor during winter, with whales
typically migrating up to 4 km from shore (Heckel et al. 2020). In
2012, 45 sightings were made off Oaxaca (Castillejos-Moguel and
Villegas-Zurita 2014 in Heckel et al. 2020) including feeding behavior
(Villegas-Zurita and Castillejos-Moguel 2013 in Heckel et al. 2020).
Feeding has also been observed in Banderas Bay, which is known to be an
aggregation area for humpbacks during the winter months (Frish-
Jord[aacute]n et al. 2019). One sighting was made during an L-DEO
survey off Guerrero and Michoac[aacute]n in May-June 2022 (RPS 2022).
Although sightings are regularly made within the region during winter,
sightings during the proposed fall survey in deep offshore waters are
likely to be less common.
Although there are other stocks of humpback whales found in Mexico
near the project area, it's likely that humpbacks from the Mexico DPS
(Mexico-North Pacific Stock and Mainland Mexico-CA/OR/WA Stock) would
still be migrating south from their northern feeding grounds off of the
U.S. west coast and are not likely to be found in the survey area.
Additionally, the Mexico DPS's winter breeding grounds are north of the
proposed survey area in the Revillagigedos Islands. Therefore, we
assume that all humpback whales taken by the proposed survey activities
would be from the Central America/Southern Mexico-CA/OR/WA stock.

Sei Whale

Sei whales are less common in the survey area but there have been
some reports as summarized below. Sei whales are known to occasionally
occur in the Gulf of California (Urb[aacute]n et al. 2014 in Heckel et
al. 2020), as well as off the west coast of the Baja California
Peninsula (Heckel et al. 2020). One sighting has been reported for
waters off

[[Page 19095]]

Nayarit (Urb[aacute]n et al. 1997, Guerrero et al. 2006 in Heckel et
al. 2020), and another sighting was made near the northern part of the
proposed survey area, off Jalisco (Heckel et al. 2020). Gonz[aacute]lez
et al. (2008) also reported the presence of sei whales off west coast
of Mexico south of 23[deg] N. However, neither Ferguson and Barlow
(2001) nor Jackson et al. (2004) positively identified any sei whales
in Mexican waters during surveys conducted during July-December. RPS
(2022) reported two sightings of single sei whales during an L-DEO
survey off Guerrero and Michoac[aacute]n in May-June 2022.

Fin Whale

Fin whale calls are recorded in the North Pacific year-round (e.g.,
Moore et al. 2006; Stafford et al. 2007, 2009; Edwards et al. 2015).
However, fin whales are considered rare in the proposed survey area. No
sightings were made in the proposed survey area during July-December
surveys during 1986-1996, 2003, or 2019 (Ferguson and Barlow 2001;
Jackson et al. 2004; Oedekoven et al. 2021). Similarly, Edwards et al.
(2015) reported no sightings or acoustic detections for the proposed
survey area, although sightings have been reported for the Gulf of
California and a few sightings exist for offshore waters far west of
Mexico. However, Gonz[aacute]lez et al. (2008) reported the presence of
this species off west coast of Mexico south of 23[deg] N, and a
sighting has been reported for Banderas Bay (Arroyo 2017). RPS (2022)
reported one fin whale sighting during an L-DEO survey off Guerrero and
Michoac[aacute]n in May-June 2022.

Sperm Whale

During summer and fall, sperm whales are widely distributed in the
ETP, although they are generally more abundant in deeper ``nearshore''
waters than far offshore (e.g., Polacheck 1987; Wade and Gerrodette
1993). More than 180 sightings have been reported for the ETP, with the
highest concentrations at 10[deg] N-10[deg] S, 80[deg]-100[deg] W
(Guerrero et al. 2006). Sightings for Pacific Mexico include records
off the Baja California Peninsula and in the Gulf of California
(Guerrero et al. 2006; Heckel et al. 2020). During 25,356 km of surveys
(excluding the Gulf of California) within the EEZ of Pacific Mexico,
during July-December 1986-1990, 1992 and 1993, 46 sightings of sperm
whales were made (Gerrodette and Palacios 1996). No sightings were made
along the mainland coast of Mexico during July-December surveys in
2003, although one sighting was made off the west coast of Baja
California Sur (Jackson et al. 2004). Records also exist for Banderas
Bay (Arroyo 2017) and Oaxaca (P[eacute]rez and Gordillo 2002 in Heckel
et al. 2020).

Pantropical Spotted Dolphin

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 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 designated as depleted
under the MMPA 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.

Spinner Dolphin

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)

[[Page 19096]]

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). In 2008, Cramer et al., determined that the
continued chase and encirclement by the tuna fishery may be affecting
the reproductive rates of the eastern spinner dolphin.

Guadalupe Fur Seal

During the summer season, most Guadalupe fur seal adults occur at
rookeries in Mexico (Carretta et al. 2021). Most breeding and births
occur at Isla Guadalupe, off the west coast of Baja California
Peninsula; a secondary rookery exists at Isla Benito del Este
(Maravilla-Chavez and Lowry 1999; Aurioles-Gamboa et al. 2010).
Following the breeding season, adult males tend to move north to
forage. All rookeries are outside of the project area as the proposed
area is offshore. While at sea, this species is usually solitary but
typically gathers in the hundreds to thousands at breeding sites.
Guadalupe fur seals prefer rocky habitat for breeding and hauling out.
They generally haul out at the base of towering cliffs on shores
characterized by solid rock and large lava blocks (Peterson et al.
1968), although they can also inhabit caves and recesses (Belcher and
Lee 2002). Guadalupe fur seals are unlikely to be encountered during
the proposed seismic survey, as they typically occur farther north.
However, Heckel et al. (2020) reported occasional records for Guerrero
and Oaxaca.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals
underwater, and exposure to anthropogenic sound can have deleterious
effects. To appropriately assess the potential effects of exposure to
sound, it is necessary to understand the frequency ranges marine
mammals are able to hear. Not all marine mammal species have equal
hearing capabilities (e.g., Richardson et al., 1995; Wartzok and
Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al.
(2007, 2019) recommended that marine mammals be divided into hearing
groups based on directly measured (behavioral or auditory evoked
potential techniques) or estimated hearing ranges (behavioral response
data, anatomical modeling, etc.). Generalized hearing ranges were
chosen based on the ~65 dB threshold from composite audiograms,
previous analyses in NMFS (2018), and/or data from Southall et al.
(2007) and Southall et al. (2019). We note that the names of two
hearing groups and the generalized hearing ranges of all marine mammal
hearing groups have been recently updated (NMFS 2024) as reflected
below in table 2.

Table 2--Marine Mammal Hearing Groups
[NMFS, 2024]
------------------------------------------------------------------------
Hearing group Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen 7 Hz to 36 kHz.
whales).
High-frequency (HF) cetaceans (dolphins, 150 Hz to 160 kHz.
toothed whales, beaked whales, bottlenose
whales).
Very High-frequency (VHF) cetaceans (true 200 Hz to 165 kHz.
porpoises, Kogia, river dolphins,
Cephalorhynchid, Lagenorhynchus cruciger
& L. australis).
Phocid pinnipeds (PW) (underwater) (true 40 Hz to 90 kHz.
seals).
Otariid pinnipeds (OW) (underwater) (sea 60 Hz to 68 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 may not be as broad. Generalized hearing range
chosen based on ~65 dB threshold from composite audiogram, previous
analysis in NMFS 2018, and/or data from Southall et al. 2007; Southall
et al. 2019. Additionally, animals are able to detect very loud sounds
above and below that ``generalized'' hearing range.

For more detail concerning these groups and associated frequency
ranges, please see NMFS (2024) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their
Habitat

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

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

[[Page 19097]]

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 array 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.,
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 anthropogenic 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 this 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. 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., NMFS, 2018; 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
(American National Standards Institute (ANSI), 1986, 2005; Harris,
1998; National Institute for Occupational Health and Safety (NIOSH),
1998; International Organization for Standardization (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.

[[Page 19098]]

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 \1\--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, if it
occurs at all, will occur almost exclusively in cases where a noise is
within an animal's hearing frequency range. We first describe specific
manifestations of acoustic effects before providing discussion specific
to the use of airgun arrays.
---------------------------------------------------------------------------

\1\ 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.
---------------------------------------------------------------------------

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 to elicit behavioral or physiological response.
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.
Marine mammals, like all mammals, develop increased hearing
thresholds over time due to age-related degeneration of auditory
pathways and sensory cells of the inner ear. This natural, age-related
hearing loss is contrasted by noise-induced hearing loss
(M[oslash]ller, 2012). Marine mammals exposed to high-intensity sound
or to lower-intensity sound for prolonged periods can experience a
noise-induced hearing threshold shift (TS), which NMFS defines as a
change, usually an increase, in the threshold of audibility at a
specified frequency or portion of an individual's hearing range above a
previously established reference level as a result of noise exposure
(NMFS, 2018, 2024). The amount of TS is customarily expressed in dB.
Noise-induced hearing TS can be temporary (TTS) or permanent (PTS), and
higher-level sound exposures are more likely to cause PTS or other AUD
INJ. As described in NMFS (2018, 2024) there are numerous factors to
consider when examining the consequence of TS, including, but not
limited to, the signal temporal pattern (e.g., impulsive or non-
impulsive), likelihood an individual would be exposed for a long enough
duration or to a high enough level to induce a TS, the magnitude of the
TS, time to recovery (seconds to minutes or hours to days), the
frequency range of the exposure (i.e., spectral content), the hearing
frequency range of the exposed species relative to the signal's
frequency spectrum (i.e., how animal uses sound within the frequency
band of the signal; e.g., Kastelein et al., 2014), and the overlap
between the animal and the source (e.g., spatial, temporal, and
spectral).

Auditory Injury (AUD INJ)

NMFS (2024) defines AUD INJ as damage to the inner ear that can
result in destruction of tissue, such as the loss of cochlear neuron
synapses or auditory neuropathy (Houser 2021; Finneran 2024). AUD INJ
may or may not result in a PTS. PTS is subsequently defined as a
permanent, irreversible increase in the threshold of audibility at a
specified frequency or portion of an individual's hearing range above a
previously established reference level (NMFS, 2024). PTS does not
generally affect more than a limited frequency range, and an animal
that has incurred PTS has some level of hearing loss at the relevant
frequencies; typically animals with PTS or other AUD INJ are not
functionally deaf (Au and Hastings, 2008; Finneran, 2016). For marine
mammals, AUD INJ is considered to be possible when sound exposures are
sufficient to produce 40 dB of TTS measured after exposure (Southall et
al. 2007, 1019). AUD INJ levels for marine mammals are estimates, as
with the exception of a single study unintentionally inducing PTS in a
harbor seal (Phoca vitulina) (Kastak et al., 2008; Reichmuth et al.
2019), there are no empirical data measuring AUD INJ in marine mammals
largely due to the fact that, for various ethical reasons, experiments
involving anthropogenic noise exposure at levels inducing AUD INJ are
not typically pursued or authorized (NMFS, 2024).

Temporary Threshold Shift (TTS)

TTS is the mildest form of hearing impairment that can occur during
exposure to sound. TTS is a temporary, reversible increase in the
threshold of audibility at a specified frequency or portion of an
individual's hearing range above a previously established reference
level (NMFS, 2024) that represents primarily tissue fatigue (Henderson
et al., 2008), and is not considered an AUD INJ. Based on data from
marine mammal

[[Page 19099]]

TTS measurements (see Southall et al., 2007, 2019), a TTS of 6 dB is
considered the minimum threshold shift clearly larger than any day-to-
day or session-to-session variation in a subject's normal hearing
ability (Finneran et al., 2000, 2002; Schlundt et al., 2000). 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 (i.e., there is recovery back to baseline/pre-exposure
levels), can occur within a specific frequency range (i.e., an animal
might only have a temporary loss of hearing sensitivity within a
limited frequency band of its auditory range), and can be of varying
amounts (e.g., an animal's hearing sensitivity might be reduced by only
6 dB or reduced by 30 dB). In many cases, hearing sensitivity recovers
rapidly after exposure to the sound ends. While there are data on sound
levels and durations necessary to elicit mild TTS for marine mammals,
recovery is complicated to predict and dependent on multiple factors.
Relationships between TTS and AUD INJ thresholds have not been
studied in marine mammals, and there are no measured PTS data for
cetaceans, but such relationships are assumed to be similar to those in
humans and other terrestrial mammals. AUD INJ typically occurs at
exposure levels at least several dB above that inducing mild TTS (e.g.,
a 40-dB threshold shift approximates AUD INJ onset (Kryter et al.,
1966; Miller, 1974), while a 6-dB threshold shift approximates TTS
onset (Southall et al., 2007, 2019). Based on data from terrestrial
mammals, a precautionary assumption is that the AUD INJ thresholds for
impulsive sounds (such as airgun pulses as received close to the
source) are at least 6 dB higher than the TTS threshold on a peak sound
pressure level (PK SPL) basis and AUD INJ cumulative SEL
(SEL<INF>24h</INF>) thresholds are 15 (impulsive sound criteria) to 20
dB (non-impulsive criteria) higher than TTS cumulative SEL thresholds
(Southall et al., 2007, 2019). Given the higher level of sound or
longer exposure duration necessary to cause AUD INJ as compared with
TTS, it is considerably less likely that AUD INJ could occur.
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 3 captive
bottlenose dolphins before and after exposure to 10 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 was 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 high-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.
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 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, 2024).
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

[[Page 19100]]

an area for feeding (Richardson et al., 1995; National Research Council
(NRC), 2003; Wartzok et al., 2003). Controlled experiments with captive
marine mammals have shown 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). 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 disruptions 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.,
2007a, b). A determination of whether foraging disruptions affect
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.
Visual tracking, passive acoustic monitoring (PAM), 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, or
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).
Changes in respiration naturally vary with different behaviors and
alterations to breathing rate as a function of acoustic exposure can be
expected to co-occur with other behavioral reactions, such as a flight
response or an alteration in diving. However, respiration rates in and
of themselves may be representative of annoyance or an acute stress
response. Various studies have shown that respiration rates may either
be unaffected or could increase, depending on the species and signal
characteristics, again highlighting the importance in understanding
species differences in the tolerance of underwater noise when
determining the potential for impacts resulting from anthropogenic
sound exposure (e.g., Kastelein et al., 2001, 2005, 2006; Gailey et
al., 2007, 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 PAM 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 minutes sampled period) on singer number. The number of
singers significantly decreased with increasing received level of
noise, suggesting that humpback whale communication 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,

[[Page 19101]]

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 cumulative SEL (SEL<INF>cum</INF>) 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 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 show 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. Avoidance of overlap between
disturbing noise and areas and/or times of particular importance for
sensitive species may be critical to avoiding population-level impacts
because (particularly for animals with high site fidelity) there may be
a strong motivation to remain in the area despite negative impacts.
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.
Forney et al. (2017) specifically discuss beaked whales, stating
that until recently most knowledge of beaked whales was derived from
strandings, as they have been involved in atypical mass stranding
events associated with mid-frequency active (MFA) sonar training
operations. Given these observations and recent research, beaked whales
appear to be particularly sensitive and vulnerable to certain types of
acoustic disturbance relative to most other marine mammal species.
Individual beaked whales reacted strongly to experiments using
simulated MFA sonar at low received levels, by moving away from the
sound source and stopping foraging for extended periods. These
responses, if on a frequent basis, could result in significant fitness
costs to individuals (Forney et al., 2017). Additionally, difficulty in
detection of beaked whales due to their cryptic surfacing behavior and
silence when near the surface pose problems for mitigation measures
employed to protect beaked whales. Forney et al. (2017) specifically
states that failure to consider both displacement of beaked whales from
their habitat and noise exposure could lead to more severe biological
consequences.
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 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 5-day period did not cause any sleep
deprivation or stress effects.
Many animals perform vital functions, such as feeding, resting,
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption
of such functions resulting from reactions to stressors, such as sound
exposure, are more likely to be significant if they last more than one
diel cycle or recur on subsequent days (Southall et al., 2007).
Consequently, a behavioral response lasting less than 1 day and not
recurring on subsequent days is not considered particularly severe
unless it could directly affect reproduction or survival (Southall et
al., 2007). Note that there is a difference between multi-day
substantive behavioral reactions and multi-day anthropogenic
activities. For example, just because an activity lasts for multiple
days does not necessarily mean that individual animals are either
exposed to activity-related stressors for multiple days or, further,
exposed in a manner resulting in sustained multi-day substantive
behavioral responses.
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

[[Page 19102]]

in\3\ (8,294 cc) or more in that study) 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, significant masking could disrupt
behavioral patterns, which in turn could affect fitness for survival
and reproduction. 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 a TS) is not
associated with abnormal physiological function, it is not considered a
physiological effect, but rather a potential behavioral effect.
The frequency range of the potentially masking sound is important
in predicting any potential behavioral impacts. For example, low-
frequency signals may have less effect on high-frequency echolocation
sounds produced by odontocetes but are more likely to affect detection
of mysticete communication calls and other potentially important
natural sounds such as those produced by surf and some prey species.
The masking of communication signals by anthropogenic noise may be
considered as a reduction in the communication space of animals (e.g.,
Clark et al., 2009) and may result in energetic or other costs as
animals change their vocalization behavior (e.g., Miller et al., 2000;
Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2010; Holt
et al., 2009). Masking may be less 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.

[[Page 19103]]

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 noise levels during
intervals between seismic 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 2,000 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). 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 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. 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).
Vessel 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; 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.
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. 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 vessels (Richardson et al.
1995). Pirotta et al. (2015) noted that the physical presence of
vessels, not just ship noise, disturbed the foraging activity of
bottlenose dolphins. There is little 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).
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).

Vessel Strike

Vessel collisions with marine mammals, or vessel strikes, can
result in death or serious injury of the animal. Wounds resulting from
vessel 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 vessels 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
increased from 45 to 75 percent as vessel speed increased from 10 to 14
knots (kn, 26 kilometer per hour (kph)), and exceeded 90 percent at 17
kn (31 kph). 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

[[Page 19104]]

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 kn
(28 kph). The chances of a lethal injury decline from approximately 80
percent at 15 kn (28 kph) to approximately 20 percent at 8.6 kn (16
kph). At speeds below 11.8 kn (22 kph), the chances of lethal injury
drop below 50 percent, while the probability asymptotically increases
toward one hundred percent above 15 kn (28 kph).
The Langseth will travel at a speed of 5 kn (9 kph) while towing
seismic survey gear. At this speed, both the possibility of striking a
marine mammal and the possibility of a strike resulting in serious
injury or mortality are 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 discountable. Vessel 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. Jensen and Silber (2004) summarized vessel 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). No such incidents were reported for geophysical survey
vessels during that time period.
It is possible for vessel strikes to occur while traveling at slow
speeds. For example, a hydrographic survey vessel traveling at low
speed (5.5 kn (10 kph)) 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 confidence interval = 0-5.5 x
10-6; NMFS, 2013). In addition, a research vessel 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 propose a robust vessel strike avoidance protocol (see Proposed
Mitigation), which we believe eliminates any foreseeable risk of vessel
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 proposed 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, the possibility of vessel
strike is discountable and, further, 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 vessel 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 marine mammal is dead and is on a
beach or shore of the United States; or in waters under the
jurisdiction of the United States (including any navigable waters); or
a marine mammal is alive and is on a beach or shore of the United
States and is unable to return to the water; 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 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, vessel 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
predispose 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 MFA sonar. MFA 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 military 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 very high-frequency cetaceans (e.g., Kogia spp.)
have a generalized hearing range of frequencies between 200 Hz and 165
kHz, while high-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 high-
frequency cetaceans and very 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

[[Page 19105]]

these effects than other hearing groups (NMFS, 2018, 2024). 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 high-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 high-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).
Military MFA sonar effects beaked whales differently than airguns
do because it produces energy at different frequencies than airguns.
High-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, 2024). 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 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 in the historical high-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 high-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. 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 high-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., MFA sonar) 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

[[Page 19106]]

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 10 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 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
(International Council for the Exploration for the Sea, 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 review of possible stranding associations with seismic surveys
(Castellote and Llorens, 2016) states 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' 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 10 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 be broadly associated with the survey itself, as opposed to
use of seismic airguns. An 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). 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 high-frequency cetaceans. We have considered the potential for
the proposed surveys to result in marine mammal stranding and, based on
the best available information, do not expect a stranding to occur.
Entanglement--Entanglements occur when marine mammals become
wrapped around cables, lines, nets, or other objects suspended in the
water column. During seismic 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 marine
mammals in seismic survey equipment. No incidents of entanglement of
marine mammals with seismic survey gear have been documented in over
54,000 nautical miles (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. There are relatively 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.

[[Page 19107]]

Anticipated Effects on Marine Mammal Habitat

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., 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; Pe[ntilde]a et al., 2013; Chapman and Hawkins,
1969; Wardle et al., 2001; 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 (Eng[aring]s et al., 1996; Eng[aring]s 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. (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 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 (Andr[eacute] et al., 2011;
Sol[eacute] 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 3 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

[[Page 19108]]

downstream of the survey areas, either spatially or temporally.
Notably, a more recently described 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 1 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, 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 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 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 generally 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.,
2000). 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 of Marine Mammals

This section provides an estimate of the number of incidental takes
proposed for authorization through the IHA, which will inform NMFS'
consideration of ``small numbers,'' the negligible impact
determinations, and impacts on subsistence uses.
Harassment is the only type of take expected to result from these
activities. Except with respect to certain activities

[[Page 19109]]

not pertinent here, section 3(18) of the MMPA defines ``harassment'' as
any act of pursuit, torment, or annoyance, which (i) has the potential
to injure a marine mammal or marine mammal stock in the wild (Level A
harassment); or (ii) has the potential to disturb a marine mammal or
marine mammal stock in the wild by causing disruption of behavioral
patterns, including, but not limited to, migration, breathing, nursing,
breeding, feeding, or sheltering (Level B harassment).
Authorized takes would be by Level B harassment only, in the form
of behavioral reactions and/or TTS, for individual marine mammals
resulting from exposure to noise from the use of seismic airguns. Based
on the nature of the activity and the anticipated effectiveness of the
mitigation measures (i.e., shutdown) discussed in detail below in the
Proposed Mitigation section, Level A harassment is neither anticipated
nor proposed to be authorized.
As described previously, no serious injury or mortality is
anticipated or proposed to be authorized for this activity. Below we
describe how the proposed take numbers are estimated.
For acoustic impacts, generally speaking, we estimate take by
considering: (1) acoustic criteria above which NMFS believes the best
available science indicates marine mammals will likely be behaviorally
harassed or incur some degree of AUD INJ; (2) the area or volume of
water that will be ensonified above these levels in a day; (3) the
density or occurrence of marine mammals within these ensonified areas;
and, (4) the number of days of activities. We note that while these
factors can contribute to a basic calculation to provide an initial
prediction of potential takes, additional information that can
qualitatively inform take estimates is also sometimes available (e.g.,
previous monitoring results or average group size). Below, we describe
the factors considered here in more detail and present the proposed
take estimates.

Acoustic Criteria

NMFS recommends the use of acoustic criteria 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 AUD INJ of some degree (equated to
Level A harassment). We note that the criteria for AUD INJ, as well as
the names of two hearing groups, have been recently updated (NMFS 2024)
as reflected below in the Level A Harassment section.
Level B Harassment--Though significantly driven by received level,
the onset of behavioral disturbance from anthropogenic noise exposure
is also informed to varying degrees by other factors related to the
source or exposure context (e.g., frequency, predictability, duty
cycle, duration of the exposure, signal-to-noise ratio, distance to the
source), the environment (e.g., bathymetry, other noises in the area,
predators in the area), and the receiving animals (hearing, motivation,
experience, demography, life stage, depth) and can be difficult to
predict (e.g., Southall et al., 2007, 2021, Ellison et al., 2012).
Based on what the available science indicates and the practical need to
use a threshold based on a metric that is both predictable and
measurable for most activities, NMFS typically uses a generalized
acoustic threshold based on received level to estimate the onset of
behavioral harassment. NMFS generally predicts that marine mammals are
likely to be behaviorally harassed in a manner considered to be Level B
harassment when exposed to underwater anthropogenic noise above root-
mean-squared pressure received levels (RMS SPL) of 120 dB (referenced
to 1 micropascal (re 1 [mu]Pa)) for continuous (e.g., vibratory pile
driving, drilling) and above RMS SPL 160 dB re 1 [mu]Pa for non-
explosive impulsive (e.g., seismic airguns) or intermittent (e.g.,
scientific sonar) sources. Generally speaking, Level B harassment take
estimates based on these behavioral harassment thresholds are expected
to include any likely takes by TTS as, in most cases, the likelihood of
TTS occurs at distances from the source less than those at which
behavioral harassment is likely. TTS of a sufficient degree can
manifest as behavioral harassment, as reduced hearing sensitivity and
the potential reduced opportunities to detect important signals
(conspecific communication, predators, prey) may result in changes in
behavior patterns that would not otherwise occur.
L-DEO's proposed activity includes the use of impulsive seismic
sources (i.e., airguns), and therefore the RMS SPL thresholds of 160 dB
re 1 [mu]Pa is applicable.
Level A harassment--NMFS' Updated Technical Guidance for Assessing
the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version
3.0) (Updated Technical Guidance, 2024) identifies dual criteria to
assess AUD INJ (Level A harassment) to five different underwater 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 activity includes the use of impulsive seismic sources
(i.e., airguns).
The 2024 Updated Technical Guidance criteria include both updated
thresholds and updated weighting functions for each hearing group. The
thresholds are provided in table 3. The references, analysis, and
methodology used in the development of the criteria are described in
NMFS' 2024 Updated Technical Guidance, which may be accessed at:
<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools</a>.

Table 3--Thresholds Identifying the Onset of Auditory Injury
----------------------------------------------------------------------------------------------------------------
AUD INJ onset acoustic thresholds * (received level)
Hearing group ------------------------------------------------------------------------
Impulsive Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans........... Cell 1: Lpk,flat: 222 dB; Cell 2: LE,LF,24h: 197 dB.
LE,LF,24h: 183 dB.
High-Frequency (HF) Cetaceans.......... Cell 3: Lpk,flat: 230 dB; Cell 4: LE,HF,24h: 201 dB.
LE,HF,24h: 193 dB.
Very High-Frequency (VHF) Cetaceans.... Cell 5: Lpk,flat: 202 dB; Cell 6: LE,VHF,24h: 181 dB.
LE,VHF,24h: 159 dB.
Phocid Pinnipeds (PW) (Underwater)..... Cell 7: Lpk,flat: 223 dB; Cell 8: LE,PW,24h: 195 dB.
LE,PW,24h: 183 dB.
Otariid Pinnipeds (OW) (Underwater).... Cell 9: Lpk,flat: 230 dB; Cell 10: LE,OW,24h: 199 dB.
LE,OW,24h: 185 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric criteria for impulsive sounds: Use whichever criteria results in the larger isopleth for
calculating AUD INJ onset. If a non-impulsive sound has the potential of exceeding the peak SPL criteria
associated with impulsive sounds, the PK SPL criteria are recommended for consideration for non-impulsive
sources.

[[Page 19110]]

Note: Peak SPL (Lp,0-pk) has a reference value of 1 [mu]Pa, and weighted cumulative SEL (LE,p) has a reference
value of 1 [mu]Pa\2\s. In this table, criteria are abbreviated to be more reflective of International
Organization for Standardization standards (ISO 2017; ISO 2020). The subscript ``flat'' is being included to
indicate peak sound pressure are flat weighted or unweighted within the generalized hearing range of marine
mammals underwater (i.e., 7 Hz to 165 kHz). The subscript associated with cumulative SEL criteria indicates
the designated marine mammal auditory weighting function (LF, HF, and VHF cetaceans, and PW and OW pinnipeds)
and that the recommended accumulation period is 24 hours. The LE,p criteria 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 criteria will be exceeded.

Ensonified Area

Here, we describe operational and environmental parameters of the
activity that are used in estimating the area ensonified above the
acoustic thresholds, including source levels and transmission loss
coefficient.
The ensonified area associated with Level A harassment is more
technically challenging to predict due to the need to account for a
duration component. Therefore, NMFS developed an optional User
Spreadsheet tool to accompany the 2024 Updated Technical Guidance that
can be used to relatively simply predict an isopleth distance for use
in conjunction with marine mammal density or occurrence to help predict
potential takes. We note that because of some of the assumptions
included in the methods underlying this optional tool, we anticipate
that the resulting isopleth estimates are typically going to be
overestimates of some degree, which may result in an overestimate of
potential take by Level A harassment. However, this optional tool
offers the best way to estimate isopleth distances when more
sophisticated modeling methods are not available or practical.
The proposed survey would entail the use of a cluster of two GI
airguns with a total discharge volume of 90 in\3\ (1,475 cc) at a tow
depth of 3 m. L-DEO model results are used to determine the 160 dB RMS
radius for the airgun source down to a maximum depth of 2,000 m.
Received sound levels have been predicted by L-DEO's model (Diebold et
al. 2010) as a function of distance from the airgun array. This
modeling approach 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 (~1,600 m), intermediate water depth on the
slope (~600-1,100 m), and shallow water (~50 m) in the Gulf of America
(previously Gulf of Mexico) (Tolstoy et al. 2009; Diebold et al. 2010).
For deep and intermediate water cases, the field measurements
cannot be used readily to derive the harassment isopleths, as at those
sites the calibration hydrophone was located at a roughly constant
depth of 350-550 m, which may not intersect all the SPL isopleths at
their widest point from the sea surface down to the assumed maximum
relevant water depth (~2000 m) for marine mammals. At short ranges,
where the direct arrivals dominate and the effects of seafloor
interactions are minimal, the data at the deep 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 at short ranges, sound levels
for direct arrivals recorded by the calibration hydrophone and L-DEO
model results for the same array tow depth are in good alignment (see
figures 12 and 14 in Diebold et al. 2010). 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
(see figures 11, 12, and 16 in Diebold et al. 2010). 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 America calibration measurements
demonstrates that although simple, the L-DEO model is a robust tool for
conservatively estimating isopleths.
The proposed low-energy survey would acquire data with the 2 GI
airgun array at a tow depth of 3 m. For deep water (>1,000 m), we use
the deep-water radii obtained from the L-DEO model results down to a
maximum water depth of 2,000 m for the airgun array.
L-DEO's modeling methodology is described in greater detail in
their application. The estimated distances to the Level B harassment
isopleth for the proposed airgun configuration are shown in table 4.

Table 4--Predicted Radial Distances From the Langseth Seismic Source to Isopleth Corresponding to Level B
Harassment Threshold
----------------------------------------------------------------------------------------------------------------
Predicted distances (in
Airgun configuration Tow depth Water depth (m) m) to the Level B
(m) harassment threshold
----------------------------------------------------------------------------------------------------------------
Two 45 in\3\ airguns.................................. 3 >1,000 438
----------------------------------------------------------------------------------------------------------------

Table 5--Modeled Radial Distance to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
Low High Very high
frequency frequency frequency Phocid Otariid
cetaceans cetaceans cetaceans pinnipeds pinnipeds
----------------------------------------------------------------------------------------------------------------
PTS SELcum..................................... 31.5 0 0.1 0.5 0
PTS Peak....................................... 3.9 1.1 35.3 3.4 1.1
----------------------------------------------------------------------------------------------------------------
The largest distance (in bold) of the dual criteria (SELcum or Peak) was used to estimate threshold distances
and potential takes by Level A harassment.

[[Page 19111]]

Table 5 presents the modeled Level A harassment isopleths for each
marine mammal hearing group based on L-DEO modeling incorporated in the
companion user spreadsheet, for the low-energy surveys with the
shortest shot interval (i.e., greatest potential to cause PTS based on
accumulated sound energy) (NMFS 2018, 2024).
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 software program and the
NMFS user spreadsheet, described below. The acoustic thresholds for
impulsive sounds contained in the NMFS Technical Guidance were
presented as dual metric acoustic thresholds using both
SEL<INF>cum</INF> and peak sound pressure metrics (NMFS, 2016). 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 SEL<INF>cum</INF> metric
considers both level and duration of exposure, as well as auditory
weighting functions by marine mammal hearing group.
The SEL<INF>cum</INF> for the 2 GI airgun array is derived from
calculating the modified farfield signature. The farfield signature is
often used as a theoretical representation of the source level. To
compute the farfield signature, the source level is estimated at a
large distance (right) 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, it has been recognized that the
source level from the theoretical farfield signature is never
physically achieved at the source when the source is an array of
multiple airguns separated in space (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 farfield 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 farfield signature. Because the farfield
signature does not take into account the large array effect near the
source and is calculated as a point source, the farfield signature is
not an appropriate measure of the sound source level for large arrays.
See L-DEO's application for further detail on acoustic modeling.
In consideration of the received sound levels in the near-field as
described above, we expect the potential for Level A harassment of any
species 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 anticipate that auditory injury or
Level A harassment is a likely outcome for any species and do not
propose to authorize any take by Level A harassment for any species,
given the very small modeled zones of injury for those species
(estimated zones are less than 36 m for all species), in context of
distributed source dynamics.
The Level B harassment estimates are based on a consideration of
the number of marine mammals that could be within the area around the
operating airgun array where received levels of sound >=160 dB re 1
[mu]Pa RMS are predicted to occur. The estimated numbers are based on
the densities (numbers per unit area) of marine mammals expected to
occur in the area in the absence of seismic surveys. To the extent that
marine mammals tend to move away from seismic sources before the sound
level reaches the criterion level and tend not to approach an operating
airgun array, these estimates likely overestimate the numbers actually
exposed to the specified level of sound.

Marine Mammal Occurrence

In this section we provide information about the occurrence of
marine mammals, including density or other relevant information which
will inform the take calculations.
L-DEO used habitat-based stratified marine mammal densities for
summer (July-December) for the ETP when available (Barlow et al.,
2009), and densities for the ETP from NMFS (2015b) for all other
species (See table 3 in L-DEO's application). 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 geographic
information system (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 2015a). 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 (2015) reported a density of
zero, L-DEO used the spring density for Baja from U.S. Navy (2017).
This was done because even though there is a modeled density of zero,
we do expect there is some potential for sei whale to be in the project
area during the proposed survey. No densities were available for
Blainville's beaked whale, ginkgo-toothed beaked whale, Deraniyagala's
beaked whale, or pygmy beaked whale so density for Mesoplodon species
was used. For California sea lion only 10 percent of the density from
the wider ETP was used to account for the fact that California sea
lions typically do not occur in water greater than 1,000 m.

Take Estimation

Here we describe how the information provided above is synthesized
to produce a quantitative estimate of the take that is reasonably
likely to occur and proposed for authorization.
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 the predicted
isopleth corresponding to the Level A harassment and Level B harassment
thresholds are calculated, as described above. Those radial distances
were then used to calculate the area(s) around the airgun array
predicted to be ensonified to sound levels that exceed the harassment
thresholds. The distance

[[Page 19112]]

for the 160-dB Level B harassment threshold and auditory injury (Level
A harassment) thresholds (based on L-DEO model results) was used to
draw a buffer around the area expected to be ensonified (i.e., the
survey area). The ensonified areas were then increased by 25 percent to
account for potential delays, which is equivalent to adding 25 percent
to the proposed line km to be surveyed. The density for each species
was then multiplied by the daily ensonified areas (increased as
described above) and then multiplied by the number of survey days
(seven) to estimate potential takes (see appendix B of L-DEO's
application for more information).
L-DEO assumed that their estimates of marine mammal exposures above
harassment thresholds equate to take and requested authorization of
those takes. Those estimates in turn form the basis for our proposed
take authorization numbers. Based on the nature of the activity and the
anticipated effectiveness of the mitigation measures (i.e., shutdown)
discussed in detail below in the Proposed Mitigation section, and due
to no Level A harassment being calculated, Level A harassment is
neither anticipated nor proposed to be authorized. Estimated exposures
and proposed take numbers for authorization are shown in table 6.

Table 6--Estimated Take Proposed for Authorization
----------------------------------------------------------------------------------------------------------------
Estimated takes Proposed takes
Species by Level B by Level B Population Percent of
harassment harassment abundance population
----------------------------------------------------------------------------------------------------------------
Humpback whale \1\............................... 0 \b\ 1 \d\ 2,566 0.04
Minke whale...................................... 0 \c\ 2 115 1.74
Bryde's whale.................................... 1 \a\ 2 \d\ 649 0.31
Fin whale........................................ 0 \c\ 1 \d\ 145 0.69
Sei whale........................................ 0 \c\ 1 \e\ 29,600 <0.01
Sperm whale...................................... 0 \a\ 8 2,810 0.28
Cuvier's beaked whale............................ 2 2 \e\ 20,000 0.01
Longman's beaked whale........................... 0 \a\ 3 \e\ 1,007 0.3
Mesoplodon beaked whales \2\..................... 1 \a\ 12 \e\ 25,300 0.01
Risso's dolphin.................................. 27 27 \d\ 24,084 0.11
Rough-toothed dolphin............................ 16 16 \d\ 37,511 0.04
Bottlenose dolphin............................... 62 62 \d\ 61,536 0.1
Pantropical spotted dolphin...................... 223 223 \d\ 146,296 0.15
Spinner dolphin \3\.............................. 222 222 \d\ 186,906 0.12
Striped dolphin.................................. 57 \a\ 6 \d\ 128,867 0.05
Common dolphin................................... 75 \a\ 254 \d\ 283,196 0.09
Fraser's dolphin................................. 23 \a\ 39 \e\ 289,300 0.14
Short-finned pilot whales........................ 7 \a\ 18 \d\ 3,348 0.54
Killer whale..................................... 1 \a\ 5 \d\ 852 0.59
False killer whale............................... 3 \a\ 11 \e\ 39,600 0.03
Pygmy killer whale............................... 3 \a\ 28 \e\ 38,900 0.07
Melon-headed whale............................... 4 \a\ 199 \e\ 45,400 0.44
Kogia spp \4\.................................... 0 \a\ 2 \e\ 11,200 0.02
Guadalupe fur seal............................... 13 13 \e\ 34,107 0.04
California sea lion.............................. 3 3 \e\ 105,000 <0.01
----------------------------------------------------------------------------------------------------------------
\1\ Takes are assumed to be from the Central America/Southern Mexico Stock.
\2\ Includes: Blainville's, ginkgo-toothed, Deraniyagala's, and pygmy beaked whales.
\3\ Includes both whitebelly and eastern population.
\4\ Includes pygmy and dwarf sperm whales.
\a\ Increased to a group size from Wade and Gerrodette (1993).
\b\ Increased to a group size from Oedekoven et al., 2021.
\c\ Increased to a group size based on 87 FR 27111 (May 6, 2022).
\d\ Population sizes are for Pacific waters of Mexico (Gerrodette and Palacios, 1996).
\e\ Population in ETP or wider Pacific (NMFS 2015).

Proposed Mitigation

In order to issue an IHA under section 101(a)(5)(D) of the MMPA,
NMFS must set forth the permissible methods of taking pursuant to the
activity, and other means of effecting the least practicable impact on
the species or stock and its habitat, paying particular attention to
rookeries, mating grounds, and areas of similar significance, and on
the availability of the species or stock for taking for certain
subsistence uses (latter not applicable for this action). NMFS
regulations require applicants for incidental take authorizations to
include information about the availability and feasibility (economic
and technological) of equipment, methods, and manner of conducting the
activity or other means of effecting the least practicable adverse
impact upon the affected species or stocks, and their habitat (50 CFR
216.104(a)(11)).
In evaluating how mitigation may or may not be appropriate to
ensure the least practicable adverse impact on species or stocks and
their habitat, as well as subsistence uses where applicable, NMFS
considers two primary factors:
(1) The manner in which, and the degree to which, the successful
implementation of the measure(s) is expected to reduce impacts to
marine mammals, marine mammal species or stocks, and their habitat.
This considers the nature of the potential adverse impact being
mitigated (likelihood, scope, range). It further considers the
likelihood that the measure will be effective if implemented
(probability of accomplishing the mitigating result if implemented as
planned), the likelihood of effective implementation (probability
implemented as planned), and;
(2) The practicability of the measures for applicant
implementation, which may consider such things as cost, and impact on
operations.

[[Page 19113]]

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 shutdown zone (SZ), within
which observation of certain marine mammals requires shutdown of the
acoustic source, a buffer zone, and to the extent possible depending on
conditions, the surrounding waters. The buffer zone means an area
beyond the SZ to be monitored for the presence of marine mammals that
may enter the SZ. During pre-start clearance monitoring (i.e., before
ramp-up begins), the buffer zone also acts as an extension of the SZ 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 0-100 m SZ, out to a radius of 200 m from the edges of the airgun
array (100-200 m). This 200-m zone (SZ plus buffer) represents the pre-
start clearance zone. Visual monitoring of the SZ and adjacent waters
(buffer plus surrounding 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 SZ by alerting the visual observer and
crew of marine mammals that are outside of, but may approach and enter,
the SZ.
During survey operations (e.g., any day on which use of the airgun
array is planned to occur and whenever the airgun array 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 1 hour after use of the airgun array 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 SZ and buffer zone. These
zones shall be based upon the radial distance from the edges of the
airgun array (rather than being based on the center of the array or
around the vessel itself). During use of the airgun array (i.e.,
anytime airguns are active, including ramp-up), detections of marine
mammals within the buffer zone (but outside the SZ) shall be
communicated to the operator to prepare for the potential shutdown of
the airgun array. 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 airgun array is not operating for
comparison of sighting rates and behavior with and without use of the
airgun array 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 1 hour between watches and may conduct
a maximum of 12 hours of observation per 24-hour period.

Establishment of Shutdown and Pre-Start Clearance Zones

A SZ 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 SZ with a 100-m radius. The 100-m SZ
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 airgun array 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 airgun array
and includes the SZ 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 100-m SZ 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
SEL<INF>cum</INF> 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 100-m SZ 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 expect that 100 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 SZ, doubling the SZ size during pre-clearance.
An extended SZ of 500 m must be implemented for all beaked whales,
a large whale with a calf, and groups of six or more large whales. No
buffer of this extended SZ is required, as NMFS concludes that this
extended SZ is sufficiently protective to mitigate harassment to these
groups.

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.
The intent of pre-start clearance observation (30 minutes) is to ensure
no marine mammals are observed within the pre-start clearance zone (or
extended SZ, for beaked whales, a large whale with a calf, and groups
of six or more large whales) prior to the beginning of ramp-up. During
the 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 the 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 prior to the
sound source reaching full intensity. A ramp-up procedure, involving a
stepwise 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
airgun array. All operators must adhere to the following pre-start
clearance and ramp-up requirements:
<bullet> 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 SZ) for 30 minutes prior to the initiation of ramp-up
(pre-start clearance);

[[Page 19114]]

<bullet> Ramp-ups shall be scheduled so as to minimize the time
spent with the source activated prior to reaching the designated run-
in;
<bullet> 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;
<bullet> Ramp-up may not be initiated if any marine mammal is
within the applicable shutdown or buffer zone. If a marine mammal is
observed within the pre-start clearance zone (or extended SZ, for
beaked whales, a large whale with a calf, and groups of six or more
large whales) 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 30 minutes for all
mysticetes and all other odontocetes, including sperm whales, beaked
whales, and large delphinids, such as pilot whales);
<bullet> Ramp-up must begin by activating one GI airgun followed by
the second, with each stage lasting no less than 5 minutes. The
operator must provide information to the PSO documenting that
appropriate procedures were followed;
<bullet> PSOs must monitor the pre-start clearance zone and
extended SZ 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;
<bullet> Ramp-up may occur at times of poor visibility, including
nighttime, if appropriate monitoring has occurred with no observations
in the 30 minutes prior to beginning ramp-up. Airgun array activation
may only occur at times of poor visibility where operational planning
cannot reasonably avoid such circumstances;
<bullet> If the airgun array is shut down for brief periods (i.e.,
less than 30 minutes) for reasons other than implementation of
prescribed mitigation (e.g., mechanical difficulty), it may be
activated again without ramp-up if PSOs have maintained constant visual
observation and no visual observations of marine mammals have occurred
within the pre-start clearance zone (or extended SZ, where applicable).
For any longer shutdown, pre-start clearance observation and ramp-up
are required; and
<bullet> Testing of the airgun array 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 minutes.

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 call for shutdown of the airgun array
if a marine mammal is detected within the applicable SZ. The operator
must also establish and maintain clear lines of communication directly
between PSOs on duty and crew controlling the airgun array to ensure
that shutdown commands are conveyed swiftly while allowing PSOs to
maintain watch. When the airgun array is active (i.e., anytime one or
more airguns is active, including during ramp-up) and a marine mammal
appears within or enters the applicable SZ the airgun array will be
shut down. When shutdown is called for by a PSO, the airgun array will
be immediately deactivated and any dispute resolved only following
deactivation.
Following a shutdown, airgun activity would not resume until the
marine mammal has cleared the SZ. The animal would be considered to
have cleared the SZ if it is visually observed to have departed the SZ
(i.e., animal is not required to fully exit the buffer zone where
applicable), or it has not been seen within the SZ for 15 minutes for
small odontocetes or 30 minutes for all mysticetes and all other
odontocetes, including sperm whales, beaked whales, and large
delphinids, such as pilot whales.
The shutdown requirement is waived for specific genera of small
dolphins if an individual is detected within the SZ. 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 the
specific genera of small dolphins (Lagenodelphis, Stenella, Steno,
Delphinus, Tursiops, and pinnipeds).
We include this small dolphin exception because shutdown
requirements for these species 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 high-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
(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 high-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 SZ).
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 authorized 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

[[Page 19115]]

an aggregation of six or more large whales are observed at any
distance.

Vessel Strike Avoidance Mitigation Measures

Vessel personnel should use an appropriate reference guide that
includes identifying information on all marine mammals that may be
encountered. Vessel operators must comply with the below measures
except under extraordinary circumstances when the safety of the vessel
or crew is in doubt or the safety of life at sea is in question. 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.
Vessel operators and crews must maintain a vigilant watch for all
marine mammals and slow down, stop their vessel, or alter course, as
appropriate and regardless of vessel size, to avoid striking any marine
mammal. A single marine mammal at the surface may indicate the presence
of submerged animals in the vicinity of the vessel; therefore,
precautionary measures should always be exercised. A visual observer
aboard the vessel must monitor a vessel strike avoidance zone around
the vessel (separation 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 large whale (defined in this context as
sperm whales or baleen whales), or other marine mammals.
Vessel speeds must be reduced to 10 kn (18.5 kph) 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).
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.
Based on our evaluation of the applicant's proposed measures, NMFS
has preliminarily determined that the proposed mitigation measures
provide the means of effecting the least practicable impact on the
affected species or stocks and their habitat, paying particular
attention to rookeries, mating grounds, and areas of similar
significance.

Proposed Monitoring and Reporting

In order to issue an IHA for an activity, section 101(a)(5)(D) of
the MMPA states that NMFS must set forth requirements pertaining to the
monitoring and reporting of such taking. The MMPA implementing
regulations at 50 CFR 216.104(a)(13) indicate that requests for
authorizations must include the suggested means of accomplishing the
necessary monitoring and reporting that will result in increased
knowledge of the species and of the level of taking or impacts on
populations of marine mammals that are expected to be present while
conducting the activities. Effective reporting is critical both to
compliance as well as ensuring that the most value is obtained from the
required monitoring.
Monitoring and reporting requirements prescribed by NMFS should
contribute to improved understanding of one or more of the following:
<bullet> Occurrence of marine mammal species or stocks in the area
in which take is anticipated (e.g., presence, abundance, distribution,
density);
<bullet> Nature, scope, or context of likely marine mammal exposure
to potential stressors/impacts (individual or cumulative, acute or
chronic), through better understanding of: (1) action or environment
(e.g., source characterization, propagation, ambient noise); (2)
affected species (e.g., life history, dive patterns); (3) co-occurrence
of marine mammal species with the activity; or (4) biological or
behavioral context of exposure (e.g., age, calving or feeding areas);
<bullet> Individual marine mammal responses (behavioral or
physiological) to acoustic stressors (acute, chronic, or cumulative),
other stressors, or cumulative impacts from multiple stressors;
<bullet> How anticipated responses to stressors impact either: (1)
long-term fitness and survival of individual marine mammals; or (2)
populations, species, or stocks;
<bullet> Effects on marine mammal habitat (e.g., marine mammal prey
species, acoustic habitat, or other important physical components of
marine mammal habitat); and,
<bullet> 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 times during daytime hours. 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. L-DEO must use dedicated,
trained, and NMFS-approved PSOs. At least one visual PSO 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. 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.
Monitoring shall be conducted in accordance with the following
requirements:
<bullet> PSOs shall be independent, dedicated, trained visual PSOs
and must be employed by a third-party observer provider;
<bullet> PSOs shall have no tasks other than to conduct visual
observational effort, 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); and
<bullet> PSOs shall have successfully completed an approved PSO
training

[[Page 19116]]

course appropriate for their designated task (visual).
<bullet> 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;
<bullet> 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;
<bullet> 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
<bullet> 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.
<bullet> For data collection purposes, PSOs shall use standardized
electronic data collection forms. PSOs shall record detailed
information about any implementation of mitigation requirements,
including the distance of animals to the airgun array 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 airgun array. If required mitigation was
not implemented, PSOs should record a description of the circumstances.
At a minimum, the following information must be recorded:
[cir] Vessel name, vessel size and type, maximum speed capability
of vessel;
[cir] Dates (MM/DD/YYYY) of departures and returns to port with
port name;
[cir] PSO names and affiliations, PSO ID (initials or other
identifier);
[cir] Date (MM/DD/YYYY) and participants of PSO briefings;
[cir] Visual monitoring equipment used (description);
[cir] PSO location on vessel and height (meters) of observation
location above water surface;
[cir] Watch status (description);
[cir] Dates (MM/DD/YYYY) and times (Greenwich Mean Time (GMC)/
Coordinated Universal Time (UTC)) of survey on/off effort and times
(GMC/UTC) corresponding with PSO on/off effort;
[cir] Vessel location (decimal degrees) when survey effort began
and ended and vessel location at beginning and end of visual PSO duty
shifts;
[cir] Vessel location (decimal degrees) at 30-second intervals if
obtainable from data collection software, otherwise at practical
regular interval;
[cir] Vessel heading (compass heading) and speed (knots) at
beginning and end of visual PSO duty shifts and upon any change;
[cir] Water depth (meters) (if obtainable from data collection
software);
[cir] 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;
[cir] Factors that may have contributed to impaired observations
during each PSO shift change or as needed as environmental conditions
changed (description) (e.g., vessel traffic, equipment malfunctions);
and
[cir] Vessel/Survey activity information (and changes thereof)
(description), such as airgun 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.).
<bullet> Upon visual observation of any marine mammals, the
following information must be recorded:
[cir] Sighting ID (numeric);
[cir] Watch status (sighting made by PSO on/off effort,
opportunistic, crew, alternate vessel/platform);
[cir] Location of PSO/observer (description);
[cir] Vessel activity at the time of the sighting (e.g., deploying,
recovering, testing, shooting, data acquisition, other);
[cir] PSO who sighted the animal/ID;
[cir] Time/date of sighting (GMT/UTC, MM/DD/YYYY);
[cir] Initial detection method (description);
[cir] Sighting cue (description);
[cir] Vessel location at time of sighting (decimal degrees);
[cir] Water depth (meters);
[cir] Direction of vessel's travel (compass direction);
[cir] Speed (knots) of the vessel from which the observation was
made;
[cir] Direction of animal's travel relative to the vessel
(description, compass heading);
[cir] Bearing to sighting (degrees);
[cir] 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;
[cir] Species reliability (an indicator of confidence in
identification) (1 = unsure/possible, 2 = probable, 3 = definite/sure,
9 = unknown/not recorded);
[cir] Estimated distance to the animal (meters) and method of
estimating distance;
[cir] Estimated number of animals (high/low/best) (numeric);
[cir] Estimated number of animals by cohort (adults, yearlings,
juveniles, calves, group composition, etc.);
[cir] 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);
[cir] 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);
[cir] Animal's closest point of approach (meters)

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