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Notice2024-14737

Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey of the Chain Transform Fault in the Equatorial Atlantic Ocean

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Published

July 8, 2024

Issuing agencies

Commerce DepartmentNational Oceanic and Atmospheric Administration

Abstract

NMFS received a request from the Lamont-Doherty Earth Observatory of Columbia University (L-DEO) for authorization to take marine mammals incidental to a marine geophysical survey at the Chain Transform Fault in the equatorial Atlantic Ocean. 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 89, Number 130 (Monday, July 8, 2024)]
[Notices]
[Pages 56158-56188]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2024-14737]

[[Page 56157]]

Vol. 89

Monday,

No. 130

July 8, 2024

Part III

Department of Commerce

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National Oceanic and Atmospheric Administration

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Takes of Marine Mammals Incidental to Specified Activities; Taking
Marine Mammals Incidental to a Marine Geophysical Survey of the Chain
Transform Fault in the Equatorial Atlantic Ocean; Notice

Federal Register / Vol. 89 , No. 130 / Monday, July 8, 2024 /
Notices

[[Page 56158]]

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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XE034]

Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to a Marine Geophysical Survey of the
Chain Transform Fault in the Equatorial Atlantic 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 received a request from the Lamont-Doherty Earth
Observatory of Columbia University (L-DEO) for authorization to take
marine mammals incidental to a marine geophysical survey at the Chain
Transform Fault in the equatorial Atlantic Ocean. Pursuant to the
Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its
proposal to issue an incidental harassment authorization (IHA) to
incidentally take marine mammals during the specified activities. NMFS
is also requesting comments on a possible one-time, 1-year renewal that
could be issued under certain circumstances and if all requirements are
met, as described in Request for Public Comments at the end of this
notice. NMFS will consider public comments prior to making any final
decision on the issuance of the requested MMPA authorization and agency
responses will be summarized in the final notice of our decision.

DATES: Comments and information must be received no later than August
7, 2024.

ADDRESSES: Comments should be addressed to Jolie Harrison, Chief,
Permits and Conservation Division, Office of Protected Resources,
National Marine Fisheries Service and should be submitted via email to
<a href="/cdn-cgi/l/email-protection#d1988581ffb9b0a3bdb0b2b9b4a391bfbeb0b0ffb6bea7">[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/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> 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 and comment.
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 prescribe requirements pertaining to the
monitoring and reporting of the takings. The definitions of all
applicable MMPA statutory terms cited above are included in the
relevant sections below.

National Environmental Policy Act

To comply with the National Environmental Policy Act of 1969 (NEPA;
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A,
NMFS must review our proposed action (i.e., the issuance of an IHA)
with respect to potential impacts on the human environment.
This action is consistent with categories of activities identified
in Categorical Exclusion B4 (incidental harassment authorizations with
no anticipated serious injury or mortality) of the Companion Manual for
NOAA Administrative Order 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 April 15, 2024, NMFS received a request from L-DEO for an IHA to
take marine mammals incidental to conducting a marine geophysical
survey of the Chain Transform Fault in the equatorial Atlantic Ocean.
Following NMFS review of the application and additional clarifying
information from L-DEO, NMFS deemed the application adequate and
complete on May 22, 2024. L-DEO's request is for take of 28 marine
mammal species by Level B harassment, and for take of a subset of 5 of
these species, by Level A harassment. 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 Woods Hole Oceanographic Institution,
University of Delaware, University of New Hampshire, Boise State
University and Boston College, with funding from the National Science
Foundation, propose to conduct a high-energy seismic survey using
airguns as the acoustic source from the research vessel (R/V) Marcus G.
Langseth (Langseth), which is owned and operated by L-DEO. The proposed
survey would occur at the Chain Transform Fault, off the coast of
Africa, in the equatorial Atlantic Ocean during austral summer 2024 in
the Southern Hemisphere (i.e., between October 2024 and February 2025).
The proposed survey would occur within International Waters more than
600 kilometers (km) in the Gulf of Guinea, Africa. The survey would
occur in water depths ranging from approximately 2,000 to

[[Page 56159]]

5,500 meters (m). To complete this survey, the R/V Langseth would tow a
36-airgun array with a total discharge volume of approximately (~)
6,600 cubic inches (in\3\) at a depth of 9 to 12 m. The airgun array
receiving system would consist of a 15 km long solid-state hydrophone
streamer and 20 Ocean Bottom Seismometers (OBS). The airguns would fire
at a shot interval of 37.5 m (~18 seconds (s)) during seismic
acquisition. Approximately 2,058 km of total survey trackline are
proposed. Airgun arrays would introduce underwater sounds that may
result in take, by Level A and Level B harassment, of marine mammals.
The purpose of the proposed survey is to understand the rheologic
mechanisms that lead to both seismic and aseismic behavior.
Specifically, the aim of the project is to: (i) understand the tectonic
variation along slow-slipping transforms; (ii) identify the influences
of seawater and melt on transform fault rheology; (iii) identify the
influences of seawater and melt on transform fault rheology; (iv) link
slip behavior to observed variations in seismic coupling and
microseismicity; and (v) apply the results to understanding the global
spectrum of oceanic transform fault behavior. The goal of this work is
to understand how and why tectonic stresses in some places lead to
earthquakes of varying sizes while in other places the stresses are
resolved without resulting in earthquakes. The seismic survey would
image the reflectivity and velocity structure of seafloor features
related to the transform fault within the Chain transform valley,
including the fault itself, `flower' structures surrounding the fault,
and the crustal massifs that comprise the steep walls of the transform
valley.
Additional data would be collected using a multibeam echosounder
(MBES), a sub-bottom profiler (SBP), and an Acoustic Doppler Current
Profiler (ADCP), which would be operated from R/V Langseth continuously
during the seismic surveys, including during transit. No take of marine
mammals is expected to result from use of this equipment.

Dates and Duration

The proposed survey is expected to last for approximately 30 days,
with 11.5 days of seismic operations, 3.5 days of OBS deployment, 2.5
days of streamer deployment and retrieval, 2.5 days of contingency, and
10 days of transit. R/V Langseth would likely leave from and return to
port in Praia, Cape Verde during austral summer 2024 (between October
2024 and February 2025).

Specific Geographic Region

The proposed survey would occur within approximately 0-2[deg] S,
13-16.5[deg] W, within international waters more than 600 km off the
coast of the Gulf of Guinea, Africa, in water depths ranging from
approximately 2,000 to 5,500 m. The region where the survey is proposed
to occur is depicted in figure 1, and is expected to cover
approximately 2,058 km of survey trackline. 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.
BILLING CODE 3510-22-P

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[GRAPHIC] [TIFF OMITTED] TN08JY24.000

BILLING CODE 3510-22-C

Detailed Description of the Specified Activity

The procedures to be used for the proposed surveys would be similar
to those used during previous seismic surveys by L-DEO and would use
conventional seismic methodology. The survey would involve one source
vessel, R/V Langseth, which is owned and operated by L-DEO. During the
high-energy survey, R/V Langseth would tow 4 strings with 36 airguns,
consisting of a mixture of Bolt 1500LL and Bolt 1900LLX. During the
surveys, all 4 strings, totaling 36 active airguns with a total
discharge volume of 6,600 in\3\, would be used. The four airgun strings
would be spaced 8 m apart, distributed across an area of approximately
24 m x 16 m behind the R/V Langseth, and would be towed approximately
140 m behind the vessel. The airgun array configurations are
illustrated in figure 2-11 of National Science Foundation (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 15-km long solid-state hydrophone streamer and 20 OBSs. As
the airgun arrays are towed along the survey lines, the hydrophone
streamer would transfer the data to the on-board processing system, and
the OBSs would receive and store the returning acoustic signals
internally for later analysis.
Approximately 2,058 km of seismic acquisition are proposed. The
survey would take place in water depths ranging from 2,000 to 5,500 m;
all effort would occur in water more than 2,000 m deep. Twenty OBSs
would be deployed by R/V Langseth and left on the ocean floor for a
period of 1 year to record earthquakes. To retrieve the OBSs, the
instrument is released to float to the surface via an acoustic release
system from the anchor, which is not retrieved. In addition to the
operations of the airgun array, the ocean floor would be mapped with
the Kongsberg EM 122 MBES and a Knudsen Chirp 3260 SBP. A Teledyne RDI
75 kilohertz (kHz) Ocean Surveyor ADCP would be used to measure water
current velocities, and acoustic pingers would be used to retrieve
OBSs. Take of marine mammals is not expected to occur incidental to the
use of the MBES, SBP, and ADCP, regardless of whether the airguns are
operating simultaneously with the other sources. Given their
characteristics (e.g., narrow downward-directed beam), marine mammals
would

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experience no more than one or two brief ping exposures, if any
exposure were to occur, which would not be expected to provoke a
response equating to take. NMFS does not expect that the use of these
sources presents any reasonable potential to cause take of marine
mammals.
Proposed mitigation, monitoring, and reporting measures are
described in detail later in this Notice (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.
The populations of marine mammals found in the survey area do not
occur within the U.S. exclusive economic zone (EEZ) and therefore, are
not assessed in NMFS' Stock Assessment Reports (SARs). For most
species, there are no stocks defined for management purposes in the
survey area, and NMFS is evaluating impacts at the species level. As
such, information on potential biological removal level (PBR; 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) and annual levels of serious injury and mortality from
anthropogenic sources are not available for these marine mammal
populations. Abundance estimates for marine mammals in the survey
location are lacking; therefore, the modeled abundances presented here
are based on a variety of proxy sources, including the U.S Navy
Atlantic Fleet Training and Testing Area Marine Mammal Density (AFTT)
model (Roberts et al., 2023) and the International Whaling Commission
(IWC) Population (Abundance) Estimates (IWC 2024). The modeled
abundance is considered the best scientific information available on
the abundance of marine mammal populations in the area.
Table 1 lists all species that occur in the survey area that may be
taken as a result of the proposed survey and summarizes information
related to the population, including regulatory status under the MMPA
and Endangered Species Act (ESA).

Table 1--Species Likely Impacted by the Specified Activities
----------------------------------------------------------------------------------------------------------------
ESA/MMPA status; Modeled abundance
Common name Scientific name Stock Strategic (Y/N) \1\ \2\
----------------------------------------------------------------------------------------------------------------
Order Artiodactyla--Cetacea--Mysticeti (baleen whales)
----------------------------------------------------------------------------------------------------------------
Family Balaenopteridae (rorquals):
Blue Whale.................. Balaenoptera NA E, D, Y \2\ 191/\4\ 2,300
musculus.
Fin Whale................... Balaenoptera NA E, D, Y 11,672
physalus.
Humpback Whale.............. Megaptera NA -, -, N \2\ 4,990/\5\
novaeangliae. 42,000
Common Minke Whale.......... Balaenoptera NA -, -, N 13,784
acutorostrata.
Antarctic Minke Whale....... Balaenoptera NA -, -, N \3\ 515,000
bonaerensis.
Sei Whale................... Balaenoptera NA E, D, Y 19,530
borealis.
Bryde's Whale............... Balaenoptera edeni NA -, -, N 536
----------------------------------------------------------------------------------------------------------------
Odontoceti (toothed whales, dolphins, and porpoises)
----------------------------------------------------------------------------------------------------------------
Family Physeteridae:
Sperm Whale................. Physeter NA E, D, Y 64,015
macrocephalus.
Family Kogiidae:
Pygmy Sperm Whale........... Kogia breviceps... NA -, -, N \7\ 26,043
Dwarf Sperm Whale........... Kogia sima........ NA -, -, N
Family Ziphiidae (beaked
whales):
Blainville's Beaked Whale... Mesoplodon NA -, -, N \8\ 65,069
densirostris.
Cuvier's Beaked Whale....... Ziphius NA -, -, N
cavirostris.
Gervais' Beaked Whale....... Mesoplodon NA -, -, N
europaeus.
Family Delphinidae:
Killer Whale................ Orcinus orca...... NA -, -, N 972
Short-Finned Pilot Whale.... Globicephala melas NA -, -, N \6\ 264,907
Rough-toothed Dolphin....... Steno bredanensis. NA -, -, N 32,848
Bottlenose Dolphin.......... Tursiops truncatus NA -, -, N 418,151
Risso's Dolphin............. Grampus griseus... NA -, -, N 78,205
Common Dolphin.............. Delphinus delphis. NA -, -, N 473,260
Striped Dolphin............. Stenella NA -, -, N 412,729
coeruleoalba.
Pantropical Spotted Dolphin. Stenella attenuata NA -, -, N 321,740
Atlantic Spotted Dolphin.... Stenella frontalis NA -, -, N 259,519
Spinner Dolphin............. Stenella NA -, -, N 152,511
longirostris.
Clymene Dolphin............. Stenella clymene.. NA -, -, N 181,209
Fraser's Dolphin............ Lagenodelphis NA -, -, N 19,585
hosei.
Melon-headed Whale.......... Peponocephala NA -, -, N 64,114
electra.
Pygmy Killer Whale.......... Feresa attenuata.. NA -, -, N 9,001

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False Killer Whale.......... Pseudorca NA -, -, N 12,682
crassidens.
----------------------------------------------------------------------------------------------------------------
\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\ Modeled abundance value from U.S Navy Atlantic Fleet Training and Testing Area Marine Mammal Density (AFTT)
(Roberts et al., 2023) unless otherwise noted.
\3\ Abundance of minke whales (species unspecified) for the Southern Hemisphere (IWC 2024)
\4\ Abundance of blue whales (excluding pygmy blue whales) for Southern Hemisphere (IWC 2024)
\5\ Abundance of humpback whales on Antarctic feeding grounds (IWC 2024)
\6\ Pilot whale guild.
\7\ Estimate includes dwarf and pygmy sperm whales.
\8\ Beaked whale guild.

All 28 species in table 1 temporally and spatially co-occur with
the activity to the degree that take is reasonably likely to occur. All
species that could potentially occur in the proposed survey area are
listed in section 3 of the application. In addition to what is included
in sections 3 and 4 of the application, and NMFS' website, further
detail informing the baseline for select species of particular or
unique vulnerability (i.e., information regarding ESA listed species)
is provided below.

Blue Whale

The blue whale has a cosmopolitan distribution and tends to be
pelagic, only coming nearshore to feed and possibly to breed (Jefferson
et al. 2015). The distribution of the species, at least during times of
the year when feeding is a major activity, occurs in areas that provide
large seasonal concentrations of euphausiids (Yochem and Leatherwood
1985). Blue whales are most often found in cool, productive waters
where upwelling occurs (Reilly and Thayer 1990). Generally, blue whales
are seasonal migrants between high latitudes in summer, where they
feed, and low latitudes in winter, where they mate and give birth
(Lockyer and Brown 1981). Their summer range in the North Atlantic
extends from Davis Strait, Denmark Strait, and the waters north of
Svalbard and the Barents Sea, south to the Gulf of St. Lawrence and the
Bay of Biscay (Rice 1998). Although the winter range is mostly unknown,
some occur near Cape Verde at that time of year (Rice 1998). One
individual has been seen in Cape Verde in the month of June (Reiner et
al. 1996). Blue whales have also been sighted elsewhere off
northwestern Africa (Camphuysen 2015; Camphuysen et al. 2012, 2022;
Baines and Reichelt 2014; Djiba et al. 2015; Correia 2020; Samba Bilal
et al. 2023).
An extensive data review and analysis by Branch et al. (2007a)
showed that blue whales are essentially absent from the central regions
of major ocean basins, including in the equatorial Atlantic Ocean,
where the proposed survey area is located. Similarly, Jefferson et al.
(2015) indicate that the proposed survey area falls within the
secondary range of the blue whale. Blue whales were captured by the
thousands off Angola, Namibia, and South Africa in the 1900s, and a few
catches were made near the proposed survey area (Branch et al. 2007a;
Figueiredo and Weir 2014). However, whales were nearly extirpated in
this region, and sightings of Antarctic blue whales in the region are
now rare (Branch et al. 2007a). At least four records of blue whales
exist for Angola; all sightings were made in 2012, with at least one
sighting in July, two in August, and one in October (Figueiredo and
Weir 2014).
Sightings were also made off Namibia in 2014 from seismic vessels
(Brownell et al. 2016). Waters off Namibia may serve as a possible
wintering and possible breeding grounds for Antarctic blue whales (Best
1998, 2007; Thomisch 2017). Offshore sightings in the southern Atlantic
Ocean include one sighting at 13.4[deg] S, 26.8[deg] W and another at
15.9[deg] S, 4.6[deg] W (Branch et al. 2007a). Most blue whales off
southeastern Africa are expected to be Antarctic blue whales; however,
~4 percent may be pygmy blue whales (Branch et al. 2007b, 2008). In
fact, pygmy blue whale vocalizations were detected off northern Angola
in October 2008; these calls were attributed to the Sri Lanka
population (Cerchio et al. 2010). Antarctic blue whale calls were
detected on acoustic recorders that were deployed northwest of Walvis
Ridge from November 2011 through May 2013 during all months except
during September and October, indicating that not all whales migrate to
higher latitudes during the summer (Thomisch 2017). There are no blue
whale records near the proposed survey area in the Ocean Biodiversity
Information System (OBIS) database (OBIS 2024).

Fin Whale

The fin whale is widely distributed in all the world's oceans
(Gambell 1985), although it is most abundant in temperate and cold
waters (Aguilar and Garc[iacute]a-Vernet 2018). Nonetheless, its
overall range and distribution are not well known (Jefferson et al.
2015). Fin whales most commonly occur offshore but can also be found in
coastal areas (Jefferson et al. 2015). Most populations migrate
seasonally between temperate waters where mating and calving occur in
winter, and polar waters where feeding occurs in summer (Aguilar and
Garc[iacute]a-Vernet 2018).
In the Southern Hemisphere, fin whales are typically distributed
south of 50[deg] S in the austral summer, migrating northward to breed
in the winter (Gambell 1985). According to Edwards et al. (2015),
sightings have been made off northwestern Africa throughout the year
and south of South Africa from December-February. Edwards did not
report any sightings or acoustic detections near the proposed project
area, although it is possible that fin whales could occur there. Fin
whales were seen off Mauritania during April 2004 (Tulp and Leopold
2004), November 2012-January 2013 (Camphuysen et al. 2012; Baines and
Reichelt 2014), 2015-2016 (Camphuysen et al. 2017; Correia 2020), and
February-March 2022 (Camphuysen et al. 2022). Samba Bilal et al. (2023)
reported several other records for Mauritania.
Several fin whale records exist for Angola (Weir 2011; Weir et al.
2012), South Africa (Shirshov Institute n.d.),

[[Page 56163]]

Namibia (NDP unpublished data in Pisces Environmental Services 2017),
and historical whaling data showed several catches off Namibia and
southern Africa (Best 2007), and Tristan da Cunha (Best et al. 2009).
Fin whales appear to be somewhat common in the Tristan da Cunha
archipelago from October-December (Bester and Ryan 2007). Fin whale
calls were detected on acoustic recorders that were deployed northwest
of Walvis Ridge from November 2011 through May 2013 during the months
of November, January, and June through August, indicating that the
waters off Namibia serve as wintering grounds (Thomisch 2017).
Similarly, Best (2007) also suggested that waters off Namibia may be
wintering grounds. Forty fin whales were seen during a trans-Atlantic
voyage along 20[deg] S during August 1943 between 5[deg] and 25[deg] W
(Wheeler 1946 in Best 2007). Although Edwards et al. (2015) reported
sightings in Cape Verde, there were no records of fin whales for the
proposed survey area to the south of Cape Verde. There were no records
of fin whales in the OBIS database near the proposed survey area; the
closest record of fin whales in the OBIS database is off the coast of
West Africa north of the proposed survey area (OBIS 2024).

Humpback Whale

For most North Atlantic humpbacks, the summer feeding grounds range
from the northeast coast of the U.S. to the Barents Sea (Katona and
Beard 1990; Smith et al. 1999). In the winter, the majority of humpback
whales migrate to wintering areas in the West Indies (Smith et al.
1999); this is known as the West Indies distinct population segment
(DPS) (Bettridge et al. 2015). Some individuals from the North Atlantic
migrate to Cape Verde to breed (Wenzel et al. 2009, 2020); this is
known as the Cape Verde/Northwest Africa DPS which is listed as
endangered under the ESA (Wenzel et al. 2020). A small proportion of
the Atlantic humpback whale population remains at high latitudes in the
eastern North Atlantic during winter (e.g., Christensen et al. 1992).
Based on known migration routes of humpbacks from these breeding areas
in the North Atlantic (see Jann et al. 2003); Bettridge et al. 2015;
NMFS 2016b), it is unlikely that individuals from the aforementioned
DPSs would occur in the proposed survey area, south of the Equator.
In the Southern Hemisphere, humpback whales migrate annually from
summer foraging areas in the Antarctic to breeding grounds in tropical
seas (Clapham 2018). It is uncertain whether humpbacks occur in the
proposed offshore survey area; Jefferson et al. (2015) indicated this
region to be within the possible range of this species and deep
offshore waters off West Africa to be the secondary range. The IWC
recognizes seven breeding populations in the Southern Hemisphere that
are linked to six foraging areas in the Antarctic (Clapham 2018). Two
of the breeding grounds are in the South Atlantic--off Brazil and West
Africa (Engel and Martin 2009). Bettridge et al. (2015) identified
humpback whales at these breeding locations as the Brazil and Gabon/
Southwest Africa DPSs. Migrations, song similarity, and genetic studies
indicate some interchange between these two DPSs (Darling and Sousa-
Lima 2005; Rosenbaum et al. 2009; Kershaw et al. 2017). Based on photo-
identification work, one female humpback whale traveled from Brazil to
Madagascar, a distance of >9,800 km (Stevick et al. 2011).
Deoxyribonucleic acid (DNA) sampling showed evidence of a male humpback
having traveled from West Africa to Madagascar (Pomilla and Rosenbaum
2005). Humpback whales likely to be encountered in the proposed survey
area would be from the Gabon/Southwest Africa DPS.
There may be at least two breeding substocks in Gabon/Southwest
Africa, including individuals in the main breeding area in the Gulf of
Guinea and those animals that feed and migrate off Namibia and South
Africa (Rosenbaum et al. 2009, 2014; Barendse et al. 2010a; Branch
2011; Carvalho et al. 2011). In addition, wintering humpbacks have also
been reported on the continental shelf of northwestern Africa (from
Senegal to Guinea) from July through November, which may represent the
northernmost component of Southern Hemisphere humpback whales that are
known to winter in the Gulf of Guinea (Van Waerebeek et al. 2013). Some
humpbacks have also been reported in the northern Gulf of Guinea during
December (Hazevoet et al. 2011). Migration rates are relatively high
between populations within the southeastern Atlantic (Rosenbaum et al.
2009). However, Barendse et al. (2010a) reported no matches between
individuals sighted in Namibia and South Africa based on a comparison
of tail flukes. Feeding areas for Gabon/Southwest Africa DPS include
Bouvet Island (Rosenbaum et al. 2014) and waters of the Antarctic
Peninsula (Barendse et al. 2010b).
Humpbacks have been seen on breeding grounds around S[atilde]o
Tom[eacute] in the Gulf of Guinea from August through November
(Carvalho et al. 2011). They are regularly seen in the northern Gulf of
Guinea off Togo and Benin during December (Van Waerebeek et al. 2001;
Van Waerebeek 2002). Off Gabon, humpback whales occur from late June-
December (Carvalho et al. 2011). Weir (2011) reported year-round
occurrence of humpback whales off Gabon and Angola, with the highest
sighting rates from June through October. The west coast of South
Africa might not be a `typical' migration corridor, as humpbacks are
also known to feed in the area; they are known to occur in the region
during the northward migration (July-August), the southward migration
(October-November), and into February (Barendse et al. 2010b; Carvalho
et al. 2011; Seakamela et al. 2015). The highest sighting rates in the
area occurred during mid-spring through summer (Barendse et al. 2010b).
Humpback whale calls were detected on acoustic recorders that were
deployed northwest of Walvis Ridge from November 2011 through May 2013
during the months of November, December, January, and May through
August, indicating that not all whales migrate to higher latitudes
during the summer (Thomisch 2017). Based on whales that were satellite-
tagged in Gabon in winter 2002, migration routes southward include
offshore waters along Walvis Ridge (Rosenbaum et al. 2014). Humpback
whales have also been sighted off Namibia (Elwen et al. 2014), South
Africa (Barendse et al. 2010b), Tristan da Cunha (Bester and Ryan 2007;
Best et al. 2009), St. Helena (MacLeod and Bennett 2007; Clingham et
al. 2013), and they have been detected visually and acoustically off
Angola (Best et al. 1999; Weir 2011; Cerchio et al. 2010, 2014; Weir et
al. 2012). In the OBIS database, there are no records of humpback
whales within the proposed survey area; the closest records of humpback
whales are from whaling catches closer to shore in the Gulf of Guinea
and farther north than the proposed survey location (OBIS 2024).

Minke Whale

In the Northern Hemisphere, minke whales are usually seen in
coastal areas but may also be seen in pelagic waters during their
northward migration in spring and summer and southward migration in
fall (Stewart and Leatherwood, 1985). Although some populations of
common minke whale have been well studied on summer feeding grounds,
information on wintering areas and migration routes is lacking (Risch
et al. 2014). Minke whales migrate north of 30[deg] N from March-April
and migrate south from Iceland from late September through

[[Page 56164]]

October (Risch et al. 2014; V[iacute]kingsson and Heide-Jorgensen
2015). Sightings have been made off northwestern Africa (Correia 2020;
Samba Bilal et al. 2023; Shakhovskoy 2023), including off Mauritania
during February 2022 (Camphuysen et al. 2022). The Antarctic minke
whale occurs south of 60[deg] S during austral summer and moves
northwards to the coasts off western South Africa and northeast Brazil
during austral winter (Perrin et al. 2018).
A smaller form (unnamed subspecies) of the common minke whale,
known as the dwarf minke whale, occurs in the Southern Hemisphere,
where its distribution overlaps with that of the Antarctic minke whale
during summer (Perrin et al. 2018). The dwarf minke whale is generally
found in shallow coastal waters and over the outer continental shelf in
regions where it overlaps with the Antarctic minke whale (Perrin et al.
2018). The range of the dwarf minke whale is thought to extend as far
south as 65[deg] S off Antarctica in the South Atlantic Ocean
(Jefferson et al. 2015) and as far north as 2[deg] S in the Atlantic
off South America, where dwarf minke whales can be found nearly year-
round (Perrin et al. 2018). Dwarf minke whales are known to occur off
South Africa during autumn and winter (Perrin et al. 2018), but have
not been reported for the waters off Angola or Namibia (Best 2007).
It is unclear which species or form, if any, would occur in the
proposed survey area, as this region is considered to be within the
possible range of the common minke whale and just north of the primary
range of the Antarctic minke whale (Jefferson et al. 2015). There are
no records of common or Antarctic minke whales near the proposed survey
area in the OBIS database (OBIS 2024).

Sei Whale

Sei whales are found in all ocean basins (Horwood 2018) but appear
to prefer mid-latitude temperate waters (Jefferson et al. 2015).
Habitat suitability models indicate that sei whale distribution is
related to cool water with high chlorophyll levels (Palka et al., 2017;
Chavez-Rosales et al. 2019). They occur in deeper waters characteristic
of the continental shelf edge region (Hain et al. 1985) and in other
regions of steep bathymetric relief such as seamounts and canyons
(Kenney and Winn 1987; Gregr and Trites 2001).
Sei whales undertake seasonal migrations to feed in subpolar
latitudes during summer and return to lower latitudes during winter to
calve (Gambell 1985; Horwood 2018). On summer feeding grounds, sei
whales associate with oceanic frontal systems (Horwood 1987). Sei
whales that have been tagged in the Azores have traveled to the
Labrador Sea, where they spend extended periods of time presumably
feeding (Olsen et al. 2009; Prieto et al. 2010, 2014). Sei whales were
the most commonly sighted species during a summer survey along the Mid-
Atlantic Ridge from Iceland to north of the Azores (Waring et al.
2008). One sighting was made on the shelf break off Mauritania during
March 2003 (Burton and Camphuysen 2003), at least seven sightings were
made off Mauritania during November 2012-January 2013 (Baines and
Reichelt 2014), and six sightings were made off Mauritania during
February-March 2022 (Camphuysen et al. 2022). Correia (2020) and Samba
Bilal et al. (2023) reported additional records for the waters off
northwestern Africa.
In the South Atlantic, waters off northern Namibia may serve as
wintering grounds (Best 2007). Summer concentrations are found between
the subtropical and Antarctic convergences (Horwood 2018). A sighting
of a mother and calf were made off Namibia in March 2012, and one
stranding was reported in July 2013 (NDP unpublished data in Pisces
Environmental Services 2017). One sighting was made during seismic
surveys off the coast of northern Angola between 2004 and 2009 (Weir
2011; Weir et al. 2012). A group of two to four sei whales was seen
near St. Helena during April 2011 (Clingham et al. 2013). Sei whales
were also taken by whaling vessels off southern Africa during the 1960s
(Best and Lockyer 2002). There are no records of sei whales near the
proposed survey in the OBIS database (OBIS 2024). However, one sighting
was made just northeast of the proposed survey area during March 2014
(Jungblut et al. 2017).

Sperm Whale

The sperm whale is widely distributed, occurring from the edge of
the polar pack ice to the Equator in both hemispheres, with the sexes
occupying different distributions (Whitehead 2018). Their distribution
and relative abundance can vary in response to prey availability, most
notably squid (Jaquet and Gendron 2002). Females generally inhabit
waters >1,000 m deep at latitudes <40[deg] where sea surface
temperatures are <15[deg] C; adult males move to higher latitudes as
they grow older and larger in size, returning to warm-water breeding
grounds (Whitehead 2018).
The primary range of sperm whales includes the waters off West
Africa (Jefferson et al. 2015), including Cape Verde (Reiner et al.
1996; Hazevoet et al. 2010). Sperm whales have also been reported off
Mauritania (Camphuysen 2015; Camphuysen et al. 2017). Sperm whales were
the most frequently sighted cetacean during seismic surveys off the
coast of northern Angola between 2004 and 2009; hundreds of sightings
were made off Angola and a few sightings were reported off Gabon (Weir
2011). They occur there throughout the year, although sighting rates
were highest from April through June (Weir 2011). de Boer (2010) also
reported sightings off Gabon in 2009, and Weir et al. (2012) reported
numerous sightings of sperm whales off Angola, the Republic of the
Congo, and the Democratic Republic of the Congo during 2004-2009. Van
Waerebeek et al. (2010) reported sightings off South Africa, and one
group was seen at St. Helena during July 2009 (Clingham et al. 2013).
Bester and Ryan (2007) noted that sperm whales might be common in the
Tristan da Cunha archipelago, and catches of sperm whales were made
there in the 19th and 20th centuries (Best et al. 2009). The waters of
northern Angola, Namibia, and South Africa were historical whaling
grounds (Best 2007; Weir 2019). There are thousands of sperm whale
records for the South Atlantic in the OBIS database, but most of these
are historical catches (OBIS 2024). Although none of the records occur
within the proposed survey area, there are several records to the north
and southwest of the proposed survey area (OBIS 2024).

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.). Note that no direct measurements of
hearing ability have been successfully completed for mysticetes (i.e.,
low-frequency cetaceans). Subsequently, NMFS (2018)

[[Page 56165]]

described generalized hearing ranges for these marine mammal hearing
groups. Generalized hearing ranges were chosen based on the
approximately 65 decibel (dB) threshold from the normalized composite
audiograms, with the exception for lower limits for low-frequency
cetaceans where the lower bound was deemed to be biologically
implausible and the lower bound from Southall et al. (2007) retained.
Marine mammal hearing groups and their associated hearing ranges are
provided in table 2.

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

For more detail concerning these groups and associated frequency
ranges, please see NMFS (2018) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their
Habitat

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

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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
(ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur
either as isolated events or repeated in some succession. Pulsed sounds
are all characterized by a relatively rapid rise from ambient pressure
to a maximal pressure value followed by a rapid decay period that may
include a period of diminishing, oscillating maximal and minimal
pressures, and generally have an increased capacity to induce physical
injury as compared with sounds that lack these features.
Non-pulsed sounds can be tonal, narrowband, or broadband, brief or
prolonged, and may be either continuous or non-continuous (ANSI, 1995;
NIOSH, 1998). Some of these non-pulsed sounds can be transient signals
of short duration but without the essential properties of pulses (e.g.,
rapid rise time). Examples of non-pulsed sounds include those produced
by vessels, aircraft, machinery operations such as drilling or
dredging, vibratory pile driving, and active sonar systems (such as
those used by the U.S. Navy). The duration of such sounds, as received
at a distance, can be greatly extended in a highly reverberant
environment.
Airgun arrays produce pulsed signals with energy in a frequency
range from about 10-2,000 Hz, with most energy radiated at frequencies
below 200 Hz. The amplitude of the acoustic wave emitted from the
source is equal in all directions (i.e., omnidirectional), but airgun
arrays do possess some directionality due to different phase delays
between guns in different directions. Airgun arrays are typically tuned
to maximize functionality for data acquisition purposes, meaning that
sound transmitted in horizontal directions and at higher frequencies is
minimized to the extent possible.

Acoustic Effects

Here, we discuss the effects of active acoustic sources on marine
mammals.
Potential Effects of Underwater Sound \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

[[Page 56167]]

area within which masking (i.e., when a sound interferes with or masks
the ability of an animal to detect a signal of interest that is above
the absolute hearing threshold) may occur; the masking zone may be
highly variable in size.
We describe the more severe effects of certain non-auditory
physical or physiological effects only briefly as we do not expect that
use of airgun arrays are reasonably likely to result in such effects
(see below for further discussion). Potential effects from impulsive
sound sources can range in severity from effects such as behavioral
disturbance or tactile perception to physical discomfort, slight injury
of the internal organs and the auditory system, or mortality (Yelverton
et al., 1973). Non-auditory physiological effects or injuries that
theoretically might occur in marine mammals exposed to high level
underwater sound or as a secondary effect of extreme behavioral
reactions (e.g., change in dive profile as a result of an avoidance
reaction) caused by exposure to sound include neurological effects,
bubble formation, resonance effects, and other types of organ or tissue
damage (Cox et al., 2006; Southall et al., 2007; Zimmer and Tyack,
2007; Tal et al., 2015). The survey activities considered here do not
involve the use of devices such as explosives or mid-frequency tactical
sonar that are associated with these types of effects.
Threshold Shift--Marine mammals exposed to high-intensity sound, or
to lower-intensity sound for prolonged periods, can experience hearing
threshold shift (TS), which is the loss of hearing sensitivity at
certain frequency ranges (Finneran, 2015). Threshold shift can be
permanent (PTS), in which case the loss of hearing sensitivity is not
fully recoverable, or temporary (TTS), in which case the animal's
hearing threshold would recover over time (Southall et al., 2007).
Repeated sound exposure that leads to TTS could cause PTS. In severe
cases of PTS, there can be total or partial deafness, while in most
cases the animal has an impaired ability to hear sounds in specific
frequency ranges (Kryter, 1985).
When PTS occurs, there is physical damage to the sound receptors in
the ear (i.e., tissue damage), whereas TTS represents primarily tissue
fatigue and is reversible (Southall et al., 2007). In addition, other
investigators have suggested that TTS is within the normal bounds of
physiological variability and tolerance and does not represent physical
injury (e.g., Ward, 1997). Therefore, NMFS does not typically consider
TTS to constitute auditory injury.
Relationships between TTS and PTS thresholds have not been studied
in marine mammals. There is no PTS data for cetaceans, but such
relationships are assumed to be similar to those in humans and other
terrestrial mammals. PTS typically occurs at exposure levels at least
several dBs above (a 40-dB threshold shift approximates PTS onset;
e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB
threshold shift approximates TTS onset; e.g., Southall et al. 2007).
Based on data from terrestrial mammals, a precautionary assumption is
that the PTS thresholds for 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-pressure basis and PTS cumulative sound exposure
level thresholds are 15 to 20 dB higher than TTS cumulative sound
exposure level thresholds (Southall et al., 2007). Given the higher
level of sound or longer exposure duration necessary to cause PTS as
compared with TTS, it is considerably less likely that PTS could occur.
TTS is the mildest form of hearing impairment that can occur during
exposure to sound (Kryter, 1985). While experiencing TTS, the hearing
threshold rises, and a sound must be at a higher level in order to be
heard. In terrestrial and marine mammals, TTS can last from minutes or
hours to days (in cases of strong TTS). In many cases, hearing
sensitivity recovers rapidly after exposure to the sound ends. Few data
on sound levels and durations necessary to elicit mild TTS have been
obtained for marine mammals.
Marine mammal hearing plays a critical role in communication with
conspecifics, and interpretation of environmental cues for purposes
such as predator avoidance and prey capture. Depending on the degree
(elevation of threshold in dB), duration (i.e., recovery time), and
frequency range of TTS, and the context in which it is experienced, TTS
can have effects on marine mammals ranging from discountable to
serious. For example, a marine mammal may be able to readily compensate
for a brief, relatively small amount of TTS in a non-critical frequency
range that occurs during a time where ambient noise is lower and there
are not as many competing sounds present. Alternatively, a larger
amount and longer duration of TTS sustained during time when
communication is critical for successful mother/calf interactions could
have more serious impacts.
Finneran et al. (2015) measured hearing thresholds in 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 mid-frequency cetaceans.
Currently, TTS data only exist for four species of cetaceans
(bottlenose dolphin (Tursiops truncatus), beluga whale (Delphinapterus
leucas), harbor porpoise (Phocoena phocoena), and Yangtze finless
porpoise (Neophocaena asiaeorientalis)) exposed to a limited number of
sound sources (i.e., mostly tones and octave-band noise) in laboratory
settings (Finneran, 2015). In general, harbor porpoises have a lower
TTS onset than other measured cetacean species (Finneran, 2015).
Additionally, the existing marine mammal TTS data come from a limited
number of individuals within these species. There is no direct data
available on noise-induced hearing loss for mysticetes.
Critical questions remain regarding the rate of TTS growth and
recovery after exposure to intermittent noise and the effects of single
and multiple pulses. Data at present are also insufficient to construct
generalized models for recovery and determine the time necessary to
treat subsequent exposures as independent events. More information is
needed on the relationship between auditory evoked potential and
behavioral measures of TTS for various stimuli. For summaries of data
on TTS in marine mammals or for further discussion of TTS onset
thresholds, please see Southall et al. (2007, 2019), Finneran and
Jenkins (2012), Finneran (2015), and NMFS (2018).
Behavioral Effects--Behavioral disturbance may include a variety of
effects, including subtle changes in behavior (e.g., minor or brief
avoidance of an area or changes in vocalizations), more conspicuous
changes in similar

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behavioral activities, and more sustained and/or potentially severe
reactions, such as displacement from or abandonment of high-quality
habitat. Behavioral responses to sound are highly variable and context-
specific, and any reactions depend on numerous intrinsic and extrinsic
factors (e.g., species, state of maturity, experience, current
activity, reproductive state, auditory sensitivity, time of day), as
well as the interplay between factors (e.g., Richardson et al., 1995;
Wartzok et al., 2003; Southall et al., 2007, 2019; Weilgart, 2007;
Archer et al., 2010). Behavioral reactions can vary not only among
individuals but also within an individual, depending on previous
experience with a sound source, context, and numerous other factors
(Ellison et al., 2012), and can vary depending on characteristics
associated with the sound source (e.g., whether it is moving or
stationary, number of sources, distance from the source). Please see
appendices B-C of Southall et al. (2007) for a review of studies
involving marine mammal behavioral responses to sound.
Habituation can occur when an animal's response to a stimulus wanes
with repeated exposure, usually in the absence of unpleasant associated
events (Wartzok et al., 2003). Animals are most likely to habituate to
sounds that are predictable and unvarying. It is important to note that
habituation is appropriately considered as a ``progressive reduction in
response to stimuli that are perceived as neither aversive nor
beneficial,'' rather than as, more generally, moderation in response to
human disturbance (Bejder et al., 2009). The opposite process is
sensitization, when an unpleasant experience leads to subsequent
responses, often in the form of avoidance, at a lower level of
exposure. As noted, behavioral state may affect the type of response.
For example, animals that are resting may show greater behavioral
change in response to disturbing sound levels than animals that are
highly motivated to remain in an area for feeding (Richardson et al.,
1995; NRC, 2003; Wartzok et al., 2003). Controlled experiments with
captive marine mammals have 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) vary 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).
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 reacts briefly to underwater sound by
changing its behavior or moving a small distance, the impacts of the
behavioral 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 changes in dive behavior,
disruption of foraging (feeding) behavior, changes in respiration
(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 foraging (feeding) behavior can be difficult to
correlate with anthropogenic sound exposure, so it is usually inferred
by observed displacement from known foraging areas, the appearance of
secondary indicators (e.g., bubble nets or sediment plumes), or changes
in dive behavior. As for other types of behavioral response, the
frequency, duration, and temporal pattern of signal presentation, as
well as differences in species sensitivity, are likely contributing
factors to differences in response in any given circumstance (e.g.,
Croll et al., 2001; Nowacek et al.; 2004; Madsen et al., 2006; Yazvenko
et al., 2007). A determination of whether foraging disruptions
adversely affect fitness 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 of 140-160 dB and 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 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 they were during control periods
(Miller et al., 2009). These data raise concerns that seismic surveys
may impact foraging behavior in sperm whales, although more data is
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

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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, 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 sound exposure level
(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 spatiotemporal
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 sonar (MFAS) 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 MFAS 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 alone or in groups may
influence the response.

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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 in\3\ 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 TS) is not
associated with abnormal physiological function, it is

[[Page 56171]]

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, 2009; 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.
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 is little 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 R/V 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; Erbe et al., 2015; Jones et al.,
2017; Putland et al., 2017). In addition to the frequency and duration
of the masking sound, the strength, temporal pattern, and location of
the introduced sound also play a role in the extent of the masking
(Branstetter et al., 2013, 2016; Finneran and Branstetter 2013; Sills
et al., 2017). Branstetter et al. (2013) reported that time-domain
metrics are also important in describing and predicting masking.
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).

[[Page 56172]]

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
vessel strikes. 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 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 100 percent above 15 kn (28 kph).
The R/V 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 the animal 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).

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There is no conclusive evidence that exposure to airgun noise
results in behaviorally-mediated forms of injury. Behaviorally-mediated
injury (i.e., mass stranding events) has been primarily associated with
beaked whales exposed to mid-frequency active (MFA) naval sonar. MFA
sonar and the alerting stimulus used in Nowacek et al. (2004) are very
different from the noise produced by airguns. 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 high-frequency cetaceans (e.g., Kogia spp.) have a
generalized hearing range of frequencies between 275 Hz and 160 kHz,
while mid-frequency cetaceans--such as dolphins and beaked whales--have
a generalized hearing range between 150 Hz to 160 kHz. Regarding
auditory susceptibility within the hearing range, while mid-frequency
cetaceans and high-frequency cetaceans have roughly similar hearing
ranges, the high-frequency group is much more susceptible to noise-
induced hearing loss during sound exposure, i.e., these species have
lower thresholds for these effects than other hearing groups (NMFS,
2018). Referring to a species as behaviorally sensitive to noise simply
means that an animal of that species is more likely to respond to lower
received levels of sound than an animal of another species that is
considered less behaviorally sensitive. So, while dolphin species and
beaked whale species--both in the mid-frequency cetacean hearing
group--are assumed to generally hear the same sounds equally well and
be equally susceptible to noise-induced hearing loss (auditory injury),
the best available information indicates that a beaked whale is more
likely to behaviorally respond to that sound at a lower received level
compared to an animal from other mid-frequency cetacean species that
are less behaviorally sensitive. This distinction is important because,
while beaked whales are more likely to respond behaviorally to sounds
than are many other species (even at lower levels), they cannot hear
the predominant, lower frequency sounds from seismic airguns as well as
sounds that have more energy at frequencies that beaked whales can hear
better (such as military MFA sonar).
Military MFA sonar affects beaked whales differently than airguns
do because it produces energy at different frequencies than airguns.
Mid-frequency cetacean hearing is generically thought to be best
between 8.8 to 110 kHz, i.e., these cutoff values define the range
above and below which a species in the group is assumed to have
declining auditory sensitivity, until reaching frequencies that cannot
be heard (NMFS, 2018). However, beaked whale hearing is likely best
within a higher, narrower range (20-80 kHz, with best sensitivity
around 40 kHz), based on a few measurements of hearing in stranded
beaked whales (Cook et al., 2006; Finneran et al., 2009; Pacini et al.,
2011) and several studies of acoustic signals produced by beaked whales
(e.g., Frantzis et al., 2002; Johnson et al., 2004, 2006; Zimmer et
al., 2005). While precaution requires that the full range of 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 mid-frequency hearing
group (beaked whales, sperm whales, and killer whales) are likely more
sensitive to lower frequencies within the group's generalized hearing
range than are other species within the group, and state that the data
for beaked whales suggest sensitivity to approximately 5 kHz. However,
this information is consistent with the general conclusion that beaked
whales (and other mid-frequency cetaceans) are relatively insensitive
to the frequencies where most energy of an airgun signal is found.
Military MFA sonar is typically considered to operate in the frequency
range of approximately 3-14 kHz (D'Amico et al., 2009), i.e., outside
the range of likely best hearing for beaked whales but within or close
to the lower bounds, whereas most energy in an airgun signal is
radiated at much lower frequencies, below 500 Hz (Dragoset, 1990).
It is important to distinguish between energy (loudness, measured
in dB) and frequency (pitch, measured in Hz). In considering the
potential impacts of mid-frequency components of airgun noise (1-10
kHz, where beaked whales can be expected to hear) on marine mammal
hearing, one needs to account for the energy associated with these
higher frequencies and determine what energy is truly ``significant.''
Although there is mid-frequency energy associated with airgun noise (as
expected from a broadband source), airgun sound is predominantly below
1 kHz (Breitzke et al., 2008; Tashmukhambetov et al., 2008; Tolstoy et
al., 2009). As stated by Richardson et al. (1995), ``[. . .] most
emitted [seismic airgun] energy is at 10-120 Hz, but the pulses contain
some energy up to 500-1,000 Hz.'' Tolstoy et al. (2009) conducted
empirical measurements, demonstrating that sound energy levels
associated with airguns were at least 20 dB lower at 1 kHz (considered
``mid-frequency'') compared to higher energy levels associated with
lower frequencies (below 300 Hz) (``all but a small fraction of the
total energy being concentrated in the 10-300 Hz range'' [Tolstoy et
al., 2009]), and at higher frequencies (e.g., 2.6-4 kHz), power might
be less than 10 percent of the peak power at 10 Hz (Yoder, 2002).
Energy levels measured by Tolstoy et al. (2009) were even lower at
frequencies above 1 kHz. In addition, as sound propagates away from the
source, it tends to lose higher-frequency components faster than low-
frequency components (i.e., low-frequency sounds typically propagate
longer distances than high-frequency sounds) (Diebold et al., 2010).
Although higher-frequency components of airgun signals have been
recorded, it is typically in surface-ducting conditions (e.g., DeRuiter
et al., 2006; Madsen et al., 2006) or in shallow water, where there are
advantageous propagation conditions for the higher frequency (but low-
energy) components of the airgun signal (Hermannsen et al., 2015). This
should not be of concern because the likely behavioral reactions of
beaked whales that can result in acute physical injury would result
from noise exposure at depth (because of the potentially greater
consequences of severe behavioral reactions). In summary, the frequency
content of airgun signals is such that beaked whales will not be able
to hear the signals well (compared to MFA sonar), especially at depth
where we expect the

[[Page 56174]]

consequences of noise exposure could be more severe.
Aside from frequency content, there are other significant
differences between MFA sonar signals and the sounds produced by
airguns that minimize the risk of severe behavioral reactions that
could lead to strandings or deaths at sea, e.g., significantly longer
signal duration, horizontal sound direction, typical fast and
unpredictable source movement. All of these characteristics of MFA
sonar tend towards greater potential to cause severe behavioral or
physiological reactions in exposed beaked whales that may contribute to
stranding. Although both sources are powerful, MFA sonar contains
significantly greater energy in the mid-frequency range, where beaked
whales hear better. Short-duration, high energy pulses--such as those
produced by airguns--have greater potential to cause damage to auditory
structures (though this is unlikely for mid-frequency cetaceans, as
explained later in this document), but it is longer duration signals
that have been implicated in the vast majority of beaked whale
strandings. Faster, less predictable movements in combination with
multiple source vessels are more likely to elicit a severe, potentially
anti-predator response. Of additional interest in assessing the
divergent characteristics of MFA sonar and airgun signals and their
relative potential to cause stranding events or deaths at sea is the
similarity between the MFA sonar signals and stereotyped calls of
beaked whales' primary predator: the killer whale (Zimmer and Tyack,
2007). Although generic disturbance stimuli--as airgun noise may be
considered in this case for beaked whales--may also trigger
antipredator responses, stronger responses should generally be expected
when perceived risk is greater, as when the stimulus is confused for a
known predator (Frid and Dill, 2002). In addition, because the source
of the perceived predator (i.e., 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 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 (ICES,
2005). In contrast, very few such associations have been made to
seismic surveys, despite widespread use of airguns as a geophysical
sound source in numerous locations around the world.
A 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

[[Page 56175]]

not be considered conclusive, it is clear that there is very little
evidence that seismic surveys should be considered as posing a
significant risk of acute harm to beaked whales or other mid-frequency
cetaceans. We have considered the potential for the proposed surveys to
result in marine mammal stranding and, 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 R/V 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., 2005a; Haley and Ireland 2006; SIO and NSF 2006b; 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.

Anticipated Effects on Marine Mammal Habitat

Physical Disturbance--Sources of seafloor disturbance related to
geophysical surveys that may impact marine mammal habitat include
placement of anchors, nodes, cables, sensors, or other equipment on or
in the seafloor for various activities. Equipment deployed on the
seafloor has the potential to cause direct physical damage and could
affect bottom-associated fish resources. During this survey, OBSs would
be deployed on the seafloor, secured with anchors that would eventually
disintegrate on the seafloor.
Placement of equipment could damage areas of hard bottom where
direct contact with the seafloor occurs and could crush epifauna
(organisms that live on the seafloor or surface of other organisms).
Damage to unknown or unseen hard bottom could occur, but because of the
small area covered by most bottom-founded equipment and the patchy
distribution of hard bottom habitat, contact with unknown hard bottom
is expected to be rare and impacts minor. Seafloor disturbance in areas
of soft bottom can cause loss of small patches of epifauna and infauna
due to burial or crushing, and bottom-feeding fishes could be
temporarily displaced from feeding areas. Overall, any effects of
physical damage to habitat are expected to be minor and temporary.
Effects to Prey--Marine mammal prey varies by species, season, and
location and, for some, is not well documented. Fish react to sounds
which are especially strong and/or intermittent low-frequency sounds,
and behavioral responses such as flight or avoidance are the most
likely effects. However, the reaction of fish to airguns depends on the
physiological state of the fish, past exposures, motivation (e.g.,
feeding, spawning, migration), and other environmental factors. Several
studies have demonstrated that airgun sounds might affect the
distribution and behavior of some fishes, potentially impacting marine
mammal 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; Pena et al., 2013; Chapman and
Hawkins, 1969; Wardle et al., 2001; Sara et al., 2007; Jorgenson and
Gyselman, 2009; Blaxter et al., 1981; Cott et al., 2012; Boeger et al.,
2006), and that, most commonly, while there are likely to be impacts to
fish as a result of noise from nearby airguns, such effects will be
temporary. For example, investigators reported significant, short-term
declines in commercial fishing catch rate of gadid fishes during and
for up to 5 days after seismic survey operations, but the catch rate
subsequently returned to normal (Engas et al., 1996; Engas and
Lokkeborg, 2002). Other studies have reported similar findings (Hassel
et al., 2004).
Skalski et al., (1992) also found a reduction in catch rates--for
rockfish (Sebastes spp.) in response to controlled airgun exposure--but
suggested that the mechanism underlying the decline was not dispersal
but rather decreased responsiveness to baited hooks associated with an
alarm behavioral response. A companion study showed that alarm and
startle responses were not sustained following the removal of the sound
source (Pearson et al., 1992). Therefore, Skalski et al. (1992)
suggested that the effects on fish abundance may be transitory,
primarily occurring during the sound exposure itself. In some cases,
effects on catch rates are variable within a study, which may be more
broadly representative of temporary displacement of fish in response to
airgun noise (i.e., catch rates may increase in some locations and
decrease in others) than any long-term damage to the fish themselves
(Streever et al., 2016).
Sound pressure levels 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

[[Page 56176]]

recording) occurred on the same day that the seismic survey passed, and
no subsequent data is presented to support an inference that the
response was long-lasting. Additionally, given that the finding is
based on video images, the lack of recorded fish presence does not
support a conclusion that the fish actually moved away from the site or
suffered any serious impairment. In summary, this particular study
corroborates prior studies indicating that a startle response or short-
term displacement should be expected.
Available data suggest that cephalopods are capable of sensing the
particle motion of sounds and detect low frequencies up to 1-1.5 kHz,
depending on the species, and so are likely to detect airgun noise
(Kaifu et al., 2008; Hu et al., 2009; Mooney et al., 2010; Samson et
al., 2014). Auditory injuries (lesions occurring on the statocyst
sensory hair cells) have been reported upon controlled exposure to low-
frequency sounds, suggesting that cephalopods are particularly
sensitive to low-frequency sound (Andre et al., 2011; Sole et al.,
2013). Behavioral responses, such as inking and jetting, have also been
reported upon exposure to low-frequency sound (McCauley et al., 2000b;
Samson et al., 2014). Similar to fish, however, the transient nature of
the survey leads to an expectation that effects will be largely limited
to behavioral reactions and would occur as a result of brief,
infrequent exposures.
With regard to potential impacts on zooplankton, McCauley et al.
(2017) found that exposure to airgun noise resulted in significant
depletion for more than half the taxa present and that there were two
to three times more dead zooplankton after airgun exposure compared
with controls for all taxa, within 1 km of the airguns. However, the
authors also stated that in order to have significant impacts on r-
selected species (i.e., those with high growth rates and that produce
many offspring) such as plankton, the spatial or temporal scale of
impact must be large in comparison with the ecosystem concerned, and it
is possible that the findings reflect avoidance by zooplankton rather
than mortality (McCauley et al., 2017). In addition, the results of
this study are inconsistent with a large body of research that
generally finds limited spatial and temporal impacts to zooplankton as
a result of exposure to airgun noise (e.g., Dalen and Knutsen, 1987;
Payne, 2004; Stanley et al., 2011). Most prior research on this topic,
which has focused on relatively small spatial scales, has showed
minimal effects (e.g., Kostyuchenko, 1973; Booman et al., 1996;
S[aelig]tre and Ona, 1996; Pearson et al., 1994; Bolle et al., 2012).
A modeling exercise was conducted as a follow-up to the McCauley et
al. (2017) study (as recommended by McCauley et al.), in order to
assess the potential for impacts on ocean ecosystem dynamics and
zooplankton population dynamics (Richardson et al., 2017). Richardson
et al. (2017) found that for copepods with a short life cycle in a
high-energy environment, a full-scale airgun survey would impact
copepod abundance up to 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 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 be limited to behavioral responses, the majority of
prey species will be capable of moving out of the area during the
survey, a rapid return to normal recruitment, distribution, and
behavior for prey species is anticipated, and, overall, impacts to prey
species will be minor and temporary. Prey species exposed to sound
might move away from the sound source, experience TTS, experience
masking of biologically relevant sounds, or show no obvious direct
effects. Mortality from decompression injuries is possible in close
proximity to a sound, but only limited data on mortality in response to
airgun noise exposure are available (Hawkins et al., 2014). The most
likely impacts for most prey species in the survey area would be
temporary avoidance of the area. The proposed survey would move through
an area relatively quickly, limiting exposure to multiple impulsive
sounds. In all cases, sound levels would return to ambient once the
survey moves out of the area or ends and the noise source is shut down
and, when exposure to sound ends, behavioral and/or physiological
responses are expected to end relatively quickly (McCauley et al.,
2000b). The duration of fish avoidance of a given area after survey
effort stops is unknown, but a rapid return to normal recruitment,
distribution, and behavior is anticipated. While the potential for
disruption of spawning aggregations or schools of important prey
species can be meaningful on a local scale, the mobile and temporary
nature of this survey and the likelihood of temporary avoidance
behavior suggest that impacts would be minor.
Acoustic Habitat--Acoustic habitat is the soundscape--which
encompasses all of the sound present in a particular location and time,
as a whole--when

[[Page 56177]]

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 both
NMFS' consideration of ``small numbers,'' and the negligible impact
determinations.
Harassment is the only type of take expected to result from these
activities. Except with respect to certain activities not pertinent
here, section 3(18) of the MMPA defines ``harassment'' as any act of
pursuit, torment, or annoyance, which (i) has the potential to injure a
marine mammal or marine mammal stock in the wild (Level A harassment);
or (ii) has the potential to disturb a marine mammal or marine mammal
stock in the wild by causing disruption of behavioral patterns,
including, but not limited to, migration, breathing, nursing, breeding,
feeding, or sheltering (Level B harassment).
Anticipated takes would primarily be by Level B harassment, the
noise from use of the airgun array has the potential to result in
disruption of behavioral patterns for individual marine mammals. There
is also some potential for auditory injury (Level A harassment) to
result for species of certain hearing groups (LF and HF) due to the
size of the predicted auditory injury zones for those groups. Auditory
injury is less likely to occur for mid-frequency species due to their
relative lack of sensitivity to the frequencies at which the primary
energy of an airgun signal is found as well as such species' general
lower sensitivity to auditory injury as compared to high-frequency
cetaceans. As discussed in further detail below, we do not expect
auditory injury for mid-frequency cetaceans. No mortality or serious
injury is anticipated as a result of these activities. Below we
describe how the proposed take numbers are estimated.
For acoustic impacts, generally speaking, we estimate take by
considering: (1) acoustic thresholds above which NMFS believes the best
available science indicates marine mammals will be behaviorally
harassed or incur some degree of permanent hearing impairment; (2) the
area or volume of water that will be ensonified above these levels in a
day; (3) the density or occurrence of marine mammals within these
ensonified areas; and, (4) the number of days of activities. We note
that while these factors can contribute to a basic calculation to
provide an initial prediction of potential takes, additional
information that can qualitatively inform take estimates is also
sometimes available (e.g., previous monitoring results or average group
size). Below, we describe the factors considered here in more detail
and present the proposed take estimates.

Acoustic Thresholds

NMFS recommends the use of acoustic thresholds that identify the
received level of underwater sound above which exposed marine mammals
would be reasonably expected to be behaviorally harassed (equated to
Level B harassment) or to incur PTS of some degree (equated to Level A
harassment).
Level B Harassment--Though significantly driven by received level,
the onset of behavioral disturbance from anthropogenic noise exposure
is also informed to varying degrees by other factors related to the
source or exposure context (e.g., frequency, predictability, duty
cycle, duration of the exposure, signal-to-noise ratio, distance to the
source), the environment (e.g., bathymetry, other noises in the area,
predators in the area), and the receiving animals (hearing, motivation,
experience, demography, life stage, depth) and can be difficult to
predict (e.g., Southall et al., 2007, 2021, Ellison et al., 2012).
Based on what the available science indicates and the practical need to
use a threshold based on a metric that is both predictable and
measurable for most activities, NMFS typically uses a generalized
acoustic threshold based on received level to estimate the onset of
behavioral harassment. NMFS generally predicts that marine mammals are
likely to be behaviorally harassed in a manner considered to be Level B
harassment when exposed to underwater anthropogenic noise above root-
mean-squared pressure received levels (RMS SPL) of 120 dB (re 1 [mu]Pa)
for continuous (e.g., vibratory pile driving, drilling) and above RMS
SPL 160 dB (re 1 [mu]Pa) for non-explosive impulsive (e.g., seismic
airguns) or intermittent (e.g., scientific sonar) sources. Generally
speaking, Level B harassment take estimates based on these behavioral
harassment thresholds are expected to include any likely takes by TTS
as, in most cases, the likelihood of TTS occurs at distances from the
source less than those at which behavioral harassment is likely. TTS of
a sufficient degree can manifest as behavioral harassment, as reduced
hearing sensitivity and the potential reduced opportunities to detect
important signals (conspecific communication, predators, prey) may

[[Page 56178]]

result in changes in behavior patterns that would not otherwise occur.
L-DEO's proposed survey includes the use of impulsive seismic
sources (i.e., airguns), and therefore the 160 dB re 1 [mu]Pa is
applicable for analysis of Level B harassment.
Level A harassment--NMFS' Technical Guidance for Assessing the
Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0)
(Technical Guidance, 2018) identifies dual criteria to assess auditory
injury (Level A harassment) to five different marine mammal groups
(based on hearing sensitivity) as a result of exposure to noise from
two different types of sources (impulsive or non-impulsive). L-DEO's
proposed survey includes the use of impulsive seismic sources (i.e.,
airguns).
These thresholds are provided in the table below. The references,
analysis, and methodology used in the development of the thresholds are
described in NMFS' 2018 Technical Guidance, which may be accessed at:
<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance</a>.

Table 3--Thresholds Identifying the Onset of Permanent Threshold Shift
----------------------------------------------------------------------------------------------------------------
PTS onset acoustic thresholds * (received level)
----------------------------------------------------------------------------------------------------------------
Hearing group Impulsive Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans........... Cell 1: Lpk,flat: 219 dB; Cell 2: LE,LF,24h: 199 dB.
LE,LF,24h: 183 dB.
Mid-Frequency (MF) Cetaceans........... Cell 3: Lpk,flat: 230 dB; Cell 4: LE,MF,24h: 198 dB.
LE,MF,24h: 185 dB.
High-Frequency (HF) Cetaceans.......... Cell 5: Lpk,flat: 202 dB; Cell 6: LE,HF,24h: 173 dB.
LE,HF,24h: 155 dB.
Phocid Pinnipeds (PW) (Underwater)..... Cell 7: Lpk,flat: 218 dB; Cell 8: LE,PW,24h: 201 dB.
LE,PW,24h: 185 dB.
Otariid Pinnipeds (OW) (Underwater).... Cell 9: Lpk,flat: 232 dB; Cell 10: LE,OW,24h: 219 dB.
LE,OW,24h: 203 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for
calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level
thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure (Lpk) has a reference value of 1 [mu]Pa, and cumulative sound exposure level (LE) has
a reference value of 1[mu]Pa\2\s. In this table, thresholds are abbreviated to reflect American National
Standards Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as incorporating
frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript ``flat'' is
being included to indicate peak sound pressure should be flat weighted or unweighted within the generalized
hearing range. The subscript associated with cumulative sound exposure level thresholds indicates the
designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and
that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could be
exceeded in a multitude of ways (i.e., varying exposure levels and durations, duty cycle). When possible, it
is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be
exceeded.

Ensonified Area

Here, we describe operational and environmental parameters of the
activity that are used in estimating the area ensonified above the
acoustic thresholds, including source levels and transmission loss
coefficient.
When the Technical Guidance was published (NMFS, 2016), in
recognition of the fact that ensonified area/volume could be more
technically challenging to predict because of the duration component in
the new thresholds, we developed a user spreadsheet that includes tools
to help predict a simple isopleth that can be used in conjunction with
marine mammal density or occurrence to help predict takes. We note that
because of some of the assumptions included in the methods used for
these tools, we anticipate that isopleths produced are typically going
to be overestimates of some degree, which may result in some degree of
overestimate of Level A harassment take. However, these tools offer the
best way to predict appropriate isopleths when more sophisticated 3D
modeling methods are not available, and NMFS continues to develop ways
to quantitatively refine these tools and will qualitatively address the
output where appropriate.
The proposed survey would entail the use of a 36-airgun array with
a total discharge volume of 6,600 in\3\ at a tow depth of 9 m to 12 m.
L-DEO's model results are used to determine the 160 dB<INF>rms</INF>
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 36-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 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 (~2,000 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 Mexico calibration measurements
demonstrates that although simple, the L-DEO model is a robust tool for
conservatively estimating isopleths.
The proposed high-energy survey would acquire data with the 36-
airgun array at a tow depth of 9 to 12 m. For this survey, which occurs
only in deep water (>1,000 m), we use the deep-water radii obtained
from L-DEO model

[[Page 56179]]

results down to a maximum water depth of 2,000 m for the 36-airgun
array.
L-DEO's modeling methodology is described in greater detail in L-
DEO's 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 R/V Langseth Seismic Source to Isopleth Corresponding to Level B
Harassment Threshold
----------------------------------------------------------------------------------------------------------------
Predicted
distances (in m)
Airgun configuration Tow depth (m)\1\ Water depth (m) to the Level B
harassment
threshold
----------------------------------------------------------------------------------------------------------------
4 strings, 36 airguns, 6,600 in\3\.................. 12 >1,000 \2\ 6,733
----------------------------------------------------------------------------------------------------------------
\1\ Maximum tow depth was used for conservative distances.
\2\ Distance is based on L-DEO model results.

Table 5--Modeled Radial Distance to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
Low frequency Mid frequency High frequency
cetaceans cetaceans cetaceans
----------------------------------------------------------------------------------------------------------------
PTS SELcum...................................................... 426.9 0 1.3
PTS Peak........................................................ 38.9 13.6 268.3
----------------------------------------------------------------------------------------------------------------
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.

Table 5 presents the modeled PTS isopleths for each cetacean
hearing group based on L-DEO modeling incorporated in the companion
user spreadsheet, for the high-energy surveys with the shortest shot
interval (i.e., greatest potential to cause PTS based on accumulated
sound energy) (NMFS 2018).
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 36-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 far-field signature. Because the far-
field signature does not take into account the large array effect near
the source and is calculated as a point source, the far-field 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.
Auditory injury is unlikely to occur for mid-frequency cetaceans,
given the very small modeled zones of injury for those species (all
estimated zones are less than 15 m for mid-frequency cetaceans), in the
context of distributed source dynamics.
In consideration of the received sound levels in the near-field as
described above, we expect the potential for Level A harassment of mid-
frequency cetaceans 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
Level A harassment is a likely outcome for any mid-frequency cetacean
and do not propose to authorize any take by Level A harassment for
these species.
The Level A and 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 [micro]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.
Habitat-based stratified marine mammal densities for the North
Atlantic are taken from the US Navy Atlantic Fleet Training and Testing
Area Marine Mammal Density (Roberts et al., 2023;

[[Page 56180]]

Mannocci et al., 2017), which represent the best available information
regarding marine mammal densities in the region. This density
information incorporates visual line-transect surveys of marine mammals
for over 35 years, resulting in various studies that estimated the
abundance, density, and distributions of marine mammal populations. The
habitat-based density models consisted of 5 km x 5 km grid cells. As
the AFTT model does not overlap the proposed survey area, the average
densities in the grid cells for the AFTT area that encompassed a
similar-sized area as the proposed survey area in the southeastern-most
part of the AFTT area were used (between ~21.1[deg] N-22.5[deg] N and
~45.1[deg] W-49.5[deg] W). Even though these densities are for the
western Atlantic Ocean, they are for an area of the Mid-Atlantic Ridge,
which would be most representative of densities occurring at the Mid-
Atlantic Ridge in the proposed survey area. More information is
available online at <a href="https://seamap.env.duke.edu/models/Duke/AFTT/">https://seamap.env.duke.edu/models/Duke/AFTT/</a>.
Since there was no density data available for the actual proposed
survey area, L-DEO used OBIS sightings, available literature, and
regional distribution maps of the actual survey area (or greater
region) to determine which species would be expected to be encountered
in the proposed survey area. From the AFTT models, L-DEO excluded the
following species, as they were not expected to occur in the survey
area: seals, northern bottlenose whales, North Atlantic right whale
(these had densities of zero) and harbor porpoise, white-beaked
dolphin, and Atlantic white-sided dolphin (these species had non-zero
densities). There were no additional species that might occur in the
survey area that were not available in the AFTT model.
For most species, only annual densities were available. For some
baleen whale species (fin, sei and humpback whale), monthly densities
were available. For these species, the highest monthly densities were
used. Densities for fin whales were near zero and the calculations did
not result in any estimated takes. However, because this species could
be encountered in the proposed survey area, we propose to authorize
take of one individual.

Take Estimate

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 for the 160-
dB Level B harassment threshold and PTS (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 (11.5) 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. For the species for which NMFS does not
expect there to be a reasonable potential for take by Level A
harassment to occur (i.e., mid-frequency cetaceans), we have added L-
DEO's estimated exposures above Level A harassment thresholds to their
estimated exposures above the Level B harassment threshold to produce a
total number of incidents of take by Level B harassment that is
proposed for authorization. Estimated exposures and proposed take
numbers for authorization are shown in table 6.

Table 6--Estimated Take Proposed for Authorization
----------------------------------------------------------------------------------------------------------------
Estimated take Proposed authorized take
Species ---------------------------------------------------- Modeled Percent of
Level B Level A Level B Level A abundance \1\ abundance \2\
----------------------------------------------------------------------------------------------------------------
Humpback whale.............. 39 2 39 2 4,990 0.82
Bryde's whale............... 4 0 4 0 536 0.75
Minke whale \3\............. 23 1 23 1 13,784 0.17
Fin whale................... 0 0 1 0 11,672 0.01
Sei whale................... 11 1 11 1 19,530 0.06
Blue whale.................. 1 0 1 0 191 0.52
Sperm whale................. 110 0 110 0 64,015 0.17
Beaked whales \4\........... 106 0 106 0 65,069 0.16
Risso's dolphin............. 88 0 88 0 78,205 0.11
Rough-toothed dolphin....... 166 0 166 0 32,848 0.51
Bottlenose dolphin.......... 1229 2 1231 0 418,151 0.30
Pantropical spotted dolphin. 46 0 \7\ 76 0 321,740 0.02
Atlantic spotted dolphin.... 435 1 436 0 259,519 0.17
Spinner dolphin............. 898 2 900 0 152,511 0.59
Striped dolphin............. 55 0 \7\ 73 0 412,729 0.02
Clymene dolphin............. 1038 2 1040 0 181,209 0.57
Fraser's dolphin............ 110 0 110 0 19,585 0.56
Common dolphin.............. 27 0 \7\ 92 0 473,206 0.02
Short-finned pilot whale \5\ 1301 2 1303 0 264,907 0.49
Melon-headed whale.......... 502 1 503 0 64,114 0.78
False killer whale.......... 99 0 99 0 12,682 0.78
Pygmy killer whale.......... 71 0 71 0 9,001 0.79
Killer whale................ 1 0 \7\ 5 0 972 0.51
Kogia spp \6\............... 122 5 122 5 26,043 0.49
----------------------------------------------------------------------------------------------------------------
\1\ Modeled abundance (Roberts et al. 2023) or North Atlantic abundance (NAMMCO 2023), where applicable.

[[Page 56181]]

\2\ Requested take authorization is expressed as percent of population for the AFTT Area only (Roberts et al.
2023).
\3\ Takes assigned equally between Common minke whales (11 Level B takes and 1 Level A take) and Antarctic minke
whales (12 Level B takes).
\4\ Beaked whale guild. Includes Cuvier's beaked whale, Blaineville's beaked whale, and Gervais' beaked whale.
\5\ Takes based on density for Globicephala sp. All takes are assumed to be for short-finned pilot whales
\6\ Kogia spp. Includes Pygmy sperm whale and Dwarf sperm whale.
\7\ Takes rounded to a mean group size (Weir 2011)

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 SZor 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.

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 0-500 m SZ, out to a radius of 1,000 m from the edges of the airgun
array (500-1,000 m). This 1,000-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. Visual PSOs will immediately communicate all
observations to the on duty acoustic PSO(s), including any
determination by the visual PSO regarding species identification,
distance, and bearing and the degree of confidence in the
determination. Any observations of marine mammals by crew members shall
be relayed to the PSO team. During good conditions (e.g., daylight
hours; Beaufort sea state (BSS) 3 or less), visual PSOs shall conduct
observations when the 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. Combined
observational duties (visual and acoustic but not at same time) may not
exceed 12 hours per 24-hour period for any individual PSO.

Passive Acoustic Monitoring

Passive acoustic monitoring means the use of trained personnel
(sometimes referred to as PAM operators, herein referred to as acoustic
PSOs) to operate PAM equipment to acoustically detect the presence of
marine mammals. Acoustic monitoring involves acoustically detecting
marine mammals regardless of distance from the source, as localization
of animals may not always be possible. Acoustic monitoring is intended
to further support visual monitoring (during daylight hours) in
maintaining a SZ around the sound source that is clear of marine
mammals. In cases where visual monitoring is not effective (e.g., due
to weather, nighttime), acoustic monitoring may be used to allow
certain activities to occur, as further detailed below.

[[Page 56182]]

PAM would take place in addition to the visual monitoring program.
Visual monitoring typically is not effective during periods of poor
visibility or at night and even with good visibility, is unable to
detect marine mammals when they are below the surface or beyond visual
range. Acoustic monitoring can be used in addition to visual
observations to improve detection, identification, and localization of
cetaceans. The acoustic monitoring would serve to alert visual PSOs (if
on duty) when vocalizing cetaceans are detected. It is only useful when
marine mammals vocalize, but it can be effective either by day or by
night and does not depend on good visibility. It would be monitored in
real time so that the visual observers can be advised when cetaceans
are detected.
The R/V Langseth will use a towed PAM system, which must be
monitored by at a minimum one on duty acoustic PSO beginning at least
30 minutes prior to ramp-up and at all times during use of the airgun
array. Acoustic 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.
Combined observational duties (acoustic and visual but not at same
time) may not exceed 12 hours per 24-hour period for any individual
PSO.
Survey activity may continue for 30 minutes when the PAM system
malfunctions or is damaged, while the PAM operator diagnoses the issue.
If the diagnosis indicates that the PAM system must be repaired to
solve the problem, operations may continue for an additional 10 hours
without acoustic monitoring during daylight hours only under the
following conditions:
<bullet> Sea state is less than or equal to BSS 4;
<bullet> No marine mammals (excluding delphinids) detected solely
by PAM in the SZ in the previous 2 hours;
<bullet> NMFS is notified via email as soon as practicable with the
time and location in which operations began occurring without an active
PAM system; and
<bullet> Operations with an active airgun array, but without an
operating PAM system, do not exceed a cumulative total of 10 hours in
any 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 500-m radius. The 500-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 500-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 500-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 500 m is likely
regularly attainable for PSOs using the naked eye during typical
conditions. The pre-start clearance zone simply represents the addition
of a buffer to the SZ, doubling the SZ size during pre-clearance.
An extended SZ of 1,500 m must be enforced for all beaked whales,
Kogia spp, 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.
Ramp-up begins by first activating a single airgun of the smallest
volume, followed by doubling the number of active elements in stages
until the full complement of an array's airguns are active. Each stage
should be approximately the same duration, and the total duration
should not be less than approximately 20 minutes. The intent of pre-
start clearance observation (30 minutes) is to ensure no marine mammals
are observed within the pre-start clearance zone (or extended SZ, for
beaked whales, Kogia spp, 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);
<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 shall begin by activating a single airgun of the
smallest volume in the array and shall continue in stages by doubling
the number of active elements at the commencement of each stage, with
each stage of approximately the same duration. Duration shall not be
less than 20 minutes. The operator must

[[Page 56183]]

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 acoustic monitoring has occurred with no
detections 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
and/or acoustic observation and no visual or acoustic detections 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
watch 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 both visual and acoustic PSOs are on duty, all
detections will be immediately communicated to the remainder of the on-
duty PSO team for potential verification of visual observations by the
acoustic PSO or of acoustic detections by visual PSOs. When the airgun
array is active (i.e., anytime one or more airguns is active, including
during ramp-up) and (1) a marine mammal appears within or enters the
applicable SZ and/or (2) a marine mammal (other than delphinids, see
below) is detected acoustically and localized within 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. Additionally, shutdown will occur
whenever PAM alone (without visual sighting), confirms the presence of
marine mammal(s) in the SZ. If the acoustic PSO cannot confirm presence
within the SZ, visual PSOs will be notified but shutdown is not
required.
Following a shutdown, airgun activity would not resume until the
marine mammal has cleared the 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 (Delphinus, Lagenodelphis, Stenella,
Steno and Tursiops).
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 mid-frequency cetaceans (e.g., delphinids), as this group
is relatively insensitive to sound produced at the predominant
frequencies in an airgun pulse while also having a relatively high
threshold for the onset of auditory injury (i.e., permanent threshold
shift).
A large body of anecdotal evidence indicates that small dolphins
commonly approach vessels and/or towed arrays during active sound
production for purposes of bow riding with no apparent effect observed
(e.g., Barkaszi et al., 2012, Barkaszi and Kelly, 2018). The potential
for increased shutdowns resulting from such a measure would require the
R/V Langseth to revisit the missed track line to reacquire data,
resulting in an overall increase in the total sound energy input to the
marine environment and an increase in the total duration over which the
survey is active in a given area. Although other mid-frequency hearing
specialists (e.g., large delphinids) are no more likely to incur
auditory injury than are small dolphins, they are much less likely to
approach vessels. Therefore, retaining a shutdown requirement for large
delphinids would not have similar impacts in terms of either
practicability for the applicant or corollary increase in sound energy
output and time on the water. We do anticipate some benefit for a
shutdown requirement for large delphinids in that it simplifies
somewhat the total range of decision-making for PSOs and may preclude
any potential for physiological effects other than to the auditory
system as well as some more severe behavioral reactions for any such
animals in close proximity to the R/V 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 an extended
shutdown of 1,500 m if any large whale (defined as a sperm whale or any
mysticete species) with a calf (defined as an animal less than two-
thirds the body size of an adult observed to be in close association
with an adult) and/or an aggregation of six or more large whales.

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

[[Page 56184]]

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, as
well as other measures considered by NMFS, NMFS has preliminarily
determined that the proposed mitigation measures provide the means of
effecting the least practicable impact on the affected species or
stocks and their habitat, paying particular attention to rookeries,
mating grounds, 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.
L-DEO must use dedicated, trained, and NMFS-approved PSOs. The PSOs
must have no tasks other than to conduct observational effort, record
observational data, and communicate with and instruct relevant vessel
crew with regard to the presence of marine mammals and mitigation
requirements. PSO resumes shall be provided to NMFS for advance
approval (prior to embarking on the vessel).
At least one of the visual and two of the acoustic PSOs (discussed
below) aboard the vessel must have a minimum of 90 days at-sea
experience working in those roles, respectively, with no more than 18
months elapsed since the conclusion of the at-sea experience. One
visual PSO with such experience shall be designated as the lead for the
entire protected species observation team. The lead PSO shall serve as
primary point of contact for the vessel operator and ensure all PSO
requirements per the IHA are met. To the maximum extent practicable,
the experienced PSOs should be scheduled to be on duty with those PSOs
with appropriate training but who have not yet gained relevant
experience.
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 R/V Langseth. Two visual
PSOs would be on duty at all times during daytime hours. Monitoring
shall be conducted in accordance with the following requirements:
<bullet> The operator shall provide PSOs with bigeye reticle
binoculars (e.g., 25 x 150; 2.7 view angle; individual ocular focus;
height control) of appropriate quality solely for PSO use. These
binoculars shall be pedestal-mounted on the deck at the most
appropriate vantage point that provides for optimal sea surface
observation, PSO safety, and safe operation of the vessel; and
<bullet> The operator will work with the selected third-party
observer provider to ensure PSOs have all equipment (including backup
equipment) needed to adequately perform necessary tasks, including
accurate determination of distance and bearing to observed marine
mammals.
PSOs must have the following requirements and qualifications:
<bullet> PSOs shall be independent, dedicated, trained visual and
acoustic PSOs and must be employed by a third-party observer provider;
<bullet> PSOs shall have no tasks other than to conduct
observational effort (visual or acoustic), collect data, and
communicate with and instruct relevant vessel crew with regard to the
presence of protected species and mitigation

[[Page 56185]]

requirements (including brief alerts regarding maritime hazards);
<bullet> PSOs shall have successfully completed an approved PSO
training course appropriate for their designated task (visual or
acoustic). Acoustic PSOs are required to complete specialized training
for operating PAM systems and are encouraged to have familiarity with
the vessel with which they will be working;
<bullet> PSOs can act as acoustic or visual observers (but not at
the same time) as long as they demonstrate that their training and
experience are sufficient to perform the task at hand;
<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 de

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