[Federal Register Volume 88, Number 160 (Monday, August 21, 2023)]
[Notices]
[Pages 56964-56993]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-17836]



[[Page 56963]]

Vol. 88

Monday,

No. 160

August 21, 2023

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 Puerto Rico 
in the Northwest Atlantic Ocean; Notice

  Federal Register / Vol. 88, No. 160 / Monday, August 21, 2023 / 
Notices  

[[Page 56964]]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XD216]


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to a Marine Geophysical Survey of 
Puerto Rico in the Northwest 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 has 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. 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 
September 20, 2023.

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

FOR FURTHER INFORMATION CONTACT: Jenna Harlacher, Office of Protected 
Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

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

National Environmental Policy Act

    To comply with the National Environmental Policy Act of 1969 (NEPA; 
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A, 
NMFS must review our proposed action (i.e., the issuance of an IHA) 
with respect to potential impacts on the human environment.
    Accordingly, NMFS plans to adopt the National Science Foundation's 
(NSF) Environmental Assessment (EA), as we have preliminarily 
determined that it includes adequate information analyzing the effects 
on the human environment of issuing the IHA. NSF's draft EA is 
available at https://www.nsf.gov/geo/oce/envcomp.

Summary of Request

    On April 27, 2023, NMFS received a request from L-DEO for an IHA to 
take marine mammals incidental to a marine geophysical survey of the 
Puerto Rico Trench and the southern slope of Puerto Rico in the 
northwest Atlantic Ocean. The application was deemed adequate and 
complete on July 27, 2023. L-DEO's request is for take of 27 marine 
mammal species by Level B harassment, and for 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 (WHOI), 
University of Texas Institute of Geophysics (UTIG), and University of 
Puerto Rico Mayaguez (UPRM), with funding from the U.S. National 
Science Foundation (NSF) and in collaboration with the United States 
Geological Survey (USGS) and researchers from the GEOMAR Helmholtz 
Centre for Ocean Research (GEOMAR) in Kiel, Germany, propose to conduct 
research, including high-energy seismic surveys using airguns as the 
acoustic source, from the research vessel (R/V) Marcus G. Langseth 
(Langseth). The proposed surveys (high and low energy surveys) would 
occur in the Puerto Rico Trench and the southern slope of Puerto Rico 
in the northwestern Atlantic Ocean during fall 2023. The proposed 
survey would occur within the U.S. Exclusive Economic Zone (EEZ) around 
Puerto Rico and the U.S. Virgin Islands and within the coastal zone of 
Puerto Rico, and within the EEZs of the Dominican Republic and the 
British Virgin Islands. The survey would occur in water depths ranging 
from approximately 1,000 to 8,400 meters (m) for the high energy survey 
portion and approximately 100-3,000 m for the low energy survey 
portion. To complete this survey, the R/V Langseth would tow two 
different airgun configurations: (a) 36-airgun

[[Page 56965]]

towed array with a total discharge volume of ~6600 in\3\ at a depth of 
12 m for the high-energy surveys, and (b) two 45/105-in\3\ generator-
injector (GI) airguns with a total discharge volume of 90 in\3\ off 
southern Puerto Rico at a depth of 3 m for the low-energy surveys. The 
airgun array receiving systems for the different survey segments would 
consist of a 15 kilometer (km) long solid-state hydrophone streamer, 
approximately 31 short-period Ocean Bottom Seismometers (OBS), and 10 
ultra-deep-water broadband OBS for the high-energy portion, and 150 m 
solid-state hydrophone streamer for the low-energy portion. For the 
high-energy survey, the airguns would fire at a shot interval of 50 m 
(~24 seconds (s)) during multi-channel seismic (MCS) reflection surveys 
with the hydrophone streamer and at a 400-m (~155 s) interval during 
OBS seismic refraction surveys. For the low energy survey, the airgun 
would fire at a shot interval of 6.25 m (2.7 s). Approximately 4,630 
kilometer (km) of total survey trackline are proposed.
    The purpose of the proposed high-energy survey is to investigate 
the Puerto Rico Trench, its outer rise, and across the island of Puerto 
Rico, and provide data necessary to illuminate the depth, geometry, and 
physical properties of the seismogenic fault interface between the 
subducting Atlantic plate and the overlying accretionary wedge/Puerto 
Rico arc/Caribbean plate, as well as seismogenic structures in the 
accretionary wedge and submarine slopes of the island of Puerto Rico. 
The low-energy seismic surveys would be located over a 2019-2020 area 
of seismic activity in the Caribbean Sea to define the geometry of the 
faults that ruptured and other potential seismogenic structures. 
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 high-energy survey is expected to last for 
approximately 42 days, with 21 days of seismic operations, 20 days for 
equipment deployment/recovery, and 2 days transit/contingency time. The 
low-energy survey would consist of approximately 3 days of seismic 
operations. R/V Langseth would likely leave from and return to port in 
San Juan, Puerto Rico during fall 2023.

Specific Geographic Region

    The proposed survey would occur within approximately 17-21[deg] N, 
63.6-68.2[deg] W, within the EEZs of Puerto Rico, U.S. Virgin Islands, 
British Virgin Islands, and the Dominican Republic, in water depths 
ranging from approximately 100-8,400 m. The closest approach of the 
proposed low-energy survey lines to land on the south side of Puerto 
Rico is ~2.5 km from Isla de Ratones (Isla Pi[ntilde]ero), ~3.4 km from 
Cayo Maria Langa, and ~3 km from Cayo Aurora. The closest approach of 
the high-energy survey lines to the coast of Puerto Rico is ~22 km, 28 
km to the British Virgin Islands, 42 km to Dominican Republic, and 77 
km to the U.S. Virgin Islands. The region where the survey is proposed 
to occur is depicted in Figure 1; the tracklines could occur anywhere 
within the polygon shown in Figure 1. Representative survey tracklines 
are shown, however, some deviation in actual tracklines, including the 
order of survey operations, could be necessary for reasons such as 
science drivers, poor data quality, inclement weather, or mechanical 
issues with the research vessel and/or equipment.
[GRAPHIC] [TIFF OMITTED] TN21AU23.000


[[Page 56966]]



Figure 1--Location of the Proposed Puerto Rico Seismic Surveys in the 
Northwest Atlantic Ocean

Representative survey tracklines are included in the figure; 
however, the tracklines could occur anywhere within the survey area. 
EBSA = Ecologically or Biologically Significant Marine Areas. CBD = 
Convention on Biological Diversity. N = North. HAPC = habitat of 
particular concern.

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 high-energy surveys would involve 
one source vessel, R/V Langseth, which is owned and operated by L-DEO. 
During the high-energy MCS seismic reflection and OBS seismic 
refraction surveys, 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 16 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. During the low energy survey, R/V Langseth 
would tow a 2 GI-airgun cluster in true GI (45/105 in3) mode as the 
seismic source, with a total discharge volume of 90 in3. The two inline 
GI airguns would be spaced 2.46 m apart. The airgun array 
configurations are illustrated in Figure 2-13 of NSF and USGS's 
Programmatic Environmental Impact Statement (PEIS; NSF-USGS, 2011). 
(The PEIS is available online at: www.nsf.gov/geo/oce/envcomp/usgs-nsf-marine-seismic-research/nsf-usgs-final-eis-oeis-with-appendices.pdf). 
The receiving system would consist of a 15-km long solid-state 
hydrophone streamer, 31 short-period OBSs, and 10 GEOMAR ultra-deep-
water broadband OBSs. For the low-energy surveys, the receiving system 
would consist of a 150-m long solid-state hydrophone streamer. As the 
airgun arrays are towed along the survey lines, the hydrophone streamer 
would transfer the data to the on-board processing system for the MCS 
survey, and the OBSs would receive and store the returning acoustic 
signals internally for later analysis.
    Approximately 4630 km of seismic acquisition are proposed. During 
the high-energy surveys, ~4070 km of transect lines would be surveyed 
(~2565 km of 2-D MCS seismic reflection data and 1505 km of OBS 
refraction data); the low-energy USGS surveys would consist of ~560 
line km. All of the high-energy surveys with the 36-airgun array would 
occur in deep water >1000 m deep. For the low-energy USGS surveys 
conducted with the 2-GI airguns, 43 percent would occur in 
intermediate-depth water 100-1000 m deep, and 57 percent would take 
place in deep water >1000 m; no effort would occur in shallow water 
(<100 m deep). Following refraction shooting of one line, OBSs on that 
line would be recovered, serviced, and redeployed on a subsequent 
refraction line. 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 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 use of the MBES, SBP, and ADCP, whether or not the 
airguns are operating simultaneously with the other sources. Given 
their characteristics (e.g., narrow downward-directed beam), marine 
mammals would experience no more than one or two brief ping exposures, 
if any exposure were to occur. NMFS does not expect that the use of 
these sources presents any reasonable potential to cause take of marine 
mammals.
    Proposed mitigation, monitoring, and reporting measures are 
described in detail later in this document (please see Proposed 
Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

    Sections 3 and 4 of the application summarize available information 
regarding status and trends, distribution and habitat preferences, and 
behavior and life history of the potentially affected species. NMFS 
fully considered all of this information, and we refer the reader to 
these descriptions, instead of reprinting the information. Additional 
information regarding population trends and threats may be found in 
NMFS' Stock Assessment Reports (SARs; https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments) and 
more general information about these species (e.g., physical and 
behavioral descriptions) may be found on NMFS' website (https://www.fisheries.noaa.gov/find-species). NMFS refers the reader to the 
application and to the aforementioned sources for general information 
regarding the species listed in Table 1.
    Table 1 lists all species or stocks for which take is expected and 
proposed to be authorized for this activity, and summarizes information 
related to the population or stock, including regulatory status under 
the MMPA and Endangered Species Act (ESA) and potential biological 
removal (PBR), where known. PBR is defined by the MMPA as the maximum 
number of animals, not including natural mortalities, that may be 
removed from a marine mammal stock while allowing that stock to reach 
or maintain its optimum sustainable population (as described in NMFS' 
SARs). While no serious injury or mortality is anticipated or proposed 
to be authorized here, PBR and annual serious injury and mortality from 
anthropogenic sources are included here as gross indicators of the 
status of the species or stocks and other threats.
    Marine mammal abundance estimates presented in this document 
represent the total number of individuals that make up a given stock or 
the total number estimated within a particular study or survey area. 
NMFS' stock abundance estimates for most species represent the total 
estimate of individuals within the geographic area, if known, that 
comprises that stock. For some species, this geographic area may extend 
beyond U.S. waters. All stocks managed under the MMPA in this region 
are assessed in NMFS' U.S. Atlantic and Gulf of Mexico SARs (e.g., 
Hayes et al., 2019, 2020, 2022). All values presented in Table 1 are 
the most recent available (including the draft 2022 SARs) at the time 
of publication and are available online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.
    Aside from the few species with stocks assigned for Puerto Rico and 
the U.S. Virgin Islands, individuals from the species affected would 
not be from the stocks described in the SARs. These stocks are not 
extensively studied but are provisionally being considered separate 
stocks for management purposes and further work to differentiate them 
from stocks in the Atlantic and Gulf of Mexico are being conducted. 
However, these stocks are likely trans-boundary within, at minimum, 
waters near adjacent Caribbean Islands and are not likely to occur 
exclusively within the bounds of the U.S. EEZ.

[[Page 56967]]



                          Table 1--Species Likely Impacted by the Specified Activities
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                                                                                 Stock abundance
                                                                     ESA/MMPA    (CV, Nmin, most
         Common name            Scientific name        Stock         status;    recent abundance      Modeled
                                                                    Strategic      survey) \2\     abundance \3\
                                                                    (Y/N) \1\
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                      Order Cetartiodactyla--Cetacea--Superfamily Mysticeti (baleen whales)
----------------------------------------------------------------------------------------------------------------
Family Balaenopteridae
 (rorquals):
Humpback whale...............  Megaptera         ................  -/-; N       1,396 (0; 1,380;           4,990
                                novaeangliae.                                    2016).
Fin whale....................  Balaenoptera      ................  E/D; Y       6,802 (0.24;              11,672
                                physalus.                                        5,573; 2016).
Sei whale....................  Balaenoptera      ................  E/D; Y       6,292 (1.02;              19,530
                                borealis.                                        3,098; 2016).
Minke whale..................  Balaenoptera      ................  -/-; N       21,968 (0.31;             13,784
                                acutorostrata.                                   17,002; 2016).
Blue whale...................  Balaenoptera      ................  E/D; Y       unk (unk; 402;               191
                                musculus.                                        1980-2008).
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                        Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
----------------------------------------------------------------------------------------------------------------
Family Physeteridae:
Sperm whale..................  Physeter          Puerto Rico and   E/D; Y       4,349 (0.28;              64,015
                                macrocephalus.    U.S. Virgin                    3,451; 2016)\4\.
                                                  Islands.
Family Kogiidae:
Pygmy sperm whale............  Kogia breviceps.  ................  -/-; N       7,750 (0.38;              26,043
                                                                                 5,689; 2016).
Dwarf sperm whale............  Kogia sima......  ................  -/-; N
Family Ziphiidae (beaked
 whales):
Cuvier's beaked Whale........  Ziphius           Puerto Rico and   -/-; Y       5,744 (0.36,              65,069
                                cavirostris.      U.S. Virgin                    4,282, 2016)\
                                                  Islands.                       4\.
Blainville's beaked Whale....  Mesoplodon        ................  -/-; N       10,107 (0.27;     ..............
                                densirostris.                                    8,085; 2016).
True's beaked whale..........  Mesoplodon mirus  ................  -/-; N
Gervais' beaked whale........  Mesoplodon        ................  -/-; N
                                europaeus.
Family Delphinidae:
Short finned pilot whale.....  Globicephala      Puerto Rico and   -/-; Y       28,924 (0.24;            264,907
                                macrorhynchus.    U.S. Virgin                    23,637; 2016)\
                                                  Islands.                       4\.
Rough-toothed dolphin........  Steno             ................  -/-; N       136 (1.0; 67;             32,848
                                bredanensis.                                     2016).
Bottlenose dolphin...........  Tursiops          Puerto Rico and   -/-; Y       62,851 (0.23;            418,151
                                truncatus.        U.S. Virgin                    51,914, 2016)\
                                                  Islands.                       4\.
Pantropical spotted dolphin..  Stenella          ................  -/-; N       6,593 (0.52;             321,740
                                attenuata.                                       4,367; 2016).
Atlantic spotted dolphin.....  Stenella          Puerto Rico and   -/-; Y       39,921 (0.27;            259,519
                                frontalis.        U.S. Virgin                    32,032; 2016)\
                                                  Islands.                       4\.
Spinner dolphin..............  Stenella          Puerto Rico and   -/-; Y       4,102 (0.99;             152,511
                                longirostris.     U.S. Virgin                    2,045; 2016)\
                                                  Islands.                       4\.
Clymene dolphin..............  Stenella clymene  ................  -/-; N       4,237 (1.03;             181,209
                                                                                 2,071; 2016).
Striped dolphin..............  Stenella          ................  -/-; N       67,036 (0.29;            412,729
                                coeruleoalba.                                    52,939; 2016).
Fraser's dolphin.............  Lagenodelphis     ................  -/-; N       unk.............          19,585
                                hosei.
Risso's dolphin..............  Grampus griseus.  ................  -/-; N       35,215 (0.19;             78,205
                                                                                 30,051; 2016).
Common dolphin...............  Delphinus         ................  -/-; N       172,947 (0.21;           473,260
                                delphis.                                         145,216; 2016).
Melon-headed whale...........  Peponocephala     ................  -/-; N       unk.............          64,114
                                electra.
Pygmy killer whale...........  Feresa attenuate  ................  -/-; N       unk.............           9,001
False killer whale...........  Pseudorca         ................  -/-; N       1,791 (0.56;              12,682
                                crassidens.                                      1,154; 2016).
Killer whale.................  Orcinus orca....  ................  -/-; N       unk.............             972
----------------------------------------------------------------------------------------------------------------
\1\ ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species
  is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one
  for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and
  likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is
  automatically designated under the MMPA as depleted and as a strategic stock.
\2\ NMFS marine mammal stock assessment reports online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region/. CV is coefficient of variation; Nmin is the minimum
  estimate of stock abundance; unknown (unk).
\3\ Modeled abundance value from U.S Navy Atlantic Fleet Training and Testing Area Marine Mammal Density (AFTT)
  (Roberts et al., 2023; Mannocci et al., 2017)
\4\ Puerto Rico and U.S. Virgin Islands stocks have unknown abundance, therefore providing abundance information
  associated with the Atlantic stocks as point of reference.

    In Table 1 above, NMFS reports two sets of abundance estimates: 
Those from NMFS' SARs and those predicted by Roberts et al. (2023). The 
latter represent density data developed for use in environmental 
analyses covering areas of the northwest Atlantic Ocean outside of the 
U.S. EEZ, also referred to as the U.S. Navy Atlantic Fleet Training and 
Testing Area (AFTT) https://seamap.env.duke.edu/models/Duke/AFTT/. We 
refer to these data hereafter as the AFTT models. NMFS' SAR estimates 
do not include areas covered by this survey and therefore the AFTT 
abundance value was included as it covers the Caribbean Sea and waters 
off Puerto Rico. The SAR abundances provided with no stock listed are 
for the other Western North Atlantic stocks as a point of reference.
    Additionally, NMFS' SAR estimates are typically generated from the 
most recent shipboard and/or aerial surveys conducted. The spatial 
scale of these surveys along the Atlantic coast is small relative to 
the ability of most cetacean species to travel within their ranges. As 
an example, only one sighting of rough-toothed dolphin occurred in the 
last two dedicated cetacean abundance surveys near L-DEO's proposed 
survey area during 2011 or 2016. Multiple species with modeled take 
proposed for authorization also do not have a population abundance 
listed in the SAR's even though the last surveys were conducted on 
these species in 2019. Studies based on abundance and distribution 
surveys restricted to U.S. waters are unable to detect temporal shifts 
in distribution beyond U.S. waters that might account for any changes 
in abundance within U.S. waters. NMFS' SAR estimates also typically do 
not incorporate correction for detection bias. Therefore, they should 
generally be considered underestimates, especially for cryptic or long-
diving species (e.g., beaked whales, Kogia spp., sperm whales).

[[Page 56968]]

    As indicated above, all 27 number species in Table 1 temporally and 
spatially co-occur with the activity to the degree that take is 
reasonably likely to occur. Species that could potentially occur in the 
proposed research area but are not likely to be harassed due to the 
rarity of their occurrence (i.e., are considered extralimital or rare 
visitors to the waters off southeast U.S.), or because their known 
migration through the area does not align with the proposed survey 
dates, are listed in section 3 of the application; however, they are 
omitted from further analysis. These generally include species that do 
not normally occur in the area, but for which there are one or more 
occurrence records that are considered beyond the normal range of the 
species. In addition to what is included in Sections 3 and 4 of the 
application, the SARs, and NMFS' website, further detail informing the 
baseline for select species of particular or unique vulnerability 
(i.e., information regarding current Unusual Mortality Events (UME) and 
important habitat areas) is provided below.

Humpback Whale

    In the western North Atlantic, the humpback whale occurs from 
Greenland to Venezuela (W[uuml]rsig et al. 2000). 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). The whales that feed on the eastern coast of the United 
States are recognized as a distinct feeding stock, known as the Gulf of 
Maine stock (Palsb[oslash]ll et al. 2001; Vigness-Raposa et al. 2010). 
During winter, these whales mate and calve in the West Indies, where 
spatial and genetic mixing among feeding stocks occurs (Katona and 
Beard 1990; Clapham et al. 1993; Palsb[oslash]ll et al. 1997; Stevick 
et al. 1998; Kennedy et al. 2013).
    Humpback whales were listed as endangered under the Endangered 
Species Conservation Act (ESCA) in June 1970. In 1973, the ESA replaced 
the ESCA, and humpbacks continued to be listed as endangered. NMFS re-
evaluated the status of the species in 2015, and on September 8, 2016, 
divided the species into 14 distinct population segments (DPS), removed 
the current species-level listing, and in its place listed 4 DPSs as 
endangered and 1 DPS as threatened (81 FR 62259, September 8, 2016). 
The remaining nine DPSs were not listed. Only one DPS occurs in the 
proposed survey area, the West Indies DPS, which is not listed under 
the ESA.
    Stevick et al. (2018) found that the timing and migration 
destinations of humpback whales in the northwestern and southeastern 
Caribbean are different and suggested that there could be two different 
breeding populations in the West Indies. Stevick et al. (2003b) 
reported that males were often seen on breeding grounds earlier than 
females. Some individuals from the North Atlantic are known to migrate 
to Cape Verde to breed (e.g., Wenzel et al. 2009). A small proportion 
of the Atlantic humpback whale population remains in high latitudes in 
the eastern North Atlantic during winter (e.g., Christensen et al. 
1992).
    The largest winter concentration of humpbacks occurs at Silver and 
Navidad Banks off northeastern Dominican Republic (Mattila et al. 1989; 
Whitehead and Moore 1992). Hundreds of humpbacks aggregate there from 
January through March to calve (Mattila et al. 1989). Mona Passage 
(Puerto Rico), Virgin Bank, and Anguilla Bank are also considered to be 
major calving grounds (Mattila and Clapham 1989). Humpback whales are 
commonly sighted in Puerto Rico and the Virgin Islands during the 
winter (Mignucci-Giannoni 1998). Hotspots for humpback whales off the 
west coast of Puerto Rico are related to bathymetry, with groups of two 
or more primarily occurring in deeper water, singing males occur near 
the shelf edge, whereas non-singing individuals occur farther from the 
shelf edge; mother-calf pairs primarily occur in shallow water, unless 
they are with an escort, in which case they were seen farther from 
shore (MacKay et al. 2016). Similarly, Sanders et al. (2005) reported 
that mother-calf pairs sighted off northwestern Puerto Rico from 
January-March were most frequently reported in shallow water <100 m 
deep.
    Saman[aacute] Bay, on the northeastern coast of the Dominican 
Republic, is also recognized as an important winter ground for western 
North Atlantic humpback whales (Mattila et al. 1994; Betancourt et al. 
2012). Photo identification has shown that whales that occurred in the 
Dominican Republic were seen at high-latitude feeding areas, such as 
the Gulf of Maine, Newfoundland, Gulf of St. Lawrence, and Greenland as 
well as at other regions in the West Indies, such as Silver Bank and 
Navidad Bank off Dominican Republic, Puerto Rico, Guadeloupe, Virgin 
Bank, and Anguilla Bank (Mattila et al. 1989, 1994; MacKay et al. 
2019), even within the same season (e.g., MacKay et al. 2019). Two 
humpbacks outfitted with satellite transmitters near the Dominican 
Republic during winter and spring of 2008-2012 were later reported off 
the east coast of Canada (Kennedy et al. 2014). Humpback whale 
vocalizations were recorded off the northern Dominican Republic during 
each month from December 2016 through May 2017 (Heenehan et al. 2019). 
Humpback whales were sighted within the proposed survey areas during 
winter 1995 (Roden and Mullin 2000), winter 2000 (Swartz et al. 2001), 
and winter 2001 (Swartz et al. 2002); they were also detected there 
acoustically during winter 2001 (Swartz et al. 2002). Although most 
sightings of humpbacks occur off the northern Dominican Republic, four 
sightings were made during March 2005 off the southern coast (Whaley et 
al. 2006). There are numerous records of humpbacks throughout the 
proposed study area, including sightings in offshore waters to the 
north of Puerto Rico, nearshore sightings off western Puerto Rico and 
around the Virgin Islands, and numerous sightings on Silver and Navidad 
banks north of the Dominican Republic; all sightings were reported for 
January-March (Ocean Biodiversity Information System (OBIS) 2021). 
However, some sightings have been reported in nearshore waters of 
northern Puerto Rico and the U.S. Virgin Islands during fall 
(Department of Navy (DoN) 2002).
    Since January 2016, elevated humpback whale mortalities have 
occurred along the Atlantic coast from Maine to Florida. The event was 
declared a UME in April 2017, and includes stranding's starting in 
2016. Partial or full necropsy examinations have been conducted on 
approximately half of the 200 known cases. Of the whales examined, 
about 40 percent had evidence of human interaction, either ship strike 
or entanglement. While a portion of the whales have shown evidence of 
pre-mortem vessel strike, this finding is not consistent across all 
whales examined and more research is needed. NMFS is consulting with 
researchers that are conducting studies on the humpback whale 
populations, and these efforts may provide information on changes in 
whale distribution and habitat use that could provide additional 
insight into how these vessel interactions occurred. Three additional 
UMEs involving humpback whales have occurred since 2000, in 2003, 2005, 
and 2006. More information is available at: https://www.fisheries.noaa.gov/national/marine-life-distress/2016-2021-humpback-whale-unusual-mortality-event-along-atlantic-coast.

Minke Whale

    Minke whales occur in the southeastern U.S. and Caribbean during

[[Page 56969]]

the winter; however, a lack of acoustic detection in the region during 
summer indicates either absence of minke whales at that time of year, 
or a change in vocal behavior at different times of the year (Risch et 
al. 2014). Risch et al. (2014) deployed acoustic detectors throughout 
the North Atlantic to detect minke whale occurrence; one recorder was 
deployed in the Caribbean, at Saba Bank. There, minke whales were 
acoustically detected during winter and spring (Risch et al. 2014). 
Minke whale vocalizations were also recorded 200-350 km off 
northeastern Puerto Rico, March 1994 (Mellinger et al. 2000). Mignucci-
Giannoni (1998) reported three sightings for Puerto Rico and the Virgin 
Islands up to 1989. One minke whale was sighted in the proposed survey 
area north of Puerto Rico during winter 1995 (Roden and Mullin 2000). 
Another sighting of a minke was made in offshore waters of the proposed 
survey area north of Puerto Rico on 20 January 2014 (Rodriguez-Ferrer 
et al. 2018). In the OBIS database, there are 16 records of minke 
whales for the northeastern portion of the proposed survey area; all 
sightings were reported during March 1994 (OBIS 2021).
    Since January 2017, elevated minke whale mortalities have occurred 
along the U.S. Atlantic coast from Maine through South Carolina, with a 
total of 148 known strandings. This event has been declared a UME. Full 
or partial necropsy examinations were conducted on more than 60 percent 
of the whales. Preliminary findings in several of the whales have shown 
evidence of human interactions or infectious disease, but these 
findings are not consistent across all of the whales examined, so more 
research is needed. More information is available at: https://www.fisheries.noaa.gov/national/marine-life-distress/2017-2021-minke-whale-unusual-mortality-event-along-atlantic-coast.
    Both the humpback whale and minke whale UME's are of populations of 
whales found on the Atlantic Coast and may not be the same populations 
found near the survey area. Additionally, further detailed descriptions 
and regional information of all potentially affected marine mammal 
species can be found in Section 3 of the L-DEO's application.

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) 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           150 Hz to 160 kHz.
 (dolphins, 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)     50 Hz to 86 kHz.
 (true seals).
Otariid pinnipeds (OW) (underwater)    60 Hz to 39 kHz.
 (sea 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

[[Page 56970]]

water. Amplitude is the height of the sound pressure wave or the 
``loudness'' of a sound and is typically described using the relative 
unit of the dB. A sound pressure level (SPL) in dB is described as the 
ratio between a measured pressure and a reference pressure (for 
underwater sound, this is 1 micropascal ([mu]Pa)) and is a logarithmic 
unit that accounts for large variations in amplitude; therefore, a 
relatively small change in dB corresponds to large changes in sound 
pressure. The source level (SL) represents the SPL referenced at a 
distance of 1 m from the source (referenced to 1 [mu]Pa) while the 
received level is the SPL at the listener's position (referenced to 1 
[mu]Pa).
    Root mean square (RMS) is the quadratic mean sound pressure over 
the duration of an impulse. Root mean square is calculated by squaring 
all of the sound amplitudes, averaging the squares, and then taking the 
square root of the average (Urick, 1983). Root mean square accounts for 
both positive and negative values; squaring the pressures makes all 
values positive so that they may be accounted for in the summation of 
pressure levels (Hastings and Popper, 2005). This measurement is often 
used in the context of discussing behavioral effects, in part because 
behavioral effects, which often result from auditory cues, may be 
better expressed through averaged units than by peak pressures.
    Sound exposure level (SEL; represented as dB re 1 [mu]Pa\2\-s) 
represents the total energy contained within a pulse and considers both 
intensity and duration of exposure. Peak sound pressure (also referred 
to as zero-to-peak sound pressure or 0-p) is the maximum instantaneous 
sound pressure measurable in the water at a specified distance from the 
source and is represented in the same units as the RMS sound pressure. 
Another common metric is peak-to-peak sound pressure (pk-pk), which is 
the algebraic difference between the peak positive and peak negative 
sound pressures. Peak-to-peak pressure is typically approximately 6 dB 
higher than peak pressure (Southall et al., 2007).
    When underwater objects vibrate or activity occurs, sound-pressure 
waves are created. These waves alternately compress and decompress the 
water as the sound wave travels. Underwater sound waves radiate in a 
manner similar to ripples on the surface of a pond and may be either 
directed in a beam or beams or may radiate in all directions 
(omnidirectional sources), as is the case for pulses produced by the 
airgun arrays considered here. The compressions and decompressions 
associated with sound waves are detected as changes in pressure by 
aquatic life and man-made sound receptors such as hydrophones.
    Even in the absence of sound from the specified activity, the 
underwater environment is typically loud due to ambient sound. Ambient 
sound is defined as environmental background sound levels lacking a 
single source or point (Richardson et al., 1995), and the sound level 
of a region is defined by the total acoustical energy being generated 
by known and unknown sources. These sources may include physical (e.g., 
wind and waves, earthquakes, ice, atmospheric sound), biological (e.g., 
sounds produced by marine mammals, fish, and invertebrates), and 
anthropogenic (e.g., vessels, dredging, construction) sound. A number 
of sources contribute to ambient sound, including the following 
(Richardson et al., 1995):
    Wind and waves: The complex interactions between wind and water 
surface, including processes such as breaking waves and wave-induced 
bubble oscillations and cavitation, are a main source of naturally 
occurring ambient sound for frequencies between 200 Hz and 50 kHz 
(Mitson, 1995). In general, ambient sound levels tend to increase with 
increasing wind speed and wave height. Surf sound becomes important 
near shore, with measurements collected at a distance of 8.5 km from 
shore showing an increase of 10 dB in the 100 to 700 Hz band during 
heavy surf conditions;
    Precipitation: Sound from rain and hail impacting the water surface 
can become an important component of total sound at frequencies above 
500 Hz, and possibly down to 100 Hz during quiet times;
    Biological: Marine mammals can contribute significantly to ambient 
sound levels, as can some fish and snapping shrimp. The frequency band 
for biological contributions is from approximately 12 Hz to over 100 
kHz; and
    Anthropogenic: Sources of anthropogenic sound related to human 
activity include transportation (surface vessels), dredging and 
construction, oil and gas drilling and production, seismic surveys, 
sonar, explosions, and ocean acoustic studies. Vessel noise typically 
dominates the total ambient sound for frequencies between 20 and 300 
Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz 
and, if higher frequency sound levels are created, they attenuate 
rapidly. Sound from identifiable anthropogenic sources other than the 
activity of interest (e.g., a passing vessel) is sometimes termed 
background sound, as opposed to ambient sound.
    The sum of the various natural and anthropogenic sound sources at 
any given location and time--which comprise ``ambient'' or 
``background'' sound--depends not only on the source levels (as 
determined by current weather conditions and levels of biological and 
human activity) but also on the ability of sound to propagate through 
the environment. In turn, sound propagation is dependent on the 
spatially and temporally varying properties of the water column and sea 
floor, and is frequency-dependent. As a result of this dependence on a 
large number of varying factors, ambient sound levels can be expected 
to vary widely over both coarse and fine spatial and temporal scales. 
Sound levels at a given frequency and location can vary by 10-20 dB 
from day to day (Richardson et al., 1995). The result is that, 
depending on the source type and its intensity, sound from a given 
activity may be a negligible addition to the local environment or could 
form a distinctive signal that may affect marine mammals. Details of 
source types are described in the following text.
    Sounds are often considered to fall into one of two general types: 
Pulsed and non-pulsed. The distinction between these two sound types is 
important because they have differing potential to cause physical 
effects, particularly with regard to hearing (e.g., NMFS, 2018; Ward, 
1997 in Southall et al., 2007). Please see Southall et al. (2007) for 
an in-depth discussion of these concepts.
    Pulsed sound sources (e.g., airguns, explosions, gunshots, sonic 
booms, impact pile driving) produce signals that are brief (typically 
considered to be less than one second), broadband, atonal transients 
(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

[[Page 56971]]

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 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, and there is no PTS data for cetaceans but such 
relationships are assumed to be similar to those in humans and other 
terrestrial mammals. PTS typically occurs at exposure levels at least 
several dBs above (a 40-dB threshold shift approximates PTS onset; 
e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB 
threshold shift approximates TTS onset; e.g., Southall et al. 2007). 
Based on data from terrestrial mammals, a precautionary assumption is 
that the PTS thresholds for 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

[[Page 56972]]

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, 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 behavioral activities, and more sustained and/or 
potentially severe reactions, such as displacement from or abandonment 
of high-quality habitat. Behavioral responses to sound are highly 
variable and context-specific, and any reactions depend on numerous 
intrinsic and extrinsic factors (e.g., species, state of maturity, 
experience, current activity, reproductive state, auditory sensitivity, 
time of day), as well as the interplay between factors (e.g., 
Richardson et al., 1995; Wartzok et al., 2003; Southall et al., 2007, 
2019; Weilgart, 2007; Archer et al., 2010). Behavioral reactions can 
vary not only among individuals but also within an individual, 
depending on previous experience with a sound source, context, and 
numerous other factors (Ellison et al., 2012), and can vary depending 
on characteristics associated with the sound source (e.g., whether it 
is moving or stationary, number of sources, distance from the source). 
Please see Appendices B-C of Southall et al. (2007) for a review of 
studies involving marine mammal behavioral responses to sound.
    Habituation can occur when an animal's response to a stimulus wanes 
with repeated exposure, usually in the absence of unpleasant associated 
events (Wartzok et al., 2003). Animals are most likely to habituate to 
sounds that are predictable and unvarying. It is important to note that 
habituation is appropriately considered as a ``progressive reduction in 
response to stimuli that are perceived as neither aversive nor 
beneficial,'' rather than as, more generally, moderation in response to 
human disturbance (Bejder et al., 2009). The opposite process is 
sensitization, when an unpleasant experience leads to subsequent 
responses, often in the form of avoidance, at a lower level of 
exposure. As noted, behavioral state may affect the type of response. 
For example, animals that are resting may show greater behavioral 
change in response to disturbing sound levels than animals that are 
highly motivated to remain in an area for feeding (Richardson et al., 
1995; NRC, 2003; Wartzok et al., 2003). Controlled experiments with 
captive marine mammals have showed pronounced behavioral reactions, 
including avoidance of loud sound sources (Ridgway et al., 1997). 
Observed responses of wild marine mammals to loud pulsed sound sources 
(typically seismic airguns or acoustic harassment devices) have been 
varied but often consist of avoidance behavior or other behavioral 
changes suggesting discomfort (Morton and Symonds, 2002; see also 
Richardson et al., 1995; Nowacek et al., 2007). However, many 
delphinids approach acoustic source vessels with no apparent discomfort 
or obvious behavioral change (e.g., Barkaszi et al., 2012).
    Available studies show wide variation in response to underwater 
sound; therefore, it is difficult to predict specifically how any given 
sound in a particular instance might affect marine mammals perceiving 
the signal. If a marine mammal does react briefly to an underwater 
sound by changing its behavior or moving a small distance, the impacts 
of the change are unlikely to be significant to the individual, let 
alone the stock or population. However, if a sound source displaces 
marine mammals from an important feeding or breeding area for a 
prolonged period, impacts on individuals and populations could be 
significant (e.g., Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 
2005). However, there are broad categories of potential response, which 
we describe in greater detail here, that include alteration of dive 
behavior, alteration of foraging behavior, effects to breathing, 
interference with or alteration of vocalization, avoidance, and flight.
    Changes in dive behavior can vary widely, and may consist of 
increased or decreased dive times and surface intervals as well as 
changes in the rates of ascent and descent during a dive (e.g., Frankel 
and Clark, 2000; Ng and Leung, 2003; Nowacek et al., 2004; Goldbogen et 
al., 2013 a, b). Variations in dive behavior may reflect disruptions in 
biologically significant activities (e.g., foraging) or they may be of 
little biological significance. The impact of an alteration to dive 
behavior resulting from an acoustic exposure depends on what the animal 
is doing at the time of the exposure and the type and magnitude of the 
response.
    Disruption of feeding behavior can be difficult to correlate with 
anthropogenic

[[Page 56973]]

sound exposure, so it is usually inferred by observed displacement from 
known foraging areas, the appearance of secondary indicators (e.g., 
bubble nets or sediment plumes), or changes in dive behavior. As for 
other types of behavioral response, the frequency, duration, and 
temporal pattern of signal presentation, as well as differences in 
species sensitivity, are likely contributing factors to differences in 
response in any given circumstance (e.g., Croll et al., 2001; Nowacek 
et al.; 2004; Madsen et al., 2006; Yazvenko et al., 2007). A 
determination of whether foraging disruptions incur fitness 
consequences would require information on or estimates of the energetic 
requirements of the affected individuals and the relationship between 
prey availability, foraging effort and success, and the life history 
stage of the animal.
    Visual tracking, passive acoustic monitoring (PAM), and movement 
recording tags were used to quantify sperm whale behavior prior to, 
during, and following exposure to airgun arrays at received levels in 
the range 140-160 dB at distances of 7-13 km, following a phase-in of 
sound intensity and full array exposures at 1-13 km (Madsen et al., 
2006; Miller et al., 2009). Sperm whales did not exhibit horizontal 
avoidance behavior at the surface. However, foraging behavior may have 
been affected. The sperm whales exhibited 19 percent less vocal, or 
buzz, rate during full exposure relative to post exposure, and the 
whale that was approached most closely had an extended resting period 
and did not resume foraging until the airguns had ceased firing. The 
remaining whales continued to execute foraging dives throughout 
exposure; however, swimming movements during foraging dives were 6 
percent lower during exposure than control periods (Miller et al., 
2009). These data raise concerns that seismic surveys may impact 
foraging behavior in sperm whales, although more data are required to 
understand whether the differences were due to exposure or natural 
variation in sperm whale behavior (Miller et al., 2009).
    Variations in respiration naturally vary with different behaviors 
and alterations to breathing rate as a function of acoustic exposure 
can be expected to co-occur with other behavioral reactions, such as a 
flight response or an alteration in diving. However, respiration rates 
in and of themselves may be representative of annoyance or an acute 
stress response. Various studies have shown that respiration rates may 
either be unaffected or could increase, depending on the species and 
signal characteristics, again highlighting the importance in 
understanding species differences in the tolerance of underwater noise 
when determining the potential for impacts resulting from anthropogenic 
sound exposure (e.g., Kastelein et al., 2001, 2005, 2006; Gailey et 
al., 2007, 2016).
    Marine mammals vocalize for different purposes and across multiple 
modes, such as whistling, echolocation click production, calling, and 
singing. Changes in vocalization behavior in response to anthropogenic 
noise can occur for any of these modes and may result from a need to 
compete with an increase in background noise or may reflect increased 
vigilance or a startle response. For example, in the presence of 
potentially masking signals, humpback whales and killer whales have 
been observed to increase the length of their songs or amplitude of 
calls (Miller et al., 2000; Fristrup et al., 2003; Foote et al., 2004; 
Holt et al., 2012), while right whales have been observed to shift the 
frequency content of their calls upward while reducing the rate of 
calling in areas of increased anthropogenic noise (Parks et al., 2007). 
In some cases, animals may cease sound production during production of 
aversive signals (Bowles et al., 1994).
    Cerchio et al. (2014) used PAM to document the presence of singing 
humpback whales off the coast of northern Angola and to 
opportunistically test for the effect of seismic survey activity on the 
number of singing whales. Two recording units were deployed between 
March and December 2008 in the offshore environment; numbers of singers 
were counted every hour. Generalized Additive Mixed Models were used to 
assess the effect of survey day (seasonality), hour (diel variation), 
moon phase, and received levels of noise (measured from a single pulse 
during each 10 minutes sampled period) on singer number. The number of 
singers significantly decreased with increasing received level of 
noise, suggesting that humpback whale communication was disrupted to 
some extent by the survey activity.
    Castellote et al. (2012) reported acoustic and behavioral changes 
by fin whales in response to shipping and airgun noise. Acoustic 
features of fin whale song notes recorded in the Mediterranean Sea and 
northeast Atlantic Ocean were compared for areas with different 
shipping noise levels and traffic intensities and during a seismic 
airgun survey. During the first 72 hours of the survey, a steady 
decrease in song received levels and bearings to singers indicated that 
whales moved away from the acoustic source and out of the study area. 
This displacement persisted for a time period well beyond the 10-day 
duration of seismic airgun activity, 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 
(SELcum) of ~127 dB). Overall, these results suggest that 
bowhead whales may adjust their vocal output in an effort to compensate 
for noise before ceasing vocalization effort and ultimately deflecting 
from the acoustic source (Blackwell et al., 2013, 2015). These studies 
demonstrate that even low levels of noise received far from the source 
can induce changes in vocalization and/or behavior for mysticetes.
    Avoidance is the displacement of an individual from an area or 
migration path as a result of the presence of 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

[[Page 56974]]

changes in abundance or distribution patterns of the affected species 
in the affected region if habituation to the presence of the sound does 
not occur (e.g., Bejder et al., 2006; Teilmann et al., 2006).
    Forney et al. (2017) detail the potential effects of noise on 
marine mammal populations with high site fidelity, including 
displacement and auditory masking, noting that a lack of observed 
response does not imply absence of fitness costs and that apparent 
tolerance of disturbance may have population-level impacts that are 
less obvious and difficult to document. Avoidance of overlap between 
disturbing noise and areas and/or times of particular importance for 
sensitive species may be critical to avoiding population-level impacts 
because (particularly for animals with high site fidelity) there may be 
a strong motivation to remain in the area despite negative impacts. 
Forney et al. (2017) state that, for these animals, remaining in a 
disturbed area may reflect a lack of alternatives rather than a lack of 
effects.
    Forney et al. (2017) specifically discuss beaked whales, stating 
that until recently most knowledge of beaked whales was derived from 
strandings, as they have been involved in atypical mass stranding 
events associated with mid-frequency active 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 solitary or in groups may 
influence the response.
    Behavioral disturbance can also impact marine mammals in more 
subtle ways. Increased vigilance may result in costs related to 
diversion of focus and attention (i.e., when a response consists of 
increased vigilance, it may come at the cost of decreased attention to 
other critical behaviors such as foraging or resting). These effects 
have generally not been demonstrated for marine mammals, but studies 
involving fish and terrestrial animals have shown that increased 
vigilance may substantially reduce feeding rates (e.g., Beauchamp and 
Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In 
addition, chronic disturbance can cause population declines through 
reduction of fitness (e.g., decline in body condition) and subsequent 
reduction in reproductive success, survival, or both (e.g., Harrington 
and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, 
Ridgway et al. (2006) reported that increased vigilance in bottlenose 
dolphins exposed to sound over a 5-day period did not cause any sleep 
deprivation or stress effects.
    Many animals perform vital functions, such as feeding, resting, 
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption 
of such functions resulting from reactions to stressors, such as sound 
exposure, are more likely to be significant if they last more than one 
diel cycle or recur on subsequent days (Southall et al., 2007). 
Consequently, a behavioral response lasting less than 1 day and not 
recurring on subsequent days is not considered particularly severe 
unless it could directly affect reproduction or survival (Southall et 
al., 2007). Note that there is a difference between multi-day 
substantive behavioral reactions and multi-day anthropogenic 
activities. For example, just because an activity lasts for multiple 
days does not necessarily mean that individual animals are either 
exposed to activity-related stressors for multiple days or, further, 
exposed in a manner resulting in sustained multi-day substantive 
behavioral responses.
    Stone (2015) reported data from at-sea observations during 1,196 
seismic surveys from 1994 to 2010. When arrays of large 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

[[Page 56975]]

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 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 are few specific data on this. Because of 
the intermittent nature and low duty cycle of seismic pulses, animals 
can emit and receive sounds in the relatively quiet intervals between 
pulses. However, in exceptional situations, reverberation occurs for 
much or all of the interval between pulses (e.g., Simard et al. 2005; 
Clark and Gagnon 2006), which could mask calls. Situations with 
prolonged strong reverberation are infrequent. However, it is common 
for reverberation to cause some lesser degree of elevation of the 
background level between airgun pulses (e.g., Gedamke 2011; Guerra et 
al. 2011, 2016; Klinck et al. 2012; Guan et al. 2015), and this weaker 
reverberation presumably reduces the detection range of calls and other 
natural sounds to some degree. Guerra et al. (2016) reported that 
ambient noise levels between seismic pulses were elevated as a result 
of reverberation at ranges of 50 km from the seismic source. Based on 
measurements in deep water of the Southern Ocean, Gedamke (2011) 
estimated that the slight elevation of background noise levels during 
intervals between seismic pulses reduced blue and fin whale 
communication space by as much as 36-51 percent when a seismic survey 
was operating 450-2,800 km away. Based on preliminary modeling, 
Wittekind et al. (2016) reported that airgun sounds could reduce the 
communication range of blue and fin whales 2,000 km from the seismic 
source. Nieukirk et al. (2012) and Blackwell et al. (2013) noted the 
potential for masking effects from seismic surveys on large whales.
    Some baleen and toothed whales are known to continue calling in the 
presence of seismic pulses, and their calls usually can be heard 
between the pulses (e.g., Nieukirk et al. 2012; Thode et al. 2012; 
Br[ouml]ker et al. 2013; Sciacca et al. 2016). Cerchio et al. (2014) 
suggested that the breeding display of humpback whales off Angola could 
be disrupted by seismic sounds, as singing activity declined with 
increasing received levels. In addition, some cetaceans are known to 
change their calling rates, shift their peak frequencies, or otherwise 
modify their vocal behavior in response to airgun sounds (e.g., Di 
Iorio and Clark 2010; Castellote et al. 2012; Blackwell et al. 2013, 
2015). The hearing systems of baleen whales are more sensitive to low-

[[Page 56976]]

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.

Ship Noise

    Vessel noise from the Langseth could affect marine animals in the 
proposed survey areas. Houghton et al. (2015) proposed that vessel 
speed is the most important predictor of received noise levels, and 
Putland et al. (2017) also reported reduced sound levels with decreased 
vessel speed. However, some energy is also produced at higher 
frequencies (Hermannsen et al., 2014); low levels of high-frequency 
sound from vessels has been shown to elicit responses in harbor 
porpoise (Dyndo et al., 2015).
    Ship noise, through masking, can reduce the effective communication 
distance of a marine mammal if the frequency of the sound source is 
close to that used by the animal, and if the sound is present for a 
significant fraction of time (e.g., Richardson et al. 1995; Clark et 
al., 2009; Jensen et al., 2009; Gervaise et al., 2012; Hatch et al., 
2012; Rice et al., 2014; Dunlop 2015; Erbe et al., 2015; Jones et al., 
2017; Putland et al., 2017). In addition to the frequency and duration 
of the masking sound, the strength, temporal pattern, and location of 
the introduced sound also play a role in the extent of the masking 
(Branstetter et al., 2013, 2016; Finneran and Branstetter 2013; Sills 
et al., 2017). Branstetter et al. (2013) reported that time-domain 
metrics are also important in describing and predicting masking.
    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 ships (Richardson et al. 
1995). Pirotta et al. (2015) noted that the physical presence of 
vessels, not just ship noise, disturbed the foraging activity of 
bottlenose dolphins. There is little data on the behavioral reactions 
of beaked whales to vessel noise, though they seem to avoid approaching 
vessels (e.g., W[uuml]rsig et al., 1998) or dive for an extended period 
when approached by a vessel (e.g., Kasuya 1986).
    In summary, project vessel sounds would not be at levels expected 
to cause anything more than possible localized and temporary behavioral 
changes in marine mammals, and would not be expected to result in 
significant negative effects on individuals or at the population level. 
In addition, in all oceans of the world, large vessel traffic is 
currently so prevalent that it is commonly considered a usual source of 
ambient sound (NSF-USGS 2011).

Vessel Strike

    Vessel collisions with marine mammals, or ship 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 ships upon arrival in 
port. Although smaller cetaceans are more maneuverable in relation to 
large vessels than are large whales, they may also be susceptible to 
strike. The severity of injuries typically depends on the size and 
speed of the vessel, with the probability of death or serious injury 
increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist 
et al., 2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013). 
Impact forces increase with speed, as does the probability of a strike 
at a given distance (Silber et al., 2010; Gende et al., 2011).
    Pace and Silber (2005) also found that the probability of death or 
serious injury increased rapidly with increasing vessel speed. 
Specifically, the predicted probability of serious injury or death 
increased from 45 to 75 percent as vessel speed increased from 10 to 14 
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 one hundred percent above 15 kn (28 kph).
    The Langseth will travel at a speed of 5 kn (9 kph) while towing 
seismic survey gear. At this speed, both the possibility of striking a 
marine mammal and the possibility of a strike resulting in serious 
injury or mortality are discountable. At average transit speed, the 
probability of serious injury or mortality resulting from a strike is 
less than 50 percent. However, the likelihood of a strike actually 
happening is again discountable. Vessel strikes, as analyzed in the 
studies cited above, generally involve commercial shipping, which is 
much more common in both space and time than is geophysical survey 
activity. Jensen and Silber (2004) summarized vessel strikes of large 
whales worldwide from 1975-2003 and found that most collisions occurred 
in the open ocean and involved large vessels (e.g., commercial 
shipping). No such incidents were reported for geophysical survey 
vessels during that time period.
    It is possible for vessel strikes to occur while traveling at slow 
speeds. For example, a hydrographic survey vessel traveling at low 
speed (5.5 kn (10 kph)) while conducting mapping surveys off the 
central California coast struck and killed a blue whale in 2009. The 
State of California determined that the whale had suddenly and 
unexpectedly surfaced beneath the hull, with the result that the 
propeller severed the whale's vertebrae, and that this was an 
unavoidable event. This strike represents the only such incident in 
approximately 540,000 hours of similar coastal mapping activity (p = 
1.9 x 10-6; 95 percent confidence interval = 0-5.5 x 
10-6; NMFS, 2013). In addition, a research vessel reported a 
fatal strike in 2011 of a dolphin in the Atlantic, demonstrating that 
it is possible for strikes involving smaller cetaceans to occur. In 
that case, the incident report indicated that an animal apparently was 
struck by the vessel's propeller as it was intentionally swimming near 
the vessel. While indicative of the type of unusual events that cannot 
be ruled out, neither of these instances represents a

[[Page 56977]]

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 pre-
dispose them to strand when exposed to another phenomenon. These 
suggestions are consistent with the conclusions of numerous other 
studies that have demonstrated that combinations of dissimilar 
stressors commonly combine to kill an animal or dramatically reduce its 
fitness, even though one exposure without the other does not produce 
the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; 
Fair and Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a, 
2005b; Romero, 2004; Sih et al., 2004).
    There is no conclusive evidence that exposure to airgun noise 
results in behaviorally-mediated forms of injury. Behaviorally-mediated 
injury (i.e., mass stranding events) has been primarily associated with 
beaked whales exposed to mid-frequency active (MFA) naval sonar. MFA 
sonar and the alerting stimulus used in Nowacek et al. (2004) are very 
different from the noise produced by airguns. One should therefore not 
expect the same reaction to airgun noise as to these other sources. As 
explained below, military MFA sonar is very different from airguns, and 
one should not assume that airguns will cause the same effects as MFA 
sonar (including strandings).
    To understand why military MFA sonar affects beaked whales 
differently than airguns do, it is important to note the distinction 
between behavioral sensitivity and susceptibility to auditory injury. 
To understand the potential for auditory injury in a particular marine 
mammal species in relation to a given acoustic signal, the frequency 
range the species is able to hear is critical, as well as the species' 
auditory sensitivity to frequencies within that range. Current data 
indicate that not all marine mammal species have equal hearing 
capabilities across all frequencies and, therefore, species are grouped 
into hearing groups with generalized hearing ranges assigned on the 
basis of available data (Southall et al., 2007, 2019). Hearing ranges 
as well as auditory sensitivity/susceptibility to frequencies within 
those ranges vary across the different groups. For example, in terms of 
hearing range, the 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

[[Page 56978]]

species within the group, and state that the data for beaked whales 
suggest sensitivity to approximately 5 kHz. However, this information 
is consistent with the general conclusion that beaked whales (and other 
mid-frequency cetaceans) are relatively insensitive to the frequencies 
where most energy of an airgun signal is found. Military MFA sonar is 
typically considered to operate in the frequency range of approximately 
3-14 kHz (D'Amico et al., 2009), i.e., outside the range of likely best 
hearing for beaked whales but within or close to the lower bounds, 
whereas most energy in an airgun signal is radiated at much lower 
frequencies, below 500 Hz (Dragoset, 1990).
    It is important to distinguish between energy (loudness, measured 
in dB) and frequency (pitch, measured in Hz). In considering the 
potential impacts of mid-frequency components of airgun noise (1-10 
kHz, where beaked whales can be expected to hear) on marine mammal 
hearing, one needs to account for the energy associated with these 
higher frequencies and determine what energy is truly ``significant.'' 
Although there is mid-frequency energy associated with airgun noise (as 
expected from a broadband source), airgun sound is predominantly below 
1 kHz (Breitzke et al., 2008; Tashmukhambetov et al., 2008; Tolstoy et 
al., 2009). As stated by Richardson et al. (1995), ``[. . .] most 
emitted [seismic airgun] energy is at 10-120 Hz, but the pulses contain 
some energy up to 500-1,000 Hz.'' Tolstoy et al. (2009) conducted 
empirical measurements, demonstrating that sound energy levels 
associated with airguns were at least 20 dB lower at 1 kHz (considered 
``mid-frequency'') compared to higher energy levels associated with 
lower frequencies (below 300 Hz) (``all but a small fraction of the 
total energy being concentrated in the 10-300 Hz range'' [Tolstoy et 
al., 2009]), and at higher frequencies (e.g., 2.6-4 kHz), power might 
be less than 10 percent of the peak power at 10 Hz (Yoder, 2002). 
Energy levels measured by Tolstoy et al. (2009) were even lower at 
frequencies above 1 kHz. In addition, as sound propagates away from the 
source, it tends to lose higher-frequency components faster than low-
frequency components (i.e., low-frequency sounds typically propagate 
longer distances than high-frequency sounds) (Diebold et al., 2010). 
Although higher-frequency components of airgun signals have been 
recorded, it is typically in surface-ducting conditions (e.g., DeRuiter 
et al., 2006; Madsen et al., 2006) or in shallow water, where there are 
advantageous propagation conditions for the higher frequency (but low-
energy) components of the airgun signal (Hermannsen et al., 2015). This 
should not be of concern because the likely behavioral reactions of 
beaked whales that can result in acute physical injury would result 
from noise exposure at depth (because of the potentially greater 
consequences of severe behavioral reactions). In summary, the frequency 
content of airgun signals is such that beaked whales will not be able 
to hear the signals well (compared to MFA sonar), especially at depth 
where we expect the consequences of noise exposure could be more 
severe.
    Aside from frequency content, there are other significant 
differences between MFA sonar signals and the sounds produced by 
airguns that minimize the risk of severe behavioral reactions that 
could lead to strandings or deaths at sea, e.g., significantly longer 
signal duration, horizontal sound direction, typical fast and 
unpredictable source movement. All of these characteristics of MFA 
sonar tend towards greater potential to cause severe behavioral or 
physiological reactions in exposed beaked whales that may contribute to 
stranding. Although both sources are powerful, MFA sonar contains 
significantly greater energy in the mid-frequency range, where beaked 
whales hear better. Short-duration, high energy pulses--such as those 
produced by airguns--have greater potential to cause damage to auditory 
structures (though this is unlikely for mid-frequency cetaceans, as 
explained later in this document), but it is longer duration signals 
that have been implicated in the vast majority of beaked whale 
strandings. Faster, less predictable movements in combination with 
multiple source vessels are more likely to elicit a severe, potentially 
anti-predator response. Of additional interest in assessing the 
divergent characteristics of MFA sonar and airgun signals and their 
relative potential to cause stranding events or deaths at sea is the 
similarity between the MFA sonar signals and stereotyped calls of 
beaked whales' primary predator: the killer whale (Zimmer and Tyack, 
2007). Although generic disturbance stimuli--as airgun noise may be 
considered in this case for beaked whales--may also trigger 
antipredator responses, stronger responses should generally be expected 
when perceived risk is greater, as when the stimulus is confused for a 
known predator (Frid and Dill, 2002). In addition, because the source 
of the perceived predator (i.e., 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,

[[Page 56979]]

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 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 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 a relative few deployed devices, and no interaction 
between marine mammals and any such device has been recorded during 
prior NSF surveys using the devices. There are no meaningful 
entanglement risks posed by the proposed survey, and entanglement risks 
are not discussed further in this document.

Anticipated Effects on Marine Mammal Habitat

    Physical Disturbance--Sources of seafloor disturbance related to 
geophysical surveys that may impact marine mammal habitat include 
placement of anchors, nodes, cables, sensors, or other equipment on or 
in the seafloor for various activities. Equipment deployed on the 
seafloor has the potential to cause direct physical damage and could 
affect bottom-associated fish resources.
    Placement of 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 
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

[[Page 56980]]

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 recent comprehensive review (Carroll et al., 2017) found that 
results are mixed as to the effects of airgun noise on the prey of 
marine mammals. While some studies suggest a change in prey 
distribution and/or a reduction in prey abundance following the use of 
seismic airguns, others suggest no effects or even positive effects in 
prey abundance. As one specific example, Paxton et al. (2017), which 
describes findings related to the effects of a 2014 seismic survey on a 
reef off of North Carolina, showed a 78 percent decrease in observed 
nighttime abundance for certain species. It is important to note that 
the evening hours during which the decline in fish habitat use was 
recorded (via video recording) occurred on the same day that the 
seismic survey passed, and no subsequent data is presented to support 
an inference that the response was long-lasting. Additionally, given 
that the finding is based on video images, the lack of recorded fish 
presence does not support a conclusion that the fish actually moved 
away from the site or suffered any serious impairment. In summary, this 
particular study corroborates prior studies indicating that a startle 
response or short-term displacement should be expected.
    Available data suggest that cephalopods are capable of sensing the 
particle motion of sounds and detect low frequencies up to 1-1.5 kHz, 
depending on the species, and so are likely to detect airgun noise 
(Kaifu et al., 2008; Hu et al., 2009; Mooney et al., 2010; Samson et 
al., 2014). Auditory injuries (lesions occurring on the statocyst 
sensory hair cells) have been reported upon controlled exposure to low-
frequency sounds, suggesting that cephalopods are particularly 
sensitive to low-frequency sound (Andre et al., 2011; Sole et al., 
2013). Behavioral responses, such as inking and jetting, have also been 
reported upon exposure to low-frequency sound (McCauley et al., 2000b; 
Samson et al., 2014). Similar to fish, however, the transient nature of 
the survey leads to an expectation that effects will be largely limited 
to behavioral reactions and would occur as a result of brief, 
infrequent exposures.
    With regard to potential impacts on zooplankton, McCauley et al. 
(2017) found that exposure to airgun noise resulted in significant 
depletion for more than half the taxa present and that there were two 
to three times more dead zooplankton after airgun exposure compared 
with controls for all taxa, within 1 km of the airguns. However, the 
authors also stated that in order to have significant impacts on r-
selected species (i.e., those with high growth rates and that produce 
many offspring) such as plankton, the spatial or temporal scale of 
impact must be large in comparison with the ecosystem concerned, and it 
is possible that the findings reflect avoidance by zooplankton rather 
than mortality (McCauley et al., 2017). In addition, the results of 
this study are inconsistent with a large body of research that 
generally finds limited spatial and temporal impacts to zooplankton as 
a result of exposure to airgun noise (e.g., Dalen and Knutsen, 1987; 
Payne, 2004; Stanley et al., 2011). Most prior research on this topic, 
which has focused on relatively small spatial scales, has showed 
minimal effects (e.g., Kostyuchenko, 1973; Booman et al., 1996; 
S[aelig]tre and Ona, 1996; Pearson et al., 1994; Bolle et al., 2012).
    A modeling exercise was conducted as a follow-up to the McCauley et 
al. (2017) study (as recommended by McCauley et al.), in order to 
assess the potential for impacts on ocean ecosystem dynamics and 
zooplankton population dynamics (Richardson et al., 2017). Richardson 
et al. (2017) found that for copepods with a short life cycle in a 
high-energy environment, a full-scale airgun survey would impact 
copepod abundance up to 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

[[Page 56981]]

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 recent 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 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 this IHA, which will inform both 
NMFS' consideration of ``small numbers,'' and the negligible impact 
determinations.
    Harassment is the only type of take expected to result from these 
activities. Except with respect to certain activities not pertinent 
here, section 3(18) of the MMPA defines ``harassment'' as any act of 
pursuit, torment, or annoyance, which (i) has the potential to injure a 
marine mammal or marine mammal stock in the wild (Level A harassment); 
or (ii) has the potential to disturb a marine mammal or marine mammal 
stock in the wild by causing disruption of behavioral patterns, 
including, but not limited to, migration, breathing, nursing, breeding, 
feeding, or sheltering (Level B harassment).
    Anticipated takes would primarily be Level B harassment, as use of 
the airgun arrays have 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 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. The proposed mitigation and monitoring measures 
are expected to minimize the severity of such taking to the extent 
practicable. No mortality is anticipated as a result of these 
activities. Below we

[[Page 56982]]

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 (referenced 
to 1 micropascal (re 1 [mu]Pa)) for continuous (e.g., vibratory pile 
driving, drilling) and above RMS SPL 160 dB re 1 [mu]Pa for non-
explosive impulsive (e.g., seismic airguns) or intermittent (e.g., 
scientific sonar) sources. Generally speaking, Level B harassment take 
estimates based on these behavioral harassment thresholds are expected 
to include any likely takes by TTS as, in most cases, the likelihood of 
TTS occurs at distances from the source less than those at which 
behavioral harassment is likely. TTS of a sufficient degree can 
manifest as behavioral harassment, as reduced hearing sensitivity and 
the potential reduced opportunities to detect important signals 
(conspecific communication, predators, prey) may result in changes in 
behavior patterns that would not otherwise occur.
    L-DEO's proposed 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 (e.g., 
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: 
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

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

Ensonified Area

    Here, we describe operational and environmental parameters of the 
activity that 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

[[Page 56983]]

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 12 m and two 
45/105 in\3\ GI airguns at a tow depth of 3 m. L-DEO's model results 
are used to determine the 160 dBrms radius for both the 
airgun sources 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 (~1600 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 12 m and the low-energy surveys would 
use two GI airguns at a 3m tow depth. For deep water (>1000 m), we use 
the deep-water radii obtained from L-DEO model results down to a 
maximum water depth of 2,000 m for the 36-airgun array and the two GI 
airguns. The radii for intermediate water depths (100-1,000 m) are 
derived from the deep-water ones by applying a correction factor 
(multiplication) of 1.5, such that observed levels at very near offsets 
fall below the corrected mitigation curve (see Figure 16 in Diebold et 
al. 2010).
    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
                                                                                    Water depth      m) to the
                      Airgun configuration                         Tow depth (m)        (m)           Level B
                                                                                                    harassment
                                                                                                     threshold
----------------------------------------------------------------------------------------------------------------
4 strings, 36 airguns, 6,600 in\3\..............................              12          >1,000       \1\ 6,733
Two 45/105 in GI airguns........................................               3          >1,000         \1\ 438
                                                                                       100-1,000         \2\ 657
----------------------------------------------------------------------------------------------------------------
\1\ Distance is based on L-DEO model results.
\2\ Distance is based on L-DEO model results with a 1.5 x correction factor between deep and intermediate water
  depths.


          Table 5--Modeled Radial Distance to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
                                                                                                       High
                                                                   Low frequency   Mid frequency     frequency
----------------------------------------------------------------------------------------------------------------
                                                   MCS Surveys
----------------------------------------------------------------------------------------------------------------
PTS SELcum......................................................           320.2               0               1
PTS Peak........................................................            38.9            13.6           268.3
----------------------------------------------------------------------------------------------------------------
The largest distance (in bold) of the dual criteria (SEL cum or Peak) was used to estimate threshold distances
  and potential takes by Level A harassment.


[[Page 56984]]

    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 (e.g., airguns) contained in the NMFS Technical 
Guidance were presented as dual metric acoustic thresholds using both 
SELcum 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 SELcum metric 
considers both level and duration of exposure, as well as auditory 
weighting functions by marine mammal hearing group.
    The SELcum 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 very small modeled zones of injury for those species (all 
estimated zones less than 15 m for mid-frequency cetaceans), in 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 believe 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 (see Table 1). 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 and Puerto Rico are taken from the US Navy Atlantic Fleet 
Training and Testing Area Marine Mammal Density (Roberts et al., 2023; 
Mannocci et al., 2017), which represent the best available information 
regarding marine mammal densities in the survey area. 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 10 km x 10 km grid cells. 
Densities in the grid cells for the AFTT Area south of 21[deg] N were 
averaged per month for each of two water depth categories (intermediate 
and deep); for most months, the densities for each species were the 
same. More information is available online at https://seamap.env.duke.edu/models/Duke/AFTT/.
    For most species, the average monthly densities were the same 
throughout the year; densities for fin whale, sei whale, humpback 
whale, and Atlantic white-sided dolphin varied by month, so the highest 
monthly densities were used.

Take Estimation

    Here we describe how the information provided above is synthesized 
to produce a quantitative estimate of the take that is reasonably 
likely to occur and proposed for authorization. In order to estimate 
the number of marine mammals predicted to be exposed to sound levels 
that would result in Level A or Level B harassment, radial distances 
from the airgun array to the predicted isopleth corresponding to the 
Level A harassment and Level B harassment thresholds are calculated, as 
described above. Those radial distances are 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 the 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 (24) to 
estimate potential takes (see Appendix B of L-DEO's application for 
more information).
    L-DEO generally 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. As

[[Page 56985]]

requested by L-DEO with NMFS concurrence, when zero take was calculated 
we have authorized one group size of take as a precaution for species 
that could potentially occur in the survey area.

                                                   Table 6--Estimated Take Proposed for Authorization
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                           Estimated take       Proposed authorized take
                 Species                             Stock           ----------------------------------------------------     Modeled       Percent of
                                                                        Level B      Level A      Level B      Level A     abundance \2\       stock
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale..........................  Gulf of Maine.............          262           12          262           12           4,990             5.5
Fin whale...............................  Western North Atlantic....          0.4            0        \1\ 2            0          11,672             0.2
Sei whale...............................  Nova Scotia...............           22            1           22            1          19,530             0.1
Minke whale.............................  Canadian East Coast.......           58            3           58            3          13,784             0.4
Blue whale..............................  Western North Atlantic....            1            0            1            0             191             0.5
Sperm whale.............................  North Atlantic............          481            1          482            0          64,105             0.8
Kogia spp...............................  ..........................          354           14          354           14          26,043             1.4
Beaked whale............................  ..........................          539            1          540            0          65,069             0.8
Pilot whales............................  ..........................        1,830            3        1,833            0         264,907             0.7
Rough-toothed dolphin...................  Western North Atlantic....          476            1          477            0          32,848             1.5
Bottlenose dolphin......................  Western North Atlantic            2,128            4        2,132            0         418,151             0.5
                                           Offshore.
Pantropical spotted dolphin.............  Western North Atlantic....          778            1          779            0         321,740             0.2
Atlantic spotted dolphin................  Western North Atlantic....        1,537            3        1,540            0         259,519             0.6
Spinner dolphin.........................  Western North Atlantic....        1,928            4        1,932            0         152,511             1.3
Clymene dolphin.........................  Western North Atlantic....        1,586            3        1,589            0         181,209             0.9
Striped dolphin.........................  Western North Atlantic....          317            1          318            0         412,729             0.1
Fraser's dolphin........................  Western North Atlantic....          213            0          213            0          19,585             1.1
Risso's dolphin.........................  Western North Atlantic....          164            0          164            0          78,205             0.2
Common dolphin..........................  Western North Atlantic....           88            0           88            0         473,260            <0.1
Melon-headed whale......................  Western North Atlantic....          985            2          987            0          64,114             1.5
Pygmy killer whale......................  Western North Atlantic....          130            0          130            0           9,001             1.4
False killer whale......................  Western North Atlantic....          218            0          218            0          12,682             1.7
Killer whale............................  Western North Atlantic....            2            0            2            0             972             0.2
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Group size from Jefferson et al., 2015.
\2\ Modeled abundance (Roberts et al., 2023).

Proposed Mitigation

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

Vessel-Based Visual Mitigation Monitoring

    Visual monitoring requires the use of trained observers (herein 
referred to as visual protected species observers (PSO)) 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, but also 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 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.
    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 approval.
    At least one of the visual and two of the acoustic PSOs (discussed 
below) aboard the vessel must have a minimum of 90 days at-sea 
experience working in those roles, respectively, with no more

[[Page 56986]]

than 18 months elapsed since the conclusion of the at-sea experience. 
One visual PSO with such experience shall be designated as the lead for 
the entire protected species observation team. The lead PSO shall serve 
as primary point of contact for the vessel operator and ensure all PSO 
requirements per the IHA are met. To the maximum extent practicable, 
the experienced PSOs should be scheduled to be on duty with those PSOs 
with appropriate training but who have not yet gained relevant 
experience.
    During survey operations (e.g., any day on which use of the 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 shutdown and buffer zones. 
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 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.
    L-DEO must notify the NMFS Southeast Regional Office (SERO), Nicole 
Angeli (DPNR Virgin Islands), and Grisel Rodriguez Ferrer (DNR Puerto 
Rico) of the start and end date of airgun operations in the survey area 
via email ([email protected]; 
[email protected]; [email protected]).

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 an 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.
    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:
     Sea state is less than or equal to BSS 4;
     No marine mammals (excluding delphinids) detected solely 
by PAM in the applicable SZ in the previous 2 hours;
     NMFS is notified via email as soon as practicable with the 
time and location in which operations began occurring without an active 
PAM system; and
     Operations with an active 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

    An 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 
SELcum and peak SPL), while also providing a consistent, 
reasonably observable zone within which PSOs would typically be able to 
conduct effective observational effort.

[[Page 56987]]

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 
believe that 500 m is likely regularly attainable for PSOs using the 
naked eye during typical conditions. The pre-start clearance zone 
simply represents the addition of a buffer to the SZ, doubling the SZ 
size during pre-clearance.
    An extended SZ of 1,500 m must be enforced for all beaked whales 
and Kogia species. No buffer of this extended SZ is required, as NMFS 
concludes that this extended SZ is sufficiently protective to mitigate 
harassment to beaked whales and Kogia species.

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 and Kogia spp.) 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 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 step-wise 
increase in the number of airguns firing and total array volume until 
all operational airguns are activated and the full volume is achieved, 
is required at all times as part of the activation of the airgun array. 
All operators must adhere to the following pre-start clearance and 
ramp-up requirements:
     The operator must notify a designated PSO of the planned 
start of ramp-up as agreed upon with the lead PSO; the notification 
time should not be less than 60 minutes prior to the planned ramp-up in 
order to allow the PSOs time to monitor the pre-start clearance zone 
(and extended SZ) for 30 minutes prior to the initiation of ramp-up 
(pre-start clearance);
     Ramp-ups shall be scheduled so as to minimize the time 
spent with the source activated prior to reaching the designated run-
in;
     One of the PSOs conducting pre-start clearance 
observations must be notified again immediately prior to initiating 
ramp-up procedures and the operator must receive confirmation from the 
PSO to proceed;
     Ramp-up may not be initiated if any marine mammal is 
within the applicable shutdown or buffer zone. If a marine mammal is 
observed within the pre-start clearance zone (or extended SZ, for 
beaked whales and Kogia species) during the 30 minute pre-start 
clearance period, ramp-up may not begin until the animal(s) has been 
observed exiting the zones or until an additional time period has 
elapsed with no further sightings (15 minutes for small odontocetes, 
and 30 minutes for all mysticetes and all other odontocetes, including 
sperm whales, beaked whales, and large delphinids, such as pilot 
whales);
     Ramp-up shall begin by activating a single airgun of the 
smallest volume in the array and shall continue in stages by doubling 
the number of active elements at the commencement of each stage, with 
each stage of approximately the same duration. Duration shall not be 
less than 20 minutes. The operator must provide information to the PSO 
documenting that appropriate procedures were followed;
     PSOs must monitor the pre-start clearance zone (and 
extended 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;
     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;
     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
     Testing of the airgun array involving all elements 
requires ramp-up. Testing limited to individual source elements or 
strings does not require ramp-up but does require pre-start clearance 
of 30 minutes.

Shutdown

    The shutdown of an airgun array requires the immediate de-
activation of all individual airgun elements of the array. Any PSO on 
duty will have the authority to delay the start of survey operations or 
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 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, Kogia species, and 
large delphinids, such as pilot whales.

[[Page 56988]]

    The shutdown requirement is waived for small dolphins if an 
individual is detected within the SZ. As defined here, the small 
dolphin group is intended to encompass those members of the Family 
Delphinidae most likely to voluntarily approach the source vessel for 
purposes of interacting with the vessel and/or airgun array (e.g., bow 
riding). This exception to the shutdown requirement applies solely to 
specific genera of small dolphins (Delphinus, Lagenodelphis, Stenella, 
Steno, and Tursiops).
    We include this small dolphin exception because shutdown 
requirements for small dolphins under all circumstances represent 
practicability concerns without likely commensurate benefits for the 
animals in question. Small dolphins are generally the most commonly 
observed marine mammals in the specific geographic region and would 
typically be the only marine mammals likely to intentionally approach 
the vessel. As described above, auditory injury is extremely unlikely 
to occur for mid-frequency cetaceans (e.g., delphinids), as this group 
is relatively insensitive to sound produced at the predominant 
frequencies in an airgun pulse while also having a relatively high 
threshold for the onset of auditory injury (i.e., permanent threshold 
shift).
    A large body of anecdotal evidence indicates that small dolphins 
commonly approach vessels and/or towed arrays during active sound 
production for purposes of bow riding, with no apparent effect observed 
(e.g., Barkaszi et al., 2012, Barkaszi and Kelly, 2018). The potential 
for increased shutdowns resulting from such a measure would require the 
Langseth to revisit the missed track line to reacquire data, resulting 
in an overall increase in the total sound energy input to the marine 
environment and an increase in the total duration over which the survey 
is active in a given area. Although other mid-frequency hearing 
specialists (e.g., large delphinids) are no more likely to incur 
auditory injury than are small dolphins, they are much less likely to 
approach vessels. Therefore, retaining a shutdown requirement for large 
delphinids would not have similar impacts in terms of either 
practicability for the applicant or corollary increase in sound energy 
output and time on the water. We do anticipate some benefit for a 
shutdown requirement for large delphinids in that it simplifies 
somewhat the total range of decision-making for PSOs and may preclude 
any potential for physiological effects other than to the auditory 
system as well as some more severe behavioral reactions for any such 
animals in close proximity to the Langseth.
    Visual PSOs shall use best professional judgment in making the 
decision to call for a shutdown if there is uncertainty regarding 
identification (i.e., whether the observed marine mammal(s) belongs to 
one of the delphinid genera for which shutdown is waived or one of the 
species with a larger SZ).
    L-DEO must implement shutdown if a marine mammal species for which 
take was not authorized, or a species for which authorization was 
granted but the authorized takes have been met, approaches the Level A 
or Level B harassment zones. L-DEO must also implement shutdown if any 
large whale (defined as a sperm whale or any mysticete species) with a 
calf (defined as an animal less than two-thirds the body size of an 
adult observed to be in close association with an adult) and/or an 
aggregation of six or more large whales are observed at any distance.

Vessel Strike Avoidance

    Vessel personnel should use an appropriate reference guide that 
includes identifying information on all marine mammals that may be 
encountered. Vessel operators must comply with the below measures 
except under extraordinary circumstances when the safety of the vessel 
or crew is in doubt or the safety of life at sea is in question. These 
requirements do not apply in any case where compliance would create an 
imminent and serious threat to a person or vessel or to the extent that 
a vessel is restricted in its ability to maneuver and, because of the 
restriction, cannot comply.
    Vessel operators and crews must maintain a vigilant watch for all 
marine mammals and slow down, stop their vessel, or alter course, as 
appropriate and regardless of vessel size, to avoid striking any marine 
mammal. A single marine mammal at the surface may indicate the presence 
of submerged animals in the vicinity of the vessel; therefore, 
precautionary measures should always be exercised. A visual observer 
aboard the vessel must monitor a vessel strike avoidance zone around 
the vessel (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 right 
whale, other whale (defined in this context as sperm whales or baleen 
whales other than right 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.
    Monitoring and reporting requirements prescribed by NMFS should 
contribute to improved understanding of one or more of the following:
     Occurrence of marine mammal species or stocks in the area 
in which

[[Page 56989]]

take is anticipated (e.g., presence, abundance, distribution, density);
     Nature, scope, or context of likely marine mammal exposure 
to potential stressors/impacts (individual or cumulative, acute or 
chronic), through better understanding of: (1) action or environment 
(e.g., source characterization, propagation, ambient noise); (2) 
affected species (e.g., life history, dive patterns); (3) co-occurrence 
of marine mammal species with the activity; or (4) biological or 
behavioral context of exposure (e.g., age, calving or feeding areas);
     Individual marine mammal responses (behavioral or 
physiological) to acoustic stressors (acute, chronic, or cumulative), 
other stressors, or cumulative impacts from multiple stressors;
     How anticipated responses to stressors impact either: (1) 
long-term fitness and survival of individual marine mammals; or (2) 
populations, species, or stocks;
     Effects on marine mammal habitat (e.g., marine mammal prey 
species, acoustic habitat, or other important physical components of 
marine mammal habitat); and,
     Mitigation and monitoring effectiveness.

Vessel-Based Visual Monitoring

    As described above, PSO observations would take place during 
daytime airgun operations. During seismic survey operations, at least 
five visual PSOs would be based aboard the Langseth. Two visual PSOs 
would be on duty at all times during daytime hours. Monitoring shall be 
conducted in accordance with the following requirements:
     The operator shall provide PSOs with bigeye binoculars 
(e.g., 25 x 150; 2.7 view angle; individual ocular focus; height 
control) of appropriate quality solely for PSO use. These shall be 
pedestal-mounted on the deck at the most appropriate vantage point that 
provides for optimal sea surface observation, PSO safety, and safe 
operation of the vessel; and
     The operator will work with the selected third-party 
observer provider to ensure PSOs have all equipment (including backup 
equipment) needed to adequately perform necessary tasks, including 
accurate determination of distance and bearing to observed marine 
mammals.
    PSOs must have the following requirements and qualifications:
     PSOs shall be independent, dedicated, trained visual and 
acoustic PSOs and must be employed by a third-party observer provider;
     PSOs shall have no tasks other than to conduct 
observational effort (visual or acoustic), collect data, and 
communicate with and instruct relevant vessel crew with regard to the 
presence of protected species and mitigation requirements (including 
brief alerts regarding maritime hazards);
     PSOs shall have successfully completed an approved PSO 
training course appropriate for their designated task (visual or 
acoustic). Acoustic PSOs are required to complete specialized training 
for operating PAM systems and are encouraged to have familiarity with 
the vessel with which they will be working;
     PSOs can act as acoustic or visual observers (but not at 
the same time) as long as they demonstrate that their training and 
experience are sufficient to perform the task at hand;
     NMFS must review and approve PSO resumes accompanied by a 
relevant training course information packet that includes the name and 
qualifications (i.e., experience, training completed, or educational 
background) of the instructor(s), the course outline or syllabus, and 
course reference material as well as a document stating successful 
completion of the course;
     PSOs must successfully complete relevant training, 
including completion of all required coursework and passing (80 percent 
or greater) a written and/or oral examination developed for the 
training program;
     PSOs must have successfully attained a bachelor's degree 
from an accredited college or university with a major in one of the 
natural sciences, a minimum of 30 semester hours or equivalent in the 
biological sciences, and at least one undergraduate course in math or 
statistics; and
     The educational requirements may be waived if the PSO has 
acquired the relevant skills through alternate experience. Requests for 
such a waiver shall be submitted to NMFS and must include written 
justification. Requests shall be granted or denied (with justification) 
by NMFS within 1 week of receipt of submitted information. Alternate 
experience that may be considered includes, but is not limited to (1) 
secondary education and/or experience comparable to PSO duties; (2) 
previous work experience conducting academic, commercial, or 
government-sponsored protected species surveys; or (3) previous work 
experience as a PSO; the PSO should demonstrate good standing and 
consistently good performance of PSO duties.
     For data collection purposes, PSOs shall use standardized 
electronic data collection forms. PSOs shall record detailed 
information about any implementation of mitigation requirements, 
including the distance of animals to the airgun array and description 
of specific actions that ensued, the behavior of the animal(s), any 
observed changes in behavior before and after implementation of 
mitigation, and if shutdown was implemented, the length of time before 
any subsequent ramp-up of the airgun array. If required mitigation was 
not implemented, PSOs should record a description of the circumstances. 
At a minimum, the following information must be recorded:
    [cir] Vessel name, vessel size and type, maximum speed capability 
of vessel;
    [cir] Dates (MM/DD/YYYY) of departures and returns to port with 
port name;
    [cir] PSO names and affiliations, PSO ID (initials or other 
identifier);
    [cir] Date (MM/DD/YYYY) and participants of PSO briefings (as 
discussed in 3(d));
    [cir] Visual monitoring equipment used (description);
    [cir] PSO location on vessel and height (meters) of observation 
location above water surface;
    [cir] Watch status (description);
    [cir] Dates (MM/DD/YYYY) and times (Greenwich Mean Time/UTC) of 
survey on/off effort and times (GMC/UTC) corresponding with PSO on/off 
effort;
    [cir] Vessel location (decimal degrees) when survey effort began 
and ended and vessel location at beginning and end of visual PSO duty 
shifts;
    [cir] Vessel location (decimal degrees) at 30-second intervals if 
obtainable from data collection software, otherwise at practical 
regular interval;
    [cir] Vessel heading (compass heading) and speed (knots) at 
beginning and end of visual PSO duty shifts and upon any change;
    [cir] Water depth (meters) (if obtainable from data collection 
software);
    [cir] Environmental conditions while on visual survey (at beginning 
and end of PSO shift and whenever conditions changed significantly), 
including BSS and any other relevant weather conditions including cloud 
cover, fog, sun glare, and overall visibility to the horizon;
    [cir] Factors that may have contributed to impaired observations 
during each PSO shift change or as needed as environmental conditions 
changed (description) (e.g., vessel traffic, equipment malfunctions); 
and
    [cir] Vessel/Survey activity information (and changes thereof) 
(description), such as airgun power output while in operation, number 
and volume of airguns operating in the array, tow

[[Page 56990]]

depth of the array, and any other notes of significance (i.e., pre-
start clearance, ramp-up, shutdown, testing, shooting, ramp-up 
completion, end of operations, streamers, etc.).
     Upon visual observation of any marine mammals, the 
following information must be recorded:
    [cir] Sighting ID (numeric);
    [cir] Watch status (sighting made by PSO on/off effort, 
opportunistic, crew, alternate vessel/platform);
    [cir] Location of PSO/observer (description);
    [cir] Vessel activity at the time of the sighting (e.g., deploying, 
recovering, testing, shooting, data acquisition, other);
    [cir] PSO who sighted the animal/ID;
    [cir] Time/date of sighting (GMT/UTC, MM/DD/YYYY);
    [cir] Initial detection method (description);
    [cir] Sighting cue (description);
    [cir] Vessel location at time of sighting (decimal degrees);
    [cir] Water depth (meters);
    [cir] Direction of vessel's travel (compass direction);
    [cir] Speed (knots) of the vessel from which the observation was 
made;
    [cir] Direction of animal's travel relative to the vessel 
(description, compass heading);
    [cir] Bearing to sighting (degrees);
    [cir] Identification of the animal (e.g., genus/species, lowest 
possible taxonomic level, or unidentified) and the composition of the 
group if there is a mix of species;
    [cir] Species reliability (an indicator of confidence in 
identification) (1 = unsure/possible, 2 = probable, 3 = definite/sure, 
9 = unknown/not recorded);
    [cir] Estimated distance to the animal (meters) and method of 
estimating distance;
    [cir] Estimated number of animals (high/low/best) (numeric);
    [cir] Estimated number of animals by cohort (adults, yearlings, 
juveniles, calves, group composition, etc.);
    [cir] Description (as many distinguishing features as possible of 
each individual seen, including length, shape, color, pattern, scars or 
markings, shape and size of dorsal fin, shape of head, and blow 
characteristics);
    [cir] Detailed behavior observations (e.g., number of blows/
breaths, number of surfaces, breaching, spyhopping, diving, feeding, 
traveling; as explicit and detailed as possible; note any observed 
changes in behavior);
    [cir] Animal's closest point of approach (meters) and/or closest 
distance from any element of the airgun array; and
    [cir] Description of any actions implemented in response to the 
sighting (e.g., delays, shutdown, ramp-up) and time and location of the 
action.
    [cir] Photos (Yes/No);
    [cir] Photo Frame Numbers (List of numbers);
    [cir] Conditions at time of sighting (Visibility; Beaufort Sea 
State);
    If a marine mammal is detected while using the PAM system, the 
following information should be recorded:
     An acoustic encounter identification number, and whether 
the detection was linked with a visual sighting;
     Date and time when first and last heard;
     Types and nature of sounds heard (e.g., clicks, whistles, 
creaks, burst pulses, continuous, sporadic, strength of signal); and
     Any additional information recorded such as water depth of 
the hydrophone array, bearing of the animal to the vessel (if 
determinable), species or taxonomic group (if determinable), 
spectrogram screenshot, and any other notable information.

Reporting

    The Holder shall submit a draft comprehensive report on all 
activities and monitoring results within 90 days of the completion of 
the survey or expiration of the IHA, whichever comes sooner. The report 
must describe all activities conducted and sightings of marine mammals, 
must provide full documentation of methods, results, and interpretation 
pertaining to all monitoring, and must summarize the dates and 
locations of survey operations and all marine mammal sightings (dates, 
times, locations, activities, associated survey activities). The draft 
report shall also include geo-referenced time-stamped vessel tracklines 
for all time periods during which airgun arrays were operating. 
Tracklines should include points recording any change in airgun array 
status (e.g., when the sources began operating, when they were turned 
off, or when they changed operational status such as from full array to 
single gun or vice versa). Geographic Information System files shall be 
provided in Environmental Systems Research Institute shapefile format 
and include the UTC date and time, latitude in decimal degrees, and 
longitude in decimal degrees. All coordinates shall be referenced to 
the WGS84 geographic coordinate system. In addition to the report, all 
raw observational data shall be made available. The report must 
summarize data collected as described above in Data Collection. A final 
report must be submitted within 30 days following resolution of any 
comments on the draft report.
    The report must include a validation document concerning the use of 
PAM, which should include necessary noise validation diagrams and 
demonstrate whether background noise levels on the PAM deployment 
limited achievement of the planned detection goals. Copies of any 
vessel self-noise assessment reports must be included with the report.

Reporting Injured or Dead Marine Mammals

    Discovery of injured or dead marine mammals--In the event that 
personnel involved in the survey activities discover an injured or dead 
marine mammal, the L-DEO shall report the incident to the Office of 
Protected Resources (OPR), NMFS, and to the NMFS Southeast Regional 
Stranding Coordinator as soon as feasible. The report must include the 
following information:
     Time, date, and location (latitude/longitude) of the first 
discovery (and updated location information if known and applicable);
     Species identification (if known) or description of the 
animal(s) involved;
     Condition of the animal(s) (including carcass condition if 
the animal is dead);
     Observed behaviors of the animal(s), if alive;
     If available, photographs or video footage of the 
animal(s); and
     General circumstances under which the animal was 
discovered.
    Vessel strike--In the event of a strike of a marine mammal by any 
vessel involved in the activities covered by the authorization, L-DEO 
shall report the incident to OPR, NMFS, and to the NMFS Southeast 
Regional Stranding Coordinator as soon as feasible. The report must 
include the following information:
     Time, date, and location (latitude/longitude) of the 
incident;
     Vessel's speed during and leading up to the incident;
     Vessel's course/heading and what operations were being 
conducted (if applicable);
     Status of all sound sources in use;
     Description of avoidance measures/requirements that were 
in place at the time of the strike and what additional measure were 
taken, if any, to avoid strike;
     Environmental conditions (e.g., wind speed and direction, 
BSS, cloud cover, visibility) immediately preceding the strike;
     Species identification (if known) or description of the 
animal(s) involved;
     Estimated size and length of the animal that was struck;

[[Page 56991]]

     Description of the behavior of the marine mammal 
immediately preceding and following the strike;
     If available, description of the presence and behavior of 
any other marine mammals present immediately preceding the strike;
     Estimated fate of the animal (e.g., dead, injured but 
alive, injured and moving, blood or tissue observed in the water, 
status unknown, disappeared); and
     To the extent practicable, photographs or video footage of 
the animal(s).

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

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

Negligible Impact Analysis and Determination

    NMFS has defined negligible impact as an impact resulting from the 
specified activity that cannot be reasonably expected to, and is not 
reasonably likely to, adversely affect the species or stock through 
effects on annual rates of recruitment or survival (50 CFR 216.103). A 
negligible impact finding is based on the lack of likely adverse 
effects on annual rates of recruitment or survival (i.e., population-
level effects). An estimate of the number of takes alone is not enough 
information on which to base an impact determination. In addition to 
considering estimates of the number of marine mammals that might be 
``taken'' through harassment, NMFS considers other factors, such as the 
likely nature of any impacts or responses (e.g., intensity, duration), 
the context of any impacts or responses (e.g., critical reproductive 
time or location, foraging impacts affecting energetics), as well as 
effects on habitat, and the likely effectiveness of the mitigation. We 
also assess the number, intensity, and context of estimated takes by 
evaluating this information relative to population status. Consistent 
with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, 
September 29, 1989), the impacts from other past and ongoing 
anthropogenic activities are incorporated into this analysis via their 
impacts on the baseline (e.g., as reflected in the regulatory status of 
the species, population size and growth rate where known, ongoing 
sources of human-caused mortality, or ambient noise levels).
    To avoid repetition, the discussion of our analysis applies to all 
the species listed in Table 1, given that the anticipated effects of 
this activity on these different marine mammal stocks are expected to 
be similar. Where there are meaningful differences between species or 
stocks they are included as separate subsections below. NMFS does not 
anticipate that serious injury or mortality would occur as a result of 
L-DEO's planned survey, even in the absence of mitigation, and no 
serious injury or mortality is proposed to be authorized. As discussed 
in the Potential Effects of Specified Activities on Marine Mammals and 
Their Habitat section above, non-auditory physical effects and vessel 
strike are not expected to occur. NMFS expects that the majority of 
potential takes would be in the form of short-term Level B behavioral 
harassment, resulting from temporary avoidance of the area or decreased 
foraging (if such activity was occurring), reactions that are 
considered to be of low severity and with no lasting biological 
consequences (e.g., Southall et al., 2007).
    We are proposing to authorize a limited number of Level A 
harassment events of five species in the form of PTS (humpback whale, 
minke whale, sei whale, and Kogia spp), and Level B harassment only of 
the remaining marine mammal species. If any PTS is incurred in marine 
mammals as a result of the planned activity, we expect only a small 
degree of PTS that would not result in severe hearing impairment 
because of the constant movement of both the Langseth and of the marine 
mammals in the project areas, as well as the fact that the vessel is 
not expected to remain in any one area in which individual marine 
mammals would be expected to concentrate for an extended period of 
time. Additionally, L-DEO would shut down the airgun array if marine 
mammals approach within 500 m (with the exception of specific genera of 
dolphins, see Proposed Mitigation), further reducing the expected 
duration and intensity of sound, and therefore the likelihood of marine 
mammals incurring PTS. Since the duration of exposure to loud sounds 
will be relatively short it would be unlikely to affect the fitness of 
any individuals. Also, as described above, we expect that marine 
mammals would likely move away from a sound source that represents an 
aversive stimulus, especially at levels that would be expected to 
result in PTS, given sufficient notice of the Langseth's approach due 
to the vessel's relatively low speed when conducting seismic surveys.
    In addition, the maximum expected Level B harassment zone around 
the survey vessel is 6,733 m for water depths greater than 1,000 m (and 
up to

[[Page 56992]]

10,100 m in water depths of 100 to 1,000 m). Therefore, the ensonified 
area surrounding the vessel is relatively small compared to the overall 
distribution of animals in the area and their use of the habitat. 
Feeding behavior is not likely to be significantly impacted as prey 
species are mobile and are broadly distributed throughout the survey 
area; therefore, marine mammals that may be temporarily displaced 
during survey activities are expected to be able to resume foraging 
once they have moved away from areas with disturbing levels of 
underwater noise. Because of the short duration (24 days) and temporary 
nature of the disturbance and the availability of similar habitat and 
resources in the surrounding area, the impacts to marine mammals and 
the food sources that they utilize are not expected to cause 
significant or long-term consequences for individual marine mammals or 
their populations.
    There are no rookeries, mating, or calving grounds known to be 
biologically important to marine mammals within the survey area and 
there are no feeding areas known to be biologically important to marine 
mammals within the survey area. There is no designated critical habitat 
for any ESA-listed marine mammals in the survey area.

Marine Mammal Species with Active UMEs

    As discussed above, there are several active UMEs occurring in the 
vicinity of L-DEO's survey area. Elevated humpback whale mortalities 
have occurred along the Atlantic coast from Maine through Florida since 
January 2016. Of the cases examined, approximately half had evidence of 
human interaction (ship strike or entanglement). The UME does not yet 
provide cause for concern regarding population-level impacts. Despite 
the UME, the relevant population of humpback whales (the West Indies 
breeding population, or DPS) remains stable at approximately 12,000 
individuals.
    Beginning in January 2017, elevated minke whale strandings have 
occurred along the Atlantic coast from Maine through South Carolina, 
with highest numbers in Massachusetts, Maine, and New York. This event 
does not provide cause for concern regarding population level impacts, 
as the likely population abundance is greater than 20,000 whales, and 
the UME is pending closure. Although, the populations experiencing the 
UME's may not be the same as the populations impacted by the proposed 
survey.
    Additionally, the proposed mitigation measures are expected to 
reduce the number and/or severity of takes for all species listed in 
Table 1, including those with active UMEs, to the level of least 
practicable adverse impact. In particular they would provide animals 
the opportunity to move away from the sound source throughout the 
survey area before seismic survey equipment reaches full energy, thus 
preventing them from being exposed to sound levels that have the 
potential to cause injury (Level A harassment) or more severe Level B 
harassment.
    In summary and as described above, the following factors primarily 
support our preliminary determination that the impacts resulting from 
this activity are not expected to adversely affect any of the species 
or stocks through effects on annual rates of recruitment or survival:
     No serious injury or mortality is anticipated or 
authorized;
     The proposed activity is temporary and of relatively short 
duration (40 days);
     The vast majority of anticipated impacts of the proposed 
activity on marine mammals would be temporary behavioral changes due to 
avoidance of the area around the vessel;
     The availability of alternative areas of similar habitat 
value for marine mammals to temporarily vacate the survey area during 
the proposed survey to avoid exposure to sounds from the activity is 
readily abundant;
     The potential adverse effects on fish or invertebrate 
species that serve as prey species for marine mammals from the proposed 
survey would be temporary and spatially limited, and impacts to marine 
mammal foraging would be minimal;
     The proposed mitigation measures are expected to reduce 
the number of takes by Level A harassment (in the form of PTS) by 
allowing for detection of marine mammals in the vicinity of the vessel 
by visual and acoustic observers; and
     The proposed mitigation measures, including visual and 
acoustic shutdowns are expected to minimize potential impacts to marine 
mammals (both amount and severity).
    Based on the analysis contained herein of the likely effects of the 
specified activity on marine mammals and their habitat, and taking into 
consideration the implementation of the proposed monitoring and 
mitigation measures, NMFS preliminarily finds that the total marine 
mammal take from the proposed activity will have a negligible impact on 
all affected marine mammal species or stocks.

Small Numbers

    As noted previously, only take of small numbers of marine mammals 
may be authorized under sections 101(a)(5)(A) and (D) of the MMPA for 
specified activities other than military readiness activities. The MMPA 
does not define small numbers and so, in practice, where estimated 
numbers are available, NMFS compares the number of individuals taken to 
the most appropriate estimation of abundance of the relevant species or 
stock in our determination of whether an authorization is limited to 
small numbers of marine mammals. When the predicted number of 
individuals to be taken is fewer than one-third of the species or stock 
abundance, the take is considered to be of small numbers. Additionally, 
other qualitative factors may be considered in the analysis, such as 
the temporal or spatial scale of the activities.
    The amount of take NMFS authorizes is below one-third of the 
estimated modeled abundance for all species (in fact, take of 
individuals is less than six percent of the abundance of the affected 
stocks, see Table 6). This is likely a conservative estimate because we 
assume all takes are of different individual animals, which is likely 
not the case. Some individuals may be encountered multiple times in a 
day, but PSOs would count them as separate individuals if they cannot 
be identified.
    Based on the analysis contained herein of the proposed activity 
(including the proposed mitigation and monitoring measures) and the 
anticipated take of marine mammals, NMFS preliminarily finds that small 
numbers of marine mammals would be taken relative to the population 
size of the affected species or stocks.

Unmitigable Adverse Impact Analysis and Determination

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

Endangered Species Act

    Section 7(a)(2) of the Endangered Species Act of 1973 (ESA; 16 
U.S.C. 1531 et seq.) requires that each Federal agency insure that any 
action it authorizes, funds, or carries out is not likely to jeopardize 
the continued existence of any endangered or threatened species or 
result in the

[[Page 56993]]

destruction or adverse modification of designated critical habitat. To 
ensure ESA compliance for the issuance of IHAs, NMFS consults 
internally whenever we propose to authorize take for endangered or 
threatened species, in this case with the ESA Interagency Cooperation 
Division within the NMFS OPR.
    NMFS is proposing to authorize take of blue whales, fin whales, sei 
whales, and sperm whales, which are listed under the ESA. The OPR 
Permits and Conservation Division has requested initiation of section 7 
consultation with the OPR Interagency Cooperation Division for the 
issuance of this IHA. NMFS will conclude the ESA consultation prior to 
reaching a determination regarding the proposed issuance of the 
authorization.

Proposed Authorization

    As a result of these preliminary determinations, NMFS proposes to 
issue an IHA to L-DEO for conducting a marine geophysical survey in 
Puerto Rico in the Northwest Atlantic Ocean during fall of 2023, 
provided the previously mentioned mitigation, monitoring, and reporting 
requirements are incorporated. A draft of the proposed IHA can be found 
at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities.

Request for Public Comments

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

    Dated: August 15, 2023.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2023-17836 Filed 8-18-23; 8:45 am]
BILLING CODE 3510-22-P