[Federal Register Volume 88, Number 56 (Thursday, March 23, 2023)]
[Notices]
[Pages 17646-17677]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-05966]



[[Page 17645]]

Vol. 88

Thursday,

No. 56

March 23, 2023

Part II





Department of Commerce





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National Oceanic and Atmospheric Administration





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Takes of Marine Mammals Incidental to Specified Activities; Taking 
Marine Mammals Incidental to a Marine Geophysical Survey Off North 
Carolina in the Northwest Atlantic Ocean; Notice

  Federal Register / Vol. 88, No. 56 / Thursday, March 23, 2023 / 
Notices  

[[Page 17646]]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XC686]


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

DATES: Comments and information must be received no later than April 
24, 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].
    Instructions: NMFS is not responsible for comments sent by any 
other method, to any other address or individual, or received after the 
end of the comment period. Comments, including all attachments, must 
not exceed a 25-megabyte file size. All comments received are a part of 
the public record and will generally be posted online at 
www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act without change. All personal identifying 
information (e.g., name, address) voluntarily submitted by the 
commenter may be publicly accessible. Do not submit confidential 
business information or otherwise sensitive or protected information.

FOR FURTHER INFORMATION CONTACT: Rachel Wachtendonk, Office of 
Protected Resources, NMFS, (301) 427-8401. Electronic copies of the 
application and supporting documents, as well as a list of the 
references cited in this document, may be obtained online at: 
www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities. In case of problems 
accessing these documents, please call the contact listed above.

SUPPLEMENTARY INFORMATION: 

Background

    The MMPA prohibits the ``take'' of marine mammals, with certain 
exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 
et seq.) direct the Secretary of Commerce (as delegated to NMFS) to 
allow, upon request, the incidental, but not intentional, taking of 
small numbers of marine mammals by U.S. citizens who engage in a 
specified activity (other than commercial fishing) within a specified 
geographical region if certain findings are made and either regulations 
are proposed or, if the taking is limited to harassment, a notice of a 
proposed 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), provided our independent 
evaluation of the document finds that it includes adequate information 
analyzing the effects on the human environment of issuing the IHA. 
NSF's EA was made available for public comment from January 27, 2023 to 
February 26, 2023, additionally, notice was sent to the South and Mid 
Atlantic Fishery Management Councils, the North Carolina state clearing 
house, the North Carolina Coastal Zone Management Program Office, and 
North Carolina Department of Environment and Natural Resources. NSF's 
EA can be viewed at https://www.nsf.gov/geo/oce/envcomp/north-carolina-2023/LDEO-NC-EA-7-Oct2022.pdf.

Summary of Request

    On October 12, 2022, NMFS received a request from L-DEO for an IHA 
to take marine mammals incidental to a marine geophysical survey off 
the coast of North Carolina in the northwest Atlantic Ocean. The 
application was deemed adequate and complete on January 13, 2023. L-
DEO's request is for the take of 30 species of marine mammals by Level 
B harassment and, for 2 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.
    NMFS previously issued an IHA to L-DEO for similar work in the same 
region (79 FR 57512; November 25, 2014). L-DEO complied with all the 
requirements (e.g., mitigation, monitoring, and reporting) of the 
previous IHA.

Description of Proposed Activity

Overview

    Researchers from the University of Texas at Austin (UT) and L-DEO, 
with funding from the NSF, and in collaboration with international and 
domestic researchers including the United States Geological Survey 
(USGS), 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 surveys would occur off North 
Carolina in the northwestern Atlantic Ocean during Spring/Summer 2023. 
The proposed multi-channel seismic (MCS) reflection survey would occur 
within the Exclusive Economic Zone (EEZ) of the United States and in 
International Waters, in depths ranging from 200 to

[[Page 17647]]

5,500 meters (m). To complete this survey, the R/V Langseth would tow 
an 18-airgun array consisting of Bolt airguns ranging from 40-360 cubic 
inch (in\3\) each on two strings spaced 6 m apart, with a total 
discharge volume of 3,300 in\3\. The acoustic source would be towed at 
6 m deep along the survey lines, while the receiving system would 
consist of a 5 kilometer (km) solid-state hydrophone streamer towed at 
a depth of 6 m and a 600 m long solid-state hydrophone streamer towed 
at a depth of 2 to 3 m.
    The proposed study would acquire high-resolution two-dimensional 
(2-D) seismic reflection data to examine large submarine landslide 
behavior over the past 23 million years in the Cape Fear submarine 
slide complex off North Carolina, which has experienced large, recent 
submarine landslides. Additional data would be collected using 
echosounders, piston cores, and magnetic, gravity, and heat flow 
measurements. No take of marine mammals is expected to result from use 
of this equipment.

Dates and Duration

    The proposed survey is expected to last for 33 days, with 
approximately 28 days of seismic operations, 3 days of piston coring 
and heat flow measurements, and 2 days of transit. R/V Langseth would 
likely leave from and return to port in Norfolk, VA, during spring/
summer 2023.

Specific Geographic Region

    The proposed survey would occur within ~31-35[deg] N, ~72-75[deg] W 
off the coast of North Carolina in the Northwest Atlantic Ocean. The 
closest point of approach of the proposed survey area to the coast 
would be approximately 40 km (from Cape Hatteras, North Carolina). 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. The surveys are proposed to occur within the EEZ of the U.S. 
and in international waters, in depths ranging from 200-5,500 m deep.
BILLING CODE 3510-22-P
[GRAPHIC] [TIFF OMITTED] TN23MR23.004


[[Page 17648]]


BILLING CODE 3510-22-C

Detailed Description of the Specified Activity

    The procedures to be used for the proposed surveys would be similar 
to those used during previous seismic surveys by L-DEO and would use 
conventional seismic methodology. The surveys would involve one source 
vessel, R/V Langseth, which is owned and operated by L-DEO. R/V 
Langseth would deploy eighteen 40 to 360 in\3\ Bolt airguns on two 
strings as an energy source with a total volume of ~3300 in\3\. The 2 
airgun strings would be spaced 6 m apart and distributed across an area 
of 6 x 16 m behind the R/V Langseth and would be towed approximately 
140 m behind the vessel. The array would be towed at a depth of 6 m, 
and the shot interval would be 25 m (~10 seconds (s)). The airgun array 
configuration is 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 5 km solid-state hydrophone 
streamer (solid flexible polymer) towed at a depth of 6 m and a 600 m 
long solid-state hydrophone streamer towed at a depth of 2 to 3 m. As 
the airguns are towed along the survey lines, the hydrophone streamer 
would transfer data to the on-board processing system.
    Approximately 6,083 km of transect lines are proposed for the study 
area. All survey effort would occur in water deeper than 100 m, with 10 
percent (629 km) in intermediate water (100-1,000 m) and 90 percent 
(5,454 km) in deep water (>1,000 m). Approximately 10 percent of 
seismic acquisition would occur in International Waters beyond the U.S. 
Exclusive Economic Zone. In addition to the operations of the airgun 
array, the ocean floor would be mapped with the Kongsberg EM 122 
multibeam echosounder (MBES) and a Knudsen Chirp 3260 sub-bottom 
profiler (SBP). A Teledyne RDI 75 kilohertz (kHz) Ocean Surveyor 
Acoustic Doppler Current Profiler (ADCP) would be used to measure water 
current velocities.
    Approximately 10-20 cores would be collected throughout the survey 
area above locations where strong Bottom Simulating Reflectors (BSR) 
have been imaged and/or near the locations of seafloor gas seeps; the 
locations would be determined during the cruise based on the seismic 
data collected. Coring operations would include collection of gravity 
and piston cores at coring sites. The piston corer would consist of a 
12 m long core pipe that takes a core sample 10 centimeter (cm) in 
diameter, and a weight stand. The core pipe would weigh about 70 
kilograms (kg) and the weight stand would weigh approximately 1,270 kg 
and is 90 cm in diameter. A piston corer would be lowered by wire to 
near the seabed where a tripping mechanism would release the corer and 
allow it to fall to the seabed, where the heavy weight stand would 
drive the core pipe into the seabed. A sliding piston inside the core 
barrel would reduce inside wall friction with the sediment and assist 
in the evacuation of displaced water from the top of the corer. The 
gravity corer would consist of a 3 m long core pipe that takes a core 
sample 10 cm in diameter, a head weight about 45 cm in diameter, and a 
stabilizing fin. It would ``free fall'' from the vessel, and its 
stabilizing fin would ensure that the corer penetrates the seabed in a 
straight line. The coring equipment would be deployed over the side of 
the vessel with standard oceanographic wire. The wire would be taut 
with the weight of the equipment preventing species entanglements. 
Thermal data would be collected with outrigger temperature probes 
mounted to the outside of a piston core barrel.
    All planned geophysical data acquisition activities would be 
conducted by L-DEO with on-board assistance by the scientists who have 
proposed the studies. The vessel would be self-contained, and the crew 
would live aboard the vessel. 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 L-DEO's application summarize available 
information regarding status and trends, distribution and habitat 
preferences, and behavior and life history, of the potentially affected 
species. Additional information regarding population trends and threats 
may be found in NMFS' Stock Assessment Reports (SARs; 
www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments) and more general information about these species 
(e.g., physical and behavioral descriptions) may be found on NMFS' 
website (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 expected to occur, PBR 
and annual serious injury and mortality from anthropogenic sources are 
included here as gross indicators of the status of the species or 
stocks and other threats.
    Marine mammal abundance estimates presented in this document 
represent the total number of individuals that make up a given stock or 
the total number estimated within a particular study or survey area. 
NMFS' stock abundance estimates for most species represent the total 
estimate of individuals within the geographic area, if known, that 
comprises that stock. For some species, this geographic area may extend 
beyond U.S. waters. All stocks managed under the MMPA in this region 
are assessed in NMFS' U.S. 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: www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

[[Page 17649]]



                                              Table 1--Species Likely Impacted by the Specified Activities
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                                                                                         ESA/ MMPA status;   Stock abundance (CV,
             Common name                  Scientific name               Stock             strategic (Y/N)      Nmin, most recent       PBR     Annual M/
                                                                                                \1\          abundance survey) \2\               SI \3\
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                                          Order Cetartiodactyla--Cetacea--Superfamily Mysticeti (baleen whales)
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Family Balaenopteridae (rorquals):
Humpback whale......................  Megaptera novaeangliae.  Gulf of Maine..........  -/-; N              1,396 (0; 1,380; 2016)         22      12.15
Fin whale...........................  Balaenoptera physalus..  Western North Atlantic.  E/D; Y              6,802 (0.24; 5,573;            11        1.8
                                                                                                             2016).
Sei whale...........................  Balaenoptera borealis..  Nova Scotia............  E/D; Y              6,292 (1.02; 3,098;           6.2        0.8
                                                                                                             2016).
Minke whale.........................  Balaenoptera             Canadian East Coast....  -/-; N              21,968 (0.31; 17,002;         170       10.6
                                       acutorostrata.                                                        2016).
Blue whale..........................  Balaenoptera musculus..  Western North Atlantic.  E/D;Y               unk (unk; 402; 1980-          0.8          0
                                                                                                             2008).
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                                            Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Physeteridae:
Sperm whale.........................  Physeter macrocephalus.  North Atlantic.........  E/D;Y               4,349 (0.28; 3,451;           3.9          0
                                                                                                             2016).
Family Kogiidae:
Pygmy sperm whale...................  Kogia breviceps........  Western North Atlantic.  -/-; N              7,750 (0.38; 5,689;            46          0
                                                                                                             2016).
Dwarf sperm whale...................  Kogia sima.............  Western North Atlantic.  -/-; N              7,750 (0.38; 5,689;            46          0
                                                                                                             2016).
Family Ziphiidae (beaked whales):
Cuvier's beaked Whale...............  Ziphius cavirostris....  Western North Atlantic.  -/-; N              5,744 (0.36, 4,282,            43        0.2
                                                                                                             2016).
Blainville's beaked Whale...........  Mesoplodon densirostris  Western North Atlantic.  -/-; N              10,107 (0.27; 8,085;           81          0
                                                                                                             2016).
True's beaked whale.................  Mesoplodon mirus.......  Western North Atlantic.  -/-; N              10,107 (0.27; 8,085;           81          0
                                                                                                             2016).
Gervais' beaked whale...............  Mesoplodon europaeus...  Western North Atlantic.  -/-; N              10,107 (0.27; 8,085;           81          0
                                                                                                             2016).
Family Delphinidae:
Long-finned pilot whale.............  Globicephala melas.....  Western North Atlantic.  -/-; N              39,215 (0.30; 30,627;         306          9
                                                                                                             2016).
Short finned pilot whale............  Globicephala             Western North Atlantic.  -/-;Y               28,924 (0.24; 23,637;         236        136
                                       macrorhynchus.                                                        2016).
Rough-toothed dolphin...............  Steno bredanensis......  Western North Atlantic.  -/-; N              136 (1.0; 67; 2016)...        0.7          0
Bottlenose dolphin..................  Tursiops truncates.....  Western North Atlantic   -/-; N              62,851 (0.23; 51,914,         519         28
                                                                Offshore.                                    2016).
Atlantic white-sided dolphin........  Lagenorhynchus acutus..  Western North Atlantic.  -/-; N              93,233 (0.71; 54,443;         544         27
                                                                                                             2016).
Pantropical spotted dolphin.........  Stenella attenuate.....  Western North Atlantic.  -/-; N              6,593 (0.52; 4,367;            44          0
                                                                                                             2016).
Atlantic spotted dolphin............  Stenella frontalis.....  Western North Atlantic.  -/-; N              39,921 (0.27; 32,032;         320          0
                                                                                                             2016).
Spinner dolphin.....................  Stenella longirostris..  Western North Atlantic.  -/-; N              4,102 (0.99; 2,045;            21          0
                                                                                                             2016).
Clymene dolphin.....................  Stenella clymene.......  Western North Atlantic.  -/-; N              4,237 (1.03; 2,071;            21          0
                                                                                                             2016).
Striped dolphin.....................  Stenella coeruleoalba..  Western North Atlantic.  -/-; N              67,036 (0.29; 52,939;         529          0
                                                                                                             2016).
Fraser's dolphin....................  Lagenodelphis hosei....  Western North Atlantic.  -/-; N              unk...................        unk          0
Risso's dolphin.....................  Grampus griseus........  Western North Atlantic.  -/-; N              35,215(0.19; 30,051;          301         34
                                                                                                             2016).
Common dolphin......................  Delphinus delphis......  Western North Atlantic.  -/-; N              172,947 (0.21;              1,452        390
                                                                                                             145,216; 2016).
Melon-headed whale..................  Peponocephala electra..  Western North Atlantic.  -/-; N              unk...................        unk          0
Pygmy killer whale..................  Feresa attenuate.......  Western North Atlantic.  -/-; N              unk...................        unk          0
False killer whale..................  Pseudorca crassidens...  Western North Atlantic.  -/-; N              1,791 (0.56; 1,154;            12          0
                                                                                                             2016).
Killer whale........................  Orcinus orca...........  Western North Atlantic.  -/-; N              unk...................        unk          0
Family Phocoenidae (porpoises):
Harbor porpoise.....................  Phocoena phocoena......  Gulf of Maine/Bay of     -/-; N              95,543 (0.31; 74,034;         851        164
                                                                Fundy.                                       2016).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed
  under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality
  exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed
  under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\2\ NMFS marine mammal stock assessment reports online at: www.nmfs.noaa.gov/pr/sars/. CV is coefficient of variation; Nmin is the minimum estimate of
  stock abundance.
\3\These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g., commercial
  fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated
  with estimated mortality due to commercial fisheries is presented in some cases.

    As indicated above, all 30 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 North Carolina), or because their known 
migration through the area does not align with the proposed survey 
dates, are described briefly but omitted from further analysis. These 
generally include species that do not normally occur in the area, but 
for which there are one or more occurrence records that are considered 
beyond the normal range of the species. These species include northern 
bottlenose whales (Hyperoodon ampullatus), Sowerby's

[[Page 17650]]

beaked whales (Mesoplodon bidens), white-beaked dolphins 
(Lagenorhynchus albirostris), harp seals (Pagophilus groenlandicus), 
hooded seals (Cystophora cristata), gray seals (Halichoerus grypus), 
and harbor seals (Phoca vitulina), which are all typically distributed 
further north on the eastern coast of the United States.
    This also includes the North Atlantic right whale (Eubalaena 
glacialis), as their migration through waters directly adjacent to the 
study area does not align with the proposed survey dates. Based on the 
timing of migratory behavior relative to the proposed survey, in 
conjunction with the location of the survey in primarily deep waters 
beyond the shelf, no right whales would be expected to be subject to 
take incidental to the survey. A quantitative, density-based analysis 
confirms these conclusions (see Estimated Take, later in this notice).
    Elevated North Atlantic right whale mortalities have occurred since 
June 7, 2017, along the U.S. and Canadian coast. This event has been 
declared an Unusual Mortality Event (UME), with human interactions, 
including entanglement in fixed fishing gear and vessel strikes, 
implicated in at least 20 of the mortalities thus far. As of February 
14, 2023, a total of 36 confirmed dead stranded whales (21 in Canada; 
15 in the United States) have been documented. The cumulative total 
number of animals in the North Atlantic right whale UME has been 
updated to 57 individuals to include both the confirmed mortalities 
(dead stranded or floaters) (n=36) and seriously injured free-swimming 
whales (n=22) to better reflect the confirmed number of whales likely 
removed from the population during the UME and more accurately reflect 
the population impacts. More information is available online at: 
www.fisheries.noaa.gov/national/marine-life-distress/2017-2022-north-atlantic-right-whale-unusual-mortality-event.
    The offshore waters of North Carolina, including waters adjacent to 
the survey area, are used as part of the migration corridor for right 
whales. Right whales occur here during seasonal movements north or 
south between their feeding and breeding grounds (Firestone et al. 
2008; Knowlton et al. 2002). Right whales have been observed in or near 
North Carolina waters from October through December, as well as in 
February and March, which coincides with the migratory timeframe for 
this species (Knowlton et al. 2002). They have been acoustically 
detected off Georgia and North Carolina in 7 of 11 months monitored 
(Hodge et al. 2015) and other recent passive acoustic studies of right 
whales off the Virginia coast demonstrate their year-round presence in 
Virginia (Salisbury et al. 2018), with increased detections in fall and 
late winter/early spring. They are typically most common in the spring 
(late March) when they are migrating north and, in the fall (i.e., 
October and November) during their southbound migration (NOAA Fisheries 
2017).
    There are no seasonal management areas (SMA) designated within the 
proposed survey area, however vessel transit routes do spatially 
overlap with one SMA, which exists from November 1 through April 30 
within a 20-nautical mile (nmi) (37 km) radius of the entrance to the 
Chesapeake Bay, which leads to the port in Norfolk, VA. L-DEO intends 
to complete the survey before November 1, 2023, and NMFS proposes that 
use of airguns be limited to the period May 1 through October 31. The 
regulations identifying SMAs (50 CFR 224.105) also establish a process 
under which dynamic management areas (DMA) can be established based on 
North Atlantic right whale sightings. NMFS established a Slow Zone 
program in 2020 that notifies vessel operators of areas where 
maintaining speeds of 10 knots (kn) or less can help protect North 
Atlantic right whales from vessel collisions. Right Whale Slow Zones 
are established around areas where right whales have been recently seen 
or heard; these areas are identical to DMAs when triggered by right 
whale visual sightings but they can also be established when right 
whale detections are confirmed from acoustic receivers. More 
information on SMAs, DMAs, and Slow Zones can be found at: https://
www.fisheries.noaa.gov/national/endangered-species-conservation/
reducing-vessel-strikes-north-atlantic-right-
whales#:~:text=Right%20Whale%20Slow%20Zones%20is,right%20whales%20have%2
0been%20detected.
    On August 1, 2022, NMFS announced proposed changes to the existing 
North Atlantic right whale vessel speed regulations to further reduce 
the likelihood of mortalities and serious injuries to endangered right 
whales from vessel collisions, which are a leading cause of the 
species' decline and a primary factor in an ongoing UME (87 FR 46921). 
Should a final vessel speed rule be issued and become effective during 
the effective period of this IHA (or any other MMPA incidental take 
authorization), the authorization holder would be required to comply 
with any and all applicable requirements contained within the final 
rule. Specifically, where measures in any final vessel speed rule are 
more protective or restrictive than those in this or any other MMPA 
authorization, authorization holders would be required to comply with 
the requirements of the rule. Alternatively, where measures in this or 
any other MMPA authorization are more restrictive or protective than 
those in any final vessel speed rule, the measures in the MMPA 
authorization would remain in place. The responsibility to comply with 
the applicable requirements of any vessel speed rule would become 
effective immediately upon the effective date of any final vessel speed 
rule and, when notice is published of the effective date, NMFS would 
also notify L-DEO if the measures in the speed rule were to supersede 
any of the measures in the MMPA authorization such that they were no 
longer applicable.
    The proposed survey area is also adjacent to the migratory corridor 
Biologically Important Area (BIA) identified for North Atlantic right 
whales that extends from Massachusetts to Florida in March-April and 
November-December (LeBrecque et al., 2015). This important migratory 
area is approximately 269,488 km\2\ in and is comprised of the waters 
of the continental shelf offshore the East Coast of the United States, 
extending from Florida through Massachusetts. During their migration, 
North Atlantic right whales prefer shallower waters, with the majority 
of sightings occurring within 56 km of the coast and in water depths 
shallower than 45 m. When whales are seen further offshore, it is in 
the northern part of their migratory path south of New England. 
Comparatively, this survey would occur at a minimum of 40 km off the 
coast in water depths ranging from 200 m to 5,550 m, with 90 percent of 
the survey taking place in depths greater than 1,000 m. No critical 
habitat is designated within the survey area.

Humpback Whale

    Humpback whales are found worldwide in all oceans. The worldwide 
population is divided into northern and southern ocean populations, but 
genetic analyses suggest some gene flow (either past or present) 
between the North and South Pacific (e.g., Jackson et al., 2014; 
Bettriddge et al., 2015). Although considered to be mainly a coastal 
species, humpback whales often traverse deep pelagic areas while 
migrating (Calambokidis et al., 2001; Garrigue et al., 2002; Zerbini et 
al., 2011). Humpbacks migrate between summer feeding grounds in high 
latitudes and winter calving and breeding grounds in tropical waters

[[Page 17651]]

(Clapham and Mead 1999). In the western North Atlantic, humpback whales 
feed during spring, summer and fall over a geographic range 
encompassing the eastern coast of the United States (including the Gulf 
of Maine), the Gulf of St. Lawrence, Newfoundland/Labrador, and western 
Greenland (Katona and Beard 1990). 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 one 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.
    The Gulf of Maine stock of humpback whales, a feeding population of 
the West Indies DPS, occurs primarily in the southern Gulf of Maine and 
east of Cape Cod during summers to feed (Clapham et al. 1993; Hayes et 
al. 2020). Off North Carolina, most sightings of humpback whales have 
been reported for winter and mostly nearshore (DoN 2008a,b; Conley et 
al. 2017); there were fewer sightings in spring, most along the shelf 
break or in deep, offshore water (DoN 2008a,b). There were no sightings 
in summer, and several sightings occurred nearshore during fall (DoN 
2008a,b). Summer surveys by the Northeast Fisheries Science Center 
(NEFSC) and Southeast Fisheries Science Center (SEFSC) show no 
sightings of humpback whales for North Carolina (Hayes et al. 2020). 
One satellite-tagged humpback whale transited through the study area 
during January 2021 (DoN 2022). Davis et al. (2020) detected humpback 
whales acoustically off North Carolina during all seasons, with the 
greatest number of detections during winter and spring. Summer (May-
July) and fall (August-October) had fewer detections. There are three 
records in the Ocean Biodiversity Information System (OBIS) database 
for the proposed survey area--one each during April, May, and July 
(OBIS 2022). Humpback whales present in waters off the U.S. Mid-
Atlantic are members of the West Indies DPS, but could be from multiple 
feeding populations (i.e., are not necessarily part of the Gulf of 
Maine stock).
    Since January 2016, elevated humpback whale mortalities have 
occurred along the Atlantic coast from Maine to Florida. Partial or 
full necropsy examinations have been conducted on approximately half of 
the 187 known cases. Of the whales examined, about 50 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 previous UMEs involving humpback whales 
have occurred since 2000, in 2003, 2005, and 2006. More information is 
available at: www.fisheries.noaa.gov/national/marine-life-distress/2016-2021-humpback-whale-unusual-mortality-event-along-atlantic-coast.

Minke Whale

    The minke whale has a cosmopolitan distribution that spans from 
tropical to polar regions in both hemispheres (Jefferson et al., 2015). 
In the Northern Hemisphere, the minke whale is usually seen in coastal 
areas, but can also be seen in pelagic waters during its northward 
migration in spring and summer and southward migration in autumn 
(Stewart and Leatherwood, 1985). The Canadian East Coast stock can be 
found in the area from the western half of the Davis Strait (45 [deg]W) 
to the Gulf of Mexico (Hayes et al., 2020). Little is known about minke 
whales' specific movements through the Mid-Atlantic region; however, 
there appears to be a strong seasonal component to minke whale 
distribution, with acoustic detections indicating that they migrate 
south in mid-October to early November, and return from wintering 
grounds starting in March through early April (Hayes et al., 2020). 
Northward migration appears to track the warmer waters of the Gulf 
Stream along the continental shelf, while southward migration is made 
farther offshore (Risch et al., 2014).
    Since January 2017, elevated minke whale mortalities have occurred 
along the U.S. Atlantic coast from Maine through South Carolina, with a 
total of 140 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: 
www.fisheries.noaa.gov/national/marine-life-distress/2017-2021-minke-whale-unusual-mortality-event-along-atlantic-coast.

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.

[[Page 17652]]



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

Description of Active Acoustic Sound Sources

    This section contains a brief technical background on sound, the 
characteristics of certain sound types, and on metrics used in this 
proposal inasmuch as the information is relevant to the specified 
activity and to a discussion of the potential effects of the specified 
activity on marine mammals found later in this document.
    Sound travels in waves, the basic components of which are 
frequency, wavelength, velocity, and amplitude. Frequency is the number 
of pressure waves that pass by a reference point per unit of time and 
is measured in hertz (Hz) or cycles per second. Wavelength is the 
distance between two peaks or corresponding points of a sound wave 
(length of one cycle). Higher frequency sounds have shorter wavelengths 
than lower frequency sounds, and typically attenuate (decrease) more 
rapidly, except in certain cases in shallower water. Amplitude is the 
height of the sound pressure wave or the ``loudness'' of a sound and is 
typically described using the relative unit of the dB. A sound pressure 
level (SPL) in dB is described as the ratio between a measured pressure 
and a reference pressure (for underwater sound, this is 1 microPascal 
([mu]Pa)) and is a logarithmic unit that accounts for large variations 
in amplitude; therefore, a relatively small change in dB corresponds to 
large changes in sound pressure. The source level (SL) represents the 
SPL referenced at a distance of 1 m from the source (referenced to 1 
[mu]Pa) while the received level is the SPL at the listener's position 
(referenced to 1 [mu]Pa).
    Root mean square (rms) is the quadratic mean sound pressure over 
the duration of an impulse. Root mean square is calculated by squaring 
all of the sound amplitudes, averaging the squares, and then taking the 
square root of the average (Urick, 1983). Root mean square accounts for 
both positive and negative values; squaring the pressures makes all 
values positive so that they may be accounted for in the summation of 
pressure levels (Hastings and Popper, 2005). This measurement is often 
used in the context of discussing behavioral effects, in part because 
behavioral effects, which often result from auditory cues, may be 
better expressed through averaged units than by peak pressures.
    Sound exposure level (SEL; represented as dB re 1 [mu]Pa\2\-s) 
represents the total energy contained within a pulse and considers both 
intensity and duration of exposure. Peak sound pressure (also referred 
to as zero-to-peak sound pressure or 0-p) is the maximum instantaneous 
sound pressure measurable in the water at a specified distance from the 
source and is represented in the same units as the rms sound pressure. 
Another common metric is peak-to-peak sound pressure (pk-pk), which is 
the algebraic difference between the peak positive and peak negative 
sound pressures. Peak-to-peak pressure is typically approximately 6 dB 
higher than peak pressure (Southall et al., 2007).
    When underwater objects vibrate or activity occurs, sound-pressure 
waves are created. These waves alternately compress and decompress the 
water as the sound wave travels. Underwater sound waves radiate in a 
manner similar to ripples on the surface of a pond and may be either 
directed in a beam or beams or may radiate in all directions 
(omnidirectional sources), as is the case for pulses produced by the 
airgun arrays considered here. The compressions and decompressions 
associated with sound waves are detected as changes in pressure by 
aquatic life and man-made sound receptors such as hydrophones.
    Even in the absence of sound from the specified activity, the 
underwater environment is typically loud due to ambient sound. Ambient 
sound is defined as environmental background sound levels lacking a 
single source or point (Richardson et al., 1995), and the sound level 
of a region is defined by the total acoustical energy being generated 
by known and unknown sources. These sources may include physical (e.g., 
wind and waves, earthquakes, ice, atmospheric sound), biological (e.g., 
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

[[Page 17653]]

important near shore, with measurements collected at a distance of 8.5 
km from shore showing an increase of 10 dB in the 100 to 700 Hz band 
during heavy surf conditions;
     Precipitation: Sound from rain and hail impacting the 
water surface can become an important component of total sound at 
frequencies above 500 Hz, and possibly down to 100 Hz during quiet 
times;
     Biological: Marine mammals can contribute significantly to 
ambient sound levels, as can some fish and snapping shrimp. The 
frequency band for biological contributions is from approximately 12 Hz 
to over 100 kHz; and
     Anthropogenic: Sources of ambient sound related to human 
activity include transportation (surface vessels), dredging and 
construction, oil and gas drilling and production, seismic surveys, 
sonar, explosions, and ocean acoustic studies. Vessel noise typically 
dominates the total ambient sound for frequencies between 20 and 300 
Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz 
and, if higher frequency sound levels are created, they attenuate 
rapidly. Sound from identifiable anthropogenic sources other than the 
activity of interest (e.g., a passing vessel) is sometimes termed 
background sound, as opposed to ambient sound.
    The sum of the various natural and anthropogenic sound sources at 
any given location and time--which comprise ``ambient'' or 
``background'' sound--depends not only on the source levels (as 
determined by current weather conditions and levels of biological and 
human activity) but also on the ability of sound to propagate through 
the environment. In turn, sound propagation is dependent on the 
spatially and temporally varying properties of the water column and sea 
floor, and is frequency-dependent. As a result of 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 (defined in the following). The distinction 
between these two sound types is important because they have differing 
potential to cause physical effects, particularly with regard to 
hearing (e.g., Ward, 1997 in Southall et al., 2007). Please see 
Southall et al., (2007) for an in-depth discussion of these concepts.
    Pulsed sound sources (e.g., airguns, explosions, gunshots, sonic 
booms, impact pile driving) produce signals that are brief (typically 
considered to be less than one second), broadband, atonal transients 
(ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur 
either as isolated events or repeated in some succession. Pulsed sounds 
are all characterized by a relatively rapid rise from ambient pressure 
to a maximal pressure value followed by a rapid decay period that may 
include a period of diminishing, oscillating maximal and minimal 
pressures, and generally have an increased capacity to induce physical 
injury as compared with sounds that lack these features.
    Non-pulsed sounds can be tonal, narrowband, or broadband, brief or 
prolonged, and may be either continuous or non-continuous (ANSI, 1995; 
NIOSH, 1998). Some of these non-pulsed sounds can be transient signals 
of short duration but without the essential properties of pulses (e.g., 
rapid rise time). Examples of non-pulsed sounds include those produced 
by vessels, aircraft, machinery operations such as drilling or 
dredging, vibratory pile driving, and active sonar systems (such as 
those used by the U.S. Navy). The duration of such sounds, as received 
at a distance, can be greatly extended in a highly reverberant 
environment.
    Airgun arrays produce pulsed signals with energy in a frequency 
range from about 10-2,000 Hz, with most energy radiated at frequencies 
below 200 Hz. The amplitude of the acoustic wave emitted from the 
source is equal in all directions (i.e., omnidirectional), but airgun 
arrays do possess some directionality due to different phase delays 
between guns in different directions. Airgun arrays are typically tuned 
to maximize functionality for data acquisition purposes, meaning that 
sound transmitted in horizontal directions and at higher frequencies is 
minimized to the extent possible.

Acoustic Effects

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

[[Page 17654]]

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 impulse sounds (such as airgun pulses as 
received close to the source) are at least 6 dB higher than the TTS 
threshold on a peak-pressure basis and PTS cumulative sound exposure 
level thresholds are 15 to 20 dB higher than TTS cumulative sound 
exposure level thresholds (Southall et al., 2007). Given the higher 
level of sound or longer exposure duration necessary to cause PTS as 
compared with TTS, it is considerably less likely that PTS could occur.
    For mid-frequency cetaceans in particular, potential protective 
mechanisms may help limit onset of TTS or prevent onset of PTS. Such 
mechanisms include dampening of hearing, auditory adaptation, or 
behavioral amelioration (e.g., Nachtigall and Supin, 2013; Miller et 
al., 2012; Finneran et al., 2015; Popov et al., 2016).
    Temporary TS is the mildest form of hearing impairment that can 
occur during exposure to sound (Kryter, 1985). While experiencing TTS, 
the hearing threshold rises, and a sound must be at a higher level in 
order to be heard. In terrestrial and marine mammals, TTS can last from 
minutes or hours to days (in cases of strong TTS). In many cases, 
hearing sensitivity recovers rapidly after exposure to the sound ends. 
Few data on sound levels and durations necessary to elicit mild TTS 
have been obtained for marine mammals.
    Marine mammal hearing plays a critical role in communication with 
conspecifics, and interpretation of environmental cues for purposes 
such as predator avoidance and prey capture. Depending on the degree 
(elevation of threshold in dB), duration (i.e., recovery time), and 
frequency range of TTS, and the context in which it is experienced, TTS 
can have effects on marine mammals ranging from discountable to 
serious. For example, a marine mammal may be able to readily compensate 
for a brief, relatively small amount of TTS in a non-critical frequency 
range that occurs during a time where ambient noise is lower and there 
are not as many competing sounds present. Alternatively, a larger 
amount and longer duration of TTS sustained during time when 
communication is critical for successful mother/calf interactions could 
have more serious impacts.
    Finneran et al. (2015) \2\ measured hearing thresholds in three 
captive bottlenose dolphins before and after exposure to ten pulses 
produced by a seismic airgun in order to study TTS induced after 
exposure to multiple pulses. Exposures began at relatively low levels 
and gradually increased over a period of several months, with the 
highest exposures at peak SPLs from 196 to 210 dB and cumulative 
(unweighted) SELs from 193-195 dB. No substantial TTS was observed. In 
addition, behavioral reactions were observed that indicated that 
animals can learn behaviors that effectively mitigate noise exposures 
(although exposure patterns must be learned, which is less likely in 
wild animals than for the captive animals considered in this study). 
The authors note that the failure to induce more significant auditory 
effects 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.
---------------------------------------------------------------------------

    \2\ Note that, in the following discussion, we refer in many 
cases to Finneran (2015), a review article concerning studies of 
noise-induced hearing loss conducted from 1996-2015. For study-
specific citations, please see Finneran (2015).
---------------------------------------------------------------------------

    Currently, TTS data only exist for four species of cetaceans 
(bottlenose dolphin, beluga whale, harbor porpoise, and Yangtze finless 
porpoise) 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

[[Page 17655]]

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., 2013a, b). Variations in dive behavior may reflect disruptions in 
biologically significant activities (e.g., foraging) or they may be of 
little biological significance. The impact of an alteration to dive 
behavior resulting from an acoustic exposure depends on what the animal 
is doing at the time of the exposure and the type and magnitude of the 
response.
    Disruption of feeding behavior can be difficult to correlate with 
anthropogenic sound exposure, so it is usually inferred by observed 
displacement from known foraging areas, the appearance of secondary 
indicators (e.g., bubble nets or sediment plumes), or changes in dive 
behavior. As for other types of behavioral response, the frequency, 
duration, and temporal pattern of signal presentation, as well as 
differences in species sensitivity, are likely contributing factors to 
differences in response in any given circumstance (e.g., Croll et al., 
2001; Nowacek et al.; 2004; Madsen et al., 2006; Yazvenko et al., 
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 (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

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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 breeding activity was disrupted 
to some extent by the survey activity.
    Castellote et al., (2012) reported acoustic and behavioral changes 
by fin whales in response to shipping and airgun noise. Acoustic 
features of fin whale song notes recorded in the Mediterranean Sea and 
northeast Atlantic Ocean were compared for areas with different 
shipping noise levels and traffic intensities and during a seismic 
airgun survey. During the first 72 hours of the survey, a steady 
decrease in song received levels and bearings to singers indicated that 
whales moved away from the acoustic source and out of the study area. 
This displacement persisted for a time period well beyond the 10-day 
duration of seismic airgun activity, providing evidence that fin whales 
may avoid an area for an extended period in the presence of increased 
noise. The authors hypothesize that fin whale acoustic communication is 
modified to compensate for increased background noise and that a 
sensitization process may play a role in the observed temporary 
displacement.
    Seismic pulses at average received levels of 131 dB re 1 [mu]Pa\2\-
s caused blue whales to increase call production (Di Iorio and Clark, 
2010). In contrast, McDonald et al. (1995) tracked a blue whale with 
seafloor seismometers and reported that it stopped vocalizing and 
changed its travel direction at a range of 10 km from the acoustic 
source vessel (estimated received level 143 dB pk-pk). Blackwell et al. 
(2013) found that bowhead whale call rates dropped significantly at 
onset of airgun use at sites with a median distance of 41-45 km from 
the survey. Blackwell et al. (2015) expanded this analysis to show that 
whales actually increased calling rates as soon as airgun signals were 
detectable before ultimately decreasing calling rates at higher 
received levels (i.e., 10-minute 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 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. The authors discuss several case studies in which a small 
population of mysticetes believed to be adversely affected by oil and 
gas development off Sakhalin Island, Russia (Weller et al., 2002; 
Reeves et al., 2005). Forney et al. (2017) also discuss beaked whales, 
noting that anthropogenic effects in areas where they are resident 
could cause severe biological consequences, in part because 
displacement may adversely affect foraging rates, reproduction, or 
health, while an overriding instinct to remain could lead to more 
severe acute effects.
    A flight response is a dramatic change in normal movement to a 
directed and rapid movement away from the perceived location of a sound 
source. The flight response differs from other avoidance responses in 
the intensity of the response (e.g., directed movement, rate of 
travel). Relatively little information on flight responses of marine 
mammals to anthropogenic signals exist, although observations of flight 
responses to the presence of predators have occurred (Connor and 
Heithaus, 1996). The result of a flight response could range from 
brief, temporary exertion and displacement from the area where the 
signal provokes flight to, in extreme cases, marine mammal strandings 
(Evans and England, 2001). However, it should be noted that response to 
a perceived predator does not necessarily invoke flight (Ford and 
Reeves, 2008), and whether individuals are solitary or in groups may 
influence the response.
    Behavioral disturbance can also impact marine mammals in more 
subtle ways. Increased vigilance may result in 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

[[Page 17657]]

reproductive success, survival, or both (e.g., Harrington and Veitch, 
1992; Daan et al., 1996; Bradshaw et al., 1998). However, Ridgway et 
al. (2006) reported that increased vigilance in bottlenose dolphins 
exposed to sound over a five-day period did not cause any sleep 
deprivation or stress effects.
    Many animals perform vital functions, such as feeding, resting, 
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption 
of such functions resulting from reactions to stressors, such as sound 
exposure, are more likely to be significant if they last more than one 
diel cycle or recur on subsequent days (Southall et al., 2007). 
Consequently, a behavioral response lasting less than one day and not 
recurring on subsequent days is not considered particularly severe 
unless it could directly affect reproduction or survival (Southall et 
al., 2007). Note that there is a difference between multi-day 
substantive behavioral reactions and multi-day anthropogenic 
activities. For example, just because an activity lasts for multiple 
days does not necessarily mean that individual animals are either 
exposed to activity-related stressors for multiple days or, further, 
exposed in a manner resulting in sustained multi-day substantive 
behavioral responses.
    Stone (2015) reported data from at-sea observations during 1,196 
seismic surveys from 1994 to 2010. When arrays of large airguns 
(considered to be 500 in\3\ or more) were firing, lateral displacement, 
more localized avoidance, or other changes in behavior were evident for 
most odontocetes. However, significant responses to large arrays were 
found only for the minke whale and fin whale. Behavioral responses 
observed included changes in swimming or surfacing behavior, with 
indications that cetaceans remained near the water surface at these 
times. Cetaceans were recorded as feeding less often when large arrays 
were active. Behavioral observations of gray whales during a seismic 
survey monitored whale movements and respirations pre-, during, and 
post-seismic survey (Gailey et al., 2016). Behavioral state and water 
depth were the best `natural' predictors of whale movements and 
respiration and, after considering natural variation, none of the 
response variables were significantly associated with seismic survey or 
vessel sounds.
    Stress Responses--An animal's perception of a threat may be 
sufficient to trigger stress responses consisting of some combination 
of behavioral responses, autonomic nervous system responses, 
neuroendocrine responses, or immune responses (e.g., Seyle, 1950; 
Moberg, 2000). In many cases, an animal's first and sometimes most 
economical (in terms of energetic costs) response is behavioral 
avoidance of the potential stressor. Autonomic nervous system responses 
to stress typically involve changes in heart rate, blood pressure, and 
gastrointestinal activity. These responses have a relatively short 
duration and may or may not have a significant long-term effect on an 
animal's fitness.
    Neuroendocrine stress responses often involve the hypothalamus-
pituitary-adrenal system. Virtually all neuroendocrine functions that 
are affected by stress--including immune competence, reproduction, 
metabolism, and behavior--are regulated by pituitary hormones. Stress-
induced changes in the secretion of pituitary hormones have been 
implicated in failed reproduction, altered metabolism, reduced immune 
competence, and behavioral disturbance (e.g., Moberg, 1987; Blecha, 
2000). Increases in the circulation of glucocorticoids are also equated 
with stress (Romano et al., 2004).
    The primary distinction between stress (which is adaptive and does 
not normally place an animal at risk) and ``distress'' is the cost of 
the response. During a stress response, an animal uses glycogen stores 
that can be quickly replenished once the stress is alleviated. In such 
circumstances, the cost of the stress response would not pose serious 
fitness consequences. However, when an animal does not have sufficient 
energy reserves to satisfy the energetic costs of a stress response, 
energy resources must be diverted from other functions. This state of 
distress will last until the animal replenishes its energetic reserves 
sufficiently to restore normal function.
    Relationships between these physiological mechanisms, animal 
behavior, and the costs of stress responses are well-studied through 
controlled experiments and for both laboratory and free-ranging animals 
(e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003; 
Krausman et al., 2004; Lankford et al., 2005). Stress responses due to 
exposure to anthropogenic sounds or other stressors and their effects 
on marine mammals have also been reviewed (Fair and Becker, 2000; 
Romano et al., 2002b) and, more rarely, studied in wild populations 
(e.g., Romano et al., 2002a). For example, Rolland et al. (2012) found 
that noise reduction from reduced ship traffic in the Bay of Fundy was 
associated with decreased stress in North Atlantic right whales. These 
and other studies lead to a reasonable expectation that some marine 
mammals will experience physiological stress responses upon exposure to 
acoustic stressors and that it is possible that some of these would be 
classified as ``distress.'' In addition, any animal experiencing TTS 
would likely also experience stress responses (NRC, 2003).
    Auditory Masking--Sound can disrupt behavior through masking, or 
interfering with, an animal's ability to detect, recognize, or 
discriminate between acoustic signals of interest (e.g., those used for 
intraspecific communication and social interactions, prey detection, 
predator avoidance, navigation) (Richardson et al., 1995; Erbe et al., 
2016). Masking occurs when the receipt of a sound is interfered with by 
another coincident sound at similar frequencies and at similar or 
higher intensity, and may occur whether the sound is natural (e.g., 
snapping shrimp, wind, waves, precipitation) or anthropogenic (e.g., 
shipping, sonar, seismic exploration) in origin. The ability of a noise 
source to mask biologically important sounds depends on the 
characteristics of both the noise source and the signal of interest 
(e.g., signal-to-noise ratio, temporal variability, direction), in 
relation to each other and to an animal's hearing abilities (e.g., 
sensitivity, frequency range, critical ratios, frequency 
discrimination, directional discrimination, age or TTS hearing loss), 
and existing ambient noise and propagation conditions.
    Under certain circumstances, 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

[[Page 17658]]

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 levels during 
intervals between pulses reduced blue and fin whale communication space 
by as much as 36-51 percent when a seismic survey was operating 450-
2,800 km away. Based on preliminary modeling, Wittekind et al. (2016) 
reported that airgun sounds could reduce the communication range of 
blue and fin whales 2000 km from the seismic source. Nieukirk et al. 
(2012) and Blackwell et al. (2013) noted the potential for masking 
effects from seismic surveys on large whales.
    Some baleen and toothed whales are known to continue calling in the 
presence of seismic pulses, and their calls usually can be heard 
between the pulses (e.g., Nieukirk et al. 2012; Thode et al. 2012; 
Br[ouml]ker et al. 2013; Sciacca et al. 2016). As noted above, Cerchio 
et al. (2014) suggested that the breeding display of humpback whales 
off Angola could be disrupted by seismic sounds, as singing activity 
declined with increasing received levels. In addition, some cetaceans 
are known to change their calling rates, shift their peak frequencies, 
or otherwise modify their vocal behavior in response to airgun sounds 
(e.g., Di Iorio and Clark 2010; Castellote et al. 2012; Blackwell et 
al. 2013, 2015). The hearing systems of baleen whales are undoubtedly 
more sensitive to low-frequency sounds than are the ears of the small 
odontocetes that have been studied directly (e.g., MacGillivray et al., 
2014). The sounds important to small odontocetes are predominantly at 
much higher frequencies than are the dominant components of airgun 
sounds, thus limiting the potential for masking. In general, masking 
effects of seismic pulses are expected to be minor, given the normally 
intermittent nature of seismic pulses.

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. Sounds produced by large vessels generally dominate 
ambient noise at frequencies from 20 to 300 Hz (Richardson et al., 
1995). However, some energy is also produced at higher frequencies 
(Hermannsen et al., 2014); low levels of high-frequency sound from 
vessels has been shown to elicit responses in harbor porpoise (Dyndo et 
al., 2015). Increased levels of ship noise have been shown to affect 
foraging by porpoise (Teilmann et al., 2015; Wisniewska et al., 2018); 
Wisniewska et al. (2018) suggest that a decrease in foraging success 
could have long-term fitness consequences.
    Ship noise, through masking, can reduce the effective communication 
distance of a marine mammal if the frequency of the sound source is 
close to that used by the animal, and if the sound is present for a 
significant fraction of time (e.g., Richardson et al. 1995; Clark et 
al., 2009; Jensen et al., 2009; Gervaise et al., 2012; Hatch et al., 
2012; Rice et al., 2014; Dunlop 2015; Erbe et al., 2015; Jones et al., 
2017; Putland et al., 2017). In addition to the frequency and duration 
of the masking sound, the strength, temporal pattern, and location of 
the introduced sound also play a role in the extent of the masking 
(Branstetter et al., 2013, 2016; Finneran and Branstetter 2013; Sills 
et al., 2017). Branstetter et al. (2013) reported that time-domain 
metrics are also important in describing and predicting masking. In 
order to compensate for increased ambient noise, some cetaceans are 
known to increase the source levels of their calls in the presence of 
elevated noise levels from shipping, shift their peak frequencies, or 
otherwise change their vocal behavior (e.g., Martins et al., 2016; 
O'Brien et al., 2016; Tenessen and Parks 2016). Harp seals did not 
increase their call frequencies in environments with increased low-
frequency sounds (Terhune and Bosker 2016). Holt et al. (2015) reported 
that changes in vocal modifications can have increased energetic costs 
for individual marine mammals. A negative correlation between the 
presence of some cetacean species and the number of vessels in an area 
has been demonstrated by several studies (e.g., Campana et al. 2015; 
Culloch et al. 2016).
    Baleen whales are thought to be more sensitive to sound at these 
low frequencies than are toothed whales (e.g., MacGillivray et al. 
2014), possibly causing localized avoidance of the proposed survey area 
during seismic operations. Reactions of gray and humpback whales to 
vessels have been studied, and there is limited information available 
about the reactions of right whales and rorquals (fin, blue, and minke 
whales). Reactions of humpback whales to boats are variable, ranging 
from approach to avoidance (Payne 1978; Salden 1993). Baker et al., 
(1982, 1983) and Baker and Herman (1989) found humpbacks often move 
away when vessels are within several kilometers. Humpbacks seem less 
likely to react overtly when actively feeding than when resting or 
engaged in other activities (Krieger and Wing 1984, 1986). Increased 
levels of ship noise have been shown to affect foraging by

[[Page 17659]]

humpback whales (Blair et al., 2016). Fin whale sightings in the 
western Mediterranean were negatively correlated with the number of 
vessels in the area (Campana et al. 2015). Minke whales and gray seals 
have shown slight displacement in response to construction-related 
vessel traffic (Anderwald et al., 2013).
    Many odontocetes show considerable tolerance of vessel traffic, 
although they sometimes react at long distances if confined by ice or 
shallow water, if previously harassed by vessels, or have had little or 
no recent exposure to ships (Richardson et al. 1995). Dolphins of many 
species tolerate and sometimes approach vessels (e.g., Anderwald et 
al., 2013). Some dolphin species approach moving vessels to ride the 
bow or stern waves (Williams et al., 1992). Pirotta et al. (2015) noted 
that the physical presence of vessels, not just ship noise, disturbed 
the foraging activity of bottlenose dolphins. Sightings of striped 
dolphin, Risso's dolphin, sperm whale, and Cuvier's beaked whale in the 
western Mediterranean were negatively correlated with the number of 
vessels in the area (Campana et al., 2015).
    There 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). Based on a single 
observation, Aguilar Soto et al. (2006) suggest foraging efficiency of 
Cuvier's beaked whales may be reduced by close approach of vessels.
    Sounds emitted by the Langseth are low frequency and continuous, 
but would be widely dispersed in both space and time. Vessel traffic 
associated with the proposed survey is of low density compared to 
traffic associated with commercial shipping, industry support vessels, 
or commercial fishing vessels, and would therefore be expected to 
represent an insignificant incremental increase in the total amount of 
anthropogenic sound input to the marine environment, and the effects of 
vessel noise described above are not expected to occur as a result of 
this survey. In summary, project vessel sounds would not be at levels 
expected to cause anything more than possible localized and temporary 
behavioral changes in marine mammals, and would not be expected to 
result in significant negative effects on individuals or at the 
population level. In addition, in all oceans of the world, large vessel 
traffic is currently so prevalent that it is commonly considered a 
usual source of ambient sound (NSF-USGS 2011).

Ship Strike

    Vessel collisions with marine mammals, or ship strikes, can result 
in death or serious injury of the animal. Wounds resulting from ship 
strike may include massive trauma, hemorrhaging, broken bones, or 
propeller lacerations (Knowlton and Kraus, 2001). An animal at the 
surface may be struck directly by a vessel, a surfacing animal may hit 
the bottom of a vessel, or an animal just below the surface may be cut 
by a vessel's propeller. Superficial strikes may not kill or result in 
the death of the animal. These interactions are typically associated 
with large whales (e.g., fin whales), which are occasionally found 
draped across the bulbous bow of large commercial ships upon arrival in 
port. Although smaller cetaceans are more maneuverable in relation to 
large vessels than are large whales, they may also be susceptible to 
strike. The severity of injuries typically depends on the size and 
speed of the vessel, with the probability of death or serious injury 
increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist 
et al., 2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013). 
Impact forces increase with speed, as does the probability of a strike 
at a given distance (Silber et al., 2010; Gende et al., 2011).
    Pace and Silber (2005) also found that the probability of death or 
serious injury increased rapidly with increasing vessel speed. 
Specifically, the predicted probability of serious injury or death 
increased from 45 to 75 percent as vessel speed increased from 10 to 14 
kn, and exceeded 90 percent at 17 kn. 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. The chances of a lethal 
injury decline from approximately 80 percent at 15 kn to approximately 
20 percent at 8.6 kn. At speeds below 11.8 kn, the chances of lethal 
injury drop below 50 percent, while the probability asymptotically 
increases toward one hundred percent above 15 kn.
    The Langseth will travel at a speed of 5 kn 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. Ship strikes, as analyzed in the studies cited 
above, generally involve commercial shipping, which is much more common 
in both space and time than is geophysical survey activity. Jensen and 
Silber (2004) summarized ship strikes of large whales worldwide from 
1975-2003 and found that most collisions occurred in the open ocean and 
involved large vessels (e.g., commercial shipping). No such incidents 
were reported for geophysical survey vessels during that time period.
    It is possible for ship strikes to occur while traveling at slow 
speeds. For example, a hydrographic survey vessel traveling at low 
speed (5.5 kn) 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% 
CI = 0-5.5 x 10-\6\; NMFS, 2013b). In addition, a research 
vessel reported a fatal strike in 2011 of a dolphin in the Atlantic, 
demonstrating that it is possible for strikes involving smaller 
cetaceans to occur. In that case, the incident report indicated that an 
animal apparently was struck by the vessel's propeller as it was 
intentionally swimming near the vessel. While indicative of the type of 
unusual events that cannot be ruled out, neither of these instances 
represents a circumstance that would be considered reasonably 
foreseeable or that would be considered preventable.
    Although the likelihood of the vessel striking a marine mammal is 
low, we propose a robust ship strike avoidance protocol (see Proposed 
Mitigation), which we believe eliminates any foreseeable risk of ship 
strike during transit. We anticipate that vessel collisions involving a 
seismic data acquisition vessel towing gear, while not impossible, 
represent unlikely, unpredictable events for which there are no 
preventive measures. Given the 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

[[Page 17660]]

presence of marine mammal observers, the possibility of ship 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 ship strike is anticipated, and this 
potential effect of the specified activity will not be discussed 
further in the following analysis.
    Stranding --When a living or dead marine mammal swims or floats 
onto shore and becomes ``beached'' or incapable of returning to sea, 
the event is a ``stranding'' (Geraci et al., 1999; Perrin and Geraci, 
2002; Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for 
a stranding under the MMPA is that a 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, ship strike, 
unusual oceanographic or weather events, sound exposure, or 
combinations of these stressors sustained concurrently or in series. 
However, the cause or causes of most strandings are unknown (Geraci et 
al., 1976; Eaton, 1979; Odell et al., 1980; Best, 1982). Numerous 
studies suggest that the physiology, behavior, habitat relationships, 
age, or condition of cetaceans may cause them to strand or might pre-
dispose them to strand when exposed to another phenomenon. These 
suggestions are consistent with the conclusions of numerous other 
studies that have demonstrated that combinations of dissimilar 
stressors commonly combine to kill an animal or dramatically reduce its 
fitness, even though one exposure without the other does not produce 
the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; 
Fair and Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a; 
2005b, Romero, 2004; Sih et al., 2004).
    There is no conclusive evidence that exposure to airgun noise 
results in behaviorally-mediated forms of injury. Behaviorally-mediated 
injury (i.e., mass stranding events) has been primarily associated with 
beaked whales exposed to mid-frequency active (MFA) naval sonar. 
Tactical sonar and the alerting stimulus used in Nowacek et al. (2004) 
are very different from the noise produced by airguns. One should 
therefore not expect the same reaction to airgun noise as to these 
other sources. As explained below, military MFA sonar is very different 
from airguns, and one should not assume that airguns will cause the 
same effects as MFA sonar (including strandings).
    To understand why 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, 2019a2019), animals typically produce sound at 
frequencies where they hear best. More recently, Southall et al. (2019) 
suggested that certain species in the historical mid-frequency hearing 
group (beaked whales, sperm whales, and killer whales) are likely more 
sensitive to lower frequencies within the group's generalized hearing 
range than are other species within the group, and state that the data 
for beaked whales suggest sensitivity to approximately 5 kHz. However, 
this information is consistent with the general conclusion that beaked 
whales (and other mid-frequency cetaceans) are relatively insensitive 
to the frequencies where most energy of an airgun signal is found. 
Military MFA sonar is typically considered to operate in the frequency 
range of approximately 3-14 kHz (D'Amico et al., 2009), i.e., outside 
the range of likely best hearing for beaked whales but within or close 
to the lower bounds, whereas most energy in an airgun signal is 
radiated at much lower frequencies, below 500 Hz (Dragoset, 1990).
    It is important to distinguish between energy (loudness, measured 
in dB) and

[[Page 17661]]

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 ten events were at 
minimum spatially and temporally coincident with naval activity likely 
to have included MFA sonar use and, despite incomplete knowledge of 
timing and location of the stranding or the naval activity in some 
cases, there was no evidence for an alternative cause of stranding. The 
U.S. Navy has publicly stated agreement that five such events since 
1996 were associated in time and space with MFA sonar use, either by 
the U.S. Navy alone or in joint training exercises with the North 
Atlantic Treaty Organization. The U.S. Navy additionally noted that, as 
of 2017, a 2014 beaked whale stranding event in Crete coincident with 
naval exercises was under review and had not yet been determined to be 
linked to sonar activities (U.S. Navy, 2017). Separately, the 
International Council for the Exploration of the Sea reported in 2005 
that, worldwide, there have been about 50 known strandings, consisting 
mostly of beaked whales, with a potential causal link to MFA sonar 
(ICES, 2005). In contrast, very few such associations have been made to 
seismic surveys, despite widespread use of airguns as a geophysical 
sound source in numerous locations around the world.
    A more recent review of possible stranding associations with 
seismic surveys (Castellote and Llorens, 2016) states plainly that, 
``[s]peculation concerning possible links between seismic survey noise 
and cetacean strandings is available for a dozen events but without 
convincing causal evidence.'' The authors' ``exhaustive'' search of 
available information found

[[Page 17662]]

ten events worth further investigation via a ranking system 
representing a rough metric of the relative level of confidence offered 
by the data for inferences about the possible role of the seismic 
survey in a given stranding event. Only three of these events involved 
beaked whales. Whereas D'Amico et al., (2009) used a 1-5 ranking 
system, in which ``1'' represented the most robust evidence connecting 
the event to MFA sonar use, Castellote and Llorens (2016) used a 1-6 
ranking system, in which ``6'' represented the most robust evidence 
connecting the event to the seismic survey. As described above, D'Amico 
et al. (2009) found that two events were ranked ``1'' and ten events 
were ranked ``2'' (i.e., 12 beaked whale stranding events were found to 
be associated with MFA sonar use). In contrast, Castellote and Llorens 
(2016) found that none of the three beaked whale stranding events 
achieved their highest ranks of 5 or 6. Of the 10 total events, none 
achieved the highest rank of 6. Two events were ranked as 5: 1 
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 exhaustive 
investigation of this stranding event, which did not involve beaked 
whales, concluded that use of a high-frequency mapping system (12-kHz 
multibeam echosounder) was the most plausible and likely initial 
behavioral trigger of the event, which was likely exacerbated by 
several site- and situation-specific secondary factors. The review 
panel found that seismic airguns were used after the initial strandings 
and animals entering a lagoon system, that airgun use clearly had no 
role as an initial trigger, and that there was no evidence that airgun 
use dissuaded animals from leaving (Southall et al., 2013).
    However, one of these stranding events, involving two Cuvier's 
beaked whales, was contemporaneous with and reasonably associated 
spatially with a 2002 seismic survey in the Gulf of California 
conducted by L-DEO, as was the case for the 2007 Gulf of Cadiz seismic 
survey discussed by Castellote and Llorens (also involving two Cuvier's 
beaked whales). However, neither event was considered a ``true atypical 
mass stranding'' (according to Frantzis (1998)) as used in the analysis 
of Castellote and Llorens (2016). While we agree with the authors that 
this lack of evidence should not be considered conclusive, it is clear 
that there is very little evidence that seismic surveys should be 
considered as posing a significant risk of acute harm to beaked whales 
or other mid-frequency cetaceans. We have considered the potential for 
the proposed surveys to result in marine mammal stranding and have 
concluded that, based on the best available information, stranding is 
not expected to occur.
    Entanglement--Entanglements occur when marine mammals become 
wrapped around cables, lines, nets, or other objects suspended in the 
water column. During seismic operations, numerous cables, lines, and 
other objects primarily associated with the airgun array and hydrophone 
streamers will be towed behind the Langseth near the water's surface. 
However, we are not aware of any cases of entanglement of mysticetes in 
seismic survey equipment. No incidents of entanglement of marine 
mammals with seismic survey gear have been documented in over 54,000 kt 
(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, such as the heat flow probe in the 
seafloor, could damage areas of hard bottom where direct contact with 
the seafloor occurs and could crush epifauna (organisms that live on 
the seafloor or surface of other organisms). Damage to unknown or 
unseen hard bottom could occur, but because of the small area covered 
by most bottom-founded equipment and the patchy distribution of hard 
bottom habitat, contact with unknown hard bottom is expected to be rare 
and impacts minor. Seafloor disturbance in areas of soft bottom can 
cause loss of small patches of epifauna and infauna due to burial or 
crushing, and bottom-feeding fishes could be temporarily displaced from 
feeding areas. Overall, any effects of physical damage to habitat are 
expected to be minor and temporary.
    Effects to Prey--Marine mammal prey varies by species, season, and 
location and, for some, is not well documented. Fish react to sounds 
which are especially strong and/or intermittent low-frequency sounds, 
and behavioral responses such as flight or avoidance are the most 
likely effects. However, the reaction of fish to airguns depends on the 
physiological state of the fish, past exposures, motivation (e.g., 
feeding, spawning, migration), and other environmental factors. Several 
studies have demonstrated that airgun sounds might affect the 
distribution and behavior of some fishes, potentially impacting 
foraging opportunities or increasing energetic costs (e.g., Fewtrell 
and McCauley, 2012; Pearson et al., 1992; Skalski et al., 1992; 
Santulli et al., 1999; Paxton et al., 2017), though the bulk of studies 
indicate no or slight reaction to noise (e.g., Miller and Cripps, 2013; 
Dalen and Knutsen, 1987; Pena et al., 2013; Chapman and Hawkins, 1969; 
Wardle et al., 2001; Sara et al., 2007; Jorgenson and Gyselman, 2009; 
Blaxter et al., 1981; Cott et al., 2012; Boeger et al., 2006), and 
that, most commonly, while there are likely to be impacts to fish as a 
result of noise from nearby airguns, such effects will be temporary. 
For example, investigators reported significant, short-term declines in 
commercial fishing catch rate of gadid fishes during and for up to five 
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

[[Page 17663]]

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. (2012b. (2012) showed that a TTS of 4-
6 dB was recoverable within 24 hours for one species. Impacts would be 
most severe when the individual fish is close to the source and when 
the duration of exposure is long; both of which are conditions unlikely 
to occur for this survey that is necessarily transient in any given 
location and likely result in brief, infrequent noise exposure to prey 
species in any given area. For this survey, the sound source is 
constantly moving, and most fish would likely avoid the sound source 
prior to receiving sound of sufficient intensity to cause physiological 
or anatomical damage. In addition, ramp-up may allow certain fish 
species the opportunity to move further away from the sound source.
    A recent comprehensive review (Carroll et al., 2017) found that 
results are mixed as to the effects of airgun noise on the prey of 
marine mammals. While some studies suggest a change in prey 
distribution and/or a reduction in prey abundance following the use of 
seismic airguns, others suggest no effects or even positive effects in 
prey abundance. As one specific example, Paxton et al. (2017), which 
describes findings related to the effects of a 2014 seismic survey on a 
reef off of North Carolina, showed a 78 percent decrease in observed 
nighttime abundance for certain species. It is important to note that 
the evening hours during which the decline in fish habitat use was 
recorded (via video recording) occurred on the same day that the 
seismic survey passed, and no subsequent data is presented to support 
an inference that the response was long-lasting. Additionally, given 
that the finding is based on video images, the lack of recorded fish 
presence does not support a conclusion that the fish actually moved 
away from the site or suffered any serious impairment. In summary, this 
particular study corroborates prior studies indicating that a startle 
response or short-term displacement should be expected.
    Available data suggest that cephalopods are capable of sensing the 
particle motion of sounds and detect low frequencies up to 1-1.5 kHz, 
depending on the species, and so are likely to detect airgun noise 
(Kaifu et al., 2008; Hu et al., 2009; Mooney et al., 2010; Samson et 
al., 2014). Auditory injuries (lesions occurring on the statocyst 
sensory hair cells) have been reported upon controlled exposure to low-
frequency sounds, suggesting that cephalopods are particularly 
sensitive to low-frequency sound (Andre et al., 2011; Sole et al., 
2013). Behavioral responses, such as inking and jetting, have also been 
reported upon exposure to low-frequency sound (McCauley et al., 2000b; 
Samson et al., 2014). Similar to fish, however, the transient nature of 
the survey leads to an expectation that effects will be largely limited 
to behavioral reactions and would occur as a result of brief, 
infrequent exposures.
    With regard to potential impacts on zooplankton, McCauley et al. 
(2017) found that exposure to airgun noise resulted in significant 
depletion for more than half the taxa present and that there were 2 to 
3 times more dead zooplankton after airgun exposure compared with 
controls for all taxa, within 1 km of the airguns. However, the authors 
also stated that in order to have significant impacts on r-selected 
species (i.e., those with high growth rates and that produce many 
offspring) such as plankton, the spatial or temporal scale of impact 
must be large in comparison with the ecosystem concerned, and it is 
possible that the findings reflect avoidance by zooplankton rather than 
mortality (McCauley et al., 2017). In addition, the results of this 
study are inconsistent with a large body of research that generally 
finds limited spatial and temporal impacts to zooplankton as a result 
of exposure to airgun noise (e.g., Dalen and Knutsen, 1987; Payne, 
2004; Stanley et al., 2011). Most prior research on this topic, which 
has focused on relatively small spatial scales, has showed minimal 
effects (e.g., Kostyuchenko, 1973; Booman et al., 1996; S[aelig]tre and 
Ona, 1996; Pearson et al., 1994; Bolle et al., 2012).
    A modeling exercise was conducted as a follow-up to the McCauley et 
al. (2017) study (as recommended by McCauley et al.), in order to 
assess the potential for impacts on ocean ecosystem dynamics and 
zooplankton population dynamics (Richardson et al., 2017). Richardson 
et al., (2017) found that for copepods with a short life cycle in a 
high-energy environment, a full-scale airgun survey would impact 
copepod abundance up to three days following the end of the survey, 
suggesting that effects such as those found by McCauley et al., (2017) 
would not be expected to be detectable downstream of the survey areas, 
either spatially or temporally.
    Notably, a more 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 five m or less from the airguns. Mortality one week 
after the airgun blast was significantly higher in the copepods placed 
10 m from the airgun but was not significantly different from the 
controls at a distance of 20 m from the airgun. The increase in 
mortality, relative to controls, did not exceed 30 percent at any 
distance from the airgun. Moreover, the authors caution that even this 
higher mortality in the immediate vicinity of the airguns may be more 
pronounced than what would be observed in free-swimming animals due to 
increased flow speed of fluid inside bags containing the experimental 
animals. There were no sublethal effects on the escape performance or 
the sensory threshold needed to initiate an escape response at any of 
the distances from the airgun that were tested. Whereas McCauley et al. 
(2017) reported an SEL of 156 dB at a range of 509-658 m, with 
zooplankton mortality observed at that range, Fields et al. (2019) 
reported an SEL of 186 dB at a range of 25 m, with no reported 
mortality at that distance. Regardless, if we assume a worst-case 
likelihood of severe impacts to zooplankton within approximately one 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

[[Page 17664]]

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

    This section provides an estimate of the number of incidental takes 
proposed for authorization through the IHA, which will inform both 
NMFS' consideration of ``small numbers,'' and the negligible impact 
determinations.
    Harassment is the only type of take expected to result from these 
activities. Except with respect to certain activities not pertinent 
here, section 3(18) of the MMPA defines ``harassment'' as any act of 
pursuit, torment, or annoyance, which (i) has the potential to injure a 
marine mammal or marine mammal stock in the wild (Level A harassment); 
or (ii) has the potential to disturb a marine mammal or marine mammal 
stock in the wild by causing disruption of behavioral patterns, 
including, but not limited to, migration, breathing, nursing, breeding, 
feeding, or sheltering (Level B harassment).
    Anticipated takes would primarily be Level B harassment, as use of 
the described acoustic sources, particularly airgun arrays, is likely 
to disrupt behavioral patterns of marine mammals. There is also some 
potential for auditory injury (Level A harassment) to result for low- 
and high-frequency species due to the size of the predicted auditory 
injury zones for those species. 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 
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

[[Page 17665]]

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 (e.g., Bolt 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 5 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: 
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)..................  Cell 7: Lpk,flat: 218 dB;   Cell 8: LE,PW,24h: 201 dB.
(Underwater)...........................   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 NMFS Technical Guidance (2016) was published, in 
recognition of the fact that ensonified area/volume could be more 
technically challenging to predict because of the duration component in 
the new thresholds, we developed a User Spreadsheet that includes tools 
to help predict a simple isopleth that can be used in conjunction with 
marine mammal density or occurrence to help predict takes. We note that 
because of some of the assumptions included in the methods used for 
these tools, we anticipate that isopleths produced are typically going 
to be overestimates of some degree, which may result in some degree of 
overestimate of Level A harassment take. However, these tools offer the 
best way to predict appropriate isopleths when more sophisticated 3D 
modeling methods are not available, and NMFS continues to develop ways 
to quantitatively refine these tools, and will qualitatively address 
the output where appropriate.
    The proposed survey would entail the use of a 18-airgun array with 
a total discharge of 3300 in\3\ at a tow depth of

[[Page 17666]]

6 m. L-DEO model results are used to determine the 160 dBrms 
radius for the 18-airgun array in water depth ranging from 200-5500 m. 
Received sound levels were predicted by L-DEO's model (Diebold et al., 
2010) as a function of distance from L-DEO's full 36 airgun array 
(versus the smaller array planned for use here). Models for the 36-
airgun array used a 12-m tow depth, versus the 6-m tow depth planned 
for this survey. 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 
(~600-1100 m), and shallow water (~50 m) in the Gulf of Mexico in 2007-
2008 (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 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 Appendix H of the NSF-USGS PEIS). 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 Appendix H of the NSF-USGS PEIS). 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 survey would acquire data with the 18-airgun array at 
a tow depth of 6 m. 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 18-airgun array. 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 Appendix H of PEIS).
    L-DEO's modeling methodology is described in greater detail in the 
IHA 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
----------------------------------------------------------------------------------------------------------------
18 airguns, 3300 in\3\..........................................               6         >1000 m       \1\ 2,886
                                                                                      100-1000 m       \2\ 4,329
----------------------------------------------------------------------------------------------------------------
\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 presents the modeled PTS isopleths for each marine mammal 
hearing group based on L-DEO modeling incorporated in the companion 
User Spreadsheet (NMFS 2018).

          Table 5--Modeled Radial Distance to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
                                                                        LF              MF              HF
----------------------------------------------------------------------------------------------------------------
PTS SELcum......................................................           101.9               0             0.5
PTS Peak........................................................            23.3            11.2           116.9
----------------------------------------------------------------------------------------------------------------
The largest distance (in bold) of the dual criteria (SELcum or Peak) was used to estimate threshold distances
  and potential takes by Level A harassment.

    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 Technical Guidance 
were presented as dual metric acoustic thresholds using both 
SELcum and peak sound pressure metrics (NMFS 2016a). 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

[[Page 17667]]

group. In recognition of the fact that the requirement to calculate 
Level A harassment ensonified areas could be more technically 
challenging to predict due to the duration component and the use of 
weighting functions in the new SELcum thresholds, NMFS 
developed an optional User Spreadsheet that includes tools to help 
predict a simple isopleth that can be used in conjunction with marine 
mammal density or occurrence to facilitate the estimation of take 
numbers.
    The SELcum for the 18-airgun array is derived from 
calculating the modified farfield signature. The farfield signature is 
often used as a theoretical representation of the source level. To 
compute the farfield signature, the source level is estimated at a 
large distance (right) below the array (e.g., 9 km), and this level is 
back projected mathematically to a notional distance of 1 m from the 
array's geometrical center. However, it has been recognized that the 
source level from the theoretical farfield signature is never 
physically achieved at the source when the source is an array of 
multiple airguns separated in space (Tolstoy et al., 2009). Near the 
source (at short ranges, distances <1 km), the pulses of sound pressure 
from each individual airgun in the source array do not stack 
constructively as they do for the theoretical farfield signature. The 
pulses from the different airguns spread out in time such that the 
source levels observed or modeled are the result of the summation of 
pulses from a few airguns, not the full array (Tolstoy et al., 2009). 
At larger distances, away from the source array center, sound pressure 
of all the airguns in the array stack coherently, but not within one 
time sample, resulting in smaller source levels (a few dB) than the 
source level derived from the farfield signature. Because the farfield 
signature does not take into account the large array effect near the 
source and is calculated as a point source, the farfield signature is 
not an appropriate measure of the sound source level for large arrays. 
See the 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. The source level of the array is a 
theoretical definition assuming a point source and measurement in the 
far-field of the source (MacGillivray, 2006). As described by Caldwell 
and Dragoset (2000), an array is not a point source, but one that spans 
a small area. In the far-field, individual elements in arrays will 
effectively work as one source because individual pressure peaks will 
have coalesced into one relatively broad pulse. The array can then be 
considered a ``point source.'' For distances within the near-field, 
i.e., approximately 2-3 times the array dimensions, pressure peaks from 
individual elements do not arrive simultaneously because the 
observation point is not equidistant from each element. The effect is 
destructive interference of the outputs of each element, so that peak 
pressures in the near-field will be significantly lower than the output 
of the largest individual element. Here, the relevant peak isopleth 
distances would in all cases be expected to be within the near-field of 
the array where the definition of source level breaks down. Therefore, 
actual locations within this distance of the array center where the 
sound level exceeds the relevant peak SPL thresholds would not 
necessarily exist. In general, Caldwell and Dragoset (2000) suggest 
that the near-field for airgun arrays is considered to extend out to 
approximately 250 m.
    In order to provide quantitative support for this theoretical 
argument, we calculated expected maximum distances at which the near-
field would transition to the far-field (Table 5). For a specific array 
one can estimate the distance at which the near-field transitions to 
the far-field by:
[GRAPHIC] [TIFF OMITTED] TN23MR23.005

with the condition that D >> [lambda], and where D is the distance, L 
is the longest dimension of the array, and [lambda] is the wavelength 
of the signal (Lurton, 2002). Given that [lambda] can be defined by:
[GRAPHIC] [TIFF OMITTED] TN23MR23.006

where f is the frequency of the sound signal and v is the speed of the 
sound in the medium of interest, one can rewrite the equation for D as:
[GRAPHIC] [TIFF OMITTED] TN23MR23.007

and calculate D directly given a particular frequency and known speed 
of sound (here assumed to be 1,500 meters per second in water, although 
this varies with environmental conditions).
    To determine the closest distance to the arrays at which the source 
level predictions in Table 5 are valid (i.e., maximum extent of the 
near-field), we calculated D based on an assumed frequency of 1 kHz. A 
frequency of 1 kHz is commonly used in near-field/far-field 
calculations for airgun arrays (Zykov and Carr, 2014; MacGillivray, 
2006; NSF and USGS, 2011), and based on representative airgun spectrum 
data and field measurements of an airgun array used on the Langseth, 
nearly all (greater than 95 percent) of the energy from airgun arrays 
is below 1 kHz (Tolstoy et al., 2009). Thus, using one kHz as the upper 
cut-off for calculating the maximum extent of the near-field should 
reasonably represent the near-field extent in field conditions.
    If the largest distance to the peak sound pressure level threshold 
was equal to or less than the longest dimension of the array (i.e., 
under the array), or within the near-field, then received levels that 
meet or exceed the threshold in most cases are not expected to occur. 
This is because within the near-field and within the dimensions of the 
array, the source levels specified in Appendix A of L-DEO's application 
are overestimated and not applicable. In fact, until one reaches a 
distance of approximately three or four times the near-field distance 
the average intensity of sound at any given distance from the array is 
still less than that based on calculations that assume a directional 
point source (Lurton, 2002). The 3,300-in\3\ airgun array planned for 
use during the proposed survey has an approximate diagonal of 18.6 m, 
resulting in a near-field distance of approximately 58 m at 1 kHz (NSF 
and USGS, 2011). Field measurements of this array indicate that the 
source behaves like multiple discrete sources, rather than a 
directional point source, beginning at approximately 400 m (deep site) 
to 1 km (shallow site) from the center of the array (Tolstoy et al., 
2009), distances that are actually greater than four times the 
calculated 58-m near-field distance. Within these distances, the 
recorded received levels were always lower than would be predicted 
based on calculations that assume a directional point source, and 
increasingly so as one moves closer towards the array (Tolstoy et al., 
2009). Given this, relying on the calculated distance (58 m) as the 
distance at which we expect to be in the near-field is a conservative 
approach since even beyond this distance the acoustic modeling still 
overestimates the actual received level. Within the near-field, in 
order to explicitly evaluate the likelihood of exceeding any particular 
acoustic threshold, one would need to consider the exact position of 
the animal, its relationship to individual array elements, and how the 
individual acoustic sources propagate and their acoustic fields 
interact. Given that within the near-field and dimensions of

[[Page 17668]]

the array source levels would be below those assumed here, we believe 
exceedance of the peak pressure threshold would only be possible under 
highly unlikely circumstances.
    In consideration of the received sound levels in the near-field as 
described above, we expect the potential for Level A harassment of mid-
frequency cetaceans 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 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]Parms 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 that 
will inform the take calculations.
    Habitat-based density models produced by the Duke University Marine 
Geospatial Ecology Laboratory (Roberts et al., 2016; Roberts and 
Halpin, 2022) represent the best available information regarding marine 
mammal densities in the survey area. The density data presented by 
Roberts et al. (2016 and 2022) incorporates aerial and shipboard line-
transect survey data from NMFS and other organizations and incorporates 
data from 8 physiographic and 16 dynamic oceanographic and biological 
covariates, and controls for the influence of sea state, group size, 
availability bias, and perception bias on the probability of making a 
sighting. These density models were originally developed for all 
cetacean taxa in the U.S. Atlantic (Roberts et al., 2016). In 
subsequent years, certain models have been updated based on additional 
data as well as certain methodological improvements. More information 
is available online at https://seamap.env.duke.edu/models/Duke/EC/. 
Marine mammal density estimates in the survey area (animals/km\2\) were 
obtained using the most recent model results for all taxa (Roberts et 
al., 2016 and 2022).
    Monthly density grids (e.g., rasters) for each species were 
overlaid with the Survey Area and values from all grid cells that 
overlapped the Survey Area (plus a 40 km buffer) were averaged to 
determine monthly mean density values for each species. Monthly mean 
density values within the Survey Area were averaged for each of the two 
water depth categories (intermediate and deep) for the months May to 
October. The highest mean monthly density estimates for each species 
were used to estimate take.

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 highest mean monthly density for each 
species was then multiplied by the daily ensonified areas, increased by 
25 percent, and then multiplied by the number of survey days (28) 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 to equate to take and requested 
authorization of those takes. Those estimates in turn form the basis 
for our proposed take authorization numbers. For the species for which 
NMFS does not expect there to be a reasonable potential for take by 
Level A harassment to occur, i.e., mid-frequency cetaceans, we have 
added L-DEO's estimated exposures above Level A harassment thresholds 
to their estimated exposures above the Level B harassment threshold to 
produce a total number of incidents of take by Level B harassment that 
is proposed for authorization. Estimated exposures and proposed take 
numbers for authorization are shown in Table 6.

                                                   Table 6--Estimated Take Proposed for Authorization
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                        Estimated  take     Proposed authorized
                                                                                    ----------------------         take             Stock     Percent of
                    Species                                     Stock                                     ----------------------  abundance      stock
                                                                                      Level B    Level A    Level B    Level A
--------------------------------------------------------------------------------------------------------------------------------------------------------
North Atlantic right whale.....................  Western North Atlantic............       0.03          0          0          0          368         n/a
Humpback whale.................................  Gulf of Maine.....................       0.06          0      \1\ 2          0        1,396        0.14
Fin whale......................................  Western North Atlantic............          4          0          4          0        6,802        0.06
Sei whale......................................  Nova Scotia.......................          8          0          8          0        6,292        0.13
Minke whale....................................  Canadian East Coast...............         10          0         10          0       21,968        0.05
Blue whale.....................................  Western North Atlantic............          1          0          1          0          402        0.17
Sperm whale....................................  North Atlantic....................        405          1        406          0        4,349        9.34
Kogia spp......................................  ..................................        678         31        678         31       15,500        0.04
Cuvier's beaked whale..........................  Western North Atlantic............        394          2        396          0        5,744        6.89
Mesoplodont Beaked whales......................  ..................................        418          2        420          0       30,321        1.38
Pilot whales...................................  ..................................        384          1        385          0       15,500        2.48
Rough-toothed dolphin..........................  Western North Atlantic............         82          0         82          0          136       10.79
Bottlenose dolphin.............................  Western North Atlantic Offshore...      1,473          4      1,477          0       62,851        2.35
Atlantic white-sided dolphin...................  Western North Atlantic............          0          0     \1\ 14          0       93,233        0.02
Pantropical spotted dolphin....................  Western North Atlantic............        114          0        114          0        6,593        1.73
Atlantic spotted dolphin.......................  Western North Atlantic............      1,232          5      1,237          0       39,921         3.1
Spinner dolphin................................  Western North Atlantic............         41          0         41          0        4,102        1.00

[[Page 17669]]

 
Clymene dolphin................................  Western North Atlantic............         79          0         79          0        4,237        1.87
Striped dolphin................................  Western North Atlantic............         19          0     \1\ 45          0       67,036        0.07
Fraser's dolphin...............................  Western North Atlantic............         62          0    \2\ 163          0          unk  ..........
Risso's dolphin................................  Western North Atlantic............        189          0        189          0       35,215        0.54
Common dolphin.................................  Western North Atlantic............         56          0         56          0      172,947       11.99
Melon-headed whale.............................  Western North Atlantic............         58          0     \2\ 83          0        3,965        2.15
Pygmy killer whale.............................  Western North Atlantic............          6          0          6          0          unk  ..........
False killer whale.............................  Western North Atlantic............          1          0      \2\ 6          0        1,791        0.34
Killer whale...................................  Western North Atlantic............          2          0      \1\ 4          0          unk  ..........
Harbor porpoise................................  Gulf of Maine/Bay of Fundy........       0.01          0      \1\ 3          0       95,543        0.00
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Proposed take increased to mean group size from AMAPPS (Palka et al., 2017 and 2021).
\2\ Proposed take increased to mean group size from OBIS (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, as 
well as subsistence uses. 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, NMFS-approved PSOs. The PSOs 
must have no tasks other than to conduct observational effort, record 
observational data, and communicate with and instruct relevant vessel 
crew with regard to the presence of marine mammals and mitigation 
requirements. PSO resumes shall be provided to NMFS for approval.
    At least one of the visual and two of the acoustic PSOs (discussed 
below) aboard the vessel must have a minimum of 90 days at-sea 
experience working in those roles, respectively, with no more than 18 
months elapsed since the conclusion of the at-sea experience. One 
visual PSO with such experience shall be designated as the lead for the 
entire protected species observation team. The lead PSO shall serve as 
primary point of contact for the vessel operator and ensure all PSO 
requirements per the IHA are met. To the maximum extent practicable, 
the experienced PSOs should be scheduled to be on duty with those PSOs 
with appropriate training but who have not yet gained relevant 
experience.
    During survey operations (e.g., any day on which use of the 
acoustic source is planned to occur, and whenever the acoustic source 
is in the water, whether activated or not), a minimum of two visual 
PSOs must be on duty and conducting visual observations at all times 
during daylight hours (i.e., from 30 minutes prior to sunrise through 
30 minutes following sunset). Visual monitoring of the pre-start 
clearance zone must begin no less than 30 minutes prior to ramp-up, and 
monitoring must continue until one hour after use of the acoustic 
source ceases or until 30 minutes past sunset. Visual PSOs shall 
coordinate to ensure 360[deg] visual coverage around the vessel from 
the most appropriate observation posts, and shall conduct visual 
observations using binoculars and the naked eye while free

[[Page 17670]]

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 acoustic source (rather than being based on the center of the array 
or around the vessel itself). During use of the acoustic source (i.e., 
anytime airguns are active, including ramp-up), detections of marine 
mammals within the buffer zone (but outside the SZ) shall be 
communicated to the operator to prepare for the potential shutdown of 
the acoustic source. Visual PSOs will immediately communicate all 
observations to the on duty acoustic PSO(s), including any 
determination by the PSO regarding species identification, distance, 
and bearing and the degree of confidence in the determination. Any 
observations of marine mammals by crew members shall be relayed to the 
PSO team. During good conditions (e.g., daylight hours; Beaufort sea 
state (BSS) 3 or less), visual PSOs shall conduct observations when the 
acoustic source is not operating for comparison of sighting rates and 
behavior with and without use of the acoustic source and between 
acquisition periods, to the maximum extent practicable.
    Visual PSOs may be on watch for a maximum of 4 consecutive hours 
followed by a break of at least one hour between watches and may 
conduct a maximum of 12 hours of observation per 24-hour period. 
Combined observational duties (visual and acoustic but not at same 
time) may not exceed 12 hours per 24-hour period for any individual 
PSO.

Passive Acoustic Monitoring

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

Establishment of 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 acoustic source would be 
shut down.
    The pre-start clearance zone is defined as the area that must be 
clear of marine mammals prior to beginning ramp-up of the acoustic 
source, and includes the 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. 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.

Pre-Start Clearance and Ramp-Up

    Ramp-up (sometimes referred to as ``soft start'') means the gradual 
and systematic increase of emitted sound levels from an airgun array. 
Ramp-up begins by first activating a single airgun of the smallest 
volume, followed by doubling the number of active elements in stages 
until the full complement of an array's airguns are active. Each stage 
should be approximately the same duration, and the total duration 
should not be less than approximately 20 minutes. The intent of pre-
start clearance observation (30 minutes) is to ensure no protected 
species are observed within the pre-clearance zone (or extended SZ, for 
beaked whales and Kogia spp.) prior to the beginning of ramp-up. During 
pre-start clearance period is the only time observations of marine 
mammals in the buffer zone would prevent operations (i.e., the 
beginning of ramp-up). The intent of ramp-up is to warn marine mammals 
of pending seismic survey operations and

[[Page 17671]]

to allow sufficient time for those animals to leave the immediate 
vicinity. A ramp-up procedure, involving a step-wise increase in the 
number of airguns firing and total array volume until all operational 
airguns are activated and the full volume is achieved, is required at 
all times as part of the activation of the acoustic source. All 
operators must adhere to the following pre-start clearance and ramp-up 
requirements:
     The operator must notify a designated PSO of the planned 
start of ramp-up as agreed upon with the lead PSO; the notification 
time should not be less than 60 minutes prior to the planned ramp-up in 
order to allow the PSOs time to monitor the pre-start clearance zone 
(and extended 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. Acoustic 
source activation may only occur at times of poor visibility where 
operational planning cannot reasonably avoid such circumstances;
     If the acoustic source is shut down for brief periods 
(i.e., less than 30 minutes) for reasons other than that described for 
shutdown (e.g., mechanical difficulty), it may be activated again 
without ramp-up if PSOs have maintained constant visual and/or acoustic 
observation and no visual or acoustic detections of marine mammals have 
occurred within the applicable SZ. For any longer shutdown, pre-start 
clearance observation and ramp-up are required. For any shutdown at 
night or in periods of poor visibility (e.g., BSS 4 or greater), ramp-
up is required, but if the shutdown period was brief and constant 
observation was maintained, pre-start clearance watch of 30 minutes is 
not required; and
     Testing of the acoustic source involving all elements 
requires ramp-up. Testing limited to individual source elements or 
strings does not require ramp-up but does require pre-start clearance 
of 30 min.

Shutdown

    The shutdown of an airgun array requires the immediate de-
activation of all individual airgun elements of the array. Any PSO on 
duty will have the authority to delay the start of survey operations or 
to call for shutdown of the acoustic source if a marine mammal is 
detected within the applicable SZ. The operator must also establish and 
maintain clear lines of communication directly between PSOs on duty and 
crew controlling the acoustic source to ensure that shutdown commands 
are conveyed swiftly while allowing PSOs to maintain watch. When both 
visual and acoustic PSOs are on duty, all detections will be 
immediately communicated to the remainder of the on-duty PSO team for 
potential verification of visual observations by the acoustic PSO or of 
acoustic detections by visual PSOs. When the airgun array is active 
(i.e., anytime one or more airguns is active, including during ramp-up) 
and (1) a marine mammal appears within or enters the applicable SZ and/
or (2) a marine mammal (other than delphinids, see below) is detected 
acoustically and localized within the applicable SZ, the acoustic 
source will be shut down. When shutdown is called for by a PSO, the 
acoustic source will be immediately deactivated and any dispute 
resolved only following deactivation. Additionally, shutdown will occur 
whenever PAM alone (without visual sighting), confirms presence of 
marine mammal(s) in the 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.
    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 
in those delphinoids (e.g., Barkaszi et al., 2012, Barkaszi and Kelly, 
2018). The potential for increased shutdowns resulting from such a 
measure would require the Langseth to revisit the missed track line to 
reacquire data, resulting in an overall

[[Page 17672]]

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 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. 
Finally, L-DEO must implement shutdown upon detection (visual or 
acoustic) of a North Atlantic right whale at any distance.

Vessel Strike Avoidance

    Vessel operators and crews must maintain a vigilant watch for all 
protected species and slow down, stop their vessel, or alter course, as 
appropriate and regardless of vessel size, to avoid striking any marine 
mammal. A visual observer aboard the vessel must monitor a vessel 
strike avoidance zone around the vessel (distances stated below). 
Visual observers monitoring the vessel strike avoidance zone may be 
third-party observers (i.e., PSOs) or crew members, but crew members 
responsible for these duties must be provided sufficient training to 
(1) distinguish marine mammals from other phenomena and (2) broadly to 
identify a marine mammal as a whale or other marine mammal.
    Vessel speeds must be reduced to 10 kn 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 500 m 
from North Atlantic right whales and 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.
    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.
    All survey vessels, regardless of size, must observe a 10-kn speed 
restriction in specific areas designated by NMFS for the protection of 
North Atlantic right whales from vessel strikes. These include all 
Seasonal Management Areas (SMA) established under 50 CFR 224.105 (when 
in effect), any dynamic management areas (DMA) (when in effect), and 
Slow Zones. See www.fisheries.noaa.gov/national/endangered-species-conservation/reducing-ship-strikes-north-atlantic-right-whales for 
specific detail regarding these areas.

Operational Restrictions

    L-DEO must limit airgun use to between May 1 and October 31. Vessel 
movement and other activities that do not require use of airguns may 
occur outside of these dates.
    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 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.

[[Page 17673]]

Vessel-Based Visual Monitoring

    As described above, PSO observations would take place during 
daytime airgun operations. During seismic survey operations, at least 
five visual PSOs would be based aboard the Langseth. Two visual PSOs 
would be on duty at all time during daytime hours. Monitoring shall be 
conducted in accordance with the following requirements:
     The operator shall provide PSOs with bigeye binoculars 
(e.g., 25 x 150; 2.7 view angle; individual ocular focus; height 
control) of appropriate quality (i.e., Fujinon or equivalent) solely 
for PSO use. These shall be pedestal-mounted on the deck at the most 
appropriate vantage point that provides for optimal sea surface 
observation, PSO safety, and safe operation of the vessel; and
     The operator will work with the selected third-party 
observer provider to ensure PSOs have all equipment (including backup 
equipment) needed to adequately perform necessary tasks, including 
accurate determination of distance and bearing to observed marine 
mammals.
    PSOs must have the following requirements and qualifications:
     PSOs shall be independent, dedicated, trained visual and 
acoustic PSOs and must be employed by a third-party observer provider;
     PSOs shall have no tasks other than to conduct 
observational effort (visual or acoustic), collect data, and 
communicate with and instruct relevant vessel crew with regard to the 
presence of protected species and mitigation requirements (including 
brief alerts regarding maritime hazards);
     PSOs shall have successfully completed an approved PSO 
training course appropriate for their designated task (visual or 
acoustic). Acoustic PSOs are required to complete specialized training 
for operating PAM systems and are encouraged to have familiarity with 
the vessel with which they will be working;
     PSOs can act as acoustic or visual observers (but not at 
the same time) as long as they demonstrate that their training and 
experience are sufficient to perform the task at hand;
     NMFS must review and approve PSO resumes accompanied by a 
relevant training course information packet that includes the name and 
qualifications (i.e., experience, training completed, or educational 
background) of the instructor(s), the course outline or syllabus, and 
course reference material as well as a document stating successful 
completion of the course;
     PSOs must successfully complete relevant training, 
including completion of all required coursework and passing (80 percent 
or greater) a written and/or oral examination developed for the 
training program;
     PSOs must have successfully attained a bachelor's degree 
from an accredited college or university with a major in one of the 
natural sciences, a minimum of 30 semester hours or equivalent in the 
biological sciences, and at least one undergraduate course in math or 
statistics; and
     The educational requirements may be waived if the PSO has 
acquired the relevant skills through alternate experience. Requests for 
such a waiver shall be submitted to NMFS and must include written 
justification. Requests shall be granted or denied (with justification) 
by NMFS within 1 week of receipt of submitted information. Alternate 
experience that may be considered includes, but is not limited to (1) 
secondary education and/or experience comparable to PSO duties; (2) 
previous work experience conducting academic, commercial, or 
government-sponsored protected species surveys; or (3) previous work 
experience as a PSO; the PSO should demonstrate good standing and 
consistently good performance of PSO duties.
    For data collection purposes, PSOs shall use standardized data 
collection forms, whether hard copy or electronic. PSOs shall record 
detailed information about any implementation of mitigation 
requirements, including the distance of animals to the acoustic source 
and description of specific actions that ensued, the behavior of the 
animal(s), any observed changes in behavior before and after 
implementation of mitigation, and if shutdown was implemented, the 
length of time before any subsequent ramp-up of the acoustic source. If 
required mitigation was not implemented, PSOs should record a 
description of the circumstances. At a minimum, the following 
information must be recorded:
     Vessel names (source vessel and other vessels associated 
with survey) and call signs;
     PSO names and affiliations;
     Dates of departures and returns to port with port name;
     Date and participants of PSO briefings;
     Dates and times (Greenwich Mean Time) of survey effort and 
times corresponding with PSO effort;
     Vessel location (latitude/longitude) when survey effort 
began and ended and vessel location at beginning and end of visual PSO 
duty shifts;
     Vessel heading and speed at beginning and end of visual 
PSO duty shifts and upon any line change;
     Environmental conditions while on visual survey (at 
beginning and end of PSO shift and whenever conditions changed 
significantly), including BSS and any other relevant weather conditions 
including cloud cover, fog, sun glare, and overall visibility to the 
horizon;
     Factors that may have contributed to impaired observations 
during each PSO shift change or as needed as environmental conditions 
changed (e.g., vessel traffic, equipment malfunctions); and
     Survey activity information, such as acoustic source power 
output while in operation, number and volume of airguns operating in 
the array, tow depth of the array, and any other notes of significance 
(i.e., pre-start clearance, ramp-up, shutdown, testing, shooting, ramp-
up completion, end of operations, streamers, etc.).
    The following information should be recorded upon visual 
observation of any protected species:
     Watch status (sighting made by PSO on/off effort, 
opportunistic, crew, alternate vessel/platform);
     PSO who sighted the animal;
     Time of sighting;
     Vessel location at time of sighting;
     Water depth;
     Direction of vessel's travel (compass direction);
     Direction of animal's travel relative to the vessel;
     Pace of the animal;
     Estimated distance to the animal and its heading relative 
to vessel at initial sighting;
     Identification of the animal (e.g., genus/species, lowest 
possible taxonomic level, or unidentified) and the composition of the 
group if there is a mix of species;
     Estimated number of animals (high/low/best);
     Estimated number of animals by cohort (adults, yearlings, 
juveniles, calves, group composition, etc.);
     Description (as many distinguishing features as possible 
of each individual seen, including length, shape, color, pattern, scars 
or markings, shape and size of dorsal fin, shape of head, and blow 
characteristics);
     Detailed behavior observations (e.g., number of blows/
breaths, number of surfaces, breaching, spyhopping, diving, feeding, 
traveling; as explicit and detailed as possible; note any observed 
changes in behavior);
     Animal's closest point of approach (CPA) and/or closest 
distance from any element of the acoustic source;

[[Page 17674]]

     Platform activity at time of sighting (e.g., deploying, 
recovering, testing, shooting, data acquisition, other); and
     Description of any actions implemented in response to the 
sighting (e.g., delays, shutdown, ramp-up) and time and location of the 
action.
    If a marine mammal is detected while using the PAM system, the 
following information should be recorded:
     An acoustic encounter identification number, and whether 
the detection was linked with a visual sighting;
     Date and time when first and last heard;
     Types and nature of sounds heard (e.g., clicks, whistles, 
creaks, burst pulses, continuous, sporadic, strength of signal); and
     Any additional information recorded such as water depth of 
the hydrophone array, bearing of the animal to the vessel (if 
determinable), species or taxonomic group (if determinable), 
spectrogram screenshot, and any other notable information.

Reporting

    L-DEO must submit a draft comprehensive report to NMFS on all 
activities and monitoring results within 90 days of the completion of 
the survey or expiration of the IHA, whichever comes sooner. A final 
report must be submitted within 30 days following resolution of any 
comments on the draft report. The report would describe the operations 
that were conducted and sightings of marine mammals near the 
operations. The report would provide full documentation of methods, 
results, and interpretation pertaining to all monitoring. The 90-day 
report would summarize the dates and locations of seismic operations, 
and all marine mammal sightings (dates, times, locations, activities, 
associated seismic survey activities). The report would also include 
estimates of the number and nature of exposures that occurred above the 
harassment threshold based on PSO observations and including an 
estimate of those that were not detected, in consideration of both the 
characteristics and behaviors of the species of marine mammals that 
affect detectability, as well as the environmental factors that affect 
detectability.
    The draft report shall also include geo-referenced time-stamped 
vessel tracklines for all time periods during which airguns were 
operating. Tracklines should include points recording any change in 
airgun status (e.g., when the airguns began operating, when they were 
turned off, or when they changed from full array to single gun or vice 
versa). GIS files shall be provided in ESRI shapefile format and 
include the UTC date and time, latitude in decimal degrees, and 
longitude in decimal degrees. All coordinates shall be referenced to 
the WGS84 geographic coordinate system. In addition to the report, all 
raw observational data shall be made available to NMFS. A final report 
must be submitted within 30 days following resolution of any comments 
on the draft report.

Reporting Species of Concern

    Although not anticipated, if a North Atlantic right whale is 
observed at any time by PSOs or personnel on any project vessels, 
during surveys or during vessel transit, L-DEO must immediately report 
sighting information to the NMFS North Atlantic Right Whale Sighting 
Advisory System: (866) 755-6622. North Atlantic right whale sightings 
in any location must also be reported to the U.S. Coast Guard via 
channel 16.

Reporting Injured or Dead Marine Mammals

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

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

    In the event of a live stranding (or near-shore atypical milling) 
event within 50 km of the survey operations, where the NMFS stranding 
network is engaged in herding or other interventions to return animals 
to the water, the Director of OPR, NMFS (or designee) will advise L-DEO 
of the need to implement shutdown procedures for all active acoustic 
sources 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 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

[[Page 17675]]

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 
potential takes would be in the form of short-term Level B behavioral 
harassment in the form of temporary avoidance of the area or decreased 
foraging (if such activity was occurring), reactions that are 
considered to be of low severity and with no lasting biological 
consequences (e.g., Southall et al., 2007). Even repeated Level B 
harassment of some small subset of an overall stock is unlikely to 
result in any significant realized decrease in viability for the 
affected individuals, and thus would not result in any adverse impact 
to the stock as a whole.
    We are proposing to authorize a limited number of instances of 
Level A harassment of two species (pygmy and dwarf sperm whales, which 
are members of the high-frequency cetacean hearing group) in the form 
of PTS, and Level B harassment only of the remaining marine mammal 
species. Any PTS incurred in marine mammals as a result of the planned 
activity is expected to be in the form of a small degree of PTS, and 
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. Accordingly, we expect that the 
majority of takes would be in the form of short-term Level B behavioral 
harassment in the form of temporary avoidance of the area or decreased 
foraging (if such activity were occurring), reactions that are 
considered to be of low severity and with no lasting biological 
consequences (e.g., Southall et al., 2007, Ellison et al., 2012).
    In addition to being temporary, the maximum expected Level B 
harassment zone around the survey vessel is 2886 m for water depths 
greater than 1000 m (and up to 4329 m in water depths of 100 to 1000 
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 
(28 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.

[[Page 17676]]

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.
    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. No Level A 
harassment is anticipated, even in the absence of mitigation measures, 
or proposed for authorization for species with active UMEs.
    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 (28 days);
     The 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 small numbers of incidental take may be 
authorized under sections 101(a)(5)(A) and (D) of the MMPA for 
specified activities other than military readiness activities. The MMPA 
does not define small numbers and so, in practice, where estimated 
numbers are available, NMFS compares the number of individuals taken to 
the most appropriate estimation of abundance of the relevant species or 
stock in our determination of whether an authorization is limited to 
small numbers of marine mammals. When the predicted number of 
individuals to be taken is fewer than one-third of the species or stock 
abundance, the take is considered to be of small numbers. Additionally, 
other qualitative factors may be considered in the analysis, such as 
the temporal or spatial scale of the activities.
    The amount of take NMFS proposes to authorize is below one third of 
the estimated stock abundance for all species with available abundance 
estimates (in fact, take of individuals is less than fifteen 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.
    NMFS considers it appropriate to make a small numbers finding in 
the case of a species or stock that may potentially be taken but is 
either rarely encountered or only expected to be taken on rare 
occasions. In that circumstance, one or two assumed encounters with a 
group of animals (meaning a group that is traveling together or 
aggregated, and thus exposed to a stressor at the same approximate 
time) should reasonably be considered small numbers, regardless of 
consideration of the proportion of the stock (if known), as rare 
encounters resulting in take of one or two groups should be considered 
small relative to the range and distribution of any stock. In this 
case, NMFS proposes to authorize take resulting from a single exposure 
of one group each for Fraser's dolphin and killer whale (using average 
group size), and find that a single incident of take of one group of 
either of these species represents take of small numbers for that 
species.
    For pygmy killer whale, we propose to authorize six incidents of 
take by Level B harassment. No abundance information is available for 
this species in the proposed survey area. Therefore, we refer to other 
SAR abundance estimates for the species. NMFS estimates that the Hawaii 
stock of pygmy killer whales has a minimum abundance estimate of 5,885 
whales (Carretta et al., 2020). In the Gulf of Mexico, NMFS estimates a 
minimum abundance of 613 whales for that stock (Hayes et al., 2020). 
Therefore, NMFS assumes that the estimated take number of six would be 
small relative to any reasonable estimate of population abundance for 
the species in the Atlantic.
    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

[[Page 17677]]

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 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 NMFS' Office of Protected Resources (OPR).
    NMFS is proposing to authorize take of 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 at the 
Cape Fear submarine slide complex off North Carolina in the Northwest 
Atlantic Ocean during the spring/summer 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 
seismic 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, one-year 
renewal IHA following notice to the public providing an additional 15 
days for public comments when (1) up to another year of identical or 
nearly identical activities as described in the Description of Proposed 
Activities section of this notice is planned or (2) the activities as 
described in the Description of Proposed Activities section of this 
notice would not be completed by the time the IHA expires and a renewal 
would allow for completion of the activities beyond that described in 
the Dates and Duration section of this notice, provided all of the 
following conditions are met:
     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); and
     The request for renewal must include the following:
    (1) An explanation that the activities to be conducted under the 
requested renewal IHA are identical to the activities analyzed under 
the initial IHA, are a subset of the activities, or include changes so 
minor (e.g., reduction in pile size) that the changes do not affect the 
previous analyses, mitigation and monitoring requirements, or take 
estimates (with the exception of reducing the type or amount of take); 
and
    (2) A preliminary monitoring report showing the results of the 
required monitoring to date and an explanation showing that the 
monitoring results do not indicate impacts of a scale or nature not 
previously analyzed or authorized.
    Upon review of the request for renewal, the status of the affected 
species or stocks, and any other pertinent information, NMFS determines 
that there are no more than minor changes in the activities, the 
mitigation and monitoring measures will remain the same and 
appropriate, and the findings in the initial IHA remain valid.

    Dated: March 15, 2023.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2023-05966 Filed 3-22-23; 8:45 am]
BILLING CODE 3510-22-P