[Federal Register Volume 89, Number 130 (Monday, July 8, 2024)]
[Notices]
[Pages 56158-56188]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-14737]



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Vol. 89

Monday,

No. 130

July 8, 2024

Part III





Department of Commerce





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National Oceanic and Atmospheric Administration





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

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

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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XE034]


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

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and 
Atmospheric Administration (NOAA), Commerce.

ACTION: Notice; proposed incidental harassment authorization; request 
for comments on proposed authorization and possible renewal.

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

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

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

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

SUPPLEMENTARY INFORMATION:

Background

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

National Environmental Policy Act

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

Summary of Request

    On April 15, 2024, NMFS received a request from L-DEO for an IHA to 
take marine mammals incidental to conducting a marine geophysical 
survey of the Chain Transform Fault in the equatorial Atlantic Ocean. 
Following NMFS review of the application and additional clarifying 
information from L-DEO, NMFS deemed the application adequate and 
complete on May 22, 2024. L-DEO's request is for take of 28 marine 
mammal species by Level B harassment, and for take of a subset of 5 of 
these species, by Level A harassment. Neither L-DEO nor NMFS expect 
serious injury or mortality to result from this activity and, 
therefore, an IHA is appropriate.

Description of Proposed Activity

Overview

    Researchers from the Woods Hole Oceanographic Institution, 
University of Delaware, University of New Hampshire, Boise State 
University and Boston College, with funding from the National Science 
Foundation, propose to conduct a high-energy seismic survey using 
airguns as the acoustic source from the research vessel (R/V) Marcus G. 
Langseth (Langseth), which is owned and operated by L-DEO. The proposed 
survey would occur at the Chain Transform Fault, off the coast of 
Africa, in the equatorial Atlantic Ocean during austral summer 2024 in 
the Southern Hemisphere (i.e., between October 2024 and February 2025). 
The proposed survey would occur within International Waters more than 
600 kilometers (km) in the Gulf of Guinea, Africa. The survey would 
occur in water depths ranging from approximately 2,000 to

[[Page 56159]]

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

Dates and Duration

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

Specific Geographic Region

    The proposed survey would occur within approximately 0-2[deg] S, 
13-16.5[deg] W, within international waters more than 600 km off the 
coast of the Gulf of Guinea, Africa, in water depths ranging from 
approximately 2,000 to 5,500 m. The region where the survey is proposed 
to occur is depicted in figure 1, and is expected to cover 
approximately 2,058 km of survey trackline. Representative survey 
tracklines are shown; however, some deviation in actual tracklines, 
including the order of survey operations, could be necessary for 
reasons such as science drivers, poor data quality, inclement weather, 
or mechanical issues with the research vessel and/or equipment.
BILLING CODE 3510-22-P

[[Page 56160]]

[GRAPHIC] [TIFF OMITTED] TN08JY24.000

BILLING CODE 3510-22-C

Detailed Description of the Specified Activity

    The procedures to be used for the proposed surveys would be similar 
to those used during previous seismic surveys by L-DEO and would use 
conventional seismic methodology. The survey would involve one source 
vessel, R/V Langseth, which is owned and operated by L-DEO. During the 
high-energy survey, R/V Langseth would tow 4 strings with 36 airguns, 
consisting of a mixture of Bolt 1500LL and Bolt 1900LLX. During the 
surveys, all 4 strings, totaling 36 active airguns with a total 
discharge volume of 6,600 in\3\, would be used. The four airgun strings 
would be spaced 8 m apart, distributed across an area of approximately 
24 m x 16 m behind the R/V Langseth, and would be towed approximately 
140 m behind the vessel. The airgun array configurations are 
illustrated in figure 2-11 of National Science Foundation (NSF) and the 
U.S. Geological Survey's (USGS) Programmatic Environmental Impact 
Statement (PEIS; NSF-USGS, 2011). (The PEIS is available online at: 
https://www.nsf.gov/geo/oce/envcomp/usgs-nsf-marine-seismic-research/nsf-usgs-final-eis-oeis_3june2011.pdf). The receiving system would 
consist of a 15-km long solid-state hydrophone streamer and 20 OBSs. As 
the airgun arrays are towed along the survey lines, the hydrophone 
streamer would transfer the data to the on-board processing system, and 
the OBSs would receive and store the returning acoustic signals 
internally for later analysis.
    Approximately 2,058 km of seismic acquisition are proposed. The 
survey would take place in water depths ranging from 2,000 to 5,500 m; 
all effort would occur in water more than 2,000 m deep. Twenty OBSs 
would be deployed by R/V Langseth and left on the ocean floor for a 
period of 1 year to record earthquakes. To retrieve the OBSs, the 
instrument is released to float to the surface via an acoustic release 
system from the anchor, which is not retrieved. In addition to the 
operations of the airgun array, the ocean floor would be mapped with 
the Kongsberg EM 122 MBES and a Knudsen Chirp 3260 SBP. A Teledyne RDI 
75 kilohertz (kHz) Ocean Surveyor ADCP would be used to measure water 
current velocities, and acoustic pingers would be used to retrieve 
OBSs. Take of marine mammals is not expected to occur incidental to the 
use of the MBES, SBP, and ADCP, regardless of whether the airguns are 
operating simultaneously with the other sources. Given their 
characteristics (e.g., narrow downward-directed beam), marine mammals 
would

[[Page 56161]]

experience no more than one or two brief ping exposures, if any 
exposure were to occur, which would not be expected to provoke a 
response equating to take. NMFS does not expect that the use of these 
sources presents any reasonable potential to cause take of marine 
mammals.
    Proposed mitigation, monitoring, and reporting measures are 
described in detail later in this Notice (please see Proposed 
Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

    Sections 3 and 4 of the application summarize available information 
regarding status and trends, distribution and habitat preferences, and 
behavior and life history of the potentially affected species. NMFS 
fully considered all of this information, and we refer the reader to 
these descriptions, instead of reprinting the information. Additional 
information about these species (e.g., physical and behavioral 
descriptions) may be found on NMFS' website (https://www.fisheries.noaa.gov/find-species). NMFS refers the reader to the 
aforementioned source for general information regarding the species 
listed in table 1.
    The populations of marine mammals found in the survey area do not 
occur within the U.S. exclusive economic zone (EEZ) and therefore, are 
not assessed in NMFS' Stock Assessment Reports (SARs). For most 
species, there are no stocks defined for management purposes in the 
survey area, and NMFS is evaluating impacts at the species level. As 
such, information on potential biological removal level (PBR; defined 
by the MMPA as the maximum number of animals, not including natural 
mortalities, that may be removed from a marine mammal stock while 
allowing that stock to reach or maintain its optimum sustainable 
population) and annual levels of serious injury and mortality from 
anthropogenic sources are not available for these marine mammal 
populations. Abundance estimates for marine mammals in the survey 
location are lacking; therefore, the modeled abundances presented here 
are based on a variety of proxy sources, including the U.S Navy 
Atlantic Fleet Training and Testing Area Marine Mammal Density (AFTT) 
model (Roberts et al., 2023) and the International Whaling Commission 
(IWC) Population (Abundance) Estimates (IWC 2024). The modeled 
abundance is considered the best scientific information available on 
the abundance of marine mammal populations in the area.
    Table 1 lists all species that occur in the survey area that may be 
taken as a result of the proposed survey and summarizes information 
related to the population, including regulatory status under the MMPA 
and Endangered Species Act (ESA).

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

[[Page 56162]]

 
    False Killer Whale..........  Pseudorca                       NA  -, -, N                             12,682
                                   crassidens.
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\1\ ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species
  is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one
  for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and
  likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is
  automatically designated under the MMPA as depleted and as a strategic stock.
\2\ Modeled abundance value from U.S Navy Atlantic Fleet Training and Testing Area Marine Mammal Density (AFTT)
  (Roberts et al., 2023) unless otherwise noted.
\3\ Abundance of minke whales (species unspecified) for the Southern Hemisphere (IWC 2024)
\4\ Abundance of blue whales (excluding pygmy blue whales) for Southern Hemisphere (IWC 2024)
\5\ Abundance of humpback whales on Antarctic feeding grounds (IWC 2024)
\6\ Pilot whale guild.
\7\ Estimate includes dwarf and pygmy sperm whales.
\8\ Beaked whale guild.

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

Blue Whale

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

Fin Whale

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

[[Page 56163]]

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

Humpback Whale

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

Minke Whale

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

[[Page 56164]]

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

Sei Whale

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

Sperm Whale

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

Marine Mammal Hearing

    Hearing is the most important sensory modality for marine mammals 
underwater, and exposure to anthropogenic sound can have deleterious 
effects. To appropriately assess the potential effects of exposure to 
sound, it is necessary to understand the frequency ranges marine 
mammals are able to hear. Not all marine mammal species have equal 
hearing capabilities (e.g., Richardson et al., 1995; Wartzok and 
Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al. 
(2007, 2019) recommended that marine mammals be divided into hearing 
groups based on directly measured (behavioral or auditory evoked 
potential techniques) or estimated hearing ranges (behavioral response 
data, anatomical modeling, etc.). Note that no direct measurements of 
hearing ability have been successfully completed for mysticetes (i.e., 
low-frequency cetaceans). Subsequently, NMFS (2018)

[[Page 56165]]

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

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

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

Potential Effects of Specified Activities on Marine Mammals and Their 
Habitat

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

Description of Active Acoustic Sound Sources

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

[[Page 56166]]

construction) sound. A number of sources contribute to ambient sound, 
including the following (Richardson et al., 1995):
    Wind and waves: The complex interactions between wind and water 
surface, including processes such as breaking waves and wave-induced 
bubble oscillations and cavitation, are a main source of naturally 
occurring ambient sound for frequencies between 200 Hz and 50 kHz 
(Mitson, 1995). In general, ambient sound levels tend to increase with 
increasing wind speed and wave height. Surf sound becomes important 
near shore, with measurements collected at a distance of 8.5 km from 
shore showing an increase of 10 dB in the 100 to 700 Hz band during 
heavy surf conditions;
    Precipitation: Sound from rain and hail impacting the water surface 
can become an important component of total sound at frequencies above 
500 Hz, and possibly down to 100 Hz during quiet times;
    Biological: Marine mammals can contribute significantly to ambient 
sound levels, as can some fish and snapping shrimp. The frequency band 
for biological contributions is from approximately 12 Hz to over 100 
kHz; and
    Anthropogenic: Sources of anthropogenic sound related to human 
activity include transportation (surface vessels), dredging and 
construction, oil and gas drilling and production, seismic surveys, 
sonar, explosions, and ocean acoustic studies. Vessel noise typically 
dominates the total ambient sound for frequencies between 20 and 300 
Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz 
and, if higher frequency sound levels are created, they attenuate 
rapidly. Sound from identifiable anthropogenic sources other than the 
activity of interest (e.g., a passing vessel) is sometimes termed 
background sound, as opposed to ambient sound.
    The sum of the various natural and anthropogenic sound sources at 
any given location and time--which comprise ``ambient'' or 
``background'' sound--depends not only on the source levels (as 
determined by current weather conditions and levels of biological and 
human activity) but also on the ability of sound to propagate through 
the environment. In turn, sound propagation is dependent on the 
spatially and temporally varying properties of the water column and sea 
floor, and is frequency-dependent. As a result of this dependence on a 
large number of varying factors, ambient sound levels can be expected 
to vary widely over both coarse and fine spatial and temporal scales. 
Sound levels at a given frequency and location can vary by 10-20 dB 
from day to day (Richardson et al., 1995). The result is that, 
depending on the source type and its intensity, sound from a given 
activity may be a negligible addition to the local environment or could 
form a distinctive signal that may affect marine mammals. Details of 
source types are described in the following text.
    Sounds are often considered to fall into one of two general types: 
Pulsed and non-pulsed. The distinction between these two sound types is 
important because they have differing potential to cause physical 
effects, particularly with regard to hearing (e.g., NMFS, 2018; Ward, 
1997 in Southall et al., 2007). Please see Southall et al. (2007) for 
an in-depth discussion of these concepts.
    Pulsed sound sources (e.g., airguns, explosions, gunshots, sonic 
booms, impact pile driving) produce signals that are brief (typically 
considered to be less than one second), broadband, atonal transients 
(ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur 
either as isolated events or repeated in some succession. Pulsed sounds 
are all characterized by a relatively rapid rise from ambient pressure 
to a maximal pressure value followed by a rapid decay period that may 
include a period of diminishing, oscillating maximal and minimal 
pressures, and generally have an increased capacity to induce physical 
injury as compared with sounds that lack these features.
    Non-pulsed sounds can be tonal, narrowband, or broadband, brief or 
prolonged, and may be either continuous or non-continuous (ANSI, 1995; 
NIOSH, 1998). Some of these non-pulsed sounds can be transient signals 
of short duration but without the essential properties of pulses (e.g., 
rapid rise time). Examples of non-pulsed sounds include those produced 
by vessels, aircraft, machinery operations such as drilling or 
dredging, vibratory pile driving, and active sonar systems (such as 
those used by the U.S. Navy). The duration of such sounds, as received 
at a distance, can be greatly extended in a highly reverberant 
environment.
    Airgun arrays produce pulsed signals with energy in a frequency 
range from about 10-2,000 Hz, with most energy radiated at frequencies 
below 200 Hz. The amplitude of the acoustic wave emitted from the 
source is equal in all directions (i.e., omnidirectional), but airgun 
arrays do possess some directionality due to different phase delays 
between guns in different directions. Airgun arrays are typically tuned 
to maximize functionality for data acquisition purposes, meaning that 
sound transmitted in horizontal directions and at higher frequencies is 
minimized to the extent possible.

Acoustic Effects

    Here, we discuss the effects of active acoustic sources on marine 
mammals.
    Potential Effects of Underwater Sound \1\--Anthropogenic sounds 
cover a broad range of frequencies and sound levels and can have a 
range of highly variable impacts on marine life, from none or minor to 
potentially severe responses, depending on received levels, duration of 
exposure, behavioral context, and various other factors. The potential 
effects of underwater sound from active acoustic sources can 
potentially result in one or more of the following: Temporary or 
permanent hearing impairment; non-auditory physical or physiological 
effects; behavioral disturbance; stress; and masking (Richardson et 
al., 1995; Gordon et al., 2004; Nowacek et al., 2007; Southall et al., 
2007; G[ouml]tz et al., 2009). The degree of effect is intrinsically 
related to the signal characteristics, received level, distance from 
the source, and duration of the sound exposure. In general, sudden, 
high level sounds can cause hearing loss, as can longer exposures to 
lower level sounds. Temporary or permanent loss of hearing, if it 
occurs at all, will occur almost exclusively in cases where a noise is 
within an animal's hearing frequency range. We first describe specific 
manifestations of acoustic effects before providing discussion specific 
to the use of airgun arrays.
---------------------------------------------------------------------------

    \1\ Please refer to the information given previously 
(``Description of Active Acoustic Sound Sources'') regarding sound, 
characteristics of sound types, and metrics used in this document.
---------------------------------------------------------------------------

    Richardson et al. (1995) described zones of increasing intensity of 
effect that might be expected to occur, in relation to distance from a 
source and assuming that the signal is within an animal's hearing 
range. First is the area within which the acoustic signal would be 
audible (potentially perceived) to the animal, but not strong enough to 
elicit any overt behavioral or physiological response. The next zone 
corresponds with the area where the signal is audible to the animal and 
of sufficient intensity to elicit behavioral or physiological response. 
Third is a zone within which, for signals of high intensity, the 
received level is sufficient to potentially cause discomfort or tissue 
damage to auditory or other systems. Overlaying these zones to a 
certain extent is the

[[Page 56167]]

area within which masking (i.e., when a sound interferes with or masks 
the ability of an animal to detect a signal of interest that is above 
the absolute hearing threshold) may occur; the masking zone may be 
highly variable in size.
    We describe the more severe effects of certain non-auditory 
physical or physiological effects only briefly as we do not expect that 
use of airgun arrays are reasonably likely to result in such effects 
(see below for further discussion). Potential effects from impulsive 
sound sources can range in severity from effects such as behavioral 
disturbance or tactile perception to physical discomfort, slight injury 
of the internal organs and the auditory system, or mortality (Yelverton 
et al., 1973). Non-auditory physiological effects or injuries that 
theoretically might occur in marine mammals exposed to high level 
underwater sound or as a secondary effect of extreme behavioral 
reactions (e.g., change in dive profile as a result of an avoidance 
reaction) caused by exposure to sound include neurological effects, 
bubble formation, resonance effects, and other types of organ or tissue 
damage (Cox et al., 2006; Southall et al., 2007; Zimmer and Tyack, 
2007; Tal et al., 2015). The survey activities considered here do not 
involve the use of devices such as explosives or mid-frequency tactical 
sonar that are associated with these types of effects.
    Threshold Shift--Marine mammals exposed to high-intensity sound, or 
to lower-intensity sound for prolonged periods, can experience hearing 
threshold shift (TS), which is the loss of hearing sensitivity at 
certain frequency ranges (Finneran, 2015). Threshold shift can be 
permanent (PTS), in which case the loss of hearing sensitivity is not 
fully recoverable, or temporary (TTS), in which case the animal's 
hearing threshold would recover over time (Southall et al., 2007). 
Repeated sound exposure that leads to TTS could cause PTS. In severe 
cases of PTS, there can be total or partial deafness, while in most 
cases the animal has an impaired ability to hear sounds in specific 
frequency ranges (Kryter, 1985).
    When PTS occurs, there is physical damage to the sound receptors in 
the ear (i.e., tissue damage), whereas TTS represents primarily tissue 
fatigue and is reversible (Southall et al., 2007). In addition, other 
investigators have suggested that TTS is within the normal bounds of 
physiological variability and tolerance and does not represent physical 
injury (e.g., Ward, 1997). Therefore, NMFS does not typically consider 
TTS to constitute auditory injury.
    Relationships between TTS and PTS thresholds have not been studied 
in marine mammals. There is no PTS data for cetaceans, but such 
relationships are assumed to be similar to those in humans and other 
terrestrial mammals. PTS typically occurs at exposure levels at least 
several dBs above (a 40-dB threshold shift approximates PTS onset; 
e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB 
threshold shift approximates TTS onset; e.g., Southall et al. 2007). 
Based on data from terrestrial mammals, a precautionary assumption is 
that the PTS thresholds for impulsive sounds (such as airgun pulses as 
received close to the source) are at least 6 dB higher than the TTS 
threshold on a peak-pressure basis and PTS cumulative sound exposure 
level thresholds are 15 to 20 dB higher than TTS cumulative sound 
exposure level thresholds (Southall et al., 2007). Given the higher 
level of sound or longer exposure duration necessary to cause PTS as 
compared with TTS, it is considerably less likely that PTS could occur.
    TTS is the mildest form of hearing impairment that can occur during 
exposure to sound (Kryter, 1985). While experiencing TTS, the hearing 
threshold rises, and a sound must be at a higher level in order to be 
heard. In terrestrial and marine mammals, TTS can last from minutes or 
hours to days (in cases of strong TTS). In many cases, hearing 
sensitivity recovers rapidly after exposure to the sound ends. Few data 
on sound levels and durations necessary to elicit mild TTS have been 
obtained for marine mammals.
    Marine mammal hearing plays a critical role in communication with 
conspecifics, and interpretation of environmental cues for purposes 
such as predator avoidance and prey capture. Depending on the degree 
(elevation of threshold in dB), duration (i.e., recovery time), and 
frequency range of TTS, and the context in which it is experienced, TTS 
can have effects on marine mammals ranging from discountable to 
serious. For example, a marine mammal may be able to readily compensate 
for a brief, relatively small amount of TTS in a non-critical frequency 
range that occurs during a time where ambient noise is lower and there 
are not as many competing sounds present. Alternatively, a larger 
amount and longer duration of TTS sustained during time when 
communication is critical for successful mother/calf interactions could 
have more serious impacts.
    Finneran et al. (2015) measured hearing thresholds in 3 captive 
bottlenose dolphins before and after exposure to 10 pulses produced by 
a seismic airgun in order to study TTS induced after exposure to 
multiple pulses. Exposures began at relatively low levels and gradually 
increased over a period of several months, with the highest exposures 
at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from 
193-195 dB. No substantial TTS was observed. In addition, behavioral 
reactions were observed that indicated that animals can learn behaviors 
that effectively mitigate noise exposures (although exposure patterns 
must be learned, which is less likely in wild animals than for the 
captive animals considered in this study). The authors note that the 
failure to induce more significant auditory effects was likely due to 
the intermittent nature of exposure, the relatively low peak pressure 
produced by the acoustic source, and the low-frequency energy in airgun 
pulses as compared with the frequency range of best sensitivity for 
dolphins and other mid-frequency cetaceans.
    Currently, TTS data only exist for four species of cetaceans 
(bottlenose dolphin (Tursiops truncatus), beluga whale (Delphinapterus 
leucas), harbor porpoise (Phocoena phocoena), and Yangtze finless 
porpoise (Neophocaena asiaeorientalis)) exposed to a limited number of 
sound sources (i.e., mostly tones and octave-band noise) in laboratory 
settings (Finneran, 2015). In general, harbor porpoises have a lower 
TTS onset than other measured cetacean species (Finneran, 2015). 
Additionally, the existing marine mammal TTS data come from a limited 
number of individuals within these species. There is no direct data 
available on noise-induced hearing loss for mysticetes.
    Critical questions remain regarding the rate of TTS growth and 
recovery after exposure to intermittent noise and the effects of single 
and multiple pulses. Data at present are also insufficient to construct 
generalized models for recovery and determine the time necessary to 
treat subsequent exposures as independent events. More information is 
needed on the relationship between auditory evoked potential and 
behavioral measures of TTS for various stimuli. For summaries of data 
on TTS in marine mammals or for further discussion of TTS onset 
thresholds, please see Southall et al. (2007, 2019), Finneran and 
Jenkins (2012), Finneran (2015), and NMFS (2018).
    Behavioral Effects--Behavioral disturbance may include a variety of 
effects, including subtle changes in behavior (e.g., minor or brief 
avoidance of an area or changes in vocalizations), more conspicuous 
changes in similar

[[Page 56168]]

behavioral activities, and more sustained and/or potentially severe 
reactions, such as displacement from or abandonment of high-quality 
habitat. Behavioral responses to sound are highly variable and context-
specific, and any reactions depend on numerous intrinsic and extrinsic 
factors (e.g., species, state of maturity, experience, current 
activity, reproductive state, auditory sensitivity, time of day), as 
well as the interplay between factors (e.g., Richardson et al., 1995; 
Wartzok et al., 2003; Southall et al., 2007, 2019; Weilgart, 2007; 
Archer et al., 2010). Behavioral reactions can vary not only among 
individuals but also within an individual, depending on previous 
experience with a sound source, context, and numerous other factors 
(Ellison et al., 2012), and can vary depending on characteristics 
associated with the sound source (e.g., whether it is moving or 
stationary, number of sources, distance from the source). Please see 
appendices B-C of Southall et al. (2007) for a review of studies 
involving marine mammal behavioral responses to sound.
    Habituation can occur when an animal's response to a stimulus wanes 
with repeated exposure, usually in the absence of unpleasant associated 
events (Wartzok et al., 2003). Animals are most likely to habituate to 
sounds that are predictable and unvarying. It is important to note that 
habituation is appropriately considered as a ``progressive reduction in 
response to stimuli that are perceived as neither aversive nor 
beneficial,'' rather than as, more generally, moderation in response to 
human disturbance (Bejder et al., 2009). The opposite process is 
sensitization, when an unpleasant experience leads to subsequent 
responses, often in the form of avoidance, at a lower level of 
exposure. As noted, behavioral state may affect the type of response. 
For example, animals that are resting may show greater behavioral 
change in response to disturbing sound levels than animals that are 
highly motivated to remain in an area for feeding (Richardson et al., 
1995; NRC, 2003; Wartzok et al., 2003). Controlled experiments with 
captive marine mammals have shown pronounced behavioral reactions, 
including avoidance of loud sound sources (Ridgway et al., 1997). 
Observed responses of wild marine mammals to loud pulsed sound sources 
(typically seismic airguns or acoustic harassment devices) vary but 
often consist of avoidance behavior or other behavioral changes 
suggesting discomfort (Morton and Symonds, 2002; see also Richardson et 
al., 1995; Nowacek et al., 2007). However, many delphinids approach 
acoustic source vessels with no apparent discomfort or obvious 
behavioral change (e.g., Barkaszi et al., 2012).
    Available studies show wide variation in response to underwater 
sound; therefore, it is difficult to predict specifically how any given 
sound in a particular instance might affect marine mammals perceiving 
the signal. If a marine mammal reacts briefly to underwater sound by 
changing its behavior or moving a small distance, the impacts of the 
behavioral change are unlikely to be significant to the individual, let 
alone the stock or population. However, if a sound source displaces 
marine mammals from an important feeding or breeding area for a 
prolonged period, impacts on individuals and populations could be 
significant (e.g., Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 
2005). There are broad categories of potential response, which we 
describe in greater detail here, that include changes in dive behavior, 
disruption of foraging (feeding) behavior, changes in respiration 
(breathing), interference with or alteration of vocalization, 
avoidance, and flight.
    Changes in dive behavior can vary widely, and may consist of 
increased or decreased dive times and surface intervals as well as 
changes in the rates of ascent and descent during a dive (e.g., Frankel 
and Clark, 2000; Ng and Leung, 2003; Nowacek et al., 2004; Goldbogen et 
al., 2013a, b). Variations in dive behavior may reflect disruptions in 
biologically significant activities (e.g., foraging) or they may be of 
little biological significance. The impact of an alteration to dive 
behavior resulting from an acoustic exposure depends on what the animal 
is doing at the time of the exposure and the type and magnitude of the 
response.
    Disruption of foraging (feeding) behavior can be difficult to 
correlate with anthropogenic sound exposure, so it is usually inferred 
by observed displacement from known foraging areas, the appearance of 
secondary indicators (e.g., bubble nets or sediment plumes), or changes 
in dive behavior. As for other types of behavioral response, the 
frequency, duration, and temporal pattern of signal presentation, as 
well as differences in species sensitivity, are likely contributing 
factors to differences in response in any given circumstance (e.g., 
Croll et al., 2001; Nowacek et al.; 2004; Madsen et al., 2006; Yazvenko 
et al., 2007). A determination of whether foraging disruptions 
adversely affect fitness would require information on or estimates of 
the energetic requirements of the affected individuals and the 
relationship between prey availability, foraging effort and success, 
and the life history stage of the animal.
    Visual tracking, passive acoustic monitoring (PAM), and movement 
recording tags were used to quantify sperm whale behavior prior to, 
during, and following exposure to airgun arrays at received levels in 
the range of 140-160 dB and distances of 7-13 km, following a phase-in 
of sound intensity and full array exposures at 1-13 km (Madsen et al., 
2006; Miller et al., 2009). Sperm whales did not exhibit horizontal 
avoidance behavior at the surface. However, foraging behavior may have 
been affected. The sperm whales exhibited 19 percent less vocal, or 
buzz, rate during full exposure relative to post exposure, and the 
whale that was approached most closely had an extended resting period 
and did not resume foraging until the airguns ceased firing. The 
remaining whales continued to execute foraging dives throughout 
exposure; however, swimming movements during foraging dives were 6 
percent lower during exposure than they were during control periods 
(Miller et al., 2009). These data raise concerns that seismic surveys 
may impact foraging behavior in sperm whales, although more data is 
required to understand whether the differences were due to exposure or 
natural variation in sperm whale behavior (Miller et al., 2009).
    Changes in respiration naturally vary with different behaviors and 
alterations to breathing rate as a function of acoustic exposure can be 
expected to co-occur with other behavioral reactions, such as a flight 
response or an alteration in diving. However, respiration rates in and 
of themselves may be representative of annoyance or an acute stress 
response. Various studies have shown that respiration rates may either 
be unaffected or could increase, depending on the species and signal 
characteristics, again highlighting the importance in understanding 
species differences in the tolerance of underwater noise when 
determining the potential for impacts resulting from anthropogenic 
sound exposure (e.g., Kastelein et al., 2001, 2005, 2006; Gailey et 
al., 2007, 2016).
    Marine mammals vocalize for different purposes and across multiple 
modes, such as whistling, echolocation click production, calling, and 
singing. Changes in vocalization behavior in response to anthropogenic 
noise can occur for any of these modes and may result from a need to 
compete with an increase in background noise or may

[[Page 56169]]

reflect increased vigilance or a startle response. For example, in the 
presence of potentially masking signals, humpback whales and killer 
whales have been observed to increase the length of their songs or 
amplitude of calls (Miller et al., 2000; Fristrup et al., 2003; Foote 
et al., 2004; Holt et al., 2012), while right whales have been observed 
to shift the frequency content of their calls upward while reducing the 
rate of calling in areas of increased anthropogenic noise (Parks et 
al., 2007). In some cases, animals may cease sound production during 
production of aversive signals (Bowles et al., 1994).
    Cerchio et al. (2014) used PAM to document the presence of singing 
humpback whales off the coast of northern Angola and to 
opportunistically test for the effect of seismic survey activity on the 
number of singing whales. Two recording units were deployed between 
March and December 2008 in the offshore environment; numbers of singers 
were counted every hour. Generalized Additive Mixed Models were used to 
assess the effect of survey day (seasonality), hour (diel variation), 
moon phase, and received levels of noise (measured from a single pulse 
during each 10 minutes sampled period) on singer number. The number of 
singers significantly decreased with increasing received level of 
noise, suggesting that humpback whale communication was disrupted to 
some extent by the survey activity.
    Castellote et al. (2012) reported acoustic and behavioral changes 
by fin whales in response to shipping and airgun noise. Acoustic 
features of fin whale song notes recorded in the Mediterranean Sea and 
northeast Atlantic Ocean were compared for areas with different 
shipping noise levels and traffic intensities and during a seismic 
airgun survey. During the first 72 hours of the survey, a steady 
decrease in song received levels and bearings to singers indicated that 
whales moved away from the acoustic source and out of the study area. 
This displacement persisted for a time period well beyond the 10-day 
duration of seismic airgun activity, providing evidence that fin whales 
may avoid an area for an extended period in the presence of increased 
noise. The authors hypothesize that fin whale acoustic communication is 
modified to compensate for increased background noise and that a 
sensitization process may play a role in the observed temporary 
displacement.
    Seismic pulses at average received levels of 131 dB re 1 [mu]Pa\2\-
s caused blue whales to increase call production (Di Iorio and Clark, 
2010). In contrast, McDonald et al. (1995) tracked a blue whale with 
seafloor seismometers and reported that it stopped vocalizing and 
changed its travel direction at a range of 10 km from the acoustic 
source vessel (estimated received level 143 dB pk-pk). Blackwell et al. 
(2013) found that bowhead whale call rates dropped significantly at 
onset of airgun use at sites with a median distance of 41-45 km from 
the survey. Blackwell et al. (2015) expanded this analysis to show that 
whales actually increased calling rates as soon as airgun signals were 
detectable before ultimately decreasing calling rates at higher 
received levels (i.e., 10-minute cumulative sound exposure level 
(SELcum) of ~127 dB). Overall, these results suggest that 
bowhead whales may adjust their vocal output in an effort to compensate 
for noise before ceasing vocalization effort and ultimately deflecting 
from the acoustic source (Blackwell et al., 2013, 2015). These studies 
demonstrate that even low levels of noise received far from the source 
can induce changes in vocalization and/or behavior for mysticetes.
    Avoidance is the displacement of an individual from an area or 
migration path as a result of the presence of sound or other stressors, 
and is one of the most obvious manifestations of disturbance in marine 
mammals (Richardson et al., 1995). For example, gray whales are known 
to change direction--deflecting from customary migratory paths--in 
order to avoid noise from seismic surveys (Malme et al., 1984). 
Humpback whales show avoidance behavior in the presence of an active 
seismic array during observational studies and controlled exposure 
experiments in western Australia (McCauley et al., 2000). Avoidance may 
be short-term, with animals returning to the area once the noise has 
ceased (e.g., Bowles et al., 1994; Goold, 1996; Stone et al., 2000; 
Morton and Symonds, 2002; Gailey et al., 2007). Longer-term 
displacement is possible, however, which may lead to changes in 
abundance or distribution patterns of the affected species in the 
affected region if habituation to the presence of the sound does not 
occur (e.g., Bejder et al., 2006; Teilmann et al., 2006).
    Forney et al. (2017) detail the potential effects of noise on 
marine mammal populations with high site fidelity, including 
displacement and auditory masking, noting that a lack of observed 
response does not imply absence of fitness costs and that apparent 
tolerance of disturbance may have population-level impacts that are 
less obvious and difficult to document. Avoidance of spatiotemporal 
overlap between disturbing noise and areas and/or times of particular 
importance for sensitive species may be critical to avoiding 
population-level impacts because (particularly for animals with high 
site fidelity) there may be a strong motivation to remain in the area 
despite negative impacts. Forney et al. (2017) state that, for these 
animals, remaining in a disturbed area may reflect a lack of 
alternatives rather than a lack of effects.
    Forney et al. (2017) specifically discuss beaked whales, stating 
that until recently most knowledge of beaked whales was derived from 
strandings, as they have been involved in atypical mass stranding 
events associated with mid-frequency active sonar (MFAS) training 
operations. Given these observations and recent research, beaked whales 
appear to be particularly sensitive and vulnerable to certain types of 
acoustic disturbance relative to most other marine mammal species. 
Individual beaked whales reacted strongly to experiments using 
simulated MFAS at low received levels, by moving away from the sound 
source and stopping foraging for extended periods. These responses, if 
on a frequent basis, could result in significant fitness costs to 
individuals (Forney et al., 2017). Additionally, difficulty in 
detection of beaked whales due to their cryptic surfacing behavior and 
silence when near the surface pose problems for mitigation measures 
employed to protect beaked whales. Forney et al. (2017) specifically 
states that failure to consider both displacement of beaked whales from 
their habitat and noise exposure could lead to more severe biological 
consequences.
    A flight response is a dramatic change in normal movement to a 
directed and rapid movement away from the perceived location of a sound 
source. The flight response differs from other avoidance responses in 
the intensity of the response (e.g., directed movement, rate of 
travel). Relatively little information on flight responses of marine 
mammals to anthropogenic signals exist, although observations of flight 
responses to the presence of predators have occurred (Connor and 
Heithaus, 1996). The result of a flight response could range from 
brief, temporary exertion and displacement from the area where the 
signal provokes flight to, in extreme cases, marine mammal strandings 
(Evans and England, 2001). However, it should be noted that response to 
a perceived predator does not necessarily invoke flight (Ford and 
Reeves, 2008), and whether individuals are alone or in groups may 
influence the response.

[[Page 56170]]

    Behavioral disturbance can also impact marine mammals in more 
subtle ways. Increased vigilance may result in costs related to 
diversion of focus and attention (i.e., when a response consists of 
increased vigilance, it may come at the cost of decreased attention to 
other critical behaviors such as foraging or resting). These effects 
have generally not been demonstrated for marine mammals, but studies 
involving fish and terrestrial animals have shown that increased 
vigilance may substantially reduce feeding rates (e.g., Beauchamp and 
Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In 
addition, chronic disturbance can cause population declines through 
reduction of fitness (e.g., decline in body condition) and subsequent 
reduction in reproductive success, survival, or both (e.g., Harrington 
and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, 
Ridgway et al. (2006) reported that increased vigilance in bottlenose 
dolphins exposed to sound over a 5-day period did not cause any sleep 
deprivation or stress effects.
    Many animals perform vital functions, such as feeding, resting, 
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption 
of such functions resulting from reactions to stressors, such as sound 
exposure, are more likely to be significant if they last more than one 
diel cycle or recur on subsequent days (Southall et al., 2007). 
Consequently, a behavioral response lasting less than 1 day and not 
recurring on subsequent days is not considered particularly severe 
unless it could directly affect reproduction or survival (Southall et 
al., 2007). Note that there is a difference between multi-day 
substantive behavioral reactions and multi-day anthropogenic 
activities. For example, just because an activity lasts for multiple 
days does not necessarily mean that individual animals are either 
exposed to activity-related stressors for multiple days or, further, 
exposed in a manner resulting in sustained multi-day substantive 
behavioral responses.
    Stone (2015) reported data from at-sea observations during 1,196 
seismic surveys from 1994 to 2010. When large arrays of airguns 
(considered to be 500 in\3\ or more in that study) were firing, lateral 
displacement, more localized avoidance, or other changes in behavior 
were evident for most odontocetes. However, significant responses to 
large arrays were found only for the minke whale and fin whale. 
Behavioral responses observed included changes in swimming or surfacing 
behavior, with indications that cetaceans remained near the water 
surface at these times. Cetaceans were recorded as feeding less often 
when large arrays were active. Behavioral observations of gray whales 
during a seismic survey monitored whale movements and respirations pre-
, during, and post-seismic survey (Gailey et al., 2016). Behavioral 
state and water depth were the best ``natural'' predictors of whale 
movements and respiration and, after considering natural variation, 
none of the response variables were significantly associated with 
seismic survey or vessel sounds.
    Stress Responses--An animal's perception of a threat may be 
sufficient to trigger stress responses consisting of some combination 
of behavioral responses, autonomic nervous system responses, 
neuroendocrine responses, or immune responses (e.g., Seyle, 1950; 
Moberg, 2000). In many cases, an animal's first and sometimes most 
economical (in terms of energetic costs) response is behavioral 
avoidance of the potential stressor. Autonomic nervous system responses 
to stress typically involve changes in heart rate, blood pressure, and 
gastrointestinal activity. These responses have a relatively short 
duration and may or may not have a significant long-term effect on an 
animal's fitness.
    Neuroendocrine stress responses often involve the hypothalamus-
pituitary-adrenal system. Virtually all neuroendocrine functions that 
are affected by stress--including immune competence, reproduction, 
metabolism, and behavior--are regulated by pituitary hormones. Stress-
induced changes in the secretion of pituitary hormones have been 
implicated in failed reproduction, altered metabolism, reduced immune 
competence, and behavioral disturbance (e.g., Moberg, 1987; Blecha, 
2000). Increases in the circulation of glucocorticoids are also equated 
with stress (Romano et al., 2004).
    The primary distinction between stress (which is adaptive and does 
not normally place an animal at risk) and distress is the cost of the 
response. During a stress response, an animal uses glycogen stores that 
can be quickly replenished once the stress is alleviated. In such 
circumstances, the cost of the stress response would not pose serious 
fitness consequences. However, when an animal does not have sufficient 
energy reserves to satisfy the energetic costs of a stress response, 
energy resources must be diverted from other functions. This state of 
distress will last until the animal replenishes its energetic reserves 
sufficiently to restore normal function.
    Relationships between these physiological mechanisms, animal 
behavior, and the costs of stress responses are well-studied through 
controlled experiments and for both laboratory and free-ranging animals 
(e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003; 
Krausman et al., 2004; Lankford et al., 2005). Stress responses due to 
exposure to anthropogenic sounds or other stressors and their effects 
on marine mammals have also been reviewed (Fair and Becker, 2000; 
Romano et al., 2002b) and, more rarely, studied in wild populations 
(e.g., Romano et al., 2002a). For example, Rolland et al. (2012) found 
that noise reduction from reduced ship traffic in the Bay of Fundy was 
associated with decreased stress in North Atlantic right whales. These 
and other studies lead to a reasonable expectation that some marine 
mammals will experience physiological stress responses upon exposure to 
acoustic stressors and that it is possible that some of these would be 
classified as ``distress.'' In addition, any animal experiencing TTS 
would likely also experience stress responses (NRC, 2003).
    Auditory Masking--Sound can disrupt behavior through masking, or 
interfering with, an animal's ability to detect, recognize, or 
discriminate between acoustic signals of interest (e.g., those used for 
intraspecific communication and social interactions, prey detection, 
predator avoidance, navigation) (Richardson et al., 1995; Erbe et al., 
2016). Masking occurs when the receipt of a sound is interfered with by 
another coincident sound at similar frequencies and at similar or 
higher intensity, and may occur whether the sound is natural (e.g., 
snapping shrimp, wind, waves, precipitation) or anthropogenic (e.g., 
shipping, sonar, seismic exploration) in origin. The ability of a noise 
source to mask biologically important sounds depends on the 
characteristics of both the noise source and the signal of interest 
(e.g., signal-to-noise ratio, temporal variability, direction), in 
relation to each other and to an animal's hearing abilities (e.g., 
sensitivity, frequency range, critical ratios, frequency 
discrimination, directional discrimination, age or TTS hearing loss), 
and existing ambient noise and propagation conditions.
    Under certain circumstances, significant masking could disrupt 
behavioral patterns, which in turn could affect fitness for survival 
and reproduction. It is important to distinguish TTS and PTS, which 
persist after the sound exposure, from masking, which occurs during the 
sound exposure. Because masking (without resulting in TS) is not 
associated with abnormal physiological function, it is

[[Page 56171]]

not considered a physiological effect, but rather a potential 
behavioral effect.
    The frequency range of the potentially masking sound is important 
in predicting any potential behavioral impacts. For example, low-
frequency signals may have less effect on high-frequency echolocation 
sounds produced by odontocetes but are more likely to affect detection 
of mysticete communication calls and other potentially important 
natural sounds such as those produced by surf and some prey species. 
The masking of communication signals by anthropogenic noise may be 
considered as a reduction in the communication space of animals (e.g., 
Clark et al., 2009) and may result in energetic or other costs as 
animals change their vocalization behavior (e.g., Miller et al., 2000; 
Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2009; Holt 
et al., 2009). Masking may be less in situations where the signal and 
noise come from different directions (Richardson et al., 1995), through 
amplitude modulation of the signal, or through other compensatory 
behaviors (Houser and Moore, 2014). Masking can be tested directly in 
captive species (e.g., Erbe, 2008), but in wild populations it must be 
either modeled or inferred from evidence of masking compensation. There 
are few studies addressing real-world masking sounds likely to be 
experienced by marine mammals in the wild (e.g., Branstetter et al., 
2013).
    Masking affects both senders and receivers of acoustic signals and 
can potentially have long-term chronic effects on marine mammals at the 
population level as well as at the individual level. Low-frequency 
ambient sound levels have increased by as much as 20 dB (more than 
three times in terms of SPL) in the world's ocean from pre-industrial 
periods, with most of the increase from distant commercial shipping 
(Hildebrand, 2009). All anthropogenic sound sources, but especially 
chronic and lower-frequency signals (e.g., from vessel traffic), 
contribute to elevated ambient sound levels, thus intensifying masking.
    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited, although there is little specific data on this. Because 
of the intermittent nature and low duty cycle of seismic pulses, 
animals can emit and receive sounds in the relatively quiet intervals 
between pulses. However, in exceptional situations, reverberation 
occurs for much or all of the interval between pulses (e.g., Simard et 
al. 2005; Clark and Gagnon 2006), which could mask calls. Situations 
with prolonged strong reverberation are infrequent. However, it is 
common for reverberation to cause some lesser degree of elevation of 
the background level between airgun pulses (e.g., Gedamke 2011; Guerra 
et al. 2011, 2016; Klinck et al. 2012; Guan et al. 2015), and this 
weaker reverberation presumably reduces the detection range of calls 
and other natural sounds to some degree. Guerra et al. (2016) reported 
that ambient noise levels between seismic pulses were elevated as a 
result of reverberation at ranges of 50 km from the seismic source. 
Based on measurements in deep water of the Southern Ocean, Gedamke 
(2011) estimated that the slight elevation of background noise levels 
during intervals between seismic pulses reduced blue and fin whale 
communication space by as much as 36-51 percent when a seismic survey 
was operating 450-2,800 km away. Based on preliminary modeling, 
Wittekind et al. (2016) reported that airgun sounds could reduce the 
communication range of blue and fin whales 2,000 km from the seismic 
source. Nieukirk et al. (2012) and Blackwell et al. (2013) noted the 
potential for masking effects from seismic surveys on large whales.
    Some baleen and toothed whales are known to continue calling in the 
presence of seismic pulses, and their calls usually can be heard 
between the pulses (e.g., Nieukirk et al. 2012; Thode et al. 2012; 
Br[ouml]ker et al. 2013; Sciacca et al. 2016). Cerchio et al. (2014) 
suggested that the breeding display of humpback whales off Angola could 
be disrupted by seismic sounds, as singing activity declined with 
increasing received levels. In addition, some cetaceans are known to 
change their calling rates, shift their peak frequencies, or otherwise 
modify their vocal behavior in response to airgun sounds (e.g., Di 
Iorio and Clark 2010; Castellote et al. 2012; Blackwell et al. 2013, 
2015). The hearing systems of baleen whales are more sensitive to low-
frequency sounds than are the ears of the small odontocetes that have 
been studied directly (e.g., MacGillivray et al., 2014). The sounds 
important to small odontocetes are predominantly at much higher 
frequencies than are the dominant components of airgun sounds, thus 
limiting the potential for masking. In general, masking effects of 
seismic pulses are expected to be minor, given the normally 
intermittent nature of seismic pulses.

Vessel Noise

    Vessel noise from the R/V Langseth could affect marine animals in 
the proposed survey areas. Houghton et al. (2015) proposed that vessel 
speed is the most important predictor of received noise levels, and 
Putland et al. (2017) also reported reduced sound levels with decreased 
vessel speed. However, some energy is also produced at higher 
frequencies (Hermannsen et al., 2014); low levels of high-frequency 
sound from vessels has been shown to elicit responses in harbor 
porpoise (Dyndo et al., 2015).
    Vessel noise, through masking, can reduce the effective 
communication distance of a marine mammal if the frequency of the sound 
source is close to that used by the animal, and if the sound is present 
for a significant fraction of time (e.g., Richardson et al. 1995; Clark 
et al., 2009; Jensen et al., 2009; Gervaise et al., 2012; Hatch et al., 
2012; Rice et al., 2014; Dunlop 2015; Erbe et al., 2015; Jones et al., 
2017; Putland et al., 2017). In addition to the frequency and duration 
of the masking sound, the strength, temporal pattern, and location of 
the introduced sound also play a role in the extent of the masking 
(Branstetter et al., 2013, 2016; Finneran and Branstetter 2013; Sills 
et al., 2017). Branstetter et al. (2013) reported that time-domain 
metrics are also important in describing and predicting masking.
    Baleen whales are thought to be more sensitive to sound at these 
low frequencies than are toothed whales (e.g., MacGillivray et al. 
2014), possibly causing localized avoidance of the proposed survey area 
during seismic operations. Many odontocetes show considerable tolerance 
of vessel traffic, although they sometimes react at long distances if 
confined by ice or shallow water, if previously harassed by vessels, or 
have had little or no recent exposure to vessels (Richardson et al. 
1995). Pirotta et al. (2015) noted that the physical presence of 
vessels, not just ship noise, disturbed the foraging activity of 
bottlenose dolphins. There is little data on the behavioral reactions 
of beaked whales to vessel noise, though they seem to avoid approaching 
vessels (e.g., W[uuml]rsig et al., 1998) or dive for an extended period 
when approached by a vessel (e.g., Kasuya 1986).
    In summary, project vessel sounds would not be at levels expected 
to cause anything more than possible localized and temporary behavioral 
changes in marine mammals, and would not be expected to result in 
significant negative effects on individuals or at the population level. 
In addition, in all oceans of the world, large vessel traffic is 
currently so prevalent that it is commonly considered a usual source of 
ambient sound (NSF-USGS 2011).

[[Page 56172]]

Vessel Strike

    Vessel collisions with marine mammals, or vessel strikes, can 
result in death or serious injury of the animal. Wounds resulting from 
vessel strike may include massive trauma, hemorrhaging, broken bones, 
or propeller lacerations (Knowlton and Kraus, 2001). An animal at the 
surface may be struck directly by a vessel, a surfacing animal may hit 
the bottom of a vessel, or an animal just below the surface may be cut 
by a vessel's propeller. Superficial strikes may not kill or result in 
the death of the animal. These interactions are typically associated 
with large whales (e.g., fin whales), which are occasionally found 
draped across the bulbous bow of large commercial vessels upon arrival 
in port. Although smaller cetaceans are more maneuverable in relation 
to large vessels than are large whales, they may also be susceptible to 
vessel strikes. The severity of injuries typically depends on the size 
and speed of the vessel, with the probability of death or serious 
injury increasing as vessel speed increases (Knowlton and Kraus, 2001; 
Laist et al., 2001; Vanderlaan and Taggart, 2007; Conn and Silber, 
2013). Impact forces increase with speed, as does the probability of a 
strike at a given distance (Silber et al., 2010; Gende et al., 2011).
    Pace and Silber (2005) also found that the probability of death or 
serious injury increased rapidly with increasing vessel speed. 
Specifically, the predicted probability of serious injury or death 
increased from 45 to 75 percent as vessel speed increased from 10 to 14 
knots (kn (26 kilometer per hour (kph)), and exceeded 90 percent at 17 
kn (31 kph). Higher speeds during collisions result in greater force of 
impact, but higher speeds also appear to increase the chance of severe 
injuries or death through increased likelihood of collision by pulling 
whales toward the vessel (Clyne, 1999; Knowlton et al., 1995). In a 
separate study, Vanderlaan and Taggart (2007) analyzed the probability 
of lethal mortality of large whales at a given speed, showing that the 
greatest rate of change in the probability of a lethal injury to a 
large whale as a function of vessel speed occurs between 8.6 and 15 kn 
(28 kph). The chances of a lethal injury decline from approximately 80 
percent at 15 kn (28 kph) to approximately 20 percent at 8.6 kn (16 
kph). At speeds below 11.8 kn (22 kph), the chances of lethal injury 
drop below 50 percent, while the probability asymptotically increases 
toward 100 percent above 15 kn (28 kph).
    The R/V Langseth will travel at a speed of 5 kn (9 kph) while 
towing seismic survey gear. At this speed, both the possibility of 
striking a marine mammal and the possibility of a strike resulting in 
serious injury or mortality are discountable. At average transit speed, 
the probability of serious injury or mortality resulting from a strike 
is less than 50 percent. However, the likelihood of a strike actually 
happening is again discountable. Vessel strikes, as analyzed in the 
studies cited above, generally involve commercial shipping, which is 
much more common in both space and time than is geophysical survey 
activity. Jensen and Silber (2004) summarized vessel strikes of large 
whales worldwide from 1975-2003 and found that most collisions occurred 
in the open ocean and involved large vessels (e.g., commercial 
shipping). No such incidents were reported for geophysical survey 
vessels during that time period.
    It is possible for vessel strikes to occur while traveling at slow 
speeds. For example, a hydrographic survey vessel traveling at low 
speed (5.5 kn (10 kph)) while conducting mapping surveys off the 
central California coast struck and killed a blue whale in 2009. The 
State of California determined that the whale had suddenly and 
unexpectedly surfaced beneath the hull, with the result that the 
propeller severed the whale's vertebrae, and that this was an 
unavoidable event. This strike represents the only such incident in 
approximately 540,000 hours of similar coastal mapping activity (p = 
1.9 x 10-6; 95 percent confidence interval = 0-5.5 x 
10-6; NMFS, 2013). In addition, a research vessel reported a 
fatal strike in 2011 of a dolphin in the Atlantic, demonstrating that 
it is possible for strikes involving smaller cetaceans to occur. In 
that case, the incident report indicated that an animal apparently was 
struck by the vessel's propeller as the animal was intentionally 
swimming near the vessel. While indicative of the type of unusual 
events that cannot be ruled out, neither of these instances represents 
a circumstance that would be considered reasonably foreseeable or that 
would be considered preventable.
    Although the likelihood of the vessel striking a marine mammal is 
low, we propose a robust vessel strike avoidance protocol (see Proposed 
Mitigation), which we believe eliminates any foreseeable risk of vessel 
strike during transit. We anticipate that vessel collisions involving a 
seismic data acquisition vessel towing gear, while not impossible, 
represent unlikely, unpredictable events for which there are no 
preventive measures. Given the proposed mitigation measures, the 
relatively slow speed of the vessel towing gear, the presence of bridge 
crew watching for obstacles at all times (including marine mammals), 
and the presence of marine mammal observers, the possibility of vessel 
strike is discountable and, further, were a strike of a large whale to 
occur, it would be unlikely to result in serious injury or mortality. 
No incidental take resulting from vessel strike is anticipated, and 
this potential effect of the specified activity will not be discussed 
further in the following analysis.
    Stranding--When a living or dead marine mammal swims or floats onto 
shore and becomes ``beached'' or incapable of returning to sea, the 
event is a ``stranding'' (Geraci et al., 1999; Perrin and Geraci, 2002; 
Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a 
stranding under the MMPA is that a marine mammal is dead and is on a 
beach or shore of the United States; or in waters under the 
jurisdiction of the United States (including any navigable waters); or 
a marine mammal is alive and is on a beach or shore of the United 
States and is unable to return to the water; on a beach or shore of the 
United States and, although able to return to the water, is in need of 
apparent medical attention; or in the waters under the jurisdiction of 
the United States (including any navigable waters), but is unable to 
return to its natural habitat under its own power or without 
assistance.
    Marine mammals strand for a variety of reasons, such as infectious 
agents, biotoxicosis, starvation, fishery interaction, vessel strike, 
unusual oceanographic or weather events, sound exposure, or 
combinations of these stressors sustained concurrently or in series. 
However, the cause or causes of most strandings are unknown (Geraci et 
al., 1976; Eaton, 1979; Odell et al., 1980; Best, 1982). Numerous 
studies suggest that the physiology, behavior, habitat relationships, 
age, or condition of cetaceans may cause them to strand or might 
predispose them to strand when exposed to another phenomenon. These 
suggestions are consistent with the conclusions of numerous other 
studies that have demonstrated that combinations of dissimilar 
stressors commonly combine to kill an animal or dramatically reduce its 
fitness, even though one exposure without the other does not produce 
the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; 
Fair and Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a; 
2005b, Romero, 2004; Sih et al., 2004).

[[Page 56173]]

    There is no conclusive evidence that exposure to airgun noise 
results in behaviorally-mediated forms of injury. Behaviorally-mediated 
injury (i.e., mass stranding events) has been primarily associated with 
beaked whales exposed to mid-frequency active (MFA) naval sonar. MFA 
sonar and the alerting stimulus used in Nowacek et al. (2004) are very 
different from the noise produced by airguns. As explained below, 
military MFA sonar is very different from airguns, and one should not 
assume that airguns will cause the same effects as MFA sonar (including 
strandings).
    To understand why military MFA sonar affects beaked whales 
differently than airguns do, it is important to note the distinction 
between behavioral sensitivity and susceptibility to auditory injury. 
To understand the potential for auditory injury in a particular marine 
mammal species in relation to a given acoustic signal, the frequency 
range the species is able to hear is critical, as well as the species' 
auditory sensitivity to frequencies within that range. Current data 
indicate that not all marine mammal species have equal hearing 
capabilities across all frequencies and, therefore, species are grouped 
into hearing groups with generalized hearing ranges assigned on the 
basis of available data (Southall et al., 2007, 2019). Hearing ranges 
as well as auditory sensitivity/susceptibility to frequencies within 
those ranges vary across the different groups. For example, in terms of 
hearing range, the high-frequency cetaceans (e.g., Kogia spp.) have a 
generalized hearing range of frequencies between 275 Hz and 160 kHz, 
while mid-frequency cetaceans--such as dolphins and beaked whales--have 
a generalized hearing range between 150 Hz to 160 kHz. Regarding 
auditory susceptibility within the hearing range, while mid-frequency 
cetaceans and high-frequency cetaceans have roughly similar hearing 
ranges, the high-frequency group is much more susceptible to noise-
induced hearing loss during sound exposure, i.e., these species have 
lower thresholds for these effects than other hearing groups (NMFS, 
2018). Referring to a species as behaviorally sensitive to noise simply 
means that an animal of that species is more likely to respond to lower 
received levels of sound than an animal of another species that is 
considered less behaviorally sensitive. So, while dolphin species and 
beaked whale species--both in the mid-frequency cetacean hearing 
group--are assumed to generally hear the same sounds equally well and 
be equally susceptible to noise-induced hearing loss (auditory injury), 
the best available information indicates that a beaked whale is more 
likely to behaviorally respond to that sound at a lower received level 
compared to an animal from other mid-frequency cetacean species that 
are less behaviorally sensitive. This distinction is important because, 
while beaked whales are more likely to respond behaviorally to sounds 
than are many other species (even at lower levels), they cannot hear 
the predominant, lower frequency sounds from seismic airguns as well as 
sounds that have more energy at frequencies that beaked whales can hear 
better (such as military MFA sonar).
    Military MFA sonar affects beaked whales differently than airguns 
do because it produces energy at different frequencies than airguns. 
Mid-frequency cetacean hearing is generically thought to be best 
between 8.8 to 110 kHz, i.e., these cutoff values define the range 
above and below which a species in the group is assumed to have 
declining auditory sensitivity, until reaching frequencies that cannot 
be heard (NMFS, 2018). However, beaked whale hearing is likely best 
within a higher, narrower range (20-80 kHz, with best sensitivity 
around 40 kHz), based on a few measurements of hearing in stranded 
beaked whales (Cook et al., 2006; Finneran et al., 2009; Pacini et al., 
2011) and several studies of acoustic signals produced by beaked whales 
(e.g., Frantzis et al., 2002; Johnson et al., 2004, 2006; Zimmer et 
al., 2005). While precaution requires that the full range of audibility 
be considered when assessing risks associated with noise exposure 
(Southall et al., 2007, 2019), animals typically produce sound at 
frequencies where they hear best. More recently, Southall et al. (2019) 
suggested that certain species in the historical mid-frequency hearing 
group (beaked whales, sperm whales, and killer whales) are likely more 
sensitive to lower frequencies within the group's generalized hearing 
range than are other species within the group, and state that the data 
for beaked whales suggest sensitivity to approximately 5 kHz. However, 
this information is consistent with the general conclusion that beaked 
whales (and other mid-frequency cetaceans) are relatively insensitive 
to the frequencies where most energy of an airgun signal is found. 
Military MFA sonar is typically considered to operate in the frequency 
range of approximately 3-14 kHz (D'Amico et al., 2009), i.e., outside 
the range of likely best hearing for beaked whales but within or close 
to the lower bounds, whereas most energy in an airgun signal is 
radiated at much lower frequencies, below 500 Hz (Dragoset, 1990).
    It is important to distinguish between energy (loudness, measured 
in dB) and frequency (pitch, measured in Hz). In considering the 
potential impacts of mid-frequency components of airgun noise (1-10 
kHz, where beaked whales can be expected to hear) on marine mammal 
hearing, one needs to account for the energy associated with these 
higher frequencies and determine what energy is truly ``significant.'' 
Although there is mid-frequency energy associated with airgun noise (as 
expected from a broadband source), airgun sound is predominantly below 
1 kHz (Breitzke et al., 2008; Tashmukhambetov et al., 2008; Tolstoy et 
al., 2009). As stated by Richardson et al. (1995), ``[. . .] most 
emitted [seismic airgun] energy is at 10-120 Hz, but the pulses contain 
some energy up to 500-1,000 Hz.'' Tolstoy et al. (2009) conducted 
empirical measurements, demonstrating that sound energy levels 
associated with airguns were at least 20 dB lower at 1 kHz (considered 
``mid-frequency'') compared to higher energy levels associated with 
lower frequencies (below 300 Hz) (``all but a small fraction of the 
total energy being concentrated in the 10-300 Hz range'' [Tolstoy et 
al., 2009]), and at higher frequencies (e.g., 2.6-4 kHz), power might 
be less than 10 percent of the peak power at 10 Hz (Yoder, 2002). 
Energy levels measured by Tolstoy et al. (2009) were even lower at 
frequencies above 1 kHz. In addition, as sound propagates away from the 
source, it tends to lose higher-frequency components faster than low-
frequency components (i.e., low-frequency sounds typically propagate 
longer distances than high-frequency sounds) (Diebold et al., 2010). 
Although higher-frequency components of airgun signals have been 
recorded, it is typically in surface-ducting conditions (e.g., DeRuiter 
et al., 2006; Madsen et al., 2006) or in shallow water, where there are 
advantageous propagation conditions for the higher frequency (but low-
energy) components of the airgun signal (Hermannsen et al., 2015). This 
should not be of concern because the likely behavioral reactions of 
beaked whales that can result in acute physical injury would result 
from noise exposure at depth (because of the potentially greater 
consequences of severe behavioral reactions). In summary, the frequency 
content of airgun signals is such that beaked whales will not be able 
to hear the signals well (compared to MFA sonar), especially at depth 
where we expect the

[[Page 56174]]

consequences of noise exposure could be more severe.
    Aside from frequency content, there are other significant 
differences between MFA sonar signals and the sounds produced by 
airguns that minimize the risk of severe behavioral reactions that 
could lead to strandings or deaths at sea, e.g., significantly longer 
signal duration, horizontal sound direction, typical fast and 
unpredictable source movement. All of these characteristics of MFA 
sonar tend towards greater potential to cause severe behavioral or 
physiological reactions in exposed beaked whales that may contribute to 
stranding. Although both sources are powerful, MFA sonar contains 
significantly greater energy in the mid-frequency range, where beaked 
whales hear better. Short-duration, high energy pulses--such as those 
produced by airguns--have greater potential to cause damage to auditory 
structures (though this is unlikely for mid-frequency cetaceans, as 
explained later in this document), but it is longer duration signals 
that have been implicated in the vast majority of beaked whale 
strandings. Faster, less predictable movements in combination with 
multiple source vessels are more likely to elicit a severe, potentially 
anti-predator response. Of additional interest in assessing the 
divergent characteristics of MFA sonar and airgun signals and their 
relative potential to cause stranding events or deaths at sea is the 
similarity between the MFA sonar signals and stereotyped calls of 
beaked whales' primary predator: the killer whale (Zimmer and Tyack, 
2007). Although generic disturbance stimuli--as airgun noise may be 
considered in this case for beaked whales--may also trigger 
antipredator responses, stronger responses should generally be expected 
when perceived risk is greater, as when the stimulus is confused for a 
known predator (Frid and Dill, 2002). In addition, because the source 
of the perceived predator (i.e., MFA sonar) will likely be closer to 
the whales (because attenuation limits the range of detection of mid-
frequencies) and moving faster (because it will be on faster-moving 
vessels), any antipredator response would be more likely to be severe 
(with greater perceived predation risk, an animal is more likely to 
disregard the cost of the response; Frid and Dill, 2002). Indeed, when 
analyzing movements of a beaked whale exposed to playback of killer 
whale predation calls, Allen et al. (2014) found that the whale engaged 
in a prolonged, directed avoidance response, suggesting a behavioral 
reaction that could pose a risk factor for stranding. Overall, these 
significant differences between sound from MFA sonar and the mid-
frequency sound component from airguns and the likelihood that MFA 
sonar signals will be interpreted in error as a predator are critical 
to understanding the likely risk of behaviorally-mediated injury due to 
seismic surveys.
    The available scientific literature also provides a useful contrast 
between airgun noise and MFA sonar regarding the likely risk of 
behaviorally-mediated injury. There is strong evidence for the 
association of beaked whale stranding events with MFA sonar use, and 
particularly detailed accounting of several events is available (e.g., 
a 2000 Bahamas stranding event for which investigators concluded that 
MFA sonar use was responsible; Evans and England, 2001). D'Amico et 
al., (2009) reviewed 126 beaked whale mass stranding events over the 
period from 1950 (i.e., from the development of modern MFA sonar 
systems) through 2004. Of these, there were two events where detailed 
information was available on both the timing and location of the 
stranding and the concurrent nearby naval activity, including 
verification of active MFA sonar usage, with no evidence for an 
alternative cause of stranding. An additional 10 events were at minimum 
spatially and temporally coincident with naval activity likely to have 
included MFA sonar use and, despite incomplete knowledge of timing and 
location of the stranding or the naval activity in some cases, there 
was no evidence for an alternative cause of stranding. The U.S. Navy 
has publicly stated agreement that five such events since 1996 were 
associated in time and space with MFA sonar use, either by the U.S. 
Navy alone or in joint training exercises with the North Atlantic 
Treaty Organization. The U.S. Navy additionally noted that, as of 2017, 
a 2014 beaked whale stranding event in Crete coincident with naval 
exercises was under review and had not yet been determined to be linked 
to sonar activities (U.S. Navy, 2017). Separately, the International 
Council for the Exploration of the Sea reported in 2005 that, 
worldwide, there have been about 50 known strandings, consisting mostly 
of beaked whales, with a potential causal link to MFA sonar (ICES, 
2005). In contrast, very few such associations have been made to 
seismic surveys, despite widespread use of airguns as a geophysical 
sound source in numerous locations around the world.
    A review of possible stranding associations with seismic surveys 
(Castellote and Llorens, 2016) states that, ``[s]peculation concerning 
possible links between seismic survey noise and cetacean strandings is 
available for a dozen events but without convincing causal evidence.'' 
The authors' search of available information found 10 events worth 
further investigation via a ranking system representing a rough metric 
of the relative level of confidence offered by the data for inferences 
about the possible role of the seismic survey in a given stranding 
event. Only three of these events involved beaked whales. Whereas 
D'Amico et al., (2009) used a 1-5 ranking system, in which ``1'' 
represented the most robust evidence connecting the event to MFA sonar 
use, Castellote and Llorens (2016) used a 1-6 ranking system, in which 
``6'' represented the most robust evidence connecting the event to the 
seismic survey. As described above, D'Amico et al. (2009) found that 
two events were ranked ``1'' and 10 events were ranked ``2'' (i.e., 12 
beaked whale stranding events were found to be associated with MFA 
sonar use). In contrast, Castellote and Llorens (2016) found that none 
of the three beaked whale stranding events achieved their highest ranks 
of 5 or 6. Of the 10 total events, none achieved the highest rank of 6. 
Two events were ranked as 5: one stranding in Peru involving dolphins 
and porpoises and a 2008 stranding in Madagascar. This latter ranking 
can only be broadly associated with the survey itself, as opposed to 
use of seismic airguns. An investigation of this stranding event, which 
did not involve beaked whales, concluded that use of a high-frequency 
mapping system (12-kHz multibeam echosounder) was the most plausible 
and likely initial behavioral trigger of the event, which was likely 
exacerbated by several site- and situation-specific secondary factors. 
The review panel found that seismic airguns were used after the initial 
strandings and animals entering a lagoon system, that airgun use 
clearly had no role as an initial trigger, and that there was no 
evidence that airgun use dissuaded animals from leaving (Southall et 
al., 2013).
    However, one of these stranding events, involving two Cuvier's 
beaked whales, was contemporaneous with and reasonably associated 
spatially with a 2002 seismic survey in the Gulf of California 
conducted by L-DEO, as was the case for the 2007 Gulf of Cadiz seismic 
survey discussed by Castellote and Llorens (also involving two Cuvier's 
beaked whales). Neither event was considered a ``true atypical mass 
stranding'' (according to Frantzis (1998)) as used in the analysis of 
Castellote and Llorens (2016). While we agree with the authors that 
this lack of evidence should

[[Page 56175]]

not be considered conclusive, it is clear that there is very little 
evidence that seismic surveys should be considered as posing a 
significant risk of acute harm to beaked whales or other mid-frequency 
cetaceans. We have considered the potential for the proposed surveys to 
result in marine mammal stranding and, based on the best available 
information, do not expect a stranding to occur.
    Entanglement--Entanglements occur when marine mammals become 
wrapped around cables, lines, nets, or other objects suspended in the 
water column. During seismic operations, numerous cables, lines, and 
other objects primarily associated with the airgun array and hydrophone 
streamers will be towed behind the R/V Langseth near the water's 
surface. However, we are not aware of any cases of entanglement of 
marine mammals in seismic survey equipment. No incidents of 
entanglement of marine mammals with seismic survey gear have been 
documented in over 54,000 nautical miles (100,000 km) of previous NSF-
funded seismic surveys when observers were aboard (e.g., Smultea and 
Holst 2003; Haley and Koski 2004; Holst 2004; Smultea et al., 2004; 
Holst et al., 2005a; Haley and Ireland 2006; SIO and NSF 2006b; Hauser 
et al., 2008; Holst and Smultea 2008). Although entanglement with the 
streamer is theoretically possible, it has not been documented during 
tens of thousands of miles of NSF-sponsored seismic cruises or, to our 
knowledge, during hundreds of thousands of miles of industrial seismic 
cruises. There are relatively few deployed devices, and no interaction 
between marine mammals and any such device has been recorded during 
prior NSF surveys using the devices. There are no meaningful 
entanglement risks posed by the proposed survey, and entanglement risks 
are not discussed further in this document.

Anticipated Effects on Marine Mammal Habitat

    Physical Disturbance--Sources of seafloor disturbance related to 
geophysical surveys that may impact marine mammal habitat include 
placement of anchors, nodes, cables, sensors, or other equipment on or 
in the seafloor for various activities. Equipment deployed on the 
seafloor has the potential to cause direct physical damage and could 
affect bottom-associated fish resources. During this survey, OBSs would 
be deployed on the seafloor, secured with anchors that would eventually 
disintegrate on the seafloor.
    Placement of equipment could damage areas of hard bottom where 
direct contact with the seafloor occurs and could crush epifauna 
(organisms that live on the seafloor or surface of other organisms). 
Damage to unknown or unseen hard bottom could occur, but because of the 
small area covered by most bottom-founded equipment and the patchy 
distribution of hard bottom habitat, contact with unknown hard bottom 
is expected to be rare and impacts minor. Seafloor disturbance in areas 
of soft bottom can cause loss of small patches of epifauna and infauna 
due to burial or crushing, and bottom-feeding fishes could be 
temporarily displaced from feeding areas. Overall, any effects of 
physical damage to habitat are expected to be minor and temporary.
    Effects to Prey--Marine mammal prey varies by species, season, and 
location and, for some, is not well documented. Fish react to sounds 
which are especially strong and/or intermittent low-frequency sounds, 
and behavioral responses such as flight or avoidance are the most 
likely effects. However, the reaction of fish to airguns depends on the 
physiological state of the fish, past exposures, motivation (e.g., 
feeding, spawning, migration), and other environmental factors. Several 
studies have demonstrated that airgun sounds might affect the 
distribution and behavior of some fishes, potentially impacting marine 
mammal foraging opportunities or increasing energetic costs (e.g., 
Fewtrell and McCauley, 2012; Pearson et al., 1992; Skalski et al., 
1992; Santulli et al., 1999; Paxton et al., 2017), though the bulk of 
studies indicate no or slight reaction to noise (e.g., Miller and 
Cripps, 2013; Dalen and Knutsen, 1987; Pena et al., 2013; Chapman and 
Hawkins, 1969; Wardle et al., 2001; Sara et al., 2007; Jorgenson and 
Gyselman, 2009; Blaxter et al., 1981; Cott et al., 2012; Boeger et al., 
2006), and that, most commonly, while there are likely to be impacts to 
fish as a result of noise from nearby airguns, such effects will be 
temporary. For example, investigators reported significant, short-term 
declines in commercial fishing catch rate of gadid fishes during and 
for up to 5 days after seismic survey operations, but the catch rate 
subsequently returned to normal (Engas et al., 1996; Engas and 
Lokkeborg, 2002). Other studies have reported similar findings (Hassel 
et al., 2004).
    Skalski et al., (1992) also found a reduction in catch rates--for 
rockfish (Sebastes spp.) in response to controlled airgun exposure--but 
suggested that the mechanism underlying the decline was not dispersal 
but rather decreased responsiveness to baited hooks associated with an 
alarm behavioral response. A companion study showed that alarm and 
startle responses were not sustained following the removal of the sound 
source (Pearson et al., 1992). Therefore, Skalski et al. (1992) 
suggested that the effects on fish abundance may be transitory, 
primarily occurring during the sound exposure itself. In some cases, 
effects on catch rates are variable within a study, which may be more 
broadly representative of temporary displacement of fish in response to 
airgun noise (i.e., catch rates may increase in some locations and 
decrease in others) than any long-term damage to the fish themselves 
(Streever et al., 2016).
    Sound pressure levels of sufficient strength have been known to 
cause injury to fish and fish mortality and, in some studies, fish 
auditory systems have been damaged by airgun noise (McCauley et al., 
2003; Popper et al., 2005; Song et al., 2008). However, in most fish 
species, hair cells in the ear continuously regenerate and loss of 
auditory function likely is restored when damaged cells are replaced 
with new cells. Halvorsen et al. (2012) showed that a TTS of 4-6 dB was 
recoverable within 24 hours for one species. Impacts would be most 
severe when the individual fish is close to the source and when the 
duration of exposure is long; both of which are conditions unlikely to 
occur for this survey that is necessarily transient in any given 
location and likely result in brief, infrequent noise exposure to prey 
species in any given area. For this survey, the sound source is 
constantly moving, and most fish would likely avoid the sound source 
prior to receiving sound of sufficient intensity to cause physiological 
or anatomical damage. In addition, ramp-up may allow certain fish 
species the opportunity to move further away from the sound source.
    A comprehensive review (Carroll et al., 2017) found that results 
are mixed as to the effects of airgun noise on the prey of marine 
mammals. While some studies suggest a change in prey distribution and/
or a reduction in prey abundance following the use of seismic airguns, 
others suggest no effects or even positive effects in prey abundance. 
As one specific example, Paxton et al. (2017), which describes findings 
related to the effects of a 2014 seismic survey on a reef off of North 
Carolina, showed a 78 percent decrease in observed nighttime abundance 
for certain species. It is important to note that the evening hours 
during which the decline in fish habitat use was recorded (via video

[[Page 56176]]

recording) occurred on the same day that the seismic survey passed, and 
no subsequent data is presented to support an inference that the 
response was long-lasting. Additionally, given that the finding is 
based on video images, the lack of recorded fish presence does not 
support a conclusion that the fish actually moved away from the site or 
suffered any serious impairment. In summary, this particular study 
corroborates prior studies indicating that a startle response or short-
term displacement should be expected.
    Available data suggest that cephalopods are capable of sensing the 
particle motion of sounds and detect low frequencies up to 1-1.5 kHz, 
depending on the species, and so are likely to detect airgun noise 
(Kaifu et al., 2008; Hu et al., 2009; Mooney et al., 2010; Samson et 
al., 2014). Auditory injuries (lesions occurring on the statocyst 
sensory hair cells) have been reported upon controlled exposure to low-
frequency sounds, suggesting that cephalopods are particularly 
sensitive to low-frequency sound (Andre et al., 2011; Sole et al., 
2013). Behavioral responses, such as inking and jetting, have also been 
reported upon exposure to low-frequency sound (McCauley et al., 2000b; 
Samson et al., 2014). Similar to fish, however, the transient nature of 
the survey leads to an expectation that effects will be largely limited 
to behavioral reactions and would occur as a result of brief, 
infrequent exposures.
    With regard to potential impacts on zooplankton, McCauley et al. 
(2017) found that exposure to airgun noise resulted in significant 
depletion for more than half the taxa present and that there were two 
to three times more dead zooplankton after airgun exposure compared 
with controls for all taxa, within 1 km of the airguns. However, the 
authors also stated that in order to have significant impacts on r-
selected species (i.e., those with high growth rates and that produce 
many offspring) such as plankton, the spatial or temporal scale of 
impact must be large in comparison with the ecosystem concerned, and it 
is possible that the findings reflect avoidance by zooplankton rather 
than mortality (McCauley et al., 2017). In addition, the results of 
this study are inconsistent with a large body of research that 
generally finds limited spatial and temporal impacts to zooplankton as 
a result of exposure to airgun noise (e.g., Dalen and Knutsen, 1987; 
Payne, 2004; Stanley et al., 2011). Most prior research on this topic, 
which has focused on relatively small spatial scales, has showed 
minimal effects (e.g., Kostyuchenko, 1973; Booman et al., 1996; 
S[aelig]tre and Ona, 1996; Pearson et al., 1994; Bolle et al., 2012).
    A modeling exercise was conducted as a follow-up to the McCauley et 
al. (2017) study (as recommended by McCauley et al.), in order to 
assess the potential for impacts on ocean ecosystem dynamics and 
zooplankton population dynamics (Richardson et al., 2017). Richardson 
et al. (2017) found that for copepods with a short life cycle in a 
high-energy environment, a full-scale airgun survey would impact 
copepod abundance up to 3 days following the end of the survey, 
suggesting that effects such as those found by McCauley et al. (2017) 
would not be expected to be detectable downstream of the survey areas, 
either spatially or temporally.
    Notably, a more recently described study produced results 
inconsistent with those of McCauley et al. (2017). Researchers 
conducted a field and laboratory study to assess if exposure to airgun 
noise affects mortality, predator escape response, or gene expression 
of the copepod Calanus finmarchicus (Fields et al., 2019). Immediate 
mortality of copepods was significantly higher, relative to controls, 
at distances of 5 m or less from the airguns. Mortality 1 week after 
the airgun blast was significantly higher in the copepods placed 10 m 
from the airgun but was not significantly different from the controls 
at a distance of 20 m from the airgun. The increase in mortality, 
relative to controls, did not exceed 30 percent at any distance from 
the airgun. Moreover, the authors caution that even this higher 
mortality in the immediate vicinity of the airguns may be more 
pronounced than what would be observed in free-swimming animals due to 
increased flow speed of fluid inside bags containing the experimental 
animals. There were no sublethal effects on the escape performance or 
the sensory threshold needed to initiate an escape response at any of 
the distances from the airgun that were tested. Whereas McCauley et al. 
(2017) reported an SEL of 156 dB at a range of 509-658 m, with 
zooplankton mortality observed at that range, Fields et al. (2019) 
reported an SEL of 186 dB at a range of 25 m, with no reported 
mortality at that distance. Regardless, if we assume a worst-case 
likelihood of severe impacts to zooplankton within approximately 1 km 
of the acoustic source, the brief time to regeneration of the 
potentially affected zooplankton populations does not lead us to expect 
any meaningful follow-on effects to the prey base for marine mammals.
    A review article concluded that, while laboratory results provide 
scientific evidence for high-intensity and low-frequency sound-induced 
physical trauma and other negative effects on some fish and 
invertebrates, the sound exposure scenarios in some cases are not 
realistic to those encountered by marine organisms during routine 
seismic operations (Carroll et al., 2017). The review finds that there 
has been no evidence of reduced catch or abundance following seismic 
activities for invertebrates, and that there is conflicting evidence 
for fish with catch observed to increase, decrease, or remain the same. 
Further, where there is evidence for decreased catch rates in response 
to airgun noise, these findings provide no information about the 
underlying biological cause of catch rate reduction (Carroll et al., 
2017).
    In summary, impacts of the specified activity on marine mammal prey 
species will likely be limited to behavioral responses, the majority of 
prey species will be capable of moving out of the area during the 
survey, a rapid return to normal recruitment, distribution, and 
behavior for prey species is anticipated, and, overall, impacts to prey 
species will be minor and temporary. Prey species exposed to sound 
might move away from the sound source, experience TTS, experience 
masking of biologically relevant sounds, or show no obvious direct 
effects. Mortality from decompression injuries is possible in close 
proximity to a sound, but only limited data on mortality in response to 
airgun noise exposure are available (Hawkins et al., 2014). The most 
likely impacts for most prey species in the survey area would be 
temporary avoidance of the area. The proposed survey would move through 
an area relatively quickly, limiting exposure to multiple impulsive 
sounds. In all cases, sound levels would return to ambient once the 
survey moves out of the area or ends and the noise source is shut down 
and, when exposure to sound ends, behavioral and/or physiological 
responses are expected to end relatively quickly (McCauley et al., 
2000b). The duration of fish avoidance of a given area after survey 
effort stops is unknown, but a rapid return to normal recruitment, 
distribution, and behavior is anticipated. While the potential for 
disruption of spawning aggregations or schools of important prey 
species can be meaningful on a local scale, the mobile and temporary 
nature of this survey and the likelihood of temporary avoidance 
behavior suggest that impacts would be minor.
    Acoustic Habitat--Acoustic habitat is the soundscape--which 
encompasses all of the sound present in a particular location and time, 
as a whole--when

[[Page 56177]]

considered from the perspective of the animals experiencing it. Animals 
produce sound for, or listen for sounds produced by, conspecifics 
(communication during feeding, mating, and other social activities), 
other animals (finding prey or avoiding predators), and the physical 
environment (finding suitable habitats, navigating). Together, sounds 
made by animals and the geophysical environment (e.g., produced by 
earthquakes, lightning, wind, rain, waves) make up the natural 
contributions to the total acoustics of a place. These acoustic 
conditions, termed acoustic habitat, are one attribute of an animal's 
total habitat.
    Soundscapes are also defined by, and acoustic habitat influenced 
by, the total contribution of anthropogenic sound. This may include 
incidental emissions from sources such as vessel traffic, or may be 
intentionally introduced to the marine environment for data acquisition 
purposes (as in the use of airgun arrays). Anthropogenic noise varies 
widely in its frequency content, duration, and loudness and these 
characteristics greatly influence the potential habitat-mediated 
effects to marine mammals (please see also the previous discussion on 
masking under Acoustic Effects), which may range from local effects for 
brief periods of time to chronic effects over large areas and for long 
durations. Depending on the extent of effects to habitat, animals may 
alter their communications signals (thereby potentially expending 
additional energy) or miss acoustic cues (either conspecific or 
adventitious). For more detail on these concepts see, e.g., Barber et 
al., 2010; Pijanowski et al., 2011; Francis and Barber, 2013; Lillis et 
al., 2014.
    Problems arising from a failure to detect cues are more likely to 
occur when noise stimuli are chronic and overlap with biologically 
relevant cues used for communication, orientation, and predator/prey 
detection (Francis and Barber, 2013). Although the signals emitted by 
seismic airgun arrays are generally low frequency, they would also 
likely be of short duration and transient in any given area due to the 
nature of these surveys. As described previously, exploratory surveys 
such as these cover a large area but would be transient rather than 
focused in a given location over time and therefore would not be 
considered chronic in any given location.
    Based on the information discussed herein, we conclude that impacts 
of the specified activity are not likely to have more than short-term 
adverse effects on any prey habitat or populations of prey species. 
Further, any impacts to marine mammal habitat are not expected to 
result in significant or long-term consequences for individual marine 
mammals, or to contribute to adverse impacts on their populations.

Estimated Take of Marine Mammals

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

Acoustic Thresholds

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

[[Page 56178]]

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

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

Ensonified Area

    Here, we describe operational and environmental parameters of the 
activity that are used in estimating the area ensonified above the 
acoustic thresholds, including source levels and transmission loss 
coefficient.
    When the Technical Guidance was published (NMFS, 2016), in 
recognition of the fact that ensonified area/volume could be more 
technically challenging to predict because of the duration component in 
the new thresholds, we developed a user spreadsheet that includes tools 
to help predict a simple isopleth that can be used in conjunction with 
marine mammal density or occurrence to help predict takes. We note that 
because of some of the assumptions included in the methods used for 
these tools, we anticipate that isopleths produced are typically going 
to be overestimates of some degree, which may result in some degree of 
overestimate of Level A harassment take. However, these tools offer the 
best way to predict appropriate isopleths when more sophisticated 3D 
modeling methods are not available, and NMFS continues to develop ways 
to quantitatively refine these tools and will qualitatively address the 
output where appropriate.
    The proposed survey would entail the use of a 36-airgun array with 
a total discharge volume of 6,600 in\3\ at a tow depth of 9 m to 12 m. 
L-DEO's model results are used to determine the 160 dBrms 
radius for the airgun source down to a maximum depth of 2,000 m. 
Received sound levels have been predicted by L-DEO's model (Diebold et 
al. 2010) as a function of distance from the 36-airgun array. This 
modeling approach uses ray tracing for the direct wave traveling from 
the array to the receiver and its associated source ghost (reflection 
at the air-water interface in the vicinity of the array), in a 
constant-velocity half-space (infinite homogeneous ocean layer, 
unbounded by a seafloor). In addition, propagation measurements of 
pulses from the 36-airgun array at a tow depth of 6 m have been 
reported in deep water (~1,600 m), intermediate water depth on the 
slope (~600-1,100 m), and shallow water (~50 m) in the Gulf of Mexico 
(Tolstoy et al. 2009; Diebold et al. 2010).
    For deep and intermediate water cases, the field measurements 
cannot be used readily to derive the harassment isopleths, as at those 
sites the calibration hydrophone was located at a roughly constant 
depth of 350-550 m, which may not intersect all the SPL isopleths at 
their widest point from the sea surface down to the assumed maximum 
relevant water depth (~2,000 m) for marine mammals. At short ranges, 
where the direct arrivals dominate and the effects of seafloor 
interactions are minimal, the data at the deep sites are suitable for 
comparison with modeled levels at the depth of the calibration 
hydrophone. At longer ranges, the comparison with the model--
constructed from the maximum SPL through the entire water column at 
varying distances from the airgun array--is the most relevant.
    In deep and intermediate water depths at short ranges, sound levels 
for direct arrivals recorded by the calibration hydrophone and L-DEO 
model results for the same array tow depth are in good alignment (see 
figures 12 and 14 in Diebold et al. 2010). Consequently, isopleths 
falling within this domain can be predicted reliably by the L-DEO 
model, although they may be imperfectly sampled by measurements 
recorded at a single depth. At greater distances, the calibration data 
show that seafloor-reflected and sub-seafloor-refracted arrivals 
dominate, whereas the direct arrivals become weak and/or incoherent 
(see figures 11, 12, and 16 in Diebold et al. 2010). Aside from local 
topography effects, the region around the critical distance is where 
the observed levels rise closest to the model curve. However, the 
observed sound levels are found to fall almost entirely below the model 
curve. Thus, analysis of the Gulf of Mexico calibration measurements 
demonstrates that although simple, the L-DEO model is a robust tool for 
conservatively estimating isopleths.
    The proposed high-energy survey would acquire data with the 36-
airgun array at a tow depth of 9 to 12 m. For this survey, which occurs 
only in deep water (>1,000 m), we use the deep-water radii obtained 
from L-DEO model

[[Page 56179]]

results down to a maximum water depth of 2,000 m for the 36-airgun 
array.
    L-DEO's modeling methodology is described in greater detail in L-
DEO's application. The estimated distances to the Level B harassment 
isopleth for the proposed airgun configuration are shown in table 4.

  Table 4--Predicted Radial Distances From the R/V Langseth Seismic Source to Isopleth Corresponding to Level B
                                              Harassment Threshold
----------------------------------------------------------------------------------------------------------------
                                                                                                   Predicted
                                                                                               distances (in m)
                Airgun configuration                   Tow depth (m)\1\     Water depth (m)     to the Level B
                                                                                                  harassment
                                                                                                   threshold
----------------------------------------------------------------------------------------------------------------
4 strings, 36 airguns, 6,600 in\3\..................                 12              >1,000           \2\ 6,733
----------------------------------------------------------------------------------------------------------------
\1\ Maximum tow depth was used for conservative distances.
\2\ Distance is based on L-DEO model results.


          Table 5--Modeled Radial Distance to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
                                                                   Low frequency   Mid frequency  High frequency
                                                                     cetaceans       cetaceans       cetaceans
----------------------------------------------------------------------------------------------------------------
PTS SELcum......................................................           426.9               0             1.3
PTS Peak........................................................            38.9            13.6           268.3
----------------------------------------------------------------------------------------------------------------
The largest distance (in bold) of the dual criteria (SELcum or Peak) was used to estimate threshold distances
  and potential takes by Level A harassment.

    Table 5 presents the modeled PTS isopleths for each cetacean 
hearing group based on L-DEO modeling incorporated in the companion 
user spreadsheet, for the high-energy surveys with the shortest shot 
interval (i.e., greatest potential to cause PTS based on accumulated 
sound energy) (NMFS 2018).
    Predicted distances to Level A harassment isopleths, which vary 
based on marine mammal hearing groups, were calculated based on 
modeling performed by L-DEO using the Nucleus software program and the 
NMFS user spreadsheet, described below. The acoustic thresholds for 
impulsive sounds contained in the NMFS Technical Guidance were 
presented as dual metric acoustic thresholds using both 
SELcum and peak sound pressure metrics (NMFS 2016). As dual 
metrics, NMFS considers onset of PTS (Level A harassment) to have 
occurred when either one of the two metrics is exceeded (i.e., metric 
resulting in the largest isopleth). The SELcum metric 
considers both level and duration of exposure, as well as auditory 
weighting functions by marine mammal hearing group.
    The SELcum for the 36-airgun array is derived from 
calculating the modified farfield signature. The farfield signature is 
often used as a theoretical representation of the source level. To 
compute the farfield signature, the source level is estimated at a 
large distance (right) below the array (e.g., 9 km), and this level is 
back projected mathematically to a notional distance of 1 m from the 
array's geometrical center. However, it has been recognized that the 
source level from the theoretical farfield signature is never 
physically achieved at the source when the source is an array of 
multiple airguns separated in space (Tolstoy et al., 2009). Near the 
source (at short ranges, distances <1 km), the pulses of sound pressure 
from each individual airgun in the source array do not stack 
constructively as they do for the theoretical farfield signature. The 
pulses from the different airguns spread out in time such that the 
source levels observed or modeled are the result of the summation of 
pulses from a few airguns, not the full array (Tolstoy et al., 2009). 
At larger distances, away from the source array center, sound pressure 
of all the airguns in the array stack coherently, but not within one 
time sample, resulting in smaller source levels (a few dB) than the 
source level derived from the far-field signature. Because the far-
field signature does not take into account the large array effect near 
the source and is calculated as a point source, the far-field signature 
is not an appropriate measure of the sound source level for large 
arrays. See L-DEO's application for further detail on acoustic 
modeling.
    Auditory injury is unlikely to occur for mid-frequency cetaceans, 
given the very small modeled zones of injury for those species (all 
estimated zones are less than 15 m for mid-frequency cetaceans), in the 
context of distributed source dynamics.
    In consideration of the received sound levels in the near-field as 
described above, we expect the potential for Level A harassment of mid-
frequency cetaceans to be de minimis, even before the likely moderating 
effects of aversion and/or other compensatory behaviors (e.g., 
Nachtigall et al., 2018) are considered. We do not anticipate that 
Level A harassment is a likely outcome for any mid-frequency cetacean 
and do not propose to authorize any take by Level A harassment for 
these species.
    The Level A and Level B harassment estimates are based on a 
consideration of the number of marine mammals that could be within the 
area around the operating airgun array where received levels of sound 
>=160 dB re 1 [micro]Pa rms are predicted to occur. The estimated 
numbers are based on the densities (numbers per unit area) of marine 
mammals expected to occur in the area in the absence of seismic 
surveys. To the extent that marine mammals tend to move away from 
seismic sources before the sound level reaches the criterion level and 
tend not to approach an operating airgun array, these estimates likely 
overestimate the numbers actually exposed to the specified level of 
sound.

Marine Mammal Occurrence

    In this section, we provide information about the occurrence of 
marine mammals, including density or other relevant information, which 
will inform the take calculations.
    Habitat-based stratified marine mammal densities for the North 
Atlantic are taken from the US Navy Atlantic Fleet Training and Testing 
Area Marine Mammal Density (Roberts et al., 2023;

[[Page 56180]]

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

Take Estimate

    Here, we describe how the information provided above is synthesized 
to produce a quantitative estimate of the take that is reasonably 
likely to occur and proposed for authorization. In order to estimate 
the number of marine mammals predicted to be exposed to sound levels 
that would result in Level A or Level B harassment, radial distances 
from the airgun array to the predicted isopleth corresponding to the 
Level A harassment and Level B harassment thresholds are calculated, as 
described above. Those radial distances were then used to calculate the 
area(s) around the airgun array predicted to be ensonified to sound 
levels that exceed the harassment thresholds. The distance for the 160-
dB Level B harassment threshold and PTS (Level A harassment) thresholds 
(based on L-DEO model results) was used to draw a buffer around the 
area expected to be ensonified (i.e., the survey area). The ensonified 
areas were then increased by 25 percent to account for potential 
delays, which is equivalent to adding 25 percent to the proposed line 
km to be surveyed. The density for each species was then multiplied by 
the daily ensonified areas (increased as described above) and then 
multiplied by the number of survey days (11.5) to estimate potential 
takes (see appendix B of L-DEO's application for more information).
    L-DEO assumed that their estimates of marine mammal exposures above 
harassment thresholds equate to take and requested authorization of 
those takes. Those estimates in turn form the basis for our proposed 
take authorization numbers. For the species for which NMFS does not 
expect there to be a reasonable potential for take by Level A 
harassment to occur (i.e., mid-frequency cetaceans), we have added L-
DEO's estimated exposures above Level A harassment thresholds to their 
estimated exposures above the Level B harassment threshold to produce a 
total number of incidents of take by Level B harassment that is 
proposed for authorization. Estimated exposures and proposed take 
numbers for authorization are shown in table 6.

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

[[Page 56181]]

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

Proposed Mitigation

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

Vessel-Based Visual Mitigation Monitoring

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

Passive Acoustic Monitoring

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

[[Page 56182]]

    PAM would take place in addition to the visual monitoring program. 
Visual monitoring typically is not effective during periods of poor 
visibility or at night and even with good visibility, is unable to 
detect marine mammals when they are below the surface or beyond visual 
range. Acoustic monitoring can be used in addition to visual 
observations to improve detection, identification, and localization of 
cetaceans. The acoustic monitoring would serve to alert visual PSOs (if 
on duty) when vocalizing cetaceans are detected. It is only useful when 
marine mammals vocalize, but it can be effective either by day or by 
night and does not depend on good visibility. It would be monitored in 
real time so that the visual observers can be advised when cetaceans 
are detected.
    The R/V Langseth will use a towed PAM system, which must be 
monitored by at a minimum one on duty acoustic PSO beginning at least 
30 minutes prior to ramp-up and at all times during use of the airgun 
array. Acoustic PSOs may be on watch for a maximum of 4 consecutive 
hours followed by a break of at least 1 hour between watches and may 
conduct a maximum of 12 hours of observation per 24-hour period. 
Combined observational duties (acoustic and visual but not at same 
time) may not exceed 12 hours per 24-hour period for any individual 
PSO.
    Survey activity may continue for 30 minutes when the PAM system 
malfunctions or is damaged, while the PAM operator diagnoses the issue. 
If the diagnosis indicates that the PAM system must be repaired to 
solve the problem, operations may continue for an additional 10 hours 
without acoustic monitoring during daylight hours only under the 
following conditions:
     Sea state is less than or equal to BSS 4;
     No marine mammals (excluding delphinids) detected solely 
by PAM in the SZ in the previous 2 hours;
     NMFS is notified via email as soon as practicable with the 
time and location in which operations began occurring without an active 
PAM system; and
     Operations with an active airgun array, but without an 
operating PAM system, do not exceed a cumulative total of 10 hours in 
any 24-hour period.

Establishment of Shutdown and Pre-Start Clearance Zones

    A SZ is a defined area within which occurrence of a marine mammal 
triggers mitigation action intended to reduce the potential for certain 
outcomes (e.g., auditory injury, disruption of critical behaviors). The 
PSOs would establish a minimum SZ with a 500-m radius. The 500-m SZ 
would be based on radial distance from the edge of the airgun array 
(rather than being based on the center of the array or around the 
vessel itself). With certain exceptions (described below), if a marine 
mammal appears within or enters this zone, the airgun array would be 
shut down.
    The pre-start clearance zone is defined as the area that must be 
clear of marine mammals prior to beginning ramp-up of the airgun array 
and includes the SZ plus the buffer zone. Detections of marine mammals 
within the pre-start clearance zone would prevent airgun operations 
from beginning (i.e., ramp-up).
    The 500-m SZ is intended to be precautionary in the sense that it 
would be expected to contain sound exceeding the injury criteria for 
all cetacean hearing groups, (based on the dual criteria of 
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 expect that 500 m is likely 
regularly attainable for PSOs using the naked eye during typical 
conditions. The pre-start clearance zone simply represents the addition 
of a buffer to the SZ, doubling the SZ size during pre-clearance.
    An extended SZ of 1,500 m must be enforced for all beaked whales, 
Kogia spp, a large whale with a calf, and groups of six or more large 
whales. No buffer of this extended SZ is required, as NMFS concludes 
that this extended SZ is sufficiently protective to mitigate harassment 
to these groups.

Pre-Start Clearance and Ramp-up

    Ramp-up (sometimes referred to as ``soft start'') means the gradual 
and systematic increase of emitted sound levels from an airgun array. 
Ramp-up begins by first activating a single airgun of the smallest 
volume, followed by doubling the number of active elements in stages 
until the full complement of an array's airguns are active. Each stage 
should be approximately the same duration, and the total duration 
should not be less than approximately 20 minutes. The intent of pre-
start clearance observation (30 minutes) is to ensure no marine mammals 
are observed within the pre-start clearance zone (or extended SZ, for 
beaked whales, Kogia spp, a large whale with a calf, and groups of six 
or more large whales) prior to the beginning of ramp-up. During the 
pre-start clearance period is the only time observations of marine 
mammals in the buffer zone would prevent operations (i.e., the 
beginning of ramp-up). The intent of the ramp-up is to warn marine 
mammals of pending seismic survey operations and to allow sufficient 
time for those animals to leave the immediate vicinity prior to the 
sound source reaching full intensity. A ramp-up procedure, involving a 
stepwise increase in the number of airguns firing and total array 
volume until all operational airguns are activated and the full volume 
is achieved, is required at all times as part of the activation of the 
airgun array. All operators must adhere to the following pre-start 
clearance and ramp-up requirements:
     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, a large whale with a calf, and groups of six or more 
large whales) during the 30 minute pre-start clearance period, ramp-up 
may not begin until the animal(s) has been observed exiting the zones 
or until an additional time period has elapsed with no further 
sightings (15 minutes for small odontocetes, and 30 minutes for all 
mysticetes and all other odontocetes, including sperm whales, beaked 
whales, and large delphinids, such as pilot whales);
     Ramp-up shall begin by activating a single airgun of the 
smallest volume in the array and shall continue in stages by doubling 
the number of active elements at the commencement of each stage, with 
each stage of approximately the same duration. Duration shall not be 
less than 20 minutes. The operator must

[[Page 56183]]

provide information to the PSO documenting that appropriate procedures 
were followed;
     PSOs must monitor the pre-start clearance zone and 
extended SZ during ramp-up, and ramp-up must cease and the source must 
be shut down upon detection of a marine mammal within the applicable 
zone. Once ramp-up has begun, detections of marine mammals within the 
buffer zone do not require shutdown, but such observation shall be 
communicated to the operator to prepare for the potential shutdown;
     Ramp-up may occur at times of poor visibility, including 
nighttime, if appropriate acoustic monitoring has occurred with no 
detections in the 30 minutes prior to beginning ramp-up. Airgun array 
activation may only occur at times of poor visibility where operational 
planning cannot reasonably avoid such circumstances;
     If the airgun array is shut down for brief periods (i.e., 
less than 30 minutes) for reasons other than implementation of 
prescribed mitigation (e.g., mechanical difficulty), it may be 
activated again without ramp-up if PSOs have maintained constant visual 
and/or acoustic observation and no visual or acoustic detections of 
marine mammals have occurred within the pre-start clearance zone (or 
extended SZ, where applicable). For any longer shutdown, pre-start 
clearance observation and ramp-up are required; and
     Testing of the airgun array involving all elements 
requires ramp-up. Testing limited to individual source elements or 
strings does not require ramp-up but does require pre-start clearance 
watch of 30 minutes.

Shutdown

    The shutdown of an airgun array requires the immediate de-
activation of all individual airgun elements of the array. Any PSO on 
duty will have the authority to call for shutdown of the airgun array 
if a marine mammal is detected within the applicable SZ. The operator 
must also establish and maintain clear lines of communication directly 
between PSOs on duty and crew controlling the airgun array to ensure 
that shutdown commands are conveyed swiftly while allowing PSOs to 
maintain watch. When both visual and acoustic PSOs are on duty, all 
detections will be immediately communicated to the remainder of the on-
duty PSO team for potential verification of visual observations by the 
acoustic PSO or of acoustic detections by visual PSOs. When the airgun 
array is active (i.e., anytime one or more airguns is active, including 
during ramp-up) and (1) a marine mammal appears within or enters the 
applicable SZ and/or (2) a marine mammal (other than delphinids, see 
below) is detected acoustically and localized within the applicable SZ, 
the airgun array will be shut down. When shutdown is called for by a 
PSO, the airgun array will be immediately deactivated and any dispute 
resolved only following deactivation. Additionally, shutdown will occur 
whenever PAM alone (without visual sighting), confirms the presence of 
marine mammal(s) in the SZ. If the acoustic PSO cannot confirm presence 
within the SZ, visual PSOs will be notified but shutdown is not 
required.
    Following a shutdown, airgun activity would not resume until the 
marine mammal has cleared the SZ. The animal would be considered to 
have cleared the SZ if it is visually observed to have departed the SZ 
(i.e., animal is not required to fully exit the buffer zone where 
applicable), or it has not been seen within the SZ for 15 minutes for 
small odontocetes or 30 minutes for all mysticetes and all other 
odontocetes, including sperm whales, beaked whales, and large 
delphinids, such as pilot whales.
    The shutdown requirement is waived for specific genera of small 
dolphins if an individual is detected within the SZ. The small dolphin 
group is intended to encompass those members of the Family Delphinidae 
most likely to voluntarily approach the source vessel for purposes of 
interacting with the vessel and/or airgun array (e.g., bow riding). 
This exception to the shutdown requirement applies solely to the 
specific genera of small dolphins (Delphinus, Lagenodelphis, Stenella, 
Steno and Tursiops).
    We include this small dolphin exception because shutdown 
requirements for these species under all circumstances represent 
practicability concerns without likely commensurate benefits for the 
animals in question. Small dolphins are generally the most commonly 
observed marine mammals in the specific geographic region and would 
typically be the only marine mammals likely to intentionally approach 
the vessel. As described above, auditory injury is extremely unlikely 
to occur for mid-frequency cetaceans (e.g., delphinids), as this group 
is relatively insensitive to sound produced at the predominant 
frequencies in an airgun pulse while also having a relatively high 
threshold for the onset of auditory injury (i.e., permanent threshold 
shift).
    A large body of anecdotal evidence indicates that small dolphins 
commonly approach vessels and/or towed arrays during active sound 
production for purposes of bow riding with no apparent effect observed 
(e.g., Barkaszi et al., 2012, Barkaszi and Kelly, 2018). The potential 
for increased shutdowns resulting from such a measure would require the 
R/V Langseth to revisit the missed track line to reacquire data, 
resulting in an overall increase in the total sound energy input to the 
marine environment and an increase in the total duration over which the 
survey is active in a given area. Although other mid-frequency hearing 
specialists (e.g., large delphinids) are no more likely to incur 
auditory injury than are small dolphins, they are much less likely to 
approach vessels. Therefore, retaining a shutdown requirement for large 
delphinids would not have similar impacts in terms of either 
practicability for the applicant or corollary increase in sound energy 
output and time on the water. We do anticipate some benefit for a 
shutdown requirement for large delphinids in that it simplifies 
somewhat the total range of decision-making for PSOs and may preclude 
any potential for physiological effects other than to the auditory 
system as well as some more severe behavioral reactions for any such 
animals in close proximity to the R/V Langseth.
    Visual PSOs shall use best professional judgment in making the 
decision to call for a shutdown if there is uncertainty regarding 
identification (i.e., whether the observed marine mammal(s) belongs to 
one of the delphinid genera for which shutdown is waived or one of the 
species with a larger SZ).
    L-DEO must implement shutdown if a marine mammal species for which 
take was not authorized or a species for which authorization was 
granted but the authorized takes have been met approaches the Level A 
or Level B harassment zones. L-DEO must also implement an extended 
shutdown of 1,500 m if any large whale (defined as a sperm whale or any 
mysticete species) with a calf (defined as an animal less than two-
thirds the body size of an adult observed to be in close association 
with an adult) and/or an aggregation of six or more large whales.

Vessel Strike Avoidance Mitigation Measures

    Vessel personnel should use an appropriate reference guide that 
includes identifying information on all marine mammals that may be 
encountered. Vessel operators must comply with the below measures 
except under extraordinary circumstances when the safety of the vessel 
or crew is in doubt or the safety of life at sea is in question. These 
requirements do not

[[Page 56184]]

apply in any case where compliance would create an imminent and serious 
threat to a person or vessel or to the extent that a vessel is 
restricted in its ability to maneuver and, because of the restriction, 
cannot comply.
    Vessel operators and crews must maintain a vigilant watch for all 
marine mammals and slow down, stop their vessel, or alter course, as 
appropriate and regardless of vessel size, to avoid striking any marine 
mammal. A single marine mammal at the surface may indicate the presence 
of submerged animals in the vicinity of the vessel; therefore, 
precautionary measures should always be exercised. A visual observer 
aboard the vessel must monitor a vessel strike avoidance zone around 
the vessel (separation distances stated below). Visual observers 
monitoring the vessel strike avoidance zone may be third-party 
observers (i.e., PSOs) or crew members, but crew members responsible 
for these duties must be provided sufficient training to 1) distinguish 
marine mammals from other phenomena and 2) broadly to identify a marine 
mammal as a large whale (defined in this context as sperm whales or 
baleen whales), or other marine mammals.
    Vessel speeds must be reduced to 10 kn (18.5 kph) or less when 
mother/calf pairs, pods, or large assemblages of cetaceans are observed 
near a vessel. All vessels must maintain a minimum separation distance 
of 100 m from sperm whales and all other baleen whales. All vessels 
must, to the maximum extent practicable, attempt to maintain a minimum 
separation distance of 50 m from all other marine mammals, with an 
understanding that at times this may not be possible (e.g., for animals 
that approach the vessel).
    When marine mammals are sighted while a vessel is underway, the 
vessel shall take action as necessary to avoid violating the relevant 
separation distance (e.g., attempt to remain parallel to the animal's 
course, avoid excessive speed or abrupt changes in direction until the 
animal has left the area). If marine mammals are sighted within the 
relevant separation distance, the vessel must reduce speed and shift 
the engine to neutral, not engaging the engines until animals are clear 
of the area. This does not apply to any vessel towing gear or any 
vessel that is navigationally constrained.
    Based on our evaluation of the applicant's proposed measures, as 
well as other measures considered by NMFS, NMFS has preliminarily 
determined that the proposed mitigation measures provide the means of 
effecting the least practicable impact on the affected species or 
stocks and their habitat, paying particular attention to rookeries, 
mating grounds, and areas of similar significance.

Proposed Monitoring and Reporting

    In order to issue an IHA for an activity, section 101(a)(5)(D) of 
the MMPA states that NMFS must set forth requirements pertaining to the 
monitoring and reporting of such taking. The MMPA implementing 
regulations at 50 CFR 216.104(a)(13) indicate that requests for 
authorizations must include the suggested means of accomplishing the 
necessary monitoring and reporting that will result in increased 
knowledge of the species and of the level of taking or impacts on 
populations of marine mammals that are expected to be present while 
conducting the activities. Effective reporting is critical both to 
compliance as well as ensuring that the most value is obtained from the 
required monitoring.
    L-DEO must use dedicated, trained, and NMFS-approved PSOs. The PSOs 
must have no tasks other than to conduct observational effort, record 
observational data, and communicate with and instruct relevant vessel 
crew with regard to the presence of marine mammals and mitigation 
requirements. PSO resumes shall be provided to NMFS for advance 
approval (prior to embarking on the vessel).
    At least one of the visual and two of the acoustic PSOs (discussed 
below) aboard the vessel must have a minimum of 90 days at-sea 
experience working in those roles, respectively, with no more than 18 
months elapsed since the conclusion of the at-sea experience. One 
visual PSO with such experience shall be designated as the lead for the 
entire protected species observation team. The lead PSO shall serve as 
primary point of contact for the vessel operator and ensure all PSO 
requirements per the IHA are met. To the maximum extent practicable, 
the experienced PSOs should be scheduled to be on duty with those PSOs 
with appropriate training but who have not yet gained relevant 
experience.
    Monitoring and reporting requirements prescribed by NMFS should 
contribute to improved understanding of one or more of the following:
     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.

Vessel-Based Visual Monitoring

    As described above, PSO observations would take place during 
daytime airgun operations. During seismic survey operations, at least 
five visual PSOs would be based aboard the R/V Langseth. Two visual 
PSOs would be on duty at all times during daytime hours. Monitoring 
shall be conducted in accordance with the following requirements:
     The operator shall provide PSOs with bigeye reticle 
binoculars (e.g., 25 x 150; 2.7 view angle; individual ocular focus; 
height control) of appropriate quality solely for PSO use. These 
binoculars shall be pedestal-mounted on the deck at the most 
appropriate vantage point that provides for optimal sea surface 
observation, PSO safety, and safe operation of the vessel; and
     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

[[Page 56185]]

requirements (including brief alerts regarding maritime hazards);
     PSOs shall have successfully completed an approved PSO 
training course appropriate for their designated task (visual or 
acoustic). Acoustic PSOs are required to complete specialized training 
for operating PAM systems and are encouraged to have familiarity with 
the vessel with which they will be working;
     PSOs can act as acoustic or visual observers (but not at 
the same time) as long as they demonstrate that their training and 
experience are sufficient to perform the task at hand;
     NMFS must review and approve PSO resumes accompanied by a 
relevant training course information packet that includes the name and 
qualifications (i.e., experience, training completed, or educational 
background) of the instructor(s), the course outline or syllabus, and 
course reference material as well as a document stating successful 
completion of the course;
     PSOs must successfully complete relevant training, 
including completion of all required coursework and passing (80 percent 
or greater) a written and/or oral examination developed for the 
training program;
     PSOs must have successfully attained a bachelor's degree 
from an accredited college or university with a major in one of the 
natural sciences, a minimum of 30 semester hours or equivalent in the 
biological sciences, and at least one undergraduate course in math or 
statistics; and
     The educational requirements may be waived if the PSO has 
acquired the relevant skills through alternate experience. Requests for 
such a waiver shall be submitted to NMFS and must include written 
justification. Requests shall be granted or denied (with justification) 
by NMFS within 1 week of receipt of submitted information. Alternate 
experience that may be considered includes, but is not limited to (1) 
secondary education and/or experience comparable to PSO duties; (2) 
previous work experience conducting academic, commercial, or 
government-sponsored protected species surveys; or (3) previous work 
experience as a PSO; the PSO should demonstrate good standing and 
consistently good performance of PSO duties.
     For data collection purposes, PSOs shall use standardized 
electronic data collection forms. PSOs shall record detailed 
information about any implementation of mitigation requirements, 
including the distance of animals to the airgun array and description 
of specific actions that ensued, the behavior of the animal(s), any 
observed changes in behavior before and after implementation of 
mitigation, and if shutdown was implemented, the length of time before 
any subsequent ramp-up of the airgun array. If required mitigation was 
not implemented, PSOs should record a description of the circumstances. 
At a minimum, the following information must be recorded:
    [cir] Vessel name, vessel size and type, maximum speed capability 
of vessel;
    [cir] Dates (MM/DD/YYYY) of departures and returns to port with 
port name;
    [cir] PSO names and affiliations, PSO ID (initials or other 
identifier);
    [cir] Date (MM/DD/YYYY) and participants of PSO briefings;
    [cir] Visual monitoring equipment used (description);
    [cir] PSO location on vessel and height (meters) of observation 
location above water surface;
    [cir] Watch status (description);
    [cir] Dates (MM/DD/YYYY) and times (Greenwich Mean Time/UTC) of 
survey on/off effort and times (GMC/UTC) corresponding with PSO on/off 
effort;
    [cir] Vessel location (decimal degrees) when survey effort began 
and ended and vessel location at beginning and end of visual PSO duty 
shifts;
    [cir] Vessel location (decimal degrees) at 30-second intervals if 
obtainable from data collection software, otherwise at practical 
regular interval;
    [cir] Vessel heading (compass heading) and speed (knots) at 
beginning and end of visual PSO duty shifts and upon any change;
    [cir] Water depth (meters) (if obtainable from data collection 
software);
    [cir] Environmental conditions while on visual survey (at beginning 
and end of PSO shift and whenever conditions changed significantly), 
including BSS and any other relevant weather conditions including cloud 
cover, fog, sun glare, and overall visibility to the horizon;
    [cir] Factors that may have contributed to impaired observations 
during each PSO shift change or as needed as environmental conditions 
changed (description) (e.g., vessel traffic, equipment malfunctions); 
and
    [cir] Vessel/Survey activity information (and changes thereof) 
(description), such as airgun power output while in operation, number 
and volume of airguns operating in the array, tow depth of the array, 
and any other notes of significance (i.e., pre-start clearance, ramp-
up, shutdown, testing, shooting, ramp-up completion, end of operations, 
streamers, etc.).
     Upon visual observation of any marine mammals, the 
following information must be recorded:
    [cir] Sighting ID (numeric);
    [cir] Watch status (sighting made by PSO on/off effort, 
opportunistic, crew, alternate vessel/platform);
    [cir] Location of PSO/observer (description);
    [cir] Vessel activity at the time of the sighting (e.g., deploying, 
recovering, testing, shooting, data acquisition, other);
    [cir] PSO who sighted the animal/ID;
    [cir] Time/date of sighting (GMT/UTC, MM/DD/YYYY);
    [cir] Initial detection method (description);
    [cir] Sighting cue (description);
    [cir] Vessel location at time of sighting (decimal degrees);
    [cir] Water depth (meters);
    [cir] Direction of vessel's travel (compass direction);
    [cir] Speed (knots) of the vessel from which the observation was 
made;
    [cir] Direction of animal's travel relative to the vessel 
(description, compass heading);
    [cir] Bearing to sighting (degrees);
    [cir] Identification of the animal (e.g., genus/species, lowest 
possible taxonomic level, or unidentified) and the composition of the 
group if there is a mix of species;
    [cir] Species reliability (an indicator of confidence in 
identification) (1 = unsure/possible, 2 = probable, 3 = definite/sure, 
9 = unknown/not recorded);
    [cir] Estimated distance to the animal (meters) and method of 
estimating distance;
    [cir] Estimated number of animals (high/low/best) (numeric);
    [cir] Estimated number of animals by cohort (adults, yearlings, 
juveniles, calves, group composition, etc.);
    [cir] Description (as many distinguishing features as possible of 
each individual seen, including length, shape, color, pattern, scars or 
markings, shape and size of dorsal fin, shape of head, and blow 
characteristics);
    [cir] Detailed behavior observations (e.g., number of blows/
breaths, number of surfaces, breaching, spyhopping, diving, feeding, 
traveling; as explicit and detailed as possible; note any observed 
changes in behavior);
    [cir] Animal's closest point of approach (meters) and/or closest 
distance from any element of the airgun array;
    [cir] Description of any actions implemented in response to the 
sighting (e.g., delays, shutdown, ramp-up) and time and location of the 
action.
    [cir] Photos (Yes/No);
    [cir] Photo Frame Numbers (List of numbers); and
    [cir] Conditions at time of sighting (Visibility; Beaufort Sea 
State).

[[Page 56186]]

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

Reporting Injured or Dead Marine Mammals

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

Negligible Impact Analysis and Determination

    NMFS has defined negligible impact as an impact resulting from the 
specified activity that cannot be reasonably expected to, and is not 
reasonably likely to, adversely affect the species or stock through 
effects on annual rates of recruitment or survival (50 CFR 216.103). A 
negligible impact finding is based on the lack of likely adverse 
effects on annual rates of recruitment or survival (i.e., population-
level effects). An estimate of the number of takes alone is not enough 
information on which to base an impact determination. In addition to 
considering estimates of the number of marine mammals that might be 
``taken'' through harassment, NMFS considers other factors, such as the 
likely nature of any impacts or responses (e.g., intensity, duration), 
the context of any impacts or responses (e.g., critical reproductive 
time or location, foraging impacts affecting energetics), as well as 
effects on habitat, and the likely effectiveness of the mitigation. We 
also assess the number, intensity, and context of estimated takes by 
evaluating this information relative to population status. Consistent 
with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, 
September 29, 1989), the impacts from other past and ongoing 
anthropogenic activities are incorporated into this analysis via their 
impacts on the baseline (e.g., as reflected in the regulatory status of 
the species, population size and growth rate where known, ongoing 
sources of human-caused mortality, or ambient noise levels).
    To avoid repetition, the discussion of our analysis applies to all 
the species listed in table 1, given that the anticipated effects of 
this activity on these different marine mammal stocks are expected to 
be similar. Where there are meaningful differences between species or 
stocks they are included as separate subsections below. NMFS does not 
anticipate that serious injury or mortality would occur as a result of 
L-DEO's planned survey, even in the absence of mitigation, and no 
serious injury or mortality is proposed to be authorized. As discussed 
in the Potential Effects of Specified Activities on Marine Mammals and 
Their Habitat section above, non-auditory physical effects and vessel 
strike are not expected to occur. NMFS expects that the majority of 
potential takes would be in the form of short-term Level B

[[Page 56187]]

harassment, resulting from temporary avoidance of the area or decreased 
foraging (if such activity was occurring), reactions that are 
considered to be of low severity and with no lasting biological 
consequences (e.g., Southall et al., 2007).
    We are proposing to authorize a limited number of Level A 
harassment events of five species in the form of PTS (humpback whale, 
minke whale, sei whale, and Kogia spp (i.e., pygmy and dwarf sperm 
whales)) and Level B harassment of all 28 marine mammal species (table 
6). If any PTS is incurred in marine mammals as a result of the 
specified activity, we expect only a small degree of PTS that would not 
result in severe hearing impairment because of the constant movement of 
both the R/V Langseth and of the marine mammals in the project areas, 
as well as the fact that the vessel is not expected to remain in any 
one area in which individual marine mammals would be expected to 
concentrate for an extended period of time. Additionally, L-DEO would 
shut down the airgun array if marine mammals approach within 500 m 
(with the exception of specific genera of dolphins, see Proposed 
Mitigation), further reducing the expected duration and intensity of 
sound and therefore, the likelihood of marine mammals incurring PTS. 
Since the duration of exposure to loud sounds will be relatively short, 
it would be unlikely to affect the fitness of any individuals. Also, as 
described above, we expect that marine mammals would likely move away 
from a sound source that represents an aversive stimulus, especially at 
levels that would be expected to result in PTS, given sufficient notice 
of the R/V Langseth's approach due to the vessel's relatively low speed 
when conducting seismic surveys.
    In addition, the maximum expected Level B harassment zone around 
the survey vessel is 6,733 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 (11.5 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 marine mammal prey species are not expected to cause 
significant or long-term fitness consequences for individual marine 
mammals or their populations.
    Additionally, the acoustic ``footprint'' of the proposed survey 
would be very small relative to the ranges of all marine mammals that 
would potentially be affected. Sound levels would increase in the 
marine environment in a relatively small area surrounding the vessel 
compared to the range of the marine mammals within the proposed survey 
area. The seismic array would be active 24 hours per day throughout the 
duration of the proposed survey. However, the very brief overall 
duration of the proposed survey (30 survey days) would further limit 
potential impacts that may occur as a result of the proposed activity.
    Of the marine mammal species that are likely to occur in the 
project area, the following species are listed as endangered under the 
ESA: blue whales, fin whales, sei whales, and sperm whales. The take 
numbers proposed for authorization for these species (table 6) are 
minimal relative to their modeled population sizes; therefore, we do 
not expect population-level impacts to any of these species. Moreover, 
the actual range of the populations extends past the area covered by 
the model, so modeled population sizes are likely smaller than their 
actual population size. The other marine mammal species that may be 
taken by harassment during L-DEO's seismic survey are not listed as 
threatened or endangered under the ESA. There is no designated critical 
habitat for any ESA-listed marine mammals within the project area.
    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.
    The proposed mitigation measures are expected to reduce, to the 
extent practicable, the intensity and/or duration of takes for all 
species listed in table 1. In particular, they would provide animals 
the opportunity to move away from the sound source throughout the 
survey area before seismic survey equipment reaches full energy, thus, 
preventing them from being exposed to sound levels that have the 
potential to cause injury (Level A harassment) or more severe Level B 
harassment.
    In summary and as described above, the following factors primarily 
support our preliminary determination that the impacts resulting from 
this activity are not expected to adversely affect any of the species 
or populations through effects on annual rates of recruitment or 
survival:
     No serious injury or mortality is anticipated or proposed 
to be authorized;
     We are proposing to authorize a limited number of Level A 
harassment events of five species in the form of PTS; if any PTS is 
incurred as a result of the specified activity, we expect only a small 
degree of PTS that would not result in severe hearing impairment 
because of the constant movement of both the vessel 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.
     The proposed activity is temporary and of relatively short 
duration (11.5 days of planned survey activity);
     The vast majority of anticipated impacts of the proposed 
activity on marine mammals would be temporary behavioral changes due to 
avoidance of the ensonified area, which is relatively small (see table 
4);
     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 and severity of takes, to the extent practicable, by 
visually and/or acoustically detecting marine mammals within the 
established zones and implementing corresponding mitigation measures 
(e.g., delay; shutdown).
    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 marine mammal 
take from the proposed activity will have a negligible impact on all 
affected marine mammal species or populations.

Small Numbers

    As noted previously, only take of small numbers of marine mammals 
may be authorized under sections 101(a)(5)(A) and (D) of the MMPA for

[[Page 56188]]

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 
population 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 
population 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 number of takes NMFS proposes to authorize is below one-third 
of the most appropriate abundance estimate for all relevant populations 
(specifically, take of individuals is less than 1 percent of the 
modeled abundance of each affected population, see table 6). This is 
conservative because the modeled abundance represents a population of 
the species and we assume all takes are of different individual 
animals, which is likely not the case. Some individuals may be 
encountered multiple times in a day, but PSOs would count them as 
separate individuals if they cannot be identified.
    Based on the analysis contained herein of the proposed activity, 
including the proposed mitigation and monitoring measures, and the 
proposed authorized take of marine mammals, NMFS preliminarily finds 
that small numbers of marine mammals would be taken relative to the 
size of the affected species or populations.

Unmitigable Adverse Impact Analysis and Determination

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

Endangered Species Act

    Section 7(a)(2) of the Endangered Species Act of 1973 (ESA; 16 
U.S.C. 1531 et seq.) requires that each Federal agency insure that any 
action it authorizes, funds, or carries out is not likely to jeopardize 
the continued existence of any endangered or threatened species or 
result in the destruction or adverse modification of designated 
critical habitat. To ensure ESA compliance for the issuance of IHAs, 
NMFS consults internally whenever we propose to authorize take for 
endangered or threatened species.
    NMFS is proposing to authorize take of blue whales, fin whales, sei 
whales, and sperm whales, which are listed under the ESA. The NMFS OPR 
Permits and Conservation Division has requested initiation of section 7 
consultation with the OPR ESA Interagency Cooperation Division for the 
issuance of this IHA. NMFS will conclude the ESA consultation prior to 
reaching a determination regarding the proposed issuance of the 
authorization.

Proposed Authorization

    As a result of these preliminary determinations, NMFS proposes to 
issue an IHA to L-DEO for conducting a marine geophysical survey at the 
Chain Transform Fault in the equatorial Atlantic Ocean during austral 
summer 2024, provided the previously mentioned mitigation, monitoring, 
and reporting requirements are incorporated. A draft of the proposed 
IHA can be found at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities.

Request for Public Comments

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

    Dated: July 1, 2024.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2024-14737 Filed 7-5-24; 8:45 am]
BILLING CODE 3510-22-P