Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Geophysical Surveys in the Southeastern Gulf of Mexico, 71427-71453 [2021-27272]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 86, Number 239 (Thursday, December 16, 2021)]
[Notices]
[Pages 71427-71453]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-27272]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XA203]


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to Geophysical Surveys in the 
Southeastern Gulf of Mexico

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

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

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SUMMARY: NMFS has received a request from Scripps Institution of 
Oceanography (Scripps) for authorization to take marine mammals 
incidental to marine geophysical surveys in the southeastern Gulf of 
Mexico. 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 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 
authorizations and agency responses will be summarized in the final 
notice of our decision.

DATES: Comments and information must be received no later than January 
18, 2022.

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

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

SUPPLEMENTARY INFORMATION:

Background

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

National Environmental Policy Act

    To comply with the National Environmental Policy Act of 1969 (NEPA; 
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO)

[[Page 71428]]

216-6A, NMFS must review our proposed action (i.e., the issuance of an 
incidental harassment authorization) 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.
    We will review all comments submitted in response to this notice 
prior to concluding our NEPA process or making a final decision on the 
IHA request.

Summary of Request

    On March 17, 2020, NMFS received a request from Scripps for an IHA 
to take marine mammals incidental to low-energy geophysical surveys in 
the southeastern Gulf of Mexico, initially planned to occur in summer 
2020. The application was deemed adequate and complete on May 26, 2020. 
On June 9, 2020, Scripps notified NMFS that the proposed survey had 
been postponed and tentatively rescheduled for summer 2021. On April 8, 
2021, Scripps notified NMFS that the survey had been further postponed 
and is now proposed to occur in July-August 2022. NMFS has reviewed 
recent draft Stock Assessment Reports and other scientific literature, 
and determined that neither this nor any other new information affects 
which species or stocks have the potential to be affected, the 
potential effects to marine mammals and their habitat as described in 
the IHA application, or any other aspect of the analysis. Therefore, 
NMFS has determined that Scripps' IHA application remains adequate and 
complete. Scripps' request is for take of 20 species of marine mammals 
by Level B harassment only. Neither Scripps nor NMFS expects serious 
injury or mortality to result from this activity and, therefore, an IHA 
is appropriate.

Description of Proposed Activity

Overview

    Scripps plans to support a research project that would involve low-
energy seismic surveys in the Gulf of Mexico during summer 2022. The 
study would be conducted on the R/V Justo Sierra, owned by Universidad 
Nacional Aut[oacute]noma de M[eacute]xico (UNAM), using a portable 
multi-channel seismic (MCS) system operated by marine technicians from 
Scripps. The survey would use a pair of low-energy Generator-Injector 
(GI) airguns with a total discharge volume of 90 cubic inches (in\3\). 
The surveys would take place within the Exclusive Economic Zones (EEZs) 
of Mexico and Cuba in the southeastern Gulf of Mexico.

Dates and Duration

    The specific dates of the survey have not been determined but the 
cruise is expected to occur in July to August 2022. The proposed 
research cruise is expected to consist of 15 days at sea, including ~12 
days of seismic operations (10 planned days and 2 contingency days) and 
~3 days of transit. R/V Justo Sierra would depart from Tampamochaco, 
Mexico and return to Progreso, Mexico after the program is completed.

Specific Geographic Region

    The proposed surveys would take place in the Gulf of Mexico between 
~22[deg]-25[deg] N and 83.8[deg]-88[deg] W (see Figure 1). Seismic 
acquisition would occur in two primary survey areas. The Yucat[aacute]n 
Channel survey area is located in the deep-water channel between the 
Campeche and Florida escarpments, within the EEZ of Cuba in water 
depths ranging from ~1,500 to 3,600 meters (m; 4,921 to 11,811 feet 
(ft)). The Campeche Bank survey area is located in the northeastern 
flank of the Campeche escarpment, within the EEZs of Cuba and Mexico in 
waters ranging in depth from ~110 to 3,000 m (361 to 9,843 ft).

[[Page 71429]]

[GRAPHIC] [TIFF OMITTED] TN16DE21.000

Detailed Description of Specific Activity

    The proposed project consists of low-energy seismic surveys to 
image sediment drifts along Campeche Bank and in the deep water north 
of Yucat[aacute]n Channel in order to reconstruct bottom water current 
changes through the Cenozoic era. Data collected would also be used to 
inform potential future site locations for the International Ocean 
Discovery Program (IODP). To achieve the program's goals, researchers 
from UNAM and the University of Texas Institute of Geophysics (UTIG) 
propose to collect low-energy, high-resolution MCS profiles.
    The surveys would involve one source vessel, the R/V Justo Sierra, 
using the portable MCS system operated by marine technicians from 
Scripps. R/V Justo Sierra would deploy up to two 45-in\3\ GI airguns as 
an energy source with a maximum total discharge volume of ~90 in\3\. 
The generator chamber of each GI gun, the one responsible for 
introducing the sound pulse into the ocean, is 45 in\3\. The larger 
(105 in\3\) injector chamber injects air into the previously generated 
bubble to maintain its shape and does not introduce more sound into the 
water. The two 45-in\3\ GI airguns would be spaced 2 m (6.6 ft) apart, 
and towed 25 m (82 ft) behind the R/V Justo Sierra at a depth of 2-4 m 
(6.6-13.1 ft). An operational speed of ~7.4-9.3 kilometers (km) per 
hour (~4-5 knots) would be used during seismic acquisition, and seismic 
pulses would be emitted at intervals of 8-10 seconds from the GI 
airguns. The receiving system would consist of one hydrophone streamer, 
1,500 m (4,921 ft) in length. As the airguns are towed along the survey 
lines, the hydrophone streamer would receive the returning acoustic 
signals and transfer the data to the on-board processing system.
    The proposed cruise would acquire ~2,171 km (~1,349 miles) of 
seismic data in the southeastern Gulf of Mexico. All survey effort 
proposed in the Yucat[aacute]n Channel survey area would occur in water 
>1,000 m (3,281 ft) deep. In the Campeche Bank survey area, 
approximately 80 percent of survey effort would occur in deep water, 
and 20 percent would occur in intermediate water 100-1,000 m (328-3,281 
ft) deep. No survey effort is proposed in waters less than 100 m (328 
ft) deep.
    In the Yucat[aacute]n Channel survey area, a grid is proposed that 
consists of southwest-northeast trending strike profiles with crossing 
dip profiles to provide images of the deep water connection between the 
Straits of Florida and the basinal southeastern Gulf of Mexico (see 
Figure 1). In the Campeche Bank survey area, several long dip profiles 
would be acquired that are connected by several strike lines. The 
survey area also includes three proposed sites for future IODP coring 
(one in the Campeche Bank survey area and two within the Yucat[aacute]n 
Channel survey area, all within the EEZ of Cuba). Around each site, an 
additional survey of a single 5 km by 5 km (3.1 by 3.1 miles) box would 
be conducted around the proposed site to better characterize the 
sediments and provide a number of options to choose the ideal location 
for proposed future drilling.
    A hull-mounted multi-beam echosounder (MBES) and an Acoustic 
Doppler Current Profiler (ADCP) would also be operated from the R/V 
Justo Sierra continuously throughout the seismic surveys, but not 
during transits or and from the survey area or when airguns are not 
operating. All planned geophysical data acquisition activities would be 
conducted by Scripps and UNAM with on-board assistance by the 
scientists who have proposed the studies. The vessel would be self-
contained, and the crew would live aboard the vessel. Take of marine 
mammals is not expected to occur incidental to use of the MBES or ADCP 
because, whether or not the airguns are

[[Page 71430]]

operating simultaneously with the other sources, given their 
characteristics (e.g., narrow downward-directed beam), marine mammals 
would experience no more than one or two brief ping exposures, if any 
exposure were to occur. NMFS does not expect that use of these sources 
presents any reasonable potential to cause take of marine mammals.
    Proposed mitigation, monitoring, and reporting measures are 
described in detail later in this document (please see Proposed 
Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

    Sections 3 and 4 of the IHA application summarize available 
information regarding status and trends, distribution and habitat 
preferences, and behavior and life history, of the potentially affected 
species. We refer the reader to these descriptions, incorporated here 
by reference, instead of reprinting the information. Additional 
information regarding population trends and threats may be found in 
NMFS's Stock Assessment Reports (SARs; https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments) and 
more general information about these species (e.g., physical and 
behavioral descriptions) may be found on NMFS's website (https://www.fisheries.noaa.gov/find-species).
    Table 1 lists all species or stocks for which take is expected and 
proposed to be authorized for this action, and summarizes information 
related to the population or stock, including regulatory status under 
the MMPA and Endangered Species Act (ESA) and potential biological 
removal (PBR), where known. For taxonomy, we follow Committee on 
Taxonomy (2021). PBR is defined by the MMPA as the maximum number of 
animals, not including natural mortalities, that may be removed from a 
marine mammal stock while allowing that stock to reach or maintain its 
optimum sustainable population (as described in NMFS's SARs). While no 
mortality is anticipated or authorized here, PBR and annual serious 
injury and mortality from anthropogenic sources are included here as 
gross indicators of the status of the species and other threats.
    Marine mammal abundance estimates presented in this document 
represent the total number of individuals that make up a given stock or 
the total number estimated within a particular study or survey area. 
NMFS's stock abundance estimates for most species represent the total 
estimate of individuals within the geographic area, if known, that 
comprises that stock. For most species, stock abundance estimates are 
based on sightings within the U.S. EEZ, however for some species, this 
geographic area may extend beyond U.S. waters. Other species may use 
survey abundance estimates. Survey abundance (as compared to stock or 
species abundance) is the total number of individuals estimated within 
the survey area, which may or may not align completely with a stock's 
geographic range as defined in the SARs. These surveys may also extend 
beyond U.S. waters. In this case, the proposed survey area outside of 
the U.S. EEZ does not necessarily overlap with the ranges for stocks 
managed by NMFS. However, we assume that individuals of these species 
that may be encountered during the survey may be part of those stocks.
    All managed stocks in this region are assessed in NMFS's U.S. 
Atlantic and Gulf of Mexico SARs (e.g., Hayes et al., 2021). All values 
presented in Table 1 are the most recent available at the time of 
publication and are available in the 2020 SARs (Hayes et al., 2021) and 
draft 2021 SARs (available online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports).
    For the majority of species potentially present in the specified 
geographical region, NMFS has designated only a single generic stock 
(i.e., ``Gulf of Mexico'') for management purposes, although there is 
currently no information to differentiate the stock from the Atlantic 
Ocean stock of the same species, nor information on whether more than 
one stock may exist in the GOM (Hayes et al., 2017).

                                               Table 1--Marine Mammals That Could Occur in the Survey Area
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                                                                                                                                               Gulf of
                                                                                  Stock abundance                                               Mexico
                                                                     ESA/ MMPA    (CV, Nmin, most                                             population
          Common name            Scientific name        Stock         status;    recent abundance          PBR            Annual M/SI \3\     abundance
                                                                     strategic      survey) \2\                                              (Roberts et
                                                                     (Y/N) \1\                                                                al., 2016)
                                                                                                                                                 \4\
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                            Order Cetartiodactyla--Cetacea--Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Physeteridae:
    Sperm whale...............  Physeter          Gulf of Mexico..  E/D; Y       1,180 (0.22,      2..................  9.6................        2,207
                                 macrocephalus.                                   983, 2018).
Family Kogiidae:
    Pygmy sperm whale \6\.....  Kogia breviceps.  Gulf of Mexico..  -/-; N       336 (0.35, 253,   2.5................  31.................        4,373
                                                                                  2018).
    Dwarf sperm whale \6\.....  Kogia sima......
Family Ziphiidae (beaked
 whales):
    Cuvier's beaked whale \6\.  Ziphius           Gulf of Mexico..  -/-; N       18 (0.75, 10,     0.1................  5.2................        3,768
                                 cavirstris.                                      2018).
    Blainville's beaked whale   Mesoplodon        Gulf of Mexico..  -/-; N       98 (0.46, 68,     0.7................  5.2................
     \6\.                        densirostris.                                    2018).
    Gervais' beaked whale \6\.  Mesoplodon        Gulf of Mexico..  -/-; N       20 (0.98, 10,     0.1................  5.2................
                                 europaeus.                                       2018).
Family Delphinidae:
    Rough-toothed dolphin.....  Steno             Gulf of Mexico..  -/-; N       unknown (n/a,     undetermined.......  39.................        4,853
                                 bredanensis.                                     unknown, 2018).
    Bottlenose dolphin........  Tursiops          Gulf of Mexico    -/-; N       7,462 (0.31,      58.................  32.................  \6\ 176,108
                                 truncatus.        Oceanic.                       5,769, 2018).
    Pantropical spotted         Stenella          Gulf of Mexico..  -/-; N       37,195 (0.24,     304................  241................      102,361
     dolphin.                    attenuata.                                       30,377, 2018).
    Atlantic spotted dolphin..  Stenella          Gulf of Mexico..  -/-; N       21,506 (0.26,     166................  36.................       74,785
                                 frontalis.                                       17,339, 2018).

[[Page 71431]]

 
    Spinner dolphin...........  Stenella          Gulf of Mexico..  -/-; Y       2,991 (0.54,      20.................  113................       25,114
                                 longirostris.                                    1,954, 2018).
    Clymene dolphin...........  Stenella clymene  Gulf of Mexico..  -/-; Y       513 (1.03, 250,   2.5................  8.4................       11,895
                                                                                  2018).
    Striped dolphin...........  Stenella          Gulf of Mexico..  -/-; Y       1,817 (0.56,      12.................  13.................        5,229
                                 coeruleoalba.                                    1,172, 2018).
    Fraser's dolphin..........  Lagenodelphis     Gulf of Mexico..  -/-; N       213 (1.03, 104,   1..................  Unknown............        1,665
                                 hosei.                                           2018).
    Risso's dolphin...........  Grampus griseus.  Gulf of Mexico..  -/-; N       1,974 (0.46,      14.................  5.3................        3,764
                                                                                  1,368, 2018).
    Melon-headed whale........  Peponocephala     Gulf of Mexico..  -/-; N       1,749 (0.68,      10.................  9.5................        7,003
                                 electra.                                         1,039, 2018).
    Pygmy killer whale........  Feresa attenuata  Gulf of Mexico..  -/-; N       613 (1.15, 283,   2.8................  1.6................        2,126
                                                                                  2018).
    False killer whale........  Pseudorca         Gulf of Mexico..  -/-; N       494 (0.79, 276,   2.8................  Unknown............        3,204
                                 crassidens.                                      2018).
    Killer whale..............  Orcinus orca....  Gulf of Mexico..  -/-; N       267 (0.75, 152,   1.5................  Unknown............          185
                                                                                  2018).
    Short-finned pilot whale..  Globicephalus     Gulf of Mexico..  -/-; N       1,321 (0.43,      7.5................  3.9................        1,981
                                 macrorhynchus.                                   934, 2018).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed
  under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality
  exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed
  under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\2\ NMFS marine mammal stock assessment reports online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports. CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable.
\3\ These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g.,
  commercial fisheries, ship strike). Annual mortality/serious injury (M/SI) often cannot be determined precisely and is in some cases presented as a
  minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases.
\4\ This information represents species- or guild-specific best abundance estimate predicted by habitat-based cetacean density models (Roberts et al.,
  2016). These models provide the best available scientific information regarding predicted density patterns of cetaceans in the U.S. Gulf of Mexico,
  and we provide the corresponding abundance predictions as a point of reference. Total abundance estimates were produced by computing the mean density
  of all pixels in the modeled area and multiplying by its area. For those taxa where a density surface model predicting abundance by month was
  produced, the maximum mean seasonal abundance was used. For those taxa where abundance is not predicted by month, only mean annual abundance is
  available. For more information, see https://seamap.env.duke.edu/models/Duke/GOM/.
\5\ Abundance estimates are in some cases reported for a guild or group of species when those species are difficult to differentiate at sea. Similarly,
  the habitat-based cetacean density models produced by Roberts et al. (2016) are based in part on available observational data which, in some cases, is
  limited to genus or guild in terms of taxonomic definition. NMFS's SARs present pooled abundance estimates for Kogia spp. and Mesoplodon spp., while
  Roberts et al. (2016) produced density models to genus level for Kogia spp. and as a guild for beaked whales (Ziphius cavirostris and Mesoplodon
  spp.). Finally, Roberts et al. (2016) produced a density model for bottlenose dolphins that does not differentiate between oceanic, shelf, and coastal
  stocks.

    In Table 1 above, we report two sets of abundance estimates: Those 
from NMFS SARs and those predicted by Roberts et al. (2016). Please see 
the table footnotes for more detail. NMFS's SAR estimates are typically 
generated from the most recent shipboard and/or aerial surveys 
conducted. The Roberts et al. (2016) abundance estimates represent the 
output of predictive models derived from multi-year observations and 
associated environmental parameters and which incorporate corrections 
for detection bias. Incorporating more data over multiple years of 
observation can yield different results in either direction, as the 
result is not as readily influenced by fine-scale shifts in species 
habitat preferences or by the absence of a species in the study area 
during a given year. NMFS's abundance estimates show substantial year-
to-year variability in some cases. For example, NMFS-reported estimates 
for the Clymene dolphin vary by a maximum factor of more than 100 (2009 
estimate of 129 versus 1996-2001 estimate of 17,355), indicating that 
it may be more appropriate to use the model prediction versus a point 
estimate, as the model incorporates data from 1992-2009. The latter 
factor--incorporation of correction for detection bias--should 
systematically result in greater abundance predictions. For these 
reasons, we expect that the Roberts et al. (2016) estimates are 
generally more realistic and, for these purposes, represent the best 
available information. For purposes of assessing estimated exposures 
relative to abundance--used in this case to understand the scale of the 
predicted takes compared to the population--we generally believe that 
the Roberts et al. (2016) abundance predictions are most appropriate 
because they were used to generate the exposure estimates and therefore 
provide the most relevant comparison (see Estimated Take). Roberts et 
al. (2016) represents the best available scientific information 
regarding marine mammal occurrence and distribution in the Gulf of 
Mexico.
    As the planned survey lines are outside of the U.S. EEZ, they do 
not directly overlap with the defined stock ranges within the Gulf of 
Mexico (Hayes et al., 2021). However, some of the survey lines occur 
near the U.S. EEZ, and the distribution and abundance of species in 
U.S. EEZ waters are assumed representative of those in the survey area. 
As indicated above, all 20 species (with 20 representative stocks in 
the northern Gulf of Mexico) in Table 1 temporally and spatially co-
occur with the activity to the degree that take is reasonably likely to 
occur, and we have proposed authorizing it. All species that could 
potentially occur in the proposed survey areas are included in Table 2 
of the IHA application. While fin whales (Balaenoptera physalus), 
Rice's whales (Balaenoptera ricei, formerly known as Gulf of Mexico 
Bryde's whales), minke whales (Balaenoptera acutorostrata), and 
humpback whales (Megaptera novaeangliae) have the potential to occur in 
the southeast Gulf of Mexico, the temporal and/or spatial occurrence of 
these species is such that take is not expected to occur, and they are 
not discussed further beyond the explanation provided here. These 
species, and other mysticete species for which there exist rare 
sighting or stranding records, are considered only of accidental 
occurrence in the Gulf of Mexico and are generally historically known 
only from a very small number of strandings and/or sightings 
(W[uuml]rsig et al., 2000; W[uuml]rsig, 2017).
    The fin whale is widely distributed in all the world's oceans 
(Gambell 1985), although it is most abundant in

[[Page 71432]]

temperate and cold waters (Aguilar and Garc[iacute]a-Vernet 2018). The 
fin whale is the second-most frequently reported mysticete in the Gulf 
of Mexico (after the Rice's whale), though with only a handful of 
stranding and sighting records, and is considered here as a rare and 
likely accidental migrant. Roberts et al. (2016) developed a stratified 
density model for the fin whale in the Gulf of Mexico, on the basis of 
one observation during an aerial survey in the early 1990s. As noted by 
the model authors, while the probability of a chance encounter is not 
zero, the single sighting during NMFS survey effort should be 
considered extralimital (Roberts et al., 2015a). Duke University's 
Ocean Biodiversity Information System Spatial Ecological Analysis of 
Megavertebrate Populations (OBIS-SEAMAP) database includes 12 records 
of fin whales in the Gulf of Mexico, including six in the southern Gulf 
(OBIS 2020). Ortega-Ortiz (2002) reported a fin whale at the Campeche 
Escarpment but no sightings of fin whales have been reported in the 
Gulf of Mexico since 1998 (Roberts et al., 2016).
    Rice's whales are the only baleen whale to occur in the Gulf of 
Mexico on a regular basis throughout the year (Wursig et al., 2000) but 
according to Ortega-Ortiz (2000), they do not appear to occur in the 
southern Gulf of Mexico in Mexican and Cuban waters. Rice's whale calls 
were not detected via passive acoustic recorders at the Dry Tortugas or 
in the north-central GoM (south of Alabama) at Main Pass 
(Sirovi[cacute] et al., 2014). The OBIS database includes 30 
observation records for the northern Gulf of Mexico, but no records for 
the southern Gulf (OBIS 2020).
    The minke whale has a cosmopolitan distribution ranging from the 
tropics and subtropics to the ice edge in both hemispheres (Jefferson 
et al., 2015). Although widespread and common overall, they are rare in 
the Gulf of Mexico (W[uuml]rsig et al., 2000). W[uuml]rsig et al. 
(2000) reported ten strandings for the Gulf including the Florida Keys; 
the strandings occurred in the winter and spring and may have been 
northbound whales from the open ocean or Caribbean Sea. Based on 
Ortega-Ortiz (2002), the only record of a minke whale in the southern 
Gulf of Mexico is a single whale recorded as stranded at 
Celest[uacute]n, on the northwestern coast of the Yucat[aacute]n 
Peninsula.
    Although humpback whales only occur rarely in the Gulf of Mexico, 
several sightings have been made off the west coast of Florida, near 
Alabama, and off Texas (W[uuml]rsig et al., 2000); these may have been 
individuals from the West Indian winter grounds that strayed into the 
GoM during migration (Weller et al., 1996; Jefferson and Schiro 1997). 
In addition, W[uuml]rsig et al. (2000) reported that humpback songs 
have also been recorded with hydrophones in the northwestern Gulf of 
Mexico, and there are two stranding records. Humpbacks have also been 
sighted off the northwest coast of Cuba (Whitt et al., 2011). There are 
35 records in the OBIS database for the Gulf, including records for the 
Campeche Bank survey area, Straits of Florida, and northwestern Cuba.

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. Current data indicate that 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) recommended that marine mammals be divided 
into functional hearing groups based on directly measured or estimated 
hearing ranges on the basis of available behavioral response data, 
audiograms derived using auditory evoked potential techniques, 
anatomical modeling, and other data. Note that no direct measurements 
of hearing ability have been successfully completed for mysticetes 
(i.e., low-frequency cetaceans). Subsequently, NMFS (2018) described 
generalized hearing ranges for these marine mammal hearing groups. 
Generalized hearing ranges were chosen based on the approximately 65 
decibel (dB) threshold from the normalized composite audiograms, with 
the exception for lower limits for low-frequency cetaceans where the 
lower bound was deemed to be biologically implausible and the lower 
bound from Southall et al. (2007) retained. Marine mammal hearing 
groups and their associated hearing ranges are provided in Table 2.

                  Table 2--Marine Mammal Hearing Groups
                              [NMFS, 2018]
------------------------------------------------------------------------
              Hearing group                 Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen      7 Hz to 35 kHz.
 whales).
Mid-frequency (MF) cetaceans (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. 
Twenty species of cetacean have the reasonable potential to co-occur 
with the proposed survey activities. No pinnipeds are expected to be 
present or taken. Of the cetacean species that may be present, 18 are 
classified as mid-frequency cetaceans (i.e., all delphinid and ziphiid 
species and the sperm whale) and two are classified as high-frequency 
cetaceans (i.e., harbor porpoise and Kogia spp.). No low-frequency 
cetaceans (i.e., baleen whales) are expected to be present or taken.

Potential Effects of Specified Activities on Marine Mammals and Their 
Habitat

    This section includes a summary and discussion of the ways that 
components of the specified activity may impact marine mammals and 
their habitat. The Estimated Take section later in this document 
includes a quantitative analysis of the number of individuals

[[Page 71433]]

that are expected to be taken by this activity. The Negligible Impact 
Analysis and Determination section considers the content of this 
section, the Estimated Take section, and the Proposed Mitigation 
section, to draw conclusions regarding the likely impacts of these 
activities on the reproductive success or survivorship of individuals 
and how those impacts on individuals are likely to impact marine mammal 
species or stocks.

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 
airguns considered here. The compressions and decompressions associated 
with sound waves are detected as changes in pressure by aquatic life 
and man-made sound receptors such as hydrophones.
    Even in the absence of sound from the specified activity, the 
underwater environment is typically loud due to ambient sound. Ambient 
sound is defined as environmental background sound levels lacking a 
single source or point (Richardson et al., 1995), and the sound level 
of a region is defined by the total acoustical energy being generated 
by known and unknown sources. These sources may include physical (e.g., 
wind and waves, earthquakes, ice, atmospheric sound), biological (e.g., 
sounds produced by marine mammals, fish, and invertebrates), and 
anthropogenic (e.g., vessels, dredging, construction) sound. A number 
of sources contribute to ambient sound, including the following 
(Richardson et al., 1995):
     Wind and waves: The complex interactions between wind and 
water surface, including processes such as breaking waves and wave-
induced bubble oscillations and cavitation, are a main source of 
naturally occurring ambient sound for frequencies between 200 Hz and 50 
kHz (Mitson, 1995). In general, ambient sound levels tend to increase 
with increasing wind speed and wave height. Surf sound becomes 
important near shore, with measurements collected at a distance of 8.5 
km from shore showing an increase of 10 dB in the 100 to 700 Hz band 
during heavy surf conditions;
     Precipitation: Sound from rain and hail impacting the 
water surface can become an important component of total sound at 
frequencies above 500 Hz, and possibly down to 100 Hz during quiet 
times;
     Biological: Marine mammals can contribute significantly to 
ambient sound levels, as can some fish and snapping shrimp. The 
frequency band for biological contributions is from approximately 12 Hz 
to over 100 kHz; and
     Anthropogenic: Sources of ambient sound related to human 
activity include transportation (surface vessels), dredging and 
construction, oil and gas drilling and production, seismic surveys, 
sonar, explosions, and ocean acoustic studies. Vessel noise typically 
dominates the total ambient sound for frequencies between 20 and 300 
Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz 
and, if higher frequency sound levels are created, they attenuate 
rapidly. Sound from identifiable anthropogenic sources other than the 
activity of interest (e.g., a passing vessel) is sometimes termed 
background sound, as opposed to ambient sound.
    The sum of the various natural and anthropogenic sound sources at 
any given location and time--which comprise ``ambient'' or 
``background'' sound--depends not only on the source levels (as 
determined by current weather conditions and levels of biological and 
human activity) but also on the ability of sound to propagate through 
the environment. In turn, sound propagation is dependent on the 
spatially and temporally varying properties of the water column and sea 
floor, and is frequency-dependent. As a result of the 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.

[[Page 71434]]

    Sounds are often considered to fall into one of two general types: 
Pulsed and non-pulsed (defined in the following). The distinction 
between these two sound types is important because they have differing 
potential to cause physical effects, particularly with regard to 
hearing (e.g., Ward, 1997 in Southall et al., 2007). Please see 
Southall et al. (2007) for an in-depth discussion of these concepts.
    Pulsed sound sources (e.g., airguns, explosions, gunshots, sonic 
booms, impact pile driving) produce signals that are brief (typically 
considered to be less than one second), broadband, atonal transients 
(ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur 
either as isolated events or repeated in some succession. Pulsed sounds 
are all characterized by a relatively rapid rise from ambient pressure 
to a maximal pressure value followed by a rapid decay period that may 
include a period of diminishing, oscillating maximal and minimal 
pressures, and generally have an increased capacity to induce physical 
injury as compared with sounds that lack these features.
    Non-pulsed sounds can be tonal, narrowband, or broadband, brief or 
prolonged, and may be either continuous or non-continuous (ANSI, 1995; 
NIOSH, 1998). Some of these non-pulsed sounds can be transient signals 
of short duration but without the essential properties of pulses (e.g., 
rapid rise time). Examples of non-pulsed sounds include those produced 
by vessels, aircraft, machinery operations such as drilling or 
dredging, vibratory pile driving, and active sonar systems (such as 
those used by the U.S. Navy). The duration of such sounds, as received 
at a distance, can be greatly extended in a highly reverberant 
environment.
    Airguns 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.
    As described above, a hull-mounted MBES and an ADCP would also be 
operated from the R/V Justo Sierra continuously throughout the seismic 
surveys, but not during transits or and from the survey area or when 
airguns are not operating. Each ping emitted by the MBES consists of 
eight (in water >1,000 m deep) or four (<1,000 m) successive fan-shaped 
transmissions, each ensonifying a sector that extends 1[deg] fore-aft. 
Given the movement and speed of the vessel, the intermittent and narrow 
downward-directed nature of the sounds emitted by the MBES mean that no 
exposure of marine mammals is likely to occur. In the unlikely event 
that exposure did occur, it would result in no more than one or two 
brief ping exposures of any individual marine mammal. Due to the lower 
source level of the ADCP relative to the R/V Justo Sierra's airguns, 
sounds from the SBP and ADCP are expected to be effectively subsumed by 
sounds from the airguns. Thus, any marine mammal potentially exposed to 
sounds from the ADCP would already have been exposed to sounds from the 
airguns, which are expected to propagate further in the water. As such, 
we conclude that the likelihood of marine mammal take resulting from 
exposure to sound from the MBES or ADCP is discountable and therefore 
we do not consider noise from the MBES or ADCP further in this 
analysis.

Acoustic Effects

    Here, we discuss the effects of active acoustic sources on marine 
mammals.
    Potential Effects of Underwater Sound--Please refer to the 
information given previously (``Description of Active Acoustic 
Sources'') regarding sound, characteristics of sound types, and metrics 
used in this document. 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 will occur almost exclusively for noise 
within an animal's hearing range. We first describe specific 
manifestations of acoustic effects before providing discussion specific 
to the use of airguns.
    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 
responsiveness. Third is a zone within which, for signals of high 
intensity, the received level is sufficient to potentially cause 
discomfort or tissue damage to auditory or other systems. Overlaying 
these zones to a certain extent is the area within which masking (i.e., 
when a sound interferes with or masks the ability of an animal to 
detect a signal of interest that is above the absolute hearing 
threshold) may occur; the masking zone may be highly variable in size.
    We describe the more severe effects of certain non-auditory 
physical or physiological effects only briefly as we do not expect that 
use of airgun arrays are reasonably likely to result in such effects 
(see below for further discussion). Potential effects from impulsive 
sound sources can range in severity from effects such as behavioral 
disturbance or tactile perception to physical discomfort, slight injury 
of the internal organs and the auditory system, or mortality (Yelverton 
et al., 1973). Non-auditory physiological effects or injuries that 
theoretically might occur in marine mammals exposed to high level 
underwater sound or as a secondary effect of extreme behavioral 
reactions (e.g., change in dive profile as a result of an avoidance 
reaction) caused by exposure to sound include neurological effects, 
bubble formation, resonance effects, and other types of organ or tissue 
damage (Cox et al., 2006; Southall et al., 2007; Zimmer and Tyack, 
2007; Tal et al., 2015). The survey activities considered here do not 
involve the use of devices such as explosives or mid-frequency tactical 
sonar that are associated with these types of effects.
    Threshold Shift--Marine mammals exposed to high-intensity sound, or 
to lower-intensity sound for prolonged periods, can experience hearing 
threshold shift (TS), which is the loss of hearing sensitivity at 
certain frequency ranges (Finneran, 2015). TS can be permanent (PTS), 
in which case the loss

[[Page 71435]]

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; Houser, 2021). 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 
consider TTS to constitute auditory injury.
    Relationships between TTS and PTS thresholds have not been studied 
in marine mammals, and there is no PTS data for cetaceans but such 
relationships are assumed to be similar to those in humans and other 
terrestrial mammals. PTS typically occurs at exposure levels at least 
several dBs above (a 40-dB threshold shift approximates PTS onset; 
e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB 
threshold shift approximates TTS onset; e.g., Southall et al. 2007). 
Based on data from terrestrial mammals, a precautionary assumption is 
that the PTS thresholds for impulse sounds (such as airgun pulses as 
received close to the source) are at least 6 dB higher than the TTS 
threshold on a peak-pressure basis and PTS cumulative sound exposure 
level thresholds are 15 to 20 dB higher than TTS cumulative sound 
exposure level thresholds (Southall et al., 2007). Given the higher 
level of sound or longer exposure duration necessary to cause PTS as 
compared with TTS, it is considerably less likely that PTS could occur.
    For mid-frequency cetaceans in particular, potential protective 
mechanisms may help limit onset of TTS or prevent onset of PTS. Such 
mechanisms include dampening of hearing, auditory adaptation, or 
behavioral amelioration (e.g., Nachtigall and Supin, 2013; Miller et 
al., 2012; Finneran et al., 2015; Popov et al., 2016).
    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 three captive 
bottlenose dolphins before and after exposure to ten pulses produced by 
a seismic airgun in order to study TTS induced after exposure to 
multiple pulses. Exposures began at relatively low levels and gradually 
increased over a period of several months, with the highest exposures 
at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from 
193-195 dB. No substantial TTS was observed. In addition, behavioral 
reactions were observed that indicated that animals can learn behaviors 
that effectively mitigate noise exposures (although exposure patterns 
must be learned, which is less likely in wild animals than for the 
captive animals considered in this study). The authors note that the 
failure to induce more significant auditory effects likely due to the 
intermittent nature of exposure, the relatively low peak pressure 
produced by the acoustic source, and the low-frequency energy in airgun 
pulses as compared with the frequency range of best sensitivity for 
dolphins and other mid-frequency cetaceans.
    Currently, TTS data only exist for four species of cetaceans 
(bottlenose dolphin, beluga whale, harbor porpoise, and Yangtze finless 
porpoise) exposed to a limited number of sound sources (i.e., mostly 
tones and octave-band noise) in laboratory settings (Finneran, 2015). 
In general, harbor porpoises have a lower TTS onset than other measured 
cetacean species (Finneran, 2015). Additionally, the existing marine 
mammal TTS data come from a limited number of individuals within these 
species. There are no 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), Finneran and Jenkins 
(2012), Finneran (2015), and NMFS (2016a).
    Behavioral Effects--Behavioral disturbance may include a variety of 
effects, including subtle changes in behavior (e.g., minor or brief 
avoidance of an area or changes in vocalizations), more conspicuous 
changes in similar behavioral activities, and more sustained and/or 
potentially severe reactions, such as displacement from or abandonment 
of high-quality habitat. Behavioral responses to sound are highly 
variable and context-specific and any reactions depend on numerous 
intrinsic and extrinsic factors (e.g., species, state of maturity, 
experience, current activity, reproductive state, auditory sensitivity, 
time of day), as well as the interplay between factors (e.g., 
Richardson et al., 1995; Wartzok et al., 2003; Southall et al., 2007; 
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

[[Page 71436]]

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

[[Page 71437]]

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 (h) 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 SEL (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 a 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 showed 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).
    A flight response is a dramatic change in normal movement to a 
directed and rapid movement away from the perceived location of a sound 
source. The flight response differs from other avoidance responses in 
the intensity of the response (e.g., directed movement, rate of 
travel). Relatively little information on flight responses of marine 
mammals to anthropogenic signals exist, although observations of flight 
responses to the presence of predators have occurred (Connor and 
Heithaus, 1996). The result of a flight response could range from 
brief, temporary exertion and displacement from the area where the 
signal provokes flight to, in extreme cases, marine mammal strandings 
(Evans and England, 2001). However, it should be noted that response to 
a perceived predator does not necessarily invoke flight (Ford and 
Reeves, 2008), and whether individuals are solitary or in groups may 
influence the response.
    Behavioral disturbance can also impact marine mammals in more 
subtle ways. Increased vigilance may result in costs related to 
diversion of focus and attention (i.e., when a response consists of 
increased vigilance, it may come at the cost of decreased attention to 
other critical behaviors such as foraging or resting). These effects 
have generally not been demonstrated for marine mammals, but studies 
involving fish and terrestrial animals have shown that increased 
vigilance may substantially reduce feeding rates (e.g., Beauchamp and 
Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In 
addition, chronic disturbance can cause population declines through 
reduction of fitness (e.g., decline in body condition) and subsequent 
reduction in reproductive success, survival, or both (e.g., Harrington 
and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, 
Ridgway et al. (2006) reported that increased vigilance in bottlenose 
dolphins exposed to sound over a 5 day period did not cause any sleep 
deprivation or stress effects.
    Many animals perform vital functions, such as feeding, resting, 
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption 
of such functions resulting from reactions to stressors such as sound 
exposure are more likely to be significant if they last more than one 
diel cycle or recur on subsequent days (Southall et al., 2007). 
Consequently, a behavioral response lasting less than one day and not 
recurring on subsequent days is not considered particularly severe 
unless it could directly affect reproduction or survival (Southall et 
al., 2007). Note that there is a difference between multi-day 
substantive behavioral reactions and multi-day anthropogenic 
activities. For example, just because an activity lasts for multiple 
days does not necessarily mean that individual animals are either 
exposed to activity-related stressors for multiple days or, further, 
exposed in a manner resulting in sustained multi-day substantive 
behavioral responses.
    Stone (2015) reported data from at-sea observations during 1,196 
seismic surveys from 1994 to 2010. When large arrays of airguns 
(considered to be 500 in\3\ or more) were firing, lateral displacement, 
more localized avoidance, or other changes in behavior were evident for 
most odontocetes. However, significant responses to large arrays were 
found only for the minke whale and fin whale. Behavioral responses 
observed included changes in swimming or surfacing behavior, with 
indications that cetaceans remained near the water surface at these 
times. Cetaceans were recorded as feeding less often when large arrays 
were active. Behavioral observations of gray whales during a seismic 
survey monitored whale movements and respirations pre-, during and 
post-seismic survey (Gailey et al., 2016). Behavioral state and water 
depth were the best `natural' predictors of whale movements and 
respiration and, after considering natural variation, none of the 
response variables were significantly associated with seismic survey or 
vessel sounds.
    Stress Responses--An animal's perception of a threat may be 
sufficient to trigger stress responses consisting of some combination 
of behavioral responses, autonomic nervous system responses, 
neuroendocrine responses, or immune responses (e.g., Seyle, 1950; 
Moberg, 2000). In many cases, an animal's first and sometimes most 
economical (in terms of energetic costs) response is behavioral 
avoidance of the potential stressor. Autonomic nervous system responses 
to stress typically involve changes in heart rate, blood

[[Page 71438]]

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, marine mammals experiencing 
significant masking could also be impaired from maximizing their 
performance fitness in survival and reproduction. Therefore, when the 
coincident (masking) sound is man-made, it may be considered harassment 
when disrupting or altering critical behaviors. It is important to 
distinguish TTS and PTS, which persist after the sound exposure, from 
masking, which occurs during the sound exposure. Because masking 
(without resulting in TS) is not associated with abnormal physiological 
function, it is not considered a physiological effect, but rather a 
potential behavioral effect.
    The frequency range of the potentially masking sound is important 
in determining 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 can be reduced in situations where the signal 
and noise come from different directions (Richardson et al., 1995), 
through amplitude modulation of the signal, or through other 
compensatory behaviors (Houser and Moore, 2014). Masking can be tested 
directly in captive species (e.g., Erbe, 2008), but in wild populations 
it must be either modeled or inferred from evidence of masking 
compensation. There are few studies addressing real-world masking 
sounds likely to be experienced by marine mammals in the wild (e.g., 
Branstetter et al., 2013).
    Masking affects both senders and receivers of acoustic signals and 
can potentially have long-term chronic effects on marine mammals at the 
population level as well as at the individual level. Low-frequency 
ambient sound levels have increased by as much as 20 dB (more than 
three times in terms of SPL) in the world's ocean from pre-industrial 
periods, with most of the increase from distant commercial shipping 
(Hildebrand, 2009). All anthropogenic sound sources, but especially 
chronic and lower-frequency signals (e.g., from vessel traffic), 
contribute to elevated ambient sound levels, thus intensifying masking.
    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited, although there are few specific data on this. Because of 
the intermittent nature and low duty cycle of seismic pulses, animals 
can emit and receive sounds in the relatively quiet intervals between 
pulses. However, in exceptional situations, reverberation occurs for 
much or all of the interval between pulses (e.g., Simard et al. 2005; 
Clark and Gagnon 2006), which could mask calls. Situations with 
prolonged strong reverberation are infrequent. However, it is common 
for reverberation to cause some lesser degree of elevation of the 
background level between airgun pulses (e.g., Gedamke 2011; Guerra et 
al. 2011, 2016; Klinck et al. 2012; Guan et al. 2015), and this weaker 
reverberation presumably reduces the detection range of calls and other 
natural sounds to some degree. Guerra et al. (2016) reported that 
ambient noise levels between seismic pulses were elevated as a result 
of reverberation at ranges of 50 km from the seismic source. Based on 
measurements in deep water of the Southern Ocean, Gedamke (2011) 
estimated that the slight elevation of background levels during 
intervals between pulses reduced blue and fin

[[Page 71439]]

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

Ship Noise

    Vessel noise from the R/V Justo Sierra could affect marine animals 
in the proposed survey areas. Houghton et al. (2015) proposed that 
vessel speed is the most important predictor of received noise levels, 
and Putland et al. (2017) also reported reduced sound levels with 
decreased vessel speed. Sounds produced by large vessels generally 
dominate ambient noise at frequencies from 20 to 300 Hz (Richardson et 
al. 1995). However, some energy is also produced at higher frequencies 
(Hermannsen et al. 2014); low levels of high-frequency sound from 
vessels has been shown to elicit responses in harbor porpoise (Dyndo et 
al. 2015). Increased levels of ship noise have been shown to affect 
foraging by porpoise (Teilmann et al. 2015; Wisniewska et al. 2018); 
Wisniewska et al. (2018) suggest that a decrease in foraging success 
could have long-term fitness consequences.
    Ship noise, through masking, can reduce the effective communication 
distance of a marine mammal if the frequency of the sound source is 
close to that used by the animal, and if the sound is present for a 
significant fraction of time (e.g., Richardson et al. 1995; Clark et 
al. 2009; Jensen et al. 2009; Gervaise et al. 2012; Hatch et al. 2012; 
Rice et al. 2014; Dunlop 2015; Erbe et al. 2015; Jones et al. 2017; 
Putland et al. 2017). In addition to the frequency and duration of the 
masking sound, the strength, temporal pattern, and location of the 
introduced sound also play a role in the extent of the masking 
(Branstetter et al. 2013, 2016; Finneran and Branstetter 2013; Sills et 
al. 2017). Branstetter et al. (2013) reported that time-domain metrics 
are also important in describing and predicting masking. In order to 
compensate for increased ambient noise, some cetaceans are known to 
increase the source levels of their calls in the presence of elevated 
noise levels from shipping, shift their peak frequencies, or otherwise 
change their vocal behavior (e.g., Parks et al. 2011, 2012, 2016a,b; 
Castellote et al. 2012; Melc[oacute]n et al. 2012; Azzara et al. 2013; 
Tyack and Janik 2013; Lu[iacute]s et al. 2014; Sairanen 2014; Papale et 
al. 2015; Bittencourt et al. 2016; Dahlheim and Castellote 2016; 
Gospi[cacute] and Picciulin 2016; Gridley et al. 2016; Heiler et al. 
2016; Martins et al. 2016; O'Brien et al. 2016; Tenessen and Parks 
2016). Harp seals did not increase their call frequencies in 
environments with increased low-frequency sounds (Terhune and Bosker 
2016). Holt et al. (2015) reported that changes in vocal modifications 
can have increased energetic costs for individual marine mammals. A 
negative correlation between the presence of some cetacean species and 
the number of vessels in an area has been demonstrated by several 
studies (e.g., Campana et al. 2015; Culloch et al. 2016).
    Baleen whales are thought to be more sensitive to sound at these 
low frequencies than are toothed whales (e.g., MacGillivray et al. 
2014), possibly causing localized avoidance of the proposed survey area 
during seismic operations. Reactions of gray and humpback whales to 
vessels have been studied, and there is limited information available 
about the reactions of right whales and rorquals (fin, blue, and minke 
whales). Reactions of humpback whales to boats are variable, ranging 
from approach to avoidance (Payne 1978; Salden 1993). Baker et al. 
(1982, 1983) and Baker and Herman (1989) found humpbacks often move 
away when vessels are within several kilometers. Humpbacks seem less 
likely to react overtly when actively feeding than when resting or 
engaged in other activities (Krieger and Wing 1984, 1986). Increased 
levels of ship noise have been shown to affect foraging by humpback 
whales (Blair et al. 2016). Fin whale sightings in the western 
Mediterranean were negatively correlated with the number of vessels in 
the area (Campana et al. 2015). Minke whales and gray seals have shown 
slight displacement in response to construction-related vessel traffic 
(Anderwald et al. 2013).
    Many odontocetes show considerable tolerance of vessel traffic, 
although they sometimes react at long distances if confined by ice or 
shallow water, if previously harassed by vessels, or have had little or 
no recent exposure to ships (Richardson et al. 1995). Dolphins of many 
species tolerate and sometimes approach vessels (e.g., Anderwald et al. 
2013). Some dolphin species approach moving vessels to ride the bow or 
stern waves (Williams et al. 1992). Pirotta et al. (2015) noted that 
the physical presence of vessels, not just ship noise, disturbed the 
foraging activity of bottlenose dolphins. Sightings of striped dolphin, 
Risso's dolphin, sperm whale, and Cuvier's beaked whale in the western 
Mediterranean were negatively correlated with the number of vessels in 
the area (Campana et al. 2015).
    There are few data on the behavioral reactions of beaked whales to 
vessel noise, though they seem to avoid approaching vessels (e.g., 
W[uuml]rsig et al. 1998) or dive for an extended period when approached 
by a vessel (e.g., Kasuya 1986). Based on a single observation, Aguilar 
Soto et al. (2006) suggest foraging efficiency of Cuvier's beaked 
whales may be reduced by close approach of vessels.
    In summary, project vessel sounds would not be at levels expected 
to cause anything more than possible localized and temporary behavioral 
changes in marine mammals, and would not be expected to result in 
significant negative effects on individuals or at the population level. 
In addition, in all oceans of the world, large vessel traffic is 
currently so prevalent that it is commonly considered a usual source of 
ambient sound (NSF-USGS 2011).

Ship Strike

    Vessel collisions with marine mammals, or ship strikes, can result 
in death or serious injury of the animal. Wounds resulting from ship 
strike may include massive trauma, hemorrhaging, broken bones, or 
propeller lacerations (Knowlton and Kraus, 2001). An animal

[[Page 71440]]

at the surface may be struck directly by a vessel, a surfacing animal 
may hit the bottom of a vessel, or an animal just below the surface may 
be cut by a vessel's propeller. Superficial strikes may not kill or 
result in the death of the animal. These interactions are typically 
associated with large whales (e.g., fin whales), which are occasionally 
found draped across the bulbous bow of large commercial ships upon 
arrival in port. Although smaller cetaceans are more maneuverable in 
relation to large vessels than are large whales, they may also be 
susceptible to strike. The severity of injuries typically depends on 
the size and speed of the vessel, with the probability of death or 
serious injury increasing as vessel speed increases (Knowlton and 
Kraus, 2001; Laist et al., 2001; Vanderlaan and Taggart, 2007; Conn and 
Silber, 2013). Impact forces increase with speed, as does the 
probability of a strike at a given distance (Silber et al., 2010; Gende 
et al., 2011).
    Pace and Silber (2005) also found that the probability of death or 
serious injury increased rapidly with increasing vessel speed. 
Specifically, the predicted probability of serious injury or death 
increased from 45 to 75 percent as vessel speed increased from 10 to 14 
knots, and exceeded 90 percent at 17 knots. 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 knots. The chances of a lethal 
injury decline from approximately 80 percent at 15 knots to 
approximately 20 percent at 8.6 knots. At speeds below 11.8 knots, the 
chances of lethal injury drop below 50 percent, while the probability 
asymptotically increases toward one hundred percent above 15 knots.
    The R/V Justo Sierra travels at a speed of 4-5 knots during seismic 
acquisition. When not towing seismic equipment, the R/V Justo Sierra 
cruises at 12 knots and has a maximum speed of 12.5 knots. At survey 
speed, both the possibility of striking a marine mammal and the 
possibility of a strike resulting in serious injury or mortality are 
discountable. At average transit speed, the probability of serious 
injury or mortality resulting from a strike is less than 50 percent. 
However, the likelihood of a strike actually happening is again 
discountable. Ship strikes, as analyzed in the studies cited above, 
generally involve commercial shipping, which is much more common in 
both space and time than is geophysical survey activity. Jensen and 
Silber (2004) summarized ship strikes of large whales worldwide from 
1975-2003 and found that most collisions occurred in the open ocean and 
involved large vessels (e.g., commercial shipping). No such incidents 
were reported for geophysical survey vessels during that time period.
    It is possible for ship strikes to occur while traveling at slow 
speeds. For example, a hydrographic survey vessel traveling at low 
speed (5.5 knots) 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 CI = 0-5.5 x 10-6; NMFS, 2013b). In addition, a 
research vessel reported a fatal strike in 2011 of a dolphin in the 
Atlantic, demonstrating that it is possible for strikes involving 
smaller cetaceans to occur. In that case, the incident report indicated 
that an animal apparently was struck by the vessel's propeller as it 
was intentionally swimming near the vessel. While indicative of the 
type of unusual events that cannot be ruled out, neither of these 
instances represents a circumstance that would be considered reasonably 
foreseeable or that would be considered preventable.
    Although the likelihood of the vessel striking a marine mammal is 
low, we propose to require a robust ship strike avoidance protocol (see 
Proposed Mitigation), which we believe eliminates any foreseeable risk 
of ship strike. 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 required 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, we believe that the 
possibility of ship strike is discountable and, further, that were a 
strike of a large whale to occur, it would be unlikely to result in 
serious injury or mortality. No incidental take resulting from ship 
strike is anticipated, and this potential effect of the specified 
activity will not be discussed further in the following analysis.
    Stranding--When a living or dead marine mammal swims or floats onto 
shore and becomes ``beached'' or incapable of returning to sea, the 
event is a ``stranding'' (Geraci et al., 1999; Perrin and Geraci, 2002; 
Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a 
stranding under the MMPA is that (A) a marine mammal is dead and is (i) 
on a beach or shore of the United States; or (ii) in waters under the 
jurisdiction of the United States (including any navigable waters); or 
(B) a marine mammal is alive and is (i) on a beach or shore of the 
United States and is unable to return to the water; (ii) 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 (iii) in the waters under 
the jurisdiction of the United States (including any navigable waters), 
but is unable to return to its natural habitat under its own power or 
without assistance.
    Marine mammals strand for a variety of reasons, such as infectious 
agents, biotoxicosis, starvation, fishery interaction, ship strike, 
unusual oceanographic or weather events, sound exposure, or 
combinations of these stressors sustained concurrently or in series. 
However, the cause or causes of most strandings are unknown (Geraci et 
al., 1976; Eaton, 1979; Odell et al., 1980; Best, 1982). Numerous 
studies suggest that the physiology, behavior, habitat relationships, 
age, or condition of cetaceans may cause them to strand or might pre-
dispose them to strand when exposed to another phenomenon. These 
suggestions are consistent with the conclusions of numerous other 
studies that have demonstrated that combinations of dissimilar 
stressors commonly combine to kill an animal or dramatically reduce its 
fitness, even though one exposure without the other does not produce 
the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; 
Fair and Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a; 
2005b, Romero, 2004; Sih et al., 2004).
    Use of military tactical sonar has been implicated in a majority of 
investigated stranding events. Most known stranding events have 
involved beaked whales, though a small number have involved deep-diving 
delphinids or sperm whales (e.g., Mazzariol et al., 2010; Southall et 
al., 2013). In general, long duration (~1 second) and high-intensity 
sounds (>235 dB SPL) have been implicated in stranding events 
(Hildebrand, 2004).

[[Page 71441]]

With regard to beaked whales, mid-frequency sound is typically 
implicated (when causation can be determined) (Hildebrand, 2004). 
Although seismic airguns create predominantly low-frequency energy, the 
signal does include a mid-frequency component. We have considered the 
potential for the proposed surveys to result in marine mammal stranding 
and have concluded that, based on the best available information, 
stranding is not expected to occur.
    Effects to Prey--Marine mammal prey varies by species, season, and 
location and, for some, is not well documented. Fish react to sounds 
which are especially strong and/or intermittent low-frequency sounds, 
and behavioral responses such as flight or avoidance are the most 
likely effects. However, the reaction of fish to airguns depends on the 
physiological state of the fish, past exposures, motivation (e.g., 
feeding, spawning, migration), and other environmental factors. Several 
studies have demonstrated that airgun sounds might affect the 
distribution and behavior of some fishes, potentially impacting 
foraging opportunities or increasing energetic costs (e.g., Fewtrell 
and McCauley, 2012; Pearson et al., 1992; Skalski et al., 1992; 
Santulli et al., 1999; Paxton et al., 2017), though the bulk of studies 
indicate no or slight reaction to noise (e.g., Miller and Cripps, 2013; 
Dalen and Knutsen, 1987; Pena et al., 2013; Chapman and Hawkins, 1969; 
Wardle et al., 2001; Sara et al., 2007; Jorgenson and Gyselman, 2009; 
Blaxter et al., 1981; Cott et al., 2012; Boeger et al., 2006), and 
that, most commonly, while there are likely to be impacts to fish as a 
result of noise from nearby airguns, such effects will be temporary. 
For example, investigators reported significant, short-term declines in 
commercial fishing catch rate of gadid fishes during and for up to five 
days after seismic survey operations, but the catch rate subsequently 
returned to normal (Engas et al., 1996; Engas and Lokkeborg, 2002). 
Other studies have reported similar findings (Hassel et al., 2004). 
Skalski et al. (1992) also found a reduction in catch rates--for 
rockfish (Sebastes spp.) in response to controlled airgun exposure--but 
suggested that the mechanism underlying the decline was not dispersal 
but rather decreased responsiveness to baited hooks associated with an 
alarm behavioral response. A companion study showed that alarm and 
startle responses were not sustained following the removal of the sound 
source (Pearson et al., 1992). Therefore, Skalski et al. (1992) 
suggested that the effects on fish abundance may be transitory, 
primarily occurring during the sound exposure itself. In some cases, 
effects on catch rates are variable within a study, which may be more 
broadly representative of temporary displacement of fish in response to 
airgun noise (i.e., catch rates may increase in some locations and 
decrease in others) than any long-term damage to the fish themselves 
(Streever et al., 2016).
    SPLs of sufficient strength have been known to cause injury to fish 
and fish mortality and, in some studies, fish auditory systems have 
been damaged by airgun noise (McCauley et al., 2003; Popper et al., 
2005; Song et al., 2008). However, in most fish species, hair cells in 
the ear continuously regenerate and loss of auditory function likely is 
restored when damaged cells are replaced with new cells. Halvorsen et 
al. (2012b. (2012) showed that a TTS of 4-6 dB was recoverable within 
24 hours for one species. Impacts would be most severe when the 
individual fish is close to the source and when the duration of 
exposure is long--both of which are conditions unlikely to occur for 
this survey that is necessarily transient in any given location and 
likely result in brief, infrequent noise exposure to prey species in 
any given area. For this survey, the sound source is constantly moving, 
and most fish would likely avoid the sound source prior to receiving 
sound of sufficient intensity to cause physiological or anatomical 
damage. In addition, ramp-up may allow certain fish species the 
opportunity to move further away from the sound source.
    A recent comprehensive review (Carroll et al., 2017) found that 
results are mixed as to the effects of airgun noise on the prey of 
marine mammals. While some studies suggest a change in prey 
distribution and/or a reduction in prey abundance following the use of 
seismic airguns, others suggest no effects or even positive effects in 
prey abundance. As one specific example, Paxton et al. (2017), which 
describes findings related to the effects of a 2014 seismic survey on a 
reef off of North Carolina, showed a 78 percent decrease in observed 
nighttime abundance for certain species. It is important to note that 
the evening hours during which the decline in fish habitat use was 
recorded (via video recording) occurred on the same day that the 
seismic survey passed, and no subsequent data is presented to support 
an inference that the response was long-lasting. Additionally, given 
that the finding is based on video images, the lack of recorded fish 
presence does not support a conclusion that the fish actually moved 
away from the site or suffered any serious impairment. In summary, this 
particular study corroborates prior studies indicating that a startle 
response or short-term displacement should be expected.
    Available data suggest that cephalopods are capable of sensing the 
particle motion of sounds and detect low frequencies up to 1-1.5 kHz, 
depending on the species, and so are likely to detect airgun noise 
(Kaifu et al., 2008; Hu et al., 2009; Mooney et al., 2010; Samson et 
al., 2014). Auditory injuries (lesions occurring on the statocyst 
sensory hair cells) have been reported upon controlled exposure to low-
frequency sounds, suggesting that cephalopods are particularly 
sensitive to low-frequency sound (Andre et al., 2011; Sole et al., 
2013). Behavioral responses, such as inking and jetting, have also been 
reported upon exposure to low-frequency sound (McCauley et al., 2000b; 
Samson et al., 2014). Similar to fish, however, the transient nature of 
the survey leads to an expectation that effects will be largely limited 
to behavioral reactions and would occur as a result of brief, 
infrequent exposures.
    With regard to potential impacts on zooplankton, McCauley et al. 
(2017) found that exposure to airgun noise resulted in significant 
depletion for more than half the taxa present and that there were 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

[[Page 71442]]

population dynamics (Richardson et al., 2017). Richardson et al. (2017) 
found that for copepods with a short life cycle in a high-energy 
environment, a full-scale airgun survey would impact copepod abundance 
up to three days following the end of the survey, suggesting that 
effects such as those found by McCauley et al. (2017) would not be 
expected to be detectable downstream of the survey areas, either 
spatially or temporally.
    Notably, a 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 one week after the airgun 
blast was significantly higher in the copepods placed 10 m from the 
airgun but was not significantly different from the controls at a 
distance of 20 m from the airgun. The increase in mortality, relative 
to controls, did not exceed 30 percent at any distance from the airgun. 
Moreover, the authors caution that even this higher mortality in the 
immediate vicinity of the airguns may be more pronounced than what 
would be observed in free-swimming animals due to increased flow speed 
of fluid inside bags containing the experimental animals. There were no 
sublethal effects on the escape performance or the sensory threshold 
needed to initiate an escape response at any of the distances from the 
airgun that were tested. Whereas McCauley et al. (2017) reported an SEL 
of 156 dB at a range of 509-658 m, with zooplankton mortality observed 
at that range, Fields et al. (2019) reported an SEL of 186 dB at a 
range of 25 m, with no reported mortality at that distance. Regardless, 
if we assume a worst-case likelihood of severe impacts to zooplankton 
within approximately 1 km of the acoustic source, the brief time to 
regeneration of the potentially affected zooplankton populations does 
not lead us to expect any meaningful follow-on effects to the prey base 
for marine mammals.
    A recent review article concluded that, while laboratory results 
provide scientific evidence for high-intensity and low-frequency sound-
induced physical trauma and other negative effects on some fish and 
invertebrates, the sound exposure scenarios in some cases are not 
realistic to those encountered by marine organisms during routine 
seismic operations (Carroll et al., 2017). The review finds that there 
has been no evidence of reduced catch or abundance following seismic 
activities for invertebrates, and that there is conflicting evidence 
for fish with catch observed to increase, decrease, or remain the same. 
Further, where there is evidence for decreased catch rates in response 
to airgun noise, these findings provide no information about the 
underlying biological cause of catch rate reduction (Carroll et al., 
2017).
    In summary, impacts of the specified activity on marine mammal prey 
species will likely be limited to behavioral responses, the majority of 
prey species will be capable of moving out of the area during the 
survey, a rapid return to normal recruitment, distribution, and 
behavior for prey species is anticipated, and, overall, impacts to prey 
species will be minor and temporary. Prey species exposed to sound 
might move away from the sound source, experience TTS, experience 
masking of biologically relevant sounds, or show no obvious direct 
effects. Mortality from decompression injuries is possible in close 
proximity to a sound, but only limited data on mortality in response to 
airgun noise exposure are available (Hawkins et al., 2014). The most 
likely impacts for most prey species in the survey area would be 
temporary avoidance of the area. The proposed survey would move through 
an area relatively quickly, limiting exposure to multiple impulsive 
sounds. In all cases, sound levels would return to ambient once the 
survey moves out of the area or ends and the noise source is shut down 
and, when exposure to sound ends, behavioral and/or physiological 
responses are expected to end relatively quickly (McCauley et al., 
2000b). The duration of fish avoidance of a given area after survey 
effort stops is unknown, but a rapid return to normal recruitment, 
distribution, and behavior is anticipated. While the potential for 
disruption of spawning aggregations or schools of important prey 
species can be meaningful on a local scale, the mobile and temporary 
nature of this survey and the likelihood of temporary avoidance 
behavior suggest that impacts would be minor.
    Acoustic Habitat--Acoustic habitat is the soundscape--which 
encompasses all of the sound present in a particular location and time, 
as a whole--when considered from the perspective of the animals 
experiencing it. Animals produce sound for, or listen for sounds 
produced by, conspecifics (communication during feeding, mating, and 
other social activities), other animals (finding prey or avoiding 
predators), and the physical environment (finding suitable habitats, 
navigating). Together, sounds made by animals and the geophysical 
environment (e.g., produced by earthquakes, lightning, wind, rain, 
waves) make up the natural contributions to the total acoustics of a 
place. These acoustic conditions, termed acoustic habitat, are one 
attribute of an animal's total habitat.
    Soundscapes are also defined by, and acoustic habitat influenced 
by, the total contribution of anthropogenic sound. This may include 
incidental emissions from sources such as vessel traffic, or may be 
intentionally introduced to the marine environment for data acquisition 
purposes (as in the use of airgun arrays). Anthropogenic noise varies 
widely in its frequency content, duration, and loudness and these 
characteristics greatly influence the potential habitat-mediated 
effects to marine mammals (please see also the previous discussion on 
masking under Acoustic Effects), which may range from local effects for 
brief periods of time to chronic effects over large areas and for long 
durations. Depending on the extent of effects to habitat, animals may 
alter their communications signals (thereby potentially expending 
additional energy) or miss acoustic cues (either conspecific or 
adventitious). For more detail on these concepts see, e.g., Barber et 
al., 2010; Pijanowski et al., 2011; Francis and Barber, 2013; Lillis et 
al., 2014.
    Problems arising from a failure to detect cues are more likely to 
occur when noise stimuli are chronic and overlap with biologically 
relevant cues used for communication, orientation, and predator/prey 
detection (Francis and Barber, 2013). Although the signals emitted by 
seismic airgun arrays are generally low frequency, they would also 
likely be of short duration and transient in any given area due to the 
nature of these surveys. As described previously, exploratory surveys 
such as this one 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.
    In summary, activities associated with the proposed action are not 
likely to have a permanent, adverse effect on any fish habitat or 
populations of fish species or on the quality of acoustic habitat. 
Thus, any impacts to marine mammal habitat are not expected to cause 
significant or long-term consequences for individual marine mammals or 
their populations.

[[Page 71443]]

Estimated Take

    This section provides an estimate of the number of incidental takes 
proposed for authorization through this IHA, which will inform both 
NMFS' consideration of ``small numbers'' and the negligible impact 
determination.
    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).
    Authorized takes would be by Level B harassment only, as use of the 
acoustic sources (i.e., seismic airgun) has the potential to result in 
disruption of behavioral patterns for individual marine mammals. Based 
on the nature of the activity and the anticipated effectiveness of the 
mitigation measures (i.e., marine mammal exclusion zones) discussed in 
detail below in Proposed Mitigation section, Level A harassment is 
neither anticipated nor proposed to be authorized. As described 
previously, no mortality is anticipated or proposed to be authorized 
for this activity. Below we describe how the take is estimated.
    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) 
and the number of days of activities. We note that while these basic 
factors can contribute to a basic calculation to provide an initial 
prediction of 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 
estimate.

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 for non-explosive sources--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 (e.g., frequency, predictability, 
duty cycle), the environment (e.g., bathymetry), and the receiving 
animals (hearing, motivation, experience, demography, behavioral 
context) and can be difficult to predict (Southall et al., 2007, 
Ellison et al., 2012). Based on what the available science indicates 
and the practical need to use a threshold based on a factor that is 
both predictable and measurable for most activities, NMFS uses a 
generalized acoustic threshold based on received level to estimate the 
onset of behavioral harassment. NMFS predicts that marine mammals are 
likely to be behaviorally harassed in a manner we consider Level B 
harassment when exposed to underwater anthropogenic noise above 
received levels of 120 dB re 1 [mu]Pa (rms) for continuous (e.g., 
vibratory pile-driving, drilling) and above 160 dB re 1 [mu]Pa (rms) 
for non-explosive impulsive (e.g., seismic airguns) or intermittent 
(e.g., scientific sonar) sources.
    Scripps' proposed activity includes the use of impulsive seismic 
sources, and therefore the 160 dB re 1 [mu]Pa (rms) is applicable.
    Level A harassment for non-explosive sources--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). Scripps' proposed activity includes the 
use of impulsive seismic sources.
    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)
----------------------------------------------------------------------------------------------------------------
                                                     PTS onset acoustic thresholds * (received level)
             Hearing group              ------------------------------------------------------------------------
                                                  Impulsive                         Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans...........  Cell 1: Lpk,flat: 219 dB;   Cell 2: LE,LF,24h: 199 dB.
                                          LE,LF,24h: 183 dB.
Mid-Frequency (MF) Cetaceans...........  Cell 3: Lpk,flat: 230 dB;   Cell 4: LE,MF,24h: 198 dB.
                                          LE,MF,24h: 185 dB.
High-Frequency (HF) Cetaceans..........  Cell 5: Lpk,flat: 202 dB;   Cell 6: LE,HF,24h: 173 dB.
                                          LE,HF,24h: 155 dB.
Phocid Pinnipeds (PW)(Underwater)......  Cell 7: Lpk,flat: 218 dB;   Cell 8: LE,PW,24h: 201 dB.
                                          LE,PW,24h: 185 dB.
Otariid Pinnipeds (OW)(Underwater).....  Cell 9: Lpk,flat: 232 dB;   Cell 10: LE,OW,24h: 219 dB.
                                          LE,OW,24h: 203 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for
  calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level
  thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure (Lpk) has a reference value of 1 [micro]Pa, and cumulative sound exposure level (LE)
  has a reference value of 1[micro]Pa\2\s. In this Table, thresholds are abbreviated to reflect American
  National Standards Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as
  incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript
  ``flat'' is being included to indicate peak sound pressure should be flat weighted or unweighted within the
  generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates
  the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds)
  and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could
  be exceeded in a multitude of ways (i.e., varying exposure levels and durations, duty cycle). When possible,
  it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be
  exceeded.


[[Page 71444]]

Ensonified Area

    Here, we describe operational and environmental parameters of the 
activity that will feed into identifying the area ensonified above the 
acoustic thresholds, which include source levels and transmission loss 
coefficient.
    The proposed survey would entail the use of a 2-airgun array with a 
total discharge of 90 in\3\ at a tow depth of 2-4 m. Lamont-Doherty 
Earth Observatory (L-DEO) model results are used to determine the 160 
dBrms radius for the 2-airgun array in deep water (>1,000 m) 
down to a maximum water depth of 2,000 m. Received sound levels were 
predicted by L-DEO's model (Diebold et al., 2010) as a function of 
distance from the airguns, for the two 45 in\3\ airguns. 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 homogenous ocean layer, unbounded by a seafloor). 
In addition, propagation measurements of pulses from a 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 in 2007-2008 (Tolstoy et al., 2009; 
Diebold et al., 2010).
    For deep and intermediate water cases, the field measurements 
cannot be used readily to derive the Level A and Level B harassment 
isopleths, as at those sites the calibration hydrophone was located at 
a roughly constant depth of 350-550 m, which may not intersect all the 
SPL isopleths at their widest point from the sea surface down to the 
maximum relevant water depth (~2,000 m) for marine mammals. At short 
ranges, where the direct arrivals dominate and the effects of seafloor 
interactions are minimal, the data at the deep sites are suitable for 
comparison with modeled levels at the depth of the calibration 
hydrophone. At longer ranges, the comparison with the model--
constructed from the maximum SPL through the entire water column at 
varying distances from the airgun array--is the most relevant.
    In deep and intermediate water depths, comparisons at short ranges 
between sound levels for direct arrivals recorded by the calibration 
hydrophone and model results for the same array tow depth are in good 
agreement (see Figures 12 and 14 in Appendix H of NSF-USGS 2011). 
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. 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 surveys would acquire data with two 45-in\3\ guns at a 
tow depth of 2-4 m. For deep water (>1,000 m), we use the deep-water 
radii obtained from L-DEO model results down to a maximum water depth 
of 2,000 m for the airgun array with 2-m airgun separation. The radii 
for intermediate water depths (100-1,000 m) are derived from the deep-
water ones by applying a correction factor (multiplication) of 1.5, 
such that observed levels at very near offsets fall below the corrected 
mitigation curve (see Figure 16 in Appendix H of NSF-USGS 2011). No 
survey effort is planned to occur in shallow water (<100 m).
    L-DEO's modeling methodology is described in greater detail in 
SIO's IHA application. The estimated distances to the Level B 
harassment isopleths for the proposed airgun configuration in each 
water depth category are shown in Table 4.

Table 4--Predicted Radial Distances From R/V Justo Sierra Seismic Source
       to Isopleths Corresponding to Level B Harassment Threshold
------------------------------------------------------------------------
                                                             Predicted
                                                           distances (m)
          Airgun configuration              Water depth    to 160 dB rms
                                                (m)        SPL received
                                                            sound level
------------------------------------------------------------------------
Two 45 in\3\ guns, 2-m separation, 4-m            >1,000         \a\ 539
 tow depth..............................
                                               100-1,000         \b\ 809
------------------------------------------------------------------------
\a\ Distance based on L-DEO model results.
\b\ Distance based on L-DEO model results with a 1.5 x correction factor
  between deep and intermediate water depths.

    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. The updated acoustic thresholds for onset of 
hearing impacts from impulsive sounds (e.g., airguns) contained in the 
Technical Guidance were presented as dual metric acoustic thresholds 
using both SELcum and peak sound pressure metrics (NMFS 
2016a). As dual metrics, NMFS considers onset of PTS (Level A 
harassment) to have occurred when either one of the two metrics is 
exceeded (i.e., metric resulting in the largest isopleth). The 
SELcum metric considers both level and duration of exposure, 
as well as auditory weighting functions by marine mammal hearing group. 
In recognition of the fact that the requirement to calculate Level A 
harassment ensonified areas could be more technically challenging to 
predict due to the duration component and the use of weighting 
functions in the new SELcum thresholds, NMFS developed an 
optional User Spreadsheet that includes tools to help predict a simple 
isopleth that can be used in conjunction with marine mammal density or 
occurrence to facilitate the estimation of take numbers.
    The SELcum for the 2-GI airgun array is derived from 
calculating the modified farfield signature. The farfield signature is 
often used as a theoretical representation of the source level. To 
compute the farfield signature, the source level is estimated at a 
large distance 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

[[Page 71445]]

signature is never physically achieved at the source when the source is 
an array of multiple airguns separated in space (Tolstoy et al., 2009). 
Near the source (at short ranges, distances <1 km), the pulses of sound 
pressure from each individual airgun in the source array do not stack 
constructively as they do for the theoretical farfield signature. The 
pulses from the different airguns spread out in time such that the 
source levels observed or modeled are the result of the summation of 
pulses from a few airguns, not the full array (Tolstoy et al., 2009). 
At larger distances, away from the source array center, sound pressure 
of all the airguns in the array stack coherently, but not within one 
time sample, resulting in smaller source levels (a few dB) than the 
source level derived from the farfield signature. Because the farfield 
signature does not take into account the interactions of the two 
airguns that occur near the source center and is calculated as a point 
source (single airgun), the modified farfield signature is a more 
appropriate measure of the sound source level for large arrays. For 
this smaller array, the modified farfield changes will be 
correspondingly smaller as well, but we use this method for consistency 
across all array sizes.
    Scripps used the same acoustic modeling as for Level B harassment 
with a small grid step in both the inline and depth directions to 
estimate the SELcum and peak SPL. The propagation modeling 
takes into account all airgun interactions at short distances from the 
source including interactions between subarrays using the NUCLEUS 
software to estimate the notional signature and the MATLAB software to 
calculate the pressure signal at each mesh point of a grid. For a more 
complete explanation of this modeling approach, please see ``Appendix 
A: Determination of Mitigation Zones'' in Scripps' IHA application.
    In order to more realistically incorporate the Technical Guidance's 
weighting functions over the seismic array's full acoustic band, 
unweighted spectrum data for the airgun array (modeled in 1 Hz bands) 
was used to make adjustments (dB) to the unweighted spectrum levels, by 
frequency, according to the weighting functions for each relevant 
marine mammal hearing group. These adjusted/weighted spectrum levels 
were then converted to pressures ([mu]Pa) in order to integrate them 
over the entire broadband spectrum, resulting in broadband weighted 
source levels by hearing group that could be directly incorporated 
within the User Spreadsheet (i.e., to override the Spreadsheet's more 
simple weighting factor adjustment). Using the User Spreadsheet's 
``safe distance'' methodology for mobile sources (described by Sivle et 
al., 2014) with the hearing group-specific weighted source levels, and 
inputs assuming spherical spreading propagation and source velocities 
and shot intervals provided in Scripps' IHA application, potential 
radial distances to auditory injury zones were calculated for PTS 
thresholds. Calculated Level A harassment zones for all cetacean 
hearing groups are presented in Table 5 below (no pinnipeds are 
expected to occur in the survey area).

   Table 5--Modeled Radial Distances (m) to Isopleths Corresponding to
                      Level A Harassment Thresholds
------------------------------------------------------------------------
                                                              Level A
                Functional hearing group                    harassment
                                                             zone (m)
------------------------------------------------------------------------
Low-frequency cetaceans \1\.............................             9.9
Mid-frequency cetaceans.................................             1.0
High-frequency cetaceans................................            34.6
------------------------------------------------------------------------
\1\ Low-frequency cetaceans are not expected to be encountered or taken
  by Level A or Level B harassment during the proposed survey.

    Note that because of some of the assumptions included in the 
methods used, isopleths produced may be overestimates to some degree, 
which will ultimately result in some degree of overestimate of the 
potential for take by Level A harassment. 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. For mobile sources, such as the 
proposed seismic survey, the User Spreadsheet predicts the closest 
distance at which a stationary animal would not incur PTS if the sound 
source traveled by the animal in a straight line at a constant speed.
    Auditory injury is unlikely to occur for any functional hearing 
group given the very small modeled zones of injury (all estimated zones 
less than 35 meters (m)), and we therefore expect the potential for 
Level A harassment 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. Additionally, the method of 
estimating take as described below (see Take Calculation and 
Estimation) yielded only two species/guilds with calculated takes by 
Level A harassment, and the highest calculated take of those two groups 
was only two takes by Level A harassment (Table 9). We do not believe 
that Level A harassment is a likely outcome for any hearing group and 
are not proposing to authorize Level A harassment for any species.

Marine Mammal Occurrence

    In this section we provide the information about the presence, 
density, or group dynamics of marine mammals that will inform the take 
calculations.
    For the proposed survey area in the southeast Gulf of Mexico, 
Scripps determined that the best source of density data for marine 
mammal species that might be encountered in the project area was 
habitat-based density modeling conducted by Roberts et al. (2016). The 
Roberts et al. (2016) data provide abundance estimates for species or 
species guilds within 10 km x 10 km grid cells (100 square kilometer 
(km\2\)) within the U.S. EEZ in the Gulf of Mexico and Atlantic Ocean 
on a monthly or annual basis, depending on the species and location. In 
the Gulf of Mexico, marine mammals do not migrate seasonally, so a 
single estimate for each grid cell is provided and represents the 
predicted abundance of that species in that 100 km\2\ location at any 
time of year.
    As the planned survey lines are outside of the U.S. EEZ, they do 
not directly overlap the available spatial density data. However, some 
of the survey lines occur near the U.S. EEZ, and the distribution and 
abundance of species in U.S. EEZ waters are assumed representative of 
those in the nearby survey area. To select a representative sample of 
grid cells for the calculation of densities in three different water 
depth categories (>100 m, 100-1,000 m, and >1,000 m), a 200-km 
perimeter around the survey lines was created in GIS. The areas within 
this perimeter within the three depth categories was then used to 
select grid cells containing the estimates for each species in the 
Roberts et al. (2016) data (i.e., <100 m, n = 157 grid cells; 100-
1,000, n = 169 grid cells; >1,000 m, n = 410 grid cells). The average 
abundance for each species in each water depth category was calculated 
as the mean value of the grid cells within each category and then 
converted to density (individuals/1 km\2\) by dividing by 100 km\2\. 
Estimated densities for marine mammal species that could occur in the 
project area are shown in Table 6.

[[Page 71446]]



      Table 6--Marine Mammal Densities in the Proposed Survey Area
------------------------------------------------------------------------
                                            Estimated density (#/km\2\)
                                         -------------------------------
                 Species                   Intermediate
                                            water 100-      Deep water
                                              1,000 m        >1,000 m
------------------------------------------------------------------------
Sperm whale.............................         0.00384         0.00579
Atlantic spotted dolphin................         0.07022         0.00001
Beaked whale guild \a\..................         0.00498         0.00882
Common bottlenose dolphin...............         0.18043         0.00566
Clymene dolphin.........................         0.00325         0.00403
False killer whale......................         0.00744         0.00748
Frasers dolphin.........................         0.00386         0.00389
Killer whale............................         0.00007         0.00082
Melon-headed whale......................         0.00624         0.01186
Pantropical spotted dolphin.............         0.14764         0.31353
Short-finned pilot whales...............         0.00636         0.00128
Pygmy killer whale......................         0.00201         0.00648
Risso's dolphin.........................         0.02315         0.00748
Rough-toothed dolphin...................         0.00890         0.00768
Spinner dolphin.........................         0.15723         0.00412
Striped dolphin.........................         0.00212         0.01268
Kogia spp. \b\..........................         0.01052         0.00490
------------------------------------------------------------------------
\a\ Includes Cuvier's beaked whale, Blainville's beaked whale, and
  Gervais' beaked whale.
\b\ Pygmy sperm whales and dwarf sperm whales.

Take Calculation and Estimation

    Here we describe how the information provided above is brought 
together to produce a quantitative take estimate.
    The area expected to be ensonified was determined by entering the 
planned survey lines into ArcGIS and then using GIS to identify the 
relevant ensonified areas by ``drawing'' the 160-dB threshold buffer 
around each seismic line according to the depth category in which the 
lines occurred. The total ensonified area within each depth category 
was then divided by the total number of survey days to provide the 
proportional daily ensonified area within each depth category. The 
total ensonified area in each depth class was multiplied by 1.25 to add 
an additional 25 percent contingency to allow for additional airgun 
operations such as testing of the source or re-surveying lines with 
poor data quality. Due to uncertainties with respect to permitting for 
surveys in Cuban waters, ensonified areas were calculated separately 
for transect lines in Mexican and Cuban EEZs, for which 4.2 and 5.5 
survey days were estimated, respectively (Table 7). If Scripps is 
unable to operate within the Cuban EEZ, they will conduct the entire 
survey within the Mexican EEZ, with the same estimated daily 
proportions of survey activity in each depth strata occurring over a 
total of 9.7 survey days. This scenario yields a total ensonified area 
of 3,595.6 km\2\, with 1,848.6 km\2\ in intermediate waters (100-1,000 
m) and 1,747.0 km\2\ in deep waters (>1,000 m).

      Table 7--Areas (km\2\) in Mexican and Cuban EEZs To Be Ensonified Above Level B Harassment Threshold
----------------------------------------------------------------------------------------------------------------
                                                    Ensonified                                      Total area
                                     Relevant         area in       Ensonified         Total         with 25%
      Water depth category         isopleth (m)     Mexican EEZ    area in Cuban    ensonified       increase
                                                      (km\2\)       EEZ (km\2\)    area (km\2\)       (km\2\)
----------------------------------------------------------------------------------------------------------------
Intermediate (100-1,000 m)......             809          640.35               0          640.35          800.44
Deep (>1,000)...................             539          605.14        1,298.09        1,903.23        2,379.04
                                 -------------------------------------------------------------------------------
    Total.......................  ..............        1,245.49        1,298.09        2,543.58        3,179.48
----------------------------------------------------------------------------------------------------------------

    To estimate the total number of possible exposures, the total 
ensonified area within each depth category is multiplied by the 
densities in each depth category. Scripps does not expect to know 
whether surveying within Cuban waters will be permitted until 
immediately before the research cruise, therefore NMFS is proposing to 
authorize the highest calculated take number for each species across 
the two survey scenarios (Table 8).

                           Table 8--Calculated and Proposed Takes by Level B Harassment, and Percentage of Population Exposed
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                       Mexico and Cuba    Mexico and Cuba   Mexico only  Mexico only
               Species                 lines calculated   lines calculated   calculated   calculated    Proposed     Proposed    Population   Percent of
                                           Level B            Level A         Level B      Level A      Level B      Level A      size \a\    population
--------------------------------------------------------------------------------------------------------------------------------------------------------
Sperm whale.........................                 17                  0           17            0           17            0        2,207         0.78
Atlantic spotted dolphin............                 56                  0          130            0          130            0       74,785         0.17
Beaked whale guild \c\..............                 25                  0           25            0           25            0        3,768         0.66
Common bottlenose dolphin...........                158                  0          343            0          343            0      176,108         0.20
Clymene dolphin.....................             \b\ 90                  0       \b\ 90            0       \b\ 90            0       11,895         0.76
False killer whale..................             \b\ 28                  0       \b\ 28            0       \b\ 28            0        3,204         0.87
Frasers dolphin.....................             \b\ 65                  0       \b\ 65            0       \b\ 65            0        1,665         3.90

[[Page 71447]]

 
Killer whale........................              \b\ 7                  0        \b\ 7            0        \b\ 7            0          267         2.62
Melon-headed whale..................            \b\ 100                  0      \b\ 100            0      \b\ 100            0        7,003         1.43
Pantropical spotted dolphin.........                862                  2          820            1          864            0      102,361         0.84
Pygmy killer whale..................             \b\ 19                  0       \b\ 19            0       \b\ 19            0        2,126         0.89
Risso's dolphin.....................                 36                  0           56            0           56            0        3,764         1.48
Rough-toothed dolphin...............             \b\ 56                  0       \b\ 56            0       \b\ 56            0        4,853         1.15
Short-finned pilot whales...........             \b\ 25                  0       \b\ 25            0       \b\ 25            0        1,981         1.26
Spinner dolphin.....................                136                  0          298            0          298            0       25,114         1.19
Striped dolphin.....................             \b\ 46                  0       \b\ 46            0       \b\ 46            0        5,229         0.88
Kogia spp...........................                 19                  1           27            1           28            0        4,373         0.64
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Best abundance estimate. For most taxa, the best abundance estimate for purposes of comparison with take estimates is considered here to be the
  model-predicted abundance (Roberts et al., 2016). For those taxa where a density surface model predicting abundance by month was produced, the maximum
  mean seasonal abundance was used. For those taxa where abundance is not predicted by month, only mean annual abundance is available. For the killer
  whale, the larger estimated SAR abundance estimate is used.
\b\ Calculated and proposed take increased to mean group size as presented by Maze-Foley and Mullin (2006).
\c\ Cuvier's, Blainville's, and Gervais' beaked whales.

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, we 
carefully consider two primary factors:
    (1) The manner in which, and the degree to which, the successful 
implementation of the measure(s) is expected to reduce impacts to 
marine mammals, marine mammal species or stocks, and their habitat. 
This considers the nature of the potential adverse impact being 
mitigated (likelihood, scope, range). It further considers the 
likelihood that the measure will be effective if implemented 
(probability of accomplishing the mitigating result if implemented as 
planned), the likelihood of effective implementation (probability 
implemented as planned), and;
    (2) The practicability of the measures for applicant 
implementation, which may consider such things as cost, impact on 
operations, and, in the case of a military readiness activity, 
personnel safety, practicality of implementation, and impact on the 
effectiveness of the military readiness activity.
    Scripps indicated that it reviewed mitigation measures employed 
during seismic research surveys authorized by NMFS under previous 
incidental harassment authorizations, as well as recommended best 
practices in Richardson et al. (1995), Pierson et al. (1998), Weir and 
Dolman (2007), Nowacek et al. (2013), Wright (2014), and Wright and 
Cosentino (2015), and has incorporated a suite of proposed mitigation 
measures into their project description based on the above sources.
    To reduce the potential for disturbance from acoustic stimuli 
associated with the activities, Scripps has proposed to implement 
mitigation measures for marine mammals. Mitigation measures that would 
be adopted during the proposed surveys include: (1) Vessel-based visual 
mitigation monitoring; (2) Establishment of a marine mammal exclusion 
zone (EZ) and buffer zone; (3) shutdown procedures; (4) ramp-up 
procedures; and (4) vessel strike avoidance measures.

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 visually for the presence of marine mammals. PSO 
observations would take place during all daytime airgun operations and 
nighttime start ups (if applicable) of the airguns. If airguns are 
operating throughout the night, observations would begin 30 minutes 
prior to sunrise. If airguns are operating after sunset, observations 
would continue until 30 minutes following sunset. Following a shutdown 
for any reason, observations would occur for at least 30 minutes prior 
to the planned start of airgun operations. Observations would also 
occur for 30 minutes after airgun operations cease for any reason. 
Observations would also be made during daytime periods when the R/V 
Justo Sierra is underway without seismic operations, such as during 
transits, to allow for comparison of sighting rates and behavior with 
and without airgun operations and between acquisition periods. Airgun 
operations would be suspended when marine mammals are observed within, 
or about to enter, the designated exclusion zone (EZ) (as described 
below).
    During seismic operations, two visual PSOs would be on duty and 
conduct visual observations at all times during daylight hours (i.e., 
from 30 minutes prior to sunrise through 30 minutes following sunset). 
PSO(s) would be on duty in shifts of duration no longer than 4 hours. 
Other vessel crew would also be instructed to assist in detecting 
marine mammals and in implementing mitigation requirements (if 
practical). Before the start of the seismic survey, the crew would be 
given additional instruction in detecting marine mammals and 
implementing mitigation requirements.
    The R/V Justo Sierra is a suitable platform from which PSOs would 
watch for marine mammals. Standard equipment for marine mammal 
observers would be 7 x 50 reticule binoculars and optical range 
finders. At night, night-vision equipment would be available. The 
observers would be in communication with ship's officers on

[[Page 71448]]

the bridge and scientists in the vessel's operations laboratory, so 
they can advise promptly of the need for vessel strike avoidance 
measures (see Vessel Strike Avoidance Measures below) or seismic source 
shutdown.
    The PSOs must have no tasks other than to conduct observational 
effort, record observational data, and communicate with and instruct 
relevant vessel crew with regard to the presence of marine mammals and 
mitigation requirements. PSO resumes shall be provided to NMFS for 
approval. At least one PSO must have a minimum of 90 days prior at-sea 
experience working as a PSO during a seismic survey. One 
``experienced'' visual PSO will be designated as the lead for the 
entire protected species observation team. The lead will serve as 
primary point of contact for the vessel operator.

Exclusion Zone (EZ) and Buffer Zone

    An EZ 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 EZ with a 100 m radius for the airgun 
array. The 100-m EZ would be based on radial distance from any element 
of the airgun array (rather than being based around the vessel itself). 
With certain exceptions (described below), if a marine mammal appears 
within, enters, or appears on a course to enter this zone, the acoustic 
source would be shut down (see Shutdown Procedures below).
    The 100-m radial distance of the standard EZ is precautionary in 
the sense that it would be expected to contain sound exceeding injury 
criteria for all marine mammal hearing groups (Table 5) while also 
providing a consistent, reasonably observable zone within which PSOs 
would typically be able to conduct effective observational effort. In 
the 2011 Programmatic Environmental Impact Statement for marine 
scientific research funded by the National Science Foundation or the 
U.S. Geological Survey (NSF-USGS 2011), Alternative B (the Preferred 
Alternative) conservatively applied a 100-m EZ for all low-energy 
acoustic sources in water depths >100 m, with low-energy acoustic 
sources defined as any towed acoustic source with a single or a pair of 
clustered airguns with individual volumes of <=250 in\3\. Thus the 100-
m EZ proposed for this survey is consistent with the PEIS.
    Our intent in prescribing a standard EZ distance is to (1) 
encompass zones within which auditory injury could occur on the basis 
of instantaneous exposure; (2) provide additional protection from the 
potential for more severe behavioral reactions (e.g., panic, 
antipredator response) for marine mammals at relatively close range to 
the acoustic source; (3) provide consistency for PSOs, who need to 
monitor and implement the EZ; and (4) define a distance within which 
detection probabilities are reasonably high for most species under 
typical conditions.
    PSOs will also establish and monitor a 100-m buffer zone beyond the 
EZ (for a total of 200 m). During use of the acoustic source, 
occurrence of marine mammals within the buffer zone (but outside the 
EZ) will be communicated to the operator to prepare for potential 
shutdown of the acoustic source. The buffer zone is discussed further 
under Ramp-Up Procedures below.
    An extended EZ of 500 m is proposed for all beaked whales and Kogia 
species as well as for aggregations of six or more large whales (i.e., 
sperm whale) or a large whale with a calf (calf defined as an animal 
less than two-thirds the body size of an adult observed to be in close 
association with an adult).

Ramp-Up Procedures

    Ramp-up of an acoustic source is intended to provide a gradual 
increase in sound levels following a shutdown, enabling animals to move 
away from the source if the signal is sufficiently aversive prior to 
its reaching full intensity. Ramp-up would be required after the array 
is shut down for any reason for longer than 15 minutes. Ramp-up would 
begin with the activation of one 45 in\3\ airgun, with the second 45 
in\3\ airgun activated after 5 minutes.
    Two PSOs would be required to monitor during ramp-up. During ramp 
up, the PSOs would monitor the EZ, and if marine mammals were observed 
within the EZ or buffer zone, a shutdown would be implemented as though 
the full array were operational. If airguns have been shut down due to 
PSO detection of a marine mammal within or approaching the EZ, ramp-up 
would not be initiated until all marine mammals have cleared the EZ, 
during the day or night. Criteria for clearing the EZ would be as 
described above.
    Thirty minutes of pre-start clearance observation are required 
prior to ramp-up for any shutdown of longer than 30 minutes (i.e., when 
the array is shut down during transit from one line to another). This 
30-minute pre-start clearance period may occur during any vessel 
activity (i.e., transit). If a marine mammal were observed within or 
approaching the 200-m buffer or 500-m extended EZ during this pre-start 
clearance period, ramp-up would not be initiated until all marine 
mammals cleared the relevant area. Criteria for clearing the EZ would 
be as described above. If the airgun array has been shut down for 
reasons other than mitigation (e.g., mechanical difficulty) for a 
period of less than 30 minutes, it may be activated again without ramp-
up if PSOs have maintained constant visual observation and no 
detections of any marine mammal have occurred within the EZ or buffer 
zone. Ramp-up would be planned to occur during periods of good 
visibility when possible. However, ramp-up would be allowed at night 
and during poor visibility if the 100 m EZ and 200 m buffer zone have 
been monitored by visual PSOs for 30 minutes prior to ramp-up.
    The operator would be required to 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. A designated PSO must be notified again immediately 
prior to initiating ramp-up procedures and the operator must receive 
confirmation from the PSO to proceed. The operator must provide 
information to PSOs documenting that appropriate procedures were 
followed. Following deactivation of the array for reasons other than 
mitigation, the operator would be required to communicate the near-term 
operational plan to the lead PSO with justification for any planned 
nighttime ramp-up.

Shutdown Procedures

    If a marine mammal is detected outside the EZ but is likely to 
enter the EZ, the airguns would be shut down before the animal is 
within the EZ. Likewise, if a marine mammal is already within the EZ 
when first detected, the airguns would be shut down immediately.
    Following a shutdown, airgun activity would not resume until the 
marine mammal has cleared the EZ. The animal would be considered to 
have cleared the EZ if the following conditions have been met:
     It is visually observed to have departed the EZ;
     it has not been seen within the EZ for 15 min in the case 
of small odontocetes; or
     it has not been seen within the EZ for 30 min in the case 
of large odontocetes, including sperm and beaked whales.
    This shutdown requirement would be in place for all marine mammals, 
with the exception of small delphinids under certain circumstances. As 
defined here, the small delphinid group is intended to

[[Page 71449]]

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 would apply solely to specific genera of small 
dolphins--Lagenodelphis, Stenella, Steno, and Tursiops.
    We include this small delphinid exception because shutdown 
requirements for small delphinids under all circumstances represent 
practicability concerns without likely commensurate benefits for the 
animals in question. Small delphinids 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 delphinids 
commonly approach vessels and/or towed arrays during active sound 
production for purposes of bow riding, with no apparent effect observed 
in those delphinids (e.g., Barkaszi et al., 2012, 2018). The potential 
for increased shutdowns resulting from such a measure would require the 
R/V Justo Sierra 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 delphinids, 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 source vessel.
    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 EZ).
    Shutdown of the acoustic source would also be required upon 
observation of a species for which authorization has not been granted 
(e.g., baleen whales), or a species for which authorization has been 
granted but the authorized number of takes are met, observed 
approaching or within the Level B harassment zones.

Vessel Strike Avoidance Measures

    Vessel strike avoidance measures are intended to minimize the 
potential for collisions with marine mammals. These requirements do not 
apply in any case where compliance would create an imminent and serious 
threat to a person or vessel or to the extent that a vessel is 
restricted in its ability to maneuver and, because of the restriction, 
cannot comply.
    The proposed measures include the following: Vessel operator and 
crew would maintain a vigilant watch for all marine mammals and slow 
down or stop the vessel or alter course to avoid striking any marine 
mammal. A visual observer aboard the vessel would monitor a vessel 
strike avoidance zone around the vessel according to the parameters 
stated below. Visual observers monitoring the vessel strike avoidance 
zone would be either third-party observers or crew members, but crew 
members responsible for these duties would be provided sufficient 
training to distinguish marine mammals from other phenomena. Vessel 
strike avoidance measures would be followed during surveys and while in 
transit.
    The vessel would maintain a minimum separation distance of 100 m 
from large whales (i.e., baleen whales and sperm whales). If a large 
whale is within 100 m of the vessel, the vessel would reduce speed and 
shift the engine to neutral, and would not engage the engines until the 
whale has moved outside of the vessel's path and the minimum separation 
distance has been established. If the vessel is stationary, the vessel 
would not engage engines until the whale(s) has moved out of the 
vessel's path and beyond 100 m. The vessel would maintain a minimum 
separation distance of 50 m from all other marine mammals, to the 
extent practicable. If an animal is encountered during transit, the 
vessel would attempt to remain parallel to the animal's course, 
avoiding excessive speed or abrupt changes in course. Vessel speeds 
would be reduced to 10 knots or less when mother/calf pairs, pods, or 
large assemblages of cetaceans are observed near the vessel.
    Based on our evaluation of the applicant's proposed measures, NMFS 
has preliminarily determined that the proposed mitigation measures 
provide the means 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 in the 
proposed action area. Effective reporting is critical both to 
compliance as well as ensuring that the most value is obtained from the 
required monitoring.
    Monitoring and reporting requirements prescribed by NMFS should 
contribute to improved understanding of one or more of the following:
     Occurrence of marine mammal species or stocks in the area 
in which take is anticipated (e.g., presence, abundance, distribution, 
density).
     Nature, scope, or context of likely marine mammal exposure 
to potential stressors/impacts (individual or cumulative, acute or 
chronic), through better understanding of: (1) Action or environment 
(e.g., source characterization, propagation, ambient noise); (2) 
affected species (e.g., life history, dive patterns); (3) co-occurrence 
of marine mammal species with the action; 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,

[[Page 71450]]

acoustic habitat, or other important physical components of marine 
mammal habitat).
     Mitigation and monitoring effectiveness.
    Scripps submitted a marine mammal monitoring and reporting plan in 
their IHA application. Monitoring that is designed specifically to 
facilitate mitigation measures, such as monitoring of the EZ to inform 
potential shutdowns of the airgun array, are described above and are 
not repeated here. Scripps' monitoring and reporting plan includes the 
following measures:

Vessel-Based Visual Monitoring

    As described above, PSO observations would take place during 
daytime airgun operations and nighttime start-ups (if applicable) of 
the airguns. During seismic operations, visual PSOs would be based 
aboard the R/V Justo Sierra. PSOs would be appointed by Scripps with 
NMFS approval. The PSOs must have successfully completed relevant 
training, including completion of all required coursework and passing a 
written and/or oral examination developed for the training program, and 
must have successfully attained a bachelor's degree from an accredited 
college or university with a major in one of the natural sciences and a 
minimum of 30 semester hours or equivalent in the biological sciences 
and at least one undergraduate course in math or statistics. The 
educational requirements may be waived if the PSO has acquired the 
relevant skills through alternate training, including (1) secondary 
education and/or experience comparable to PSO duties; (2) previous work 
experience conducting academic, commercial, or government-sponsored 
marine mammal surveys; or (3) previous work experience as a PSO; the 
PSO should demonstrate good standing and consistently good performance 
of PSO duties.
    During seismic operations in daylight hours (30 minutes before 
sunrise through 30 minutes after sunset), two PSOs would monitor for 
marine mammals around the seismic vessel. PSOs would be on duty in 
shifts of duration no longer than 4 hours. Other crew would also be 
instructed to assist in detecting marine mammals and in implementing 
mitigation requirements (if practical). During daytime, PSOs would scan 
the area around the vessel systematically with reticle binoculars 
(e.g., 7x50 Fujinon) and with the naked eye. At night, PSOs would be 
equipped with night-vision equipment.
    For data collection purposes, PSOs shall use standardized data 
collection forms, whether hard copy or electronic. PSOs shall record 
detailed information about any implementation of mitigation 
requirements, including the distance of animals to the acoustic source 
and description of specific actions that ensued, the behavior of the 
animal(s), any observed changes in behavior before and after 
implementation of mitigation, and if shutdown was implemented, the 
length of time before any subsequent ramp-up of the acoustic source. If 
required mitigation was not implemented, PSOs should record a 
description of the circumstances. At a minimum, the following 
information must be recorded:
     Vessel names (source vessel and other vessels associated 
with survey) and call signs;
     PSO names and affiliations;
     Dates of departures and returns to port with port name;
     Date and participants of PSO briefings;
     Dates and times (Greenwich Mean Time) of survey effort and 
times corresponding with PSO effort;
     Vessel location (latitude/longitude) when survey effort 
began and ended and vessel location at beginning and end of visual PSO 
duty shifts;
     Vessel heading and speed at beginning and end of visual 
PSO duty shifts and upon any line change;
     Environmental conditions while on visual survey (at 
beginning and end of PSO shift and whenever conditions changed 
significantly), including BSS and any other relevant weather conditions 
including cloud cover, fog, sun glare, and overall visibility to the 
horizon;
     Factors that may have contributed to impaired observations 
during each PSO shift change or as needed as environmental conditions 
changed (e.g., vessel traffic, equipment malfunctions); and
     Survey activity information, such as acoustic source power 
output while in operation, number and volume of airguns operating in 
the array, tow depth of the array, and any other notes of significance 
(i.e., pre-clearance, ramp-up, shutdown, testing, shooting, ramp-up 
completion, end of operations, streamers, etc.).
    The following information should be recorded upon visual 
observation of any protected species:
     Watch status (sighting made by PSO on/off effort, 
opportunistic, crew, alternate vessel/platform);
     PSO who sighted the animal;
     Time of sighting;
     Vessel location at time of sighting;
     Water depth;
     Direction of vessel's travel (compass direction);
     Direction of animal's travel relative to the vessel;
     Pace of the animal;
     Estimated distance to the animal and its heading relative 
to vessel at initial sighting;
     Identification of the animal (e.g., genus/species, lowest 
possible taxonomic level, or unidentified) and the composition of the 
group if there is a mix of species;
     Estimated number of animals (high/low/best);
     Estimated number of animals by cohort (adults, yearlings, 
juveniles, calves, group composition, etc.);
     Description (as many distinguishing features as possible 
of each individual seen, including length, shape, color, pattern, scars 
or markings, shape and size of dorsal fin, shape of head, and blow 
characteristics);
     Detailed behavior observations (e.g., number of blows/
breaths, number of surfaces, breaching, spyhopping, diving, feeding, 
traveling; as explicit and detailed as possible; note any observed 
changes in behavior);
     Animal's closest point of approach (CPA) and/or closest 
distance from any element of the acoustic source;
     Platform activity at time of sighting (e.g., deploying, 
recovering, testing, shooting, data acquisition, other); and
     Description of any actions implemented in response to the 
sighting (e.g., delays, shutdown, ramp-up) and time and location of the 
action.

Reporting

    A report would be submitted to NMFS within 90 days after the end of 
the cruise. The report would describe the operations that were 
conducted and sightings of marine mammals near the operations. The 
report would provide full documentation of methods, results, and 
interpretation pertaining to all monitoring. The 90-day report would 
summarize the dates and locations of seismic operations, and all marine 
mammal sightings (dates, times, locations, activities, associated 
seismic survey activities).
    The draft report shall also include geo-referenced time-stamped 
vessel tracklines for all time periods during which airguns were 
operating. Tracklines should include points recording any change in 
airgun status (e.g., when the airguns began operating, when they were 
turned off, or when they changed from full array to single gun or vice 
versa). GIS files shall be provided in ESRI shapefile format and 
include the UTC date and time, latitude in decimal degrees, and 
longitude in decimal degrees. All coordinates shall be referenced to 
the WGS84 geographic

[[Page 71451]]

coordinate system. In addition to the report, all raw observational 
data shall be made available to NMFS. The report must summarize the 
data collected as described above and in the IHA. A final report must 
be submitted within 30 days following resolution of any comments on the 
draft report.

Reporting Injured or Dead Marine Mammals

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

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 responses (e.g., intensity, duration), the context 
of any responses (e.g., critical reproductive time or location, 
migration), 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's 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 environmental 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, our analysis applies to all species listed in 
Table 1, given that NMFS expects the anticipated effects of the planned 
geophysical survey to be similar in nature. Where there are meaningful 
differences between species or stocks, or groups of species, in 
anticipated individual responses to activities, impact of expected take 
on the population due to differences in population status, or impacts 
on habitat, NMFS has identified species-specific factors to inform the 
analysis.
    NMFS does not anticipate that injury, serious injury or mortality 
would occur as a result of Scripps' planned survey, even in the absence 
of mitigation, and none would be authorized. Similarly, non-auditory 
physical effects, stranding, and vessel strike are not expected to 
occur. Although a few incidents of Level A harassment were predicted 
through the quantitative exposure estimation process (see Estimated 
Take), NMFS has determined that this is not a realistic result due to 
the small estimated Level A harassment zones for the species (no 
greater than approximately 50 m) and the proposed mitigation 
requirements, and no Level A harassment is proposed for authorization. 
These estimated zones are larger than what would realistically occur, 
as discussed in the Estimated Take section.
    We expect that takes would be in the form of short-term Level B 
behavioral harassment in the form of temporary avoidance of the area or 
decreased foraging (if such activity were occurring), reactions that 
are considered to be of low severity and with no lasting biological 
consequences (e.g., Southall et al., 2007, Ellison et al., 2012).
    Marine mammal habitat may be impacted by elevated sound levels, but 
these impacts would be temporary. Prey species are mobile and are 
broadly distributed throughout the project 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 
relatively short duration (up to 12 days) and temporary nature of the 
disturbance, the availability of similar habitat and resources in the 
surrounding area, the impacts to marine mammals and the food sources 
that they utilize are not expected to cause significant or long-term 
consequences for individual marine mammals or their populations. No 
biologically important areas, designated critical habitat, or other 
habitat of known significance would be impacted by the planned 
activities.

Negligible Impact Conclusions

    The proposed survey would be of short duration (up to 12 days of 
seismic operations), and the acoustic ``footprint'' of the proposed 
survey would be small relative to the ranges of the 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. Short-term exposures to survey operations are expected to only

[[Page 71452]]

temporarily affect marine mammal behavior in the form of avoidance, and 
the potential for longer-term avoidance of important areas is limited. 
Short-term exposures to survey operations are not likely to impact 
marine mammal behavior, and the potential for longer-term avoidance of 
important areas is limited.
    The proposed mitigation measures are expected to reduce the number 
and/or severity of takes by allowing for detection of marine mammals in 
the vicinity of the vessel by visual observers, and by minimizing the 
severity of any potential exposures via shutdowns of the airgun array.
    NMFS concludes that exposures to marine mammal species and stocks 
due to Scripps' proposed survey would result in only short-term 
(temporary and short in duration) effects to individuals exposed, over 
relatively small areas of the affected animals' ranges. Animals may 
temporarily avoid the immediate area, but are not expected to 
permanently abandon the area. Major shifts in habitat use, 
distribution, or foraging success are not expected. NMFS does not 
anticipate the proposed take estimates to impact annual rates of 
recruitment or survival.
    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 the species or stock 
through effects on annual rates of recruitment or survival:
     No Level A harassment, serious injury or mortality is 
anticipated or proposed to be authorized;
     The proposed activity is temporary and of relatively short 
duration (up to 12 days);
     The anticipated impacts of the proposed activity on marine 
mammals would primarily be temporary behavioral changes in the form of 
avoidance of the area around the survey vessel;
     The availability of alternate 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;
     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; and
     The proposed mitigation measures, including visual 
monitoring, shutdowns, ramp-up, and prescribed measures based on energy 
size are expected to minimize potential impacts to marine mammals (both 
amount and severity).
    Based on the analysis contained herein of the likely effects of the 
specified activity on marine mammals and their habitat, and taking into 
consideration the implementation of the proposed monitoring and 
mitigation measures, NMFS preliminarily finds that the total marine 
mammal take from the proposed activity will have a negligible impact on 
all affected marine mammal species or stocks.

Small Numbers

    As noted above, only small numbers of incidental take may be 
authorized under Sections 101(a)(5)(A) and (D) of the MMPA for 
specified activities other than military readiness activities. The MMPA 
does not define small numbers and so, in practice, where estimated 
numbers are available, NMFS compares the number of individuals taken to 
the most appropriate estimation of abundance of the relevant species or 
stock in our determination of whether an authorization is limited to 
small numbers of marine mammals. When the predicted number of 
individuals to be taken is fewer than one third of the species or stock 
abundance, the take is considered to be of small numbers. Additionally, 
other qualitative factors may be considered in the analysis, such as 
the temporal or spatial scale of the activities.
    The amount of take NMFS authorizes is below one third of the 
estimated population abundance of all species (Roberts et al., 2016). 
In fact, take of individuals is less than 4 percent of the abundance of 
the affected populations (see Table 8).
    Based on the analysis contained herein of the proposed activity 
(including the proposed mitigation and monitoring measures) and the 
anticipated take of marine mammals, NMFS preliminarily finds that small 
numbers of marine mammals will be taken relative to the population size 
of the affected species or stocks.

Unmitigable Adverse Impact Analysis and Determination

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

Endangered Species Act (ESA)

    Section 7(a)(2) of the 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 sperm whales, which are 
listed under the ESA. The NMFS Office of Protected Resources' (OPR) 
Permits and Conservation Division has requested initiation of Section 7 
consultation with the OPR Endangered Species Act 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 Scripps for conducting geophysical surveys in the 
southeast Gulf of Mexico in summer 2022, 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/permit/incidental-take-authorizations-under-marine-mammal-protection-act.

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 
geophysical survey. We also request at this time comment on the 
potential Renewal of this proposed IHA as described in the paragraph 
below. Please include with your comments any supporting data or 
literature citations to help inform decisions on the request for this 
IHA or a subsequent Renewal IHA.
    On a case-by-case basis, NMFS may issue a one-time, one-year 
renewal IHA following notice to the public providing an additional 15 
days for public comments when (1) up to another year of identical or 
nearly identical, 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:

[[Page 71453]]

     A request for renewal is received no later than 60 days 
prior to the needed renewal IHA effective date (recognizing that the 
renewal IHA expiration date cannot extend beyond one year from 
expiration of the initial IHA).
     The request for renewal must include the following:
    (1) An explanation that the activities to be conducted under the 
requested renewal IHA are identical to the activities analyzed under 
the initial IHA, are a subset of the activities, or include changes so 
minor (e.g., reduction in pile size) that the changes do not affect the 
previous analyses, mitigation and monitoring requirements, or take 
estimates (with the exception of reducing the type or amount of take).
    (2) A preliminary monitoring report showing the results of the 
required monitoring to date and an explanation showing that the 
monitoring results do not indicate impacts of a scale or nature not 
previously analyzed or authorized.
    Upon review of the request for renewal, the status of the affected 
species or stocks, and any other pertinent information, NMFS determines 
that there are no more than minor changes in the activities, the 
mitigation and monitoring measures will remain the same and 
appropriate, and the findings in the initial IHA remain valid.

    Dated: December 13, 2021.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2021-27272 Filed 12-15-21; 8:45 am]
BILLING CODE 3510-22-P