`[Federal Register Volume 89, Number 223 (Tuesday, November 19, 2024)]
[Notices]
[Pages 91340-91364]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-26903]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XE398]


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to a Marine Geophysical Survey in the 
Northwest 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 the University of Texas at 
Austin (UT) for authorization to take marine mammals incidental to a 
marine geophysical survey in coastal waters off Texas in the northwest 
(NW) Gulf of Mexico (GOM). Pursuant to the Marine Mammal Protection Act 
(MMPA), NMFS is requesting comments on its proposal to issue an 
incidental harassment authorization (IHA) to incidentally take marine 
mammals during the specified activities. NMFS is also requesting 
comments on a possible one-time, 1-year renewal that could be issued 
under certain circumstances and if all requirements are met, as 
described in the Request for Public Comments section at the end of this 
notice. NMFS will consider public comments prior to making any final 
decision on the issuance of the requested MMPA authorization and agency 
responses will be summarized in the final notice of our decision.

DATES: Comments and information must be received no later than December 
19, 2024.

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

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

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

[[Page 91341]]

intentional, taking of small numbers of marine mammals by U.S. citizens 
who engage in a specified activity (other than commercial fishing) 
within a specified geographical region if certain findings are made and 
either regulations are proposed or, if the taking is limited to 
harassment, a notice of a proposed IHA is provided to the public for 
review.
    Authorization for incidental takings shall be granted if NMFS finds 
that the taking will have a negligible impact on the species or 
stock(s) and will not have an unmitigable adverse impact on the 
availability of the species or stock(s) for taking for subsistence uses 
(where relevant). Further, NMFS must prescribe the permissible methods 
of taking and other ``means of effecting the least practicable adverse 
impact'' on the affected species or stocks and their habitat, paying 
particular attention to rookeries, mating grounds, and areas of similar 
significance, and on the availability of the species or stocks for 
taking for certain subsistence uses (referred to in shorthand as 
``mitigation''); and requirements pertaining to the monitoring and 
reporting of the takings. The definitions of all applicable MMPA 
statutory terms used above are included in the relevant sections below 
and can be found in section 3 of the MMPA (16 U.S.C. 1362) and NMFS 
regulations at 50 CFR 216.103.

National Environmental Policy Act

    To comply with the National Environmental Policy Act of 1969 (NEPA; 
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A, 
NMFS must review our proposed action (i.e., the issuance of an IHA) 
with respect to potential impacts on the human environment. This action 
is consistent with categories of activities identified in Categorical 
Exclusion B4 (IHAs with no anticipated serious injury or mortality) of 
the Companion Manual for NAO 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 July 25, 2024, NMFS received a request from UT for an IHA to 
take marine mammals incidental to a marine geophysical survey in 
coastal waters off Texas in the NW GOM. The application was deemed 
adequate and complete on September 24, 2024. UT's request is for take 
of bottlenose dolphins, Atlantic spotted dolphins, and rough-toothed 
dolphins by Level B harassment only. Neither UT nor NMFS expect serious 
injury or mortality to result from this activity and, therefore, an IHA 
is appropriate.

Description of Proposed Activity

Overview

    Researchers from UT propose to conduct a low-energy marine seismic 
survey using airguns as the acoustic source from the research vessel 
(R/V) Brooks McCall (McCall) or similar vessel operated by TDI-Brooks 
International. The proposed survey would occur within Texas State 
waters in the NW GOM from approximately January to April 2025. The 
proposed survey would occur within the Exclusive Economic Zone (EEZ) of 
the United States and in Texas State waters, in water depths less than 
30 meters (m). To complete this high resolution 3D (HR3D) seismic 
survey, the McCall would tow a 2-airgun array with a total discharge 
volume of ~210 cubic inches (in\3\) at a depth of 3-4 m, with a shot 
interval of 12.5 m (5-10 seconds (s)) as the primary acoustic source. 
The airgun array receiver would consist of four 25-m-long solid-state 
hydrophone streamers, spaced 10 m apart. Approximately 4,440 km of 
seismic acquisition is proposed. The airgun array would introduce 
underwater sounds that may result in take, by Level B harassment, of 
marine mammals.
    The purpose of the proposed survey is to study the geologic section 
beneath the GOM for secure, long-term, large-scale carbon dioxide 
storage and enhanced hydrocarbon recovery.

Dates and Duration

    The proposed survey is anticipated to take place from January to 
April 2025. The survey is expected to last 23 days, including 
approximately 20 days of seismic operations and 3 days of transit and 
equipment deployment.

Specific Geographic Region

    The proposed survey would occur within approximately lat. 27.1-
29.6[deg] N, long. 93.6-97.4[deg] W, the EEZ of the United States and 
in Texas State waters, in water depths less than 30 m. The primary 
study area is around the 10 m isobaths, and if no suitable sites are 
within Texas State waters, the alternate study area is on the outer 
continental shelf within the 30 m isobaths. The region where the survey 
is proposed to occur is depicted in figure 1; the tracklines could 
occur anywhere within the polygon shown in figure 1. The McCall would 
likely mobilize and demobilize from the nearest available port.

[[Page 91342]]

[GRAPHIC] [TIFF OMITTED] TN19NO24.000

Detailed Description of the Specified Activity

    The procedures to be used for the proposed survey would be similar 
to those used during previous seismic surveys by UT and would use 
conventional seismic methodology. The survey would involve one source 
vessel, the McCall, or similar vessel operated by TDI-Brooks. During 
the low-energy HR3D seismic survey, the McCall would tow two Generator-
Injector (GI) airguns with a total discharge volume of 210 in\3\. The 
airgun array would be deployed at a depth of about 3-4 m below the 
surface, spaced about 2 m apart, and have a shot interval of 12.5 m 
(about 5-10 s). The receiving system would consist of four 25-m solid-
state hydrophone streamers, spaced 10 m apart and towed at a depth of 2 
m. As the airguns are towed along the survey lines, the hydrophone 
streamer would transfer data to the on-board processing system. 
Approximately 4,440 km of seismic acquisition are planned. The survey 
would take place in water depths less than 30 m.
    Proposed mitigation, monitoring, and reporting measures are 
described in detail later in this document (please see Proposed 
Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

    Sections 3 and 4 of the application summarize available information 
regarding status and trends, distribution and habitat preferences, and 
behavior and life history of the potentially affected species. NMFS 
fully considered all of this information, and we refer the reader to 
these descriptions, instead of reprinting the information. Additional 
information regarding population trends and threats may be found in 
NMFS' Stock Assessment Reports (SARs; https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments) and 
more general information about these species (e.g., physical and 
behavioral descriptions) may be found on NMFS' website (https://www.fisheries.noaa.gov/find-species).
    Table 1 lists all species or stocks for which take is expected and 
proposed to be authorized for this activity and summarizes information 
related to the population or stock, including regulatory status under 
the MMPA and Endangered Species Act (ESA) and potential biological 
removal (PBR), where known. PBR is defined by the MMPA as the maximum 
number of animals, not including natural mortalities, that may be 
removed from a marine mammal stock while allowing that stock to reach 
or maintain its optimum sustainable population (as described in NMFS' 
SARs). While no serious injury or mortality is anticipated or proposed 
to be authorized here, PBR and annual serious injury and mortality (M/
SI) from anthropogenic sources are included here as gross indicators of 
the status of the species or stocks and other threats.
    Marine mammal abundance estimates presented in this document 
represent the total number of individuals that make up a given stock or 
the total number estimated within a particular study or survey area. 
NMFS' stock abundance estimates for most species represent the total 
estimate of individuals within the geographic area, if known, that 
comprises that stock. For some species, this geographic area may extend 
beyond U.S. waters. All managed

[[Page 91343]]

stocks in this region are assessed in NMFS' U.S. Atlantic and Gulf of 
Mexico SARs. All values presented in table 1 are the most recent 
available at the time of publication (including from the draft 2023 
SARs) and are available online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

                                            Table 1--Species \1\ Likely Affected by the Specified Activities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                              Stock abundance
                                                                               ESA/MMPA       (CV, Nmin, most                        Annual      GOM
           Common name              Scientific name           Stock             status;      recent abundance           PBR           M/SI    population
                                                                             strategic (Y/      survey) \3\                           \4\     abundance
                                                                                N) \2\                                                           \5\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                  Odontoceti (toothed whales, dolphins, and porpoises)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Delphinidae:
    Atlantic spotted dolphin....  Stenella frontalis.  GOM................  -/-; N          21,506 (0.26;       166...............   \6\ 36   \7\ 12,240
                                                                                             17,339; 2018).
    Rough-toothed dolphin.......  Steno bredanensis..  GOM................  -/-; N          unk (n/a; unk;      undetermined......       39        4,853
                                                                                             2018).
    Bottlenose dolphin..........  Tursiops truncatus.  GOM Western Coastal  -/-; N          20,759 (0.13;       167...............       36  \7\ 151,886
                                                                                             18,585; 2018).
                                                       Northern GOM         -/-; N          63,280 (0.11;       556...............   \5\ 65
                                                        Continental Shelf.                   57,917; 2018).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy
  (https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/).
\2\ 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.
\3\ NMFS marine mammal stock assessment reports online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region. CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable.
\4\ These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g.,
  commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV
  associated with estimated mortality due to commercial fisheries is presented in some cases.
\5\ Model-predicted stock abundance for Atlantic spotted dolphins and bottlenose dolphins from the most recent GOM density models (Garrison et al.,
  2023). Stock abundance for rough-toothed dolphins was taken from Roberts et al. (2016) density models, as Garrison et al. (2023) did not create a
  model for this species.
\6\ M/SI is a minimum count and does not include projected mortality estimates for 2015-2019 due to the DWH oil spill.
\7\ This estimate includes both coastal and continental shelf bottlenose dolphins from other stocks.

    As indicated above, all three species (with four managed stocks) in 
table 1 temporally and spatially co-occur with the activity to the 
degree that take is reasonably likely to occur. All species that could 
potentially occur in the proposed survey areas are included in table 2 
of the IHA application. While the additional 11 species listed in table 
2 of UT's application have been infrequently sighted in the survey 
area, 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. Species or stocks that only occur 
in deep waters (>200 m) within the GOM are unlikely to be observed 
during this survey where the maximum water depth is 30 m, and thus, the 
following species or stocks will not be considered further: offshore 
stock of bottlenose dolphins, pantropical spotted dolphin, spinner 
dolphin, striped dolphin, Clymene dolphin, Fraser's dolphin, Risso's 
dolphin, melon-headed whale, pygmy killer whale, false killer whale, 
killer whale, and short-finned pilot whale.

Bottlenose Dolphin

    Bottlenose dolphins are cosmopolitan, occurring in tropical, 
subtropical, and temperate waters around the world (Wells and Scott 
2018). The bottlenose dolphin is the most widespread and common 
delphinid in coastal waters of the GOM (W[uuml]rsig et al., 2000; 
W[uuml]rsig 2017). While there are multiple stocks of bottlenose 
dolphins in the GOM, only the Northern GOM Continental Shelf and GOM 
Western Coastal stocks overlap with the study area, with the shelf 
stock assumed to occur in waters >20 m and the coastal stock assumed to 
occur in waters <20 m. Fall sightings have been made throughout the 
northern Gulf but primarily on the shelf, including within survey 
waters. Five sightings totaling 12 animals were made during a UT 
geophysical survey on the Texas shelf during March 2024, which is 
within the proposed study area. All sightings were made in water <20 m 
deep (RPS 2024).
    There are 31 bay, sound, and estuary (BSE) stocks in the northern 
GOM, which are small, resident populations of bottlenose dolphins that 
live inshore or, occasionally, close to shore or in passes, and are 
genetically discrete. There are two of the BSE stocks that occur near 
the survey area, the West Bay stock and the Galveston Bay/East Bay/
Trinity Bay stock. These areas in and near West Bay and Galveston Bay, 
along with numerous other ones along the coast of Texas, have been 
identified as year-round Biologically Important Areas (BIAs) for 
resident bottlenose dolphins (LeBrecque et al., 2015). Due to the 
distance that the survey will occur off the coast (between 1 and 115 
km) and general expectation that BSE dolphins are most likely to occur 
in inshore waters and around passes into inshore waters, we do not 
expect the survey to encounter any BSE stocks of bottlenose dolphins.

Marine Mammal Hearing

    Hearing is the most important sensory modality for marine mammals 
underwater, and exposure to anthropogenic sound can have deleterious 
effects. To appropriately assess the potential effects of exposure to 
sound, it is necessary to understand the frequency ranges marine 
mammals are able to hear. Not all marine mammal species have equal 
hearing capabilities (e.g., Richardson et al., 1995; Wartzok and 
Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al., 
(2007, 2019) recommended that marine mammals be divided into hearing 
groups based on directly measured (behavioral or auditory evoked 
potential techniques) or estimated hearing ranges (behavioral response 
data, anatomical modeling, etc.). On October 24, 2024, NMFS published 
(89 FR 84872) the final Updated Technical Guidance, which includes 
updated thresholds and weighting functions to inform auditory injury 
estimates, and has replaced the 2018 Technical Guidance used previously 
(NMFS 2018). The updated hearing groups are presented below (table 2). 
The references, analysis, and methodology used in the development

[[Page 91344]]

of the hearing groups are described in NMFS' 2024 Technical Guidance, 
which may be accessed at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

                  Table 2--Marine Mammal Hearing Groups
                              [NMFS, 2024]
------------------------------------------------------------------------
       Hearing group [supcaret]           Generalized hearing range *
------------------------------------------------------------------------
Underwater:
    Low-frequency (LF) cetaceans       7 Hz to 36 * kHz.\+\
     (baleen whales).
    High-frequency (HF) cetaceans      150 Hz to 160 kHz.
     (dolphins, toothed whales,
     beaked whales, bottlenose
     whales).
    Very High-frequency (VHF)          200 Hz to 165 kHz.
     cetaceans (true porpoises,
     Kogia, river dolphins,
     Cephalorhynchid, Lagenorhynchus
     cruciger & L. australis).
    Phocid pinnipeds (PW)              40 Hz to 90 kHz.
     (underwater) (true seals).
    Otariid pinnipeds (OW)             60 Hz to 68 kHz.
     (underwater) (sea lions and fur
     seals).
------------------------------------------------------------------------
[supcaret] Southall et al., 2019 indicates that as more data become
  available there may be separate hearing group designations for Very
  Low-Frequency cetaceans (blue, fin, right, and bowhead whales) and Mid-
  Frequency cetaceans (sperm, killer, and beaked whales). However, at
  this point, all baleen whales are part of the LF cetacean hearing
  group, and sperm, killer, and beaked whales are part of the HF
  cetacean hearing group. Additionally, recent data indicates that as
  more data become available for Monachinae seals, separate hearing
  group designations may be appropriate for the two phocid subfamilies
  (Ruscher et al., 2021; Sills et al., 2021).
* Represents the generalized hearing range for the entire group as a
  composite (i.e., all species within the group), where individual
  species' hearing ranges may not be as broad. Generalized hearing range
  chosen based on ~65 dB threshold from composite audiogram, previous
  analysis in NMFS 2018, and/or data from Southall et al., 2007;
  Southall et al., 2019. Additionally, animals are able to detect very
  loud sounds above and below that ``generalized'' hearing range.
\+\ NMFS is aware that the National Marine Mammal Foundation
  successfully collected preliminary hearing data on two minke whales
  during their third field season (2023) in Norway. These data have
  implications for not only the generalized hearing range for low-
  frequency cetaceans but also on their weighting function. However, at
  this time, no official results have been published. Furthermore, a
  fourth field season (2024) is proposed, where more data will likely be
  collected. Thus, it is premature for us to propose any changes to our
  current Updated Technical Guidance. However, mysticete hearing data is
  identified as a special circumstance that could merit re-evaluating
  the acoustic criteria in this document. Therefore, we anticipate that
  once the data from both field seasons are published, it will likely
  necessitate updating this document (i.e., likely after the data
  gathered in the summer 2024 field season and associated analysis are
  published).

Potential Effects of Specified Activities on Marine Mammals and Their 
Habitat

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

Description of Active Acoustic Sound Sources

    This section contains a brief technical background on sound, the 
characteristics of certain sound types, and on metrics used in this 
proposal inasmuch as the information is relevant to the specified 
activity and to a discussion of the potential effects of the specified 
activity on marine mammals found later in this document.
    Sound travels in waves, the basic components of which are 
frequency, wavelength, velocity, and amplitude. Frequency is the number 
of pressure waves that pass by a reference point per unit of time and 
is measured in hertz (Hz) or cycles per second. Wavelength is the 
distance between two peaks or corresponding points of a sound wave 
(length of 1 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

[[Page 91345]]

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

Acoustic Effects

    Here, we discuss the effects of active acoustic sources on marine 
mammals.
    Potential Effects of Underwater Sound \1\--Anthropogenic sounds 
cover a broad range of frequencies and sound levels and can have a 
range of highly variable impacts on marine life, from none or minor to 
potentially severe responses, depending on received levels, duration of 
exposure, behavioral context, and various other factors. The potential 
effects of underwater sound from active acoustic sources can 
potentially result in one or more of the following: Temporary or 
permanent hearing impairment; non-auditory physical or physiological 
effects; behavioral disturbance; stress; and masking (Richardson et 
al., 1995; Gordon et al., 2004; Nowacek et al., 2007; Southall et al., 
2007; G[ouml]tz et al., 2009). The degree of effect is intrinsically 
related to the signal characteristics, received level, distance from 
the source, and duration of the sound exposure. In general, sudden, 
high level sounds can cause hearing loss, as can longer exposures to 
lower

[[Page 91346]]

level sounds. Temporary or permanent loss of hearing, if it occurs at 
all, will occur almost exclusively in cases where a noise is within an 
animal's hearing frequency range. We first describe specific 
manifestations of acoustic effects before providing discussion specific 
to the use of airgun arrays.
---------------------------------------------------------------------------

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

    Richardson et al. (1995) described zones of increasing intensity of 
effect that might be expected to occur, in relation to distance from a 
source and assuming that the signal is within an animal's hearing 
range. First is the area within which the acoustic signal would be 
audible (potentially perceived) to the animal, but not strong enough to 
elicit any overt behavioral or physiological response. The next zone 
corresponds with the area where the signal is audible to the animal and 
of sufficient intensity to elicit behavioral or physiological response. 
Third is a zone within which, for signals of high intensity, the 
received level is sufficient to potentially cause discomfort or tissue 
damage to auditory or other systems. Overlaying these zones to a 
certain extent is the area within which masking (i.e., when a sound 
interferes with or masks the ability of an animal to detect a signal of 
interest that is above the absolute hearing threshold) may occur; the 
masking zone may be highly variable in size.
    We describe the more severe effects of certain non-auditory 
physical or physiological effects only briefly as we do not expect that 
use of airgun arrays are reasonably likely to result in such effects 
(see below for further discussion). Potential effects from impulsive 
sound sources can range in severity from effects such as behavioral 
disturbance or tactile perception to physical discomfort, slight injury 
of the internal organs and the auditory system, or mortality (Yelverton 
et al., 1973). Non-auditory physiological effects or injuries that 
theoretically might occur in marine mammals exposed to high level 
underwater sound or as a secondary effect of extreme behavioral 
reactions (e.g., change in dive profile as a result of an avoidance 
reaction) caused by exposure to sound include neurological effects, 
bubble formation, resonance effects, and other types of organ or tissue 
damage (Cox et al., 2006; Southall et al., 2007; Zimmer and Tyack, 
2007; Tal et al., 2015). The survey activities considered here do not 
involve the use of devices such as explosives or mid-frequency tactical 
sonar that are associated with these types of effects.
    Auditory Injury (AUD INJ) and Permanent Threshold Shift (PTS)--NMFS 
defines auditory injury as ``damage to the inner ear that can result in 
destruction of tissue . . . which may or may not result in PTS'' (NMFS, 
2024). NMFS defines PTS as a permanent, irreversible increase in the 
threshold of audibility at a specified frequency or portion of an 
individual's hearing range above a previously established reference 
level (NMFS, 2024). PTS does not generally affect more than a limited 
frequency range, and an animal that has PTS has incurred some level of 
hearing loss at the relevant frequencies; typically, animals with PTS 
are not functionally deaf (Au and Hastings, 2008; Finneran, 2016). 
Available data from humans and other terrestrial mammals indicate that 
a 40-dB threshold shift approximates PTS onset (see Ward et al., 1958, 
1959, 1960; Kryter et al., 1966; Miller, 1974; Ahroon et al., 1996; 
Henderson et al., 2008). PTS levels for marine mammals are estimates, 
as with the exception of a single study unintentionally inducing PTS in 
a harbor seal (Kastak et al., 2008), there are no empirical data 
measuring PTS in marine mammals largely due to the fact that, for 
various ethical reasons, experiments involving anthropogenic noise 
exposure at levels inducing PTS are not typically pursued or authorized 
(NMFS, 2018).
    Temporary Threshold Shift (TTS). A temporary, reversible increase 
in the threshold of audibility at a specified frequency or portion of 
an individual's hearing range above a previously established reference 
level (NMFS, 2018). Based on data from marine mammal TTS measurements 
(see Southall et al., 2007, 2019), a TTS of 6 dB is considered the 
minimum threshold shift clearly larger than any day-to-day or session-
to-session variation in a subject's normal hearing ability (Finneran et 
al., 2000, 2002; Schlundt et al., 2000). As described in Finneran 
(2015), marine mammal studies have shown the amount of TTS increases 
with SELcum in an accelerating fashion: at low exposures 
with lower SELcum, the amount of TTS is typically small and 
the growth curves have shallow slopes. At exposures with higher 
SELcum, the growth curves become steeper and approach linear 
relationships with the noise SEL.
    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 (similar to those discussed in auditory 
masking, below). 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 takes place during a time when the animal 
is traveling through the open ocean, 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. We note that reduced hearing sensitivity as 
a simple function of aging has been observed in marine mammals, as well 
as humans and other taxa (Southall et al., 2007), so we can infer that 
strategies exist for coping with this condition to some degree, though 
likely not without cost.
    Many studies have examined noise-induced hearing loss in marine 
mammals (see Finneran (2015) and Southall et al. (2019) for summaries). 
TTS is the mildest form of hearing impairment that can occur during 
exposure to sound (Kryter, 2013). 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. For 
cetaceans, published data on the onset of TTS are limited to captive 
bottlenose dolphin (Tursiops truncatus), beluga whale, harbor porpoise, 
and Yangtze finless porpoise (Neophocoena asiaeorientalis) (Southall et 
al., 2019). These studies examine hearing thresholds measured in marine 
mammals before and after exposure to intense or long-duration sound 
exposures. The difference between the pre-exposure and post-exposure 
thresholds can be used to determine the amount of threshold shift at 
various post-exposure times.
    The amount and onset of TTS depends on the exposure frequency. 
Sounds at low frequencies, well below the region of best sensitivity 
for a species or hearing group, are less hazardous than those at higher 
frequencies, near the region of best sensitivity (Finneran and 
Schlundt, 2013). At low frequencies, onset-TTS exposure levels are 
higher compared to those in the region of best sensitivity (i.e., a low 
frequency noise would need to be louder to cause TTS onset when TTS 
exposure level is higher), as shown for harbor porpoises and harbor 
seals (Kastelein et al., 2019a, 2019c). Note that in general, harbor 
seals and harbor porpoises have a lower TTS onset than other measured 
pinniped or cetacean species (Finneran, 2015). In addition, TTS can 
accumulate across multiple exposures, but the resulting TTS will be

[[Page 91347]]

less than the TTS from a single, continuous exposure with the same SEL 
(Mooney et al., 2009; Finneran et al., 2010; Kastelein et al., 2014, 
2015). This means that TTS predictions based on the total, cumulative 
SEL will overestimate the amount of TTS from intermittent exposures, 
such as sonars and impulsive sources. Nachtigall et al. (2018) describe 
measurements of hearing sensitivity of multiple odontocete species 
(bottlenose dolphin, harbor porpoise, beluga, and false killer whale 
(Pseudorca crassidens)) when a relatively loud sound was preceded by a 
warning sound. These captive animals were shown to reduce hearing 
sensitivity when warned of an impending intense sound. Based on these 
experimental observations of captive animals, the authors suggest that 
wild animals may dampen their hearing during prolonged exposures or if 
conditioned to anticipate intense sounds. Another study showed that 
echolocating animals (including odontocetes) might have anatomical 
specializations that might allow for conditioned hearing reduction and 
filtering of low-frequency ambient noise, including increased stiffness 
and control of middle ear structures and placement of inner ear 
structures (Ketten et al., 2021). Data available on noise-induced 
hearing loss for mysticetes are currently lacking (NMFS, 2018). 
Additionally, the existing marine mammal TTS data come from a limited 
number of individuals within these species.
    Relationships between TTS and PTS thresholds have not been studied 
in marine mammals, and there is no PTS data for cetaceans. However, 
such relationships are assumed to be similar to those in humans and 
other terrestrial mammals. PTS typically occurs at exposure levels at 
least several dB above that inducing mild TTS (e.g., a 40-dB threshold 
shift approximates PTS onset (Kryter et al., 1966; Miller, 1974), while 
a 6-dB threshold shift approximates TTS onset (Southall et al., 2007, 
2019). Based on data from terrestrial mammals, a precautionary 
assumption is that the PTS thresholds for impulsive sounds (such as 
impact pile driving 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, 2019). 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.
    Behavioral Effects--Behavioral disturbance may include a variety of 
effects, including subtle changes in behavior (e.g., minor or brief 
avoidance of an area or changes in vocalizations), more conspicuous 
changes in similar behavioral activities, and more sustained and/or 
potentially severe reactions, such as displacement from or abandonment 
of high-quality habitat. Behavioral responses to sound are highly 
variable and context-specific, and any reactions depend on numerous 
intrinsic and extrinsic factors (e.g., species, state of maturity, 
experience, current activity, reproductive state, auditory sensitivity, 
time of day), as well as the interplay between factors (e.g., 
Richardson et al., 1995; Wartzok et al., 2003; Southall et al., 2007, 
2019; Weilgart, 2007; Archer et al., 2010). Behavioral reactions can 
vary not only among individuals but also within an individual, 
depending on previous experience with a sound source, context, and 
numerous other factors (Ellison et al., 2012), and can vary depending 
on characteristics associated with the sound source (e.g., whether it 
is moving or stationary, number of sources, distance from the source). 
Please see appendices B-C of Southall et al., (2007) for a review of 
studies involving marine mammal behavioral responses to sound.
    Habituation can occur when an animal's response to a stimulus wanes 
with repeated exposure, usually in the absence of unpleasant associated 
events (Wartzok et al., 2003). Animals are most likely to habituate to 
sounds that are predictable and unvarying. It is important to note that 
habituation is appropriately considered as a ``progressive reduction in 
response to stimuli that are perceived as neither aversive nor 
beneficial,'' rather than as, more generally, moderation in response to 
human disturbance (Bejder et al., 2009). The opposite process is 
sensitization, when an unpleasant experience leads to subsequent 
responses, often in the form of avoidance, at a lower level of 
exposure. As noted, behavioral state may affect the type of response. 
For example, animals that are resting may show greater behavioral 
change in response to disturbing sound levels than animals that are 
highly motivated to remain in an area for feeding (Richardson et al., 
1995; NRC, 2003; Wartzok et al., 2003). Controlled experiments with 
captive marine mammals have shown pronounced behavioral reactions, 
including avoidance of loud sound sources (Ridgway et al., 1997). 
Observed responses of wild marine mammals to loud pulsed sound sources 
(typically seismic airguns or acoustic harassment devices) 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 briefly reacts to 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). There are 
broad categories of potential response, which we describe in greater 
detail here, that include alteration of dive behavior, alteration of 
foraging behavior, effects to breathing, interference with or 
alteration of vocalization, avoidance, and flight.
    Changes in dive behavior can vary widely, and may consist of 
increased or decreased dive times and surface intervals as well as 
changes in the rates of ascent and descent during a dive (e.g., Frankel 
and Clark, 2000; Ng and Leung, 2003; Nowacek et al., 2004; Goldbogen et 
al., 2013a, b). Variations in dive behavior may reflect disruptions in 
biologically significant activities (e.g., foraging) or they may be of 
little biological significance. The impact of an alteration to dive 
behavior resulting from an acoustic exposure depends on what the animal 
is doing at the time of the exposure and the type and magnitude of the 
response.
    Disruption of feeding behavior can be difficult to correlate with 
anthropogenic sound exposure, so it is usually inferred by observed 
displacement from known foraging areas, the appearance of secondary 
indicators (e.g., bubble nets or sediment plumes), or changes in dive 
behavior. As for other types of behavioral response, the frequency, 
duration, and temporal pattern of signal presentation, as well as 
differences in species sensitivity, are likely contributing factors to 
differences in response in any given circumstance

[[Page 91348]]

(e.g., Croll et al., 2001; Nowacek et al., 2004; Madsen et al., 2006; 
Yazvenko et al., 2007). A determination of whether foraging disruptions 
affect fitness consequences would require information on or estimates 
of the energetic requirements of the affected individuals and the 
relationship between prey availability, foraging effort and success, 
and the life history stage of the animal.
    Visual tracking, passive acoustic monitoring (PAM), and movement 
recording tags were used to quantify sperm whale behavior prior to, 
during, and following exposure to airgun arrays at received levels in 
the range 140-160 dB at distances of 7-13 km, following a phase-in of 
sound intensity and full array exposures at 1-13 km (Madsen et al., 
2006; Miller et al., 2009). Sperm whales did not exhibit horizontal 
avoidance behavior at the surface. However, foraging behavior may have 
been affected. The sperm whales exhibited 19 percent less vocal, or 
buzz, rate during full exposure relative to post exposure, and the 
whale that was approached most closely had an extended resting period 
and did not resume foraging until the airguns had ceased firing. The 
remaining whales continued to execute foraging dives throughout 
exposure; however, swimming movements during foraging dives were 6 
percent lower during exposure than control periods (Miller et al., 
2009). These data raise concerns that seismic surveys may impact 
foraging behavior in sperm whales, although more data are required to 
understand whether the differences were due to exposure or natural 
variation in sperm whale behavior (Miller et al., 2009).
    Changes in respiration naturally vary with different behaviors and 
alterations to breathing rate as a function of acoustic exposure can be 
expected to co-occur with other behavioral reactions, such as a flight 
response or an alteration in diving. However, respiration rates in and 
of themselves may be representative of annoyance or an acute stress 
response. Various studies have shown that respiration rates may either 
be unaffected or could increase, depending on the species and signal 
characteristics, again highlighting the importance in understanding 
species differences in the tolerance of underwater noise when 
determining the potential for impacts resulting from anthropogenic 
sound exposure (e.g., Kastelein et al., 2001, 2005, 2006; Gailey et 
al., 2007, 2016).
    Marine mammals vocalize for different purposes and across multiple 
modes, such as whistling, echolocation click production, calling, and 
singing. Changes in vocalization behavior in response to anthropogenic 
noise can occur for any of these modes and may result from a need to 
compete with an increase in background noise or may reflect increased 
vigilance or a startle response. For example, in the presence of 
potentially masking signals, humpback whales and killer whales have 
been observed to increase the length of their songs or amplitude of 
calls (Miller et al., 2000; Fristrup et al., 2003; Foote et al., 2004; 
Holt et al., 2012), while right whales have been observed to shift the 
frequency content of their calls upward while reducing the rate of 
calling in areas of increased anthropogenic noise (Parks et al., 2007). 
In some cases, animals may cease sound production during production of 
aversive signals (Bowles et al., 1994).
    Cerchio et al. (2014) used PAM to document the presence of singing 
humpback whales off the coast of northern Angola and to 
opportunistically test for the effect of seismic survey activity on the 
number of singing whales. Two recording units were deployed between 
March and December 2008 in the offshore environment; numbers of singers 
were counted every hour. Generalized Additive Mixed Models were used to 
assess the effect of survey day (seasonality), hour (diel variation), 
moon phase, and received levels of noise (measured from a single pulse 
during each 10 minutes sampled period) on singer number. The number of 
singers significantly decreased with increasing received level of 
noise, suggesting that humpback whale communication was disrupted to 
some extent by the survey activity.
    Castellote et al. (2012) reported acoustic and behavioral changes 
by fin whales in response to shipping and airgun noise. Acoustic 
features of fin whale song notes recorded in the Mediterranean Sea and 
northeast Atlantic Ocean were compared for areas with different 
shipping noise levels and traffic intensities and during a seismic 
airgun survey. During the first 72 hours of the survey, a steady 
decrease in song received levels and bearings to singers indicated that 
whales moved away from the acoustic source and out of the study area. 
This displacement persisted for a time period well beyond the 10-day 
duration of seismic airgun activity, providing evidence that fin whales 
may avoid an area for an extended period in the presence of increased 
noise. The authors hypothesize that fin whale acoustic communication is 
modified to compensate for increased background noise and that a 
sensitization process may play a role in the observed temporary 
displacement.
    Seismic pulses at average received levels of 131 dB re 1 [mu]Pa\2\-
s caused blue whales to increase call production (Di Iorio and Clark, 
2010). In contrast, McDonald et al. (1995) tracked a blue whale with 
seafloor seismometers and reported that it stopped vocalizing and 
changed its travel direction at a range of 10 km from the acoustic 
source vessel (estimated received level 143 dB pk-pk). Blackwell et 
al., (2013) found that bowhead whale call rates dropped significantly 
at onset of airgun use at sites with a median distance of 41-45 km from 
the survey. Blackwell et al. (2015) expanded this analysis to show that 
whales actually increased calling rates as soon as airgun signals were 
detectable before ultimately decreasing calling rates at higher 
received levels (i.e., 10-minute cumulative sound exposure level 
(SELcum) of ~127 dB). Overall, these results suggest that 
bowhead whales may adjust their vocal output in an effort to compensate 
for noise before ceasing vocalization effort and ultimately deflecting 
from the acoustic source (Blackwell et al., 2013, 2015). These studies 
demonstrate that even low levels of noise received far from the source 
can induce changes in vocalization and/or behavior for mysticetes.
    Avoidance is the displacement of an individual from an area or 
migration path as a result of the presence of sound or other stressors, 
and is one of the most obvious manifestations of disturbance in marine 
mammals (Richardson et al., 1995). For example, gray whales are known 
to change direction--deflecting from customary migratory paths--in 
order to avoid noise from seismic surveys (Malme et al., 1984). 
Humpback whales show avoidance behavior in the presence of an active 
seismic array during observational studies and controlled exposure 
experiments in western Australia (McCauley et al., 2000). Avoidance may 
be short-term, with animals returning to the area once the noise has 
ceased (e.g., Bowles et al., 1994; Goold, 1996; Stone et al., 2000; 
Morton and Symonds, 2002; Gailey et al., 2007). Longer-term 
displacement is possible, however, which may lead to changes in 
abundance or distribution patterns of the affected species in the 
affected region if habituation to the presence of the sound does not 
occur (e.g., Bejder et al., 2006; Teilmann et al., 2006).
    Forney et al. (2017) detail the potential effects of noise on 
marine mammal populations with high site fidelity, including 
displacement and auditory masking, noting that a lack of observed 
response does not imply absence of fitness costs and that

[[Page 91349]]

apparent tolerance of disturbance may have population-level impacts 
that are less obvious and difficult to document. Avoidance of overlap 
between disturbing noise and areas and/or times of particular 
importance for sensitive species may be critical to avoiding 
population-level impacts because (particularly for animals with high 
site fidelity) there may be a strong motivation to remain in the area 
despite negative impacts. Forney et al., (2017) state that, for these 
animals, remaining in a disturbed area may reflect a lack of 
alternatives rather than a lack of effects.
    Forney et al. (2017) specifically discuss beaked whales, stating 
that until recently most knowledge of beaked whales was derived from 
strandings, as they have been involved in atypical mass stranding 
events associated with mid-frequency active sonar (MFAS) training 
operations. Given these observations and recent research, beaked whales 
appear to be particularly sensitive and vulnerable to certain types of 
acoustic disturbance relative to most other marine mammal species. 
Individual beaked whales reacted strongly to experiments using 
simulated MFAS at low received levels, by moving away from the sound 
source and stopping foraging for extended periods. These responses, if 
on a frequent basis, could result in significant fitness costs to 
individuals (Forney et al., 2017). Additionally, difficulty in 
detection of beaked whales due to their cryptic surfacing behavior and 
silence when near the surface pose problems for mitigation measures 
employed to protect beaked whales. Forney et al., (2017) specifically 
states that failure to consider both displacement of beaked whales from 
their habitat and noise exposure could lead to more severe biological 
consequences.
    A flight response is a dramatic change in normal movement to a 
directed and rapid movement away from the perceived location of a sound 
source. The flight response differs from other avoidance responses in 
the intensity of the response (e.g., directed movement, rate of 
travel). Relatively little information on flight responses of marine 
mammals to anthropogenic signals exist, although observations of flight 
responses to the presence of predators have occurred (Connor and 
Heithaus, 1996). The result of a flight response could range from 
brief, temporary exertion and displacement from the area where the 
signal provokes flight to, in extreme cases, marine mammal strandings 
(Evans and England, 2001). However, it should be noted that response to 
a perceived predator does not necessarily invoke flight (Ford and 
Reeves, 2008), and whether individuals are solitary or in groups may 
influence the response.
    Behavioral disturbance can also impact marine mammals in more 
subtle ways. Increased vigilance may result in costs related to 
diversion of focus and attention (i.e., when a response consists of 
increased vigilance, it may come at the cost of decreased attention to 
other critical behaviors such as foraging or resting). These effects 
have generally not been demonstrated for marine mammals, but studies 
involving fish and terrestrial animals have shown that increased 
vigilance may substantially reduce feeding rates (e.g., Beauchamp and 
Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In 
addition, chronic disturbance can cause population declines through 
reduction of fitness (e.g., decline in body condition) and subsequent 
reduction in reproductive success, survival, or both (e.g., Harrington 
and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, 
Ridgway et al., (2006) reported that increased vigilance in bottlenose 
dolphins exposed to sound over a 5-day period did not cause any sleep 
deprivation or stress effects.
    Many animals perform vital functions, such as feeding, resting, 
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption 
of such functions resulting from reactions to stressors, such as sound 
exposure, are more likely to be significant if they last more than 1 
diel cycle or recur on subsequent days (Southall et al., 2007). 
Consequently, a behavioral response lasting less than 1 day and not 
recurring on subsequent days is not considered particularly severe 
unless it could directly affect reproduction or survival (Southall et 
al., 2007). Note that there is a difference between multi-day 
substantive behavioral reactions and multi-day anthropogenic 
activities. For example, just because an activity lasts for multiple 
days does not necessarily mean that individual animals are either 
exposed to activity-related stressors for multiple days or, further, 
exposed in a manner resulting in sustained multi-day substantive 
behavioral responses.
    Stone (2015) reported data from at-sea observations during 1,196 
seismic surveys from 1994 to 2010. When arrays of large airguns 
(considered to be 500 in\3\ or more in that study) were firing, lateral 
displacement, more localized avoidance, or other changes in behavior 
were evident for most odontocetes. However, significant responses to 
large arrays were found only for the minke whale and fin whale. 
Behavioral responses observed included changes in swimming or surfacing 
behavior, with indications that cetaceans remained near the water 
surface at these times. Cetaceans were recorded as feeding less often 
when large arrays were active. Behavioral observations of gray whales 
during a seismic survey monitored whale movements and respirations pre-
, during, and post-seismic survey (Gailey et al., 2016). Behavioral 
state and water depth were the best ``natural'' predictors of whale 
movements and respiration and, after considering natural variation, 
none of the response variables were significantly associated with 
seismic survey or vessel sounds.
    Stress Responses--An animal's perception of a threat may be 
sufficient to trigger stress responses consisting of some combination 
of behavioral responses, autonomic nervous system responses, 
neuroendocrine responses, or immune responses (e.g., Seyle, 1950; 
Moberg, 2000). In many cases, an animal's first and sometimes most 
economical (in terms of energetic costs) response is behavioral 
avoidance of the potential stressor. Autonomic nervous system responses 
to stress typically involve changes in heart rate, blood pressure, and 
gastrointestinal activity. These responses have a relatively short 
duration and may or may not have a significant long-term effect on an 
animal's fitness.
    Neuroendocrine stress responses often involve the hypothalamus-
pituitary-adrenal system. Virtually all neuroendocrine functions that 
are affected by stress--including immune competence, reproduction, 
metabolism, and behavior--are regulated by pituitary hormones. Stress-
induced changes in the secretion of pituitary hormones have been 
implicated in failed reproduction, altered metabolism, reduced immune 
competence, and behavioral disturbance (e.g., Moberg, 1987; Blecha, 
2000). Increases in the circulation of glucocorticoids are also equated 
with stress (Romano et al., 2004).
    The primary distinction between stress (which is adaptive and does 
not normally place an animal at risk) and distress is the cost of the 
response. During a stress response, an animal uses glycogen stores that 
can be quickly 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.

[[Page 91350]]

    Relationships between these physiological mechanisms, animal 
behavior, and the costs of stress responses are well-studied through 
controlled experiments and for both laboratory and free-ranging animals 
(e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003; 
Krausman et al., 2004; Lankford et al., 2005). Stress responses due to 
exposure to anthropogenic sounds or other stressors and their effects 
on marine mammals have also been reviewed (Fair and Becker, 2000; 
Romano et al., 2002b) and, more rarely, studied in wild populations 
(e.g., Romano et al., 2002a). For example, Rolland et al., (2012) found 
that noise reduction from reduced ship traffic in the Bay of Fundy was 
associated with decreased stress in North Atlantic right whales. These 
and other studies lead to a reasonable expectation that some marine 
mammals will experience physiological stress responses upon exposure to 
acoustic stressors and that it is possible that some of these would be 
classified as ``distress.'' In addition, any animal experiencing TTS 
would likely also experience stress responses (NRC, 2003).
    Auditory Masking--Sound can disrupt behavior through masking, or 
interfering with, an animal's ability to detect, recognize, or 
discriminate between acoustic signals of interest (e.g., those used for 
intraspecific communication and social interactions, prey detection, 
predator avoidance, navigation) (Richardson et al., 1995; Erbe et al., 
2016). Masking occurs when the receipt of a sound is interfered with by 
another coincident sound at similar frequencies and at similar or 
higher intensity, and may occur whether the sound is natural (e.g., 
snapping shrimp, wind, waves, precipitation) or anthropogenic (e.g., 
shipping, sonar, seismic exploration) in origin. The ability of a noise 
source to mask biologically important sounds depends on the 
characteristics of both the noise source and the signal of interest 
(e.g., signal-to-noise ratio, temporal variability, direction), in 
relation to each other and to an animal's hearing abilities (e.g., 
sensitivity, frequency range, critical ratios, frequency 
discrimination, directional discrimination, age or TTS hearing loss), 
and existing ambient noise and propagation conditions.
    Under certain circumstances, significant masking could disrupt 
behavioral patterns, which in turn could affect fitness for survival 
and reproduction. It is important to distinguish TTS and PTS, which 
persist after the sound exposure, from masking, which occurs during the 
sound exposure. Because masking (without resulting in TS) is not 
associated with abnormal physiological function, it is not considered a 
physiological effect, but rather a potential behavioral effect.
    The frequency range of the potentially masking sound is important 
in predicting any potential behavioral impacts. For example, low-
frequency signals may have less effect on high-frequency echolocation 
sounds produced by odontocetes but are more likely to affect detection 
of mysticete communication calls and other potentially important 
natural sounds such as those produced by surf and some prey species. 
The masking of communication signals by anthropogenic noise may be 
considered as a reduction in the communication space of animals (e.g., 
Clark et al., 2009) and may result in energetic or other costs as 
animals change their vocalization behavior (e.g., Miller et al., 2000; 
Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2009; Holt 
et al., 2009). Masking may be less in situations where the signal and 
noise come from different directions (Richardson et al., 1995), through 
amplitude modulation of the signal, or through other compensatory 
behaviors (Houser and Moore, 2014). Masking can be tested directly in 
captive species (e.g., Erbe, 2008), but in wild populations it must be 
either modeled or inferred from evidence of masking compensation. There 
are few studies addressing real-world masking sounds likely to be 
experienced by marine mammals in the wild (e.g., Branstetter et al., 
2013).
    Masking affects both senders and receivers of acoustic signals and 
can potentially have long-term chronic effects on marine mammals at the 
population level as well as at the individual level. Low-frequency 
ambient sound levels have increased by as much as 20 dB (more than 
three times in terms of SPL) in the world's ocean from pre-industrial 
periods, with most of the increase from distant commercial shipping 
(Hildebrand, 2009). All anthropogenic sound sources, but especially 
chronic and lower-frequency signals (e.g., from vessel traffic), 
contribute to elevated ambient sound levels, thus intensifying masking.
    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited, although there are few specific data on this. Because of 
the intermittent nature and low duty cycle of seismic pulses, animals 
can emit and receive sounds in the relatively quiet intervals between 
pulses. However, in exceptional situations, reverberation occurs for 
much or all of the interval between pulses (e.g., Simard et al., 2005; 
Clark and Gagnon 2006), which could mask calls. Situations with 
prolonged strong reverberation are infrequent. However, it is common 
for reverberation to cause some lesser degree of elevation of the 
background level between airgun pulses (e.g., Gedamke 2011; Guerra et 
al., 2011, 2016; Klinck et al., 2012; Guan et al., 2015), and this 
weaker reverberation presumably reduces the detection range of calls 
and other natural sounds to some degree. Guerra et al., (2016) reported 
that ambient noise levels between seismic pulses were elevated as a 
result of reverberation at ranges of 50 km from the seismic source. 
Based on measurements in deep water of the Southern Ocean, Gedamke 
(2011) estimated that the slight elevation of background noise levels 
during intervals between seismic pulses reduced blue and fin whale 
communication space by as much as 36-51 percent when a seismic survey 
was operating 450-2,800 km away. Based on preliminary modeling, 
Wittekind et al., (2016) reported that airgun sounds could reduce the 
communication range of blue and fin whales 2,000 km from the seismic 
source. Nieukirk et al., (2012) and Blackwell et al., (2013) noted the 
potential for masking effects from seismic surveys on large whales.
    Some baleen and toothed whales are known to continue calling in the 
presence of seismic pulses, and their calls usually can be heard 
between the pulses (e.g., Nieukirk et al., 2012; Thode et al., 2012; 
Br[ouml]ker et al., 2013; Sciacca et al., 2016). Cerchio et al., (2014) 
suggested that the breeding display of humpback whales off Angola could 
be disrupted by seismic sounds, as singing activity declined with 
increasing received levels. In addition, some cetaceans are known to 
change their calling rates, shift their peak frequencies, or otherwise 
modify their vocal behavior in response to airgun sounds (e.g., Di 
Iorio and Clark 2010; Castellote et al., 2012; Blackwell et al., 2013, 
2015). The hearing systems of baleen whales are more sensitive to low-
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

[[Page 91351]]

the normally intermittent nature of seismic pulses.

Vessel Noise

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

Vessel Strike

    Vessel collisions with marine mammals, or vessel strikes, can 
result in death or serious injury of the animal. Wounds resulting from 
vessel strike may include massive trauma, hemorrhaging, broken bones, 
or propeller lacerations (Knowlton and Kraus, 2001). An animal at the 
surface may be struck directly by a vessel, a surfacing animal may hit 
the bottom of a vessel, or an animal just below the surface may be cut 
by a vessel's propeller. Superficial strikes may not kill or result in 
the death of the animal. These interactions are typically associated 
with large whales (e.g., fin whales), which are occasionally found 
draped across the bulbous bow of large commercial vessels upon arrival 
in port. Although smaller cetaceans are more maneuverable in relation 
to large vessels than are large whales, they may also be susceptible to 
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 (kn; 26 kilometers per hour (kph)), and exceeded 90 percent at 17 
kn (31 kph). Higher speeds during collisions result in greater force of 
impact, but higher speeds also appear to increase the chance of severe 
injuries or death through increased likelihood of collision by pulling 
whales toward the vessel (Clyne, 1999; Knowlton et al., 1995). In a 
separate study, Vanderlaan and Taggart (2007) analyzed the probability 
of lethal mortality of large whales at a given speed, showing that the 
greatest rate of change in the probability of a lethal injury to a 
large whale as a function of vessel speed occurs between 8.6 and 15 kn 
(28 kph). The chances of a lethal injury decline from approximately 80 
percent at 15 kn (28 kph) to approximately 20 percent at 8.6 kn (16 
kph). At speeds below 11.8 kn (22 kph), the chances of lethal injury 
drop below 50 percent, while the probability asymptotically increases 
toward 100 percent above 15 kn (28 kph).
    The McCall will travel at a speed of 4-5 kn (7-9 kph) while towing 
seismic survey gear. At this speed, both the possibility of striking a 
marine mammal and the possibility of a strike resulting in serious 
injury or mortality are discountable. At average transit speed, the 
probability of serious injury or mortality resulting from a strike is 
less than 50 percent. However, the likelihood of a strike actually 
happening is again discountable. Vessel strikes, as analyzed in the 
studies cited above, generally involve commercial shipping, which is 
much more common in both space and time than is geophysical survey 
activity. Jensen and Silber (2004) summarized vessel strikes of large 
whales worldwide from 1975 to 2003 and found that most collisions 
occurred in the open ocean and involved large vessels (e.g., commercial 
shipping). No such incidents were reported for geophysical survey 
vessels during that time period.
    It is possible for vessel strikes to occur while traveling at slow 
speeds. For example, a hydrographic survey vessel traveling at low 
speed (5.5 kn (10 kph)) while conducting mapping surveys off the 
central California coast struck and killed a blue whale in 2009. The 
State of California determined that the whale had suddenly and 
unexpectedly surfaced beneath the hull, with the result that the 
propeller severed the whale's vertebrae, and that this was an 
unavoidable event. This strike represents the only such incident in 
approximately 540,000 hours of similar coastal mapping activity (p = 
1.9 x 10-6; 95 percent confidence interval = 0-5.5 x 
10-6; NMFS, 2013). In addition, a research vessel reported a 
fatal strike in 2011 of a dolphin in the Atlantic, demonstrating that 
it is possible for strikes involving smaller cetaceans to occur. In 
that case, the incident report indicated that an animal apparently was 
struck by the vessel's propeller as it was intentionally swimming near 
the vessel. While indicative of the type of unusual events that cannot 
be ruled out, neither of these instances represents a circumstance that 
would be considered reasonably foreseeable or that would be considered 
preventable.
    Although the likelihood of the vessel striking a marine mammal is 
low, we propose a robust vessel strike avoidance protocol (see Proposed 
Mitigation), which we believe eliminates any foreseeable risk of vessel 
strike during transit. We anticipate that vessel

[[Page 91352]]

collisions involving a seismic data acquisition vessel towing gear, 
while not impossible, represent unlikely, unpredictable events for 
which there are no preventive measures. Given the proposed mitigation 
measures, the relatively slow speed of the vessel towing gear, the 
presence of bridge crew watching for obstacles at all times (including 
marine mammals), and the presence of marine mammal observers, the 
possibility of vessel strike is discountable and, further, were a 
strike of a large whale to occur, it would be unlikely to result in 
serious injury or mortality. No incidental take resulting from vessel 
strike is anticipated, and this potential effect of the specified 
activity will not be discussed further in the following analysis.
    Stranding--When a living or dead marine mammal swims or floats onto 
shore and becomes ``beached'' or incapable of returning to sea, the 
event is a ``stranding'' (Geraci et al., 1999; Perrin and Geraci, 2002; 
Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a 
stranding under the MMPA is that a marine mammal is dead and is on a 
beach or shore of the United States; or in waters under the 
jurisdiction of the United States (including any navigable waters); or 
a marine mammal is alive and is on a beach or shore of the United 
States and is unable to return to the water; on a beach or shore of the 
United States and, although able to return to the water, is in need of 
apparent medical attention; or in the waters under the jurisdiction of 
the United States (including any navigable waters), but is unable to 
return to its natural habitat under its own power or without 
assistance.
    Marine mammals strand for a variety of reasons, such as infectious 
agents, biotoxicosis, starvation, fishery interaction, vessel strike, 
unusual oceanographic or weather events, sound exposure, or 
combinations of these stressors sustained concurrently or in series. 
However, the cause or causes of most strandings are unknown (Geraci et 
al., 1976; Eaton, 1979; Odell et al., 1980; Best, 1982). Numerous 
studies suggest that the physiology, behavior, habitat relationships, 
age, or condition of cetaceans may cause them to strand or might 
predispose them to strand when exposed to another phenomenon. These 
suggestions are consistent with the conclusions of numerous other 
studies that have demonstrated that combinations of dissimilar 
stressors commonly combine to kill an animal or dramatically reduce its 
fitness, even though one exposure without the other does not produce 
the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; 
Fair and Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a; 
2005b, Romero, 2004; Sih et al., 2004).
    There is no conclusive evidence that exposure to airgun noise 
results in behaviorally-mediated forms of injury. Behaviorally-mediated 
injury (i.e., mass stranding events) has been primarily associated with 
beaked whales exposed to mid-frequency active (MFA) naval sonar. MFA 
sonar and the alerting stimulus used in Nowacek et al., (2004) are very 
different from the noise produced by airguns. One should therefore not 
expect the same reaction to airgun noise as to these other sources.
    It is important to distinguish between energy (loudness, measured 
in dB) and frequency (pitch, measured in Hz). In considering the 
potential impacts of mid-frequency components of airgun noise (1-10 
kHz, where beaked whales can be expected to hear) on marine mammal 
hearing, one needs to account for the energy associated with these 
higher frequencies and determine what energy is truly ``significant.'' 
Although there is mid-frequency energy associated with airgun noise (as 
expected from a broadband source), airgun sound is predominantly below 
1 kHz (Breitzke et al., 2008; Tashmukhambetov et al., 2008; Tolstoy et 
al., 2009). As stated by Richardson et al., (1995), ``[. . .] most 
emitted [seismic airgun] energy is at 10-120 Hz, but the pulses contain 
some energy up to 500-1,000 Hz.'' Tolstoy et al., (2009) conducted 
empirical measurements, demonstrating that sound energy levels 
associated with airguns were at least 20 dB lower at 1 kHz (considered 
``mid-frequency'') compared to higher energy levels associated with 
lower frequencies (below 300 Hz) (``all but a small fraction of the 
total energy being concentrated in the 10-300 Hz range'' [Tolstoy et 
al., 2009]), and at higher frequencies (e.g., 2.6-4 kHz), power might 
be less than 10 percent of the peak power at 10 Hz (Yoder, 2002). 
Energy levels measured by Tolstoy et al., (2009) were even lower at 
frequencies above 1 kHz. In addition, as sound propagates away from the 
source, it tends to lose higher-frequency components faster than low-
frequency components (i.e., low-frequency sounds typically propagate 
longer distances than high-frequency sounds) (Diebold et al., 2010). 
Although higher-frequency components of airgun signals have been 
recorded, it is typically in surface-ducting conditions (e.g., DeRuiter 
et al., 2006; Madsen et al., 2006) or in shallow water, where there are 
advantageous propagation conditions for the higher frequency (but low-
energy) components of the airgun signal (Hermannsen et al., 2015). This 
should not be of concern because the likely behavioral reactions of 
beaked whales that can result in acute physical injury would result 
from noise exposure at depth (because of the potentially greater 
consequences of severe behavioral reactions). In summary, the frequency 
content of airgun signals is such that beaked whales will not be able 
to hear the signals well (compared to MFA sonar), especially at depth 
where we expect the consequences of noise exposure could be more 
severe.
    Aside from frequency content, there are other significant 
differences between MFA sonar signals and the sounds produced by 
airguns that minimize the risk of severe behavioral reactions that 
could lead to strandings or deaths at sea, e.g., significantly longer 
signal duration, horizontal sound direction, typical fast and 
unpredictable source movement. All of these characteristics of MFA 
sonar tend towards greater potential to cause severe behavioral or 
physiological reactions in exposed beaked whales that may contribute to 
stranding. Although both sources are powerful, MFA sonar contains 
significantly greater energy in the mid-frequency range, where beaked 
whales hear better. Short-duration, high energy pulses--such as those 
produced by airguns--have greater potential to cause damage to auditory 
structures (though this is unlikely for high-frequency cetaceans, as 
explained later in this document), but it is longer duration signals 
that have been implicated in the vast majority of beaked whale 
strandings. Faster, less predictable movements in combination with 
multiple source vessels are more likely to elicit a severe, potentially 
anti-predator response. Of additional interest in assessing the 
divergent characteristics of MFA sonar and airgun signals and their 
relative potential to cause stranding events or deaths at sea is the 
similarity between the MFA sonar signals and stereotyped calls of 
beaked whales' primary predator: the killer whale (Zimmer and Tyack, 
2007). Although generic disturbance stimuli--as airgun noise may be 
considered in this case for beaked whales--may also trigger 
antipredator responses, stronger responses should generally be expected 
when perceived risk is greater, as when the stimulus is confused for a 
known predator (Frid and Dill, 2002). In addition, because the source 
of the perceived predator (i.e., MFA sonar) will likely be closer to 
the whales (because attenuation limits the range of detection of mid-
frequencies) and moving faster (because it will be on faster-moving 
vessels), any antipredator

[[Page 91353]]

response would be more likely to be severe (with greater perceived 
predation risk, an animal is more likely to disregard the cost of the 
response; Frid and Dill, 2002). Indeed, when analyzing movements of a 
beaked whale exposed to playback of killer whale predation calls, Allen 
et al., (2014) found that the whale engaged in a prolonged, directed 
avoidance response, suggesting a behavioral reaction that could pose a 
risk factor for stranding. Overall, these significant differences 
between sound from MFA sonar and the mid-frequency sound component from 
airguns and the likelihood that MFA sonar signals will be interpreted 
in error as a predator are critical to understanding the likely risk of 
behaviorally-mediated injury due to seismic surveys.
    The available scientific literature also provides a useful contrast 
between airgun noise and MFA sonar regarding the likely risk of 
behaviorally-mediated injury. There is strong evidence for the 
association of beaked whale stranding events with MFA sonar use, and 
particularly detailed accounting of several events is available (e.g., 
a 2000 Bahamas stranding event for which investigators concluded that 
MFA sonar use was responsible; Evans and England, 2001). D'Amico et 
al., (2009) reviewed 126 beaked whale mass stranding events over the 
period from 1950 (i.e., from the development of modern MFA sonar 
systems) through 2004. Of these, there were two events where detailed 
information was available on both the timing and location of the 
stranding and the concurrent nearby naval activity, including 
verification of active MFA sonar usage, with no evidence for an 
alternative cause of stranding. An additional 10 events were at minimum 
spatially and temporally coincident with naval activity likely to have 
included MFA sonar use and, despite incomplete knowledge of timing and 
location of the stranding or the naval activity in some cases, there 
was no evidence for an alternative cause of stranding. The U.S. Navy 
has publicly stated agreement that five such events since 1996 were 
associated in time and space with MFA sonar use, either by the U.S. 
Navy alone or in joint training exercises with the North Atlantic 
Treaty Organization. The U.S. Navy additionally noted that, as of 2017, 
a 2014 beaked whale stranding event in Crete coincident with naval 
exercises was under review and had not yet been determined to be linked 
to sonar activities (U.S. Navy, 2017). Separately, the International 
Council for the Exploration of the Sea reported in 2005 that, 
worldwide, there have been about 50 known strandings, consisting mostly 
of beaked whales, with a potential causal link to MFA sonar (ICES, 
2005). In contrast, very few such associations have been made to 
seismic surveys, despite widespread use of airguns as a geophysical 
sound source in numerous locations around the world.
    A review of possible stranding associations with seismic surveys 
(Castellote and Llorens, 2016) states that, ``[s]peculation concerning 
possible links between seismic survey noise and cetacean strandings is 
available for a dozen events but without convincing causal evidence.'' 
The authors' search of available information found 10 events worth 
further investigation via a ranking system representing a rough metric 
of the relative level of confidence offered by the data for inferences 
about the possible role of the seismic survey in a given stranding 
event. Only three of these events involved beaked whales. Whereas 
D'Amico et al., (2009) used a 1-5 ranking system, in which ``1'' 
represented the most robust evidence connecting the event to MFA sonar 
use, Castellote and Llorens (2016) used a 1-6 ranking system, in which 
``6'' represented the most robust evidence connecting the event to the 
seismic survey. As described above, D'Amico et al., (2009) found that 2 
events were ranked ``1'' and 10 events were ranked ``2'' (i.e., 12 
beaked whale stranding events were found to be associated with MFA 
sonar use). In contrast, Castellote and Llorens (2016) found that none 
of the three beaked whale stranding events achieved their highest ranks 
of 5 or 6. Of the 10 total events, none achieved the highest rank of 6. 
Two events were ranked as 5: one stranding in Peru involving dolphins 
and porpoises and a 2008 stranding in Madagascar. This latter ranking 
can only be broadly associated with the survey itself, as opposed to 
use of seismic airguns. An investigation of this stranding event, which 
did not involve beaked whales, concluded that use of a high-frequency 
mapping system (12-kHz multibeam echosounder) was the most plausible 
and likely initial behavioral trigger of the event, which was likely 
exacerbated by several site- and situation-specific secondary factors. 
The review panel found that seismic airguns were used after the initial 
strandings and animals entering a lagoon system, that airgun use 
clearly had no role as an initial trigger, and that there was no 
evidence that airgun use dissuaded animals from leaving (Southall et 
al., 2013).
    However, one of these stranding events, involving two Cuvier's 
beaked whales, was contemporaneous with and reasonably associated 
spatially with a 2002 seismic survey in the Gulf of California 
conducted by Lamont-Doherty Earth Observatory (L-DEO), as was the case 
for the 2007 Gulf of Cadiz seismic survey discussed by Castellote and 
Llorens (also involving two Cuvier's beaked whales). Neither event was 
considered a ``true atypical mass stranding'' (according to Frantzis 
(1998)) as used in the analysis of Castellote and Llorens (2016). While 
we agree with the authors that this lack of evidence should not be 
considered conclusive, it is clear that there is very little evidence 
that seismic surveys should be considered as posing a significant risk 
of acute harm to beaked whales or other high frequency cetaceans. We 
have considered the potential for the proposed surveys to result in 
marine mammal stranding and, based on the best available information, 
do not expect a stranding to occur.
    Entanglement--Entanglements occur when marine mammals become 
wrapped around cables, lines, nets, or other objects suspended in the 
water column. During seismic operations, numerous cables, lines, and 
other objects primarily associated with the airgun array and hydrophone 
streamers will be towed behind the McCall near the water's surface. 
However, we are not aware of any cases of entanglement of marine 
mammals in seismic survey equipment. There are no meaningful 
entanglement risks posed by the proposed survey, and entanglement risks 
are not discussed further in this document.

Anticipated Effects on Marine Mammal Habitat

    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

[[Page 91354]]

Hawkins, 1969; Wardle et al., 2001; Sara et al., 2007; Jorgenson and 
Gyselman, 2009; Blaxter et al., 1981; Cott et al., 2012; Boeger et al., 
2006), and that, most commonly, while there are likely to be impacts to 
fish as a result of noise from nearby airguns, such effects will be 
temporary. For example, investigators reported significant, short-term 
declines in commercial fishing catch rate of gadid fishes during and 
for up to 5 days after seismic survey operations, but the catch rate 
subsequently returned to normal (Engas et al., 1996; Engas and 
Lokkeborg, 2002). Other studies have reported similar findings (Hassel 
et al., 2004).
    Skalski et al., (1992) also found a reduction in catch rates--for 
rockfish (Sebastes spp.) in response to controlled airgun exposure--but 
suggested that the mechanism underlying the decline was not dispersal 
but rather decreased responsiveness to baited hooks associated with an 
alarm behavioral response. A companion study showed that alarm and 
startle responses were not sustained following the removal of the sound 
source (Pearson et al., 1992). Therefore, Skalski et al., (1992) 
suggested that the effects on fish abundance may be transitory, 
primarily occurring during the sound exposure itself. In some cases, 
effects on catch rates are variable within a study, which may be more 
broadly representative of temporary displacement of fish in response to 
airgun noise (i.e., catch rates may increase in some locations and 
decrease in others) than any long-term damage to the fish themselves 
(Streever et al., 2016).
    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., (2012) showed that a TTS of 4-6 dB was recoverable within 24 hours 
for one species. Impacts would be most severe when the individual fish 
is close to the source and when the duration of exposure is long; both 
of which are conditions unlikely to occur for this survey that is 
necessarily transient in any given location and likely result in brief, 
infrequent noise exposure to prey species in any given area. For this 
survey, the sound source is constantly moving, and most fish would 
likely avoid the sound source prior to receiving sound of sufficient 
intensity to cause physiological or anatomical damage. In addition, 
ramp-up may allow certain fish species the opportunity to move further 
away from the sound source.
    A comprehensive review (Carroll et al., 2017) found that results 
are mixed as to the effects of airgun noise on the prey of marine 
mammals. While some studies suggest a change in prey distribution and/
or a reduction in prey abundance following the use of seismic airguns, 
others suggest no effects or even positive effects in prey abundance. 
As one specific example, Paxton et al., (2017), which describes 
findings related to the effects of a 2014 seismic survey on a reef off 
of North Carolina, showed a 78 percent decrease in observed nighttime 
abundance for certain species. It is important to note that the evening 
hours during which the decline in fish habitat use was recorded (via 
video 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.
    A review article concluded that, while laboratory results provide 
scientific evidence for high-intensity and low-frequency sound-induced 
physical trauma and other negative effects on some fish and 
invertebrates, the sound exposure scenarios in some cases are not 
realistic to those encountered by marine organisms during routine 
seismic operations (Carroll et al., 2017). The review finds that there 
has been no evidence of reduced catch or abundance following seismic 
activities for invertebrates, and that there is conflicting evidence 
for fish with catch observed to increase, decrease, or remain the same. 
Further, where there is evidence for decreased catch rates in response 
to airgun noise, these findings provide no information about the 
underlying biological cause of catch rate reduction (Carroll et al., 
2017).
    In summary, impacts of the specified activity on marine mammal prey 
species will likely generally 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

[[Page 91355]]

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

Estimated Take of Marine Mammals

    This section provides an estimate of the number of incidental takes 
proposed for authorization through the IHA, which will inform NMFS' 
consideration of ``small numbers,'' the negligible impact 
determinations, and impacts on subsistence uses.
    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, in the form 
of disruption of behavioral patterns for individual marine mammals 
resulting from exposure to sound from low energy seismic airguns. Based 
on the nature of the activity, i.e., use of a low energy 2-airgun 
array, auditory injury (Level A harassment) is neither anticipated nor 
proposed to be authorized. As described previously, no serious injury 
or mortality is anticipated or proposed to be authorized for this 
activity. Below we describe how the proposed take numbers are 
estimated.
    For acoustic impacts, generally speaking, we estimate take by 
considering: (1) acoustic thresholds above which NMFS believes the best 
available science indicates marine mammals will likely be behaviorally 
harassed or incur some degree of permanent hearing impairment; (2) the 
area or volume of water that will be ensonified above these levels in a 
day; (3) the density or occurrence of marine mammals within these 
ensonified areas; and, (4) the number of days of activities. We note 
that while these factors can contribute to a basic calculation to 
provide an initial prediction of potential takes, additional 
information that can qualitatively inform take estimates is also 
sometimes available (e.g., previous monitoring results or average group 
size). Below, we describe the factors considered here in more detail 
and present the proposed take estimates.

Acoustic Thresholds

    NMFS recommends the use of acoustic thresholds that identify the 
received level of underwater sound above which exposed marine mammals 
would be reasonably expected to be behaviorally harassed (equated to 
Level B harassment) or to incur auditory injury of some degree (equated 
to Level A harassment).
    Level B Harassment--Though significantly driven by received level, 
the onset of behavioral disturbance from anthropogenic noise exposure 
is also informed to varying degrees by other factors related to the 
source or exposure context (e.g., frequency, predictability, duty 
cycle, duration of the exposure, signal-to-noise ratio, distance to the 
source), the environment (e.g., bathymetry, other noises in the area, 
predators in the area), and the receiving animals (hearing, motivation, 
experience, demography, life stage, depth) and can be difficult to 
predict (e.g., Southall et al., 2007, 2021, Ellison et al., 2012). 
Based on what the available science indicates and the practical need to 
use a threshold based on a metric that is both predictable and 
measurable for most activities, NMFS typically uses a generalized 
acoustic threshold based on received level to estimate the onset of 
behavioral harassment. NMFS generally predicts that marine mammals are 
likely to be behaviorally harassed in a manner considered to be Level B 
harassment when exposed to underwater anthropogenic noise above root-
mean-squared pressure received levels (RMS SPL) of 120 dB (referenced 
to 1 micropascal (re 1 [mu]Pa)) for continuous (e.g., vibratory pile 
driving, drilling) and above RMS SPL 160 dB re 1 [mu]Pa for non-
explosive impulsive (e.g., seismic airguns) or intermittent (e.g., 
scientific sonar) sources. Generally speaking, Level B harassment take 
estimates based on these behavioral harassment thresholds are expected 
to include any likely takes by TTS as, in most cases, the likelihood of 
TTS occurs at distances from the source less than those at which 
behavioral harassment is likely. TTS of a sufficient degree can 
manifest as behavioral harassment, as reduced hearing sensitivity and 
the potential reduced opportunities to detect important signals 
(conspecific communication, predators, prey) may result in changes in 
behavior patterns that would not otherwise occur.
    UT's proposed survey includes the use of impulsive seismic sources 
(e.g., GI-airguns) and therefore, the 160 dB re 1 [mu]Pa (rms) criteria 
is applicable for analysis of Level B harassment.
    Level A harassment--NMFS' Technical Guidance for Assessing the 
Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) 
(Technical Guidance, 2018) identifies dual criteria to assess auditory 
injury

[[Page 91356]]

(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). UT's proposed 
survey includes the use of impulsive seismic sources (i.e. airguns).
    These thresholds are provided in the tables below. The references, 
analysis, and methodology used in the development of the thresholds are 
described in NMFS' 2018 Updated Technical Guidance, which may be 
accessed at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

  Table 3--NMFS' 2018 \1\ 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   Cell 2:
                                 dB; LE,LF,24h: 183 dB.  LE,LF,24h: 199
                                                         dB.
High-Frequency (HF) Cetaceans.  Cell 3: Lpk,flat: 230   Cell 4:
                                 dB; LE,MF,24h: 185 dB.  LE,MF,24h: 198
                                                         dB.
Very High-Frequency (VHF)       Cell 5: Lpk,flat: 202   Cell 6:
 Cetaceans.                      dB; LE,HF,24h: 155 dB.  LE,HF,24h: 173
                                                         dB.
Phocid Pinnipeds (PW)           Cell 7: Lpk,flat: 218   Cell 8:
 (Underwater).                   dB; LE,PW,24h: 185 dB.  LE,PW,24h: 201
                                                         dB.
Otariid Pinnipeds (OW)          Cell 9: Lpk,flat: 232   Cell 10:
 (Underwater).                   dB; LE,OW,24h: 203 dB.  LE,OW,24h: 219
                                                         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.
\1\ UT previously used modeling based on NMFS' 2018 technical guidance
  in order to calculate their isopleths. Based on the outcome of these
  comparisons/analyses using the Updated 2024 Technical Guidance, the
  low-frequency cetacean isopleth is slightly higher using the updated
  guidance, and the high-frequency cetacean and very-high frequency
  cetacean are the same as those calculated using the 2018 Technical
  Guidance. Therefore, the isopleths based on the 2018 Technical
  Guidance will be used as the basis for take numbers and mitigation
  zones for this IHA.

Ensonified Area

    Here, we describe operational and environmental parameters of the 
activity that are used in estimating the area ensonified above the 
acoustic thresholds, including source levels and transmission loss 
coefficient.
    When the Technical Guidance was initially published (NMFS, 2016), 
in recognition of the fact that ensonified area/volume could be more 
technically challenging to predict because of the duration component in 
the new thresholds, we developed a user spreadsheet that includes tools 
to help predict a simple isopleth that can be used in conjunction with 
marine mammal density or occurrence to help predict takes. We note that 
because of some of the assumptions included in the methods used for 
these tools, we anticipate that isopleths produced are typically going 
to be overestimates of some degree, which may result in some degree of 
overestimation of Level A harassment take. However, these tools offer 
the best way to predict appropriate isopleths when more sophisticated 
3D modeling methods are not available, and NMFS continues to develop 
ways to quantitatively refine these tools and will qualitatively 
address the output where appropriate.
    The proposed survey would entail the use up to two 105 in\3\ 
airguns with a maximum total discharge of 210 in\3\ at a tow depth of 
3-4 m. UT used modeling by Lamont-Doherty Earth Observatory (L-DEO), 
which determines the 160 dBrms radius for the airgun source 
down to a maximum depth of 2,000 m. Received sound levels have been 
predicted by L-DEO's model (Diebold et al., 2010) as a function of 
distance from the 2-airgun array. This modeling approach uses ray 
tracing for the direct wave traveling from the array to the receiver 
and its associated source ghost (reflection at the air-water interface 
in the vicinity of the array), in a constant-velocity half-space 
(infinite homogeneous ocean layer, unbounded by a seafloor).
    The proposed low-energy survey would acquire data with up to two 
105-in\3\ GI guns, towed in-line, at a depth of 3-4 m. The shallow-
water radii are obtained by scaling the empirically derived 
measurements from the GOM calibration survey to account for the 
differences in volume and tow depth between the calibration survey 
(6,600 in\3\ at 6 m tow depth) and the proposed survey (210 in\3\ at 4 
m tow depth). A simple scaling factor is calculated from the ratios of 
the isopleths calculated by the deep-water L-DEO model, which are 
essentially a measure of the energy radiated by the source array.
    L-DEO's methodology is described in greater detail in UT's IHA 
application. The estimated distances to the Level B harassment isopleth 
for the proposed airgun configuration are shown in table 4.

   Table 4--Predicted Radial Distances From the R/V McCall Seismic Source to Isopleth Corresponding to Level B
                                              Harassment Threshold
----------------------------------------------------------------------------------------------------------------
                                                                                                    Predicted
                                                                                                  distances  (in
                                                                Max tow depth     Water depth       m) to  the
                     Airgun configuration                            (m)              (m)            Level B
                                                                                                    harassment
                                                                                                    threshold
----------------------------------------------------------------------------------------------------------------
2 105-in\3\ airguns..........................................               4             <100            1,750
----------------------------------------------------------------------------------------------------------------


[[Page 91357]]


 Table 5--Modeled Radial Distance to Isopleths Corresponding to Level A
                          Harassment Thresholds
                               [NMFS 2018]
------------------------------------------------------------------------
                                                                 High
                                                              frequency
                                                              cetaceans
------------------------------------------------------------------------
PTS SELcum.................................................            0
PTS Peak...................................................        * 1.5
------------------------------------------------------------------------
* The largest distance of the dual criteria (SELcum or Peak) was used to
  estimate threshold distances and potential takes by Level A
  harassment.

    Table 5 presents the modeled Level A harassment isopleths for the 
high-frequency cetacean hearing group based on L-DEO modeling 
incorporated in the companion user spreadsheet, for the low-energy 
surveys with the shortest shot interval (i.e., greatest potential to 
cause auditory injury or PTS based on accumulated sound energy) (NMFS 
2018). Although NMFS' 2024 Updated Technical Guidance was finalized on 
October 24, 2024 (89 FR 84872), there was no meaningful change in the 
auditory injury (Level A harassment) isopleths, so the values based on 
the 2018 guidance was used here.
    Predicted distances to Level A harassment isopleths, which vary 
based on marine mammal hearing groups, were calculated based on 
modeling performed by L-DEO using the Nucleus software program and the 
NMFS user spreadsheet, described below. The acoustic thresholds for 
impulsive sounds contained in the NMFS Technical Guidance were 
presented as dual metric acoustic thresholds using both 
SELcum and peak sound pressure metrics (NMFS, 2024). As dual 
metrics, NMFS considers onset of PTS (Level A harassment) to have 
occurred when either one of the two metrics is exceeded (i.e., metric 
resulting in the largest isopleth). The SELcum metric 
considers both level and duration of exposure, as well as auditory 
weighting functions by marine mammal hearing group.
    The SELcum for the 2-airgun array is derived from 
calculating the modified farfield signature. The farfield signature is 
often used as a theoretical representation of the source level. To 
compute the farfield signature, the source level is estimated at a 
large distance (right) below the array (e.g., 9 km), and this level is 
back projected mathematically to a notional distance of 1 m from the 
array's geometrical center. However, it has been recognized that the 
source level from the theoretical farfield signature is never 
physically achieved at the source when the source is an array of 
multiple airguns separated in space (Tolstoy et al., 2009). Near the 
source (at short ranges, distances <1 km), the pulses of sound pressure 
from each individual airgun in the source array do not stack 
constructively as they do for the theoretical farfield signature. The 
pulses from the different airguns spread out in time such that the 
source levels observed or modeled are the result of the summation of 
pulses from a few airguns, not the full array (Tolstoy et al., 2009). 
At larger distances, away from the source array center, sound pressure 
of all the airguns in the array stack coherently, but not within one 
time sample, resulting in smaller source levels (a few dB) than the 
source level derived from the farfield signature. Because the farfield 
signature does not take into account the large array effect near the 
source and is calculated as a point source, the farfield signature is 
not an appropriate measure of the sound source level for large arrays. 
See UT's application for further detail on acoustic modeling.
    Auditory injury is unlikely to occur for high-frequency cetaceans, 
given the very small modeled zones of injury for those species (all 
estimated zones are less than 10 m for high-frequency cetaceans), in 
the context of distributed source dynamics.
    In consideration of the received sound levels in the near-field as 
described above, we expect the potential for Level A harassment of 
high-frequency cetaceans to be de minimis, even before the likely 
moderating effects of aversion and/or other compensatory behaviors 
(e.g., Nachtigall et al., 2018) are considered. We do not anticipate 
that Level A harassment is a likely outcome for any high-frequency 
cetacean and do not propose to authorize any take by Level A harassment 
for these species.
    The Level A and Level B harassment estimates are based on a 
consideration of the number of marine mammals that could be within the 
area around the operating airgun array where received levels of sound 
>=160 dB re 1 [micro]Pa rms are predicted to occur. The estimated 
numbers are based on the densities (numbers per unit area) of marine 
mammals expected to occur in the area in the absence of seismic 
surveys. To the extent that marine mammals tend to move away from 
seismic sources before the sound level reaches the criterion level and 
tend not to approach an operating airgun array, these estimates likely 
overestimate the numbers actually exposed to the specified level of 
sound.

Marine Mammal Occurrence

    In this section we provide information about the occurrence of 
marine mammals, including density or other relevant information which 
will inform the take calculations.
    For the proposed survey area in the NW GOM, UT 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 Garrison et al., (2023). The Garrison et al., (2023) data 
provides abundance estimates for marine mammal species in the GOM 
within 40 km\2\ hexagons (~3.9 km sides and ~7 km across from each 
side) on a monthly basis. To calculate expected densities specific to 
the survey area, UT calculated the mean of the predicted densities from 
the cells within the combined survey area (primary and alternate survey 
area) for each species and month. The highest mean monthly density was 
chosen for each species from the months of January to April (i.e., the 
months within which the survey is expected to occur).
    Rough-toothed dolphins were not modeled by Garrison et al., (2023) 
due to a lack of sightings, so habitat-based marine mammal density 
estimates from Roberts et al., (2016) were used. The Roberts et al., 
(2016) models consisted of 10 km x 10 km grid cells containing average 
annual densities for U.S. waters in the GOM. The combined survey area 
was used to select grid cells from the Roberts et al., (2016) dataset, 
and the mean of the selected grid cells for rough-toothed dolphins was 
calculated to estimate the annual average density of the species in the 
survey area. Estimated densities used and Level B harassment ensonified 
areas to inform take estimates are presented in table 6.

Table 6--Marine Mammal Densities and Total Ensonified Area of Activities
                       in the Proposed Survey Area
------------------------------------------------------------------------
                                                               Level B
                                                 Estimated    ensonified
                    Species                     density  (#/     area
                                                   km\2\)      (km\2\)
------------------------------------------------------------------------
Atlantic spotted dolphin......................   \b\ 0.0043        1,522
Bottlenose dolphin \a\........................   \b\ 0.8596        1,522
Rough-toothed dolphin.........................   \c\ 0.0037        1,522
------------------------------------------------------------------------
\a\ Bottlenose dolphin density estimate does not differentiate between
  coastal and shelf stocks.
\b\ Density calculated from Garrison et al., (2023).
\c\ Density calculated from Roberts et al., (2016).


[[Page 91358]]

Take Estimation

    Here we describe how the information provided above is synthesized 
to produce a quantitative estimate of the take that is reasonably 
likely to occur and proposed for authorization. In order to estimate 
the number of marine mammals predicted to be exposed to sound levels 
that would result in Level B harassment, radial distances from the 
airgun array to the predicted isopleth corresponding to the Level B 
harassment threshold was calculated, as described above. Those radial 
distances were then used to calculate the area(s) around the airgun 
array predicted to be ensonified to sound levels that exceed the 
harassment thresholds. The area expected to be ensonified on 1 day was 
determined by multiplying the number of line km possible in 1 day by 
two times the 160-dB radius plus adding endcaps to the start and 
beginning of the line. The daily ensonified area was then multiplied by 
the number of survey days (20 days). The highest mean monthly density 
for each species was then multiplied by the total ensonified area to 
calculate the estimated takes of each species.
    No takes by Level A harassment are expected or proposed for 
authorization. Estimated takes for the proposed survey are shown in 
table 7.

                               Table 7--Estimated Take Proposed for Authorization
----------------------------------------------------------------------------------------------------------------
                                                                             Proposed
                                                               Estimated    authorized     Stock      Percent of
             Common name                       Stock            Level B      Level B     abundance      stock
                                                                  take         take         \1\
----------------------------------------------------------------------------------------------------------------
Atlantic spotted dolphin............  GOM...................            7       \2\ 26       21,506         0.12
Bottlenose dolphin \3\..............  GOM Western Coastal...        1,309        1,309       20,759         6.31
                                      Northern GOM                                           63,280         2.07
                                       Continental Shelf.
Rough-toothed dolphin...............  GOM...................            6       \2\ 14        4,853         0.29
----------------------------------------------------------------------------------------------------------------
\1\ Stock abundance for Atlantic spotted dolphins and bottlenose dolphins was taken from Garrison et al.,
  (2023). Stock abundance for rough-toothed dolphins was taken from Roberts et al., (2016), as Garrison et al.,
  (2023) did not create a model for this species.
\2\ Proposed take increased to mean group size from Maze-Foley and Mullin (2006).
\3\ Estimated take for bottlenose dolphins is not apportioned to stock, as density information does not
  differentiate between coastal and shelf dolphins. However, based on the proposed survey depths, we expect that
  most of the takes would be from the coastal stock, but some takes could be from the shelf stock. Percent of
  stock was calculated as if all takes proposed for authorization accrued to the single stock with the lowest
  population abundance.

Proposed Mitigation

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

Vessel-Visual Based 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. PSOs shall 
establish and monitor a pre-start clearance zone and, to the extent 
practicable, a Level B harassment zone (Table 4). These zones shall be 
based upon the radial distance from the edges of the acoustic source 
(rather than being based on the center of the array or around the 
vessel itself). During pre-start clearance (i.e., before ramp-up 
begins), the pre-start clearance zone is the area in which observations 
of marine mammals within the zone would prevent airgun operations from 
beginning (i.e., ramp-up). The pre-start clearance zone encompasses the 
area at and below the sea surface out to a radius of 200 meters from 
the edges of the airgun array.
    During survey operations (e.g., any day on which use of the 
acoustic source is planned to occur, and whenever the acoustic source 
is in the water, whether activated or not), a minimum of two PSOs must 
be on duty and conducting visual observations at all times during 
daylight hours (i.e., from 30 minutes prior to sunrise through 30 
minutes following sunset). Visual monitoring must begin no less than 30 
minutes prior to ramp-up and must continue until 1 hour after use of 
the acoustic source ceases or until 30 minutes past sunset. Visual PSOs 
must coordinate to ensure 360 degree visual coverage around the vessel 
from the most appropriate observation posts, and must conduct visual 
observations using binoculars and the naked eye while free from 
distractions and in a consistent, systematic, and diligent manner.
    PSOs shall establish and monitor a pre-start clearance zone and to 
the extent practicable, a Level B harassment zone. These zones shall be 
based upon the radial distance from the edges of the acoustic source 
(rather than being based on the center of the array or around the 
vessel itself). Any observations of marine mammals by crew members 
shall be relayed to the PSO team. During good conditions (e.g., 
daylight hours, Beaufort sea state (BSS) 3 or less), visual PSOs shall 
conduct observations when the acoustic source is not operating for

[[Page 91359]]

comparison of sightings rates and behavior with and without use of the 
acoustic source and between acquisition periods, to the maximum extent 
practicable.
    Visual PSOs may be on watch for a maximum of 4 consecutive hours 
followed by a break of at least 1 hour between watches and may conduct 
a maximum of 12 hours of observation per 24-hour period.

Pre-Start Clearance and Ramp-Up

    Ramp-up (sometimes referred to as ``soft start'') means the gradual 
and systematic increase of emitted sound levels from an airgun array. 
The intent of pre-start clearance observation (30 minutes) is to ensure 
no marine mammals are observed within the pre-start clearance zone 
prior to the beginning of ramp-up. The intent of the ramp-up is to warn 
marine mammals of pending seismic survey operations and to allow 
sufficient time for those animals to leave the immediate vicinity prior 
to the sound source reaching full intensity. A ramp-up procedure, 
involving a stepwise increase in the number of airguns firing and total 
array volume until all operational airguns are activated and the full 
volume is achieved, is required at all times as part of the activation 
of the airgun array. All operators must adhere to the following pre-
start clearance and ramp-up requirements:
     The operator must notify a designated PSO of the planned 
start of ramp-up as agreed upon with the lead PSO; the notification 
time should not be less than 60 minutes prior to the planned ramp-up in 
order to allow PSOs time to monitor the pre-start clearance zone for 30 
minutes prior to the initiation of ramp-up (pre-start clearance).
     Ramp-ups shall be scheduled so as to minimize the time 
spent with the source activated prior to reaching the designated run-
in.
     One of the PSOs conducting pre-start clearance 
observations must be notified again immediately prior to initiating 
ramp-up procedures and the operator must receive confirmation from the 
PSO to proceed.
     Ramp-up may not be initiated if any marine mammal is 
within the pre-start clearance zone. If a marine mammal is observed 
within the pre-start clearance zone during the 30 minutes pre-clearance 
period, ramp-up may not begin until the animal(s) has been observed 
exiting the zone or until an additional time period has elapsed with no 
further sightings (15 minutes for small delphinids and 30 minutes for 
all other species).
     Ramp-up must begin by activating one GI airgun for no less 
than 5 minutes and then activating the second airgun. The operator must 
provide information to the PSO documenting that appropriate procedures 
were followed.
     PSOs must monitor the pre-start clearance zone during 
ramp-up, and ramp-up must cease and the source must be shut down upon 
detection of a marine mammal within the pre-start clearance zone. Once 
ramp-up has begun, observations of marine mammals for which take 
authorization is granted within the pre-start clearance zone does not 
require shutdown.
     If the acoustic source is shut down for brief periods 
(i.e., less than 30 minutes) for reasons other than implementation of 
prescribed mitigation (e.g., mechanical difficulty), it may be 
activated again without ramp-up if PSOs have maintained constant 
observation and no detections of marine mammals have occurred within 
the pre-start clearance zone. For any longer shutdown, pre-start 
clearance observation and ramp-up are required. Ramp-up may occur at 
times of poor visibility (e.g., BSS 4 or greater), including nighttime, 
if appropriate visual monitoring has occurred with no detections of 
marine mammals in the 30 minutes prior to beginning ramp-up. Acoustic 
source activation may only occur at night where operational planning 
cannot reasonably avoid such circumstances.
     Testing of the acoustic source involving all elements 
requires ramp-up. Testing limited to individual source elements or 
strings does not require ramp-up but does require a 30-minute pre-start 
clearance period.

Shutdown Procedures

    The shutdown of an airgun array requires the immediate de-
activation of all individual airgun elements of the array. Any PSO on 
duty will have the authority to call for shutdown of the airgun array. 
The operator must also establish and maintain clear lines of 
communication directly between PSOs on duty and crew controlling the 
airgun array to ensure that shutdown commands are conveyed swiftly 
while allowing PSOs to maintain watch. The shutdown requirement will be 
waived for small dolphins. As defined here, the small dolphin group is 
intended to encompass those members of the Family Delphinidae most 
likely to voluntarily approach the source vessel for purposes of 
interacting with the vessel and/or airgun array (e.g., bow riding). 
This exception to the shutdown requirement applies solely to specific 
genera of small dolphins--Steno, Stenella, and Tursiops. As Tursiops, 
Stenella, and Steno are the only species expected to potentially be 
encountered, there is no shutdown requirement included in the proposed 
IHA for species for which take is proposed to be authorized. UT must 
implement shutdown if a marine mammal species for which take was not 
authorized or a species for which authorization was granted but the 
authorized takes have been met approaches the Level B harassment zone.
    We include this small dolphin exception because shutdown 
requirements for these species under all circumstances represent 
practicability concerns without likely commensurate benefits for the 
animals in question. Small dolphins are generally the most commonly 
observed marine mammals in the specific geographic region and would 
typically be the only marine mammals likely to intentionally approach 
the vessel. As described above, auditory injury is extremely unlikely 
to occur for high-frequency cetaceans (e.g., delphinids), as this group 
is relatively insensitive to sound produced at the predominant 
frequencies in an airgun pulse while also having a relatively high 
threshold for the onset of auditory injury (i.e., permanent threshold 
shift).
    A large body of anecdotal evidence indicates that small dolphins 
commonly approach vessels and/or towed arrays during active sound 
production for purposes of bow riding with no apparent effect observed 
(e.g., Barkaszi et al., 2012; Barkaszi and Kelly, 2018). The potential 
for increased shutdowns resulting from such a measure would require the 
McCall 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.

Vessel Strike Avoidance Mitigation Measures

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

[[Page 91360]]

    Vessel operators and crews must maintain a vigilant watch for all 
marine mammals and slow down, stop their vessel, or alter course, as 
appropriate and regardless of vessel size, to avoid striking any marine 
mammal. A single marine mammal at the surface may indicate the presence 
of submerged animals in the vicinity of the vessel; therefore, 
precautionary measures should always be exercised. A visual observer 
aboard the vessel must monitor a vessel strike avoidance zone around 
the vessel (separation distances stated below). Visual observers 
monitoring the vessel strike avoidance zone may be third-party 
observers (i.e., PSOs) or crew members, but crew members responsible 
for these duties must be provided sufficient training to (1) 
distinguish marine mammals from other phenomena and (2) broadly to 
identify a marine mammal as a right whale, other whale (defined in this 
context as sperm whales or baleen whales other than right whales), or 
other marine mammals.
    Vessel speeds must be reduced to 10 kn (18.5 kph) or less when 
mother/calf pairs, pods, or large assemblages of cetaceans are observed 
near a vessel. The vessel must maintain a minimum separation distance 
of 500 m from baleen whales. If a baleen whale is sighted within the 
relevant separation distance, the vessel must steer a course away at 10 
knots or less until the 500-m separation distance is established. If a 
whale is observed but cannot be confirmed as a species other than a 
baleen whale, the vessel operator must assume that it is a baleen whale 
and take appropriate action. All vessels must maintain a minimum 
separation distance of 100 m from sperm whales. All vessels must, to 
the maximum extent practicable, attempt to maintain a minimum 
separation distance of 50 m from all other marine mammals, with an 
understanding that at times this may not be possible (e.g., for animals 
that approach the vessel).
    When marine mammals are sighted while a vessel is underway, the 
vessel shall take action as necessary to avoid violating the relevant 
separation distance (e.g., attempt to remain parallel to the animal's 
course, avoid excessive speed or abrupt changes in direction until the 
animal has left the area). If marine mammals are sighted within the 
relevant separation distance, the vessel must reduce speed and shift 
the engine to neutral, not engaging the engines until animals are clear 
of the area. This does not apply to any vessel towing gear or any 
vessel that is navigationally constrained.
    Based on our evaluation of the applicant's proposed measures, as 
well as other measures considered by NMFS, NMFS has preliminarily 
determined that the proposed mitigation measures provide the means of 
effecting the least practicable impact on the affected species or 
stocks and their habitat, paying particular attention to rookeries, 
mating grounds, and areas of similar significance.

Proposed Monitoring and Reporting

    In order to issue an IHA for an activity, section 101(a)(5)(D) of 
the MMPA states that NMFS must set forth requirements pertaining to the 
monitoring and reporting of such taking. The MMPA implementing 
regulations at 50 CFR 216.104(a)(13) indicate that requests for 
authorizations must include the suggested means of accomplishing the 
necessary monitoring and reporting that will result in increased 
knowledge of the species and of the level of taking or impacts on 
populations of marine mammals that are expected to be present while 
conducting the activities. Effective reporting is critical both to 
compliance as well as ensuring that the most value is obtained from the 
required monitoring.
    Monitoring and reporting requirements prescribed by NMFS should 
contribute to improved understanding of one or more of the following:
     Occurrence of marine mammal species or stocks in the area 
in which take is anticipated (e.g., presence, abundance, distribution, 
density);
     Nature, scope, or context of likely marine mammal exposure 
to potential stressors/impacts (individual or cumulative, acute or 
chronic), through better understanding of: (1) action or environment 
(e.g., source characterization, propagation, ambient noise); (2) 
affected species (e.g., life history, dive patterns); (3) co-occurrence 
of marine mammal species with the activity; or (4) biological or 
behavioral context of exposure (e.g., age, calving or feeding areas);
     Individual marine mammal responses (behavioral or 
physiological) to acoustic stressors (acute, chronic, or cumulative), 
other stressors, or cumulative impacts from multiple stressors;
     How anticipated responses to stressors impact either: (1) 
long-term fitness and survival of individual marine mammals; or (2) 
populations, species, or stocks;
     Effects on marine mammal habitat (e.g., marine mammal prey 
species, acoustic habitat, or other important physical components of 
marine mammal habitat); and,
     Mitigation and monitoring effectiveness.

Vessel-Based Visual Monitoring

    As described above, PSO observations would take place during 
daytime airgun operations. During seismic survey operations, two visual 
PSOs would be on duty at all times during daytime hours. The operator 
will work with the selected third-party observer provider to ensure 
PSOs have all equipment (including backup equipment) needed to 
adequately perform necessary tasks, including accurate determination of 
distance and bearing to observed marine mammals. SIO must use 
dedicated, trained, and NMFS-approved PSOs. At least one visual PSO 
aboard the vessel must have a minimum of 90 days at-sea experience 
working in those roles, respectively, with no more than 18 months 
elapsed since the conclusion of the at-sea experience. One visual PSO 
with such experience shall be designated as the lead for the entire 
protected species observation team. The lead PSO shall serve as primary 
point of contact for the vessel operator and ensure all PSO 
requirements per the IHA are met. To the maximum extent practicable, 
the experienced PSOs should be scheduled to be on duty with those PSOs 
with appropriate training but who have not yet gained relevant 
experience. 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. Monitoring shall be conducted in accordance with the 
following requirements:
     PSOs shall be independent, dedicated, trained visual PSOs 
and must be employed by a third-party observer provider.
     PSOs shall have no tasks other than to conduct 
observational effort, collect data, and communicate with and instruct 
relevant vessel crew with regard to the presence of protected species 
and mitigation requirements (including brief alerts regarding maritime 
hazards).
     PSOs shall have successfully completed an approved PSO 
training course appropriate for their designated task.
     NMFS must review and approve PSO resumes accompanied by a 
relevant training course information packet that includes the name and 
qualifications (i.e., experience, training completed, or educational 
background) of the

[[Page 91361]]

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

Reporting

    UT shall submit a draft comprehensive report on all activities and 
monitoring results within 90 days of the completion of the survey or 
expiration of the IHA, whichever comes sooner. The report must describe 
all activities conducted and sightings of marine mammals, must provide 
full documentation of methods, results, and interpretation pertaining 
to all monitoring, and must summarize the dates and locations of survey 
operations and all marine mammal sightings (dates, times, locations, 
activities, associated survey activities). The draft report shall also 
include geo-referenced time-stamped vessel tracklines for all time 
periods during which airgun arrays were operating. Tracklines should

[[Page 91362]]

include points recording any change in airgun array status (e.g., when 
the sources began operating, when they were turned off, or when they 
changed operational status such as from full array to single gun or 
vice versa). Geographic Information System files shall be provided in 
Environmental Systems Research Institute shapefile format and include 
the UTC date and time, latitude in decimal degrees, and longitude in 
decimal degrees. All coordinates shall be referenced to the WGS84 
geographic coordinate system. In addition to the report, all raw 
observational data shall be made available. The report must summarize 
data collected as described above in Proposed Monitoring and Reporting. 
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 the survey activities discover an injured or dead 
marine mammal, UT shall report the incident to the Office of Protected 
Resources (OPR), NMFS and the NMFS, Southeast Regional Stranding 
Coordinator as soon as feasible. The report must include the following 
information:
     Time, date, and location (latitude/longitude) of the first 
discovery (and updated location information if known and applicable);
     Species identification (if known) or description of the 
animal(s) involved;
     Condition of the animal(s) (including carcass condition if 
the animal is dead);
     Observed behaviors of the animal(s), if alive;
     If available, photographs or video footage of the 
animal(s); and
     General circumstances under which the animal was 
discovered.
    Vessel strike--In the event of a strike of a marine mammal by any 
vessel involved in the activities covered by the authorization, UT 
shall report the incident to OPR, NMFS, and the NMFS Southeast Regional 
Stranding Coordinator as soon as feasible. The report must include the 
following information:
     Time, date, and location (latitude/longitude) of the 
incident;
     Vessel's speed during and leading up to the incident;
     Vessel's course/heading and what operations were being 
conducted (if applicable);
     Status of all sound sources in use;
     Description of avoidance measures/requirements that were 
in place at the time of the strike and what additional measure were 
taken, if any, to avoid strike;
     Environmental conditions (e.g., wind speed and direction, 
BSS, cloud cover, visibility) immediately preceding the strike;
     Species identification (if known) or description of the 
animal(s) involved;
     Estimated size and length of the animal that was struck;
     Description of the behavior of the marine mammal 
immediately preceding and following the strike;
     If available, description of the presence and behavior of 
any other marine mammals present immediately preceding the strike;
     Estimated fate of the animal (e.g., dead, injured but 
alive, injured and moving, blood or tissue observed in the water, 
status unknown, disappeared); and
     To the extent practicable, photographs or video footage of 
the animal(s).

Negligible Impact Analysis and Determination

    NMFS has defined negligible impact as an impact resulting from the 
specified activity that cannot be reasonably expected to, and is not 
reasonably likely to, adversely affect the species or stock through 
effects on annual rates of recruitment or survival (50 CFR 216.103). A 
negligible impact finding is based on the lack of likely adverse 
effects on annual rates of recruitment or survival (i.e., population-
level effects). An estimate of the number of takes alone is not enough 
information on which to base an impact determination. In addition to 
considering estimates of the number of marine mammals that might be 
``taken'' through harassment, NMFS considers other factors, such as the 
likely nature of any impacts or responses (e.g., intensity, duration), 
the context of any impacts or responses (e.g., critical reproductive 
time or location, foraging impacts affecting energetics), as well as 
effects on habitat, and the likely effectiveness of the mitigation. We 
also assess the number, intensity, and context of estimated takes by 
evaluating this information relative to population status. Consistent 
with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, 
September 29, 1989), the impacts from other past and ongoing 
anthropogenic activities are incorporated into this analysis via their 
impacts on the baseline (e.g., as reflected in the regulatory status of 
the species, population size and growth rate where known, ongoing 
sources of human-caused mortality, or ambient noise levels).
    To avoid repetition, the discussion of our analysis applies to 
Atlantic spotted dolphins, bottlenose dolphins, and rough-toothed 
dolphins, given that the anticipated effects of this activity on these 
different marine mammal stocks are expected to be similar. There is 
little information about the nature or severity of the impacts, or the 
size, status, or structure of any of these species or stocks that would 
lead to a different analysis for this activity.
    NMFS does not anticipate that serious injury or mortality would 
occur as a result of UT's planned survey, even in the absence of 
mitigation, and no serious injury or mortality is proposed to be 
authorized. As discussed in the Potential Effects of Specified 
Activities on Marine Mammals and Their Habitat section above, non-
auditory physical effects and vessel strike are not expected to occur. 
NMFS expects that all potential take would be in the form of Level B 
behavioral harassment in the form of temporary avoidance of the area or 
decreased foraging (if such activity was occurring), responses that are 
considered to be of low severity, and with no lasting biological 
consequences (e.g., Southall et al., 2007, 2021). These low-level 
impacts of behavioral harassment are not likely to impact the overall 
fitness of any individual or lead to population level effects of any 
species. As described above, auditory injury (Level A harassment) is 
not expected to occur given the estimated small size of the Level A 
harassment zones.
    In addition, the maximum expected Level B harassment zone around 
the survey vessel is 1,750 m. Therefore, the ensonified area 
surrounding the vessel is relatively small compared to the overall 
distribution of animals in the area and their use of the habitat. 
Feeding behavior is not likely to be significantly impacted as prey 
species are mobile and are broadly distributed throughout the survey 
area; therefore, marine mammals that may be temporarily displaced 
during survey activities are expected to be able to resume foraging 
once they have moved away from areas with disturbing levels of 
underwater noise. Because of the short duration (20 survey days) and 
temporary nature of the disturbance and the availability of similar 
habitat and resources in the surrounding area, the impacts to marine 
mammals and marine mammal prey species are not expected to cause 
significant or long-term fitness consequences for individual marine 
mammals or their populations.

[[Page 91363]]

    Additionally, the acoustic ``footprint'' of the proposed survey 
would be very small relative to the ranges of all marine mammals that 
would potentially be affected. Sound levels would increase in the 
marine environment in a relatively small area surrounding the vessel 
compared to the range of the marine mammals within the proposed survey 
area. The seismic array would be active 24 hours per day throughout the 
duration of the proposed survey. However, the very brief overall 
duration of the proposed survey (20 survey days) would further limit 
potential impacts that may occur as a result of the proposed activity.
    There are no rookeries, mating, or calving grounds known to be 
biologically important to marine mammals within the planned survey area 
and there are no feeding areas known to be biologically important to 
marine mammals within the survey area. There is no designated critical 
habitat for any ESA-listed marine mammals within the project area.
    In summary and as described above, the following factors primarily 
support our preliminary determination that the impacts resulting from 
this activity are not expected to adversely affect any of the species 
or stocks through effects on annual rates of recruitment or survival:
     No serious injury or mortality is anticipated or 
authorized;
     No auditory injury (Level A harassment) is anticipated or 
proposed to be authorized;
     The proposed activity is temporary and of relatively short 
duration (23 days total with 20 days of planned survey activity);
     The anticipated impacts of the proposed activity on marine 
mammals would be temporary behavioral changes due to avoidance of the 
ensonified area, which is relatively small (see tables 4 and 5);
     The availability of alternative areas of similar habitat 
value for marine mammals to temporarily vacate the survey area during 
the proposed survey to avoid exposure to sounds from the activity is 
readily abundant;
     The potential adverse effects on fish or invertebrate 
species that serve as prey species for marine mammals from the proposed 
survey would be temporary and spatially limited and impacts to marine 
mammal foraging would be minimal; and
     The proposed mitigation measures are expected to reduce 
the number and severity of takes, to the extent practicable, by 
visually detecting marine mammals within the established zones and 
implementing corresponding mitigation measures (e.g., delay; ramp-up).
    Based on the analysis contained herein of the likely effects of the 
specified activity on marine mammals and their habitat, and taking into 
consideration the implementation of the proposed monitoring and 
mitigation measures, NMFS preliminarily finds that the total marine 
mammal take from the proposed activity will have a negligible impact on 
all affected marine mammal species or stocks.

Small Numbers

    As noted previously, only take of small numbers of marine mammals 
may be authorized under sections 101(a)(5)(A) and (D) of the MMPA for 
specified activities other than military readiness activities. The MMPA 
does not define small numbers and so, in practice, where estimated 
numbers are available, NMFS compares the number of individuals taken to 
the most appropriate estimation of abundance of the relevant species or 
stock in our determination of whether an authorization is limited to 
small numbers of marine mammals. When the predicted number of 
individuals to be taken is fewer than one-third of the species or stock 
abundance, the take is considered to be of small numbers. Additionally, 
other qualitative factors may be considered in the analysis, such as 
the temporal or spatial scale of the activities.
    The number of takes NMFS proposes to authorize is below one-third 
of the modeled abundance for all relevant populations (specifically, 
take of individuals is less than 7 percent of the most appropriate 
abundance estimate for each stock, see table 6). This is conservative 
because this approach assumes all takes are of different individual 
animals, which is likely not the case. Some individuals may be 
encountered multiple times in a day, but PSOs would count them as 
separate individuals if they cannot be identified.
    Based on the analysis contained herein of the proposed activity 
(including the proposed mitigation and monitoring measures) and the 
anticipated take of marine mammals, NMFS preliminarily finds that small 
numbers of marine mammals would be taken relative to the population 
size of the affected species or stocks.

Unmitigable Adverse Impact Analysis and Determination

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

Endangered Species Act

    Section 7(a)(2) of the ESA of 1973 (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.
    No incidental take of ESA-listed species is proposed for 
authorization or expected to result from this activity. Therefore, NMFS 
has determined that formal consultation under section 7 of the ESA is 
not required for this action.

Proposed Authorization

    As a result of these preliminary determinations, NMFS proposes to 
issue an IHA to UT for conducting marine geophysical surveys in coastal 
waters off Texas in the NW GOM from approximately January to April 
2025, provided the previously mentioned mitigation, monitoring, and 
reporting requirements are incorporated. A draft of the proposed IHA 
can be found at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities.

Request for Public Comments

    We request comment on our analyses, the proposed authorization, and 
any other aspect of this notice of proposed IHA for the proposed marine 
geophysical survey. We also request comment on the potential renewal of 
this proposed IHA as described in the paragraph below. Please include 
with your comments any supporting data or literature citations to help 
inform decisions on the request for this IHA or a subsequent renewal 
IHA.
    On a case-by-case basis, NMFS may issue a one-time, 1-year renewal 
IHA following notice to the public providing an additional 15 days for 
public comments when (1) up to another year of identical or nearly 
identical activities as described in the Description of Proposed 
Activity section of this notice is planned or (2) the activities as 
described in the Description of Proposed Activity section of this 
notice would not be completed by the time the IHA expires and a renewal 
would allow for completion of the activities beyond

[[Page 91364]]

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

    Dated: November 12, 2024.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2024-26903 Filed 11-18-24; 8:45 am]
BILLING CODE 3510-22-P`