Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey in Coastal Waters Off of Texas, 53453-53473 [2023-16945]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 88, Number 151 (Tuesday, August 8, 2023)]
[Notices]
[Pages 53453-53473]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-16945]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XC993]


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to a Marine Geophysical Survey in 
Coastal Waters Off of Texas

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 of Texas. Pursuant to 
the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on 
its proposal

[[Page 53454]]

to issue an incidental harassment authorization (IHA) to incidentally 
take marine mammals during the specified activities. NMFS is also 
requesting comments on a possible one-time, 1-year renewal that could 
be issued under certain circumstances and if all requirements are met, 
as described in Request for Public Comments at the end of this notice. 
NMFS will consider public comments prior to making any final decision 
on the issuance of the requested MMPA authorization and agency 
responses will be summarized in the final notice of our decision.

DATES: Comments and information must be received no later than 
September 7, 2023.

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

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

SUPPLEMENTARY INFORMATION: 

Background

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

National Environmental Policy Act

    To comply with the National Environmental Policy Act of 1969 (NEPA; 
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A, 
NMFS must review our proposed action (i.e., the issuance of an IHA) 
with respect to potential impacts on the human environment. 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 NOAA Administrative Order 216-6A, which do not 
individually or cumulatively have the potential for significant impacts 
on the quality of the human environment and for which we have not 
identified any extraordinary circumstances that would preclude this 
categorical exclusion. Accordingly, NMFS has preliminarily determined 
that the issuance of the proposed IHA qualifies to be categorically 
excluded from further NEPA review. We will review all comments 
submitted in response to this notice prior to concluding our NEPA 
process or making a final decision on the IHA request.

Summary of Request

    On March 7, 2023, NMFS received a request from UT for an IHA to 
take marine mammals incidental to conducting a marine geophysical 
survey in coastal waters off of Texas. Following NMFS' review of the 
application, UT submitted a revised version on April 25, 2023. The 
application was deemed adequate and complete on April 27, 2023. UT's 
request is for take of bottlenose dolphins, Atlantic spotted dolphins, 
and rough-toothed dolphin 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

    UT proposes to conduct a marine geophysical survey, specifically a 
low energy seismic survey, in coastal waters off of Texas during a 10 
day period in the fall of 2023. The survey would take place in coastal 
waters off of Texas, in water depths of less than 20 meters (m). To 
complete this survey the vessel would tow one to two Generator-Injector 
(GI) airguns, each with a volume of 105 cubic inch (in\3\; 1,721 cubic 
cm (cm\3\)), for a total volume of 210 in\3\ (3,441 cm\3\). The airguns 
would be deployed at a depth of about 4 m below the surface, spaced 
about 2 m apart, while the receiving system consists of four 25 m 
hydrophone streamers towed at a depth of about 2 m.
    The purpose of the proposed survey is to validate novel dynamic 
positioning technology for improving the accuracy in time and space of 
high resolution 3-dimensional (HR3D) seismic datasets, in particular as 
it pertains to field technology of offshore carbon capture systems.

Dates and Duration

    The proposed survey is planned to occur over a 10 day period during 
the fall of 2023 (the exact dates are uncertain). During that time, the 
airguns would operate continuously (i.e., 24-hours per day).

Specific Geographic Region

    The proposed survey area is 222 km2 and would occur within the 
approximate area of 28.9-29.1[deg] N latitude, 94.9-95.2[deg] W 
longitude in the coastal waters off of Texas. This location is offshore 
San Luis Pass, which defines the southern tip of Galveston Island, 
Texas. The closest point of approach of the proposed survey area to the 
coast is approximately 3 kilometers (km). The proposed survey area is 
depicted in Figure 1, and the survey lines could occur anywhere within 
the survey area. The water depth of the proposed survey area ranges 
from 10 to 20 m. The survey vessel (the R/V Brooks McCall (McCall) or 
similar vessel operated by TDI-Brooks

[[Page 53455]]

International) would likely depart and return to Freeport or Galveston, 
Texas.
BILLING CODE 3510-22-P
[GRAPHIC] [TIFF OMITTED] TN08AU23.009

BILLING CODE 3510-22-C

Detailed Description of the Specified Activity

    The proposed survey would entail use of conventional seismic 
methodology. The survey would involve one source vessel, the McCall or 
similar, and would tow one or two 105 in\3\ GI airguns with a total 
volume of up to 210 in\3\. The airgun array would be deployed at a 
depth of about 4 m below the surface, spaced about 2 m apart, and have 
a shot interval of 12.5 m about 5-10 seconds (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 1,704 km of transect lines would 
be surveyed within the survey area. When not towing seismic survey 
gear, the McCall has a maximum speed of 11 knots (kn; 20.4 kilometers 
per hour (kmh)), but cruises at an average speed of 4-5 kn (7.4-9.3 
kmh) while towing airgun arrays. All survey effort would occur in water 
10-20 m. The vessel would be self-contained, and the crew would live 
aboard the vessel.
    Proposed mitigation, monitoring, and reporting measures are 
described in detail later in this Notice (please see Proposed 
Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

    Sections 3 and 4 of the application summarize available information 
regarding status and trends, distribution and habitat preferences, and 
behavior and life history of the potentially affected species. NMFS 
fully considered all of this information, and we refer the reader to 
these descriptions, instead of reprinting the information. Additional 
information regarding population trends and threats may be found in 
NMFS' Stock Assessment Reports (SARs; www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments) and more 
general information about these species (e.g., physical and behavioral 
descriptions) may be found on NMFS' website (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

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and annual serious injury and mortality from anthropogenic sources are 
included here as gross indicators of the status of the species or 
stocks and other threats.
    Marine mammal abundance estimates presented in this document 
represent the total number of individuals that make up a given stock or 
the total number estimated within a particular study or survey area. 
NMFS' stock abundance estimates for most species represent the total 
estimate of individuals within the geographic area, if known, that 
comprises that stock. For some species, this geographic area may extend 
beyond U.S. waters. All managed 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 2022 SARs) and are available online at: 
www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

                                            Table 1--Species Likely Impacted by the Specified Activities \1\
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                                                                                       Stock abundance                                    Gulf of Mexico
                                                                          ESA/MMPA     (CV, Nmin, most                                      population
          Common name              Scientific name         Stock           status;     recent abundance           PBR          Annual M/    abundance;
                                                                        strategic (Y/    survey) \3\                             SI \4\     (Roberts et
                                                                           N) \2\                                                          al. 2016) \5\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                  Odontoceti (toothed whales, dolphins, and porpoises)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Delphinidae:
                                ------------------------------------------------------------------------------------------------------------------------
    Atlantic spotted dolphin...  Stenella frontalis  Gulf of Mexico...  -/-; N        21,506 (0.26;      166.................         36          47,488
                                                                                       17,339; 2018).
    Rough-toothed dolphin......  Steno bredanensis.  Gulf of Mexico...  -/-; N        unk (n/a; unk;     undetermined........         39           4,853
                                                                                       2018).
    Bottlenose dolphin.........  Tursiops truncatus  Gulf of Mexico     -/-; N        20,759 (0.13;      167.................         36         138,602
                                                      Western Coastal.                 18,585; 2018).
                                                     Northern Gulf of   -/-; N        63,280 (0.11;      556.................         65         138,602
                                                      Mexico                           57,917; 2018).
                                                      Continental
                                                      Shelf.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\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/; Committee on Taxonomy (2022)).
\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: www.nmfs.noaa.gov/pr/sars/. CV is coefficient of variation; Nmin is the minimum estimate of
  stock abundance.
\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, vessel strike). Annual M/SI (mortality/serious injury) often cannot be determined precisely and is in some cases presented as a
  minimum value or range.

    As indicated above, all 3 species (with 4 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 Gulf of Mexico are unlikely to be 
observed during this survey where the maximum water depth is 20 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 Gulf of Mexico (W[uuml]rsig et al. 
2000; W[uuml]rsig 2017). While there are multiple stocks of bottlenose 
dolphins in the Gulf of Mexico, only the Northern Gulf of Mexico 
Continental Shelf and Gulf of Mexico 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.
    There are 31 bay, sound, and estuary (BSE) stocks in the northern 
Gulf of Mexico, 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. The West Bay stock occurs within 
roughly 20 km of the survey area, but individuals from this stock are 
only likely to occur in inshore waters or, occasionally, up to 1 km 
from shore off San Luis Pass (Hayes et al. 2022). The Galveston Bay/
East Bay/Trinity Bay stock occurs >20 km away, with most individuals 
staying within 2 km from shore and up to 5 km out from the Galveston 
jetties and ship channel (Hayes et al. 2022). 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 (LeBresque et 
al. 2015). Due to the distance that the survey will occur off the coast 
(minimum 3 km) and general expectation that BSE dolphins are most 
likely to occur in 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

[[Page 53457]]

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

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

    The pinniped functional hearing group was modified from Southall et 
al. (2007) on the basis of data indicating that phocid species have 
consistently demonstrated an extended frequency range of hearing 
compared to otariids, especially in the higher frequency range 
(Hemil[auml] et al., 2006; Kastelein et al., 2009; Reichmuth and Holt, 
2013).
    For more detail concerning these groups and associated frequency 
ranges, please see NMFS (2018) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their 
Habitat

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

Description of Active Acoustic Sound Sources

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

[[Page 53458]]

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

Acoustic Effects

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

[[Page 53459]]

be audible (potentially perceived) to the animal but not strong enough 
to elicit any overt behavioral or physiological response. The next zone 
corresponds with the area where the signal is audible to the animal and 
of sufficient intensity to elicit behavioral or physiological response. 
Third is a zone within which, for signals of high intensity, the 
received level is sufficient to potentially cause discomfort or tissue 
damage to auditory or other systems. Overlaying these zones to a 
certain extent is the area within which masking (i.e., when a sound 
interferes with or masks the ability of an animal to detect a signal of 
interest that is above the absolute hearing threshold) may occur; the 
masking zone may be highly variable in size.
    We describe the more severe effects of certain non-auditory 
physical or physiological effects only briefly as we do not expect that 
use of airgun arrays are reasonably likely to result in such effects 
(see below for further discussion). Potential effects from impulsive 
sound sources can range in severity from effects such as behavioral 
disturbance or tactile perception to physical discomfort, slight injury 
of the internal organs and the auditory system, or mortality (Yelverton 
et al., 1973). Non-auditory physiological effects or injuries that 
theoretically might occur in marine mammals exposed to high level 
underwater sound or as a secondary effect of extreme behavioral 
reactions (e.g., change in dive profile as a result of an avoidance 
reaction) caused by exposure to sound include neurological effects, 
bubble formation, resonance effects, and other types of organ or tissue 
damage (Cox et al., 2006; Southall et al., 2007; Zimmer and Tyack, 
2007; Tal et al., 2015). The survey activities considered here do not 
involve the use of devices such as explosives or mid-frequency tactical 
sonar that are associated with these types of effects.
    Threshold Shift--Marine mammals exposed to high-intensity sound or 
to lower-intensity sound for prolonged periods can experience hearing 
threshold shift (TS), which is the loss of hearing sensitivity at 
certain frequency ranges (Finneran, 2015). Threshold shift can be 
permanent (PTS), in which case the loss of hearing sensitivity is not 
fully recoverable, or temporary (TTS), in which case the animal's 
hearing threshold would recover over time (Southall et al., 2007). 
Repeated sound exposure that leads to TTS could cause PTS. In severe 
cases of PTS, there can be total or partial deafness while in most 
cases, the animal has an impaired ability to hear sounds in specific 
frequency ranges (Kryter, 1985).
    When PTS occurs, there is physical damage to the sound receptors in 
the ear (i.e., tissue damage) whereas TTS represents primarily tissue 
fatigue and is reversible (Southall et al., 2007). In addition, other 
investigators have suggested that TTS is within the normal bounds of 
physiological variability and tolerance and does not represent physical 
injury (e.g., Ward, 1997). Therefore, NMFS does not typically consider 
TTS to constitute auditory injury.
    Relationships between TTS and PTS thresholds have not been studied 
in marine mammals. There is no PTS data for cetaceans, but such 
relationships are assumed to be similar to those in humans and other 
terrestrial mammals. PTS typically occurs at exposure levels at least 
several dBs above (a 40-dB threshold shift approximates PTS onset; 
e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB 
threshold shift approximates TTS onset; e.g., Southall et al. 2007). 
Based on data from terrestrial mammals, a precautionary assumption is 
that the PTS thresholds for impulse sounds (such as airgun pulses as 
received close to the source) are at least 6 dB higher than the TTS 
threshold on a peak-pressure basis and PTS cumulative sound exposure 
level thresholds are 15 to 20 dB higher than TTS cumulative sound 
exposure level thresholds (Southall et al., 2007). Given the higher 
level of sound or longer exposure duration necessary to cause PTS as 
compared with TTS, it is considerably less likely that PTS could occur.
    For mid-frequency cetaceans in particular, potential protective 
mechanisms may help limit onset of TTS or prevent onset of PTS. Such 
mechanisms include dampening of hearing, auditory adaptation, or 
behavioral amelioration (e.g., Nachtigall and Supin, 2013; Miller et 
al., 2012; Finneran et al., 2015; Popov et al., 2016).
    TTS is the mildest form of hearing impairment that can occur during 
exposure to sound (Kryter, 1985). While experiencing TTS, the hearing 
threshold rises, and a sound must be at a higher level in order to be 
heard. In terrestrial and marine mammals, TTS can last from minutes or 
hours to days (in cases of strong TTS). In many cases, hearing 
sensitivity recovers rapidly after exposure to the sound ends. Few data 
on sound levels and durations necessary to elicit mild TTS have been 
obtained for marine mammals.
    Marine mammal hearing plays a critical role in communication with 
other members of the species and interpretation of environmental cues 
for purposes such as predator avoidance and prey capture. Depending on 
the degree (elevation of threshold in dB), duration (i.e., recovery 
time), and frequency range of TTS, and the context in which it is 
experienced, TTS can have effects on marine mammals ranging from 
discountable to serious. For example, a marine mammal may be able to 
readily compensate for a brief, relatively small amount of TTS in a 
non-critical frequency range that occurs during a time where ambient 
noise is lower and there are not as many competing sounds present. 
Alternatively, a larger amount and longer duration of TTS sustained 
during time when communication is critical for successful mother and 
calf interactions could have more serious impacts.
    Finneran et al. (2015) measured hearing thresholds in three captive 
bottlenose dolphins before and after exposure to 10 pulses produced by 
a seismic airgun in order to study TTS induced after exposure to 
multiple pulses. Exposures began at relatively low levels and gradually 
increased over a period of several months, with the highest exposures 
at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from 
193-195 dB. No substantial TTS was observed. In addition, behavioral 
reactions were observed that indicated that animals can learn behaviors 
that effectively mitigate noise exposures (although exposure patterns 
must be learned, which is less likely in wild animals than for the 
captive animals considered in this study). The authors noted that the 
failure to induce more significant auditory effects was likely due to 
the intermittent nature of exposure, the relatively low peak pressure 
produced by the acoustic source, and the low-frequency energy in airgun 
pulses as compared with the frequency range of best sensitivity for 
dolphins and other mid-frequency cetaceans.
    Currently, TTS data only exist for four species of cetaceans 
(bottlenose dolphin, beluga whale, harbor porpoise, and Yangtze finless 
porpoise) exposed to a limited number of sound sources (i.e., mostly 
tones and octave-band noise) in laboratory settings (Finneran, 2015). 
The existing marine mammal TTS data come from a limited number of 
individuals within these species.
    Critical questions remain regarding the rate of TTS growth and 
recovery after exposure to intermittent noise and the effects of single 
and multiple pulses. Data at present are also insufficient to construct 
generalized models for recovery and determine the time necessary to 
treat subsequent exposures as independent events. More

[[Page 53460]]

information is needed on the relationship between auditory evoked 
potential and behavioral measures of TTS for various stimuli. For 
summaries of data on TTS in marine mammals or for further discussion of 
TTS onset thresholds, please see Southall et al. (2007, 2019), Finneran 
and Jenkins (2012), Finneran (2015), and NMFS (2018).
    Behavioral Effects--Behavioral disturbance may include a variety of 
effects, including subtle changes in behavior (e.g., minor or brief 
avoidance of an area or changes in vocalizations), more conspicuous 
changes in similar behavioral activities, and more sustained and/or 
potentially severe reactions, such as displacement from or abandonment 
of high-quality habitat. Behavioral responses to sound are highly 
variable and context-specific, and any reactions depend on numerous 
intrinsic and extrinsic factors (e.g., species, state of maturity, 
experience, current activity, reproductive state, auditory sensitivity, 
time of day), as well as the interplay between factors (e.g., 
Richardson et al., 1995; Wartzok et al., 2003; Southall et al., 2007, 
2019; Weilgart, 2007; Archer et al., 2010). Behavioral reactions can 
vary not only among individuals but also within an individual, 
depending on previous experience with a sound source, context, and 
numerous other factors (Ellison et al., 2012), and can vary depending 
on characteristics associated with the sound source (e.g., whether it 
is moving or stationary, number of sources, distance from the source). 
Please see Appendices B-C of Southall et al. (2007) for a review of 
studies involving marine mammal behavioral responses to sound.
    Habituation can occur when an animal's response to a stimulus wanes 
with repeated exposure, usually in the absence of unpleasant associated 
events (Wartzok et al., 2003). Animals are most likely to habituate to 
sounds that are predictable and unvarying. It is important to note that 
habituation is appropriately considered as a ``progressive reduction in 
response to stimuli that are perceived as neither aversive nor 
beneficial,'' rather than as, more generally, moderation in response to 
human disturbance (Bejder et al., 2009). The opposite process is 
sensitization, when an unpleasant experience leads to subsequent 
responses, often in the form of avoidance, at a lower level of 
exposure. As noted, behavioral state may affect the type of response. 
For example, animals that are resting may show greater behavioral 
change in response to disturbing sound levels than animals that are 
highly motivated to remain in an area for feeding (Richardson et al., 
1995; NRC, 2003; Wartzok et al., 2003). Controlled experiments with 
captive marine mammals have showed pronounced behavioral reactions, 
including avoidance of loud sound sources (Ridgway et al., 1997). 
Observed responses of wild marine mammals to loud pulsed sound sources 
(typically seismic airguns or acoustic harassment devices) have been 
varied but often consist of avoidance behavior or other behavioral 
changes suggesting discomfort (Morton and Symonds, 2002; see also 
Richardson et al., 1995; Nowacek et al., 2007). However, many 
delphinids approach acoustic source vessels with no apparent discomfort 
or obvious behavioral change (e.g., Barkaszi et al., 2012).
    Available studies show wide variation in response to underwater 
sound; therefore, it is difficult to predict specifically how any given 
sound in a particular instance might affect marine mammals perceiving 
the signal. If a marine mammal does react briefly to an underwater 
sound by changing its behavior or moving a small distance, the impacts 
of the change are unlikely to be significant to the individual, let 
alone the stock or population. However, if a sound source displaces 
marine mammals from an important feeding or breeding area for a 
prolonged period, impacts on individuals and populations could be 
significant (e.g., Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 
2005). However, there are broad categories of potential response, which 
we describe in greater detail here, that include alteration of dive 
behavior, alteration of foraging behavior, effects to breathing, 
interference with or alteration of vocalization, avoidance, and flight.
    Changes in dive behavior can vary widely, and may consist of 
increased or decreased dive times and surface intervals as well as 
changes in the rates of ascent and descent during a dive (e.g., Frankel 
and Clark, 2000; Ng and Leung, 2003; Nowacek et al., 2004; Goldbogen et 
al., 2013a, b). Variations in dive behavior may reflect disruptions in 
biologically significant activities (e.g., foraging) or they may be of 
little biological significance. The impact of an alteration to dive 
behavior resulting from an acoustic exposure depends on what the animal 
is doing at the time of the exposure and the type and magnitude of the 
response.
    Disruption of feeding behavior can be difficult to correlate with 
anthropogenic sound exposure, so it is usually inferred by observed 
displacement from known foraging areas, the appearance of secondary 
indicators (e.g., bubble nets or sediment plumes), or changes in dive 
behavior. As for other types of behavioral response, the frequency, 
duration, and temporal pattern of signal presentation, as well as 
differences in species sensitivity, are likely contributing factors to 
differences in response in any given circumstance (e.g., Croll et al., 
2001; Nowacek et al., 2004; Madsen et al., 2006; Yazvenko et al., 
2007). A determination of whether foraging disruptions incur fitness 
consequences would require information on or estimates of the energetic 
requirements of the affected individuals and the relationship between 
prey availability, foraging effort and success, and the life history 
stage of the animal.
    Variations in respiration naturally vary with different behaviors 
and alterations to breathing rate as a function of acoustic exposure 
can be expected to co-occur with other behavioral reactions, such as a 
flight response or an alteration in diving. However, respiration rates 
in and of themselves may be representative of annoyance or an acute 
stress response. Various studies have shown that respiration rates may 
either be unaffected or could increase, depending on the species and 
signal characteristics, again highlighting the importance in 
understanding species differences in the tolerance of underwater noise 
when determining the potential for impacts resulting from anthropogenic 
sound exposure (e.g., Kastelein et al., 2001, 2005, 2006; Gailey et 
al., 2007, 2016).
    Marine mammals vocalize for different purposes and across multiple 
modes, such as whistling, echolocation click production, calling, and 
singing. Changes in vocalization behavior in response to anthropogenic 
noise can occur for any of these modes and may result from a need to 
compete with an increase in background noise or may reflect increased 
vigilance or a startle response. In some cases, animals may cease sound 
production during production of aversive signals (Bowles et al., 1994).
    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). 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

[[Page 53461]]

affected region if habituation to the presence of the sound does not 
occur (e.g., Bejder et al., 2006; Teilmann et al., 2006).
    A flight response is a dramatic change in normal movement to a 
directed and rapid movement away from the perceived location of a sound 
source. The flight response differs from other avoidance responses in 
the intensity of the response (e.g., directed movement, rate of 
travel). Relatively little information on flight responses of marine 
mammals to anthropogenic signals exist, although observations of flight 
responses to the presence of predators have occurred (Connor and 
Heithaus, 1996). The result of a flight response could range from 
brief, temporary exertion and displacement from the area where the 
signal provokes flight to, in extreme cases, marine mammal strandings 
(Evans and England, 2001). However, it should be noted that response to 
a perceived predator does not necessarily invoke flight (Ford and 
Reeves, 2008), and whether individuals are solitary or in groups may 
influence the response.
    Behavioral disturbance can also impact marine mammals in more 
subtle ways. Increased vigilance may result in costs related to 
diversion of focus and attention (i.e., when a response consists of 
increased vigilance, it may come at the cost of decreased attention to 
other critical behaviors such as foraging or resting). These effects 
have generally not been demonstrated for marine mammals, but studies 
involving fish and terrestrial animals have shown that increased 
vigilance may substantially reduce feeding rates (e.g., Beauchamp and 
Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In 
addition, chronic disturbance can cause population declines through 
reduction of fitness (e.g., decline in body condition) and subsequent 
reduction in reproductive success, survival, or both (e.g., Harrington 
and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, 
Ridgway et al. (2006) reported that increased vigilance in bottlenose 
dolphins exposed to sound over a five-day period did not cause any 
sleep deprivation or stress effects.
    Many animals perform vital functions, such as feeding, resting, 
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption 
of such functions resulting from reactions to stressors, such as sound 
exposure, are more likely to be significant if they last more than one 
diel cycle or recur on subsequent days (Southall et al., 2007). 
Consequently, a behavioral response lasting less than 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) were firing, lateral displacement, 
more localized avoidance, or other changes in behavior were evident for 
most odontocetes.
    Stress Responses--An animal's perception of a threat may be 
sufficient to trigger stress responses consisting of some combination 
of behavioral responses, autonomic nervous system responses, 
neuroendocrine responses, or immune responses (e.g., Seyle, 1950; 
Moberg, 2000). In many cases, an animal's first and sometimes most 
economical (in terms of energetic costs) response is behavioral 
avoidance of the potential stressor. Autonomic nervous system responses 
to stress typically involve changes in heart rate, blood pressure, and 
gastrointestinal activity. These responses have a relatively short 
duration and may or may not have a significant long-term effect on an 
animal's fitness.
    Neuroendocrine stress responses often involve the hypothalamus-
pituitary-adrenal system. Virtually all neuroendocrine functions that 
are affected by stress--including immune competence, reproduction, 
metabolism, and behavior--are regulated by pituitary hormones. Stress-
induced changes in the secretion of pituitary hormones have been 
implicated in failed reproduction, altered metabolism, reduced immune 
competence, and behavioral disturbance (e.g., Moberg, 1987; Blecha, 
2000). Increases in the circulation of glucocorticoids are also equated 
with stress (Romano et al., 2004).
    The primary distinction between ``stress'' (which is adaptive and 
does not normally place an animal at risk) and ``distress'' is the cost 
of the response. During a stress response, an animal uses glycogen 
stores that can be quickly replenished once the stress is alleviated. 
In such circumstances, the cost of the stress response would not pose 
serious fitness consequences. However, when an animal does not have 
sufficient energy reserves to satisfy the energetic costs of a stress 
response, energy resources must be diverted from other functions. This 
state of distress will last until the animal replenishes its energetic 
reserves sufficiently to restore normal function.
    Relationships between these physiological mechanisms, animal 
behavior, and the costs of stress responses are well-studied through 
controlled experiments and for both laboratory and free-ranging animals 
(e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003; 
Krausman et al., 2004; Lankford et al., 2005). Stress responses due to 
exposure to anthropogenic sounds or other stressors and their effects 
on marine mammals have also been reviewed (Fair and Becker, 2000; 
Romano et al., 2002b) and, more rarely, studied in wild populations 
(e.g., Romano et al., 2002a). 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.

[[Page 53462]]

    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 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.
    The sounds important to small odontocetes are predominantly at much 
higher frequencies than are the dominant components of airgun sounds, 
thus limiting the potential for masking. In general, masking effects of 
seismic pulses are expected to be minor, given the normally 
intermittent nature of seismic pulses.

Vessel Noise

    Vessel noise from the McCall could affect marine animals in the 
proposed survey areas. Houghton et al. (2015) proposed that vessel 
speed is the most important predictor of received noise levels, and 
Putland et al. (2017) also reported reduced sound levels with decreased 
vessel speed. Sounds produced by large vessels generally dominate 
ambient noise at frequencies from 20 to 300 Hz (Richardson et al., 
1995). However, some energy is also produced at higher frequencies 
(Hermannsen et al., 2014); low levels of high-frequency sound from 
vessels has been shown to elicit responses in harbor porpoise (Dyndo et 
al., 2015). Increased levels of vessel noise have been shown to affect 
foraging by porpoise (Teilmann et al., 2015; Wisniewska et al., 2018); 
Wisniewska et al. (2018) suggested that a decrease in foraging success 
could have long-term fitness consequences.
    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. In 
order to compensate for increased ambient noise, some cetaceans are 
known to increase the source levels of their calls in the presence of 
elevated noise levels from shipping, shift their peak frequencies, or 
otherwise change their vocal behavior (e.g., Martins et al., 2016; 
O'Brien et al., 2016; Tenessen and Parks 2016). Harp seals did not 
increase their call frequencies in environments with increased low-
frequency sounds (Terhune and Bosker 2016). Holt et al. (2015) reported 
that changes in vocal modifications can have increased energetic costs 
for individual marine mammals. A negative correlation between the 
presence of some cetacean species and the number of vessels in an area 
has been demonstrated by several studies (e.g., Campana et al., 2015; 
Culloch et al., 2016).
    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). Dolphins of 
many species tolerate and sometimes approach vessels (e.g., Anderwald 
et al., 2013). Some dolphin species approach moving vessels to ride the 
bow or stern waves (Williams et al., 1992). Pirotta et al. (2015) noted 
that the physical presence of vessels, not just vessel noise, disturbed 
the foraging activity of bottlenose dolphins. Sightings of striped 
dolphin, Risso's dolphin, sperm whale, and Cuvier's beaked whale in the 
western Mediterranean were negatively correlated with the number of 
vessels in the area (Campana et al., 2015).
    Sounds emitted by the McCall are low frequency and continuous but 
would be widely dispersed in both space and time. Vessel traffic 
associated with the proposed survey is of low density compared to 
traffic associated with commercial shipping, industry support vessels, 
or commercial fishing vessels, and would therefore be expected to 
represent an insignificant incremental increase in the total amount of 
anthropogenic sound input to the marine environment, and the effects of 
vessel noise described above are not expected to occur as a result of 
this survey. In summary, project vessel sounds would not be at levels 
expected to cause anything more than possible localized and temporary 
behavioral changes in marine mammals, and would not be expected to 
result in significant negative effects on individuals or at the 
population level. In addition, in all oceans of the world, large vessel 
traffic is currently so prevalent that it is commonly considered a 
usual source of ambient sound (NSF-USGS 2011).

[[Page 53463]]

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 
kn (25.9 kmh), and exceeded 90 percent at 17 kn (31.5 kmh). 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 (15.9 and 
27.8 kmh). The chances of a lethal injury decline from approximately 80 
percent at 15 kn (27.8 kmh) to approximately 20 percent at 8.6 kn (15.9 
kmh). At speeds below 11.8 kn (21.9 kmh), the chances of lethal injury 
drop below 50 percent, while the probability asymptotically increases 
toward one hundred percent above 15 kn (27.8 kmh).
    The McCall will travel at a speed of 4-5 kn (7.4-9.3 kmh) while 
towing seismic survey gear. At this speed, both the possibility of 
striking a marine mammal and the possibility of a strike resulting in 
serious injury or mortality are discountable. At average transit speed, 
the probability of serious injury or mortality resulting from a strike 
is less than 50 percent. However, the likelihood of a strike actually 
happening is again discountable. Vessel strikes, as analyzed in the 
studies cited above, generally involve commercial shipping, which is 
much more common in both space and time than is geophysical survey 
activity. Jensen and Silber (2004) summarized vessel strikes of large 
whales worldwide from 1975-2003 and found that most collisions occurred 
in the open ocean and involved large vessels (e.g., commercial 
shipping). No such incidents were reported for geophysical survey 
vessels during that time period.
    It is possible for vessel strikes to occur while traveling at slow 
speeds. For example, a hydrographic survey vessel traveling at low 
speed (5.5 kn; 10.2 kmh) while conducting mapping surveys off the 
central California coast struck and killed a blue whale in 2009. The 
State of California determined that the whale had suddenly and 
unexpectedly surfaced beneath the hull, with the result that the 
propeller severed the whale's vertebrae, and that this was an 
unavoidable event. This strike represents the only such incident in 
approximately 540,000 hours of similar coastal mapping activity (p = 
1.9 x 10-\6\; 95% CI = 0-5.5 x 10-\6\; NMFS, 
2013b). In addition, a research vessel reported a fatal strike in 2011 
of a dolphin in the Atlantic, demonstrating that it is possible for 
strikes involving smaller cetaceans to occur. In that case, the 
incident report indicated that an animal apparently was struck by the 
vessel's propeller as it was intentionally swimming near the vessel. 
While indicative of the type of unusual events that cannot be ruled 
out, neither of these instances represents a circumstance that would be 
considered reasonably foreseeable or that would be considered 
preventable.
    Although the likelihood of the vessel striking a marine mammal is 
low, we propose a robust vessel strike avoidance protocol (see Proposed 
Mitigation), which we believe eliminates any foreseeable risk of vessel 
strike during transit. We anticipate that vessel collisions involving a 
seismic data acquisition vessel towing gear, while not impossible, 
represent unlikely, unpredictable events for which there are no 
preventive measures. Given the proposed mitigation measures, the 
relatively slow speed of the vessel towing gear, the presence of bridge 
crew watching for obstacles at all times (including marine mammals), 
and the presence of marine mammal observers, the possibility of vessel 
strike is discountable and, further, were a strike of a large whale to 
occur, it would be unlikely to result in serious injury or mortality. 
No incidental take resulting from vessel strike is anticipated, and 
this potential effect of the specified activity will not be discussed 
further in the following analysis.
    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. Although entanglement with the 
streamer is theoretically possible, it has not been documented during 
hundreds of thousands of miles of industrial seismic cruises. 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 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

[[Page 53464]]

impacts to fish as a result of noise from nearby airguns, such effects 
will be temporary. For example, investigators reported significant, 
short-term declines in commercial fishing catch rate of gadid fishes 
during and for up to five days after seismic survey operations, but the 
catch rate subsequently returned to normal (Engas et al., 1996; Engas 
and Lokkeborg, 2002). Other studies have reported similar findings 
(Hassel et al., 2004). Skalski et al., (1992) also found a reduction in 
catch rates--for rockfish (Sebastes spp.) in response to controlled 
airgun exposure--but suggested that the mechanism underlying the 
decline was not dispersal but rather decreased responsiveness to baited 
hooks associated with an alarm behavioral response. A companion study 
showed that alarm and startle responses were not sustained following 
the removal of the sound source (Pearson et al., 1992). Therefore, 
Skalski et al. (1992) suggested that the effects on fish abundance may 
be transitory, primarily occurring during the sound exposure itself. In 
some cases, effects on catch rates are variable within a study, which 
may be more broadly representative of temporary displacement of fish in 
response to airgun noise (i.e., catch rates may increase in some 
locations and decrease in others) than any long-term damage to the fish 
themselves (Streever et al., 2016).
    Sound pressure levels of sufficient strength have been known to 
cause injury to fish and fish mortality and, in some studies, fish 
auditory systems have been damaged by airgun noise (McCauley et al., 
2003; Popper et al., 2005; Song et al., 2008). However, in most fish 
species, hair cells in the ear continuously regenerate and loss of 
auditory function likely is restored when damaged cells are replaced 
with new cells. Halvorsen et al. (2012b) showed that a TTS of 4-6 dB 
was recoverable within 24 hours for one species. Impacts would be most 
severe when the individual fish is close to the source and when the 
duration of exposure is long; both of which are conditions unlikely to 
occur for this survey that is necessarily transient in any given 
location and likely result in brief, infrequent noise exposure to prey 
species in any given area. For this survey, the sound source is 
constantly moving, and most fish would likely avoid the sound source 
prior to receiving sound of sufficient intensity to cause physiological 
or anatomical damage. In addition, ramp-up may allow certain fish 
species the opportunity to move further away from the sound source.
    A recent comprehensive review (Carroll et al., 2017) found that 
results are mixed as to the effects of airgun noise on the prey of 
marine mammals. While some studies suggest a change in prey 
distribution and/or a reduction in prey abundance following the use of 
seismic airguns, others suggest no effects or even positive effects in 
prey abundance. As one specific example, Paxton et al. (2017), which 
describes findings related to the effects of a 2014 seismic survey on a 
reef off of North Carolina, showed a 78 percent decrease in observed 
nighttime abundance for certain species. It is important to note that 
the evening hours during which the decline in fish habitat use was 
recorded (via video recording) occurred on the same day that the 
seismic survey passed, and no subsequent data is presented to support 
an inference that the response was long-lasting. Additionally, given 
that the finding is based on video images, the lack of recorded fish 
presence does not support a conclusion that the fish actually moved 
away from the site or suffered any serious impairment. In summary, this 
particular study corroborates prior studies indicating that a startle 
response or short-term displacement should be expected.
    A recent review article concluded that, while laboratory results 
provide scientific evidence for high-intensity and low-frequency sound-
induced physical trauma and other negative effects on some fish and 
invertebrates, the sound exposure scenarios in some cases are not 
realistic to those encountered by marine organisms during routine 
seismic operations (Carroll et al., 2017). The review finds that there 
has been no evidence of reduced catch or abundance following seismic 
activities for invertebrates, and that there is conflicting evidence 
for fish with catch observed to increase, decrease, or remain the same. 
Further, where there is evidence for decreased catch rates in response 
to airgun noise, these findings provide no information about the 
underlying biological cause of catch rate reduction (Carroll et al., 
2017).
    In summary, impacts of the specified activity on marine mammal prey 
species will likely be limited to behavioral responses, the majority of 
prey species will be capable of moving out of the area during the 
survey, a rapid return to normal recruitment, distribution, and 
behavior for prey species is anticipated, and, overall, impacts to prey 
species will be minor and temporary. Prey species exposed to sound 
might move away from the sound source, experience TTS, experience 
masking of biologically relevant sounds, or show no obvious direct 
effects. Mortality from decompression injuries is possible in close 
proximity to a sound, but only limited data on mortality in response to 
airgun noise exposure are available (Hawkins et al., 2014). The most 
likely impacts for most prey species in the survey area would be 
temporary avoidance of the area. The proposed survey would move through 
an area relatively quickly, limiting exposure to multiple impulsive 
sounds. In all cases, sound levels would return to ambient once the 
survey moves out of the area or ends and the noise source is shut down 
and, when exposure to sound ends, behavioral and/or physiological 
responses are expected to end relatively quickly (McCauley et al., 
2000b). The duration of fish avoidance of a given area after survey 
effort stops is unknown, but a rapid return to normal recruitment, 
distribution, and behavior is anticipated. While the potential for 
disruption of spawning aggregations or schools of important prey 
species can be meaningful on a local scale, the mobile and temporary 
nature of this survey and the likelihood of temporary avoidance 
behavior suggest that impacts would be minor.
    Acoustic Habitat--Acoustic habitat is the soundscape--which 
encompasses all of the sound present in a particular location and time, 
as a whole--when considered from the perspective of the animals 
experiencing it. Animals produce sound for, or listen for sounds 
produced by, conspecifics (communication during feeding, mating, and 
other social activities), other animals (finding prey or avoiding 
predators), and the physical environment (finding suitable habitats, 
navigating). Together, sounds made by animals and the geophysical 
environment (e.g., produced by earthquakes, lightning, wind, rain, 
waves) make up the natural contributions to the total acoustics of a 
place. These acoustic conditions, termed acoustic habitat, are one 
attribute of an animal's total habitat.
    Soundscapes are also defined by, and acoustic habitat influenced 
by, the total contribution of anthropogenic sound. This may include 
incidental emissions from sources such as vessel traffic, or may be 
intentionally introduced to the marine environment for data acquisition 
purposes (as in the use of airgun arrays). Anthropogenic noise varies 
widely in its frequency content, duration, and loudness and these 
characteristics greatly influence the potential habitat-mediated 
effects to marine mammals (please see also the previous discussion on 
masking under ``Acoustic Effects''),

[[Page 53465]]

which may range from local effects for brief periods of time to chronic 
effects over large areas and for long durations. Depending on the 
extent of effects to habitat, animals may alter their communications 
signals (thereby potentially expending additional energy) or miss 
acoustic cues (either conspecific or adventitious). For more detail on 
these concepts see, e.g., Barber et al., 2010; Pijanowski et al., 2011; 
Francis and Barber, 2013; Lillis et al., 2014.
    Problems arising from a failure to detect cues are more likely to 
occur when noise stimuli are chronic and overlap with biologically 
relevant cues used for communication, orientation, and predator/prey 
detection (Francis and Barber, 2013). Although the signals emitted by 
seismic airgun arrays are generally low frequency, they would also 
likely be of short duration and transient in any given area due to the 
nature of these surveys. As described previously, exploratory surveys 
such as these cover a large area but would be transient rather than 
focused in a given location over time and therefore would not be 
considered chronic in any given location.
    Based on the information discussed herein, we conclude that impacts 
of the specified activity are not likely to have more than short-term 
adverse effects on any prey habitat or populations of prey species. 
Further, any impacts to marine mammal habitat are not expected to 
result in significant or long-term consequences for individual marine 
mammals, or to contribute to adverse impacts on their populations.

Estimated Take of Marine Mammals

    This section provides an estimate of the number of incidental takes 
proposed for authorization through the IHA, which will inform both 
NMFS' consideration of ``small numbers,'' and the negligible impact 
determinations.
    Harassment is the only type of take expected to result from these 
activities. Except with respect to certain activities not pertinent 
here, section 3(18) of the MMPA defines ``harassment'' as any act of 
pursuit, torment, or annoyance, which (i) has the potential to injure a 
marine mammal or marine mammal stock in the wild (Level A harassment); 
or (ii) has the potential to disturb a marine mammal or marine mammal 
stock in the wild by causing disruption of behavioral patterns, 
including, but not limited to, migration, breathing, nursing, breeding, 
feeding, or sheltering (Level B harassment).
    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, 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 be behaviorally 
harassed or incur some degree of permanent hearing impairment; (2) the 
area or volume of water that will be ensonified above these levels in a 
day; (3) the density or occurrence of marine mammals within these 
ensonified areas; and, (4) the number of days of activities. We note 
that while these factors can contribute to a basic calculation to 
provide an initial prediction of potential takes, additional 
information that can qualitatively inform take estimates is also 
sometimes available (e.g., previous monitoring results or average group 
size). Below, we describe the factors considered here in more detail 
and present the proposed take estimates.

Acoustic Thresholds

    NMFS recommends the use of acoustic thresholds that identify the 
received level of underwater sound above which exposed marine mammals 
would be reasonably expected to be behaviorally harassed (equated to 
Level B harassment) or to incur PTS of some degree (equated to Level A 
harassment).
    Level B Harassment--Though significantly driven by received level, 
the onset of behavioral disturbance from anthropogenic noise exposure 
is also informed to varying degrees by other factors related to the 
source or exposure context (e.g., frequency, predictability, duty 
cycle, duration of the exposure, signal-to-noise ratio, distance to the 
source), the environment (e.g., bathymetry, other noises in the area, 
predators in the area), and the receiving animals (hearing, motivation, 
experience, demography, life stage, depth) and can be difficult to 
predict (e.g., Southall et al., 2007, 2021; Ellison et al., 2012). 
Based on what the available science indicates and the practical need to 
use a threshold based on a metric that is both predictable and 
measurable for most activities, NMFS typically uses a generalized 
acoustic threshold based on received level to estimate the onset of 
behavioral harassment. NMFS generally predicts that marine mammals are 
likely to be behaviorally harassed in a manner considered to be Level B 
harassment when exposed to underwater anthropogenic noise above root-
mean-squared pressure received levels (RMS SPL) of 120 dB (re 1 [mu]Pa) 
for continuous (e.g., vibratory pile driving, drilling) and above RMS 
SPL 160 dB re 1 [mu]Pa for non-explosive impulsive (e.g., seismic 
airguns) or intermittent (e.g., scientific sonar) sources. Generally 
speaking, Level B harassment take estimates based on these behavioral 
harassment thresholds are expected to include any likely takes by TTS 
as, in most cases, the likelihood of TTS occurs at distances from the 
source less than those at which behavioral harassment is likely. TTS of 
a sufficient degree can manifest as behavioral harassment, as reduced 
hearing sensitivity and the potential reduced opportunities to detect 
important signals (conspecific communication, predators, prey) may 
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-airgun) 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 (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 sources.
    These thresholds are provided in the Table 3 and 4 below. The 
references, analysis, and methodology used in the development of the 
thresholds are described in NMFS' 2018 Technical Guidance, which may be 
accessed at: www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

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.
    The proposed survey would entail the use of up to two 105 in\3\ 
airguns with a maximum total discharge of 210 in\3\ at a tow depth of 
3-4 m. Lamont-Doherty Earth Observatory (L-DEO) model results were used 
to determine the 160 dBrms radius for the two-airgun array 
in water depths >100 m. Received sound

[[Page 53466]]

levels were predicted by L-DEO's model (Diebold et al., 2010) as a 
function of distance from the airguns for the two 105 in\3\ airguns 
with a maximum total discharge of 210 in\3\. This modeling approach 
uses ray tracing for the direct wave traveling from the array to the 
receiver and its associated source ghost (reflection at the air-water 
interface in the vicinity of the array), in a constant-velocity half-
space (infinite homogenous ocean layer, unbounded by a seafloor).
    The proposed surveys would acquire data with up to two 105-in\3\ GI 
guns (separated by up to 2.4 m) at a tow depth of ~3-4 m. The shallow-
water radii are obtained by scaling the empirically derived 
measurements from the Gulf of Mexico 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 3.

 Table 3--Predicted Radial Distances From the R/V Brooks McCall Seismic
    Source to Isopleths Corresponding to Level B Harassment Threshold
------------------------------------------------------------------------
                                                            Predicted
                                                          distances (m)
         Airgun configuration           Water depth (m)     to 160 dB
                                                          received sound
                                                              level
------------------------------------------------------------------------
Two 105-in GI guns....................            <100        \1\ 1,750
------------------------------------------------------------------------
\1\ Distance is based on empirically derived measurements in the Gulf of
  Mexico with scaling applied to account for differences in tow depth.

    The ensonified area associated with Level A harassment is more 
technically challenging to predict due to the need to account for a 
duration component. Therefore, NMFS developed an optional user 
spreadsheet tool to accompany the Technical Guidance (2018) that can be 
used to relatively simply predict an isopleth distance for use in 
conjunction with marine mammal density or occurrence to help predict 
potential takes. We note that because of some of the assumptions 
included in the methods underlying this optional tool, we anticipate 
that the resulting isopleth estimates are typically going to be 
overestimates of some degree, which may result in an overestimate of 
potential take by Level A harassment. However, this optional tool 
offers the best way to estimate isopleth distances when more 
sophisticated modeling methods are not available or practical. Table 4 
presents the modeled PTS isopleths for mid-frequency cetaceans, the 
only hearing group for which takes are expected, based on L-DEO 
modeling incorporated in the companion User Spreadsheet (NMFS 2018).

 Table 4--Modeled Radial Distances to Isopleths Corresponding to Level A
                          Harassment Thresholds
------------------------------------------------------------------------
                      Hearing group                             MF
------------------------------------------------------------------------
PTS Peak................................................             1.5
PTS SELcum..............................................               0
------------------------------------------------------------------------

    Predicted distances to Level A harassment isopleths, which vary 
based on marine mammal hearing groups, were calculated based on 
modeling performed by L-DEO using the Nucleus software program and the 
NMFS User Spreadsheet, described below. The acoustic thresholds for 
impulsive sounds (e.g., airguns) contained in the Technical Guidance 
(2018) were presented as dual metric acoustic thresholds using both 
SELcum and peak sound pressure metrics (NMFS 2016a). As dual 
metrics, NMFS considers onset of PTS (Level A harassment) to have 
occurred when either one of the two metrics is exceeded (i.e., metric 
resulting in the largest isopleth). The SELcum metric 
considers both level and duration of exposure, as well as auditory 
weighting functions by marine mammal hearing group. In recognition of 
the fact that the requirement to calculate Level A harassment 
ensonified areas could be more technically challenging to predict due 
to the duration component and the use of weighting functions in the new 
SELcum thresholds, NMFS developed an optional User 
Spreadsheet that includes tools to help predict a simple isopleth that 
can be used in conjunction with marine mammal density or occurrence to 
facilitate the estimation of take numbers.
    The SELcum for the two-GI airgun array is derived from 
calculating the modified farfield signature. The farfield signature is 
often used as a theoretical representation of the source level. To 
compute the farfield signature, the source level is estimated at a 
large distance (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 interactions of the two 
airguns that occur near the source center and is calculated as a point 
source (single airgun), the modified farfield signature is a more 
appropriate measure of the sound source level for large arrays. For 
this smaller array, the modified farfield changes will be 
correspondingly smaller as well, but this method is used for 
consistency across all array sizes.
    Auditory injury for all species is unlikely to occur given the 
small modeled zones of injury (estimated zone less than 2 m for mid-
frequency cetaceans). Additionally, animals are expected to have 
aversive/compensatory

[[Page 53467]]

behavior in response to the activity (Nachtigall et al., 2018) further 
limiting the likelihood of auditory injury for all species. UT did not 
request authorization of take by Level A harassment, and no take by 
Level A harassment is proposed for authorization by NMFS.

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 northwest Gulf of Mexico, 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. (2022). The Garrison et 
al. (2022) data provides abundance estimates for marine mammal species 
in the Gulf of Mexico 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 created a 7-km perimeter 
around the survey area and used that perimeter to select the density 
hexagons for each species in each month. The 7-km distance was chosen 
for the perimeter to ensure that at least one full density hexagon 
outside the survey area in all directions was selected, providing a 
more robust sample for the calculations. They then calculated the mean 
of the predicted densities from the selected cells for each species and 
month. The highest mean monthly density was chosen for each species 
from the months of September to December (i.e., the months within which 
the survey is expected to occur). NMFS concurred with this approach to 
calculate species density.
    Rough-toothed dolphins were not modeled by Garrison et al. (2022) 
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 Gulf of Mexico. The same 7 km 
perimeter described above 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 5.

Table 5--Marine Mammal Densities and Total Ensonified Area of Activities
                       in the Proposed Survey Area
------------------------------------------------------------------------
                                             Estimated        Level B
                 Species                    density (#/     ensonified
                                              km\2\)       area (km\2\)
------------------------------------------------------------------------
Atlantic spotted dolphin................     \b\ 0.00082           7,866
Bottlenose dolphin \a\..................     \b\ 0.34024           7,866
Rough-toothed dolphin...................     \c\ 0.00362           7,866
------------------------------------------------------------------------
\a\ Bottlenose dolphin density estimate does not differentiate between
  coastal and shelf stocks.
\b\ Density calculated from Garrison et al. (2022).
\c\ Density calculated from Roberts et al. (2016).

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 (10 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 6.

                               Table 6--Estimated Take Proposed for Authorization
----------------------------------------------------------------------------------------------------------------
                                                  Estimated take     Proposed
                                                 ----------------   authorized
            Species                   Stock                            take            Stock        Percent of
                                                      Level B    ----------------  abundance \1\       stock
                                                                      Level B
----------------------------------------------------------------------------------------------------------------
Atlantic spotted dolphin......  Gulf of Mexico..               6          \2\ 26          21,506            0.12
Bottlenose dolphin \3\........  Gulf of Mexico             2,676           2,676          20,759           12.89
                                 Western Coastal.
                                Northern Gulf of                                          63,280            4.23
                                 Mexico
                                 Continental
                                 Shelf.
Rough-toothed dolphin.........  Gulf of Mexico..              28              28       \2\ 4,853            0.58
----------------------------------------------------------------------------------------------------------------
\1\ Stock abundance for Atlantic spotted dolphins and bottlenose dolphins was taken from Garrison et al. (2022).
  Stock abundance for rough-toothed dolphins was taken from Roberts et al. (2016), as Garrison et al. (2022) 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.


[[Page 53468]]

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.
    Mitigation measures that would be adopted during the planned survey 
include, but are not limited to: (1) vessel speed or course alteration, 
provided that doing so would not compromise operation safety 
requirements; (2) monitoring a pre-start clearance zone; and (3) ramp-
up procedures.

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 3). 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 one 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 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 is the gradual and systematic increase of emitted sound 
levels from an acoustic source. Ramp-up would begin with one GI airgun 
105 in\3\ first being activated, followed by the second after 5 
minutes. The intent of pre-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 ramp-up is to 
warn marine mammals in the vicinity of survey activities and to allow 
sufficient time for those animals to leave the immediate vicinity. A 
ramp-up procedure, involving a stepwise increase in the number of 
airguns are activated and the full volume is achieved, is required at 
all times as part of the activation of the acoustic source. All 
operators must adhere to the following pre-clearance and ramp-up 
requirements:
    (1) 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 the first airgun for 5 
minutes and then adding the second airgun; and
     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.
    (2) 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

[[Page 53469]]

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 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 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.

Vessel Strike Avoidance Measures

    These measures apply to all vessels associated with the planned 
survey activity; however, we note that 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. These measures include the following:
    (1) 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 be exercised when an animal is observed. 
A visual observer aboard the vessel must monitor a vessel strike 
avoidance zone around the vessel (specific distances detailed below), 
to ensure the potential for strike is minimized. Visual observers 
monitoring the vessel strike avoidance zone can be either third-party 
observers 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 baleen whale, sperm whale, or other marine mammals;
    (2) Vessel speeds must be reduced to 10 kn (18.5 kph) or less when 
mother and calf pairs, pods, or large assemblages of cetaceans are 
observed near a vessel;
    (3) All vessels must maintain a minimum separation distance of 100 
m from sperm whales;
    (4) All vessels must maintain a minimum separation distance of 500 
m 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 has been 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.
    (5) 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); and
    (6) When marine mammals are sighted while a vessel is underway, the 
vessel should 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). 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, 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. Two visual PSOs would be on duty at all time 
during daytime hours. Monitoring shall be conducted in accordance with 
the following requirements:
    (1) UT must 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, and to ensure that 
PSOs are capable of calibrating equipment as

[[Page 53470]]

necessary for accurate distance estimates and species identification. 
See Condition 5(d) in the IHA for list of equipment.
    PSOs must have the following requirements and qualifications:
    (1) PSOs shall be independent, dedicated and trained and must be 
employed by a third-party observer provider;
    (2) PSOs shall have no tasks other than to conduct visual 
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);
    (3) PSOs shall have successfully completed an approved PSO training 
course appropriate for their designated task (visual);
    (4) NMFS must review and approve PSO resumes accompanied by a 
relevant training course information packet that includes the name and 
qualifications (i.e., experience, training completed, or educational 
background) of the instructor(s), the course outline or syllabus, and 
course reference material as well as a document stating successful 
completion of the course;
    (5) 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;
    (6) PSOs must have successfully attained a bachelor's degree from 
an accredited college or university with a major in one of the natural 
sciences, a minimum of 30 semester hours or equivalent in the 
biological sciences, and at least one undergraduate course in math or 
statistics; and
    (7) 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 one week of receipt of submitted information. Alternate 
experience that may be considered includes, but is not limited to:
     Secondary education and/or experience comparable to PSO 
duties;
     Previous work experience conducting academic, commercial, 
or government-sponsored protected species surveys; or
     Previous work experience as a PSO; the PSO should 
demonstrate good standing and consistently good performance of PSO 
duties.
    At least one visual PSO must be unconditionally approved (i.e., 
have a minimum of 90 days at-sea experience working in that role at the 
particular Tier level (1-3) with no more than 18 months elapsed since 
the conclusion of the at-sea experience). One PSO with such experience 
shall be designated as the lead for the entire PSO team. The lead PSO 
shall serve as primary point of contact for the vessel operator. To the 
maximum extent practicable, the duty schedule shall be planned such 
that unconditionally-approved PSOs are on duty with conditionally-
approved PSOs.
    PSOs must use standardized electronic data collection forms. At a 
minimum, the following information must be recorded:
     Vessel name, vessel size and type, maximum speed 
capability of vessel;
     Dates (MM/DD/YYYY format) of departures and returns to 
port with port name;
     PSO names and affiliations, PSO identification (ID; 
initials or other identifier);
     Date (MM/DD/YYYY) and participants of PSO briefings;
     Visual monitoring equipment used (description);
     PSO location on vessel and height (in meters) of 
observation location above water surface;
     Watch status (description);
     Dates (MM/DD/YYYY) and times (Greenwich mean time (GMT) or 
coordinated universal time (UTC)) of survey on/off effort and times 
(GMC/UTC) corresponding with PSO on/off effort;
     Vessel location (decimal degrees) when survey effort began 
and ended and vessel location at beginning and end of visual PSO duty 
shifts;
     Vessel location (decimal degrees) at 30-second intervals 
if obtainable from data collection software, otherwise at practical 
regular interval;
     Vessel heading (compass heading) and speed (in knots) at 
beginning and end of visual PSO duty shifts and upon any change;
     Water depth (in meters) (if obtainable from data 
collection software);
     Environmental conditions while on visual survey (at 
beginning and end of PSO shift and whenever conditions change 
significantly), including BSS and any other relevant weather conditions 
including cloud cover, fog, sun glare, and overall visibility to the 
horizon;
     Factors that may have contributed to impaired observations 
during each PSO shift change or as needed as environmental conditions 
changed (description) (e.g., vessel traffic, equipment malfunctions); 
and
     Vessel/Survey activity information (and changes thereof) 
(description), such as acoustic source power output while in operation, 
number and volume of acoustic source operating in the array, tow depth 
of the acoustic source, and any other notes of significance (i.e., pre-
start clearance, ramp-up, shutdown, testing, shooting, ramp-up 
completion, end of operations, streamers, etc.).
    The following information should be recorded upon visual 
observation of any marine mammal:
     Sighting ID (numeric);
     Watch status (sighting made by PSO on/off effort, 
opportunistic, crew, alternate vessel/platform);
     Location of PSO/observer (description);
     Vessel activity at the time of the sighting (e.g., 
deploying, recovering, testing, shooting, data acquisition, other);
     PSO who sighted the animal/PSO ID;
     Time and date of sighting (GMT/UTC, MM/DD/YYYY);
     Initial detection method (description);
     Sighting cue (description);
     Vessel location at time of sighting (decimal degrees);
     Water depth (in meters);
     Direction of vessel's travel (compass direction);
     Speed (knots) of the vessel from which the observation was 
made;
     Direction of animal's travel relative to the vessel 
(description, compass heading);
     Bearing to sighting (degrees);
     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;
     Species reliability (an indicator of confidence in 
identification) (1 = unsure/possible, 2 = probable, 3 = definite/sure, 
9 = unknown/not recorded);
     Estimated distance to the animal (meters) and method of 
estimating distance;
     Estimated number of animals (high, low, and best) 
(numeric);
     Estimated number of animals by cohort (adults, yearlings, 
juveniles, calves, group composition, etc.);
     Description (as many distinguishing features as possible 
of each individual seen, including length, shape, color, pattern, scars 
or markings, shape and size of dorsal fin, shape of head, and blow 
characteristics);
     Detailed behavior observations (e.g., number of blows/
breaths, number of

[[Page 53471]]

surfaces, breaching, spyhopping, diving, feeding, traveling; as 
explicit and detailed as possible; note any observed changes in 
behavior);
     Animal's closest point of approach (in meters) and/or 
closest distance from any element of the acoustic source;
     Description of any actions implemented in response to the 
sighting (e.g., delays, shutdown, ramp-up) and time and location of the 
action.
     Photos (Yes or No);
     Photo Frame Numbers (List of numbers); and
     Conditions at time of sighting (Visibility; BSS).

Reporting

    UT must submit a draft comprehensive report to NMFS on all 
activities and monitoring results within 90 days of the completion of 
the survey or expiration of the IHA, whichever comes sooner. The report 
would describe the activities that were conducted and sightings of 
marine mammals. The report would provide full documentation of methods, 
results, and interpretation pertaining to all monitoring. The 90-day 
report would summarize the dates and locations of survey operations, 
and all marine mammal sightings (dates, times, locations, activities, 
associated seismic survey activities).
    The draft report shall also include geo-referenced time-stamped 
vessel tracklines for all time periods during which airguns were 
operating. Tracklines should include points recording any change in 
airgun status (e.g., when the airguns began operating, when they were 
turned off, or when they changed from full array to single gun or vice 
versa). Geographic information system (GIS) files shall be provided in 
Environmental Systems Research Institute (ESRI) shapefile format and 
include the UTC date and time, latitude in decimal degrees, and 
longitude in decimal degrees. All coordinates shall be referenced to 
the WGS84 geographic coordinate system. In addition to the report, all 
raw observational data shall be made available to NMFS. A final report 
must be submitted within 30 days following resolution of any comments 
on the draft report.

Reporting Injured or Dead Marine Mammals

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

Negligible Impact Analysis and Determination

    NMFS has defined negligible impact as an impact resulting from the 
specified activity that cannot be reasonably expected to, and is not 
reasonably likely to, adversely affect the species or stock through 
effects on annual rates of recruitment or survival (50 CFR 216.103). A 
negligible impact finding is based on the lack of likely adverse 
effects on annual rates of recruitment or survival (i.e., population-
level effects). An estimate of the number of takes alone is not enough 
information on which to base an impact determination. In addition to 
considering estimates of the number of marine mammals that might be 
``taken'' through harassment, NMFS considers other factors, such as the 
likely nature of any impacts or responses (e.g., intensity, duration), 
the context of any impacts or responses (e.g., critical reproductive 
time or location, foraging impacts affecting energetics), as well as 
effects on habitat, and the likely effectiveness of the mitigation. We 
also assess the number, intensity, and context of estimated takes by 
evaluating this information relative to population status. Consistent 
with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, 
September 29, 1989), the impacts from other past and ongoing 
anthropogenic activities are incorporated into this analysis via their 
impacts on the baseline (e.g., as reflected in the regulatory status of 
the species, population size and growth rate where known, ongoing 
sources of human-caused mortality, or ambient noise levels).
    To avoid repetition, the discussion of our analysis applies to all 
the species listed in Table 1, given that the anticipated effects of 
this activity on these different marine mammal stocks are expected to 
be similar. 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 from low-energy survey, 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, 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).
    In addition to being temporary, the maximum expected Level B 
harassment

[[Page 53472]]

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 (10 days) of the 
disturbance and the availability of similar habitat and resources in 
the surrounding area, the impacts to marine mammals and the food 
sources that they utilize are not expected to cause significant or 
long-term consequences for individual marine mammals or their 
populations.
    There are no rookeries, mating, or calving grounds known to be 
biologically important to marine mammals within the 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 the species or stock 
through effects on annual rates of recruitment or survival:
    (1) No serious injury or mortality is anticipated or proposed to be 
authorized;
    (2) No Level A harassment is anticipated, even in the absence of 
mitigation measures or proposed to be authorized;
    (3) Take is anticipated to be by Level B harassment only consisting 
of temporary behavioral changes of small percentages of the affected 
species due to avoidance of the area around the survey vessel. The 
relatively short duration of the proposed survey (10 days) would 
further limit the potential impacts of any temporary behavioral changes 
that would occur;
    (4) The availability of alternate areas of similar habitat value 
for marine mammals to temporarily vacate the survey area during the 
proposed survey to avoid exposure to sounds from the activity;
    (5) Foraging success is not likely to be significantly impacted as 
effects on prey species for marine mammals would be temporary and 
spatially limited; and
    (6) The proposed mitigation measures, including visual monitoring, 
ramp-ups, and shutdowns are expected to minimize potential impacts to 
marine mammals.
    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 section 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.
    NMFS proposes to authorize incidental take by Level B harassment of 
3 marine mammal species with four managed stocks. The total amount of 
takes proposed for authorization relative to the best available 
population abundance is less than 5 percent for 3 managed stocks and 
less than 13 percent for 1 managed stock (Gulf of Mexico Western 
Coastal stock of bottlenose dolphin assuming all takes by Level b 
harassment are of this stock; see Take Estimation subsection) (Table 
6). The take numbers proposed for authorization are considered 
conservative estimates for purposes of the small numbers determination 
as they assume all takes represent different individual animals, which 
is unlikely to be the case.
    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 (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 the 
northwest Gulf of Mexico within Texas State waters during fall 2023, 
provided the previously mentioned mitigation, monitoring, and reporting 
requirements are incorporated. A draft of the proposed IHA can be found 
at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities.

Request for Public Comments

    We request comment on our analyses, the proposed authorization, and 
any other aspect of this notice of proposed IHA for the proposed marine 
geophysical survey. We also request comment on the potential renewal of 
this proposed IHA as described in the paragraph below. Please include 
with your comments any supporting data or literature citations to help 
inform decisions on the request for this IHA or a subsequent renewal 
IHA.
    On a case-by-case basis, NMFS may issue a one-time, 1-year renewal 
IHA following notice to the public providing an additional 15 days for 
public

[[Page 53473]]

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

    Dated: August 3, 2023.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2023-16945 Filed 8-7-23; 8:45 am]
BILLING CODE 3510-22-P