Marine Mammals; Incidental Take During Specified Activities; Proposed Incidental Harassment Authorization for Southwest Alaska Stock of Northern Sea Otters in Kodiak, Alaska, 4970-4984 [2024-01416]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 89, Number 17 (Thursday, January 25, 2024)]
[Notices]
[Pages 4970-4984]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-01416]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

[Docket No. FWS-R7-ES-2023-0212; FXES111607MRG01-245-FF07CAMM00]


Marine Mammals; Incidental Take During Specified Activities; 
Proposed Incidental Harassment Authorization for Southwest Alaska Stock 
of Northern Sea Otters in Kodiak, Alaska

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of receipt of application; proposed incidental 
harassment authorization; draft environmental assessment; request for 
comments.

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SUMMARY: We, the U.S. Fish and Wildlife Service, in response to a 
request under the Marine Mammal Protection Act of 1972, as amended, 
from Trident Seafoods Corporation, propose to authorize nonlethal 
incidental take by harassment of small numbers of the Southwest Alaska 
stock of northern sea otters (Enhydra lutris kenyoni) for 1 year from 
the date of issuance of the incidental harassment authorization. The 
applicant requested this authorization for take by harassment that may 
result from activities associated with pile driving and marine 
construction activities in Near Island Channel in Kodiak, Alaska. We 
estimate that this project may result in the nonlethal incidental take 
by harassment of up to 460 northern sea otters from the Southwest 
Alaska stock. This proposed authorization, if finalized, will be for up 
to 3,160 takes of 460 northern sea otters by Level B harassment. No 
take by Level A harassment or lethal take are requested, or expected, 
and no such take will be authorized.

DATES: Comments on this proposed incidental harassment authorization 
and the accompanying draft environmental assessment must be received by 
February 26, 2024.

ADDRESSES: 
    Accessing documents: You may view this proposed incidental 
harassment authorization, the application package, supporting 
information, draft environmental assessment, and the list of references 
cited herein at https://www.regulations.gov under Docket No. FWS-R7-ES-
2023-0212. Alternatively, you may request these documents from the 
person listed under FOR FURTHER INFORMATION CONTACT.
    Submitting comments: You may submit comments on the proposed 
authorization by one of the following methods:
     U.S. mail: Public Comments Processing, Attn: Docket No. 
FWS-R7-ES-2023-212, U.S. Fish and Wildlife Service, MS: PRB (JAO/3W), 
5275 Leesburg Pike, Falls Church, VA 22041-3803.
     Internet: https://www.regulations.gov. Follow the 
instructions for submitting comments to Docket No. FWS-R7-ES-2023-212.
    We will post all comments at https://www.regulations.gov. You may 
request that we withhold personal identifying information from public 
review; however, we cannot guarantee that we will be able to do so. See 
Request for Public Comments for more information.

FOR FURTHER INFORMATION CONTACT: Charles Hamilton, by U.S. mail at the 
U.S. Fish and Wildlife Service, MS 341, 1011 East Tudor Road, 
Anchorage, AK 99503; by email at [email protected]; or by 
telephone at 1-800-362-5148. Individuals in the United States who are 
deaf, deafblind, hard of hearing, or have a speech disability may dial 
711 (TTY, TDD, or TeleBraille) to access telecommunications relay 
services. Individuals outside the United States should use the relay 
services offered within their country to make international calls to 
the point-of-contact in the United States.

SUPPLEMENTARY INFORMATION:

Background

    Section 101(a)(5)(D) of the Marine Mammal Protection Act of 1972 
(MMPA; 16 U.S.C. 1361 et seq.) authorizes the Secretary of the Interior 
(Secretary) to allow, upon request, the incidental, but not 
intentional, taking by harassment of small numbers of marine mammals in 
response to requests by U.S. citizens (as defined in title 50 of the 
Code of Federal Regulations (CFR) in part 18, at 50 CFR 18.27(c)) 
engaged in a specified activity (other than commercial fishing) in a 
specified geographic region during a period of not more than 1 year. 
The Secretary has delegated authority for implementation of the MMPA to 
the U.S. Fish and Wildlife Service (``Service'' or ``we''). According 
to the MMPA, the Service shall allow this incidental taking if we make 
findings that the total of such taking for the 1-year period:
    (1) is of small numbers of marine mammals of a species or stock;
    (2) will have a negligible impact on such species or stocks; and
    (3) will not have an unmitigable adverse impact on the availability 
of these species or stocks for taking for subsistence use by Alaska 
Natives.
    If the requisite findings are made, we issue an authorization that 
sets forth the following, where applicable:
    (a) permissible methods of taking;
    (b) means of effecting the least practicable adverse impact on the 
species or stock and its habitat and the availability of the species or 
stock for subsistence uses; and
    (c) requirements for monitoring and reporting of such taking by 
harassment, including, in certain circumstances, requirements for the 
independent peer review of proposed monitoring plans or other research 
proposals.
    The term ``take'' means to harass, hunt, capture, or kill, or to 
attempt to harass, hunt, capture, or kill any marine mammal. 
``Harassment'' means any act of pursuit, torment, or annoyance which 
(i) has the potential to injure a marine mammal or marine mammal stock 
in the wild (the MMPA defines this as ``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 (the MMPA defines this as ``Level B harassment'').
    The terms ``negligible impact'' and ``unmitigable adverse impact'' 
are defined in 50 CFR 18.27 (i.e., regulations governing small takes of 
marine mammals incidental to specified activities) as follows: 
``Negligible impact'' is 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. ``Unmitigable adverse impact'' 
means an impact resulting from the specified activity: (1) that is 
likely to reduce the availability of the species to a level 
insufficient for a harvest to meet

[[Page 4971]]

subsistence needs by (i) causing the marine mammals to abandon or avoid 
hunting areas, (ii) directly displacing subsistence users, or (iii) 
placing physical barriers between the marine mammals and the 
subsistence hunters; and (2) that cannot be sufficiently mitigated by 
other measures to increase the availability of marine mammals to allow 
subsistence needs to be met.
    The term ``small numbers'' is also defined in 50 CFR 18.27. 
However, we do not rely on that definition here as it conflates ``small 
numbers'' with ``negligible impacts.'' We recognize ``small numbers'' 
and ``negligible impacts'' as two separate and distinct considerations 
when reviewing requests for incidental harassment authorizations (IHA) 
under the MMPA (see Natural Res. Def. Council, Inc. v. Evans, 232 F. 
Supp. 2d 1003, 1025 (N.D. Cal. 2003)). Instead, for our small numbers 
determination, we estimate the likely number of marine mammals to be 
taken and evaluate if that number is small relative to the size of the 
species or stock.
    The term ``least practicable adverse impact'' is not defined in the 
MMPA or its enacting regulations. For this IHA, we ensure the least 
practicable adverse impact by requiring mitigation measures that are 
effective in reducing the impact of project activities, but they are 
not so restrictive as to make project activities unduly burdensome or 
impossible to undertake and complete.
    If the requisite findings are made, we shall issue an IHA, which 
may set forth the following, where applicable: (i) permissible methods 
of taking; (ii) 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 subsistence 
uses by coastal-dwelling Alaska Natives (if applicable); and (iii) 
requirements for monitoring and reporting take by harassment.

Summary of Request

    On May 25, 2023, Trident Seafoods Corporation (hereafter 
``Trident'' or ``the applicant'') submitted a request to the Service 
for authorization to take by Level B harassment a small number of 
northern sea otters (Enhydra lutris kenyoni) (hereafter ``sea otters'' 
or ``otters'' unless another species is specified) from the Southwest 
Alaska stock. The Service sent requests for additional information on 
May 30, June 13, July 26, August 30, September 25, and October 5, 2023. 
We received updated versions of the request on July 17, September 5, 
and October 9. The Service determined the October 9, 2023, application 
to be adequate and complete. Trident expects take by harassment may 
occur during the construction of their crew bunkhouse and associated 
facilities in Near Island Channel at Kodiak, Alaska.

Description of Specified Activities and Specified Geographic Region

    The specified activity (hereafter ``project'') will include 
installation and removal of piles for the construction of a ~46-by-23-
meter (m) (~150-by-75-foot (ft)) dock at Trident's crew bunkhouse in 
Kodiak, Alaska (see figure below), between March 2024 and March 2025. 
Trident will remove sixty 41-centimeter (cm) (16-inch (in)) diameter 
steel piles, seventy-five 36-cm (14-in) steel piles, and 100 36-cm (14-
in) timber piles, and will permanently install the following types of 
piles: twenty-six 41-cm (16-in) and fifty-two 61-cm (24-in) diameter 
steel piles. Twenty 61-cm (24-in) diameter steel piles will be 
temporarily installed. Dock components that will be installed out of 
water include bull rail, fenders, mooring cleat, pre-cast concrete dock 
surface, and mast lights. Pile-driving activities will occur over 55 
nonconsecutive days for approximately 94 hours during the course of 1 
year from the date of issuance of the IHA. If the IHA is issued after 
Trident's intended start date in March 2024, the schedule for 
conducting the specified activities may be adjusted accordingly. Pile 
installation will be done with a combination of vibratory and down-the-
hole (DTH) drilling. Temporary and extant piles will be removed by the 
deadpull method; it is anticipated that up to 10 percent of piles may 
require vibratory removal. Materials and equipment will be transported 
via barges, and workers will be transported to and from the barge work 
platform via skiff.
    Additional project details may be reviewed in the application 
materials available as described under ADDRESSES or may also be 
requested as described under FOR FURTHER INFORMATION CONTACT.

[[Page 4972]]

[GRAPHIC] [TIFF OMITTED] TN25JA24.007

Description of Marine Mammals in the Specified Geographic Region

Sea Otter Biology

    There are three sea otter stocks in Alaska: the Southeast Alaska 
stock, the Southcentral Alaska stock, and the Southwest Alaska stock. 
Only the Southwest Alaska stock is represented in the project area. 
Detailed information about the biology of this stock can be found in 
the most recent Southwest Alaska revised stock assessment report (USFWS 
2023), announced in the Federal Register at 88 FR 53510, August 8, 
2023, and also available at https://www.regulations.gov/document/FWS-R7-ES-2022-0155-0012 and https://www.fws.gov/media/northern-sea-otter-southwest-alaska-stock-assessment-report-0.
    Sea otters may be distributed anywhere within the specified project 
area other than upland areas; however, they generally occur in shallow 
water near the shoreline. They are most commonly observed within the 
40-m (131-ft) depth contour (USFWS 2023), although they can be found in 
areas with deeper water. Ocean depth is generally correlated with 
distance to shore, and sea otters typically remain within 1 to 2 
kilometers (km) (0.62 to 1.24 miles (mi)) of shore (Riedman and Estes 
1990). They tend to be found closer to shore during storms but venture 
farther out during good weather and calm seas (Lensink 1962; Kenyon 
1969).
    Sea otters are nonmigratory and generally do not disperse over long 
distances (Garshelis and Garshelis 1984), usually remaining within a 
few kilometers of their established feeding grounds (Kenyon 1981). 
Breeding males stay for all or part of the year in a breeding territory 
covering up to 1 km (0.62 mi) of coastline, while adult females 
maintain home ranges of approximately 8 to 16 km (5 to 10 mi), which 
may include one or more male territories. Juveniles move greater 
distances between resting and foraging areas (Lensink 1962; Kenyon 
1969; Riedman and Estes 1990; Tinker and Estes 1996). Although sea 
otters generally remain local to an area, they are capable of long-
distance travel. Sea otters in Alaska have shown daily movement 
distances greater than 3 km (1.9 mi) at speeds up to 5.5 km per hour 
(3.4 mi per hour) (Garshelis and Garshelis 1984).

Southwest Alaska Sea Otter Stock

    The Southwest Alaska sea otter stock occurs from western Cook Inlet 
to Attu Island in the Aleutian chain (USFWS 2023). On August 9, 2005, 
the Southwest Alaska sea otter stock was listed as threatened under the 
Endangered Species Act (ESA) as a distinct population segment (DPS) (70 
FR 46366). This stock is divided into five management units: Western 
Aleutians; Eastern Aleutians; South Alaska Peninsula; Bristol Bay; and 
Kodiak, Kamishak, and Alaska Peninsula (USFWS 2013, 2023). The 
specified geographic region occurs within the ranges of the Kodiak, 
Kamishak, and Alaska Peninsula management units.
    The range of the Kodiak, Kamishak, and Alaska Peninsula management 
unit extends from Castle Cape to Western Cook Inlet on the southern 
side of the Alaska Peninsula and also encompasses Kodiak Island (USFWS 
2020). The specified geographic region is within

[[Page 4973]]

the range of the sea otter population at Kodiak Archipelago. Waters 
surrounding Kodiak Island were surveyed in 2014 using the Bodkin-
Udevitz aerial survey protocol (Cobb 2018). The estimate of sea otter 
density that resulted from these surveys is 2.54 animals per square 
kilometer (km\2\). Data collected by ABR, Inc.--Environmental Research 
& Services during work at the Kodiak ferry terminal (ABR 2016) indicate 
periods with presence of higher numbers of sea otters, occasionally 
with rafts of above 200 animals and daily counts of sea otters totaling 
over 450 individuals. It is likely that sea otters use Near Island 
Channel, which is relatively protected in comparison with surrounding 
coastline, for shelter during storm events.

Potential Impacts of the Specified Activities on Marine Mammals

Effects of Noise on Sea Otters

    We characterized ``noise'' as sound released into the environment 
from human activities that exceeds ambient levels or interferes with 
normal sound production or reception by sea otters. The terms 
``acoustic disturbance'' or ``acoustic harassment'' are disturbances or 
harassment events resulting from noise exposure. Potential effects of 
noise exposure are likely to depend on the distance of the sea otter 
from the sound source, the level and intensity of sound the sea otter 
receives, background noise levels, noise frequency, noise duration, and 
whether the noise is pulsed or continuous. The actual noise level 
perceived by individual sea otters will also depend on whether the sea 
otter is above or below water and atmospheric and environmental 
conditions. Temporary disturbance of sea otters or localized 
displacement reactions are the most likely effects to occur from noise 
exposure.

Sea Otter Hearing

    Pile driving and marine construction activities will fall within 
the hearing range of sea otters. Controlled sound exposure trials on 
southern sea otters (Enhydra lutris nereis) indicate that sea otters 
can hear frequencies between 125 hertz (Hz) and 38 kilohertz (kHz) with 
best sensitivity between 1.2 and 27 kHz (Ghoul and Reichmuth 2014). 
Aerial and underwater audiograms for a captive adult male southern sea 
otter in the presence of ambient noise suggest the sea otter's hearing 
was less sensitive to high-frequency (greater than 22 kHz) and low-
frequency (less than 2 kHz) sound than terrestrial mustelids but was 
similar to that of a California sea lion (Zalophus californianus). 
However, the sea otter was still able to hear low-frequency sounds, and 
the detection thresholds for sounds between 0.125-1 kHz were between 
116-101 decibels (dB), respectively. Dominant frequencies of southern 
sea otter vocalizations are between 3 and 8 kHz, with some energy 
extending above 60 kHz (McShane et al. 1995, Ghoul and Reichmuth 2012).
    Exposure to high levels of sound may cause changes in behavior, 
masking of communications, temporary or permanent changes in hearing 
sensitivity, discomfort, and injury to marine mammals. Unlike other 
marine mammals, sea otters do not rely on sound to orient themselves, 
locate prey, or communicate under water; therefore, masking of 
communications by anthropogenic sound is less of a concern than for 
other marine mammals. However, sea otters, especially mothers and pups, 
do use sound for communication in air (McShane et al. 1995), and sea 
otters may monitor underwater sound to avoid predators (Davis et al. 
1987).

Exposure Thresholds

Underwater Sounds
    Noise exposure criteria for identifying underwater noise levels 
capable of causing Level A harassment to marine mammal species, 
including sea otters, have been established using the same methods as 
those used by the National Marine Fisheries Service (NMFS) (Southall et 
al. 2019). These criteria are based on estimated levels of sound 
exposure capable of causing a permanent shift in sensitivity of hearing 
(i.e., a permanent threshold shift (PTS) (NMFS 2018)). PTS occurs when 
noise exposure causes hairs within the inner ear system to die (Ketten 
2012). Although the effects of PTS are, by definition, permanent, PTS 
does not equate to total hearing loss.
    Sound exposure thresholds incorporate two metrics of exposure: the 
peak level of instantaneous exposure likely to cause PTS and the 
cumulative sound exposure level (SELCUM) during a 24-hour 
period. They also include weighting adjustments for the sensitivity of 
different species to varying frequencies. PTS-based injury criteria 
were developed from theoretical extrapolation of observations of 
temporary threshold shifts (TTS) detected in lab settings during sound 
exposure trials (Finneran 2015). Southall and colleagues (2019) predict 
PTS for sea otters, which are included in the ``other marine 
carnivores'' category, will occur at 232 dB peak or 203 dB 
SELCUM for impulsive underwater sound and 219 dB 
SELCUM for non-impulsive (continuous) underwater sound.
    Thresholds based on TTS have been used as a proxy for Level B 
harassment (i.e., 70 FR 1871, January 11, 2005; 71 FR 3260, January 20, 
2006; 73 FR 41318, July 18, 2008). Southall et al. (2007) derived TTS 
thresholds for pinnipeds (walruses, seals, and sea lions) based on 212 
dB peak and 171 dB SELCUM. Exposures resulting in TTS in 
pinnipeds were found to range from 152 to 174 dB (183 to 206 dB SEL) 
(Kastak et al. 2005), with a persistent TTS, if not a PTS, after 60 
seconds of 184 dB SEL (Kastak et al. 2008). Kastelein et al. (2012) 
found small but statistically significant TTS at approximately 170 dB 
SEL (136 dB, 60 minutes) and 178 dB SEL (148 dB, 15 minutes). Based on 
these findings, Southall et al. (2019) developed TTS thresholds for sea 
otters, which are included in the ``other marine carnivores'' category, 
of 188 dB SELCUM for impulsive sounds and 199 dB 
SELCUM for non-impulsive sounds.
    The NMFS (2018) criteria do not identify thresholds for avoidance 
of Level B harassment. For pinnipeds (seals and sea lions), NMFS has 
adopted a 160-dB threshold for Level B harassment from exposure to 
impulsive noise and a 120-dB threshold for continuous noise (NMFS 1998, 
HESS 1999, NMFS 2018). These thresholds were developed from 
observations of mysticete (baleen) whales responding to airgun 
operations (e.g., Malme et al. 1983; Malme and Miles 1983; Richardson 
et al. 1986, 1995) and from equating Level B harassment with noise 
levels capable of causing TTS in lab settings. Southall et al. (2007, 
2019) assessed behavioral response studies and found considerable 
variability among pinnipeds. The authors determined that exposures 
between approximately 90 to 140 dB generally do not appear to induce 
strong behavioral responses from pinnipeds in water. However, they 
found behavioral effects, including avoidance, become more likely in 
the range between 120 to 160 dB, and most marine mammals showed some, 
albeit variable, responses to sound between 140 to 180 dB. Wood et al. 
(2012) adapted the approach identified in Southall et al. (2007) to 
develop a probabilistic scale for marine mammal taxa at which 10 
percent, 50 percent, and 90 percent of individuals exposed are assumed 
to produce a behavioral response. For many marine mammals, including 
pinnipeds, these response rates were set at sound pressure levels of 
140, 160, and 180 dB, respectively.

[[Page 4974]]

    We have evaluated these thresholds and determined that the Level B 
threshold of 120 dB for non-impulsive noise is not applicable to sea 
otters. The 120-dB threshold is based on studies in which gray whales 
(Eschrichtius robustus) were exposed to experimental playbacks of 
industrial noise (Malme et al. 1983; Malme and Miles 1983). During 
these playback studies, southern sea otter responses to industrial 
noise were also monitored (Riedman 1983, 1984). Gray whales exhibited 
avoidance to industrial noise at the 120-dB threshold; however, there 
was no evidence of disturbance reactions or avoidance in southern sea 
otters. Thus, given the different range of frequencies to which sea 
otters and gray whales are sensitive, the NMFS 120-dB threshold based 
on gray whale behavior is not appropriate for predicting sea otter 
behavioral responses, particularly for low-frequency sound.
    Based on the lack of sea otter disturbance response or any other 
reaction to the playback studies from the 1980s, as well as the absence 
of a clear pattern of disturbance or avoidance behaviors attributable 
to underwater sound levels up to about 160 dB resulting from low-
frequency broadband noise, we assume 120 dB is not an appropriate 
behavioral response threshold for sea otters exposed to continuous 
underwater noise.
    Based on the best available scientific information about sea 
otters, and closely related marine mammals when sea otter data are 
limited, the Service has set 160 dB of received underwater sound as a 
threshold for Level B harassment by disturbance for sea otters for this 
proposed IHA. Exposure to unmitigated in-water noise levels between 125 
Hz and 38 kHz that are greater than 160 dB--for both impulsive and non-
impulsive sound sources--will be considered by the Service as Level B 
harassment. Thresholds for Level A harassment (which entails the 
potential for injury) will be 232 dB peak or 203 dB SELCUM 
for impulsive sounds and 219 dB SELCUM for continuous sounds 
(table 1).
Airborne Sounds
    The NMFS (2018) guidance neither addresses thresholds for 
preventing injury or disturbance from airborne noise, nor provides 
thresholds for avoidance of Level B harassment. Southall et al. (2007) 
suggested thresholds for PTS and TTS for sea lions exposed to nonpulsed 
airborne noise of 172.5 and 159 dB re (20 [mu]Pa)\2\-s SEL. Conveyance 
of underwater noise into the air is of little concern since the effects 
of pressure release and interference at the water's surface reduce 
underwater noise transmission into the air. For activities that create 
both in-air and underwater sounds, we will estimate take based on 
parameters for underwater noise transmission. Considering sound energy 
travels more efficiently through water than through air, this 
estimation will also account for exposures to sea otters at the 
surface.

   Table 1--Temporary Threshold Shift (TTS) and Permanent Threshold Shift (PTS) Thresholds Established by Southall et al. (2019) Through Modeling and
                                        Extrapolation for ``Other Marine Carnivores,'' Which Includes Sea Otters
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                        TTS                                        PTS
                                                                    ------------------------------------------------------------------------------------
                                                                      Non-impulsive          Impulsive           Non-impulsive          Impulsive
                                                                    ------------------------------------------------------------------------------------
                                                                         SELCUM         SELCUM      Peak SPL        SELCUM         SELCUM      Peak SPL
--------------------------------------------------------------------------------------------------------------------------------------------------------
Air................................................................             157          146          170              177          161          176
Water..............................................................             199          188          226              219          203          232
--------------------------------------------------------------------------------------------------------------------------------------------------------
Note: Values are weighted for other marine carnivores' hearing thresholds and given in cumulative sound exposure level (SELCUM dB re (20 micropascal
  ([mu]Pa) in air and SELCUM dB re 1 [mu]Pa in water) for impulsive and non-impulsive sounds and unweighted peak sound pressure level (SPL) in air (dB
  re 20[mu]Pa) and water (dB 1[mu]Pa) (impulsive sounds only).

Evidence From Sea Otter Studies

    Sea otters may be more resistant to the effects of sound 
disturbance and human activities than other marine mammals. For 
example, observers have noted no changes from southern sea otters in 
regard to their presence, density, or behavior in response to 
underwater sounds from industrial noise recordings at 110 dB and a 
frequency range of 50 Hz to 20 kHz and airguns, even at the closest 
distance of 0.5 nautical miles (<1 km or 0.6 mi) (Riedman 1983). 
Southern sea otters did not respond noticeably to noise from a single 
1,638 cubic centimeters (cm\3\) (100 cubic inches [in\3\]) airgun, and 
no sea otter disturbance reactions were evident when a 67,006 cm\3\ 
(4,089 in\3\) airgun array was as close as 0.9 km (0.6 mi) to sea 
otters (Riedman 1983, 1984). However, southern sea otters displayed 
slight reactions to airborne engine noise (Riedman 1983).
    Northern sea otters were observed to exhibit a limited response to 
a variety of airborne and underwater sounds, including a warble tone, 
sea otter pup calls, calls from killer whales (Orcinus orca) (which are 
predators to sea otters), air horns, and an underwater noise harassment 
system designed to drive marine mammals away from crude oil spills 
(Davis et al. 1988). These sounds elicited reactions from northern sea 
otters, including startle responses and movement away from noise 
sources. However, these reactions were observed only when northern sea 
otters were within 100 to 200 m (328 to 656 ft) of noise sources. 
Further, northern sea otters appeared to become habituated to the 
noises within 2 hours or, at most, 3-4 days (Davis et al. 1988).
    Noise exposure may be influenced by the amount of time sea otters 
spend at the water's surface. Noise at the water's surface can be 
attenuated by turbulence from wind and waves more quickly compared to 
deeper water, reducing potential noise exposure (Greene and Richardson 
1988, Richardson et al. 1995). Additionally, turbulence at the water's 
surface limits the transference of sound from water to air. A sea otter 
with its head above water will be exposed to only a small fraction of 
the sound energy traveling through the water beneath it. The average 
amount of time that sea otters spend above the water each day while 
resting and grooming varies between males and females and across 
seasons (Esslinger et al. 2014, Zellmer et al. 2021). For example, 
female sea otters foraged for an average of 8.78 hours per day compared 
to male sea otters, which foraged for an average of 7.85 hours per day 
during the summer months (Esslinger et al. 2014). Male and female sea 
otters spend an average of 63 to 67 percent of their day at the surface 
resting and grooming during the summer months (Esslinger et al. 2014). 
Few studies have evaluated

[[Page 4975]]

foraging times during the winter months. Garshelis et al. (1986) found 
that foraging times increased from 5.1 hours per day to 16.6 hours per 
day in the winter; however, Gelatt et al. (2002) did not find a 
significant difference in seasonal foraging times. It is likely that 
seasonal variation is determined by seasonal differences in energetic 
demand and the quality and availability of prey sources (Esslinger et 
al. 2014). These findings suggest that the large portion of the day sea 
otters spend at the surface may help limit sea otters' exposure during 
noise-generating operations.
    Sea otter sensitivity to industrial activities may be influenced by 
the overall level of human activity within the sea otter population's 
range. In locations that lack frequent human activity, sea otters 
appear to have a lower threshold for disturbance. Sea otters in Alaska 
exhibited escape behaviors in response to the presence and approach of 
vessels (Udevitz et al. 1995). Behaviors included diving or actively 
swimming away from a vessel, entering the water from haulouts, and 
disbanding groups with sea otters swimming in multiple different 
directions (Udevitz et al. 1995). Sea otters in Alaska were also 
observed to avoid areas with heavy boat traffic in the summer and 
return to these areas during seasons with less vessel traffic 
(Garshelis and Garshelis 1984). In Cook Inlet, sea otters drifting on a 
tide trajectory that would have taken them within 500 m (0.3 mi) of an 
active offshore drilling rig were observed to swim in order to avoid a 
close approach of the drilling rig despite near-ambient noise levels 
(BlueCrest 2013).
    Individual sea otters in Near Island Channel will likely show a 
range of responses to noise from pile-driving activities. Some sea 
otters will likely dive, show startle responses, change direction of 
travel, or prematurely surface. Sea otters reacting to pile-driving 
activities may divert time and attention from biologically important 
behaviors, such as feeding and nursing pups. Sea otter responses to 
disturbance can result in energetic costs, which increases the amount 
of prey required by sea otters (Barrett 2019). This increased prey 
consumption may impact sea otter prey availability and cause sea otters 
to spend more time foraging and less time resting (Barrett 2019). Some 
sea otters may abandon the project area and return when the disturbance 
has ceased. Based on the observed movement patterns of sea otters 
(i.e., Lensink 1962; Kenyon 1969, 1981; Garshelis and Garshelis 1984; 
Riedman and Estes 1990; Tinker and Estes 1996), we expect some 
individuals will respond to pile-driving activities by dispersing to 
nearby areas of suitable habitat; however, other sea otters, especially 
territorial adult males, are less likely to be displaced.

Consequences of Disturbance

    The reactions of wildlife to disturbance can range from short-term 
behavioral changes to long-term impacts that affect survival and 
reproduction. When disturbed by noise, animals may respond behaviorally 
(e.g., escape response) or physiologically (e.g., increased heart rate, 
hormonal response) (Harms et al. 1997, Tempel and Guti[eacute]rrez 
2003). Theoretically, the energy expense and associated physiological 
effects from repeated disturbance could ultimately lead to reduced 
survival and reproduction (Gill and Sutherland 2000, Frid and Dill 
2002). For example, South American sea lions (Otaria byronia) visited 
by tourists exhibited an increase in the state of alertness and a 
decrease in maternal attendance and resting time on land, thereby 
potentially reducing population size (Pavez et al. 2015). In another 
example, killer whales that lost feeding opportunities due to boat 
traffic faced a substantial (18 percent) estimated decrease in energy 
intake (Williams et al. 2006). In severe cases, such disturbance 
effects could have population-level consequences. For example, 
increased disturbance by tourism vessels has been associated with a 
decline in abundance of bottlenose dolphins (Tursiops spp.) (Bejder et 
al. 2006, Lusseau et al. 2006). However, these examples evaluated 
sources of disturbance that were longer term and more consistent than 
the temporary and intermittent nature of the specified project 
activities.
    These examples illustrate direct effects on survival and 
reproductive success, but disturbances can also have indirect effects. 
Response to noise disturbance is considered a nonlethal stimulus that 
is similar to an antipredator response (Frid and Dill 2002). Sea otters 
are susceptible to predation, particularly from killer whales and 
eagles, and have a well-developed antipredator response to perceived 
threats. For example, the presence of a harbor seal (Phoca vitulina) 
did not appear to disturb southern sea otters, but they demonstrated a 
fear response in the presence of a California sea lion by actively 
looking above and beneath the water (Limbaugh 1961).
    Although an increase in vigilance or a flight response is 
nonlethal, a tradeoff occurs between risk avoidance and energy 
conservation. An animal's reactions to noise disturbance may cause 
stress and direct an animal's energy away from fitness-enhancing 
activities such as feeding and mating (Frid and Dill 2002, Goudie and 
Jones 2004). For example, southern sea otters in areas with heavy 
recreational boat traffic demonstrated changes in behavioral time 
budgeting, showing decreased time resting and changes in haulout 
patterns and distribution (Benham 2006, Maldini et al. 2012). Chronic 
stress can also lead to weakened reflexes, lowered learning responses 
(Welch and Welch 1970, van Polanen Petel et al. 2006), compromised 
immune function, decreased body weight, and abnormal thyroid function 
(Selye 1979).
    Changes in behavior resulting from anthropogenic disturbance can 
include increased agonistic interactions between individuals or 
temporary or permanent abandonment of an area (Barton et al. 1998). 
Additionally, the extent of previous exposure to humans (Holcomb et al. 
2009), the type of disturbance (Andersen et al. 2012), and the age or 
sex of the individuals (Shaughnessy et al. 2008, Holcomb et al. 2009) 
may influence the type and extent of response in individual sea otters.

Vessel Activities

    Vessel collisions with marine mammals can result in death or 
serious injury. Wounds resulting from vessel strike may include massive 
trauma, hemorrhaging, broken bones, or propeller lacerations (Knowlton 
and Kraus 2001). An animal may be harmed by a vessel when the vessel 
runs over the animal at the surface, the animal hits the bottom of a 
vessel while the animal is surfacing, or the animal is cut by a 
vessel's propeller.
    Vessel strike has been documented as a cause of death across all 
three stocks of northern sea otters in Alaska. Since 2002, the Service 
has conducted 1,433 sea otter necropsies to determine cause of death, 
disease incidence, and the general health status of sea otters in 
Alaska. Vessel strike or blunt trauma was identified as a definitive or 
presumptive cause of death in 65 cases (4 percent) (USFWS 2020). In 
most of these cases, trauma was determined to be the ultimate cause of 
death; however, there was a contributing factor, such as disease or 
biotoxin exposure, which incapacitated the sea otter and made it more 
vulnerable to vessel strike (USFWS 2023).
    Vessel speed influences the likelihood of vessel strikes involving 
sea otters. The probability of death or serious injury to a marine 
mammal increases as

[[Page 4976]]

vessel speed increases (Laist et al. 2001, Vanderlaan and Taggart 
2007). Sea otters spend a considerable portion of their time at the 
water's surface (Esslinger et al. 2014). They are typically visually 
aware of approaching vessels and can move away if a vessel is not 
traveling too quickly. Mitigation measures to be applied to vessel 
operations to prevent collisions or interactions are included below in 
the proposed authorization portion of this document under Avoidance and 
Minimization.
    Sea otters exhibit behavioral flexibility in response to vessels, 
and their responses may be influenced by the intensity and duration of 
the vessel's activity. As noted above, sea otter populations in Alaska 
were observed to avoid areas with heavy vessel traffic but return to 
those same areas during seasons with less vessel traffic (Garshelis and 
Garshelis 1984). Sea otters have also shown signs of disturbance or 
escape behaviors in response to the presence and approach of survey 
vessels, including sea otters diving and/or actively swimming away from 
a vessel, sea otters on haulouts entering the water, and groups of sea 
otters disbanding and swimming in multiple different directions 
(Udevitz et al. 1995).
    Additionally, sea otter responses to vessels may be influenced by 
the sea otter's previous experience with vessels. Groups of southern 
sea otters in two locations in California showed markedly different 
responses to kayakers approaching to within specific distances, 
suggesting a different level of tolerance between the groups (Gunvalson 
2011). Benham (2006) found evidence that the sea otters exposed to high 
levels of recreational activity may have become more tolerant than 
individuals in less-disturbed areas. Sea otters off the California 
coast showed only mild interest in vessels passing within hundreds of 
meters and appeared to have habituated to vessel traffic (Riedman 1983, 
Curland 1997). These findings indicate that sea otters may adjust their 
responses to vessel activities depending on the level of activity. 
Vessel activity during the project includes the transit of four barges 
for materials and construction, all of which will remain onsite, mostly 
stationary, to support the work; additionally, four skiffs will be used 
during the project for transporting workers short distances to the 
crane barges. Vessels will not be used extensively or over a long 
duration during the planned work; therefore, we do not anticipate that 
sea otters will experience changes in behavior indicative of tolerance 
or habituation.

Effects on Sea Otter Habitat and Prey

    Physical and biological features of habitat essential to the 
conservation of sea otters include the benthic invertebrates that sea 
otters eat and the shallow rocky areas and kelp beds that provide cover 
from predators. Sea otter habitat in the project area includes coastal 
areas within the 40-m (131-ft) depth contour where high densities of 
sea otters have been detected.
    Industrial activities, such as pile driving, may generate in-water 
noise at levels that can temporarily displace sea otters from important 
habitat and impact sea otter prey species. The primary prey species for 
sea otters are sea urchins (Strongylocentrotus spp. and Mesocentrotus 
spp.), abalone (Haliotis spp.), clams (e.g., Clinocardium nuttallii, 
Leukoma staminea, and Saxidomus gigantea), mussels (Mytilus spp.), 
crabs (e.g., Metacarcinus magister, Pugettia spp., Telemessus 
cheiragonus, and Cancer spp.), and squid (Loligo spp.) (Tinker and 
Estes 1996, LaRoche et al. 2021). When preferential prey are scarce, 
sea otters will also eat kelp, slow-moving benthic fishes, sea 
cucumbers (e.g., Apostichopus californicus), egg cases of rays, turban 
snails (Tegula spp.), octopuses (e.g., Octopus spp.), barnacles 
(Balanus spp.), sea stars (e.g., Pycnopodia helianthoides), scallops 
(e.g., Patinopecten caurinus), rock oysters (Saccostrea spp.), worms 
(e.g., Eudistylia spp.), and chitons (e.g., Mopalia spp.) (Riedman and 
Estes 1990, Davis and Bodkin 2021).
    Several studies have addressed the effects of noise on 
invertebrates (Tidau and Briffa 2016, Carroll et al. 2017). Behavioral 
changes, such as an increase in lobster (Homarus americanus) feeding 
levels (Payne et al. 2007), an increase in avoidance behavior by wild-
caught captive reef squid (Sepioteuthis australis) (Fewtrell and 
McCauley 2012), and deeper digging by razor clams (Sinonovacula 
constricta) (Peng et al. 2016) have been observed following 
experimental exposures to sound. Physical changes have also been 
observed in response to increased sound levels, including changes in 
serum biochemistry and hepatopancreatic cells in lobsters (Payne et al. 
2007) and long-term damage to the statocysts required for hearing in 
several cephalopod species (Andr[eacute] et al. 2011, Sol[eacute] et 
al. 2013). De Soto et al. (2013) found impaired embryonic development 
in scallop (Pecten novaezelandiae) larvae when exposed to 160 dB. 
Christian et al. (2003) noted a reduction in the speed of egg 
development of bottom-dwelling crabs following exposure to noise; 
however, the sound level (221 dB at 2 m or 6.6 ft) was far higher than 
the planned project activities will produce. Industrial noise can also 
impact larval settlement by masking the natural acoustic settlement 
cues for crustaceans and fish (Pine et al. 2012, Simpson et al. 2016, 
Tidau and Briffa 2016).
    While these studies provide evidence of deleterious effects to 
invertebrates as a result of increased sound levels, Carroll et al. 
(2017) caution that there is a wide disparity between results obtained 
in field and laboratory settings. In experimental settings, changes 
were observed only when animals were housed in enclosed tanks, and many 
were exposed to prolonged bouts of continuous, pure tones. We would not 
expect similar results in open marine conditions. It is unlikely that 
noises generated by project activities will have any lasting effect on 
sea otter prey given the short-term duration of sounds produced by each 
component of the planned work.
    Noise-generating activities that interact with the seabed can 
produce vibrations, resulting in the disturbance of sediment and 
increased turbidity in the water. Although turbidity is likely to have 
little impact on sea otters and prey species (Todd et al. 2015), there 
may be some impacts from vibrations and increased sedimentation. For 
example, mussels (Mytilus edulis) exhibited changes in valve gape and 
oxygen demand, and hermit crabs (Pagurus bernhardus) exhibited limited 
behavioral changes in response to vibrations caused by pile driving 
(Roberts et al. 2016). Increased sedimentation is likely to reduce sea 
otter visibility, which may result in reduced foraging efficiency and a 
potential shift to less-preferred prey species. These outcomes may 
cause sea otters to spend more energy on foraging or processing the 
prey items; however, the impacts of a change in energy expenditure are 
not likely seen at the population level (Newsome et al. 2015). 
Additionally, the benthic invertebrates may be impacted by increased 
sedimentation, resulting in higher abundances of opportunistic species 
that recover quickly from industrial activities that increase 
sedimentation (Kotta et al. 2009). Although sea otter foraging could be 
impacted by industrial activities that cause vibrations and increased 
sedimentation, it is more likely that sea otters would be temporarily 
displaced from the project area due to impacts from noise rather than 
vibrations and sedimentation.

[[Page 4977]]

Potential Impacts of the Specified Activities on Subsistence Uses

    The planned specified activities will occur near marine subsistence 
harvest areas used by Alaska Native Peoples from Kodiak and the 
surrounding areas. Subsistence harvest of sea otters around Kodiak 
Island takes place primarily in Ouzinkie, Kodiak, and Port Lions with 
totals of 422, 192, and 130 sea otters taken, respectively, from 2017 
through 2021.
    The planned project would occur within the Kodiak city limits, 
where firearm use is prohibited. The area potentially affected by the 
planned project does not significantly overlap with current subsistence 
harvest areas. Construction activities will not preclude access to 
hunting areas or interfere in any way with individuals wishing to hunt. 
Despite no conflict with subsistence use being anticipated, the Service 
will conduct outreach with potentially affected communities to see 
whether there are any questions, concerns, or potential conflicts 
regarding subsistence use in those areas. If any conflicts are 
identified in the future, Trident will develop a plan of cooperation 
specifying the steps necessary to minimize any effects the project may 
have on subsistence harvest.

Estimated Take

Definitions of Incidental Take Under the Marine Mammal Protection Act

    Below we provide definitions of three potential types of take of 
sea otters. The Service does not anticipate and is not authorizing 
lethal take as a part of this proposed IHA; however, the definitions of 
these take types are provided for context and background:
    Lethal Take--Human activity may result in biologically significant 
impacts to sea otters. In the most serious interactions, human actions 
can result in mortality of sea otters.
    Level A Harassment--Human activity may result in the injury of sea 
otters. Level A harassment, for nonmilitary readiness activities, is 
defined as any act of pursuit, torment, or annoyance that has the 
potential to injure a marine mammal or marine mammal stock in the wild.
    Level B Harassment--Level B Harassment, for nonmilitary readiness 
activities, means any act of pursuit, torment, or annoyance that 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, feeding, or sheltering. 
Changes in behavior that disrupt biologically significant behaviors or 
activities for the affected animal are indicative of take by Level B 
harassment under the MMPA.
    The Service has identified the following sea otter behaviors as 
indicative of possible Level B harassment:
     Swimming away at a fast pace on belly (i.e., porpoising);
     Repeatedly raising the head vertically above the water to 
get a better view (i.e., spyhopping) while apparently agitated or while 
swimming away;
     In the case of a pup, repeatedly spyhopping while hiding 
behind and holding onto its mother's head;
     Abandoning prey or feeding area;
     Ceasing to nurse and/or rest (applies to dependent pups);
     Ceasing to rest (applies to independent animals);
     Ceasing to use movement corridors;
     Ceasing mating behaviors;
     Shifting/jostling/agitation in a raft so that the raft 
disperses;
     Sudden diving of an entire raft; or
     Flushing animals off a haulout.
    This list is not meant to encompass all possible behaviors; other 
behavioral responses may equate to take by Level B harassment. 
Relatively minor changes in behavior such as increased vigilance or a 
short-term change in direction of travel are not likely to disrupt 
biologically important behavioral patterns, and the Service does not 
view such minor changes in behavior as indicative of a take by Level B 
harassment.

Calculating Take

    We assumed all animals exposed to underwater sound levels that meet 
the acoustic exposure criteria defined above in Exposure Thresholds 
will experience take by Level A or Level B harassment due to exposure 
to underwater noise. Spatially explicit zones of ensonification were 
established around the planned construction location to estimate the 
number of otters that may be exposed to these sound levels.
    We determined the number of otters expected to be present in Near 
Island Channel using sightings data collected during work conducted at 
the Kodiak Ferry terminal between November 2015 and June 2016 (ABR 
2016). Sea otters were generally observed in singles or small groups 
with total daily counts of fewer than ~40 animals. However, there were 
several days on which rafts of 50 to 200 sea otters were observed with 
total daily counts of up to 459 animals. Sightings of large rafts and 
high daily totals coincided with days on which the observers noted 
higher sea states and it is likely that sea otters came from nearby 
exposed coastline to seek shelter Near Island Channel during storm 
events.
    The project can be divided into three major components: DTH 
drilling, pile driving using a vibratory driver, and vessel use to 
support construction. Each of these components will generate a 
different type of in-water noise. Vibratory pile driving and the use of 
vessels will produce non-impulsive or continuous noise and DTH drilling 
is considered to produce both impulsive and continuous noise (NMFS 
2020). A summary of the sizes and types of piles, installation and 
removal methods, and time to install and remove piles is shown in table 
2.
    The level of sound anticipated from each project component was 
established using recorded data from several sources listed in table 3. 
We used the NMFS Technical Guidance and User Spreadsheet (NMFS 2018, 
2020) to determine the distance at which sound levels would attenuate 
to Level A harassment thresholds. Empirical data from the proxy 
projects were used to determine the distance at which sound levels 
would attenuate to Level B harassment thresholds (table 1). The 
weighting factor adjustment included in the NMFS user spreadsheet 
accounts for sounds created in portions of an organism's hearing range 
where they have less sensitivity. We used the weighting factor 
adjustment for otariid pinnipeds (eared seals) as they are the closest 
available physiological and anatomical proxy for sea otters. The 
spreadsheet also incorporates a transmission loss coefficient, which 
accounts for the reduction in sound level outward from a sound source. 
We used the NMFS-recommended transmission loss coefficient of 15 for 
coastal pile-driving activities to indicate practical spread (NMFS 
2020).
    We calculated the harassment zones for DTH drilling with input from 
NMFS. The sound pressure levels produced by DTH drilling were provided 
by NMFS in 2022 via correspondence with Solstice Alaska Consulting, who 
created the application for this IHA on behalf of Trident. We then used 
the NMFS Technical Guidance and User Spreadsheet (NMFS 2018, 2020) to 
determine the distance at which these sounds would attenuate to Level A 
harassment thresholds. To estimate the distances at which sounds would 
attenuate to Level B harassment thresholds, we used the NMFS-
recommended transmission loss coefficient of 15 for coastal pile-
driving activities in a practical spreading loss model (NMFS 2020) to 
determine the

[[Page 4978]]

distance at which sound levels attenuate to 160 dB re 1 [mu]Pa.

     Table 2--Summary of Timing of Sound Production, and Days of Impact From Pile Installation and Removal at Trident's Site at Near Island Channel
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                               Removal of existing piles                   Temporary piles, 24-in            Permanent installation
   Activity and pile diameter    -----------------------------------------------------------------------------------------------------------------------
                                        16-in            14-in            14-in         Installation       Removal           16-in            24-in
--------------------------------------------------------------------------------------------------------------------------------------------------------
Pile material...................  Steel...........  Steel..........  Timber.........  Steel..........  Steel..........  Steel..........  Steel.
Pile type.......................  Pipe............  H-pile.........  Round..........  Pipe...........  Pipe...........  Pipe...........  Pipe.
Total number of piles...........  60..............  75.............  100............  20.............  20.............  26.............  52.
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                 Vibratory pile driving
--------------------------------------------------------------------------------------------------------------------------------------------------------
Number of piles.................  60..............  75.............  100............  20.............  20.............  26.............  52.
Maximum number of piles per day.  20..............  20.............  25.............  6..............  8..............  5..............  4.
Vibratory time per pile           2...............  2..............  2..............  2..............  2..............  2..............  2.
 (minutes).
Vibratory time per day (minutes)  40..............  40.............  50.............  12.............  16.............  10.............  8.
Number of days..................  3...............  4..............  4..............  3..............  3..............  5..............  13.
Total vibratory time (minutes)..  120.............  150............  200............  40.............  40.............  52.............  104.
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                      DTH drilling
--------------------------------------------------------------------------------------------------------------------------------------------------------
Number of piles.................  0...............  0..............  0..............  20.............  0..............  26.............  52.
Maximum number of piles per day.  0...............  0..............  0..............  6..............  0..............  6..............  4.
DTH time per pile (minutes).....  0...............  0..............  0..............  30.............  0..............  45.............  60.
DTH time per day (minutes)......  0...............  0..............  0..............  180............  0..............  270............  240.
Number of days..................  0...............  0..............  0..............  3..............  0..............  4..............  13.
Total DTH time (minutes)........  0...............  0..............  0..............  600............  0..............  1,170..........  3,120.
--------------------------------------------------------------------------------------------------------------------------------------------------------


  Table 3--Summary of Sound Level, Timing of Sound Production, Distance (m) From Sound Source to Below Level A
 Harassment and Level B Harassment Thresholds for Sound-Producing Activities at Trident's Kodiak Bunkhouse Site
----------------------------------------------------------------------------------------------------------------
 
----------------------------------------------------------------------------------------------------------------
Source                               Sound level (dB (RMS)  Reference...........     Distance to     Distance to
                                      re 1[mu]Pa at 10 m)                          below Level A   below Level B
                                                                                      harassment      harassment
                                                                                       threshold       threshold
----------------------------------------------------------------------------------------------------------------
14-in timber (vibratory removal)..            162           Caltrans 2020.......             0.3            13.6
14-in H (vibratory removal).......            150           Caltrans 2020.......             0.2             2.2
16-in steel (vibratory                        161           NAVFAC \a\ 2015                  0.1            11.7
 installation).                                              (used 24-in piles).
16-in steel (vibratory removal)...            161           NAVFAC 2015 (used 24-            0.2            11.7
                                                             in piles).
24-in steel (vibratory                        161           NAVFAC 2015.........             0.1            11.7
 installation--temporary piles).
24-in steel (vibratory                        161           NAVFAC 2015.........             0.1            11.7
 installation--permanent piles).
24-in steel (vibratory removal)...            161           NAVFAC 2015.........             0.1            11.7
Work skiff........................            160           Richardson et al.                0.0            10.0
                                                             1995; Kipple and
                                                             Gabriele 2007.
Tug operations....................            176           LGL/JASCO/                       9.2           116.6
                                                             Greeneridge 2014.
----------------------------------------------------------------------------------------------------------------
                                                  DTH Drilling
----------------------------------------------------------------------------------------------------------------
Source                                  db rms      db SEL  Reference...........     Distance to     Distance to
                                       (bubble     (bubble                         below Level A   below Level B
                                      curtain)    curtain)                            harassment      harassment
                                                                                       threshold       threshold
----------------------------------------------------------------------------------------------------------------
16-in steel installation..........   162 (167)   141 (146)  Heyvaert & Reyff                 1.8            13.6
                                                             2021 (used 24-in
                                                             piles); Guan &
                                                             Miner 2020.
24-in steel DTH installation--       162 (167)   154 (159)  Heyvaert & Reyff                10.3            13.6
 temporary.                                                  2021.
24-in steel DTH installation--       162 (167)   154 (159)  Heyvaert & Reyff                12.5            13.6
 permanent.                                                  2021.
----------------------------------------------------------------------------------------------------------------
\a\ Naval Facilities Engineering Command.

    Sound levels for all sources are unweighted and given in dB re 1 
[mu]Pa. Non-impulsive sounds are in the form of mean maximum root mean 
square (RMS) sound pressure level (SPL) as it is more conservative than 
cumulative sound exposure level (SEL) or peak SPL for these activities.
    We used the ABR Environmental Research & Services 2016 data to 
derive a local density of sea otters in Near Island Channel on the days 
of highest presence and arrived at 710 animals per km\2\. Applying this 
density to the largest Level B harassment zone for pile driving (14 m 
[46 ft]) yielded a result of approximately 1 individual otter exposed. 
Applying this density to the Level B harassment zone for heavy towing 
operations (117m [383 ft]) yielded a result of approximately 31 
individual otters exposed. Although the harassment zone for the work 
skiff is sufficiently small to be easily monitored (10 m [33 ft]), the 
skiff will make multiple trips between the harbor and the work site 
each day. On days when several hundred sea otters occupy the relatively 
small area of Near Channel, it would not be feasible for a protected 
species observer (PSO) to determine whether the individual animals 
present in the harassment zones remain constant over time. As such, we 
assumed that it was possible that each individual sea otter in Near 
Channel would enter a Level B harassment zone at least once over the 
course of each day of operations.
    To estimate the number of sea otters anticipated in the waters 
surrounding Near Island Channel during the project,

[[Page 4979]]

we applied the distribution of daily sea otter counts observed during 
the Kodiak Ferry work (ABR 2016) to the length of Trident's work period 
(55 days). We used the result to estimate the daily sea otter counts 
anticipated during Trident's work period (table 4). The daily count 
range categories were selected based on natural breaks in the sightings 
data.

 Table 4--Distribution of Days Anticipated Within Trident's 55-Day Work
Period for Each Category of Daily Sea Otter Counts and Anticipated Total
    Number of Exposures of Sea Otters in Near Island Channel Over the
   Duration of the Project. Based on Sightings Data From Observations
                   Conducted at Kodiak Ferry Terminal
                               [ABR 2016]
------------------------------------------------------------------------
                                                        Exposures of sea
                                       Number of days        otters
   Range of daily sea otter count     in 55-day period     throughout
                                                             project
------------------------------------------------------------------------
1 to 10.............................                19               190
11 to 20............................                 9               180
21 to 30............................                 4               120
31 to 40............................                 5               200
41 to 50............................                 3               150
51 to 60............................                 1                60
61 to 75............................                 2               150
76 to 85............................                 4               340
85 to 100...........................                 2               200
101 to 135..........................                 2               270
136 to 155..........................                 1               155
156 to 225..........................                 1               225
226 to 460..........................                 2               920
                                     -----------------------------------
    Totals..........................                55             3,160
------------------------------------------------------------------------

    We assumed that the different types of activities could occur 
either sequentially or concurrently and that the total number of days 
of work would equal the full 55-day work window. While it is possible 
that more than one type