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Notice2023-14939

Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Hydaburg Seaplane Base Refurbishment Project in Hydaburg, Alaska

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Published

July 17, 2023

Issuing agencies

Commerce DepartmentNational Oceanic and Atmospheric Administration

Abstract

NMFS has received a request from the Alaska Department of Transportation and Public Facilities (DOT&PF) for authorization to take marine mammals incidental to the Hydaburg Seaplane Base Refurbishment Project in Hydaburg, Alaska. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an incidental harassment authorization (IHA) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-time, 1-year renewal that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorization and agency responses will be summarized in the final notice of our decision.

Full Text

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[Federal Register Volume 88, Number 135 (Monday, July 17, 2023)]
[Notices]
[Pages 45774-45805]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2023-14939]

[[Page 45773]]

Vol. 88

Monday,

No. 135

July 17, 2023

Part IV

Department of Commerce

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National Oceanic and Atmospheric Administration

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Takes of Marine Mammals Incidental to Specified Activities; Taking
Marine Mammals Incidental to the Hydaburg Seaplane Base Refurbishment
Project in Hydaburg, Alaska; Notice

Federal Register / Vol. 88 , No. 135 / Monday, July 17, 2023 /
Notices

[[Page 45774]]

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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XD052]

Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to the Hydaburg Seaplane Base
Refurbishment Project in Hydaburg, Alaska

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 Alaska Department of
Transportation and Public Facilities (DOT&PF) for authorization to take
marine mammals incidental to the Hydaburg Seaplane Base Refurbishment
Project in Hydaburg, Alaska. Pursuant to the Marine Mammal Protection
Act (MMPA), NMFS is requesting comments on its proposal to issue an
incidental harassment authorization (IHA) to incidentally take marine
mammals during the specified activities. NMFS is also requesting
comments on a possible one-time, 1-year renewal that could be issued
under certain circumstances and if all requirements are met, as
described in Request for Public Comments at the end of this notice.
NMFS will consider public comments prior to making any final decision
on the issuance of the requested MMPA authorization and agency
responses will be summarized in the final notice of our decision.

DATES: Comments and information must be received no later than August
16, 2023.

ADDRESSES: Comments should be addressed to Jolie Harrison, Chief,
Permits and Conservation Division, Office of Protected Resources,
National Marine Fisheries Service, and should be submitted via email to
<a href="/cdn-cgi/l/email-protection#1f564b4f316b666c7071317270706d7a5f71707e7e31787069"><span class="__cf_email__" data-cfemail="723b26225c060b011d1c5c1f1d1d0017321c1d13135c151d04">[email&#160;protected]</span></a>. 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: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities">https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities</a>. In case of problems accessing these documents,
please call the contact listed below.
Instructions: NMFS is not responsible for comments sent by any
other method, to any other address or individual, or received after the
end of the comment period. Comments, including all attachments, must
not exceed a 25-megabyte file size. All comments received are a part of
the public record and will generally be posted online at <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities">https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities</a> 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: Reny Tyson Moore, Office of Protected
Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

The MMPA prohibits the ``take'' of marine mammals, with certain
exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361
et seq.) direct the Secretary of Commerce (as delegated to NMFS) to
allow, upon request, the incidental, but not intentional, taking of
small numbers of marine mammals by U.S. citizens who engage in a
specified activity (other than commercial fishing) within a specified
geographical region if certain findings are made and either regulations
are proposed or, if the taking is limited to harassment, a notice of a
proposed IHA is provided to the public for review.
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 NAO 216-6A, which do not
individually or cumulatively have the potential for significant impacts
on the quality of the human environment and for which we have not
identified any extraordinary circumstances that would preclude this
categorical exclusion. Accordingly, NMFS has preliminarily determined
that the issuance of the proposed IHA qualifies to be categorically
excluded from further NEPA review.
We will review all comments submitted in response to this notice
prior to concluding our NEPA process or making a final decision on the
IHA request.

Summary of Request

On June 28, 2022, NMFS received a request from DOT&PF for an IHA to
take marine mammals incidental to the Hydaburg Seaplane Base
Refurbishment Project in Hydaburg, Alaska. Following NMFS' review of
the application, and multiple discussions between DOT&PF and NMFS,
DOT&PF submitted responses to NMFS questions on December 15, 2022 and a
revised application on February 22, 2023. The application was deemed
adequate and complete on March 13, 2023. DOT&PF's request is for take
of nine species of marine mammals by Level B harassment and, for a
subset of these species (i.e., harbor seal (Phoca vitulina), northern
elephant seal (Mirounga angustirostris), harbor porpoise (Phocoena
phocoena), Dall's porpoise (Phocoenoides dalli), humpback whale
(Megaptera novaeangliae), and minke whale (Balaenoptera
acutorostrata)), Level A harassment. Neither DOT&PF nor NMFS expect
serious injury or mortality to result from this activity and,
therefore, an IHA is appropriate.

Description of Proposed Activity

Overview

DOT&PF, in cooperation with the Federal Aviation Administration, is
proposing maintenance improvements to the existing Hydaburg Seaplane
Base as part of the Hydaburg Seaplane Base Refurbishment Project. The
existing facility has experienced deterioration in recent years, and
DOT&PF has conducted several repair projects. The facility is near the
end of its useful life,

[[Page 45775]]

and replacement of the existing float structures is required to
continue safe operation in the future. The in-water portion of the
project would include the removal of five existing steel piles and
installation of eight permanent steel piles to support replacement of
the floating dock structure. Up to 10 temporary steel piles would be
installed to support permanent pile installation and would be removed
following completion of permanent pile installation. Proposed
activities included as part of the project with potential to affect
marine mammals include vibratory removal, down-the-hole (DTH)
installation, and vibratory and impact installation of steel pipe
piles.

Dates and Duration

The proposed IHA would be effective from September 15, 2023,
through September 14, 2024. Construction of the proposed project is
anticipated to occur over approximately 2 months beginning in early
fall 2023. Pile installation and removal will be intermittent during
this period, depending on weather, construction and mechanical delays,
protected species shutdowns, and other potential delays and logistical
constraints. Pile installation will occur intermittently during the
work period for durations of minutes to hours at a time. Pile
installation and removal will occur over 26 nonconsecutive days within
the 2-month construction window. DOT&PF plans to conduct all work
during daylight hours.

Specific Geographic Region

The project site is located in the City of Hydaburg, on Prince of
Wales Island, approximately 76 kilometers (km) west of Ketchikan, in
southeast Alaska. The Hydaburg Seaplane Base is located at the south
end of Hydaburg, attached to the Hydaburg city dock on the north shore
of the Sukkwan Strait (Figure 1).
Hydaburg is located along the Sukkwan Strait on the southwest side
of Prince of Wales Island. A series of passes and straits lead to the
open Pacific Ocean; however, Hydaburg is tucked in a relatively calm
and secluded area. Sukkwan Strait is generally characterized by
semidiurnal tides with mean tidal ranges of around 5 meters (m).
Freshwater inputs to Sukkwan Strait include multiple anadromous
streams: Hydaburg River, Saltery Creek, and two streams originating
from unnamed lakes. The bathymetry of the bay is variable depending on
location and proximity to shore, islands, or rocks. Depths approach 76
m within Sukkwan Strait and up to 37 m in South Pass.
Ongoing vessel activities near Hydaburg, as well as land-based
industrial and commercial activities, result in elevated in-air and
underwater acoustic conditions in the project area that likely increase
with proximity to the project site. Background sound levels likely vary
seasonally, with elevated levels during summer when the commercial and
fishing industries are at their peaks. Hydaburg has no cruise ship or
ferry facilities, so only commercial and fishing vessels visit Hydaburg
regularly (Miller et al., 2019).
BILLING CODE 3510-22-P

[[Page 45776]]

[GRAPHIC] [TIFF OMITTED] TN17JY23.000

BILLING CODE 3510-22-C
Figure 1--Location of Seaplane Base in Hydaburg, Alaska

[[Page 45777]]

Detailed Description of the Specified Activity

The DOT&PF proposed project would involve the removal of five
existing cantilever steel pipe piles (16-inch (40.64-centimeter (cm))
diameter) that support the existing multiple-float structure. The
multiple-float timber structure, which covers 372 square m (m\2\),
would also be removed. A new 446-m\2\ single-float timber structure
would be installed in the same general location. Four 24-inch (60.96-
cm) and four 20-inch (50.80-cm) permanent steel pipe piles would be
installed vertically to act as restraints for the new seaplane float.
Up to 10 temporary 24-inch (60.96 cm) steel pipe piles would be
installed to support pile installation and would be removed following
completion of construction. Rock sockets and tension anchors would be
required on all 24-inch (60.96 cm) piles and two 20-inch (50.80 cm)
piles. Rock sockets would also be potentially required on five of the
temporary piles. See Table 1 for a summary of the numbers and types of
piles to be installed and removed, as well as the estimated durations
of each activity.

Table 1--Summary of Piles To Be Installed and Removed
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Tension
Rock socket anchor DTH Total Typical
Number of Number of Impact Vibratory DTH pile pile duration of production Days of
Pile diameter and type Number of rock tension strikes duration Installation, installation, activity rate in installation
piles sockets anchors per pile per pile duration per duration per per pile, piles per or removal
(minutes) pile, minutes pile, minutes hours day
(range) (range) (range)
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Pile Installation
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24'' Steel Plumb Piles (Permanent)............................... 4 4 4 50 15 240 (60-480) 120 (60-240) 6.75 0.5 (0-1) 8
20'' Steel Plumb Piles (Permanent)............................... 4 2 2 50 15 240 (60-480) 120 (60-240) \1\ 0.75/ 0.5 (0-1) 8
6.75
24'' Steel Piles (Temporary)..................................... 10 5 N/A N/A 15 240 (60-480) N/A 4.25 2.5 (1-10) 4
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Pile Removal
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16'' Steel Cantilevered Piles.................................... 5 N/A N/A N/A 30 N/A N/A 0.5 2.5 (2-4) 2
24'' Steel Piles (Temporary)..................................... 10 N/A N/A N/A 30 N/A N/A 0.5 2.5 (2-4) 2
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Totals....................................................... 23 11 6 N/A N/A N/A N/A N/A N/A 26
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\1\ Two of the 20-inch plumb piles will include vibratory and impact installation in addition to rock sockets and tension anchors, estimated at 6.75 hours duration total, and two will only use
vibratory and impact, estimated at 0.75 hours duration total.

DTH pile installation would involve drilling rock sockets into the
bedrock to support installation of piles. A rock socket is a pile
inserted into a drilled hole in the underlying bedrock after the pile
has been driven through the overlying softer sediments to refusal by
vibratory or impact methods. The pile is advanced farther into the
drilled hole to properly secure the bottom portion of the pile into the
rock. The depth of the rock socket varies, but up to 6 m may be
required for this project. The diameter of the rock socket is slightly
larger than the pile being driven. Rock sockets are constructed using a
DTH device that consists of a drill bit that drills through the bedrock
using both rotary and percussion mechanisms. This breaks up the rock to
allow removal of the fragments and insertion of the pile. The pile is
advanced at the same time that drilling occurs. Drill cuttings are
expelled from the top of the pile using compressed air. It is estimated
that drilling rock sockets into the bedrock may take on average 4 hours
per pile.
Tension anchors would be installed in six of the permanent piles
(four 24-inch (60.96-cm) and two 20-inch (50.80-cm) piles). Tension
anchors are installed within piles that are drilled into the bedrock
below the elevation of the pile tip after the pile has been driven
through the sediment layer to refusal. A 6- or 8-inch (15.24- or 20.32-
cm) diameter steel pipe casing would be inserted inside the larger
diameter production pile. A rock drill would be inserted into the
casing, and a 6- to 8-inch (15.24- to 20.32-cm) diameter hole would be
drilled into bedrock with rotary and percussion drilling methods. The
drilling work is contained within the steel pile casing and the steel
pipe pile. The typical depth of the drilled tension anchor hole varies,
but 6-9 m is common. Rock fragments would be removed through the top of
the casing with compressed air. A steel rod would then be grouted into
the drilled hole and affixed to the top of the pile. The purpose of a
tension anchor is to secure the pile to the bedrock to withstand uplift
forces. It is estimated that tension anchor installation will take
about 1-4 hours per pile. Hereafter, DTH pile installation refers to
both rock socket drilling and tension anchor installation unless
specified. See Figure 1-3 in the DOT&PF's application for a schematic
of DTH pile installation and tension anchor techniques.
Pile removal would be conducted using a vibratory hammer. Pile
installation would be conducted using both a vibratory and an impact
hammer and DTH pile installation methods. Piles would be advanced to
refusal using a vibratory hammer. After DTH pile installation, the
final approximately 3 m of driving would be conducted using an impact
hammer so that the structural capacity of the pile embedment could be
verified. The pile installation methods used would depend on sediment
depth and conditions at each pile location. Pile installation and
removal would occur in waters approximately 6-7 m in depth.
Actual numbers and sizes of piles, installation times, numbers of
impact strikes, and other design and construction details and methods
may vary slightly from the estimates outlined in this document. The
DOT&PF does not anticipate that the project will change such that
potential impacts on marine mammals will change or vary from those
described here.
Proposed mitigation, monitoring, and reporting measures are
described in detail later in this document (please see Proposed
Mitigation and Proposed Monitoring and Reporting).

[[Page 45778]]

Description of Marine Mammals in the Area of Specified Activities

Sections 3 and 4 of the DOT&PF's 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, referenced here, instead of
reprinting the information. Additional information regarding population
trends and threats may be found in NMFS' Stock Assessment Reports
(SARs; <a href="http://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>) and more general information about these
species (e.g., physical and behavioral descriptions) may be found on
NMFS' website (<a href="https://www.fisheries.noaa.gov/find-species">https://www.fisheries.noaa.gov/find-species</a>).
Table 2 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 expected to occur, PBR
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 stocks managed under the MMPA in this region
are assessed in NMFS' U.S. Alaska and Pacific SARs (e.g., Carretta, et
al., 2022; Muto et al., 2022). All values presented in Table 2 are the
most recent available at the time of publication (including from the
draft 2022 SARs, Young et al., 2022) and are available online at:
<a href="http://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>).

Table 2--Species \4\ Likely Impacted by the Specified Activities
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Stock abundance (CV,
Common name Scientific name Stock ESA/MMPA status; Nmin, most recent PBR Annual M/
strategic (Y/N) \1\ abundance survey) \2\ SI \3\
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Order Artiodactyla--Cetacea--Mysticeti (baleen whales)
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Family Eschrichtiidae:
Gray Whale..................... Eschrichtius robustus. Eastern N Pacific..... -, -, N 26,960 (0.05, 25,849, 801 131
2016).
Family Balaenopteridae (rorquals):
Humpback Whale................. Megaptera novaeangliae Central N Pacific..... -, -, Y 10,103 (0.3, 7,891, 3.4 4.46
2006).
Minke Whale.................... Balaenoptera Alaska................ -, -, N N/A (N/A, N/A, N/A).. UND 0
acutorostrata.
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Odontoceti (toothed whales, dolphins, and porpoises)
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Family Physeteridae:
Sperm Whale.................... Physeter macrocephalus N Pacific............. E, D, Y UND (UND, UND, 2015). UND 3.5
Family Delphinidae:
Killer Whale................... Orcinus orca.......... Eastern North Pacific -, -, N 1,920 (N/A, 1,920, 19 1.3
Alaska Resident. 2019).
Killer Whale................... Orcinus orca.......... Eastern Northern -, -, N 302 (N/A, 302, 2018). 2.2 0.2
Pacific Northern
Resident.
Killer Whale................... Orcinus orca.......... West Coast Transient.. -, -, N 349 (N/A, 349, 2018). 3.5 0.4
Pacific White-Sided Dolphin.... Lagenorhynchus N Pacific............. -, -, N 26,880 (N/A, N/A, UND 0
obliquidens. 1990).
Family Phocoenidae (porpoises):
Dall's Porpoise................ Phocoenoides dalli.... Alaska................ -, -, N UND (UND, UND, 2015). UND 37
Harbor Porpoise................ Phocoena.............. Southeast Alaska...... -, -, Y UND (UND, UND, 2019). UND 34
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Order Carnivora--Pinnipedia
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Family Otariidae (eared seals and
sea lions):
Steller Sea Lion............... Eumetopias jubatus.... Eastern............... -, -, N 43,201 (N/A, 43,201, 2,592 112
2017).
Family Phocidae (earless seals):
Harbor Seal.................... Phoca vitulina........ Dixon/Cape Decision... -, -, N 23,478 (N/A, 21,453, 644 69
2015).
Northern Elephant Seal......... Mirounga CA Breeding........... -, -, N 187,386 (N/A, 85,369, 5,122 13.7
angustirostris. 2013).
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\1\ ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or
designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or
which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is
automatically designated under the MMPA as depleted and as a strategic stock.
\2\ NMFS marine mammal stock assessment reports online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region/">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region/</a>. CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable (N/A)
\3\ These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g.,
commercial fisheries, ship strike). Annual human caused mortality and serious injury (M/SI) often cannot be determined precisely and is in some cases
presented as a minimum value or range.
\4\ 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
(<a href="https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/">https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/</a>; Committee on Taxonomy (2022)).

[[Page 45779]]

On January 24, 2023, NMFS published the draft 2022 SARs (<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region</a>). The Alaska and Pacific SARs include a
proposed update to the humpback whale stock structure and the Alaska
SAR includes a proposed update to the Southeast Alaska harbor porpoise
stock structure. These new structures, if finalized, would modify the
MMPA-designated humpback stocks to align more closely with the ESA-
designated distinct population segments (DPSs), and for harbor porpoise
to align with genetics, trends in abundance, and discontinuous
distribution NMFS has proposed as supporting the delineation of two
demographically independent populations. Please refer to the draft 2022
Alaska and Pacific SARs for additional information.
NMFS Office of Protected Resources, Permits and Conservation
Division has generally considered peer-reviewed data in draft SARs
(relative to data provided in the most recent final SARs), when
available, as the best available science, and has done so here for all
species and stocks, with the exception of the new proposal to revise
humpback whale and harbor porpoise stock structure. Given that the
proposed changes to the stock structures involve application of NMFS'
Guidance for Assessing Marine Mammals Stocks and could be revised
following consideration of public comments, it is more appropriate to
conduct our analysis in this proposed authorization based on the status
quo stock structure identified in the most recent final SARs for those
species (Carretta et al., 2022; Muto et al., 2022).
All species that could potentially occur in the proposed survey
areas are included in Table 2 of the IHA application. While gray whale
and sperm whale have occurred in northern Southeast Alaska in recent
years, they are highly unlikely to occur in the proposed project 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. The
remaining 9 species (with 11 managed stocks) in Table 2 temporally and
spatially co-occur with the activity to the degree that take is
reasonably likely to occur, and we have proposed authorizing it.

Steller Sea Lion

Steller sea lions are found throughout the northern Pacific Ocean,
including coastal and inland waters from Russia (Kuril Islands and the
Sea of Okhotsk), east to Alaska, and south to central California
(A[ntilde]o Nuevo Island). Steller sea lions were listed as threatened
range-wide under the ESA on November 26, 1990 (55 FR 49204); they were
subsequently partitioned into the western and eastern DPSs (and MMPA
stocks) in 1997 (62 FR 24345, May 5, 1997). The eastern DPS remained
classified as threatened (62 FR 24345) until it was delisted in
November 2013, while the western DPS (those individuals west of
144[deg] W longitude or Cape Suckling, Alaska) was upgraded to
endangered status following separation of the DPSs, and it remains
endangered today. There is regular movement of both DPSs across this
144[deg] W longitude boundary (Jemison et al., 2013), however, due to
the distance from this DPS boundary, it is likely that only eastern DPS
Steller sea lions are present in the project area. Therefore, animals
potentially affected by the project are assumed to be part of the
eastern DPS.
Steller sea lions are opportunistic predators, feeding primarily on
a wide variety of fishes and cephalopods, including Pacific herring
(Clupea pallasi), walleye pollock (Gadus chalcogramma), capelin
(Mallotus villosus), Pacific sand lance (Ammodytes hexapterus), Pacific
cod (Gadus macrocephalus), salmon (Oncorhynchus spp.), and squid
(Teuthida spp.; Jefferson et al., 2008; Wynne et al., 2011). Steller
sea lions do not generally eat every day, but tend to forage every 1-2
days and return to haulouts to rest between foraging trips (Merrick and
Loughlin, 1997; Rehberg et al., 2009).
Steller sea lions are not common in the project area and systematic
counts or surveys have not been completed in the area directly
surrounding Hydaburg. The nearest documented haulout is Point Islet
(Point Rock), about 13 km southeast of Hydaburg (see Figure 4-1 in the
DOT&PF's application). No Steller sea lions were present during aerial
surveys over Point Islet that occurred during 2013, 2015, or 2017
(Fritz et al., 2016b; Sweeney et al., 2017), and it was not surveyed in
2019 (Sweeney et al., 2019). Anecdotal evidence provided by local
residents indicates that Steller sea lions are rare and do not occur
regularly near the project area. However, Steller sea lion presence
could be higher during the late summer and early fall salmon runs.

Harbor Seal

Harbor seals range from Baja California north along the west coasts
of California, Oregon, Washington, British Columbia, and Southeast
Alaska; west through the Gulf of Alaska, Prince William Sound, and the
Aleutian Islands; and north in the Bering Sea to Cape Newenham and the
Pribilof Islands. In 2010, harbor seals in Alaska were partitioned into
12 separate stocks based largely on genetic structure (Allen and
Angliss, 2010). Harbor seals present near Hydaburg are recognized as
part of the Dixon/Cape Decision stock.
Harbor seals haul out on rocks, reefs, beaches, and drifting
glacial ice, and feed in marine, estuarine, and occasionally fresh
waters (Muto et al., 2022). Harbor seals generally are non-migratory,
with local movements associated with such factors as tides, weather,
season, food availability, and reproduction (Scheffer and Slipp, 1944;
Fisher 1952; Bigg, 1969, 1981; Hastings et al., 2004). The results of
past and recent satellite tagging studies in Southeast Alaska, Prince
William Sound, Kodiak Island, and Cook Inlet are also consistent with
the conclusion that harbor seals are non-migratory (Swain et al., 1996;
Lowry et al., 2001; Small et al., 2003; Boveng et al., 2012). However,
some long-distance movements of tagged animals in Alaska have been
recorded (Pitcher and McAllister, 1981; Lowry et al., 2001; Small et
al., 2003; Womble, 2012; Womble and Gende, 2013).
Harbor seals usually give birth to a single pup between May and
mid-July. Birthing locations are often dispersed over several haulout
sites and not confined to major rookeries (Klinkhart et al., 2008).
Strong fidelity of individuals for haul-out sites during the breeding
season though have been documented in several populations
(H[auml]rk[ouml]nen and Harding, 2001), including some regions in
Alaska such as Kodiak Island, Prince William Sound, Glacier Bay/Icy
Strait, and Cook Inlet (Pitcher and McAllister, 1981; Small et al.,
2005; Boveng et al., 2012; Womble, 2012; Womble and Gende, 2013).
Harbor seals forage on fish and invertebrates (Orr et al., 2004)
including capelin, eulachon (Thaleichthys pacificus), cod, pollock,
flatfish, shrimp, octopus, and squid (Wynne, 2012). They are
opportunistic feeders that forage in marine, estuarine, and
occasionally freshwater habitat, adjusting their foraging behavior to
take advantage of prey that are locally and seasonally abundant (Payne
and Selzer, 1989). Depending on prey availability, research has
demonstrated that harbor seals conduct both shallow and deep dives
while foraging (Tollit et al., 1997).
Harbor seals are commonly sighted in the waters of the inside
passages throughout Southeast Alaska. Surveys have been rarely carried
out on Dixon/Cape Decision, with the last surveys taking place between
2007 to 2011 and 2015. The NMFS Alaska Fisheries

[[Page 45780]]

Science Center identifies two ``key'' haulouts, or haulouts that have
had 50 or more harbor seals documented during surveys, in Sukkwan
Strait and four additional ``not key'' haulouts, those with fewer than
50 harbor seals documented during surveys, near the proposed project
area (see Figure 4-2 in the DOT&PF's application) (NOAA, 2021). NMFS
aerial survey data indicate that as few as 0 to as many as 157 harbor
seals were sighted near the project area during surveys between 2003
and 2011 (Areas BD28 and BD30; NOAA, 2022). However, local residents
report that only a few (two to four) harbor seals are regularly
observed near Hydaburg. These individuals are generally observed near
the small boat harbor outside of the proposed project area and during
peak salmon runs in late summer and early fall. Harbor seals are known
to be curious and may approach novel activity, so it is possible that
some may enter the proposed project area during pile installation and
removal.

Northern Elephant Seal

Northern elephant seals are wide-ranging throughout the North
Pacific, spending as much as 80 percent of their time at sea (Hindell
and Perrin, 2009). Populations of northern elephant seals in the U.S.
and Mexico have recovered after being nearly hunted to extinction
(Stewart et al., 1994). Northern elephant seals underwent a severe
population bottleneck and loss of genetic diversity when the population
was reduced to an estimated 10-30 individuals (Hoelzel et al., 2002).
Since 1998, northern elephant seals have been undergoing a large
population increase, estimated at 3.1 percent annually (Lowry et al.,
2020). There are two demographically isolated breeding populations: the
California breeding population and the Baja California population. No
international agreements exist for the joint management of this species
by the U.S. and Mexico. The California breeding population is
considered to be a separate stock. Any northern elephant seals observed
near Hydaburg would be considered part of the California breeding
stock.
Spatial segregation in foraging areas between males and females is
evident from satellite tag data (Le Beouf et al., 2000). Males migrate
to the Gulf of Alaska and western Aleutian Islands along the
continental shelf to feed on benthic prey, while females migrate to
pelagic areas in the Gulf of Alaska and the central North Pacific to
feed on pelagic prey (Le Beouf et al., 2000). Elephant seals spend a
majority of their time at sea (average of 74.7 days during post
breeding migration and an average of 218.5 days during the post-molting
migration; Robinson et al., 2012). Although northern elephant seals are
known to visit the Gulf of Alaska to feed on benthic prey, they rarely
occur on the beaches of Alaska.
Northern elephant seals breed and give birth in California and Baja
Mexico, primarily on offshore islands (Stewart et al., 1994, from
December to March (Stewart and Huber, 1993)) before dispersing widely
across the North Pacific (Le Boeuf et al., 2000). Although movement and
genetic exchange continues between rookeries, most elephant seals
return to natal rookeries when they start breeding (Huber et al.,
1991). Gestation in elephant seals lasts 11 months, with births taking
place onshore when seals are at the breeding colony (Stewart et al.,
1994).
There is a low probability that northern elephant seals would occur
in the proposed project area. Northern elephant seals generally feed
along the continental shelf break (Le Boeuf et al., 2000) and are not
expected to spend time in shallow areas like the Sukkwan Strait. No
sightings of elephant seals have been documented near Hydaburg;
however, protected species observers (PSOs) at a DOT&PF project site in
Ketchikan (located approximately 76 km east of Hydaburg) reported
sightings of a northern elephant seal on multiple days (C. Gentemann,
personal communication, April 8, 2022). Additional sightings of
northern elephant seals around the state concurrent to the Ketchikan
sighting were reported in Seward, King Cove, and Kodiak (L. Davis,
personal communication, April 14, 2022). Given the recent increase in
sightings, including sightings in Southeast Alaska, it is assumed that
a few northern elephant seals could be present in Hydaburg during
construction of the proposed project.

Harbor Porpoise

In the eastern North Pacific Ocean, the harbor porpoise ranges from
Point Barrow, along the Alaska coast, and down the west coast of North
America to Point Conception, California. In Alaska, harbor porpoises
are currently divided into three stocks, based primarily on geography:
the Bering Sea stock, the Southeast Alaska stock, and the Gulf of
Alaska stock. Harbor porpoises near Hydaburg are currently recognized
as members of the Southeast Alaska stock. The Southeast Alaska stock
ranges from Cape Suckling to the Canada boundary (Muto et al., 2022).
Harbor porpoises primarily frequent coastal waters in southeast
Alaska (Dahlheim et al., 2009) and occur most frequently in waters less
than 100 m deep (Hobbs and Waite, 2010). Harbor porpoises forage in
waters less than 200 m deep on small pelagic schooling fishes such as
herring, cod, pollock, octopus, smelt, and bottom-dwelling fish,
occasionally feeding on squid and crustaceans (Bj[oslash]rge and
Tolley, 2009; Wynne et al., 2011).
Calving occurs from May to August; however, this can vary by
region. Harbor porpoises are often found traveling alone, or in small
groups less than 10 individuals (Schmale, 2008). According to aerial
surveys of harbor porpoise abundance in southeast Alaska conducted in
1991-1993, mean group size was calculated to be 1.2 animals (Dahlheim
et al., 2000).
Studies of harbor porpoises reported no evidence of seasonal
changes in distribution for the inland waters of southeast Alaska
(Dahlheim et al., 2009). Their small overall size, lack of a visible
blow, low dorsal fins and overall low profile, and short surfacing time
make them difficult to observe (Dahlheim et al., 2015), likely reducing
identification and reporting of this species, and these estimates
therefore may be low.
Although there have been no systematic studies or observations of
harbor porpoises specific to Hydaburg or Sukkwan Strait, there is
potential for them to occur in the proposed project area. Abundance
data for harbor porpoises in southeast Alaska were collected during 18
seasonal surveys spanning 22 years, from 1991 to 2012 (Dahlheim et al.,
2015). During that study, a total of 81 harbor porpoises were observed
in the southern inland waters of southeast Alaska; however, the survey
terminated 80 km southeast of Hydaburg and did not include Sukkwan
Strait as part of the survey. There does not appear to be any seasonal
variation in harbor porpoise density in the inland waters of southeast
Alaska (Dahlheim et al., 2015). Harbor porpoises have not been reported
by local residents.

Dall's Porpoise

Dall's porpoises are found throughout the North Pacific, from
southern Japan to southern California and north to the Bering Sea. All
Dall's porpoises in Alaska are members of the Alaska stock, and those
off California, Oregon, and Washington are part of a separate stock.
Dall's porpoises can be found in offshore, inshore, and nearshore
habitat, but they are most commonly found in waters deeper than 183 m
(Dahlheim et al., 2009; Jefferson, 2009).
Common prey of Dall's porpoise include a variety of small,
schooling fishes (such as herrings and mackerels)

[[Page 45781]]

and cephalopods. Dall's porpoises may migrate between inshore and
offshore areas and make latitudinal movements or short seasonal
migrations, but these movements are generally not consistent
(Jefferson, 2009).
Dall's porpoises generally occur in groups of 2 to 20 individuals
but have also been recorded in groups numbering in the hundreds. The
mean group size in southeast Alaska is estimated at approximately three
individuals (Dahlheim et al., 2009; Jefferson, 2019). However, Dall's
porpoises are reported to typically occur in groups of 10-15 animals
near Ketchikan Alaska, which is located approximately 76 km east of
Hydaburg, with an estimated maximum group size of 20 animals (Freitag
2017, 83 FR 37473, August 1, 2018).
No systematic studies of Dall's porpoise abundance or distribution
have occurred in Sukkwan Strait; however, Dall's porpoises have been
observed in Cordova Bay 30 km south of Hydaburg during a summer 2011
survey (Jefferson et al., 2019). Despite generalized water depth
preferences, Dall's porpoises may occur in shallow waters. Moran et al.
(2018) recently mapped Dall's porpoise distributions in bays, shallow
water, and nearshore areas of Prince William Sound, habitats not
typically utilized by this species. If Dall's porpoises occur in the
proposed project area, they will likely be present in March or April,
given the strong seasonal patterns observed in nearby areas of
southeast Alaska (Dahlheim et al., 2009). No local residents have
described seeing Dall's porpoises within Sukkwan Strait.

Pacific White-Sided Dolphin

Pacific white-sided dolphins are a pelagic species inhabiting
temperate waters of the North Pacific Ocean and along the coasts of
California, Oregon, Washington, and Alaska (Muto et al., 2022). Despite
their distribution mostly in deep, offshore waters, they may also be
found over the continental shelf and in nearshore waters, including
inland waters of southeast Alaska (Ferrero and Walker, 1996). Pacific
white-sided dolphins are managed as two distinct stocks: the
California/Oregon/Washington stock and the North Pacific stock (north
of 45[deg] N, including Alaska). Pacific white-sided dolphins present
near the project area are recognized as being members of the North
Pacific stock, which ranges from Canada into Alaska (Muto et al.,
2022).
Pacific white-sided dolphins prey on squid and small schooling fish
such as capelin, sardines, and herring (Morton, 2006). They are known
to work in groups to herd schools of fish and can dive underwater for
up to 6 minutes to feed (Morton, 2006). Group sizes have been reported
to range from 40 to over 1,000 animals, but groups of between 10 and
100 individuals (Stacey and Baird, 1991) occur most commonly. Seasonal
movements of Pacific white-sided dolphins are not well understood, but
there is evidence of both north-south seasonal movement (Leatherwood et
al., 1984) and inshore-offshore seasonal movement (Stacey and Baird,
1991).
Pacific white-sided dolphins do not generally occur in the shallow,
inland waterways of southeast Alaska. Scientific studies and data are
lacking relative to the presence or abundance of Pacific white-sided
dolphins in or near Sukkwan Strait. When Pacific white-sided dolphins
have been observed, sighting rates were highest in spring and decreased
throughout summer and fall (Dahlheim et al., 2009).
Most observations of Pacific white-sided dolphins occur off the
outer coast or in inland waterways near entrances to the open ocean.
According to Muto et al. (2022), aerial surveys in 1997 sighted one
group of 164 Pacific white-sided dolphins in Dixon Entrance to the
southeast of Hydaburg. These observational data, combined with
anecdotal information, indicate that there is a small potential for
Pacific white-sided dolphins to occur in the proposed project area.
NMFS previously estimated that a group of up to 92 individuals (median
between 20 and 164 individuals) could be present at Metlakatla, Alaska
(86 FR 43190, August 6, 2021), which is located approximately 80 km
east of Hydaburg.

Killer Whale

Killer whales have been observed in all the world's oceans, but the
highest densities occur in colder and more productive waters found at
high latitudes (NMFS, 2016a). Killer whales occur along the entire
Alaska coast, in British Columbia and Washington inland waterways, and
along the outer coasts of Washington, Oregon, and California (NMFS,
2016a).
Based on data regarding association patterns, acoustics, movements,
and genetic differences, eight killer whale stocks are now recognized
within the Pacific U.S. exclusive economic zone. Only individuals from
the Eastern North Pacific Alaska Resident stock (Alaska Resident
stock), Eastern North Pacific Northern Resident stock (Northern
Resident stock), and West Coast Transient stock may occur in the
proposed project area (Muto et al., 2022).
There are three distinct ecotypes, or forms, of killer whales
recognized: resident, transient, and offshore. The three ecotypes
differ morphologically, ecologically, behaviorally, and genetically.
Surveys between 1991 and 2007 encountered resident killer whales during
all seasons throughout southeast Alaska. Both residents and transients
were common in a variety of habitats and all major waterways, including
protected bays and inlets. There does not appear to be strong seasonal
variation in abundance or distribution of killer whales, but there was
substantial variability between years during this study (Dahlheim et
al., 2009). Spatial distribution has been shown to vary among the
different ecotypes, with resident and, to a lesser extent, transient
killer whales more commonly observed along the continental shelf, and
offshore killer whales more commonly observed in pelagic waters (Rice
et al., 2021).
Transient killer whales hunt and feed primarily on marine mammals,
while residents forage primarily on fish. Transient killer whales feed
primarily on harbor seals, Dall's porpoises, harbor porpoises, and sea
lions. Resident killer whale populations in the eastern North Pacific
feed mainly on salmonids, showing a strong preference for Chinook
salmon (NMFS, 2016a).
Transient killer whales are often found in long-term stable social
units (pods) of 1 to 16 whales. Average pod sizes in southeast Alaska
were six in spring, five in summer, and four in fall (Dahlheim et al.,
2009). Pod sizes of transient whales are generally smaller than those
of resident social groups. Resident killer whales occur in pods ranging
from 7 to 70 whales that are seen in association with one another more
than 50 percent of the time (Dahlheim et al., 2009; NMFS 2016b). In
southeast Alaska, resident killer whale mean pod size was approximately
21.5 in spring, 32.3 in summer, and 19.3 in fall (Dahlheim et al.,
2009).
No systematic studies of killer whales have been conducted in or
around Sukkwan Strait. Dahlheim et al. (2009) observed transient killer
whales within Lynn Canal, Icy Strait, Stephens Passage, Frederick
Sound, and upper Chatham Strait. Anecdotal local information suggests
that killer whales are rarely seen near the Hydaburg area, but a pod
may be seen occasionally every few months.

Humpback Whale

Humpback whales are found throughout southeast Alaska in a variety
of marine environments, including open ocean, nearshore waters, and
areas with strong tidal currents (Dahlheim et al., 2009). Most humpback
whales are migratory and spend winters in the

[[Page 45782]]

breeding grounds off either Hawaii or Mexico. Humpback whales generally
arrive in southeast Alaska in March and return to their wintering
grounds in November. Some humpback whales depart late or arrive early
to feeding grounds, and therefore the species occurs in southeast
Alaska year-round (Straley, 1990; Straley et al., 2018). Current
threats to humpback whales include vessel strikes, spills, climate
change, and commercial fishing operations (Muto et al., 2022).
Humpback whales worldwide were designated as ``endangered'' under
the Endangered Species Conservation Act in 1970 and had been listed as
a species under the ESA since its inception in 1973. On September 8,
2016, NMFS published a final decision that changed the status of
humpback whales under the ESA (81 FR 62259), effective on October 11,
2016. The decision recognized the existence of 14 DPSs based on
distinct breeding areas in tropical and temperate waters. Five of the
14 DPSs were classified under the ESA (4 endangered and 1 threatened),
while the other 9 DPSs were delisted. Humpback whales found in the
project area are predominantly members of the Hawaii DPS, which is not
listed under the ESA. However, based on a comprehensive photo-
identification study, members of the Mexico DPS, which is listed as
threatened, are known to occur in southeast Alaska. Members of
different DPSs are known to intermix on feeding grounds; therefore, all
waters off the coast of Alaska should be considered to potentially have
ESA-listed humpback whales. Approximately 2 percent of all humpback
whales encountered in southeast Alaska and northern British Columbia
are expected to be members of the Mexico DPS, while all others are
expected to be members of the Hawaii DPS (Wade et al., 2021).
The DPSs of humpback whales that were identified through the ESA
listing process do not necessarily equate to the existing MMPA stocks.
The stock delineations of humpback whales under the MMPA are currently
under review. Until this review is complete, NMFS considers humpback
whales in southeast Alaska to be part of the Central North Pacific
stock, with a status of endangered under the ESA and designations of
strategic and depleted under the MMPA (Muto et al., 2022).
Southeast Alaska is considered a biologically important area (BIA)
for feeding humpback whales between May and September (Wild et al.,
2023), though not currently designated as critical habitat (86 FR
21082, April 21, 2021). Most humpback whales migrate to other regions
during winter to breed, but over-wintering (non-breeding) humpback
whales have been noted and may be increasingly common and attributable
to staggered migration (Straley, 1990, Straley et al., 2018). It is
thought that those humpbacks that remain in southeast Alaska do so in
response to the availability of winter schools of fish prey, which
primarily includes overwintering herring (Straley et al., 2018). In
Alaska, humpback whales filter feed on tiny crustaceans, plankton, and
small fish such as walleye pollock, Pacific sand lance, herring (Clupea
pallasii), eulachon (Thaleichthys pacificus), and capelin (Witteveen et
al., 2012). It is common to observe groups of humpback whales
cooperatively bubble feeding. Group sizes in southeast Alaska generally
range from one to four individuals (Dahlheim et al., 2009).
No systematic studies have documented humpback whale abundance near
Hydaburg. Anecdotal information from local residents suggests that
humpback whales' utilization of the area is intermittent year-round.
Their abundance, distribution, and occurrence are dependent on and
fluctuate with fish prey. Local residents estimate that one to two
humpback whales may be present in the Sukkwan Strait on a weekly basis.
Elsewhere in southeast Alaska, marine mammal monitoring for projects in
Tongass Narrows, Ketchikan, Alaska, indicate that humpback whales are
present in that area most regularly from May through October (DOT&PF,
2021; 2022) and may occur in lower numbers in winter, which we would
expect to be the case for Hydaburg.

Minke Whale

Minke whales are found throughout the northern hemisphere in polar,
temperate, and tropical waters (Jefferson et al., 2008). The population
status of minke whales is considered stable throughout most of their
range. Historically, commercial whaling reduced the population size of
this species, but given their small size, they were never a primary
target of whaling and did not experience severe population declines as
did larger cetaceans.
The International Whaling Commission has identified three minke
whale stocks in the North Pacific: one near the Sea of Japan, a second
in the rest of the western Pacific, and a third, less concentrated,
stock throughout the eastern Pacific. NMFS further splits this third
stock between Alaska whales and resident whales of California, Oregon,
and Washington (Muto et al., 2022). Minke whales in southeast Alaska
are part of the Alaska stock (Muto et al., 2022). Minke whales are
found in all Alaskan waters. There are no population estimates for
minke whales in southeast Alaska. Surveys in southeast Alaska have
consistently identified individuals throughout inland waters in low
numbers (Dahlheim et al., 2009).
In Alaska, the minke whale diet consists primarily of euphausiids
and walleye pollock. Minke whales are generally found in shallow,
coastal waters within 200 m of shore (Zerbini et al., 2006) and are
almost always solitary or in small groups of two to three. Rarely,
loose aggregations of up to 400 animals have been associated with
feeding areas in Arctic latitudes. In Alaska, seasonal movements are
associated with feeding areas that are generally located at the edge of
the pack ice (NMFS, 2014).
There are no known occurrences of minke whales within the project
area. Dedicated surveys for cetaceans in southeast Alaska found that
minke whales were scattered throughout inland waters from Glacier Bay
and Icy Strait to Clarence Strait, with small concentrations near the
entrance of Glacier Bay (Dahlheim et al., 2009). All sightings were of
single minke whales, except for a single sighting of multiple minke
whales. Surveys took place in spring, summer, and fall, and minke
whales were present in low numbers in all seasons and years. NMFS is
not aware of information on the winter occurrence of minke whales in
southeast Alaska.
Anecdotal observations suggest that minke whales are not seen near
Hydaburg and so are expected to occur rarely in the project area.
However, NMFS has previously estimated that a group of up to three
individuals could be present at nearby Metlakatla, Alaska over 4 months
(86 FR 43190, August 6, 2021). Since their ranges extend into the
project area and they have been observed in southeast Alaska, including
in Clarence Strait (Dahlheim et al., 2009), it is possible the species
could occur near the project area.

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 or hear over the same frequency range (e.g.,
Richardson et al., 1995; Wartzok and Ketten, 1999; Au and Hastings,

[[Page 45783]]

2008). To reflect this, Southall et al. (2007, 2019) recommended that
marine mammals be divided into hearing groups based on directly
measured (behavioral or auditory evoked potential techniques) or
estimated hearing ranges (behavioral response data, anatomical
modeling, etc.). Note that no direct measurements of hearing ability
have been successfully completed for mysticetes (i.e., low-frequency
cetaceans). Subsequently, NMFS (2018) 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 3.

Table 3--Marine Mammal Hearing Groups
[NMFS, 2018]
------------------------------------------------------------------------
Generalized hearing
Hearing group range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen whales).... 7 Hz to 35 kHz.
Mid-frequency (MF) cetaceans (dolphins, toothed 150 Hz to 160 kHz.
whales, beaked whales, bottlenose whales).
High-frequency (HF) cetaceans (true porpoises, 275 Hz to 160 kHz.
Kogia, river dolphins, Cephalorhynchid,
Lagenorhynchus cruciger & L. australis).
Phocid pinnipeds (PW) (underwater) (true seals). 50 Hz to 86 kHz.
Otariid pinnipeds (OW) (underwater) (sea lions 60 Hz to 39 kHz.
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 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 et al., 2013).
For more detail concerning these groups and associated generalized
hearing 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 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 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.
Acoustic effects on marine mammals during the specified activity
are expected to potentially occur from impact pile installation,
vibratory pile installation, and DTH systems. The effects of underwater
noise from the DOT&PF's proposed activities have the potential to
result in Level B harassment of marine mammals in the action area, and,
for some species as a result of certain activities, Level A harassment

Background on Sound

This section contains a brief technical background on sound, on the
characteristics of certain sound types, and on metrics used in this
proposal in as much 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. For general
information on sound and its interaction with the marine environment,
please see, e.g., Erbe and Thomas (2022); Au and Hastings (2008);
Richardson et al. (1995); Urick (1983) as well as the Discovery of
Sound in the Sea (DOSITS) website at <a href="https://dosits.org/">https://dosits.org/</a>.
Sound is a vibration that travels as an acoustic wave through a
medium such as a gas, liquid, or solid. Sound waves alternately
compress and decompress the medium as the wave travels. In water, sound
waves radiate in a manner similar to ripples on the surface of a pond
and may be either directed in a beam (narrow beam or directional
sources) or sound may radiate in all directions (omnidirectional
sources), as is the case for sound produced by the construction
activities considered here. The compressions and decompressions
associated with sound waves are detected as changes in pressure by
marine mammals and human-made sound receptors such as hydrophones.
Sound travels more efficiently in water than almost any other form
of energy, making the use of sound as a primary sensory modality ideal
for inhabitants of the aquatic environment. In seawater, sound travels
at roughly 1,500 meters per second (m/s). In air, sound waves travel
much more slowly at about 340 m/s. However, the speed of sound in water
can vary by a small amount based on characteristics such as temperature
and salinity.
The basic characteristics of a sound wave 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 with
distance, except in certain cases in shallower water. The amplitude of
a sound pressure wave is related to the subjective ``loudness'' of a
sound and is typically expressed in dB, which are a relative unit of
measurement that is used to express the ratio of one value of a power
or pressure to another. A sound pressure level (SPL) in dB is described
as the ratio between a measured pressure and a reference pressure, 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. For example, a 10-dB increase is a 10-fold increase
in acoustic power. A 20-dB increase is then a 100-fold

[[Page 45784]]

increase in power and a 30-dB increase is a 1,000-fold increase in
power. However, a 10-fold increase in acoustic power does not mean that
the sound is perceived as being 10 times louder. The dB is a relative
unit comparing two pressures; therefore, a reference pressure must
always be indicated. For underwater sound, this is 1 micropascal
([mu]Pa). For in-air sound, the reference pressure is 20 micropascal
([mu]Pa). The amplitude of a sound can be presented in various ways;
however, NMFS typically considers three metrics: sound exposure level
(SEL), root-mean-square (RMS) SPL, and peak SPL (defined below). The
source level represents the SPL referenced from a standard distance
from the source (typically 1 m) (Richardson et al., 1995; American
National Standards Institute (ANSI), 2013), while the received level is
the SPL at the receiver's position. For pile driving activities, the
SPL is typically referenced at 10 m.
SEL (represented as dB referenced to 1 micropascal squared per
second (re 1 [mu]Pa\2\-s)) represents the total energy in a stated
frequency band over a stated time interval or event, and considers both
intensity and duration of exposure. The per-pulse SEL (e.g., single
strike or single shot SEL) is calculated over the time window
containing the entire pulse (i.e., 100 percent of the acoustic energy).
SEL can also be a cumulative metric; it can be accumulated over a
single pulse (for pile driving this is the same as single-strike SEL,
above; SELss), or calculated over periods containing multiple pulses
(SELcum). Cumulative SEL (SELcum) represents the total energy
accumulated by a receiver over a defined time window or during an
event. The SEL metric is useful because it allows sound exposures of
different durations to be related to one another in terms of total
acoustic energy. The duration of a sound event and the number of
pulses, however, should be specified as there is no accepted standard
duration over which the summation of energy is measured.
RMS SPL is 10 times the logarithm (base 10) of the ratio of the
mean-square sound pressure to the specified reference value, in dB
(ISO, 2017). RMS is calculated by squaring all of the sound amplitudes,
averaging the squares, and then taking the square root of the average
(Urick, 1983). RMS 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 SPL. For impulsive sounds, RMS is calculated by the
portion of the waveform containing 90 percent of the sound energy from
the impulsive event (Madsen, 2005).
Peak SPL (also referred to as zero-to-peak sound pressure or 0-pk)
is the maximum instantaneous sound pressure measurable in the water,
which can arise from a positive or negative sound pressure, during a
specified time, for a specific frequency range (International
Organization for Standardization (ISO), 2017) at a specified distance
from the source, and is represented in the same units as the RMS sound
pressure. Along with SEL, this metric is used in evaluating the
potential for PTS (permanent threshold shift) and TTS (temporary
threshold shift) associated with impulsive sound sources.
Sounds are also characterized by their temporal component.
Continuous sounds are those whose sound pressure level remains above
that of the ambient or background sound with negligibly small
fluctuations in level (ANSI, 2005), while intermittent sounds are
defined as sounds with interrupted levels of low or no sound (National
Institute for Occupational Safety and Health (NIOSH), 1998). A key
distinction between continuous and intermittent sound sources is that
intermittent sounds have a more regular (predictable) pattern of bursts
of sounds and silent periods (i.e., duty cycle), which continuous
sounds do not.
Sounds can be either impulsive or non-impulsive (defined below).
The distinction between these two sound types is important because they
have differing potential to cause physical effects, particularly with
regard to noise-induced hearing loss (e.g., Ward, 1997 in Southall et
al., 2007). Please see NMFS et al. (2018) and Southall et al. (2007,
2019) for an in-depth discussion of these concepts.
Impulsive sound sources (e.g., explosions, gunshots, sonic booms,
seismic airgun shots, impact pile driving) produce signals that are
brief (typically considered to be less than one second), broadband,
atonal transients (ANSI, 1986; NIOSH, 1998; ANSI 2005) and occur either
as isolated events or repeated in some succession. Impulsive 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. Impulsive
sounds are intermittent in nature. The duration of such sounds, as
received at a distance, can be greatly extended in a highly reverberant
environment.
Non-impulsive 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-impulsive sounds can be transient
signals of short duration but without the essential properties of
impulses (e.g., rapid rise time). Examples of non-impulsive sounds
include those produced by vessels, aircraft, machinery operations such
as drilling or dredging, vibratory pile driving, and active sonar
systems.
Even in the absence of sound from the specified activity, the
underwater environment is typically loud due to both natural and
anthropogenic sound sources. Ambient sound is defined as a composite of
naturally-occurring (i.e., non-anthropogenic) sound from many sources
both near and far (ANSI, 1995). Background sound is similar, but
includes all sounds, including anthropogenic sounds, minus the sounds
produced by the proposed activity (NMFS, 2012; NOAA, 2016b). 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 background and
ambient sound, including wind and waves, which are a main source of
naturally occurring ambient sound for frequencies between 200 Hz and 50
kilohertz (kHz) (Mitson, 1995). In general, background and ambient
sound levels tend to increase with increasing wind speed and wave
height. Precipitation can become an important component of total sound
at frequencies above 500 Hz, and possibly down to 100 Hz during quiet
times. Marine mammals can contribute significantly to background and
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. Sources of background sound related to human activity
include transportation (surface vessels), dredging and construction,
oil and gas drilling and production, geophysical surveys, sonar, and
explosions. Vessel noise typically dominates the total background sound
for frequencies between 20 and 300 Hz.

[[Page 45785]]

In general, the frequencies of many anthropogenic sounds, particularly
those produced by construction activities, are below 1 kHz (Richardson
et al. 1995). When sounds at frequencies greater than 1 kHz are
produced, they generally attenuate relatively rapidly, particularly
above 20 kHz due to propagation losses and absorption (Urick, 1983).
Transmission loss (TL) defines the degree to which underwater sound
has spread in space and lost energy after having moved through the
environment, and reached a receiver. It is defined by the ISO as the
reduction in a specified level between two specified points that are
within an underwater acoustic field (ISO 2017). Careful consideration
of transmission loss and appropriate propagation modeling is a crucial
step in determining the impacts of underwater sound, as it helps to
define the ranges (isopleths) to which impacts are expected and depends
significantly on local environmental parameters such as seabed type,
water depth (bathymetry), and the local speed of sound. Geometric
spreading laws are powerful tools which provide a simple means of
estimating TL, based on the shape of the sound wave front in the water
column. For a sound source that is equally loud in all directions and
in deep water, the sound field takes the form of a sphere, as the sound
extends in every direction uniformly. In this case, the intensity of
the sound is spread across the surface of the sphere, and thus we can
relate intensity loss to the square of the range (as area = 4*pi*r\2\).
When expressing logarithmically in dB as TL, we find that TL =
20*Log<INF>10</INF>(range), for the case of spherical spreading. In
shallow water, the sea surface and seafloor will bound the shape of the
sound, leading to a more cylindrical shape, as the top and bottom of
the sphere is truncated by the largely reflective boundaries. This
situation is termed cylindrical spreading, and is given by TL =
10*Log<INF>10</INF>(range) (Urick, 1983). An intermediate scenario may
be defined by the equation TL = 15*Log<INF>10</INF>(range), and is
referred to as practical spreading. Though these two geometric
spreading laws defined above do not capture many often important
details (scattering, absorption, etc.), they offer a reasonable and
simple approximation of how sound decreases in intensity as it is
transmitted. In the absence of measured data indicating the level of
transmission loss at a given site for a specific activity, NMFS
recommends practical spreading (i.e., 15*Log<INF>10</INF>(range)) to
model acoustic propagation for construction activities in most
nearshore environments.
The sum of the various natural and anthropogenic sound sources at
any given location and time depends not only on the source levels but
also on the propagation of sound through the environment. Sound
propagation is dependent on the spatially and temporally varying
properties of the water column and sea floor, and is frequency-
dependent. As a result of the dependence on a large number of varying
factors, background and 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 the specified activity may be
a negligible addition to the local environment or could form a
distinctive signal that may affect marine mammals.
Ongoing marine vessel traffic, seaplane traffic and associated
activities throughout the Sukkwan Strait area, as well as land-based
industrial and commercial activities, result in elevated in-air and
underwater sound conditions in the project area that increase with
proximity to the project site. Sound levels likely vary seasonally,
with elevated levels during summer, when the commercial and fishing
industries are at their peaks.

Description of Sound Sources for the Specified Activities

In-water construction activities associated with the project would
include impact pile installation, vibratory pile installation and
removal, and DTH installation. Impact hammers operate by repeatedly
dropping and/or pushing a heavy piston onto a pile to drive the pile
into the substrate. Sound generated by impact hammers is characterized
by rapid rise times and high peak levels, a potentially injurious
combination (Hastings and Popper, 2005). Vibratory hammers install
piles by vibrating them and allowing the weight of the hammer to push
them into the sediment. Vibratory hammers typically produce less sound
(i.e., lower levels) than impact hammers. Peak SPLs may be 180 dB or
greater, but are generally 10 to 20 dB lower than SPLs generated during
impact pile driving of the same-sized pile (Oestman et al., 2009). The
rise time is slower, reducing the probability and severity of injury,
and the sound energy is distributed over a greater amount of time
(Nedwell and Edwards, 2002; Carlson et al., 2005).
DTH systems would also be used during the proposed construction to
install rock sockets and tension anchors. A DTH hammer is essentially a
drill bit that drills through the bedrock using a rotating function
like a normal drill, in concert with a hammering mechanism operated by
a pneumatic (or sometimes hydraulic) component integrated into the DTH
hammer to increase speed of progress through the substrate (i.e., it is
similar to a ``hammer drill'' hand tool). The sounds produced by the
DTH methods contain both a continuous non-impulsive component from the
drilling action and an impulsive component from the hammering effect.
Therefore, NMFS treats DTH systems as both impulsive and continuous,
non-impulsive sound source types simultaneously.
The likely or possible impacts of the DOT&PF's proposed activities
on marine mammals could involve both non-acoustic and acoustic
stressors. Potential non-acoustic stressors could result from the
physical presence of the equipment and personnel; however, given there
are no known pinniped haul-out sites in the vicinity of the proposed
project site, visual and other non-acoustic stressors would be limited,
and any impacts to marine mammals are expected to primarily be acoustic
in nature.

Acoustic Impacts

The introduction of anthropogenic noise into the aquatic
environment from pile driving or drilling is the primary means by which
marine mammals may be harassed from the DOT&PF's specified activity. In
general, animals exposed to natural or anthropogenic sound may
experience physical and psychological effects, ranging in magnitude
from none to severe (Southall et al., 2007, 2019). In general, exposure
to pile driving or drilling noise has the potential to result in
auditory threshold shifts and behavioral reactions (e.g., avoidance,
temporary cessation of foraging and vocalizing, changes in dive
behavior). Exposure to anthropogenic noise can also lead to non-
observable physiological responses, such an increase in stress
hormones. Additional noise in a marine mammal's habitat can mask
acoustic cues used by marine mammals to carry out daily functions, such
as communication and predator and prey detection. The effects of pile
driving or drilling noise on marine mammals are dependent on several
factors, including, but not limited to, sound type (e.g., impulsive vs.
non-impulsive), the species, age and sex class (e.g., adult male vs.
mom with calf), duration of exposure, the distance

[[Page 45786]]

between the pile and the animal, received levels, behavior at time of
exposure, and previous history with exposure (Wartzok et al., 2004;
Southall et al., 2007). Here we discuss physical auditory effects
(threshold shifts) followed by behavioral effects and potential impacts
on habitat.
NMFS defines a noise-induced threshold shift (TS) as a change,
usually an increase, in the threshold of audibility at a specified
frequency or portion of an individual's hearing range above a
previously established reference level (NMFS, 2018). The amount of
threshold shift is customarily expressed in dB. A TS can be permanent
or temporary. As described in NMFS (2018a), there are numerous factors
to consider when examining the consequence of TS, including, but not
limited to, the signal temporal pattern (e.g., impulsive or non-
impulsive), likelihood an individual would be exposed for a long enough
duration or to a high enough level to induce a TS, the magnitude of the
TS, time to recovery (seconds to minutes or hours to days), the
frequency range of the exposure (i.e., spectral content), the hearing
and vocalization frequency range of the exposed species relative to the
signal's frequency spectrum (i.e., how animal uses sound within the
frequency band of the signal; e.g., Kastelein et al., 2014), and the
overlap between the animal and the source (e.g., spatial, temporal, and
spectral). When considering auditory effects for the DOT&PF's proposed
activities, vibratory pile driving is considered a non-impulsive
source, while impact pile driving is treated as an impulsive source.
DTH systems are considered to have both non-impulsive and impulsive
components.
Permanent Threshold Shift (PTS)--NMFS defines PTS as a permanent,
irreversible increase in the threshold of audibility at a specified
frequency or portion of an individual's hearing range above a
previously established reference level (NMFS, 2018). PTS does not
generally affect more than a limited frequency range, and an animal
that has incurred PTS has incurred some level of hearing loss at the
relevant frequencies; typically animals with PTS are not functionally
deaf (Richardson et al., 1995; Au and Hastings, 2008). Available data
from humans and other terrestrial mammals indicate that a 40 dB
threshold shift approximates PTS onset (see Ward et al., 1958, 1959;
Ward, 1960; Kryter et al., 1966; Miller, 1974; Ahroon et al., 1996;
Henderson et al., 2008). PTS criteria for marine mammals are estimates,
as with the exception of a single study unintentionally inducing PTS in
a harbor seal (Kastak et al., 2008), there are no empirical data
measuring PTS in marine mammals largely due to the fact that, for
various ethical reasons, experiments involving anthropogenic noise
exposure at levels inducing PTS are not typically pursued or authorized
(NMFS, 2018).
Temporary Threshold Shift (TTS)--A temporary, reversible increase
in the threshold of audibility at a specified frequency or portion of
an individual's hearing range above a previously established reference
level (NMFS, 2018). Based on data from cetacean TTS measurements (see
Southall et al., 2007; 2019), a TTS of 6 dB is considered the minimum
threshold shift clearly larger than any day-to-day or session-to-
session variation in a subject's normal hearing ability (Schlundt et
al., 2000; Finneran et al., 2000, 2002). As described in Finneran
(2015), marine mammal studies have shown the amount of TTS increases
with SELcum in an accelerating fashion: at low exposures with lower
SELcum, the amount of TTS is typically small and the growth curves have
shallow slopes. At exposures with higher SELcum, the growth curves
become steeper and approach linear relationships with the noise SEL.
Depending on the degree (elevation of threshold in dB), duration
(i.e., recovery time), and frequency range of TTS, and the context in
which it is experienced, TTS can have effects on marine mammals ranging
from discountable to serious (similar to those discussed in auditory
masking, below). For example, a marine mammal may be able to readily
compensate for a brief, relatively small amount of TTS in a non-
critical frequency range that takes place during a time when the animal
is traveling through the open ocean, where ambient noise is lower and
there are not as many competing sounds present. Alternatively, a larger
amount and longer duration of TTS sustained during time when
communication is critical for successful mother/calf interactions could
have more serious impacts. We note that reduced hearing sensitivity as
a simple function of aging has been observed in marine mammals, as well
as humans and other taxa (Southall et al., 2007), so we can infer that
strategies exist for coping with this condition to some degree, though
likely not without cost.
Many studies have examined noise-induced hearing loss in marine
mammals (see Finneran (2015) and Southall et al. (2019) for summaries).
TTS is the mildest form of hearing impairment that can occur during
exposure to sound (Kryter, 2013). While experiencing TTS, the hearing
threshold rises, and a sound must be at a higher level in order to be
heard. In terrestrial and marine mammals, TTS can last from minutes or
hours to days (in cases of strong TTS). In many cases, hearing
sensitivity recovers rapidly after exposure to the sound ends. For
cetaceans, published data on the onset of TTS are limited to captive
bottlenose dolphin (Tursiops truncatus), beluga whale (Delphinapterus
leucas), harbor porpoise, and Yangtze finless porpoise (Neophocoena
asiaeorientalis) (Southall et al., 2019). For pinnipeds in water,
measurements of TTS are limited to harbor seals, elephant seals,
bearded seals (Erignathus barbatus), and California sea lions (Zalophus
californianus) (Kastak et al., 1999; 2007; Kastelein et al., 2019b;
2019c; Reichmuth et al., 2019; Sills et al., 2020; Kastelein et al.,
2021; 2022a; 2022b). These studies examine hearing thresholds measured
in marine mammals before and after exposure to intense or long-duration
sound exposures. The difference between the pre-exposure and post-
exposure thresholds can be used to determine the amount of threshold
shift at various post-exposure times.
The amount and onset of TTS depends on the exposure frequency.
Sounds at low frequencies, well below the region of best sensitivity
for a species or hearing group, are less hazardous than those at higher
frequencies, near the region of best sensitivity (Finneran and
Schlundt, 2013). At low frequencies, onset-TTS exposure levels are
higher compared to those in the region of best sensitivity (i.e., a low
frequency noise would need to be louder to cause TTS onset when TTS
exposure level is higher), as shown for harbor porpoises and harbor
seals (Kastelein et al., 2019a; Kastelein et al., 2019c). Note that in
general, harbor seals and harbor porpoises have a lower TTS onset than
other measured pinniped or cetacean species (Finneran, 2015). In
addition, TTS can accumulate across multiple exposures, but the
resulting TTS will be less than the TTS from a single, continuous
exposure with the same SEL (Mooney et al., 2009; Finneran et al., 2010;
Kastelein et al., 2014; 2015). This means that TTS predictions based on
the total, cumulative SEL will overestimate the amount of TTS from
intermittent exposures, such as sonars and impulsive sources.
Nachtigall et al. (2018) describe measurements of hearing sensitivity
of multiple odontocete species (bottlenose dolphin, harbor porpoise,
beluga, and false killer whale (Pseudorca

[[Page 45787]]

crassidens)) when a relatively loud sound was preceded by a warning
sound. These captive animals were shown to reduce hearing sensitivity
when warned of an impending intense sound. Based on these experimental
observations of captive animals, the authors suggest that wild animals
may dampen their hearing during prolonged exposures or if conditioned
to anticipate intense sounds. Another study showed that echolocating
animals (including odontocetes) might have anatomical specializations
that might allow for conditioned hearing reduction and filtering of
low-frequency ambient noise, including increased stiffness and control
of middle ear structures and placement of inner ear structures (Ketten
et al., 2021). Data available on noise-induced hearing loss for
mysticetes are currently lacking (NMFS, 2018). Additionally, the
existing marine mammal TTS data come from a limited number of
individuals within these species.
Relationships between TTS and PTS thresholds have not been studied
in marine mammals, and there is no PTS data for cetaceans, 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 decibels above (a 40-dB threshold shift approximates PTS onset;
e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB
threshold shift approximates TTS onset; e.g., Southall et al., 2007).
Based on data from terrestrial mammals, a precautionary assumption is
that the PTS thresholds for impulsive sounds (such as impact pile
driving pulses as received close to the source) are at least 6 dB
higher than the TTS threshold on a peak-pressure basis and PTS
cumulative sound exposure level thresholds are 15 to 20 dB higher than
TTS cumulative sound exposure level thresholds (Southall et al., 2007).
Given the higher level of sound or longer exposure duration necessary
to cause PTS as compared with TTS, it is considerably less likely that
PTS could occur.
Behavioral Harassment--Exposure to noise from pile driving and
drilling also has the potential to behaviorally disturb marine mammals
to a level that rises to the definition of harassment under the MMPA.
Generally speaking, NMFS considers a behavioral disturbance that rises
to the level of harassment under the MMPA a non-minor response--in
other words, not every response qualifies as behavioral disturbance,
and for responses that do, those of a higher level, or accrued across a
longer duration, have the potential to affect foraging, reproduction,
or survival. 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. Disturbance may result in changing durations of
surfacing and dives, changing direction and/or speed; reducing/
increasing vocal activities; changing/cessation of certain behavioral
activities (such as socializing or feeding); eliciting a visible
startle response or aggressive behavior (such as tail/fin slapping or
jaw clapping); avoidance of areas where sound sources are located.
Pinnipeds may increase their haul out time, possibly to avoid in-water
disturbance (Thorson and Reyff, 2006). 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., 2004; Southall et al.,
2007; Weilgart, 2007; Archer et al., 2010, Southall et al., 2021).
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). In general, pinnipeds seem more tolerant of, or at
least habituate more quickly to, potentially disturbing underwater
sound than do cetaceans, and generally seem to be less responsive to
exposure to industrial sound than most cetaceans. Please see Appendices
B and C of Southall et al. (2007) and Gomez et al. (2016) for reviews
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., 2004). 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 above, 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; National Research Council (NRC), 2003; Wartzok et al., 2004).
Controlled experiments with captive marine mammals have showed
pronounced behavioral reactions, including avoidance of loud sound
sources (Ridgway et al., 1997; Finneran et al., 2003). 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).
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; Costa et al., 2003; Ng and Leung, 2003; Nowacek et
al., 2004; Goldbogen et al., 2013a,b). Variations in dive behavior may
reflect interruptions in biologically significant activities (e.g.,
foraging) or they may be of little biological significance. The impact
of an alteration to dive behavior resulting from an acoustic exposure
depends on what the animal is doing at

[[Page 45788]]

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).
Marine mammals vocalize for different purposes and across multiple
modes, such as whistling, echolocation click production, calling, and
singing. Changes in vocalization behavior in response to anthropogenic
noise can occur for any of these modes and may result from a need to
compete with an increase in background noise or may reflect increased
vigilance or a startle response. For example, in the presence of
potentially masking signals, humpback whales and killer whales have
been observed to increase the length of their songs or vocalizations,
respectively (Miller et al., 2000; Fristrup et al., 2003; Foote et al.,
2004), while right whales (Eubalaena glacialis) have been observed to
shift the frequency content of their calls upward while reducing the
rate of calling in areas of increased anthropogenic noise (Parks et
al., 2007). In some cases, animals may cease sound production during
production of aversive signals (Bowles et al., 1994).
Avoidance is the displacement of an individual from an area or
migration path as a result of the presence of a sound or other
stressors, and is one of the most obvious manifestations of disturbance
in marine mammals (Richardson et al., 1995). For example, gray whales
are known to change direction--deflecting from customary migratory
paths--in order to avoid noise from seismic surveys (Malme et al.,
1984). Avoidance may be short-term, with animals returning to the area
once the noise has ceased (e.g., Bowles et al., 1994; Goold, 1996;
Stone et al., 2000; Morton and Symonds, 2002; Gailey et al., 2007).
Longer-term displacement is possible, however, which may lead to
changes in abundance or distribution patterns of the affected species
in the affected region if habituation to the presence of the sound does
not occur (e.g., Blackwell et al., 2004; 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, Bowers et al., 2018). 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 (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 fishes and terrestrial animals have shown that increased
vigilance may substantially reduce feeding rates (e.g., Beauchamp and
Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In
addition, chronic disturbance can cause population declines through
reduction of fitness (e.g., decline in body condition) and subsequent
reduction in reproductive success, survival, or both (e.g., Harrington
and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However,
Ridgway et al. (2006) reported that increased vigilance in bottlenose
dolphins exposed to sound over a 5-day period did not cause any sleep
deprivation or stress effects.
Many animals perform vital functions, such as feeding, resting,
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption
of such functions resulting from reactions to stressors such as sound
exposure are more likely to be significant if they last more than one
diel cycle or recur on subsequent days (Southall et al., 2007).
Consequently, a behavioral response lasting less than 1 day and not
recurring on subsequent days is not considered particularly severe
unless it could directly affect reproduction or survival (Southall et
al., 2007). Note that there is a difference between multi-day
substantive behavioral reactions and multi-day anthropogenic
activities. For example, just because an activity lasts for multiple
days does not necessarily mean that individual animals are either
exposed to activity-related stressors for multiple days or, further,
exposed in a manner resulting in sustained multi-day substantive
behavioral responses.
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., Selye, 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

[[Page 45789]]

(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 sufficient to restore normal function.
Relationships between these physiological mechanisms, animal
behavior, and the costs of stress responses are well-studied through
controlled experiments and for both laboratory and free-ranging animals
(e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003;
Krausman et al., 2004; Lankford et al., 2005). Stress responses due to
exposure to anthropogenic sounds or other stressors and their effects
on marine mammals have also been reviewed (Fair and Becker, 2000;
Romano et al., 2002b) and, more rarely, studied in wild populations
(e.g., Romano et al., 2002a). For example, Rolland et al. (2012) found
that noise reduction from reduced ship traffic in the Bay of Fundy was
associated with decreased stress in North Atlantic right whales. These
and other studies lead to a reasonable expectation that some marine
mammals will experience physiological stress responses upon exposure to
acoustic stressors and that it is possible that some of these would be
classified as ``distress.'' In addition, any animal experiencing TTS
would likely also experience stress responses (NRC, 2003), however
distress is an unlikely result of this project based on observations of
marine mammals during previous, similar construction projects.
Auditory Masking--Since many marine mammals rely on sound to find
prey, moderate social interactions, and facilitate mating (Tyack,
2008), noise from anthropogenic sound sources can interfere with these
functions, but only if the noise spectrum overlaps with the hearing
sensitivity or vocal ranges of the marine mammal (Southall et al.,
2007; Clark et al., 2009; Hatch et al., 2012). Chronic exposure to
excessive, though not high-intensity, noise could cause masking at
particular frequencies for marine mammals that utilize sound for vital
biological functions (Clark et al., 2009). Acoustic masking is when
other noises such as from human sources interfere 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). Therefore, under certain
circumstances, marine mammals whose acoustical sensors or environment
are being severely masked could also be impaired from maximizing their
performance fitness in survival and reproduction. The ability of a
noise source to mask biologically important sounds depends on the
characteristics of both the noise source and the signal of interest
(e.g., signal-to-noise ratio, temporal variability, direction), in
relation to each other and to an animal's hearing abilities (e.g.,
sensitivity, frequency range, critical ratios, frequency
discrimination, directional discrimination, age, or TTS hearing loss),
and existing ambient noise and propagation conditions.
Under certain circumstances, marine mammals experiencing
significant masking could also be impaired from maximizing their
performance fitness in survival and reproduction. Therefore, when the
coincident (masking) sound is human-made, it may be considered
harassment when disrupting or altering critical behaviors. It is
important to distinguish TTS and PTS, which persist after the sound
exposure, from masking, which occurs during the sound exposure. Because
masking (without resulting in TS) is not associated with abnormal
physiological function, it is not considered a physiological effect,
but rather a potential behavioral effect.
The frequency range of the potentially masking sound is important
in determining any potential behavioral impacts. For example, low-
frequency signals may have less effect on high-frequency echolocation
sounds produced by odontocetes but are more likely to affect detection
of mysticete communication calls and other potentially important
natural sounds such as those produced by surf and some prey species.
The masking of communication signals by anthropogenic noise may be
considered as a reduction in the communication space of animals (e.g.,
Clark et al., 2009) and may result in energetic or other costs as
animals change their vocalization behavior (e.g., Miller et al., 2000;
Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2010; Holt
et al., 2009). Masking can be reduced in situations where the signal
and noise come from different directions (Richardson et al., 1995),
through amplitude modulation of the signal, or through other
compensatory behaviors (Houser, 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).
Marine mammals near the proposed project site are exposed to
anthropogenic noise which may lead to some habituation, but is also a
source of masking. Vocalization changes may result from a need to
compete with an increase in background noise and include increasing the
source level, modifying the frequency, increasing the call repetition
rate of vocalizations, or ceasing to vocalize in the presence of
increased noise (Hotchkin and Parks, 2013).
Masking is more likely to occur in the presence of broadband,
relatively continuous noise sources. Energy distribution of pile
driving covers a broad frequency spectrum, and sound from pile driving
would be within the audible range of pinnipeds and cetaceans present in
the proposed action area. While some construction during the DOT&PF's
activities may mask some acoustic signals that are relevant to the
daily behavior of marine mammals, the short-term duration and limited
areas affected make it very unlikely that survival would be affected.
Airborne Acoustic Effects--Pinnipeds that occur near the project
site could be exposed to airborne sounds associated with construction
activities that have the potential to cause behavioral harassment,
depending on their distance from these activities. Airborne noise would
primarily be an issue for pinnipeds that are swimming or hauled out
near the project site within the range of noise levels elevated above
airborne acoustic criteria. Although pinnipeds are known to haul-out
regularly on man-made objects, incidents of take resulting solely from
airborne sound are unlikely due to the sheltered proximity between the
proposed project area and the known haulout sites (the closest known
pinniped haulout is for harbor seals, which is located 4.5 km (2.8 mi)
southeast of the proposed project site, but blocked by a land shadow).
Cetaceans are not expected to be exposed to airborne sounds that would
result in harassment as defined under the MMPA.

[[Page 45790]]

We recognize that pinnipeds in the water could be exposed to
airborne sound that may result in behavioral harassment when looking
with their heads above water. Most likely, airborne sound would cause
behavioral responses similar to those discussed above in relation to
underwater sound. For instance, anthropogenic sound could cause hauled-
out pinnipeds to exhibit changes in their normal behavior, such as
reduction in vocalizations, or cause them to temporarily abandon the
area and move further from the source. However, these animals would
previously have been ``taken'' because of exposure to underwater sound
above the behavioral harassment thresholds, which are in all cases
larger than those associated with airborne sound. Thus, the behavioral
harassment of these animals is already accounted for in these estimates
of potential take. Therefore, we do not believe that authorization of
incidental take resulting from airborne sound for pinnipeds is
warranted, and airborne sound is not discussed further here.

Potential Effects on Marine Mammal Habitat

The proposed project will occur within the same footprint as
existing marine infrastructure. The nearshore and intertidal habitat
where the proposed project will occur is an area of relatively high
marine vessel traffic. Most marine mammals do not generally use the
area within the footprint of the project area. Temporary, intermittent,
and short-term habitat alteration may result from increased noise
levels within the Level A and Level B harassment zones. Effects on
marine mammals will be limited to temporary displacement from pile
installation and removal noise, and effects on prey species will be
similarly limited in time and space.
Water Quality--Temporary and localized reduction in water quality
will occur as a result of in-water construction activities. Most of
this effect will occur during the installation and removal of piles and
bedrock removal when bottom sediments are disturbed. The installation
and removal of piles and bedrock removal will disturb bottom sediments
and may cause a temporary increase in suspended sediment in the project
area. During pile extraction, sediment attached to the pile moves
vertically through the water column until gravitational forces cause it
to slough off under its own weight. The small resulting sediment plume
is expected to settle out of the water column within a few hours.
Studies of the effects of turbid water on fish (marine mammal prey)
suggest that concentrations of suspended sediment can reach thousands
of milligrams per liter before an acute toxic reaction is expected
(Burton, 1993).
Impacts to water quality from DTH hammers are expected to be
similar to those described for pile driving. Impacts to water quality
would be localized and temporary and would have negligible impacts on
marine mammal habitat. Effects to turbidity and sedimentation are
expected to be short-term, minor, and localized. Since the currents are
strong in the area, following the completion of sediment-disturbing
activities, suspended sediments in the water column should dissipate
and quickly return to background levels in all construction scenarios.
Turbidity within the water column has the potential to reduce the level
of oxygen in the water and irritate the gills of prey fish species in
the proposed project area. However, turbidity plumes associated with
the project would be temporary and localized, and fish in the proposed
project area would be able to move away from and avoid the areas where
plumes may occur. Therefore, it is expected that the impacts on prey
fish species from turbidity, and therefore on marine mammals, would be
minimal and temporary. In general, the area likely impacted by the
proposed construction activities is relatively small compared to the
available marine mammal habitat in southeast Alaska.
Potential Effects on Prey--Sound may affect marine mammals through
impacts on the abundance, behavior, or distribution of prey species
(e.g., crustaceans, cephalopods, fish, zooplankton). Marine mammal prey
varies by species, season, and location and, for some, is not well
documented. Studies regarding the effects of noise on known marine
mammal prey are described here.
Fish utilize the soundscape and components of sound in their
environment to perform important functions such as foraging, predator
avoidance, mating, and spawning (e.g., Zelick and Mann, 1999; Fay,
2009). Depending on their hearing anatomy and peripheral sensory
structures, which vary among species, fishes hear sounds using pressure
and particle motion sensitivity capabilities and detect the motion of
surrounding water (Fay et al., 2008). The potential effects of noise on
fishes depends on the overlapping frequency range, distance from the
sound source, water depth of exposure, and species-specific hearing
sensitivity, anatomy, and physiology. Key impacts to fishes may include
behavioral responses, hearing damage, barotrauma (pressure-related
injuries), and mortality.
Fish react to sounds that are especially strong and/or intermittent
low-frequency sounds. Short duration, sharp sounds can cause overt or
subtle changes in fish behavior and local distribution. The reaction of
fish to noise depends on the physiological state of the fish, past
exposures, motivation (e.g., feeding, spawning, migration), and other
environmental factors. Hastings and Popper (2005) identified several
studies that suggest fish may relocate to avoid certain areas of sound
energy. Additional studies have documented effects of pile driving on
fishes; several are based on studies in support of large, multiyear
bridge construction projects (e.g., Scholik and Yan, 2001, 2002; Popper
and Hastings, 2009). Several studies have demonstrated that impulse
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). However,
some studies have shown no or slight reaction to impulse sounds (e.g.,
Pe[ntilde]a et al., 2013; Wardle et al., 2001; Jorgenson and Gyselman,
2009; Cott et al., 2012). More commonly, though, the impacts of noise
on fishes are temporary.
SPLs of sufficient strength have been known to cause injury to
fishes and fish mortality (summarized in Popper et al., 2014). 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. (2012a) 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. Injury caused by barotrauma can range
from slight to severe and can cause death, and is most likely for fish
with swim bladders. Barotrauma injuries have been documented during
controlled exposure to impact pile driving (Halvorsen et al., 2012b;
Casper et al., 2013).
Essential fish habitat (EFH) has been designated in the proposed
project area for all five species of salmon (i.e., chum salmon, pink
salmon, coho salmon, sockeye salmon, and Chinook salmon; NMFS 2017),
which are common prey of marine mammals. Many creeks flowing into
Sukkwan Strait and nearby areas are known to contain salmonids,
including three primary creeks: Hydaburg River, Natzuhini River, and
Saltery Creek (Giefer and Blossom

[[Page 45791]]

2020); however, adverse effects on EFH in this area are not expected.
Fish populations in the proposed project area that serve as marine
mammal prey could be temporarily affected by noise from pile
installation and removal. The frequency range in which fish generally
perceive underwater sounds is 50 to 2,000 Hz, with peak sensitivities
below 800 Hz (Popper and Hastings, 2009). Fish behavior or distribution
may change, especially with strong and/or intermittent sounds that
could harm fish. High underwater SPLs have been documented to alter
behavior, cause hearing loss, and injure or kill individual fish by
causing serious internal injury (Hastings and Popper, 2005).
The greatest potential impact to fishes during construction would
occur during impact pile driving and DTH excavation. In-water
construction activities would only occur during daylight hours allowing
fish to forage and transit the project area in the evening. Vibratory
pile driving would possibly elicit behavioral reactions from fishes
such as temporary avoidance of the area but is unlikely to cause
injuries to fishes or have persistent effects on local fish
populations. In general, impacts on marine mammal prey species are
expected to be minor, localized, and temporary.

In-Water Construction Effects on Potential Foraging Habitat

The proposed activities would not result in permanent impacts to
habitats used directly by marine mammals. The total seafloor area
affected by pile installation and removal is a very small area compared
to the vast foraging area available to marine mammals outside this
project area. Construction would have minimal permanent and temporary
impacts on benthic invertebrate species, a marine mammal prey source.
In addition, although southeast Alaska in its entirety is listed as a
BIA for humpback whales (Wild et al., 2023), the proposed project area
does not contain particularly high-value habitat and is not unusually
important for this species or any of the other species potentially
impacted by the DOT&PF's proposed activities. Therefore, impacts of the
project are not likely to have adverse effects on marine mammal
foraging habitat in the proposed project area.
The area impacted by the proposed project is relatively small
compared to the available habitat just outside the project area, and
there are no areas of particular importance that would be impacted by
this project. Any behavioral avoidance by fish of the disturbed area
would still leave significantly large areas of fish and marine mammal
foraging habitat in the nearby vicinity. As described in the preceding,
the potential for the DOT&PF's construction to affect the availability
of prey to marine mammals or to meaningfully impact the quality of
physical or acoustic habitat is considered to be insignificant.

Estimated Take

This section provides an estimate of the number of incidental takes
proposed for authorization through this IHA, which will inform both
NMFS' consideration of ``small numbers,'' and the negligible impact
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 primarily be by Level B harassment, as use
of the acoustic source (i.e., vibratory pile driving, impact pile
driving, and DTH systems) has the potential to result in disruption of
behavioral patterns for individual marine mammals. There is also some
potential for auditory (Level A harassment) to result, primarily for
mysticetes and high frequency species and phocids because predicted
auditory injury zones are larger than for mid-frequency species and
otariids. Auditory injury is unlikely to occur for mid-frequency
species or otariids. The proposed mitigation and monitoring measures
are expected to minimize the severity of the taking to the extent
practicable. 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

[[Page 45792]]

potential reduced opportunities to detect important signals
(conspecific communication, predators, prey) may result in changes in
behavior patterns that would not otherwise occur.
The DOT&PF's proposed activity includes the use of continuous
(vibratory pile driving) and intermittent (impact pile driving)
sources, and therefore the RMS SPL thresholds of 120 and 160 dB re 1
[mu]Pa are applicable. DTH systems have both continuous, non-impulsive,
and impulsive components as discussed in the Description of Sound
Sources section above. When evaluating Level B harassment, NMFS
recommends treating DTH as a continuous source and applying the RMS SPL
thresholds of 120 dB re 1 [mu]Pa.
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). The
DOT&PF's proposed construction includes the use of impulsive (impact
pile driving) and non-impulsive (vibratory pile driving) sources. As
described above, DTH includes both impulsive and non-impulsive
characteristics. When evaluating Level A harassment, NMFS recommends
treating DTH as an impulsive source.
The thresholds used to identify the onset of PTS are provided in
Table 4. The references, analysis, and methodology used in the
development of the thresholds are described in NMFS' 2018 Technical
Guidance, which may be accessed at: <a href="http://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance">www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance</a>.

Table 4--Thresholds Identifying the Onset of Permanent Threshold Shift
----------------------------------------------------------------------------------------------------------------
PTS onset acoustic thresholds * (received level)
Hearing Group ------------------------------------------------------------------------
Impulsive Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans........... Cell 1: Lpk,flat: 219 dB; Cell 2: LE,LF,24h: 199 dB.
LE,LF,24h: 183 dB.
Mid-Frequency (MF) Cetaceans........... Cell 3: Lpk,flat: 230 dB; Cell 4: LE,MF,24h: 198 dB.
LE,MF,24h: 185 dB.
High-Frequency (HF) Cetaceans.......... Cell 5: Lpk,flat: 202 dB; Cell 6: LE,HF,24h: 173 dB.
LE,HF,24h: 155 dB.
Phocid Pinnipeds (PW) (Underwater)..... Cell 7: Lpk,flat: 218 dB; Cell 8: LE,PW,24h: 201 dB.
LE,PW,24h: 185 dB.
Otariid Pinnipeds (OW) (Underwater).... Cell 9: Lpk,flat: 232 dB; Cell 10: LE,OW,24h: 219 dB.
LE,OW,24h: 203 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for
calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level
thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure (Lpk) has a reference value of 1 [micro]Pa, and cumulative sound exposure level (LE)
has a reference value of 1[micro]Pa\2\s. In this Table, thresholds are abbreviated to reflect American
National Standards Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as
incorporating frequency weighting, which is not the intent for NMFS' 2018 Technical Guidance. Hence, the
subscript ``flat'' is being included to indicate peak sound pressure should be flat weighted or unweighted
within the generalized hearing range. The subscript associated with cumulative sound exposure level thresholds
indicates the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW
pinnipeds) and that the recommended accumulation period is 24 hours. The cumulative sound exposure level
thresholds could be exceeded in a multitude of ways (i.e., varying exposure levels and durations, duty cycle).
When possible, it is valuable for action proponents to indicate the conditions under which these acoustic
thresholds will be exceeded.

Ensonified Area

Here, we describe operational and environmental parameters of the
activity that are used in estimating the area ensonified above the
acoustic thresholds, including source levels and transmission loss
coefficient.
The sound field in the project area is the existing background
noise plus additional construction noise from the proposed project.
Marine mammals are expected to be affected via sound generated by the
primary components of the project (i.e., impact pile installation,
vibratory pile installation, vibratory pile removal, and DTH).
Sound Source Levels of Proposed Activities--The intensity of pile
driving sounds is greatly influenced by factors such as the type of
piles (material and diameter), hammer type, and the physical
environment (e.g., sediment type) in which the activity takes place.
The DOT&PF evaluated SPL and TL measurements available for certain pile
types and sizes from similar activities elsewhere in Alaska or outside
of Alaska and relied on relevant sound source verification studies to
determine appropriate proxy levels for their proposed activities.
Recently proposed and issued IHAs from southeast Alaska were also
reviewed to identify the most appropriate SPLs and TL coefficients for
use in this application. NMFS agrees that the SPL values and TL
coefficients that the DOT&PF proposed for vibratory installation and
removal and impact installation of 16-inch (40.64 cm), 20-inch (50.80
cm), and 24-inch (60.96 cm) steel piles are appropriate proxy levels
for their proposed construction activities (see Table 5 for proposed
proxy levels). However, NMFS finds that DOT&PF's proposed SPL values
for 8-inch (20.32 cm) tension anchors and TL coefficients for all DTH
activities (described in further detail below) are not consistent with
what NMFS assesses to be the best available science, and instead
proposes for use SPLs and TL coefficients for DTH consistent with NMFS'
recommendations for analyses of noise from DTH systems (<a href="https://media.fisheries.noaa.gov/2022-11/PUBLIC%20DTH%20Basic%20Guidance_November%202022.pdf">https://media.fisheries.noaa.gov/2022-11/PUBLIC%20DTH%20Basic%20Guidance_November%202022.pdf</a>) (NMFS, 2022). NMFS
specifically requests comments on its proposed SPL values and TL
coefficients for DTH systems, assessment that these values are more
appropriate than those proposed by DOT&PF, as well as on its DTH
recommendations generally. Note that the values in Table 5 represent
SPL referenced at a distance of 10 m from the source.

[[Page 45793]]

Table 5--Summary of Unattenuated In-Water Pile Driving Proxy Levels (at 10 m) and Transmission Loss Coefficients
----------------------------------------------------------------------------------------------------------------
SELss (dB re 1
Installation Peak SPL (dB RMS SPL (dB re [micro]Pa\2\ Reference
Pile type method re 1 1 [micro]Pa) sec) (levels)
[micro]Pa)
----------------------------------------------------------------------------------------------------------------
16-inch steel piles.......... Vibratory hammer NA 158 NA CALTRANS
(2020).
20-inch steel piles.......... Vibratory hammer NA 161 NA Navy (2015).
24-inch steel piles.......... Vibratory hammer NA 161 NA Navy (2015).
20-inch steel piles.......... Impact hammer... 208 187 176 CALTRANS
(2020).
24-inch steel piles.......... Impact hammer... 208 193 178 CALTRANS
(2020).
8-inch tension anchors....... DTH system...... \2\ 170 156 \2\ 144 Reyff and
Heyvaert
(2019); Reyff
(2020).
20-inch rock sockets......... DTH system...... 184 167 159 Heyvaert and
Reyff (2021).
24-inch rock sockets......... DTH system...... 184 167 159 Heyvaert and
Reyff (2021).
----------------------------------------------------------------------------------------------------------------
Notes: NMFS conservatively assumes that noise levels during vibratory pile removal are the same as those during
installation for the same type and size pile; all SPLs are unattenuated and represent the SPL referenced at a
distance of 10 m from the source; NA = Not applicable; dB re 1 [micro]Pa = decibels (dB) referenced to a
pressure of 1 micropascal.

NMFS recommends that DTH system installation be treated as a
continuous sound source for Level B behavioral harassment calculations
and as an impulsive source for Level A harassment calculations (NMFS,
2022) given these systems produce noise including characteristics of
both source types (described above in the Description of Sound Sources
section). The DOT&PF reviewed projects that were most similar to the
specified activity in terms of drilling activities, type and size of
piles installed, method of pile installation, and substrate conditions.
Data from DTH system installation of 24-inch (60.96-cm) piles in
Tenakee Springs, Alaska, indicate a continuous RMS SPL of 167 dB, an
impulsive peak SPL of 184 dB, and a SEL<INF>ss</INF> level of 159 dB
(all at 10 m) (Heyvaert and Reyff, 2021). Therefore, DOT&PF proposed
these levels as proxy values for DTH system installation of 20- and 24-
inch (50.80- and 60.96-cm) rock sockets during the proposed activities.
NMFS concurs that these levels are appropriate proxy levels for the
installation of rock sockets via DTH systems for the proposed project
(Table 5).
TL coefficient data from Denes et al. (2016) and Heyvaert and Reyff
(2021) indicate that sounds from 24-inch (60.96-cm) drilling rock
sockets in Kodiak and Tenakee Springs, Alaska, decay at rates ranging
from 18.9*log<INF>10</INF>(R) to 20.3*log<INF>10</INF>(R), where R
indicates range from the subject pile, for RMS SPLs, respectively.
Therefore, Reyff (2022) recommends in Appendix C of the DOT&PF's
application that sounds from DTH activities are characteristic of a
point source and proposed a TL coefficient of 19.0 be used as a proxy
for 20- and 24-inch (50.80- and 60.96-cm) rock socket installation in
Hydaburg (Denes et al., 2016; Heyvaert and Reyff, 2021). While there is
evidence that TL coefficients can be high during DTH activities (e.g.,
Denes et al., 2016; Reyff, 2020; Heyvaert and Reyff, 2021), TL
coefficient measurements reported from DTH activities are highly
variable and in some cases have been reported to be lower, and more
representative of practical spreading models (i.e.,
15*log<INF>10</INF>(R)). For example, recent rock socket measurements
from Tongass Narrows in Ketchikan, Alaska, located approximately 76 km
east of Hydaburg, Alaska, reported TL coefficients of 14.1 for
SEL<INF>ss</INF>, 14.3 for RMS SPL, and 14.8 for Peak SPL measurements
of 24-inch (60.96-cm) open-end steel piles for ranges recorded out to
80-95 m (Miner, 2023). Other rock socket measurements from Skagway,
Alaska, reported TL coefficients of 13.3 for SEL<INF>ss</INF> and 13.8
for Peak SPL measurements of 42-inch (106.68-cm) steel piles for ranges
recorded out to 1,400 m from the pile (Reyff, 2020). Further, the TL
measurements reported by Denes et al. (2016) and Heyvaert and Reyff
(2021) in Kodiak and Tenakee Springs, Alaska, were also high for impact
and vibratory pile driving. For example, in Tenakee Springs, TL
coefficients for impact pile driving of 18-inch (45.75-cm) steel
battered piles, 24-inch (60.96-cm) steel vertical piles, and 30-inch
(76.20-cm) steel battered and vertical piles ranged from 18.8 to 19.1
for SEL<INF>ss</INF>, 19.6 to 20.1 for RMS SPL, and 18.9 to 20.0 for
Peak SPL measurements recorded out to 1,100 m (Heyvaert and Reyff,
2021). The TL coefficients reported for impact pile driving and
vibratory pile driving of 24-inch (60.96-cm) piles in Kodiak, when
considering monitoring ranges out to 1,125 m, were 20.3 and 21.9 for
RMS SPL, respectively (Denes et al., 2016). Therefore, the TL
coefficients reported by these two studies, and used by Reyff (2022)
and the DOT&PF to support a proxy TL coefficient of 19.0, may not be
representative of TL coefficients in other locations in southeast
Alaska or potentially at those same locations under different
conditions. In addition, all of the acoustic measurements (i.e., for
vibratory, impact, and DTH pile driving) from Kodiak were missing
energy on the recordings between 50-300 Hz due to the shallow
bathymetry in the region (which did not support propagation of low
frequencies), making their data less suitable for use as proxy data as
they did not include the full range of frequencies produced by the
construction activities (Denes et al., 2016).
As described in the Description of Sound Sources section, sound
propagation, and thus TL, through an environment can be complicated and
depend on a multitude of factors (e.g., seabed type, bathymetry, and
the local sound speed profiles, characteristics of the sound itself),
which can vary temporally and spatially. Many of these factors that
affect sound propagation and TL are thus site- and time-specific. For
coastal activities, such as pile driving, if area-specific information
on propagation/transmission loss is not available, NMFS generally
recommends practical spreading (TL=15 * log<INF>10</INF>(R)) (e.g.,
Stadler and Woodbury, 2009; CALTRANS, 2015; NMFS, 2020). There are no
site specific TL data available for the drilling of rock sockets in
Hydaburg, Alaska. Therefore, at this time, NMFS has preliminarily
determined that DOT&PF's proposed TL coefficient of 19.0 for the
installation of rock sockets during their proposed project is
inappropriate, and instead proposes a default TL coefficient of 15.0 be
used for these activities. This is consistent with the recommendations
outlined in NMFS (2020) and NMFS (2022).
Underwater noise from tension anchor construction is typically
lower than noise produced by other DTH activities. During tension
anchor

[[Page 45794]]

construction, the casing used during drilling is inside a larger-
diameter pile, reducing noise levels. In addition, anchor holes are
substantially smaller in diameter and deeper than rock sockets, and
therefore, result in much lower sound (Reyff and Heyvaert, 2019). The
DOT&PF and NMFS agree that a continuous RMS SPL of 156 dB (at 10 m)
(Reyff and Heyvaert, 2019) is the most appropriate proxy level to use
for the installation of 8-inch (20.32-cm) tension anchors at this time.
However, DOT&PF proposed that 8-inch (20.32-cm) tension anchors should
be considered as a solely non-impulsive, continuous sound source when
calculating Level A and Level B behavioral harassment rather than as
having both impulsive (Level A) and continuous (Level B behavioral
harassment) components as recommended by NMFS (2022). DOT&PF based this
argument on the finding that Heyvaert and Reyff (2021) could not
classify the tension anchor installation as impulsive for the purposes
of Level A harassment zone calculations because the impulse sound level
was generally not much louder than the continuous sound level. However,
there is evidence that DTH piling and DTH drilling contains impulsive
components (i.e., pulsed sounds) (Guan et al., 2022), including from
Heyvaert and Reyff (2021) who reported that sounds from tension rock
anchor installation had impulsive characteristics, but that the noise
from these pulses were not distinctly higher than the constant drilling
sounds. It is important to account for these impulsive characteristics
since they have a greater potential to cause noise-induced hearing loss
compared to non-impulsive sounds. Thus, there does not appear to be
enough evidence to indicate that 8-inch (20.32-cm) rock tension anchor
piles have no impulsive components. Therefore, as the data suggest is
appropriate, NMFS proposes impulsive SEL<INF>ss</INF> values of 144 dB
and 170 dB peak SPL (Reyff, 2020), respectively (at 10 m), for the DTH
system installation of 8-inch (20.32-cm) tension anchors during the
proposed activity.
DOT&PF propose a TL coefficient of 19.0 for 8-inch (20.32-cm)
tension anchors based on the measurements from Skagway, Alaska (Reyff
and Heyvaert, 2019; Reyff, 2020) and Tenakee Springs, Alaska (Heyvaert
and Reyff, 2021) as recommended in Reyff (2022) in Appendix C of the
DOT&PF's application. These are the only two hydroacoustic studies both
the DOT&PF and NMFS are aware of that have involved the installation of
tension anchors. Reyff and Heyvaert (2019) and Reyff (2020) (which
provides an update to Reyff and Heyvaert, 2019) reported a TL
coefficient of 24.2 for RMS SPL values recorded from 36 to 110 m from
the pile of 8-inch (20.32-cm) rock tension anchors in Skagway, Alaska.
Heyvaert and Reyff (2021) reported a TL coefficient of 19.2 for RMS SPL
values recorded from 9 to 900 m of 8-inch (20.32-cm) rock anchor
casings installed within 24-inch (60.96-cm) diameter vertical piles and
17.0 for RMS SPL values recorded from 10 to 110 m of 8-inch (20.32-cm)
rock anchor casings installed within 18-inch (45.75 cm) diameter
battered piles in Tenakee Springs, Alaska.
As discussed above, TL measurements from this particular study in
Tenakee Springs appear to be higher in general for all pile driving
activities (vibratory and impact pile driving and DTH systems) and thus
may not be representative of TL coefficients recorded elsewhere in
southeast Alaska or under different circumstances at Tenakee Springs.
For the Skagway dataset, sound level measurements were only made out to
110 m, and therefore it is unknown if the resulting TL coefficient is
representative at greater distances. While there is data to suggest
that TL coefficients from the installation of tension anchors may
typically be higher than 15*log<INF>10</INF>(R) (e.g., Reyff and
Heyvaert, 2019; Reyff, 2020; Heyvaert and Reyff, 2021), these data are
based on measurements of only a few piles and they were obtained from
study sites located over 320 km away from Hydaburg, Alaska. Thus, given
the lack of site specific TL measurements for the installation of
tension anchors in Hydaburg, at this time, NMFS does not agree with the
DOT&PF's proposed TL coefficient of 19.0 for the DTH installation of
rock tension anchor piles and instead proposes a default TL coefficient
of 15.0, which is consistent with recommendations outlined in NMFS
(2020) and NMFS (2022).
Estimated Harassment Isopleths--All Level B harassment isopleths
are reported in Table 7 considering RMS SPLs and the default TL
coefficient. Land forms (including causeways, breakwaters, islands, and
other land masses) impede the transmission of underwater sound and
create shadows behind them where sound from construction is not
audible. At Hydaburg, Level B harassment isopleths from the proposed
project will be blocked by Sukkwan Island, Spook Island, Mushroom
Island, and the coastline along Prince of Wales Island both southeast
and northwest of the project site. The maximum distance that a
harassment isopleth can extend due to these land masses is 5,162 m.
The ensonified area associated with Level A harassment is
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. For
stationary sources (such as from impact pile driving, vibratory pile
driving, and DTH), the optional User Spreadsheet tool predicts the
distance at which, if a marine mammal remained at that distance for the
duration of the activity, it would be expected to incur PTS. Inputs
used in the optional User Spreadsheet tool are reported in Table 6 and
the resulting estimated isopleths are reported in Table 7. (Please see
Table 6-5 in the DOT&PF's application for harassment isopleths
calculated using the DTH TL coefficients and source levels for 8-in
(20.32-cm) tension anchors proposed therein).

[[Page 45795]]

Table 6--NMFS User Spreadsheet Inputs
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Vibratory pile driving Impact pile driving DTH
---------------------------------------------------------------------------------------------------------------------------------------------------------------
16-inch steel 20-inch steel 24-inch steel piles 20-inch steel 24-inch steel 20- and 24-inch 8-inch tension
piles piles ---------------------------------------- piles piles rock socket anchor
---------------------------------------- -------------------------------------------------------------------------------
Installation/ Installation Removal
Removal removal Installation Installation Installation Installation
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Spreadsheet Tab Used............ A.1) Non-Impul, A.1) Non-Impul, A.1) Non-Impul, A.1) Non-Impul, E.1) Impact pile E.1) Impact pile E.2) DTH Systems.. A.1) DTH Systems.
Stat, Cont. Stat, Cont. Stat, Cont. Stat, Cont. driving. driving.
Source Level (SPL).............. 158 dB RMS........ 161 dB RMS........ 161 dB RMS........ 161 dB RMS........ 176 dB SEL........ 178 dB SEL........ 159 dB RMS........ 144 dB RMS.
Transmission Loss Coefficient... 15................ 15................ 15................ 15................ 15................ 15................ 15................ 15.
Weighting Factor Adjustment 2.5............... 2.5............... 2.5............... 2.5............... 2................. 2................. 2................. 2.
(kHz).
Time to install/remove single 30................ 15/30 \1\......... 15/30 \1\......... 30................ .................. .................. 60-480 \2\........ 60-240.\2\
pile (minutes).
Number of strikes per pile...... .................. .................. .................. .................. 50................ 50................ 15................ 15.
Piles per day................... 2................. 2/10 \1\.......... 2/10 \1\.......... 2................. 1/2 \1\........... 1/2 \1\........... 1................. 1.
Distance of sound pressure level 10................ 10................ 10................ 10................ 10................ 10................ 10................ 10.
measurement (m).
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ A maximum scenario was calculated for this activity.
\2\ A range of scenarios was calculated for this activity.

Table 7--Distances to Level A Harassment, by Hearing Group, and Distances and Areas of Level B Harassment Thresholds per Pile Type and Pile Driving
Method
--------------------------------------------------------------------------------------------------------------------------------------------------------
Level A harassment distance (m) Level B Level B
---------------------------------------- harassment harassment
Activity Pile size Minutes (min) or Piles per distance (m) area (km\2\)
strikes per pile day LF MF HF PW OW all hearing all hearing
groups groups
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vibratory Installation......... 20- and 24-inch... 15 min............ 2 5 1 7 3 1 \3\ 5,412 \4\ 4.34
30 \1\ min........ \1\ 10 20 2 30 13 1
Vibratory Removal.............. 16-inch........... 30 min............ 2 5 1 7 3 1 3,415 3.90
24-inch........... 30 min............ 2 7 1 11 5 1 \3\ 5,412 \4\ 4.34
Impact Installation............ 20-inch........... 50 strikes........ 1 47 2 56 25 2 1,585 2.14
50 \1\ strikes.... \1\ 2 74 3 88 40 3
24-inch........... 50 strikes........ 1 63 3 75 34 3 631 0.65
50 \1\ strikes.... \1\ 2 100 4 119 54 4
DTH (Rock Socket) \2\.......... 20- and 24-inch... 60 min............ 1 359 13 427 192 14 \3\ 13,594 \4\ 4.34
120 min........... 1 569 21 678 305 23
180 min........... 1 746 27 888 399 29
240 min........... 1 903 33 1,076 484 36
300 min........... 1 1,048 38 1,249 561 41
360 min........... 1 1,184 43 1,410 634 47
420 min........... 1 1,312 47 1,563 702 52
480 min........... 1 1,434 51 1,708 768 56
DTH (Tension Anchor) \2\....... 8-inch............ 60 min............ 1 36 2 43 20 2 2,512 3.07
120 min........... 1 57 2 68 31 3
180 min........... 1 75 3 89 40 3
240 min........... 1 91 4 108 4 4
300 min........... 1 105 4 125 57 5
360 min........... 1 119 5 141 64 5
420 min........... 1 132 5 157 71 6
480 min........... 1 144 6 171 77 6
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ A maximum scenario was calculated for this activity.
\2\ A range of scenarios was calculated for this activity.
\3\ Harassment distances would be truncated where appropriate to account for land masses, to a maximum distance of 5,162 m.
\4\ Harassment areas are truncated where appropriate to account for land masses, to a maximum area of 4.34 km\2\.

Marine Mammal Occurrence and Take Estimation

In this section we provide information about the occurrence of
marine mammals, including density or other relevant information that
will inform the take calculations. We also describe how this
information is synthesized to produce a quantitative estimate of the
take that is reasonably likely to occur and proposed for authorization.
Although construction is currently planned to begin in fall 2023,
unexpected delays associated with construction can occur. To account
for this uncertainty, the following exposure estimates assume that
construction would occur during the periods of peak abundance for those
species for which abundance varies seasonally.
Due to the differences in the DTH analysis between the DOT&PF's
application and this notice, estimated Level B harassment isopleths for
DTH activities are larger than those calculated by the DOT&PF (Tables
6-4 and 6-5 in the DOT&PF's application versus Table 7 in this notice).
However, because Level B harassment isopleths are truncated by local
land masses, the maximum estimated areas of ensonification for Level B
harassment are equivalent. Therefore, no adjustment is needed to
estimates of total take.

Steller Sea Lion

No density or abundance numbers exist for Steller sea lions in the
proposed action area, and they are not known to regularly occur near
Hydaburg. However, in context of a lack of local data, the DOT&PF

[[Page 45796]]

conservatively estimated that during peak salmon runs, 6 groups of 10
individuals could be exposed to project-related underwater noise each
week during pile installation and removal activities, for a total of
240 exposures (4 weeks * 60 sea lions per week = 240 total exposures).
DOT&PF's largest estimated Level A harassment zone for Steller sea
lions was 39 m (see Tables 6-4 and 6-5 in the DOT&PF's application).
Based on this assumption, the DOT&PF assumed that it would be unlikely
for a Steller sea lion to approach that closely and remain unobserved
for a period of time long enough to incur PTS. While the harassment
isopleths estimated herein are larger than those proposed by the DOT&PF
(see Table 7), the largest Level A harassment zone for Steller sea
lions is still only 59 m. Due to the small Level A harassment zones
(Table 7) and the implementation of shutdown zones, which will be
larger than Level A harassment zones (described below in the Proposed
Mitigation section), NMFS concurs with the DOT&PFs assessment that take
by Level A harassment is not anticipated for Steller sea lions.
Therefore, NMFS proposes to authorize all 240 estimated exposures as
takes by Level B harassment. Takes by Level A harassment for Steller
sea lions are not proposed to be authorized.

Harbor Seal

Up to six known harbor seal haulouts are located near the proposed
project area; however, they are all located outside of the estimated
harassment zones, with the closest haulout located just over 4.5 km
(2.8 mi) southeast of the proposed project site, but blocked by a land
shadow (see Figure 4-2 in the DOT&PF's application). Within the project
area, harbor seals remain relatively rare as described by local
residents. The DOT&PF conservatively estimated that up to 8 harbor
seals could be within estimated harassment zones each day during pile
installation and removal activities, for a total of 208 exposures (26
days * 8 seals per day = 208 total exposures).
DOT&PF's largest estimated Level A harassment zone for harbor seals
was 308 m (see Tables 6-4 and 6-5 in the DOT&PF's application). While
there are no known harbor seal haulouts located within this distance,
it is possible that harbor seals may approach and enter within this
distance for sufficient duration to incur PTS. DOT&PF estimated that up
to 12 harbor seals per week could occur within the Level A harassment
zones. Based on this analysis, and the DOT&PF's proposal to implement a
shutdown zone larger than the largest Level A harassment zone (i.e.,
310 m, see Table 6-5 in the DOT&PF's application), the DOT&PF requested
that 48 takes by Level A harassment (12 exposures per week * 4 weeks of
pile installation = 48 exposures) and 160 takes by Level B harassment
(208 total exposures minus 48 takes by Level A harassment) be proposed
for authorization.
The largest Level A harassment zone for harbor seals, as estimated
by NMFS, is 768 m. While there are still no known harbor seal haulouts
within this distance, the likelihood of harbor seals occurring within
the Level A harassment zones for sufficient duration to incur PTS
increases. Further, the largest practicable shutdown zone that the
DOT&PF states it can implement for harbor seals is 400 m (described
below in the Proposed Mitigation section), which is smaller than the
Level A harassment zones estimated to result from 240 or more minutes
of 20- and 24-inch (50.8- and 60.96-cm) DTH rock socket installation.
To account for this difference, NMFS proposes to authorize additional
takes by Level A harassment, as compared with the DOT&PF's request.
Additional takes were determined by calculating the ratio of the
largest Level A harassment area for 20- and 24-inch (50.8- and 60.96-
cm) DTH activities (i.e., 0.89 km\2\ for a Level A harassment distance
of 768 m) minus the area of the proposed shutdown zone for harbor seals
(i.e., 0.27 km\2\ for a shutdown zone distance of 400 m) to the area of
the Level B harassment isopleth (4.34 km\2\ for a Level B harassment
distance of 5,162 m) (i.e., (0.89 km\2\-0.27 km\2\)/4.34 km\2\ = 0.14).
We then multiplied this ratio by the total number of estimated harbor
seal exposures to determine additional take by Level A harassment
(i.e., 0.14 * 208 exposures = 29.12 takes, rounded up to 30 takes). The
total proposed take by Level A harassment was then calculated as the
take originally proposed and requested by the DOT&PF plus the
additional take calculated by NMFS (i.e., 48 + 30), for a total of 78
takes by Level A harassment. Takes by Level B harassment were
calculated as the number of estimated harbor seal exposures minus the
proposed amount of take by Level A harassment (i.e., 208-78).
Therefore, NMFS proposes to authorize 78 takes by Level A harassment
and 130 takes by Level B harassment for harbor seals, for a total of
208 takes.

Northern Elephant Seal

Northern elephant seal abundance throughout coastal southeast
Alaska is low, and anecdotal reports have not included northern
elephant seals near the proposed project area. However, northern
elephant seals have been observed elsewhere in southeast Alaska;
therefore, this species could occur near the proposed project area. To
account for this possibility, the DOT&PF estimated that one northern
elephant seal could be within estimated harassment zones each week
during pile installation and removal activities, for a total of four
exposures (4 weeks * 1 northern elephant seal each week = 4 total
exposures).
DOT&PF's largest estimated Level A harassment zone for northern
elephant seals was 308 m (see Tables 6-4 and 6-5 in the DOT&PF's
application). The DOT&PF assumed that northern elephant seals would be
unlikely to approach this distance without detection while underwater
activities are underway, and therefore did not request that takes by
Level A harassment be authorized for northern elephant seals. However,
the harassment isopleths for DTH activities estimated by NMFS are much
larger. In addition, the largest practical shutdown zone the DOT&PF
states it can implement for northern elephant seals (400 m) (described
below in the Proposed Mitigation section) is smaller than the Level A
harassment isopleths that result from 240 or minutes more of 20- and
24-inch (50.8- and 60.96-cm) DTH rock socket installation. To account
for this difference, NMFS followed the same method as described above
for harbor seals to calculate take by Level A harassment to propose for
northern elephant seals. This was achieved by calculating the ratio of
the largest Level A harassment area for 20- and 24-inch (50.8- and
60.96-cm) DTH activities (i.e., 0.89 km\2\ for a Level A harassment
distance of 768 m) minus the area of the proposed shutdown zone for
elephant seals (i.e., 0.27 km\2\ for a shutdown zone distance of 400 m)
to the area of the Level B harassment isopleth (4.34 km\2\ for a Level
B harassment distance of 5,162 m) (i.e., (0.89 km\2\-0.27 km\2\)/4.34
km\2\ = 0.14), and by multiplying this ratio by the total number of
estimated northern elephant seal exposures (i.e., 0.14 * 4 exposures =
0.56 takes, rounded up to 1 take by Level A harassment). Takes by Level
B harassment were calculated as the number of estimated northern
elephant exposures minus the proposed amount of take by Level A
harassment to be authorized (i.e., 4-1). Therefore, NMFS proposes to
authorize one take by Level A harassment and three takes by Level B
harassment for northern elephant seals, for a total of four takes.

[[Page 45797]]

Harbor Porpoise

There have been no systematic studies or observations of harbor
porpoises specific to Hydaburg or Sukkwan Strait, and sightings of
harbor porpoises have not been described in this region by local
residents. As such, there is limited potential for them to occur in the
proposed project area, but they could occur in low numbers as
individuals have been observed in southern inland waters of southeast
Alaska. Therefore, the DOT&PF estimated that up to two harbor porpoises
could be within estimated harassment zones each day during pile
installation and removal activities, for a total of 52 exposures (26
days * 2 porpoises per day = 52 exposures).
Harbor porpoises are small, lack a visible blow, have low dorsal
fins, an overall low profile, and a short surfacing time, making them
difficult to observe (Dahlheim et al., 2015). These characteristics
likely reduce the identification and reporting of this species. For
these reasons, the DOT&PF requested that a small number of takes by
Level A harassment be authorized for harbor porpoises. Based off of a
maximum Level A harassment isopleth distance of 579 m for harbor
porpoises estimated by the DOT&PF, the DOT&PF assumed that one pair of
harbor porpoises may enter the Level A harassment zone every 7 days of
in-water construction. Therefore, the DOT&PF requested that NMFS
propose to authorize eight takes by Level A harassment for harbor
porpoise for the proposed construction activities (4 weeks * 2 harbor
porpoise per week = 8 takes by Level A harassment).
The maximum Level A harassment isopleth estimated by NMFS for
harbor porpoises is 1,708 m, 2.9 times larger than the isopleth
estimated by the DOT&PF (580 m). The largest practicable shutdown zone
that the DOT&PF states it can implement for harbor porpoises is 500 m
(described below in the Proposed Mitigation section), which is smaller
than the Level A harassment isopleths estimated to result from 120 or
more minutes of 20- and 24-inch (50.8- and 60.96-cm) DTH rock socket
installation. To account for this difference and the increased
possibility of harbor porpoises occurring outside of the shutdown zone
and in the Level A harassment zone long enough to incur PTS, NMFS
proposes to authorize additional takes by Level A harassment, as
compared with the DOT&PF's request. Additional takes were determined by
calculating the ratio of the largest Level A harassment area for 20-
and 24-inch (50.8- and 60.96-cm) DTH activities (i.e., 2.25 km\2\ for a
Level A harassment distance of 1,708 m minus the area of the proposed
shutdown zone for harbor porpoises (i.e., 0.42 km\2\ for a shutdown
zone distance of 500 m) to the area of the Level B harassment isopleth
(4.34 km\2\ for a Level B harassment distance of 5,162 m) (i.e., (2.25
km\2\-0.42 km\2\)/4.34 km\2\ = 0.42). We then multiplied this ratio by
the total number of estimated harbor porpoise exposures to determine
additional take by Level A harassment (i.e., 0.42 * 8 exposures = 3.36
takes, rounded up to 4 takes). The total proposed take by Level A
harassment was then calculated as the take originally proposed and
requested by the DOT&PF plus the additional take calculated by NMFS to
account for the larger Level A harassment zones estimated by NMFS to
result from DTH activities (i.e., 8 + 4), for a total of 12 takes by
Level A harassment. Takes by Level B harassment were calculated as the
number of estimated harbor porpoise exposures minus the proposed amount
of take by Level A harassment (i.e., 52-12). Therefore, NMFS proposes
to authorize 12 takes by Level A harassment and 40 takes by Level B
harassment for harbor seals, for a total of 52 takes.

Dall's Porpoise

Dall's porpoises are not expected to occur in Sukkwan Strait
because the shallow water habitat of the bay is atypical of areas where
Dall's porpoises usually occur. However, recent research indicates that
Dall's porpoises may opportunistically exploit nearshore habitats where
predators, such as killer whales, are absent. Therefore, the DOT&PF
anticipates that one large Dall's porpoise pod (15 individuals) could
be within the estimated harassment zones during in-water construction,
for a total of 15 possible exposures.
DOT&PF's largest estimated Level A harassment zone for Dall's
porpoise was 579 m. Dall's porpoises typically appear in larger groups
and exhibit behaviors that make them more visible and thus easier to
observe at distance. Based on this assumption, the DOT&PF did not
request any takes by Level A harassment for this species. However,
similar to harbor porpoises, the maximum Level A harassment zone
estimated by NMFS (1,708 m) is 2.9 times larger than the zone estimated
by the DOT&PF. The largest practicable shutdown zone that the DOT&PF
states it can implement for Dall's porpoises during this project is 500
m (described below in the Proposed Mitigation section), which is
smaller than the Level A harassment zones estimated by NMFS to result
from 120 or more minutes of 20- and 24-inch (50.8- and 60.96-cm) DTH
rock socket installation. To account for this difference and the
increased possibility of Dall's porpoises occurring outside of the
shutdown zone and in the Level A harassment zones for sufficient
duration to incur PTS, NMFS proposes to add additional takes by Level A
harassment, as compared with the DOT&PF's request. Because Dall's
porpoises typically occur in groups, NMFS proposes to authorize 15
takes (i.e., one large pod) by Level A harassment in addition to the 15
takes by Level B harassment that the DOT&PF requested, for a total of
30 takes. This would help to ensure that the DOT&PF have enough takes
to account for the possibility of one large pod occurring in either the
Level A or the Level B harassment zone.

Pacific White-Sided Dolphin

Pacific white-sided dolphins do not generally occur in the shallow,
inland waterways of southeast Alaska. There are no records of this
species occurring in Sukkwan Strait, and it is uncommon for individuals
to occur in the proposed project area. However, recent fluctuations in
distribution and abundance decrease the certainty in this prediction.
Therefore, the DOT&PF conservatively estimated that one large group (92
individuals) of Pacific white-sided dolphins could be within estimated
harassment zones during the proposed in-water construction.
DOT&PF's largest estimated Level A harassment zone for Pacific
white-sided dolphins was 37 m (see Tables 6-4 and 6-5 in the DOT&PF's
application). Given the large group size and more conspicuous nature of
Pacific white-sided dolphins, the DOT&PF did not request any takes by
Level A harassment for this species as it would be unlikely they would
approach this distance for sufficient duration to incur PTS. The
largest Level A harassment zone estimated by NMFS for Pacific white
sided dolphins is still only 51 m. Due to the small Level A harassment
zones (Table 7) and the implementation of shutdown zones, which will be
larger than Level A harassment zones (described below in the Proposed
Mitigation section), NMFS concurs with the DOT&PFs assessment that take
by Level A harassment is not anticipated for Pacific white-sided
dolphins. Therefore, NMFS proposes to authorize all 92 estimated
exposures as takes by Level B harassment. Takes by Level A harassment
for Pacific white-sided dolphins are not proposed to be authorized.

[[Page 45798]]

Killer Whale

Killer whales are observed infrequently throughout Sukkwan Strait,
and their presence near Hydaburg is unlikely. However, anecdotal local
information suggests that a pod may be seen in the proposed project
area every few months. Therefore, the DOT&PF estimate that one killer
whale pod of up to 15 individuals may be within estimated harassment
zones once during the proposed pile installation and removal activities
(15 total exposures).
DOT&PF's largest estimated Level A harassment zone for killer
whales was 37 m (see Tables 6-4 and 6-5 in the DOT&PF's application).
Because killer whales are unlikely to enter Sukkwan Strait and are
relatively conspicuous, the DOT&OF did not request any takes by Level A
harassment for this species as it would be unlikely they would approach
this distance for sufficient duration to incur PTS. The largest Level A
harassment zone for killer whales estimated by NMFS is still only 51 m
(Table 7). Due to the small Level A harassment zones (Table 7) and the
implementation of shutdown zones, which will be larger than Level A
harassment zones (described below in the Proposed Mitigation section),
NMFS concurs with the DOT&PFs assessment that take by Level A
harassment is not anticipated for killer whales. Therefore, NMFS
proposes to authorize all 15 estimated exposures as takes by Level B
harassment. Takes by Level A harassment for killer whales are not
proposed to be authorized.

Humpback Whale

Use of Sukkwan Strait by humpback whales is common but intermittent
and dependent on the presence of prey fish. Based on anecdotal evidence
from local residents, the DOT&PF predicts that four groups of two
whales, up to eight individuals per week, may be within estimated
harassment zones each week during the 4 weeks of the proposed pile
installation and removal activities, for a total of 32 exposures (8 per
week * 4 weeks = 32 total exposures). Wade (2021) estimated that
approximately 2.4 percent of humpback whales in southeast Alaska are
members of the Mexico DPS, while all others are members of the Hawaii
DPS. Therefore, the DOT&PF estimates that 1 of the exposures (32 whales
* 0.024 = 0.77 rounded up to 1) would be of Mexico DPS individuals and
31 exposures would be of Hawaii DPS individuals.
DOT&PF's largest estimated Level A harassment zone for humpback
whales was 504 m (see Tables 6-4 and 6-5 in the DOT&PF's application).
However, due to the long duration of DTH piling that is anticipated,
and the potential for humpback whales to enter the Level A harassment
zones from around obstructions or landforms near the proposed project
area, the DOT&PF requested that NMFS propose to authorize 4 takes by
Level A harassment (equivalent to two groups of two individuals) of
humpback whales. Due to the small percentage of humpback whales that
may belong to the Mexico DPS in southeast Alaska, the DOT&PF assumes
that all takes by Level A harassment will be attributed to Hawaii DPS
whales.
The largest Level A harassment zone for humpback whales, as
estimated by NMFS, is 1,435 m (Table 7). The largest practicable
shutdown zone that the DOT&PF states it can implement for humpback
whales during this project is 1,000 m (described below in the Proposed
Mitigation section), which is smaller than the Level A harassment zones
estimated by NMFS to result from 300 or more minutes of 20- and 24-inch
(50.8- and 60.96-cm) DTH rock socket installation. To account for this
difference and the increased possibility of humpback whales occurring
outside of the shutdown zone and in the Level A harassment zone long
enough to incur PTS, NMFS proposes to add additional takes by Level A
harassment, compared with the DOT&PF's request.
NMFS calculated additional takes by Level A harassment by
determining the ratio of the largest Level A harassment area for 20-
and 24-inch (50.8- and 60.96-cm) DTH activities (i.e., 2.01 km\2\ for a
Level A harassment distance of 1,435 m) minus the area of the proposed
shutdown zone for humpback whales (i.e., 1.34 km\2\ for a shutdown zone
distance of 1,000 m) to the area of the Level B harassment isopleth
(4.34 km\2\ for a Level B harassment distance of 5,162 m) (i.e., (2.01
km\2\-1.34 km\2\)/4.34 km\2\ = 0.15). We then multiplied this ratio by
the total number of estimated humpback whales exposures to determine
additional take by Level A harassment (i.e., 0.15 * 32 exposures = 4.80
takes, rounded up to 5 takes). The total proposed take by Level A
harassment was then calculated as the take originally proposed and
requested by the DOT&PF plus the additional take calculated by NMFS to
account for the larger Level A harassment zones estimated to result
from DTH activities (i.e., 4 + 5), for a total of 9 takes by Level A
harassment. Takes by Level B harassment were calculated as the number
of estimated humpback whale exposures minus the proposed amount of take
by Level A harassment (i.e., 32-9). Therefore, NMFS proposes to
authorize 9 takes by Level A harassment and 23 takes by Level B
harassment for humpback whales, for a total of 32 takes. Given that
approximately 2.4 percent of humpback whales in southeast Alaska are
members of the Mexico DPS, NMFS assumes that one of the proposed take
by Level B harassment may be attributed to a humpback whale from the
Mexico DPS (32 * 2.4 percent = 0.77, rounded up to 1 take). All other
takes by Level B harassment and all takes by Level A harassment (i.e.,
31) are assumed to be attributed to humpback whales from the Hawaii
DPS.

Minke Whale

Minke whale abundance throughout southeast Alaska is low, and
anecdotal reports have not included minke whales near the proposed
project area. However, minke whales are distributed throughout a wide
variety of habitats and have been observed elsewhere in southeast
Alaska; therefore, this species could occur near the proposed project
area. NMFS has previously estimated that three individual minke whales
could occur near Metlakatla every 4 months during a similar activity
(86 FR 43190, August 6, 2021). Therefore, DOT&PF conservatively
estimated that up to three minke whales may be exposed to project-
related underwater noise during the proposed pile installation and
removal activities.
DOT&PF's largest estimated Level A harassment zone for minke whales
was 504 m (see Tables 6-4 and 6-5 in the DOT&PF's application). Due to
the low likelihood of minke whale occurrence near the proposed project
site, the DOT&PF did not request any takes by Level A harassment for
this species. However, the maximum Level A harassment isopleth
estimated by NMFS for minke whales is 1,435 m. The largest practicable
shutdown zone that the DOT&PF states it can implement for minke whales
during this project is 1,000 m (described below in the Proposed
Mitigation section), which is smaller than the Level A harassment
isopleths estimated by NMFS to result from 300 or more minutes of 20-
and 24-inch (50.8- and 60.96-cm) DTH rock socket installation. To
account for this difference and the increased possibility of minke
whales occurring outside of the shutdown zone and within the Level A
harassment zone long enough to incur PTS, NMFS proposes to add takes by
Level A harassment, compared with the DOT&PF's request.
NMFS calculated takes by Level A harassment by determining the
ratio of the largest Level A harassment area for 20- and 24-inch (50.8-
and 60.69-cm)

[[Page 45799]]

DTH activities (i.e., 2.01 km\2\ for a Level A harassment distance of
1,435 m) minus the area of the proposed shutdown zone for minke whales
(i.e., 1.34 km\2\ for a shutdown zone distance of 1,000 m) to the area
of the Level B harassment isopleth (4.34 km\2\) for a Level B
harassment distance of 5,162 m) (i.e., (2.01 km\2\-1.34 km\2\)/4.34
km\2\ = 0.15). We then multiplied this ratio by the total number of
estimated minke whales exposures to determine take by Level A
harassment (i.e., 0.15 * 3 exposures = 0.45 takes, rounded up to 1 take
by Level A harassment). Takes by Level B harassment were calculated as
the number of estimated minke whale exposures minus the proposed amount
of take by Level A harassment (i.e., 3-1). Therefore, NMFS proposes to
authorize one take by Level A harassment and two takes by Level B
harassment for minke whales, for a total of three takes.
In summary, the total amount of Level A harassment and Level B
harassment authorized for each marine mammal stock is presented in
Table 8.

Table 8--Amount of Take as a Percentage of Stock Abundance, by Stock and Harassment Type
----------------------------------------------------------------------------------------------------------------
Authorized take
Species Stock or DPS --------------------------------------- Percent of
Level A Level B Total stock
----------------------------------------------------------------------------------------------------------------
Steller sea lion.................... Eastern............... 0 240 240 0.56
Harbor seals........................ Dixon/Cape Decision... 78 130 208 0.89
Northern elephant seals............. CA Breeding........... 1 3 4 <0.01
Harbor porpoises.................... Southeast Alaska...... 12 40 52 \1\ 0.47
Dall's porpoises.................... Alaska................ 15 15 30 \2\ 0.23
Pacific white-sided dolphins........ N Pacific............. 0 92 92 0.34
Killer whales....................... Eastern North Pacific 0 15 15 \3\ 0.78
Alaska Resident.
Eastern Northern \3\ 4.97
Pacific Northern
Resident.
West Coast Transient.. \3\ 4.30
Humpback whales..................... Central N Pacific..... 9 23 32 0.32
Minke whales........................ Alaska................ 1 2 3 ...........
----------------------------------------------------------------------------------------------------------------
\1\ NMFS does not have an official abundance estimate for this stock; therefore, this percentage is based off of
the most recent abundance estimate for this stock (11,146; Hobbs and Waite, 2010).
\2\ NMFS does not have an official abundance estimate for this stock; therefore, this percentage is based off of
the minimum population estimate for this stock (13,110; Muto et al., 2022).
\3\ NMFS conservatively assumes that all 15 takes occur to each stock.

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.
The DOT&PF must employ the following standard mitigation measures,
as included in the proposed IHA:
<bullet> Ensure that construction supervisors and crews, the
monitoring team and relevant DOT&PF staff are trained prior to the
start of all pile driving and DTH activity, so that responsibilities,
communication procedures, monitoring protocols, and operational
procedures are clearly understood. New personnel joining during the
project must be trained prior to commencing work;
<bullet> Avoid direct physical interaction with marine mammals
during construction activity. If a marine mammal comes within 10 m of
such activity, operations shall cease. Should a marine mammal come
within 10 m of a vessel in transit, the boat operator would reduce
vessel speed to the minimum level required to maintain steerage and
safe working conditions. If human safety is at risk, the in-water
activity will be allowed to continue until it is safe to stop;
<bullet> Employ PSOs and establish monitoring locations as
described in Section 5 of the IHA. The DOT&PF must monitor the project
area to the maximum extent possible based on the required number of
PSOs, required monitoring locations, and environmental conditions. For
all pile driving and DTH activities at least two PSOs must be used;
<bullet> For all pile driving/removal activities, a minimum 30 m
shutdown zone must be established. The purpose of a shutdown zone is
generally to define an area within which shutdown of activity would
occur upon sighting of a marine mammal (or in anticipation of an animal
entering the defined area). Shutdown zones will vary based on the type
of driving/removal activity type and by marine mammal hearing group
(see Table 9). Here, shutdown zones are larger than or equivalent to
the calculated Level A harassment isopleths shown in Table 7, except
when indicated due to practicability and effectiveness concerns. These
concerns include the limited viewpoints available

[[Page 45800]]

to station PSOs along Sukkwan Strait, the presence of landmasses that
may obstruct viewpoints, and decreased effectiveness in sighting marine
mammals at increased distances. Further, shutdown zones at greater
distances than proposed in Table 9 would likely result in the DOT&PFs
activities being shut down more frequently than is practicable for them
to maintain their project schedule. Note the shutdown zones for DTH
activity proposed in this notice differ from those proposed by the
DOT&PF (see Table 6-5 of their application) based on the increased
Level A harassment isopleth estimates resulting from NMFS' analysis
(see detailed discussion in the Estimated Take section);

Table 9--Proposed Shutdown Zones During Project Activities
--------------------------------------------------------------------------------------------------------------------------------------------------------
Shutdown zone (m)
Activity Pile size Minutes (min) or Piles per ----------------------------------------------------------------
strikes per pile day LF MF HF PW OW
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vibratory Installation.......... 20- and 24-inch.... <=30 min........... <=10 30 30 30 30 30
Vibratory Removal............... 16- and 24-inch.... 30 min............. 2 30 30 30 30 30
Impact Installation............. 20-inch............ 50 strikes......... 1 50 30 60 30 30
50 strikes......... 2 80 30 90 \1\ 40 30
24-inch............ 50 strikes......... 1 70 30 80 40 30
50 strikes......... 2 \1\ 100 30 120 60 30
DTH (Rock Socket)............... 20- and 24-inch.... 60 min............. 1 360 30 430 200 30
120 min............ 1 570 30 \2\ 500 310 30
180 min............ 1 750 30 \2\ 500 400 30
240 min............ 1 1,000 40 \2\ 500 \2\ 400 40
300 min............ 1 \2\ 1,000 40 \2\ 500 \2\ 400 50
360 min............ 1 \2\ 1,000 50 \2\ 500 \2\ 400 50
420 min............ 1 \2\ 1,000 50 \2\ 500 \2\ 400 60
480 min............ 1 \2\ 1,000 60 \2\ 500 \2\ 400 60
DTH (Tension Anchor)............ 8-inch............. 60 min............. 1 40 30 50 30 30
120 min............ 1 60 30 70 40 30
180 min............ 1 80 30 90 \1\ 40 30
240 min............ 1 100 30 110 30 30
300 min............ 1 110 30 130 60 30
360 min............ 1 120 30 150 70 30
420 min............ 1 140 30 160 80 30
480 min............ 1 150 30 180 80 30
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ The proposed shutdown zone is equivalent to the Level A harassment distance.
\2\ The proposed shutdown is smaller than the Level A harassment distance.

<bullet> DOT&PF anticipates that the maximum number of piles to be
installed and or the daily duration of pile driving or DTH use may vary
significantly, with large differences in maximum zone sizes possible
depending on the work planned for a given day (Table 7). Given this
uncertainty, DOT&PF will utilize a tiered system to identify and
monitor the appropriate Level A harassment zones and shutdown zones on
a daily basis, based on the maximum expected number of piles to be
installed (impact or vibratory pile driving) or the maximum expected
DTH duration for each day. At the start of each work day, DOT&PF will
determine the maximum scenario for that day (according to the defined
duration intervals in Tables 7 and 9), which will determine the
appropriate Level A harassment isopleth and associated shutdown zone
for that day. This Level A harassment zone (Table 7) and associated
shutdown zone (Table 9) must be observed by PSO(s) for the entire work
day, regardless of whether DOT&PF ultimately meets the anticipated
scenario parameters for that day;
<bullet> Marine mammals observed anywhere within visual range of
the PSO will be tracked relative to construction activities. If a
marine mammal is observed entering or within the shutdown zones
indicated in Table 9, pile driving or DTH activities must be delayed or
halted. If pile driving or DTH activities are delayed or halted due to
the presence of a marine mammal, the activity may not commence or
resume until either the animal has voluntarily exited and been visually
confirmed beyond the shutdown zone (Table 9) or 15 minutes have passed
without re-detection of the animal;
<bullet> Monitoring must take place from 30 minutes prior to
initiation of pile driving (i.e., pre-clearance monitoring) through 30
minutes post-completion of pile driving or DTH activity;
<bullet> Pre-start clearance monitoring must be conducted during
periods of visibility sufficient for the lead PSO to determine that the
shutdown

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