Notice2026-09305
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Alaska Department of Transportation and Public Facilities' Ward Creek Bridge Replacement Project in Ketchikan, Alaska
Primary source
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Published
May 11, 2026
Issuing agencies
Commerce DepartmentNational Oceanic and Atmospheric Administration
Abstract
NMFS has received a request from Alaska Department of Transportation and Public Facilities (ADOT&PF) for authorization to take marine mammals incidental to the Ward Creek Bridge Replacement Project in Ketchikan, Alaska (AK). Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue two consecutive incidental harassment authorizations (IHAs) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on possible one-time, 1-year renewals that could be issued for either or both of the two IHAs under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorizations.
Full Text
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<title>Federal Register, Volume 91 Issue 90 (Monday, May 11, 2026)</title>
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[Federal Register Volume 91, Number 90 (Monday, May 11, 2026)]
[Notices]
[Pages 25528-25557]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-09305]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XF502]
Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to the Alaska Department of
Transportation and Public Facilities' Ward Creek Bridge Replacement
Project in Ketchikan, Alaska
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice; proposed incidental harassment authorizations; request
for comments on proposed authorizations and possible renewals.
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[[Page 25529]]
SUMMARY: NMFS has received a request from Alaska Department of
Transportation and Public Facilities (ADOT&PF) for authorization to
take marine mammals incidental to the Ward Creek Bridge Replacement
Project in Ketchikan, Alaska (AK). Pursuant to the Marine Mammal
Protection Act (MMPA), NMFS is requesting comments on its proposal to
issue two consecutive incidental harassment authorizations (IHAs) to
incidentally take marine mammals during the specified activities. NMFS
is also requesting comments on possible one-time, 1-year renewals that
could be issued for either or both of the two IHAs under certain
circumstances and if all requirements are met, as described in Request
for Public Comments at the end of this notice. NMFS will consider
public comments prior to making any final decision on the issuance of
the requested MMPA authorizations.
DATES: Comments and information must be received no later than June 10,
2026.
ADDRESSES: Comments should be addressed to 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#09405d592763686a666b7c7a4967666868276e667f"><span class="__cf_email__" data-cfemail="feb7aaaed0949f9d919c8b8dbe90919f9fd0999188">[email 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/permit/incidental-take-authorizations-under-marine-mammal-protection-act">https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act</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: Kristy Jacobus, Office of Protected
Resources, NMFS, (301) 427-8401.
SUPPLEMENTARY INFORMATION:
Background
The MMPA prohibits the ``take'' of marine mammals, with certain
exceptions. Section 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et
seq.) directs the Secretary of Commerce (as delegated to NMFS) to
allow, upon request, the incidental, but not intentional, taking of
small numbers of marine mammals by U.S. citizens who engage in a
specified activity (other than commercial fishing) within a specified
geographical region if certain findings are made and either regulations
are proposed or, if the taking is limited to harassment, a notice of a
proposed IHA is provided to the public for review.
Authorization for incidental takings shall be granted if NMFS finds
that the taking will have a negligible impact on the species or
stock(s) and will not have an unmitigable adverse impact on the
availability of the species or stock(s) for taking for subsistence uses
(where relevant). Further, NMFS must prescribe the permissible methods
of taking; 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 as ``mitigation'');
and requirements pertaining to the monitoring and reporting of the
takings. The definitions of all applicable MMPA statutory terms used
above are included in the relevant sections below (see also 16 U.S.C.
1362; 50 C.F.R 216.3, 216.103).
National Environmental Policy Act
To comply with the National Environmental Policy Act of 1969 (NEPA;
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A,
NMFS must review our proposed action (i.e., the issuance of an IHA)
with respect to potential impacts on the human environment.
This action is consistent with categories of activities identified
in Categorical Exclusion B4 (IHAs with no anticipated serious injury or
mortality) of the Companion Manual for NAO 216-6A, which do not
individually or cumulatively have the potential for significant impacts
on the quality of the human environment and for which we have not
identified any extraordinary circumstances that would preclude this
categorical exclusion. Accordingly, NMFS has preliminarily determined
that the issuance of the proposed IHAs qualifies to be categorically
excluded from further NEPA review.
Summary of Request
On November 18, 2025, NMFS received a request from ADOT&PF for two
consecutive IHAs to take marine mammals incidental to the Ward Creek
Bridge Replacement Project in Ketchikan, AK. Following NMFS' review of
the application, ADOT&PF submitted revised versions on March 24 and
April 30, 2026. The application was deemed adequate and complete on May
5, 2026. ADOT&PF's request is for take of 7 species of marine mammals
(comprising 10 stocks) by Level B harassment and, for a subset of 6 of
these species, Level A harassment. Neither ADOT&PF nor NMFS expect
serious injury or mortality to result from this activity and,
therefore, IHAs are appropriate.
Description of Proposed Activity
Overview
ADOT&PF plans to replace the Ward Creek Bridge which spans Ward
Creek, and reconstruct associated roadways, in Ward Cove, Ketchikan,
AK. The project includes removal of existing steel piles, installation
(and removal) of steel piles to support a temporary work trestle,
installation of new bridge steel piles, and removal of two areas of
rock along the highway via blasting. Pile removal would be conducted
with vibratory methods and pile installation would be conducted with
impact, vibratory, and/or down-the-hole (DTH) methods. Pile driving
(and removal) and DTH have the potential to introduce underwater sound
that may result in take of marine mammals by Level A harassment and
Level B harassment. Blasting of rocks has the potential to result in
Level A and Level B harassment due to introduction of underwater and
in-air sound.
Dates and Duration
The proposed IHAs would be valid from May 1, 2028, through April
30, 2029 (Year 1) and May 1, 2029, through April 30, 2030 (Year 2).
ADOT&PTF expects that during Year 1, pile driving and DTH will occur
over approximately 37 non-consecutive days and blasting will occur over
approximately 6 non-consecutive days. Pile driving and DTH during Year
2 are expected to occur over approximately 32 non-consecutive days.
Specific Geographic Region
The proposed project would occur in Ward Cove off of Tongass
Narrows in the city of Ketchikan, AK (see figure 1). The Ward Creek
Bridge spans Ward Creek at mile post 11 of the North Tongass Highway.
[[Page 25530]]
[GRAPHIC] [TIFF OMITTED] TN11MY26.015
Detailed Description of the Specified Activity
ADOT&PF proposes to replace the Ward Creek Bridge in Ward Cove,
Ketchikan, AK, over the course of 2 years, which includes pile removal,
pile installation, and removal of rock via blasting. ADOT&PF plans to
conduct pile driving and removal above and below the high tide line
(HTL). Pile installation and removal below HTL is expected to result in
harassment of marine mammals. Pile driving and removal above HTL would
not produce underwater sound that exceeds harassment thresholds.
Therefore, no harassment of marine mammals is expected or proposed for
pile driving or removal above HTL and will not be discussed further.
Blasting of rock would occur above HTL approximately 110 meters (m)
from shoreline, northwest of Ward Creek, and approximately 33 m from
shoreline, southeast from Ward Creek. NMFS expects that the sound from
blasting could result in Level A and Level B harassment of hauled out
pinnipeds in Ward Cove resulting from exposure to in-air noise, and
that, due to the proximity of the blasting to the shoreline, the sound
from blasting could transfer through the rock and result in underwater
sound that could exceed underwater Level A and Level B harassment
thresholds. The sound pressure waves produced by blasting would be
attenuated by the ground such that underwater sound pressure levels
would not reach levels sufficient to result in serious injury or
mortality of marine mammals.
Year 1
During Year 1, ADOT&PF plans to remove 18-inch steel shell piles
from the existing bridge, install 24-inch steel shell piles to support
a temporary work trestle just upstream of the existing bridge (piles
would be removed once construction during Year 1 is complete), and
install piles for new bridge pier piles (36-inch steel shell piles).
All pile removal would be conducted with vibratory methods. The 24-inch
steel shell piles will be installed using vibratory and impact pile
driving. The 36-inch steel shell piles would be installed using a
vibratory and impact hammer, then a DTH hammer would be placed inside
the piling and a shaft would be drilled into the bedrock. See table 1
for the Year 1 pile installation and removal schedule.
Excavation would be conducted using an excavator in the immediate
vicinity of the Ward Creek Bridge. Excavated material would be removed,
and riprap and fill would be placed under the bridge along the banks of
Ward Creek. Noise from excavation and fill is not expected to result in
take of marine mammals.
[[Page 25531]]
Table 1--Schedule for Pile Driving and DTH (Below HTL) During Year 1
----------------------------------------------------------------------------------------------------------------
Installation/removal Number Piles Number
Project component Pile size/type method of piles per day of days
----------------------------------------------------------------------------------------------------------------
Existing bridge................... 18-inch steel shell.. Vibratory removal... 2 2 1
Temporary trestle bridge.......... 24-inch steel shell.. Vibratory 20 6 4
installation.
24-inch steel shell.. Impact installation. 20 6 4
24-inch steel shell.. Vibratory removal... 20 6 4
New bridge........................ 36-inch steel shell.. Vibratory 8 1 8
installation.
Impact installation. 8 1 8
Vibratory 8 1 8
installation.
--------------------------------
Total......................... ..................... .................... ......... ......... 37
----------------------------------------------------------------------------------------------------------------
In addition to pile driving, ADOT&PF proposes to remove 220 linear
feet (67 m) of rock northwest of Ward Creek, approximately 110 m from
the shoreline, and 350 linear feet (106.7 m) of rock southeast from
Ward Creek, approximately 33 m from the shoreline, via blasting.
ADOT&PF expects blasting to occur over 6 days, approximately 3 days at
each site, with one blasting event per day. ADOT&PF estimates a total
of 104 charge delays ranging from 90-300 pounds net explosive weight
(NEW).
Year 2
During Year 2 of the project, 18-inch steel shell piles from the
existing bridge would be removed; 24-inch steel shell piles would be
installed downstream of the existing bridge to support a temporary work
trestle (and removed following construction); and 36-inch steel shell
piles would be installed in construction of the new bridge.
Installation and removal methods would be the same as Year 1. See table
2 for the pile installation and removal schedule during Year 2.
Table 2--Schedule for Pile Driving and DTH (Below HTL) During Year 2
----------------------------------------------------------------------------------------------------------------
Installation/removal Number Piles Number
Project component Pile size/type method of piles per day of days
----------------------------------------------------------------------------------------------------------------
Existing bridge................... 18-inch steel shell.. Vibratory removal... 10 6 2
Temporary trestle bridge.......... 24-inch steel shell.. Vibratory 20 6 4
installation.
24-inch steel shell.. Impact installation. 20 6 4
24-inch steel shell.. Vibratory removal... 20 6 4
New bridge........................ 36-inch steel shell.. Vibratory 6 1 6
installation.
36-inch steel shell.. Impact installation. 6 1 6
36-inch steel shell.. DTH installation.... 6 1 6
--------------------------------
Total......................... ..................... .................... ......... ......... 32
----------------------------------------------------------------------------------------------------------------
Riprap and fill would be placed under the bridge around the new
abutments. Placement of fill is not expected to result in take of
marine mammals.
Description of Marine Mammals in the Area of Specified Activities
Sections 3 and 4 of the application summarize available information
regarding status and trends, distribution and habitat preferences, and
behavior and life history of the potentially affected species. NMFS
fully considered all of this information, and we refer the reader to
these descriptions, instead of reprinting the information. Additional
information regarding population trends and threats may be found in
NMFS' Stock Assessment Reports (SARs; <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">https://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 3 lists all species or stocks for which take is expected and
proposed to be authorized for this activity and summarizes information
related to the population or stock, including regulatory status under
the MMPA and Endangered Species Act (ESA) and potential biological
removal (PBR), where known. PBR is defined by the MMPA as the maximum
number of animals, not including natural mortalities, that may be
removed from a marine mammal stock while allowing that stock to reach
or maintain its optimum sustainable population (as described in NMFS'
SARs). While no serious injury or mortality is anticipated or proposed
to be authorized here, PBR and annual mortality and serious injury (M/
SI) from anthropogenic sources are included here as gross indicators of
the status of the species or stocks and other threats.
Marine mammal abundance estimates presented in this document
represent the total number of individuals that make up a given stock or
the total number estimated within a particular study or survey area.
NMFS' stock abundance estimates for most species represent the total
estimate of individuals within the geographic area, if known, that
comprises that stock. For some species, this geographic area may extend
beyond U.S. waters. All managed stocks in this region are assessed in
NMFS' U.S. Pacific and Alaska SARs. All values presented in table 3 are
the most recent available at the time of publication and are available
online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>.
[[Page 25532]]
Table 3--Species\1\ With Estimated Take from the Specified Activities
--------------------------------------------------------------------------------------------------------------------------------------------------------
ESA/ MMPA status; Stock abundance (CV,
Common name Scientific name Stock strategic (Y/N) Nmin, most recent PBR Annual M/
\2\ abundance survey) \3\ SI \4\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Order Artiodactyla--Cetacea--Mysticeti (baleen whales)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Balaenopteridae (rorquals):
Humpback Whale.................... Megaptera novaeangliae. Hawai[revaps]i......... -, -, N 11,278 (0.56, 7,265, 127 27.09
2020).
Humpback Whale.................... Megaptera novaeangliae. Mexico-North Pacific... T, D, Y UND (N/A, N/A, 2006) UND 0.57
\5\.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Odontoceti (toothed whales, dolphins, and porpoises)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Delphinidae:
Killer Whale...................... Orcinus orca........... Eastern North Pacific -, -, N 1,920 (N/A, 1,920, 19 1.3
Alaska Resident. 2019) \6\.
Killer Whale...................... Orcinus orca........... Eastern North Pacific -, -, N 302 (N/A, 302, 2018) 2.2 0.2
Northern Resident. \6\.
Killer Whale...................... Orcinus orca........... West Coast Transient... -, -, N 349 (N/A, 349, 2018) 3.5 0.4
\6\.
Family Phocoenidae (porpoises):
Dall's Porpoise................... Phocoenoides dalli..... Alaska................. -, -, N UND (UND, UND, 2015) UND 37
\7\.
Harbor Porpoise................... Phocoena phocoena...... Southern Southeast -, -, Y 890 (0.37, 610, 2019). 6.1 7.4
Alaska Inland Waters.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Order Carnivora--Pinnipedia
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Otariidae (eared seals and
sea lions):
Steller Sea Lion.................. Eumetopias jubatus..... Eastern................ -, -, N 36,308 (N/A, 36,308, 2,178 93.2
2022)\8\.
Family Phocidae (earless seals):
Harbor Seal....................... Phoca vitulina......... Clarence Strait........ -, -, N 27,659 (N/A, 24,854, 746 40
2015).
Northern Elephant Seal............ Mirounga angustirostris California Breeding.... -, -, N 187,386 (N/A, 85,369, 5,122 13.7
2013).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy
(<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>).
\2\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed
under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality
exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed
under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\3\ 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.
\4\ These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g.,
commercial fisheries, vessel strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range.
\5\ Abundance estimates are based upon data collected more than 8 years ago and, therefore, current estimates are considered unknown. However, these
estimates remain the best available data regarding abundance of these stocks.
\6\ NEST is based upon counts of individuals identified from photo-ID catalogs.
\7\ The best available abundance estimate is likely an underestimate for the entire stock because it is based upon a survey that covered only a small
portion of the stock's range.
\8\ Stock abundance is best estimate of counts, which have not been corrected for animals at sea during abundance surveys. Estimates are provided for
the United States only.
As indicated above, all 7 species (with 10 managed stocks) in table
3 temporally and spatially co-occur with the activity to the degree
that take is reasonably likely to occur. While gray whales, fin whales,
minke whales, and Pacific white-sided dolphins have been reported in
the area, the occurrence of these species is so rare that take is not
expected to occur, and they are not discussed further.
In addition, the sea otter may be found in Ketchikan. However, sea
otters are managed by the U.S. Fish and Wildlife Service and are not
considered further in this document.
Humpback Whale
Humpback whales migrate seasonally from high latitude subarctic and
temperate summering areas to low latitude subtropical and tropical
wintering areas. Two stocks of humpback whale are expected in ADOT&PF's
proposed project area, the Hawai'i stock (which is not ESA-listed) and
the Mexico-North Pacific Stock (listed as threatened under the ESA).
NMFS expects that 98 percent of humpback whales in the proposed project
area are from the Hawai'i stock and 2 percent are from the Mexico-North
Pacific stock, as described in Wade (2021). Humpback whales are not
commonly seen in Ward Cove, but are common in Tongass Narrows.
Sightings of humpback whales are most common in spring and summer.
ADOT&PF's project area overlaps with a Biologically Important Area
(BIA) identified as important for humpback whale feeding (Wild et al.,
2023). This BIA is active from May through September and has an
importance score of 1 with an intensity score of 2.
Killer Whale
Killer whales from the Eastern North Pacific Alaska Resident,
Eastern North Pacific Northern Resident, and West Coast Transient
stocks may be present in ADOT&PF's proposed project area. The Alaska
Resident stock includes killer whales from Southeast Alaska to the
Aleutian Islands and Bering Sea (Young et al., 2023). The Northern
Resident stock is a transboundary stock and includes killer whales that
frequent British Columbia and southeast Alaska (Muto et al., 2020). The
West Coast transient stock is trans-boundary, occurring from California
through Southeast Alaska and including whales from British Columbia
(Muto et al., 2021).
Dall's Porpoise
Dall's porpoises are widely distributed across the entire North
[[Page 25533]]
Pacific. They are considered one of the most common cetaceans found in
Alaska waters, with a preference for both deep pelagic and inland
waters, such as southeast Alaska (Jefferson et al., 2019). Dall's
porpoises have been occasionally observed in Tongass Narrows during
monitoring for previous projects, but typically do not enter Ward Cove
due to their preference for deeper water (Solstice Alaska Consulting,
2025).
Harbor Porpoise
Harbor porpoises frequent the coastal waters of Southeast Alaska
and typically occur in waters less than 100 m deep (Young et al.,
2023). Harbor porpoises have been observed in Tongass Narrows during
monitoring for previous projects, but they typically do not enter Ward
Cove due to their preference for deeper water (Solstice Alaska
Consulting, 2025).
Steller Sea Lion
The Eastern distinct population segment (DPS) includes Steller sea
lions originating from rookeries east of Cape Suckling (144 degrees
west longitude). Steller sea lions are considered common in the
proposed project area year-round and have been observed both in Ward
Cove and in Tongass Narrows (Solstice Alaska Consulting, 2025). There
are no Steller sea lion haulouts in Ward Cove or in the adjacent waters
in Tongass Narrows. The closest haulout is approximately 25 kilometers
(km) from Ward Creek Bridge at Grindall Island (Solstice Alaska
Consulting, 2025).
Harbor Seal
Harbor seals inhabit coastal and estuarine waters off Baja
California, north along the western coast of the United States, British
Columbia, and Southeast Alaska and up through the Gulf of Alaska and
Aleutian Islands and in the Bering Sea and Pribilof Islands. They are
generally non-migratory with local movements associated with such
factors as tides, weather, season, food availability, and reproduction
(Muto et al., 2020). Harbor seals are regularly sighted in the proposed
project area and could occur on any given day (Solstice Alaska
Consulting, 2025). The only known harbor seal haulout in Ward Cove is a
dock, on the southern part of the Cove, approximately 1 km from Ward
Creek Bridge (Solstice Alaska Consulting, 2025).
Northern Elephant Seal
Northern elephant seals breed and give birth in California and Baja
California from December to March. Males migrate to the Gulf of Alaska
and western Aleutian Islands along the continental shelf, while females
migrate to pelagic areas in the Gulf of Alaska and central North
Pacific to feed on pelagic prey. Adults return to land between March
and August to molt. Northern elephant seals are uncommon around
ADOT&PF's proposed project area, although sightings of northern
elephant seals are increasing within Tongass Narrows and are
occasionally sighted in surrounding waters such as Clarence Strait and
Nichols Passage (Solstice Alaska Consulting, 2025).
Marine Mammal Hearing
Hearing is the most important sensory modality for marine mammals
underwater, and exposure to anthropogenic sound can have deleterious
effects. To appropriately assess the potential effects of exposure to
sound, it is necessary to understand the frequency ranges marine
mammals are able to hear. Not all marine mammal species have equal
hearing capabilities (e.g., Au and Hastings, 2008, Richardson et al.,
1995, Wartzok and Ketten, 1999). 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.). Generalized hearing ranges were
chosen based on the ~65 decibel (dB) threshold from composite
audiograms, previous analyses in NMFS (2018), and/or data from Southall
et al. (2007) and Southall et al. (2019). We note that the names of two
hearing groups and the generalized hearing ranges of all marine mammal
hearing groups have been recently updated (NMFS, 2024) as reflected
below in table 4. Of the species that may be potentially taken by Level
B and/or Level A harassment, humpback whales are considered low-
frequency (LF) cetaceans, killer whales are considered high-frequency
(HF) cetaceans, Dall's porpoises and harbor porpoises are considered
very high-frequency (VHF) cetaceans, Steller sea lions are otariid
pinnipeds, and harbor seals and northern elephant seals are phocid
pinnipeds.
Table 4--Marine Mammal Hearing Groups
[NMFS, 2024]
------------------------------------------------------------------------
Hearing group Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen 7 hertz (Hz) to 36 kilohertz
whales). (kHz).
High-frequency (HF) cetaceans 150 Hz to 160 kHz.
(dolphins, toothed whales, beaked
whales, bottlenose whales).
Very High-frequency (VHF) cetaceans 200 Hz to 165 kHz.
(true porpoises, Kogia, river
dolphins, Cephalorhynchid,
Lagenorhynchus cruciger & L.
australis).
Phocid pinnipeds (PW) (underwater) 40 Hz to 90 kHz.
(true seals).
Otariid pinnipeds (OW) (underwater) 60 Hz to 68 kHz.
(sea lions and fur seals).
IN-AIR:
Phocid pinnipeds (PA) (true seals). 42 Hz to 52 kHz.
Otariid pinnipeds (OA) (sea lions 90 Hz to 40 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 may not be as broad. Generalized hearing range
chosen based on approximately 65 dB threshold from composite
audiogram, previous analysis in NMFS (2018), and/or data from Southall
et al. (2007) and Southall et al. (2019). Additionally, animals are
able to detect very loud sounds above and below that ``generalized''
hearing range.
[[Page 25534]]
For more detail concerning these groups and associated frequency
ranges, please see NMFS (2024) for a review of available information.
Potential Effects of Specified Activities on Marine Mammals and Their
Habitat
This section provides a discussion of the ways in which components
of the specified activity may impact marine mammals and their habitat.
The Estimated Take of Marine Mammals section later in this document
includes a quantitative analysis of the number of individuals that are
expected to be taken by this activity. The Negligible Impact Analysis
and Determination section considers the content of this section, the
Estimated Take of Marine Mammals section, and the Proposed Mitigation
section, to draw conclusions regarding the likely impacts of these
activities on the reproductive success or survivorship of individuals
and whether those impacts are reasonably expected to, or reasonably
likely to, adversely affect the species or stock through effects on
annual rates of recruitment or survival.
Acoustic effects on marine mammals during the specified activities
are expected to potentially occur from vibratory pile installation and
removal, impact pile driving, DTH systems, and blasting. The effects of
underwater and in-air noise from ADOT&PF's proposed activities have the
potential to result in Level B harassment and Level A harassment of
marine mammals in the proposed project area.
There are a variety of types and degrees of effects on marine
mammals and their habitat (including prey) that could occur as a result
of the specified activities. Below we provide a brief description of
the types of sound generated by specified activities, the general
impacts on marine mammals and their habitat from these types of
activities, and a related project-specific analysis with consideration
of the proposed mitigation measures.
Description of Sound Sources for the Specified Activities
Activities associated with the project that have the potential to
incidentally take marine mammals through exposure to sound include
vibratory pile installation and removal, impact pile driving, DTH
systems, and blasting.
Impact hammers typically 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 impulsive,
characterized by rapid rise times and high peak sound pressure levels
(SPLs), 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 substrate, and extract
piles by using vibration to break the sediment friction and allow a
crane to pull the piles out. Vibratory hammers typically produce less
sound (i.e., lower SPLs) 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, Caltrans, 2015, Caltrans, 2020). Sounds produced by vibratory
hammers are non-impulsive; compared to sounds produced by impact
hammers, they have a slower rise time, 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 use a combination of drilling and percussive mechanisms
to advance a hole into the rock, with or without simultaneously
advancing a pile/casing into that hole. Drill cuttings and debris at
the rock face are removed by an air-lift exhaust through the inside of
the pile (Guan and Miner, 2020). Unlike other pile installation
methods, at least one sound source during DTH is found at the
intersection of the drill tip and the substrate and is often more
characteristically a point source rather than a linear source, as in
impact and vibratory pile driving. A DTH system is essentially a drill
bit that drills through the bedrock using a rotating function like a
normal drill integrated with a hammering mechanism to increase speed of
progress through the substrate (i.e., it is similar to a ``hammer
drill'' hand tool). DTH systems typically involve a single hammer
(mono-hammer), but multi- or ``cluster'' hammer drills may also be
used.
DTH systems include both DTH drilling and DTH driving techniques.
During DTH pile drilling, the DTH hammer does not make direct contact
with the pile; rather the hammer acts as a percussive drill to advance
a hole through the substrate within a casing (casing is driven through
overburden using impact or vibratory methods). After the hole is
drilled to the desired depth, the casing is removed, and the production
pile is placed inside the hole. Often, an impact hammer is then used to
confirm the pile has reached load-bearing capacity (i.e., proof). If
needed, a tension anchor can be drilled following these same methods
within the production pile to add lateral support to the pile.
During DTH pile driving, the DTH hammer directly strikes a
specially designed shoe located at the bottom of the pile, which has
wings that have a slightly larger diameter than the pile (i.e., the
hammer directly strikes the production pile itself; no pile casing is
used). The drill head locks into the bottom of the pile, and then the
drill head and pile advance simultaneously into the substrate to the
desired depth. Often, the production pile is then proofed with an
impact hammer. If needed, a tension anchor can be drilled using DTH
drilling methods within the production pile to add lateral support to
the pile.
The sounds produced by the DTH methods simultaneously contain both
a continuous non-impulsive component from the drilling action and an
impulsive component from the hammering effect. Therefore, for purposes
of evaluating Level A and Level B harassment under the MMPA, NMFS
treats DTH systems as both impulsive (Level A harassment thresholds)
and continuous, non-impulsive (Level B harassment thresholds) sound
source types simultaneously.
Typical activities for which DTH systems are used include rock
socketing and tension or rock anchoring. ADOT&PF proposes to use DTH
for rock socketing. Rock socketing involves using DTH techniques to
create a hole in the bedrock inside which a pile is placed to give it
lateral and longitudinal strength as described in DTH drilling, above.
Rock sockets are made in bedrock when overlaying sediments are too
shallow to adequately secure the bottom portion of a pile using other
methods.
Blasting is characterized as an impulsive sound source. ADOT&PF
proposes to conduct detonations on land, which can result in
propagation of sound waves both in-air and underwater. For on land
detonations in relatively close proximity to the shoreline, as proposed
by ADOT&PF, the pressure shock wave would propagate from the blast site
to the shoreline. The peak pressure of the shock wave would be highest
near the detonation but would decrease with distance from the
detonation location due to spreading and attenuation losses. The
pressure wave would continue to propagate to the interface of the
seabed and the water and would be partially transmitted into the water.
Similarly, blasting would produce an in-air sound pressure wave. Based
on the proximity of the blasting to the shoreline and the overall blast
plan, NMFS expects marine mammal take due to both in-air and underwater
sound due to the use of on-land blasting by ADOT&PF.
[[Page 25535]]
Potential Effects of Sound on Marine Mammals
The introduction of anthropogenic noise into the air from blasting
and into the aquatic environment from impact and vibratory pile
driving, DTH, and blasting is the primary means by which marine mammals
may be harassed from the ADOT&PF's specified activity. Anthropogenic
sounds cover a broad range of frequencies and sound levels and can have
a range of highly variable impacts on marine life from none or minor to
potentially severe responses depending on received levels, duration of
exposure, behavioral context, and various other factors. Broadly,
underwater and in-air sound from active acoustic sources, such as those
in ADOT&PF's proposed project, can potentially result in one or more of
the following: temporary or permanent hearing impairment, non-auditory
physical or physiological effects, behavioral disturbance, stress, and
masking (Richardson et al., 1995, Gordon et al., 2003, Nowacek et al.,
2007, Southall et al., 2007, G[ouml]tz et al., 2009).
We describe the more severe effects of certain non-auditory
physical or physiological effects only briefly as we do not expect that
use of impact and vibratory pile driving, DTH, and blasting are
reasonably likely to result in such effects (see below for further
discussion). Potential effects from impulsive sound sources can range
in severity from effects such as behavioral disturbance or tactile
perception to physical discomfort, slight injury of the internal organs
and the auditory system, or mortality (Yelverton et al., 1973). Non-
auditory physiological effects or injuries that theoretically might
occur in marine mammals exposed to high level underwater sound or as a
secondary effect of extreme behavioral reactions (e.g., change in dive
profile as a result of an avoidance reaction) caused by exposure to
sound include neurological effects, bubble formation, resonance
effects, and other types of organ or tissue damage (Cox et al., 2006,
Southall et al., 2007, Zimmer and Tyack, 2007, Tal et al., 2015).
Explosives can result in some of these more severe effects such as
organ or tissue damage, or mortality. However, these effects are
associated with underwater explosives. ADOT&PF proposes to use
explosives on land, approximately 33 m and 100 m from the shoreline.
Because of the proximity to the water, the explosives are expected to
result in auditory and behavioral effects but are not expected to
result in physical injury or mortality.
The degree of effect of an acoustic exposure on marine mammals is
dependent on several factors, including, but not limited to, sound type
(e.g., impulsive vs. non-impulsive), signal characteristics, the
species, age and sex class (e.g., adult male vs. mom with calf),
duration of exposure, the distance between the noise source and the
animal, received levels, behavioral state at time of exposure, and
previous history with exposure (Wartzok et al., 2004, Southall et al.,
2007). In general, sudden, high-intensity sounds can cause hearing loss
as can longer exposures to lower-intensity sounds. Moreover, any
temporary or permanent loss of hearing, if it occurs at all, will occur
almost exclusively for noise within an animal's hearing range. We
describe below the specific manifestations of acoustic effects that may
occur based on the activities proposed by ADOT&PF.
Richardson et al. (1995) described zones of increasing intensity of
effect that might be expected to occur in relation to distance from a
source and assuming that the signal is within an animal's hearing
range. First (at the greatest distance) is the area within which the
acoustic signal would be audible (potentially perceived) to the animal
but not strong enough to elicit any overt behavioral or physiological
response. The next zone (closer to the receiving animal) corresponds
with the area where the signal is audible to the animal and of
sufficient intensity to elicit behavioral or physiological
responsiveness. The third is a zone within which, for signals of high
intensity, the received level is sufficient to potentially cause
discomfort or tissue damage to auditory or other systems. Overlaying
these zones to a certain extent is the area within which masking (i.e.,
when a sound interferes with or masks the ability of an animal to
detect a signal of interest that is above the absolute hearing
threshold) may occur; the masking zone may be highly variable in size.
Below, we provide additional detail regarding potential impacts on
marine mammals and their habitat from noise in general, starting with
hearing impairment, as well as from the specific activities ADOT&PF
plans to conduct, to the degree it is available.
Hearing Threshold Shifts--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, 2024). The amount of threshold shift is customarily expressed in
dB. A TS can be permanent or temporary. As described in NMFS (2018,
2024) 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 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).
Auditory Injury (AUD INJ)--NMFS (2024) defines AUD INJ as damage to
the inner ear that can result in destruction of tissue, such as the
loss of cochlear neuron synapses or auditory neuropathy (Houser, 2021,
Finneran, 2024). AUD INJ may or may not result in a permanent threshold
shift (PTS). PTS is subsequently defined as a permanent, irreversible
increase in the threshold of audibility at a specified frequency or
portion of an individual's hearing range above a previously established
reference level (NMFS, 2024). PTS does not generally affect more than a
limited frequency range, and an animal that has incurred PTS has some
level of hearing loss at the relevant frequencies; typically, animals
with PTS or other AUD INJ are not functionally deaf (Au and Hastings,
2008; Finneran, 2016). Available data from humans and other terrestrial
mammals indicate that a 40-dB threshold shift approximates AUD INJ
onset (see Ward et al., 1958, 1959, Ward, 1960, Kryter et al., 1966,
Miller, 1974, Ahroon et al., 1996, Henderson et al., 2008). AUD INJ
levels for marine mammals are estimates, as with the exception of a
single study unintentionally inducing PTS in a harbor seal (Kastak et
al., 2008), there are no empirical data measuring AUD INJ in marine
mammals largely due to the fact that, for various ethical reasons,
experiments involving anthropogenic noise exposure at levels inducing
AUD INJ are not typically pursued or authorized (NMFS, 2024).
Temporary Threshold Shift (TTS)--TTS is 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, 2024), and is not considered an AUD INJ. Based
on data from marine mammal TTS measurements (see Southall et al., 2007,
2019), a TTS of 6
[[Page 25536]]
dB is considered the minimum threshold shift clearly larger than any
day-to-day or session-to-session variation in a subject's normal
hearing ability (Finneran et al., 2000, 2002, Schlundt et al., 2000).
As described in Finneran (2015), marine mammal studies have shown the
amount of TTS increases with the 24-hour cumulative sound exposure
level (SEL<INF>24</INF>) in an accelerating fashion: at low exposures
with lower SEL<INF>24</INF>, the amount of TTS is typically small and
the growth curves have shallow slopes. At exposures with higher
SEL<INF>24</INF>, the growth curves become steeper and approach linear
relationships with the sound exposure level (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 more impactful (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 severe 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) (Finneran, 2015). 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 (Phocoena phocoena), 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, 2021, 2022a, 2022b, Reichmuth et
al., 2019, Sills et al., 2020). TTS was not observed in spotted (Phoca
largha) and ringed (Pusa hispida) seals exposed to single airgun
impulse sounds at levels matching previous predictions of TTS onset
(Reichmuth et al., 2016). 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 depend on the exposure frequency.
Sounds below the region of best sensitivity for a species or hearing
group are less hazardous than those near the region of best sensitivity
(Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure
levels are higher compared to those in the region of best sensitivity
(i.e., a low frequency noise would need to be louder to cause TTS onset
when TTS exposure level is higher), as shown for harbor porpoises and
harbor seals (Kastelein et al., 2019a, 2019c). Note that in general,
harbor seals and harbor porpoises have a lower TTS onset than other
measured pinniped or cetacean species (Finneran, 2015). In addition,
TTS can accumulate across multiple exposures, but the resulting TTS
will be 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,
SEL<INF>24</INF> will overestimate the amount of TTS from intermittent
exposures, such as sonars and impulsive sources. Nachtigall et al.
(2018) describe measurements of hearing sensitivity of multiple
odontocete species (bottlenose dolphin, harbor porpoise, beluga, and
false killer whale (Pseudorca crassidens)) when a relatively loud sound
was preceded by a warning sound. These captive animals were shown to
reduce hearing sensitivity when warned of an impending intense sound.
Based on these experimental observations of captive animals, the
authors suggest that wild animals may dampen their hearing during
prolonged exposures or if conditioned to anticipate intense sounds.
Another study showed that echolocating animals (including odontocetes)
might have anatomical specializations that might allow for conditioned
hearing reduction and filtering of low-frequency ambient noise,
including increased stiffness and control of middle ear structures and
placement of inner ear structures (Ketten et al., 2021). Data available
on noise-induced hearing loss for mysticetes are currently lacking
(NMFS, 2024). Additionally, the existing marine mammal TTS data come
from a limited number of individuals within these species.
Relationships between TTS and AUD INJ thresholds have not been
studied in marine mammals, and there are no measured PTS data for
cetaceans, but such relationships are assumed to be similar to those in
humans and other terrestrial mammals. AUD INJ typically occurs at
exposure levels at least several dB above that inducing mild TTS (e.g.,
a 40-dB threshold shift approximates AUD INJ onset (Kryter et al.,
1966, Miller, 1974), while a 6-dB threshold shift approximates TTS
onset (Southall et al., 2007, 2019). Based on data from terrestrial
mammals, a precautionary assumption is that the AUD INJ 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 AUD INJ cumulative sound exposure level
thresholds are 15 to 20 dB higher than TTS cumulative sound exposure
level thresholds (Southall et al., 2007, 2019). Given the higher level
of sound or longer exposure duration necessary to cause AUD INJ as
compared with TTS, it is considerably less likely that AUD INJ could
occur.
Behavioral Effects--Exposure of marine mammals to certain sounds
could result in behavioral disturbance, not all of which constitutes
harassment under the MMPA. Behavioral disturbance may include a variety
of effects, including subtle changes in behavior (e.g., minor or brief
avoidance of an area or changes in vocalizations), more conspicuous
changes in similar behavioral activities, and more sustained and/or
potentially severe reactions, such as displacement from or abandonment
of high-quality habitat. Behavioral responses may include 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); and avoidance of areas where sound sources
are located. In addition, pinnipeds may
[[Page 25537]]
increase their haul out time, possibly to avoid in-water disturbance
(Thorson and Reyff, 2006), or for in-air noise produced by explosives,
pinnipeds may display behavioral responses such as flushing into the
water.
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, 2019 Weilgart, 2007,
Archer et al., 2010). Behavioral reactions can vary not only among
individuals but also within an individual, depending on previous
experience with a sound source, context, and numerous other factors
(Ellison et al., 2012), and can vary depending on characteristics
associated with the sound source (e.g., whether it is moving or
stationary, number of sources, distance from the source). 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, Wartzok et al., 2004, National Research Council (NRC), 2005).
Controlled experiments with captive marine mammals have shown
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 (e.g.,
seismic airguns) have been varied but often consist of avoidance
behavior or other behavioral changes (Richardson et al., 1995, Morton
and Symonds, 2002, 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 (e.g., Erbe et al., 2019). 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. 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, National Research Council (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.
Avoidance and displacement--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, 2013b,
Blair et al., 2016). Variations in dive behavior may reflect
interruptions in biologically significant activities (e.g., foraging)
or they may be of little biological significance. The impact of an
alteration to dive behavior resulting from an acoustic exposure depends
on what the animal is doing at the time of the exposure and the type
and magnitude of the response.
Disruption of feeding behavior can be difficult to correlate with
anthropogenic sound exposure, so it is usually inferred by observed
displacement from known foraging areas, the appearance of secondary
indicators (e.g., bubble nets or sediment plumes), or changes in dive
behavior. Acoustic and movement bio-logging tools also have been used
in some cases to infer responses to anthropogenic noise. For example,
Blair (2015) reported significant effects on humpback whale foraging
behavior in Stellwagen Bank in response to vessel noise including
slower descent rates, and fewer side-rolling events per dive with
increasing vessel nose. In addition, Wisniewska et al. (2018) reported
that tagged harbor porpoises demonstrated fewer prey capture attempts
when encountering occasional high-noise levels resulting from vessel
noise as well as more vigorous fluking, interrupted foraging, and
cessation of echolocation signals observed in response to some high-
noise vessel passes. 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.
Respiration rates vary naturally 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). For example, harbor porpoise respiration rates increased in
response to pile driving sounds at and above a received broadband SPL
of 136 dB (zero-peak SPL: 151 dB referenced to 1 micropascal (re 1
[mu]Pa); SEL of a single strike (SEL<INF>ss</INF>): 127 dB re 1
[mu]Pa\2\-s) (Kastelein et al., 2013).
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
(Eschrictius robustus) are known to change direction--deflecting from
customary migratory paths--in order to avoid noise from seismic surveys
(Malme et al., 1984). Harbor porpoises, Atlantic white-sided
[[Page 25538]]
dolphins (Leucopleurus actuus), and minke whales have demonstrated
avoidance in response to vessels during line transect surveys (Palka
and Hammond, 2001). In addition, beluga whales in the St. Lawrence
Estuary in Canada have been reported to increase levels of avoidance
with increased boat presence by way of increased dive durations and
swim speeds, decreased surfacing intervals, and by bunching together
into groups (Blane and Jaakson, 1994). 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 et al., 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 (i.e., meaningful) 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.
Physiological 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 (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, Ayres et al., 2012, Yang
et al., 2021). 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
vessel traffic in the Bay of Fundy was associated with decreased stress
in North Atlantic right whales. In addition, Lemos et al. (2022)
observed a correlation between higher levels of fecal glucocorticoid
metabolite concentrations (indicative of a stress response) and vessel
traffic in gray whales. Yang et al. (2021) studied behavioral and
physiological responses in captive bottlenose dolphins exposed to
playbacks of ``pile-driving-like'' impulsive sounds, finding
significant changes in cortisol and other physiological indicators but
only minor behavioral changes. 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, 2005), however distress is an
unlikely result of this project based on observations of marine mammals
during previous, similar construction projects.
[[Page 25539]]
Vocalizations and 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 of the receiving 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 (Hotchkin and
Parks, 2013).
Marine mammals vocalize for different purposes and across multiple
modes, such as whistling, echolocation click production, calling, and
singing. Changes in vocalization behavior in response to anthropogenic
noise can occur for any of these modes and may result from a need to
compete with an increase in background noise or may reflect increased
vigilance or a startle response. For example, in the presence of
potentially masking signals, humpback whales and killer whales have
been observed to increase the length of their songs (Miller et al.,
2000, Fristrup et al., 2003) or vocalizations (Foote et al., 2004),
respectively, while North Atlantic 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). Fin whales (Balaenoptera physalus) have
also been documented lowering the bandwidth, peak frequency, and center
frequency of their vocalizations under increased levels of background
noise from large vessels (Castellote et al., 2012). Other alterations
to communication signals have also been observed. For example, gray
whales, in response to playback experiments exposing them to vessel
noise, have been observed increasing their vocalization rate and
producing louder signals at times of increased outboard engine noise
(Dahlheim and Castellote, 2016). Alternatively, in some cases, animals
may cease sound production during production of aversive signals
(Bowles et al., 1994, Wisniewska et al., 2018).
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 (though not necessarily one
that would be associated with harassment).
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, including modifications of the acoustic
properties of the signal or the signaling behavior (Hotchkin and Parks,
2013). Masking can be tested directly in captive species (e.g., Erbe,
2008), but in wild populations it must be either modeled or inferred
from evidence of masking compensation. There are few studies addressing
real-world masking sounds likely to be experienced by marine mammals in
the wild (e.g., Branstetter et al., 2013).
Masking occurs in the frequency band that the animals utilize and
is more likely to occur in the presence of broadband, relatively
continuous noise sources such as vibratory pile driving. Energy
distribution of vibratory pile driving sound covers a broad frequency
spectrum, and is anticipated to be within the audible range of marine
mammals present in the proposed action area. Since noises generated
from the proposed construction activities are mostly concentrated at
low frequencies (< 2 kHz), these activities likely have less effect on
mid-frequency echolocation sounds produced by odontocetes (toothed
whales). However, lower frequency noises are more likely to affect
detection of communication calls and other potentially important
natural sounds such as surf and prey noise. Low-frequency noise may
also affect communication signals when they occur near the frequency
band for noise and thus reduce the communication space of animals
(e.g., Clark et al., 2009) and cause increased stress levels (e.g.,
Holt et al., 2009). Unlike TS, masking, which can occur over large
temporal and spatial scales, can potentially affect the species at
population, community, or even ecosystem levels, in addition to
individual levels. Masking affects both senders and receivers of the
signals, and at higher levels for longer durations, could have long-
term chronic effects on marine mammal species and populations. However,
the noise generated by the ADOT&PF's proposed activities will only
occur intermittently, across an estimated 43 non-consecutive days (37
days of pile driving and DTH and 6 days of blasting) during Year 1 and
32 non-consecutive days during Year 2 in a relatively small area
focused around the proposed construction site. Thus, while ADOT&PF's
proposed 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 the fitness of
individual marine mammals would be impacted.
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
[[Page 25540]]
pinnipeds that are swimming or hauled out near the project site within
the range of noise levels elevated above airborne acoustic harassment
criteria. 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 flush from haulouts, temporarily
abandon the area, and or move further from the source. Cetaceans are
not expected to be exposed to airborne sounds that would result in
harassment as defined under the MMPA.
Potential Effects on Marine Mammal Habitat
ADOT&PF's proposed activities could have localized, temporary
impacts on marine mammal habitat, including prey, by increasing in-
water SPLs. Increased noise levels may affect acoustic habitat and
adversely affect marine mammal prey in the vicinity of the project
areas (see discussion below). Elevated levels of underwater noise would
ensonify the project areas where both fishes and mammals occur and
could affect foraging success. Additionally, marine mammals may avoid
the area during the proposed construction activities; however,
displacement due to noise is expected to be temporary and is not
expected to result in long-term effects to the individuals or
populations.
The total area likely impacted by ADOT&PF's activities is
relatively small compared to the available habitat in southeast Alaska.
Avoidance by potential prey (i.e., fish) of the immediate area due to
increased noise is possible. The duration of fish and marine mammal
avoidance of this area after pile driving and blasting stops is
unknown, but a rapid return to normal recruitment, distribution, and
behavior is anticipated. Any behavioral avoidance by fish or marine
mammals of the disturbed area would still leave significantly large
areas of fish and marine mammal foraging habitat in the nearby
vicinity.
The proposed project would occur within the same footprint as
existing marine infrastructure. Ward Creek is a busy waterway, with
cruise ships docking at the Ward Cove cruise ship dock in spring
through summer, and seaplanes and other shoreside industrial activities
occurring year-round. Temporary, intermittent, and short-term habitat
alteration may result from increased noise levels during the proposed
construction activities. Effects on marine mammal habitat would be
limited to temporary pile installation and removal and blasting noise,
and effects on prey species would be similarly limited in time and
space.
Water quality--Temporary and localized reduction in water quality
would occur as a result of in-water construction activities. Most of
this effect would occur during the installation and removal of piles
when bottom sediments are disturbed. The installation and removal of
piles would 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 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. Drilling would have negligible impacts on water quality
from sediment resuspension because the system would operate within a
casing set into the bedrock. The drill would collect excavated material
inside of the apparatus where it would be lifted to the surface and
placed onto a barge for subsequent disposal. We expect impacts to water
quality from blasting to be mild and brief because the blasting will
occur on land at a sufficient distance from the water so as to
introduce only minor amounts of sedimentation into the water.
Effects to turbidity and sedimentation are expected to be short-
term, minor, and localized. 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, fishes, 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.
Fishes 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 et al., 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, and behavioral responses such as flight or
avoidance are the most likely effects. 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 (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.
[[Page 25541]]
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. (2012b) showed that a TTS of
4 to 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.,
2012a, Casper et al., 2013, 2017). Underwater explosive detonations
have been known to cause injury and mortality to fish (Dahl et al.,
2020). However, because the blasting proposed by ADOT&PF will occur on
land, the SPLs are expected to be attenuated by land and would not be
of sufficient levels to cause injury or death of fish.
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 fishes 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 fishes. 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).
Zooplankton is a food source for several marine mammal species, as
well as a food source for fish that are then preyed upon by marine
mammals. Population effects on zooplankton could have indirect effects
on marine mammals. Data are limited on the effects of underwater sound
on zooplankton species, particularly sound from construction (Erbe et
al., 2016). Popper and Hastings (2009) reviewed information on the
effects of human-generated sound and concluded that no substantive data
are available on whether the sound levels from pile driving, seismic
activity, or any human-made sound would have physiological effects on
invertebrates. Any such effects would be limited to the area very near
(1 to 5 m) the sound source and would result in no population effects
because of the relatively small area affected at any one time and the
reproductive strategy of most zooplankton species (short generation,
high fecundity, and very high natural mortality). No adverse impact on
zooplankton populations is expected to occur from the specified
activity due, in part, to large reproductive capacities and naturally
high levels of predation and mortality of these populations. Any
mortalities or impacts that might occur would be negligible.
The greatest potential impact to marine mammal prey during
construction would occur during impact pile driving and DTH excavation.
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. Construction also would have minimal permanent and
temporary impacts on benthic invertebrate species, a marine mammal prey
source.
Potential Effects on Foraging Habitat
ADOT&PF's Ward Creek Bridge Replacement Project is not expected to
result in any habitat-related effects that could cause significant or
long-term negative consequences for individual marine mammals or their
populations, since installation and removal of in-water piles would be
temporary and intermittent. 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. 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 ADOT&PFs activities. The area impacted by the 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 ADOT&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. Therefore, impacts of the project are not likely to have
adverse effects on marine mammal foraging habitat in the proposed
project area.
In summary, given the relatively small areas being affected, as
well as the temporary and mostly transitory nature of the proposed
construction activities, any adverse effects from ADOT&PF's activities
on prey habitat or prey populations are expected to be minor and
temporary. The most likely impact to fishes at the project site would
be temporary avoidance of the area. 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. Thus, we
conclude that impacts of the specified activities are not likely to
have more than short-term adverse effects on any prey habitat or
populations of prey species. Further, any impacts to marine mammal
habitat are not expected to result in significant or long-term
consequences for individual marine mammals, or to contribute to adverse
impacts on their populations.
Estimated Take of Marine Mammals
This section provides an estimate of the number of incidental takes
proposed for authorization through the IHAs, which will inform NMFS'
consideration of ``small numbers,'' the negligible impact
determinations, and impacts on subsistence uses.
Harassment is the only type of take expected to result from these
activities. Except with respect to certain activities not pertinent
here, section 3(18) of the MMPA defines ``harassment'' as any act of
pursuit, torment, or annoyance, which (i) has the potential to injure a
marine mammal or marine mammal stock in the wild (Level A harassment);
or (ii) has the potential to disturb a marine mammal or marine mammal
stock in the wild by causing disruption of behavioral patterns,
including, but not limited to, migration, breathing, nursing, breeding,
feeding, or sheltering (Level B harassment).
Authorized takes would primarily be by Level B harassment, as use
of the acoustic and explosive sources (i.e., vibratory and impact pile
driving and explosives) has the potential to result in disruption of
behavioral patterns for individual marine mammals. There is also some
potential for AUD INJ (Level A harassment) to result, primarily for
mysticetes, very high frequency species, phocids, and otariids because
predicted AUD INJ zones are larger than for high-frequency species. AUD
INJ is unlikely to occur for high-frequency species. The proposed
mitigation and monitoring measures are expected to minimize the
severity of the taking to the extent practicable.
[[Page 25542]]
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 criteria above which NMFS believes there is
some reasonable potential for marine mammals to be behaviorally
harassed or incur some degree of AUD INJ; (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 Criteria
NMFS recommends the use of acoustic criteria 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 AUD INJ of some degree (equated to
Level A harassment). We note that the criteria for AUD INJ, as well as
the names of two hearing groups, have been recently updated (NMFS,
2024) as reflected below in the Level A harassment section.
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 sound pressure 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. For in-air
sounds, NMFS predicts that harbor seals exposed above received levels
of 90 dB re 20 [mu]Pa (RMS) will be behaviorally harassed, and other
pinnipeds will be harassed when exposed above 100 dB re 20 [mu]Pa
(RMS). Generally speaking, Level B harassment take estimates based on
these behavioral harassment thresholds are expected to include any
likely takes by TTS as, in most cases, the likelihood of TTS occurs at
distances from the source less than those at which behavioral
harassment is likely. TTS of a sufficient degree can manifest as
behavioral harassment, as reduced hearing sensitivity and the potential
reduced opportunities to detect important signals (conspecific
communication, predators, prey) may result in changes in behavior
patterns that would not otherwise occur.
ADOT&PF's proposed construction includes the use of continuous
(vibratory pile driving) and impulsive (impact pile driving and
blasting) 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 above in the
Description of Sound Sources for the Specified Activities section. 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' Updated Technical Guidance for Assessing
the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version
3.0) (Updated Technical Guidance, 2024) identifies dual criteria to
assess AUD INJ (Level A harassment) to five different underwater marine
mammal groups (based on hearing sensitivity) as a result of exposure to
noise from two different types of sources (impulsive or non-impulsive).
ADOT&PF's proposed construction includes the use of impulsive (impact
pile driving and explosive) 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 2024 Updated Technical Guidance criteria include both updated
thresholds and updated weighting functions for each hearing group. The
thresholds are provided in table 5 below. The references, analysis, and
methodology used in the development of the criteria are described in
NMFS' 2024 Updated Technical Guidance, which may be accessed at:
<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools</a>.
Table 5--Thresholds Identifying the Onset of Auditory Injury
----------------------------------------------------------------------------------------------------------------
AUD INJ onset acoustic thresholds \*\ (received level)
Hearing group ------------------------------------------------------------------------
Impulsive Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans........... Cell 1:Lpk,flat: 222 dB; Cell 2:LE,LF,24h: 197 dB.
LE,LF,24h: 183 dB.
High-Frequency (HF) Cetaceans.......... Cell 3:Lpk,flat: 230 dB; Cell 4:LE,HF,24h: 201 dB.
LE,HF,24h: 193 dB.
Very High-Frequency (VHF) Cetaceans.... Cell 5:Lpk,flat: 202 dB; Cell 6:LE,VHF,24h: 181 dB.
LE,VHF,24h: 159 dB.
Phocid Pinnipeds (PW) (Underwater)..... Cell 7:Lpk,flat: 223 dB; Cell 8:LE,PW,24h: 195 dB.
LE,PW,24h: 183 dB.
Otariid Pinnipeds (OW) (Underwater).... Cell 9:Lpk,flat: 230 dB; Cell 10:LE,OW,24h: 199 dB.
LE,OW,24h: 185 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric criteria for impulsive sounds: Use whichever criteria results in the larger isopleth for
calculating AUD INJ onset. If a non-impulsive sound has the potential of exceeding the peak (PK) SPL criteria
associated with impulsive sounds, the PK SPL criteria are recommended for consideration for non-impulsive
sources.
[[Page 25543]]
Note: Peak SPL (Lp,0-pk) has a reference value of 1 [micro]Pa, and weighted cumulative sound exposure level
(LE,p) has a reference value of 1 [micro]Pa\2\s. In this table, criteria are abbreviated to be more reflective
of International Organization for Standardization standards (ISO, 2017). The subscript ``flat'' is being
included to indicate peak sound pressure are flat weighted or unweighted within the generalized hearing range
of marine mammals underwater (i.e., 7 Hz to 165 kHz). The subscript associated with cumulative sound exposure
level criteria indicates the designated marine mammal auditory weighting function (LF, HF, and VHF cetaceans,
and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The weighted cumulative
sound exposure level criteria 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 criteria will be exceeded.
Explosive sources--Based on the best available science, NMFS uses
the acoustic and pressure thresholds indicated in table 6 to predict
the onset of behavioral harassment, AUD INJ, and TTS.
For explosive activities using single detonations (i.e., no more
than one detonation within a day), such as those described in the
proposed activity, NMFS uses TTS onset thresholds to assess the
likelihood of behavioral harassment, rather than the Level B harassment
threshold for multiple detonations indicated in the table. While marine
mammals may also respond to single explosive detonations, these
responses are expected to more typically be in the form of startle
reaction, rather than a more meaningful disruption of a behavioral
pattern. On the rare occasion that a single detonation might result in
a behavioral response that qualifies as Level B harassment, it would be
expected to be in response to a comparatively higher received level.
Accordingly, NMFS considers the potential for these responses to be
quantitatively accounted for through the application of the TTS
criteria, which, as noted above, is 5 dB higher than the behavioral
harassment threshold for multiple explosives.
Table 6--Explosive Thresholds for Marine Mammals for AUD INJ, TTS, and Behavior (Multiple Detonations)
----------------------------------------------------------------------------------------------------------------
AUD INJ impulsive TTS impulsive threshold Behavioral threshold
Hearing group threshold * * (multiple detonations)
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans......... Cell 1: Lpk,flat: 222 Cell 2: Lpk,flat: 216 Cell 3 LE,LF,24h: 163
dB; LE,LF,24h: 183 dB. dB; LE,LF,24h: 168 dB. dB.
High-Frequency (HF) Cetaceans........ Cell 4: Lpk,flat: 230 Cell 5: Lpk,flat: 224 Cell 6: LE,HF,24h: 173
dB; LE,HF,24h: 193 dB. dB; LE,HF,24h: 178 dB. dB.
Very High-Frequency (VHF) Cetaceans.. Cell 7: Lpk,flat: 202 Cell 8: Lpk,flat: 196 Cell 9: LE,VHF,24h: 139
dB; LE,VHF,24h: 159 dB. dB; LE,VHF,24h: 144 dB. dB.
Phocid Pinnipeds (PW) (Underwater)... Cell 10: Lpk,flat: 223 Cell 11: Lpk,flat: 217 Cell 12: LE,PW,24h: 163
dB; LE,PW,24h: 183 dB. dB; LE,PW,24h: 168 dB. dB.
Otariid Pinnipeds (OW) (Underwater).. Cell 13: Lpk,flat: 230 Cell 14: Lpk,flat: 224 Cell 15: LE,OW,24h: 165
dB; LE,OW,24h: 185 dB. dB; LE,OW,24h: 170 dB. dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric criteria for impulsive sounds: Use whichever criteria results in the larger isopleth for
calculating AUD INJ onset. If a non-impulsive sound has the potential of exceeding the peak SPLcriteria
associated with impulsive sounds, the PK SPL criteria are recommended for consideration for non-impulsive
sources.
Note: Peak SPL (Lp,0-pk) has a reference value of 1 [micro]Pa, and weighted cumulative sound exposure level
(LE,) has a reference value of 1 [micro]Pa\2\s. In this table, criteria are abbreviated to be more reflective
of International Organization for Standardization standards (ISO 2017; ISO 2020). The subscript ``flat'' is
being included to indicate peak sound pressure are flat weighted or unweighted within the generalized hearing
range of marine mammals underwater (i.e., 7 Hz to 165 kHz). The subscript associated with cumulative sound
exposure level criteria indicates the designated marine mammal auditory weighting function (LF, HF, and VHF
cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The weighted
cumulative sound exposure level criteria 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 criteria 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., pile driving and explosives).
Pile Driving and DTH
The project includes vibratory pile installation and removal,
impact pile installation, and DTH installation. Source levels for these
activities are based on reviews of measurements of the same or similar
types and dimensions of piles available in the literature. Source
levels for each pile size and activity are presented in table 7. Source
levels for vibratory installation and removal of piles of the same
diameter are assumed to be the same.
Table 7--Sound Source Levels for Pile Driving and DTH
----------------------------------------------------------------------------------------------------------------
Pile size and type
----------------------------------------------------------------------- Source level
RMS (dB re 1 SEL (dB re 1 (at 10 m) Reference
Peak (dB re 1 [mu]Pa) [mu]Pa) [mu]Pa2 sec)
----------------------------------------------------------------------------------------------------------------
Vibratory
----------------------------------------------------------------------------------------------------------------
18-inch steel shell piles............. N/A N/A 163 U.S. Navy (2012, 2013),
Miner (2020).*
----------------------------------------------------------------------------------------------------------------
24-inch steel shell piles............. N/A N/A 163 U.S. Navy (2012, 2013),
Miner (2020).*
[[Page 25544]]
36-inch steel shell pile.............. N/A N/A 166 U.S. Navy (2012, 2013),
Sexton (2007), Laughlin
(2011, 2017), Miner
(2020).*
----------------------------------------------------------------------------------------------------------------
Impact
----------------------------------------------------------------------------------------------------------------
24-inch steel shell piles............. 203 190 177 Caltrans (2015).
36-inch steel shell piles............. 210 193 183 Caltrans (2015, 2020).
----------------------------------------------------------------------------------------------------------------
DTH
----------------------------------------------------------------------------------------------------------------
36-inch steel shell pile.............. 194 174 164 Denes et al. (2019),
Reyff and Heyvaert
(2019), Reyff (2020).
----------------------------------------------------------------------------------------------------------------
* Methodology followed Navy (2015) and included available data from Puget Sound, WA and Southern Alaska.
DTH systems have both continuous, non-impulsive, and impulsive
components. When evaluating Level B harassment, NMFS recommends
treating DTH as a continuous source and applying RMS SPL thresholds of
120 dB re 1 [mu]Pa, and when evaluating Level A harassment, NMFS
recommends treating DTH as an impulsive source (NMFS, 2022).
TL is the decrease in acoustic intensity as an acoustic pressure
wave propagates out from a source. TL parameters vary with frequency,
temperature, sea conditions, current, source and receiver depth, water
depth, water chemistry, and bottom composition and topography. The
general formula for underwater TL is:
TL = B x Log10 (R<INF>1</INF>/R<INF>2</INF>)
Where:
TL = transmission loss in dB
B = transmission loss coefficient
R<INF>1</INF> = the distance of the modeled SPL from the driven
pile, and
R<INF>2</INF> = the distance from the driven pile of the initial
measurement.
Absent site-specific acoustical monitoring with differing measured
transmission loss, a practical spreading value of 15 is used as the
transmission loss coefficient in the above formula. Project and site-
specific transmission loss data for Ward Cove are not available;
therefore, the default coefficient of 15 is used to determine the
distances to the Level A and Level B harassment thresholds.
The ensonified area associated with Level A harassment is more
technically challenging to predict due to the need to account for a
duration component. Therefore, NMFS developed an optional User
Spreadsheet tool to accompany the 2024 Updated Technical Guidance 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 vibratory and impact 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 AUD INJ. Inputs used in the
optional User Spreadsheet tool (table 8), and the resulting estimated
isopleths, are reported below. User Spreadsheet inputs are the same for
Year 1 and Year 2 except for the number of piles per day for vibratory
installation of 18-inch steel shell piles (see table 8). Level A and
Level B harassment isopleths for pile driving and DTH are provided in
table 9. We note that some of the isopleths will be truncated by land.
Therefore, the furthest we expect underwater sound to extend due to
ADOT&PF's proposed construction is approximately 4,000 m (see ADOT&PF's
application for a visual depiction).
Table 8--User Spreadsheet Input Parameters Used for Calculating Level A Harassment Isopleths for Pile Driving
and DTH
----------------------------------------------------------------------------------------------------------------
Weighting
Piles per Duration Strikes per Strikes per factor
Pile type/size day (minutes) pile second adjustment
(kHz)
----------------------------------------------------------------------------------------------------------------
Vibratory
----------------------------------------------------------------------------------------------------------------
18-inch steel shell............................ 2 (Year 1), 60 N/A N/A 2.5
6 (Year 2)
24-inch steel shell............................ 6 60 N/A N/A 2.5
36-inch steel shell............................ 1 60 N/A N/A 2.5
----------------------------------------------------------------------------------------------------------------
Impact
----------------------------------------------------------------------------------------------------------------
24-inch steel shell............................ 6 N/A 100 N/A 2
36-inch steel shell............................ 1 N/A 1,000 N/A 2
----------------------------------------------------------------------------------------------------------------
[[Page 25545]]
DTH
----------------------------------------------------------------------------------------------------------------
36-inch steel shell............................ 1 480 N/A 12 2
----------------------------------------------------------------------------------------------------------------
Table 9--Calculated Distances to Level A and Level B Harassment Isopleths for Pile Driving and DTH
----------------------------------------------------------------------------------------------------------------
Pile type/size Level A Level B
--------------------------------------------------------------------------------------- harassment harassment
LF HF VHF PW OW zones (m) zone (m)
----------------------------------------------------------------------------------------------------------------
Vibratory
----------------------------------------------------------------------------------------------------------------
18-inch steel shell (Year 1)...... 20 8 16 26 9 * 7,356
18-inch steel shell (Year 2)...... 41 16 34 53 18 * 7,356
24-inch steel shell............... 41 16 34 53 18 * 7,356
36-inch steel shell............... 20 8 16 26 9 * 11,659
----------------------------------------------------------------------------------------------------------------
Impact
----------------------------------------------------------------------------------------------------------------
24-inch steel shell............... 282 36 436 250 93 1,000
36-inch steel shell............... 995 127 1,540 884 330 1,585
----------------------------------------------------------------------------------------------------------------
DTH
----------------------------------------------------------------------------------------------------------------
36-inch steel shell............... 2,652 338 * 4,104 2,356 878 * 39,811
----------------------------------------------------------------------------------------------------------------
* Isopleth is truncated by land at approximately 4,000 m.
Blasting
Estimation of ranges to underwater Level A and Level B harassment
isopleths from blasting assumed a total of 104 discrete explosive
charges ranging from 90-300 pounds NEW. Detonation of these charges
occur in rapid succession such that they are assumed to comprise a
single explosive or blast event that would together only occur once per
24 hour period. However, the delay between detonations (8.5-100
milliseconds) is designed such that no two charges would produce
primary pressure waves (i.e., the short lived initial shock wave) that
would overlap directly in space and time. Therefore the peak pressure
would be that of the largest single charge. For SEL, energy is
accumulated based on the number of charge delays. As the blasting is
occurring on land, distance to the shoreline is a critical parameter,
and two scenarios were analyzed here: distances of 33 m and 110 m from
shore. The general procedure consisted of several steps: determine the
peak overpressure at the water/land interface, convert that
overpressure to PK SPL and SEL, apply single frequency weighting factor
adjustments to produce auditory injury weighted SEL for each hearing
group, and finally propagate both PK SPL and weighted SEL to the NMFS
2024 thresholds for explosives.
Underwater peak overpressures at the water/land interface were
estimated using the empirical relationship from Dunlap (2009), which
was derived from field measurements of blasting of bridges and culverts
near or in fish streams in the Tongass National Forest in Alaska. This
model is used in lieu of the commonly cited equations from Wright and
Hopky (1998) based on the similarity of the activities measured in
Dunlap (2009), as well as better agreement of the model with other
measurements which are also representative of these circumstances,
(e.g., Laughlin, 2017)). The empirical equation for peak pressure is
provided in figure 2.5 of Dunlap (2009).
To convert from PK SPL to SEL, an empirical relationship was
derived from the measurements and empirical relationships observed in
Soloway and Dahl (2014), Laughlin (2017), Dunlap (2009), and Robinson
et al. (2022). This relationship results in a range-dependent
adjustment factor in dB which approximates the difference between PK
SPL and SEL and is approximately equal to 24 dB + 3.4 log10(r/250 m),
where r is the range in meters. Based on the equation from Dunlap
(2009) for peak overpressure, as well as the relationship between PK
SPL and SEL, sound level metrics at the shoreline can be computed for
the nearest distances from shoreline indicated in the application
(i.e., 33m and 110 m). The PK SPL for distances to the shoreline of 33
m and 110 m are 203.5 and 187.8 dB re 1 uPa m\2\, respectively. The
cumulative SEL for the entire events are 194.5 and 178.7 dB 1 uPa\2\s
m\2\ for 33 and 110 m, respectively.
Before comparing the resulting SEL sound field to the appropriate
thresholds, the NMFS (2024) auditory injury weighting functions are
used to compute adjustment factors using a single frequency
approximation of 1 kHz, which is similar to what is commonly done for
pile driving. The choice of 1 kHz is based on the measurements of
Laughlin (2017), which show that the spectrum has almost no energy at
high frequencies (greater than approximately 600 Hz). Propagation is
handled via spherical spreading but considers the impact of the water/
rock interface assuming normal incidence and was based on the
methodology in Waters (1972). For more details about methodology, see
appendix C in ADOT&PF's application. See table 10 for the calculated
underwater Level A and Level B harassment zones for blasting.
[[Page 25546]]
Table 10--Underwater Level A and Level B Harassment Zones for Blasting
----------------------------------------------------------------------------------------------------------------
Activity LF HF VHF Phocids Otariids
----------------------------------------------------------------------------------------------------------------
Level A Harassment Zones (m)
----------------------------------------------------------------------------------------------------------------
Blasting, 33 m from shore...................... 285 1 21 158 1
Blasting, 110 m from shore..................... 1 1 1 1 1
----------------------------------------------------------------------------------------------------------------
Level B Harassment Zones (m)
----------------------------------------------------------------------------------------------------------------
Blasting, 33 m from shore...................... 3,162 138 719 1,967 324
Blasting, 110 m from shore..................... 1,152 1 35 572 1
----------------------------------------------------------------------------------------------------------------
For in-air impacts to pinnipeds, many of the above assumptions were
the same including the size and number of explosives, that the peak
pressure would be that of a largest single charge delay, and that SEL
is cumulative based on the number of charges.
Peak sound pressure was estimated using measurements from a proxy
project (KTN Wolfe Point Project; Breeds and Ahlfinger, 2025) with
similar blasting conditions. By plotting data from 20 previous blasts,
the common scaled range formula was used to create an empirical model
to predict the peak sound level based on the distance from the blast
and the weight of the explosive. This formula was adjusted for
agreement with the loudest singular blast and to follow a range
dependence consistent with spherical spreading. In order to estimate
RMS SPL and SEL, which were not reported in the proxy data, sound
signatures were digitized from the Wolfe Point project to find a
reliable conversion rate. It was determined that RMS can be estimated
by subtracting 10 dB from the peak pressure, and SEL can be estimated
by subtracting 13 dB. This conversion methodology was found to be
either consistent with or conservative based on a comparison with
similar data from Sharp and Yule (1998). Based on this methodology,
distances to in-air Level A and Level B harassment thresholds for
pinnipeds were determined. Calculated in-air Level A and Level B
harassment isopleths for ADOT&PF's proposed blasting activities can be
found in tables table 11 and table 12. We note that the isopleths in
tables 11 and 12 represent both the distance from the explosives and
from the shoreline. For purposes of determining shutdown zones,
monitoring areas, and estimation of take, the distance from shoreline
was used.
Notably, the distances to in-air Level B harassment for pinnipeds
extend to approximately 16.5 km for harbor seals and more than 5 km for
other pinnipeds. To understand the likelihood of in-air noise
propagating over this distance, radiosonde data (i.e., temperature and
humidity) near the proposed project site was obtained via the National
Centers for Environmental Information integrated Global Radiosonde
Archive (Durre et al., 2018), in order to construct vertical sound
speed profiles. The data showed that it is reasonable to expect upward
refracting conditions, with the sound speed decreasing from
approximately 337 m/s, at the surface, to approximately 300 m/s at an
altitude of approximately 10 km, depending on the time of year. This
indicates that the only sound likely to propagate significant distances
horizontally (e.g., 16.5 km), will be propagating very near the
horizon. Because the terrain near the project site is surrounded in
most directions with significant terrain and vegetation, and because of
the upward refracting propagation conditions, it is unlikely that the
in-air noise will propagate long distances, with the exception of the
direction towards open water (i.e. south-west). For this reason, the
isopleths for in-air behavioral disturbance are expected to be
truncated by the land at Gravina Island (approximately 4,000 m from the
blasting sites).
Table 11--Calculated In-Air Level A Harassment Isopleths for Blasting (m)
----------------------------------------------------------------------------------------------------------------
Phocids Otariids
------------------------------------------------------------------------------
Activity Distance from Distance from Distance from Distance from
blasting (m) shoreline (m) blasting (m) shoreline (m)
----------------------------------------------------------------------------------------------------------------
Blasting, 33 m from shoreline.... 257................ 224................ 18................. 0
Blasting, 110 m from shoreline... 257................ 147................ 18................. 0
----------------------------------------------------------------------------------------------------------------
Table 12--Calculated In-Air Level B Harassment Isopleths for Blasting (m)*
----------------------------------------------------------------------------------------------------------------
Harbor seals Other pinnipeds
------------------------------------------------------------------------------
Activity Distance from Distance from Distance from Distance from
blasting (m) shoreline (m) blasting (m) shoreline (m)
----------------------------------------------------------------------------------------------------------------
Blasting, 33 m from shoreline.... 16,511............. 16,478............. 5,221.............. 5,188
Blasting, 110 m from shoreline... 16,511............. 16,401............. 5,221.............. 5,111
----------------------------------------------------------------------------------------------------------------
* Isopleths are truncated by land at approximately 4,000 m.
[[Page 25547]]
Marine Mammal Occurrence
In this section we provide information about the occurrence of
marine mammals, including density or other relevant information which
will inform the take calculations.
Marine mammal density information is not available for ADOT&PF's
proposed project area. ADOT&PF used monitoring data from the Ward Cove
Cruise Ship Dock Project (Power Systems & Supplies of Alaska, 2020) and
the Tongass Narrows Ferry Berth Improvement Project (ADOT&PF, 2021,
2022, 2023a, 2023b) to estimate occurrence of marine mammals in the
project area. ADOT&PF estimated group size based on this monitoring
data and data from Dahlheim et al. 2009. For marine mammals that are
considered relatively common in the area, daily occurrence was used,
and for marine mammals that are expected to be less common, weekly or
monthly occurrence was used.
Humpback Whales
Sightings of humpback whales in Tongass Narrows are common
(Solstice Alaska Consulting, 2025), however, they are uncommon in Ward
Cove itself. During the Ward Cove Cruise Ship Dock Project, which is
approximately 800 m from the Ward Creek Bridge, 42 individuals were
observed over 18 days of in-water work from February to September.
Group sizes ranged from single whales to pods of up to six animals
(Power Systems & Supplies of Alaska, 2020). None of the whales entered
Ward Cove but passed by in Tongass Narrows. During the Tongass Narrows
Ferry Berth Improvements Project, which was conducted from October 2020
to April 2023, a total of 160 humpback whales were documented in
Tongass Narrows, 9 of which were observed entering Ward Cove during the
months of November and December (ADOT&PF, 2021, 2022, 2023a, 2023b).
Humpback whales were most commonly observed as single whales or in
pairs. ADOT&PF therefore conservatively assumes two whales per group
and one group per day, and NMFS concurs.
Killer Whales
Two groups of killer whales, one consisting of two individuals and
one group consisting of five individuals, were observed during the Ward
Cove Cruise Ship Dock Project, from February to September 2020 (Power
Systems & Supplies of Alaska, 2020). During monitoring efforts over
approximately 3 years for the Tongass Narrows Ferry Berth Improvements
Project, a total of 132 killer whales were observed in pods ranging
from 2-8 individuals. Killer whales are observed in southeast Alaska
during all months of the year but are most common in the summer
(Solstice Alaska Consulting, 2025). ADOT&PF assumes seven whales per
group and that four groups will occur per month of construction, and
NMFS concurs.
Dall's Porpoise
Dall's porpoises are not expected in Ward Cove based on their
preference for deeper waters. However, ADOT&PF expects they would be
present in Tongass Narrows during construction. A pod of three
individuals and a pod of five individuals were documented traveling
through Tongass Narrows in the spring of 2020 during the Ward Cove
Cruise Ship Dock Project (Power Systems & Supplies of Alaska, 2020).
Over approximately 3 years of monitoring for the Tongass Narrows Ferry
Berth Improvement Project, 113 Dall's porpoises were sighted, ranging
in groups of 2-13 individuals, although most commonly in groups of 2-6
animals (ADOT&PF, 2021, 2022, 2023a, 2023b). ADOT&PF conservatively
assumes a group of six animals and one group per month, and NMFS
concurs.
Harbor Porpoise
During monitoring efforts for the Ward Cove Cruise Ship Dock
Project, a total of 15 harbor porpoises were sighted, as individuals or
in a pod up to 10 individuals (Power Systems & Supplies of Alaska,
2020). During the monitoring efforts for the Tongass Narrows Ferry
Berth Improvements Project, 64 harbor porpoises were observed during
in-water work, as individuals and in groups of up to 11 animals
(ADOT&PF, 2021, 2022, 2023a, 2023b), but harbor porpoises are most
commonly seen as groups of 3 to 5 animals. ADOT&PF estimates one group
of four harbor porpoises per month, and NMFS concurs.
Harbor Seal
Harbor seals are a common species in and around Ward Cove and
Tongass Narrows. During the monitoring efforts for the Ward Cove Cruise
Ship Dock Project, a total of 271 individuals were sighted as
individuals, pairs, or groups of 3 (Power Systems & Supplies of Alaska,
2020). During the Tongass Narrows Ferry Berth Improvements Project,
harbor seals were sighted on most days of in-water work, with group
sizes ranging from one to seven animals. Several sightings occurred
within 15 to 30 m from the ferry dock construction (ADOT&PF, 2021,
2022, 2023a, 2023b). Based on this information, ADOT&PF expects two
groups of five harbor seals per day of construction, and NMFS concurs.
A group of 9-13 harbor seals has been documented on a dock in Ward Cove
(the only known harbor seal haulout in Ward Cove), approximately 1 km
from Ward Creek Bridge (Solstice Alaska Consulting, 2025). This haulout
is not regularly occupied each day, and ADOT&PF therefore assumes 1
group of 13 harbor seals will be present on the haulout per week in
order to take into account the potential for take from in-air blasting,
and NMFS concurs.
Northern Elephant Seal
Sightings of northern elephant seals are uncommon in Tongass
Narrows but have been increasing in recent years (Solstice Alaska
Consulting, 2025). During monitoring efforts for the Tongass Narrows
Ferry Berth Improvement project, one elephant seal was documented in
April 2022 and one individual was seen in September 2022 (ADOT&PF,
2023b). No northern elephant seals were observed during the Ward Cove
Improvement Project (Power Systems & Supplies of Alaska, 2020). ADOT&PF
expects one individual northern elephant seal per month of
construction, and NMFS concurs. There are no known northern elephant
seal haulouts within the in-air Level B harassment isopleths from
blasting.
Steller Sea Lion
Steller sea lions are considered common in the area around Ward
Cove and Tongass Narrows. During the Ward Cove Cruise Ship Project, 181
Steller sea lions were observed over 44 separate days during the 98
days of monitoring. Observations were mostly of individuals and pairs,
but larger groups of up to 10 individuals were seen (Power Systems &
Supplies of Alaska, 2020). During monitoring for the Tongass Narrows
Ferry Berth Improvements, 599 Steller sea lions were observed over 86
days of monitoring, mostly as individuals, but occasionally in groups
of up to 5 animals (ADOT&PF, 2021, 2022, 2023a, 2023b). ADOT&PF expects
two groups per day, with two sea lions per group. The nearest known
Steller sea lion haulout is approximately 25 km northwest of the
project area, outside of the Level B harassment isopleth from blasting.
Take Estimation
Here we describe how the information provided above is synthesized
to produce a quantitative estimate of the take that is considered
likely to occur and proposed for authorization.
[[Page 25548]]
Level B Harassment Take Estimation
The method for take calculation was the same for Years 1 and 2,
except that blasting was not used in the calculations for Year 2 since
blasting is planned only for Year 1. For all species, Level B
harassment estimates were calculated using the estimated marine mammal
occurrence (as described in the Marine Mammal Occurrence section)
multiplied by the estimated number of days of pile driving and DTH. For
humpback whales, harbor seals, northern elephant seal, and Steller sea
lion the daily occurrence was also multiplied by the number of
estimated blasting days for Year 1. Blasting was not used to calculate
take by Level B harassment for killer whales, Dall's porpoises, and
harbor porpoises. For these species (HF and VHF species), the Level B
harassment isopleths are well within Ward Cove (see table 10), and
these species are generally expected to stay in Tongass Narrows and not
enter into Ward Cove.
When calculating Level B harassment from blasting for harbor seals,
we took into account both in-water and in-air take, as there is a known
haulout in Ward Cove, about 1 km from Ward Creek Bridge. When
calculating Level B harassment from blasting for Steller sea lions and
northern elephant seals, we assume that take could be from either in-
air or in-water noise, but base our estimates solely on the larger in-
air isopleths for these species, which adequately accounts for all
likely takes.
As described above, the estimated in-air Level B harassment
isopleth for blasting is approximately 16.5 km, however, this sound
would be truncated by land and the local topography. Although there are
known harbor seal haulouts along the northwestern aspect of Gravina
Island, approximately 9 km and 10.5 km from Ward Creek Bridge, because
of the truncation of sound, we do not expect the Level B harassment
isopleth to reach these haulouts. We, therefore, did not account for
these haulouts when conducting take calculations for harbor seals.
In Year 1, we expect 37 days of pile driving and 6 days of
blasting, assuming 3 days of blasting at each site. For Year 2, we
expect 32 days of pile driving. We note here that when a monthly
occurrence is assumed, we assume a month is 30 days. See table 13 and
table 14 for Level B harassment estimates for Years 1 and 2.
Table 13--Level B Harassment Take Estimations for Year 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated Number Noumber
Species Activity group size Group occurrence Number of days calculated proposed
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale........................ Pile driving/DTH........ 2 1 group/day............. 37...................... 74 74
Blasting................ 2 1 group/day............. 6....................... 12 12
Killer whale.......................... Pile driving/DTH........ 7 4 groups/month.......... 37 (1.23 months)........ 34.5 35
Dall's porpoise....................... Pile driving/DTH........ 6 1 group/month........... 37 (1.23 months)........ 7.4 7
Harbor porpoise....................... Pile driving/DTH........ 4 1 group/month........... 37 (1.23 months)........ 4.9 5
Steller sea lion...................... Pile driving/DTH........ 2 2 groups/day............ 37...................... 148 148
Blasting................ 2 2 groups/day............ 6....................... 24 24
Harbor seal........................... Pile driving/DTH........ 5 2 groups/day............ 37...................... 370 370
Blasting................ 5\a\ 2 groups/day............ 6....................... 60 60
Blasting................ 13 (per 1 group/week............ 6....................... 11.1 11
haulout)
\b\
Northern elephant seal................ Pile driving/DTH........ 1 1 group/month........... 37 (1.23 months)........ 1.2 1
Blasting................ 1 1 group/month........... 6 (0.2 months).......... 0.2 0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ This number accounts for in-water Level B harassment takes of harbor seals during blasting.
\b\ This number accounts for in-air Level B harassment takes of harbor seals during blasting.
Table 14--Level B Harassment Take Estimations for Year 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated Number Number
Species Activity group size Group occurrence Number of days calculated proposed
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale........................ Pile driving/DTH........ 2 1 group/day............. 32...................... 64 64
Killer whale.......................... Pile driving/DTH........ 7 4 groups/month.......... 32 (1.06 months)........ 29.7 30
Dall's porpoise....................... Pile driving/DTH........ 6 1 group/month........... 32 (1.06 months)........ 6.4 6
Harbor porpoise....................... Pile driving/DTH........ 4 1 group/month........... 32 (1.06 months)........ 4.2 4
Steller sea lion...................... Pile driving/DTH........ 2 2 groups/day............ 32...................... 128 128
Harbor seal........................... Pile driving/DTH........ 5 2 groups/day............ 32...................... 320 320
Northern elephant seal................ Pile driving/DTH........ 1 1 group/month........... 32 (1.06 months)........ 1.06 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
Level A Harassment Take Estimation
Level A harassment is considered likely and is proposed for
authorization for humpback whale, Dall's porpoise, harbor porpoise,
harbor seal, northern elephant seal, and Steller sea lion. Level A
harassment is not proposed for killer whales.
The method for estimating take due to Level A harassment is similar
to that for Level B harassment, as described above, using the same
estimated marine mammal occurrence and group size. However, for Level A
harassment we only take into account the number of days in which the
Level A harassment isopleth is greater than the shutdown zone (impact
pile driving, DTH, and blasting, depending on the species). For
humpback whales, we use number of days of DTH; for VHF cetaceans we use
DTH and impact pile driving days; for Steller sea lion we use number of
days of DTH and impact pile driving of 36-inch piles; and for phocids
we use days for DTH, all impact pile driving, and blasting. Table 15
presents the estimated number of days of each of these activities for
both Year 1 and Year 2. Table 16 and table 17 present the calculated
and proposed numbers of Level A harassment takes for Years 1 and 2,
respectively.
[[Page 25549]]
Table 15--Estimated Number of Days of Impact Pile Driving, DTH, and
Blasting for Years 1 and 2
------------------------------------------------------------------------
Estimated number of days
Activity -------------------------------
Year 1 Year 2
------------------------------------------------------------------------
Impact Pile Driving of 24-inch piles.... 4 4
Impact Pile Driving of 36-inch piles.... 8 6
DTH..................................... 8 6
Blasting................................ 6 0
------------------------------------------------------------------------
Table 16--Estimated Takes by Level A Harassment for Year 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated Number Number
Species Activity group size Group occurrence Number of days calculated proposed
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale........................ DTH..................... 2 1 group/day............. 8....................... 16 16
Dall's porpoise....................... Impact pile driving and 6 1 group/month........... 20 days (0.67 months)... 4 4
DTH.
Harbor porpoise....................... Impact pile driving and 4 1 group/month........... 20 days (0.67 months)... 2.7 3
DTH.
Steller sea lion...................... Impact Pile Driving of 2 2 groups/day............ 16...................... 64 64
36-inch piles and DTH.
Harbor seal........................... Impact pile driving and 5 2 groups/day............ 20...................... 200 200
DTH.
Blasting................ 5 2 groups/day............ 6....................... 60 60
Northern elephant seal................ Impact pile driving and 1 1 group/month........... 20 days (0.67 months)... 0.7 1
DTH.
Blasting................ 1 1 group/month........... 6 days (0.2 months)..... 0.2 0
--------------------------------------------------------------------------------------------------------------------------------------------------------
Table 17--Estimated Takes by Level A Harassment for Year 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated Number Number
Species Activity group size Group occurrence Number of days calculated proposed
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale........................ DTH..................... 2 1 group/day............. 6....................... 12 12
Dall's porpoise....................... Impact pile driving and 6 1 group/month........... 16 (0.53 months)........ 3.2 3
DTH.
Harbor porpoise....................... Impact pile driving and 4 1 group/month........... 16 (0.53 months)........ 2.1 2
DTH.
Steller sea lion...................... Impact Pile Driving of 2 2 groups/day............ 12...................... 48 48
36-inch piles and DTH.
Harbor seal........................... Impact pile driving and 5 2 groups/day............ 16...................... 160 160
DTH.
Northern elephant seal................ Impact pile driving and 1 1 group/month........... 16 (0.53 months)........ 0.5 1
DTH.
--------------------------------------------------------------------------------------------------------------------------------------------------------
See table 18 and table 19 for total numbers of takes proposed for
each species and stock for Year 1 and Year 2, respectively. When
attributing take to respective humpback whale stocks, NMFS assumed that
98 percent of total calculated take would be from the Hawai[revaps]i
stock and 2 percent would be from the Mexico-North Pacific stock, as
described in Wade (2021).
Table 18--Year 1 Take Proposed for Authorization as a Percentage of Stock Abundance
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated Estimated Total
Species Stock Stock takes by level takes by level instances of Percent of
abundance B harassment A harassment take stock
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale............................ Hawai[revaps]i.............. 11,278 84 16 100 0.9
Mexico-North Pacific........ UND 2 0 2 a N/A
Killer whale \b\.......................... Eastern North Pacific Alaska 1,920 35 0 35 1.8
Resident.
Eastern Northern Pacific 302 .............. .............. .............. 11.6
Northern Resident.
West Coast Transient........ 349 .............. .............. .............. 10
Dall's porpoise........................... Alaska...................... UND 7 4 11 \a\ N/A
Harbor porpoise........................... Southern Southeast Alaska 890 5 3 8 0.9
Inland Waters.
Steller sea lion.......................... Eastern..................... 36,308 172 64 236 0.6
Harbor seal............................... Clarence Strait............. 27,659 441 260 701 2.5
[[Page 25550]]
Northern elephant seal.................... California Breeding......... 187,386 1 1 2 <0.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ See small numbers discussion below for additional information.
\b\ Scientific data is not available to determine the likelihood of each killer whale stock in ADOT&PF's proposed project area, and the stocks cannot be
differentiated in the field. When calculating the percentage of stock, we conservatively attribute the total proposed instances of take to each killer
whale stock.
Table 19--Year 2 Take Proposed for Authorization as a Percentage of Stock Abundance
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated Estimated
Stock takes by takes by Total Percent of
Species Stock abundance level B level A Instances of stock
harassment harassment take
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale............................ Hawai'i..................... 11,278 62 12 74 0.7
Mexico-North Pacific........ UND 2 0 2 \a \N/A
Killer whale \b\.......................... Eastern North Pacific Alaska 1,920 30 0 30 1.6
Resident.
Eastern Northern Pacific 302 .............. .............. .............. 9.9
Northern Resident.
West Coast Transient........ 349 .............. .............. .............. 8.6
Dall's porpoise........................... Alaska...................... UND 6 3 9 \a\ N/A
Harbor porpoise........................... Southern Southeast Alaska 890 4 2 6 0.7
Inland Waters.
Steller sea lion.......................... Eastern..................... 36,308 128 48 176 0.5
Harbor seal............................... Clarence Strait............. 27,659 320 160 480 1.7
Northern elephant seal.................... California Breeding......... 187,386 1 1 2 <0.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ See small numbers discussion below for additional information.
\b\ Scientific data is not available to determine the likelihood of each killer whale stock in ADOT&PF's proposed project area, and the stocks cannot be
differentiated in the field. When calculating the percentage of stock, we conservatively attribute the total proposed instances of take to each killer
whale 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 mitigation requirements described in the following were
proposed by ADOT&PF in its adequate and complete application or are the
result of subsequent coordination between NMFS and ADOT&PF. ADOT&PF has
agreed that all of the mitigation measures are practicable. NMFS has
fully reviewed the specified activities and the mitigation measures to
determine if the mitigation measures would result in the least
practicable adverse impact on marine mammals and their habitat, as
required by the MMPA, and has determined the proposed measures are
appropriate. NMFS describes these below as proposed mitigation
requirements and has included them in the proposed IHA.
In addition to the measures described later in this section,
ADOT&PF would follow these general mitigation measures:
<bullet> Authorized take, by Level A and Level B harassment only,
would be limited to the species and numbers listed in table 18 and
table 19 for Years 1 and 2, respectively. Construction activities must
be halted upon observation of either a species for which incidental
take is not authorized or a species for which incidental take has been
authorized but the authorized number of takes has been met, entering,
or is within the harassment zone.
<bullet> The taking by serious injury or death of any of the
species listed in table 18 and table 19 or any taking of any other
species of marine mammal would be prohibited and would result in the
modification, suspension, or revocation of the IHA, if issued. Any
taking exceeding the authorized amounts listed in table 18 during Year
1 or table 19 during Year 2 would be prohibited and would result in the
modification, suspension, or revocation of the IHA, if issued.
<bullet> Ensure that construction supervisors and crew, the marine
[[Page 25551]]
mammal monitoring team, and relevant ADOT&PF staff are trained prior to
the start of all construction activities, so that responsibilities,
communication procedures, marine mammal monitoring protocol, and
operational procedures are clearly understood. New personnel joining
during the project must be trained prior to commencing work;
<bullet> ADOT&PF, construction supervisors and crews, protected
species observers (PSOs), and relevant ADOT&PF staff must avoid direct
physical interaction with marine mammals during construction activity.
If a marine mammal comes within 10 m of such activity, operations must
cease and vessels must reduce speed to the minimum level required to
maintain steerage and safe working conditions, as necessary to avoid
direct physical interaction.
<bullet> Employ PSOs and establish monitoring location as described
in ADOT&PF's Marine Mammal Monitoring and Mitigation Plan (see appendix
B of ADOT&PF's application). ADOT&PF must monitor the project area to
the maximum extent possible based on the required number of PSOs,
required monitoring locations, and environmental conditions;
<bullet> ADOT&PF also would abide by the reasonable and prudent
measures and terms and conditions of a Biological Opinion and
Incidental Take Statement if issued by NMFS pursuant to Section 7 of
the ESA.
Additionally, the following mitigation measures apply to ADOT&PF's
in-water construction and on-land blasting activities.
Establishment of Shutdown and Clearance Zones
ADOT&PF would establish shutdown zones with radial distances as
identified in table 20 for all pile driving and DTH activities. The
purpose of a shutdown zone is generally to define an area within which
shutdown of the activity would occur upon sighting of a marine mammal
(or in anticipation of an animal entering the defined area). The
shutdown zones vary by activity type and marine mammal hearing group
and are generally based on the estimated Level A harassment zones and
distances at which PSOs would be able to observe relevant species.
ADOT&PF has proposed a maximum shutdown zone of 55 m for phocids due to
the frequency of sightings of harbor seal in Ward Cove. ADOT&PF has
determined that a larger shutdown zone would require a frequency of
shutdown that would result in significant delays, rendering the larger
zones not practicable, and NMFS concurs. If a marine mammal is observed
entering or within the shutdown zones indicated in table 20, pile
driving and DTH activity must be delayed or halted. If pile driving or
DTH activity is 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
zones or 15 minutes have passed without re-detection of the animal. If
a marine mammal comes within or approaches the shutdown zone indicated
in table 20, such operations must cease. Shutdown zones would vary
based on the activity type and marine mammal hearing group. Shutdown
zones are the same in both Year 1 and Year 2, with the exception of
vibratory installation and removal of 18-inch steel shell piles (see
table 20).
Table 20--Proposed Shutdown Zones (m) During Pile Driving and DTH *
----------------------------------------------------------------------------------------------------------------
Pile Size/Type LF HF VHF PW OW
----------------------------------------------------------------------------------------------------------------
Vibratory
----------------------------------------------------------------------------------------------------------------
18-inch steel shell (Year 1)................... 20 10 20 30 10
18-inch steel shell (Year 2)................... 45 20 35 55 20
24-inch steel shell............................ 45 20 35 55 20
36-inch steel shell............................ 20 10 20 30 10
----------------------------------------------------------------------------------------------------------------
Impact
----------------------------------------------------------------------------------------------------------------
24-inch steel shell............................ 285 40 200 55 95
36-inch steel shell............................ 995 130 200 55 200
----------------------------------------------------------------------------------------------------------------
DTH
----------------------------------------------------------------------------------------------------------------
36-inch steel shell............................ 2,000 340 200 55 200
----------------------------------------------------------------------------------------------------------------
* Shutdown zones are the same for Years 1 and 2 for each pile size/type except for 18-inch steel shell piles, as
noted above.
ADOT&PF would establish clearance zones with radial distances as
identified in table 21 and table 22 for blasting activities. The
purpose of a clearance zone is to prevent potential instances of
auditory injury and more severe behavioral disturbance the maximum
extent practicable by delaying the commencement of an activity if
marine mammals are observed within the defined area. Because ADOT&PF's
proposed blasting could result in harassment due to underwater noise
and in-air noise, clearance zones have been established for both
animals in the water and above water (in-air). The in-air clearance
zones are intended for hauled out animals. The in-water clearance zone
would be used for all swimming animals, even though they might
periodically have their heads above water. If a marine mammal is
observed entering or within the clearance zone indicated in table 21 or
table 22, blasting activities must be delayed. The sound from blasting
would occur over only a few seconds but could not be halted once it has
been initiated. If an animal were to enter the clearance zone once
blasting has been initiated, the blasting could not be halted, and the
animal would be recorded as a potential take.
Table 21--In-Water Clearance Zones (m) for Blasting *
----------------------------------------------------------------------------------------------------------------
Activity LF HF VHF PW OW
----------------------------------------------------------------------------------------------------------------
Blasting, 33 m from shore....... 285 10 25 160 10
[[Page 25552]]
Blasting, 110 m from shore...... 10 10 10 10 10
----------------------------------------------------------------------------------------------------------------
* Measured from the shoreline.
Table 22--In-Air Clearance Zones (m) for Blasting *
------------------------------------------------------------------------
Activity Phocids Otariids
------------------------------------------------------------------------
Blasting, 33 m from shore............... 225 10
Blasting, 110 m from shore.............. 150 10
------------------------------------------------------------------------
* Measured from the shoreline.
Pre- and Post-Activity Monitoring
Monitoring would take place from 30 minutes prior to initiation of
pile driving and blasting activity (i.e., pre-start clearance
monitoring) through 30 minutes post-completion of pile driving, DTH,
and blasting activity. In addition, monitoring for 30 minutes would
take place whenever a break in the specified activity (i.e., impact
pile driving, vibratory pile driving, DTH) of 30 minutes or longer
occurs. Pre-start clearance monitoring would be conducted during
periods of visibility sufficient for the lead PSO to determine that the
shutdown or pre-clearance zones indicated in table 20, table 21, and
table 22 are clear of marine mammals. Pile driving and blasting may
commence following 30 minutes of observation when the determination is
made that the shutdown and clearance zones are clear of marine mammals.
Soft Start
ADOT&PF would use soft-start techniques when impact pile driving.
Soft-start requires contractors to provide an initial set of three
strikes at reduced energy, followed by a 30-second waiting period, then
two subsequent reduced-energy strike sets. A soft-start would be
implemented at the start of each day's impact pile driving and at any
time following cessation of impact pile driving for a period of 30
minutes or longer. Soft-start procedures are used to provide additional
protection to marine mammals by providing a warning and/or giving
marine mammals a chance to leave the area prior to the hammer operating
at full capacity.
Bubble Curtains
ADOT&PF fully considered the use of bubble curtains during impact
pile driving. In general, bubble curtains reduce noise levels near the
source, minimizing exposure levels. However, due to shallow water
depths, tidal fluctuations, and associated creek flow velocities within
the project area, ADOT&PF determined that the use of bubble curtains
would not be practicable during this project, and NMFS concurs.
Further, the Level A and Level B harassment zones for impact pile
driving are relatively small and both ADOT&PF and NMFS expect that the
proposed mitigation measures, including monitoring, use of shutdown
zones, and soft starts for impact pile driving will be effective to
reduce impacts to marine mammals. Therefore, ADOT&PF has determined
that bubble curtains would not be practicable for this project, and
NMFS concurs.
NMFS conducted an independent evaluation of the proposed measures
and has preliminarily determined, for each proposed IHA, that the
proposed mitigation measures provide the means of effecting the least
practicable impact on the affected species or stocks and their habitat,
paying particular attention to rookeries, mating grounds, and areas of
similar significance.
Proposed Monitoring and Reporting
In order to issue an IHA for an activity, section 101(a)(5)(D) of
the MMPA states that NMFS must set forth requirements pertaining to the
monitoring and reporting of such taking. The MMPA implementing
regulations at 50 CFR 216.104(a)(13) indicate that requests for
authorizations must include the suggested means of accomplishing the
necessary monitoring and reporting that will result in increased
knowledge of the species and of the level of taking or impacts on
populations of marine mammals that are expected to be present while
conducting the activities. Effective reporting is critical both to
compliance as well as ensuring that the most value is obtained from the
required monitoring.
Monitoring and reporting requirements prescribed by NMFS should
contribute to improved understanding of one or more of the following:
<bullet> Occurrence of marine mammal species or stocks in the area
in which take is anticipated (e.g., presence, abundance, distribution,
density);
<bullet> Nature, scope, or context of likely marine mammal exposure
to potential stressors/impacts (individual or cumulative, acute or
chronic), through better understanding of: (1) action or environment
(e.g., source characterization, propagation, ambient noise); (2)
affected species (e.g., life history, dive patterns); (3) co-occurrence
of marine mammal species with the activity; or (4) biological or
behavioral context of exposure (e.g., age, calving or feeding areas);
<bullet> Individual marine mammal responses (behavioral or
physiological) to acoustic stressors (acute, chronic, or cumulative),
other stressors, or cumulative impacts from multiple stressors;
<bullet> How anticipated responses to stressors impact either: (1)
long-term fitness and survival of individual marine mammals; or (2)
populations, species, or stocks;
<bullet> Effects on marine mammal habitat (e.g., marine mammal prey
species, acoustic habitat, or other important physical components of
marine mammal habitat); and
<bullet> Mitigation and monitoring effectiveness.
ADOT&PF would abide by all monitoring and reporting measures
contained within the IHA, if issued, and their Marine Mammal Monitoring
and Mitigation Plan (see appendix B of ADOT&PF's application). The
monitoring and reporting requirements described in the following were
proposed by ADOT&PF in its adequate and complete application and/or are
the result of subsequent coordination between NMFS and ADOT&PF. ADOT&PF
has agreed to the requirements. NMFS describes these below as
requirements and has included them in the proposed IHA.
Visual Monitoring
All PSOs must be NMFS-approved. PSOs would be independent of the
[[Page 25553]]
activity contractor (for example, employed, by a subcontractor) and
have no other assigned tasks during monitoring periods. At least one
PSO would have prior experience performing the duties of a PSO during
an activity pursuant to a NMFS-issued Incidental Take Authorization
(ITA) or Letter of Concurrence (LOC). Other PSOs may substitute other
relevant experience (including relevant Alaska Native traditional
knowledge), education (degree in biological science or related field),
or training for prior experience performing the duties of a PSO during
construction activity pursuant to a NMFS-issued incidental take
authorization. Where a team of three or more PSOs is required, a lead
observer or monitoring coordinator would be designated. The lead
observer must have prior experience performing the duties of a PSO
during construction activity pursuant to a NMFS-issued ITA or LOC.
PSOs would also have the following additional qualifications:
<bullet> The ability to conduct field observations and collect data
according to assigned protocols;
<bullet> Experience or training in the field identification of
marine mammals, including the identification of behaviors;
<bullet> Sufficient training, orientation, or experience with the
construction operation to provide for personal safety during
observations;
<bullet> Writing skills sufficient to prepare a report of
observations including but not limited to: (1) the number and species
of marine mammals observed; (2) dates and times when in-water
construction activities were conducted; (3) dates, times, and reason
for implementation of mitigation (or why mitigation was not implemented
when required); and (4) marine mammal behavior; and
<bullet> The ability to communicate orally, by radio or in person,
with project personnel to provide real-time information on marine
mammals observed in the area as necessary.
ADOT&PF must establish monitoring locations as described in the
Marine Mammal Monitoring and Mitigation Plan (see appendix B of
ADOT&PF's application). For all pile driving and DTH activities, a
minimum of one PSO must be assigned to each active pile driving
location to monitor the shutdown zones and a minimum of one PSO must be
assigned to monitor the pre-clearance zones prior to blasting.
Between two and three PSOs will be on duty depending on the size of
the Level B harassment zone. The specific locations of the PSOs are as
follows, as described in the Marine Mammal Monitoring and Mitigation
Plan (see figure 2 for visual depiction of PSO stations):
<bullet> Station 1: at the Alaska Gymnastics Academy/FedEx parking
lot, next to Ward Creek Bridge
<bullet> Station 2: Ketchikan Pulp Company landfill property on the
northwest shore of Ward Cove
<bullet> Station 3: at Peninsula Point
During impact pile driving of 24- and 36-inch steel shell piles,
PSOs will be present at Stations 1 and 2. During vibratory pile driving
of 18-, 24,- and 36-inch steel shell piles, DTH installation of 36-inch
steel shell piles, and blasting, PSOs will be present at Stations 1, 2,
and 3.
[[Page 25554]]
[GRAPHIC] [TIFF OMITTED] TN11MY26.016
PSOs would record all observations of marine mammals, regardless of
distance from the pile being driven or from blasting, as well as the
additional data indicated below and in section 6 of the IHA, if issued.
Reporting
Marine Mammal Monitoring Report
ADOT&PF would be required to submit an annual draft summary report
on all construction activities and marine mammal monitoring results to
NMFS within 90 days following the end of construction or 60 days prior
to the requested issuance of any subsequent IHA for similar activity at
the same location, whichever comes first. The draft summary report
would include an overall description of construction work completed, a
narrative regarding marine mammal sightings, and associated raw PSO
data sheets (in electronic spreadsheet format). Specifically, the
report must include:
<bullet> Dates and times (begin and end) of all marine mammal
monitoring;
<bullet> Construction activities occurring during each daily
observation period, including: (a) how many and what type of piles were
driven or removed and the method (i.e., impact, vibratory, DTH); and
(b) the total duration of time for each pile (vibratory and DTH) or
number of strikes for each pile (impact); (c) number of boreholes, net
explosive weight per borehole, associated delays between charges,
location for each daily blasting event, and approximate distance to the
nearest shoreline;
<bullet> PSO locations during marine mammal monitoring; and
<bullet> Environmental conditions during monitoring periods (at the
beginning and end of PSO shift and whenever conditions change
significantly), including Beaufort sea state and any other relevant
weather conditions including cloud cover, fog, sun glare, and overall
visibility to the horizon, and estimated observable distance.
Upon observation of a marine mammal the following information must
be reported:
<bullet> Name of PSO who sighted the animal(s) and PSO location and
activity at the time of the sighting;
<bullet> Time of the sighting;
<bullet> Identification of the animal(s) (e.g., genus/species,
lowest possible taxonomic level, or unidentified), PSO confidence in
identification, and the composition of the group if there is a mix of
species;
<bullet> Distance and bearing of each observed marine mammal
relative to the pile being driven or removed, or blasting site, for
each sighting;
<bullet> Estimated number of animals (min/max/best estimate);
<bullet> Estimated number of animals by cohort (e.g., adults,
juveniles, neonates, group composition, etc.);
<bullet> Animal's closest point of approach and estimated time
spent within the estimated harassment zone(s);
<bullet> Description of any marine mammal behavioral observations
(e.g., observed behaviors such as feeding or traveling), including an
assessment of behavioral responses thought to have resulted from
[[Page 25555]]
the activity (e.g., no response or changes in behavioral state such as
ceasing feeding, changing direction, flushing, or breaching);
<bullet> Number of marine mammals detected within the estimated
harassment zones, by species; and
<bullet> Detailed information about implementation of any
mitigation (e.g., shutdowns and delays), a description of specified
actions that ensued, and resulting changes in behavior of the
animal(s), if any.
If no comments are received from NMFS within 30 days after the
submission of the draft summary report, the draft report would
constitute the final report. If ADOT&PF receives comments from NMFS, a
final summary report addressing NMFS' comments would be submitted
within 30 days after receipt of comments.
Reporting Injured or Dead Marine Mammals
In the event that personnel involved in ADOT&PF's activities
discover an injured or dead marine mammal, ADOT&PF would report the
incident to the NMFS Office of Protected Resources
(<a href="/cdn-cgi/l/email-protection#affffd81e6fbff81e2c0c1c6dbc0ddc6c1c8fdcadfc0dddbdcefc1c0cece81c8c0d9"><span class="__cf_email__" data-cfemail="a2f2f08cebf6f28cefcdcccbd6cdd0cbccc5f0c7d2cdd0d6d1e2cccdc3c38cc5cdd4">[email protected]</span></a>, <a href="/cdn-cgi/l/email-protection#521b06027c3833313d302721123c3d33337c353d24"><span class="__cf_email__" data-cfemail="c9809d99e7a3a8aaa6abbcba89a7a6a8a8e7aea6bf">[email protected]</span></a>) and to the
Alaska Regional Stranding Coordinator as soon as is feasible. If the
death or injury was clearly caused by the specified activity, ADOT&PF
would immediately cease the specified activities until NMFS is able to
review the circumstances of the incident and determine what, if any
additional measures appropriate to ensure compliance with the IHA.
ADOT&PF would not resume their activities until notified by NMFS. The
report would include the following information:
<bullet> Description of the incident;
<bullet> Environmental conditions (e.g., Beaufort sea state,
visibility);
<bullet> Description of all marine mammal observations in the 24
hours preceding the incident;
<bullet> Photographs or video footage of the animal(s) (if
equipment is available);
<bullet> Time, date, and location (latitude/longitude) of the first
discovery (and updated location information if known and applicable);
<bullet> Species identification (if known) or description of the
animal(s) involved;
<bullet> Condition of the animal(s) (including carcass condition if
the animal is dead);
<bullet> Observed behaviors of the animal(s), if alive; and
<bullet> General circumstances under which the animal was
discovered.
Negligible Impact Analysis and Determination
NMFS has defined negligible impact as an impact resulting from the
specified activity that cannot be reasonably expected to, and is not
reasonably likely to, adversely affect the species or stock through
effects on annual rates of recruitment or survival (50 CFR 216.103). A
negligible impact finding is based on the lack of likely adverse
effects on annual rates of recruitment or survival (i.e., population-
level effects). An estimate of the number of takes alone is not enough
information on which to base an impact determination. In addition to
considering estimates of the number of marine mammals that might be
``taken'' through harassment, NMFS considers other factors, such as the
likely nature of any impacts or responses (e.g., intensity, duration),
the context of any impacts or responses (e.g., critical reproductive
time or location, foraging impacts affecting energetics), as well as
effects on habitat, and the likely effectiveness of the mitigation. We
also assess the number, intensity, and context of estimated takes by
evaluating this information relative to population status. Consistent
with the 1989 preamble for NMFS' implementing regulations (54 FR 40338,
September 29, 1989), the impacts from other past and ongoing
anthropogenic activities are incorporated into this analysis via their
impacts on the baseline (e.g., as reflected in the regulatory status of
the species, population size and growth rate where known, ongoing
sources of human-caused mortality, or ambient noise levels).
To avoid repetition, the discussion of our analysis applies to all
species listed in table 3, given that the anticipated effects of this
activity on these different marine mammal stocks are expected to be
similar. There is little information about the nature or severity of
the impacts, or the size, status, or structure of any of these species
or stocks that would lead to a different analysis for this activity.
Impact and vibratory pile driving and DTH are planned for Year 1
and Year 2, and on-land blasting is planned for Year 1. These
activities have the potential to disturb or displace marine mammals.
Specifically, pile driving and DTH may result in take in the form of
Level B harassment for all species and stocks in table 3 and Level A
harassment for all species and stocks in table 3 except for killer
whales. On-land blasting, which is proposed for Year 1 only, may result
in Level B harassment of humpback whales, harbor seals, northern
elephant seals, and Steller sea lions and Level A harassment of harbor
seals and northern elephant seals. Potential takes could occur if
individuals of these species are present in zones ensonified above the
thresholds for Level A and Level B harassment identified above when
these activities are underway.
Given the nature of the proposed activities, NMFS does not
anticipate serious injury or mortality due to ADOT&PF's proposed
project, even in the absence of required mitigation. No Level A
harassment is anticipated for killer whales due to the relatively small
Level A harassment zones for high frequency cetaceans and required
shutdown zones that are equal to or exceed the Level A harassment
isopleths for high frequency cetaceans. Take by Level A harassment due
to pile driving and DTH is proposed for humpback whale, Dall's
porpoise, harbor porpoise, Steller sea lion, harbor seal, and northern
elephant seal to account for the potential that an animal could enter
and remain within the area between a Level A harassment zone and the
shutdown zone for a duration long enough to be taken by Level A
harassment. Take by Level A harassment due to blasting is proposed for
harbor seals and northern elephant seals to account for the potential
that an animal might enter the Level A harassment zone during blasting.
Any take by Level A harassment is expected to arise from, at most, a
small degree of AUD INJ because animals would need to be exposed to
higher levels and/or longer duration than are expected to occur here in
order to incur any more than a small degree of AUD INJ. Additionally,
some subset of the individuals that are behaviorally harassed could
also simultaneously incur some small degree of TTS for a short duration
of time. Because of the small degree anticipated, any AUD INJ or TTS
potentially incurred here is not expected to adversely impact
individual fitness, let alone annual rates of recruitment or survival.
For all species and stocks, take would occur within a limited,
confined area of the stocks' ranges. The intensity and duration of take
by Level A harassment and Level B harassment would be minimized through
use of mitigation measures described herein. Further, the amount of
take proposed is small when compared to stock abundance.
Behavioral responses of marine mammals to pile driving, pile
removal, DTH, and on-land blasting in Ward Cove are expected to be
mild, short term, and temporary. Marine mammals within the Level B
harassment zones may not show any visual cues they are disturbed by
activities or they could become alert, avoid the area, leave the area,
or display other mild responses that are not visually observable such
as change in vocalization patterns. Given that pile driving, DTH
activities, and on-
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land blasting would occur for only a limited number of days each year,
often on non-consecutive days, any harassment would be temporary.
Additionally, many of the species present in Ward Cove and Tongass
Narrows would only be present temporarily based on seasonal patterns or
during transit between other habitats. These species would be exposed
to even shorter periods of noise-generating activity, further
decreasing the impacts.
The potential for harassment is minimized through the
implementation of the proposed mitigation measures. The use of shutdown
and clearance zones reduce the likelihood of incurring AUD INJ. During
impact driving, implementation of soft start procedures shall be
required, reducing possibility for injury. Through the use of soft
start during impact pile driving, marine mammals are expected to move
away from a disturbing sound source prior to it becoming potentially
injurious.
Any impacts on prey that would occur during in-water construction
would have at most short-term effects on foraging of individual marine
mammals, and likely no effect on the populations of marine mammals as a
whole. Therefore, effects on marine mammal prey during the construction
are expected to be minimal and, therefore, are unlikely to cause
substantial effects on marine mammals at the individual or population
level.
In addition, it is unlikely that minor noise effects in a small,
localized area of habitat would have any effect on the reproduction or
survival of any individual, much less the stocks' annual rates of
recruitment or survival. In combination, we believe that these factors,
as well as the available body of evidence from other similar
activities, demonstrated that the potential effects of the specified
activities would have only short-term effects on individuals. The
specified activities are not expected to impact rates of recruitment or
survival and would, therefore, not result in population-level impacts.
For humpback whales, the inland waters of Southeast Alaska,
including Ward Cove and Tongass Narrows, are a seasonal feeding BIA
from May through September (Wild et al., 2023). However, the ensonified
area from ADOT&PF's proposed project activities, in Ward Cove and a
small portion of Tongass Narrows, represents a very small portion of
the total available habitat. We do not expect ADOT&PF's proposed
construction to have any effect on humpback whales' ability to forage
and find food.
In summary and as described above, the following factors primarily
support our preliminary determination that the impacts resulting from
this activity are not expected to adversely affect any of the species
or stocks through effects on annual rates of recruitment or survival
for either year of authorization:
<bullet> No serious injury or mortality is anticipated or
authorized;
<bullet> Authorized Level A harassment would be limited and of low
degree;
<bullet> Mitigation measures such as shutdown zones for pile
driving and DTH, clearance zones for blasting, and soft-starts for
impact pile driving will be employed to minimize the numbers of marine
mammals exposed to injurious levels of sound, and to ensure that any
take by Level A harassment is, at most, a small degree of AUD INJ;
<bullet> The anticipated incidents of Level B harassment consist
of, at worst, temporary modifications in behavior;
<bullet> The project area represents a very small portion of the
available foraging area for all potentially impacted marine mammal
species and stocks, and anticipated habitat impacts are minor;
<bullet> The project area overlaps a very small portion of a
feeding BIA for humpback whales. The project is not expected to have
any effect on humpback whales' ability to forage or feed; and
<bullet> The intensity of anticipated take by Level B harassment is
relatively low for all stocks and will not be of a duration or
intensity expected to result in impacts on reproduction or survival.
Based on the analysis contained herein of the likely effects of the
specified activity on marine mammals and their habitat, and taking into
consideration the implementation of the proposed monitoring and
mitigation measures, NMFS preliminarily finds for each proposed IHA
that the total marine mammal take from the proposed activity will have
a negligible impact on all affected marine mammal species or stocks.
Small Numbers
As noted previously, only take of small numbers of marine mammals
may be authorized under section 101(a)(5)(A) and (D) of the MMPA for
specified activities other than military readiness activities. The MMPA
does not define small numbers and so, in practice, where estimated
numbers are available, NMFS compares the number of individuals taken to
the most appropriate estimation of abundance of the relevant species or
stock in our determination of whether an authorization is limited to
small numbers of marine mammals. When the predicted number of
individuals to be taken is fewer than one-third of the species or stock
abundance, the take is considered to be of small numbers (see 86 FR
5322, January 19, 2021). Additionally, other qualitative factors may be
considered in the analysis, such as the temporal or spatial scale of
the activities.
The number of instances of take for each species or stock proposed
for authorization is included in table 18 for Year 1 and table 19 for
Year 2. Our analysis shows that for all species with available
population abundance estimates, less than one-third of the best
available population abundance estimate of each stock could be taken by
harassment during both years of proposed construction.
Abundance estimates for the Mexico-North Pacific stock of humpback
whales are based upon data collected more than 8 years ago and,
therefore, current estimates are considered unknown (Young et al.,
2024). The most recent minimum population estimates (N<INF>min</INF>)
for the population include an estimate of 2,241 individuals between
2003 and 2006 (Mart[iacute]nez-Aguilar, 2011) and 766 individuals
between 2004 and 2006 (Wade, 2021). NMFS' Guidelines for Assessing
Marine Mammal Stocks suggest that the N<INF>min</INF> estimate of the
stock should be adjusted to account for potential abundance changes
that may have occurred since the last survey and provide reasonable
assurance that the stock size is at least as large as the estimate
(NMFS, 2023). The abundance trend for this stock is unclear; therefore,
there is no basis for adjusting these estimates (Young et al., 2024).
NMFS is proposing to authorize two takes of the Mexico-North Pacific
stock of humpback whale during both Year 1 and Year 2. This represents
small numbers of this stock (0.2 percent of the stock assuming
N<INF>min</INF> of 766 individuals).
The Alaska stock of Dall's porpoise has no official NMFS abundance
estimate for this area, as the most recent estimate is greater than 8
years old. As described in the 2021 Alaska SAR (Muto et al., 2022) the
minimum population estimate is assumed to correspond to the point
estimate of the 2015 vessel-based abundance computed by (Rone et al.,
2017) in the Gulf of Alaska (N = 13,110; CV = 0.22). NMFS is proposing
to authorize 12 takes of the stock in Year 1 and 11 takes of the stock
in Year 2. Comparison to the minimum population estimate shows that
less than 0.1 percent of the stock would be expected to be impacted for
each year of ADOT&PF's proposed construction.
Based on the analysis contained herein of the proposed activity
(including the proposed mitigation and monitoring measures) and the
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anticipated take of marine mammals, NMFS preliminarily finds for each
proposed IHA that small numbers of marine mammals would be taken
relative to the population size of the affected species or stocks.
Unmitigable Adverse Impact Analysis and Determination
In order to issue an IHA, NMFS must find that the specified
activity will not have an ``unmitigable adverse impact'' on the
subsistence uses of the affected marine mammal species or stocks by
Alaskan Natives. NMFS has defined ``unmitigable adverse impact'' in 50
CFR 216.103 as an impact resulting from the specified activity: (1)
That is likely to reduce the availability of the species to a level
insufficient for a harvest to meet subsistence needs by: (i) Causing
the marine mammals to abandon or avoid hunting areas; (ii) Directly
displacing subsistence users; or (iii) Placing physical barriers
between the marine mammals and the subsistence hunters; and (2) That
cannot be sufficiently mitigated by other measures to increase the
availability of marine mammals to allow subsistence needs to be met.
Harbor seals are the most commonly harvested marine mammal by the
Ketchikan subsistence community. In 2012, the most recent survey year
of subsistence harvest in southeast Alaska, 22.2 percent of households
reported harvesting harbor seal, and 55.6 percent reported using harbor
seal (Wolfe et al., 2013). In that same year, no households reported
harvesting Steller sea lion, although 11.1 percent of households
reported using Steller sea lion (Wolfe et al., 2013). Since surveying
of subsistence harvest began in 1992, there has been a decline in the
number of households harvesting seals in Southeast Alaska. The count of
harvesters in 2012 (140 households) was the second lowest since the
seal survey began in 1992 (Wolfe et al., 2013). There have been no
apparent trends in sea lion
[…truncated; see source link]Indexed from Federal Register on May 11, 2026.
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