# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Turnagain Marine Construction's Douglas Island Cruise Ship Terminal Near Juneau, Alaska

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2026-13055

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** June 29, 2026
- **Citation:** 91 FR 39206

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XF340]
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Turnagain Marine Construction's Douglas Island Cruise Ship Terminal Near Juneau, 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 renewal.

SUMMARY:

NMFS has received a request from Turnagain Marine Construction (Turnagain) for authorization to take marine mammals incidental to construction of the Douglas Island Cruise Ship Terminal near Juneau, Alaska. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue two consecutive incidental harassment authorizations (IHAs) to take marine mammals incidental to the specified activities. NMFS is also requesting comments on possible one-time, 1-year renewals that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorizations.

DATES:

Comments and information must be received no later than July 29, 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
ITP.clevenstine@noaa.gov.
Electronic copies of the application and supporting documents, as well as a list of the references cited in this document, may be obtained online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities.
In case of problems accessing these documents, please call the contact listed below.

Instructions:
NMFS is not responsible for comments sent by any other method, to any other address or individual, or received after the end of the comment period. Comments, including all attachments, must not exceed a 25-megabyte file size. All comments received are part of the public record and will generally be posted online at
https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act
without change. All personal identifying information (
e.g.,
name, address) voluntarily submitted by the commenter may be publicly accessible. Do not submit confidential business information or otherwise sensitive or protected information.

FOR FURTHER INFORMATION CONTACT:

Alyssa Clevenstine, 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 (collectively 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 and can be found in section 3 of the MMPA (16 U.S.C. 1362) and NMFS regulations at 50 CFR 216.103.

National Environmental Policy Act

To comply with the National Environmental Policy Act of 1969 (NEPA) (42 U.S.C. 4321
et seq.
) and NOAA Administrative Order (NAO) 216-6A, NMFS must review our proposed action (
i.e.,
the issuance of two IHAs) 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 August 28, 2025, NMFS received a request from Turnagain for two consecutive IHAs to take marine mammals incidental to pile driving (installation and removal) associated with construction of a cruise ship terminal on Douglas Island near Juneau, Alaska. Following NMFS' review of the application, Turnagain submitted revised versions on January 14, March 16, April 23, May 5, and May 8, 2026. The application was deemed adequate and complete on May 18, 2026. Turnagain's request is for take of 10 species (15 stocks) of marine mammals by Level B harassment and, for a subset of these species, Level A harassment (9 species (11 stocks)). Neither Turnagain nor NMFS expect serious injury or mortality to result from this activity and, therefore, IHAs are appropriate.

NMFS previously issued IHAs to Turnagain for similar work (
i.e.,
work that utilizes in-water pile driving) at other locations in Alaska (see 88 FR 19927, April 4, 2023; 89 FR 22679, April 2, 2024; 90 FR 44047, September 11, 2025). Turnagain complied with all the requirements (
e.g.,
mitigation, monitoring, and reporting) of the previous IHAs, and information regarding their monitoring results may be found on our website (
https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities
).

Description of Proposed Activity

Overview

Turnagain proposes to construct two separate cruise ship berths and associated facilities on the western shore of Douglas Island in Stephens Passage near Juneau, Alaska. The proposed project is necessary to provide safe harbor for cruise ships and to

accommodate passengers during the Southeast Alaska visitor season (late April to mid-October) while reducing overall congestion in downtown Juneau. The new development would require the placement of 120 temporary and 345 permanent pilings installed via impact, down-the-hole (DTH), and vibratory pile driving. These methods of pile driving would introduce underwater sounds that may result in take, by Level A and Level B harassment, of marine mammals. Temporary template piles would be installed using vibratory and/or DTH driving and removed using vibratory methods while permanent piles would be installed using any or all methods.

The proposed project entails coastal construction activities that would be completed in two phases: Phase I and Phase II, which would be separated into Phase II South and Phase II North. Given the use of vibratory pile driving, impact pile driving, and DTH for in-water construction activities, there is the potential for marine mammals to be taken by Level A harassment and/or Level B harassment.

Dates and Duration

Turnagain anticipates the project would occur in two phases over 2 years. Each of the two proposed IHAs would be valid for the statutory maximum of 1 year from the date of effectiveness, and will become effective upon written notification from the applicant to NMFS. The period of effectiveness for the Phase I IHA would begin not later than 1 year from the date of issuance or extend beyond 2 years from the date of issuance. The period of effectiveness for the Phase II IHA would begin not later than 1 year from the date of expiration of the Phase I IHA or extending beyond 2 years from the date of expiration of the Phase I IHA. Phase I is expected to last approximately 122 non-consecutive days, and Phase II is expected to consist of 217 non-consecutive days. The schedule accounts for the mobilization of barges and vessels, as well as potential delays, inclement weather, and shutdowns that may occur upon presence of marine mammals.

Specific Geographic Region

The proposed project would occur on the northwest side of Douglas Island, which lies within the northern Stephens Pass of Southeast Alaska. Douglas Island is separated from Juneau, Alaska, by the Gastineau Channel and the project site is approximately 15 kilometers (km) west of Juneau (figure 1).

BILLING CODE 3510-22-P?

EN29JN26.000

BILLING CODE 3510-22-C?

Detailed Description of the Specified Activity

Turnagain proposes to install temporary and permanent piles and components to support construction of two large-class cruise ship berths and associated infrastructure on Douglas Island. In-water construction would be completed in two phases (Phase I and Phase II) over 2 years and includes both onshore and offshore components. Phase I includes the north berth, north trestle, and part of the south trestle. Phase II is further described as Phase II South and Phase II North. Phase II South includes the remainder of the south trestle, south berth, and tour boat return dock. Phase II North includes the multi-use harbor, concrete boat launch, and offshore utilities.

Phase I

The main components of Phase I include the development of the north berth and trestle, as well as the start of the south trestle. The north berth would consist of a floating cruise ship dock with a small boat float, a 262-m long curved approach trestle, a transfer span, four mooring dolphins, two float restraint dolphins, and a series of connecting catwalks. Turnagain anticipates part of the south trestle would be installed during Phase I, depending on how construction progresses. In total, Phase I is expected to require installation of the following steel piles:

• Seventy-eight 36-inch (in) (91.4-centimeters (cm)) diameter temporary template piles to guide permanent piles into place (all template piles would subsequently be removed using vibratory methods);

• Sixty-six 36-in (91.4-cm) diameter permanent piles (six of these would be installed above the high tide line); and

• Twenty-eight 48-in (121.9-cm) diameter permanent piles.

Phase II South

Phase II South consists of the installation of the remaining components of the south trestle and installation of all south berth infrastructure. The south berth would serve as a cruise ship moorage and access to onshore facilities or commercial marine tours. This includes a floating cruise ship dock with small boat float, a 189-m long curved approach trestle, a transfer span, four mooring dolphins, two float restraint dolphins, and a series of connecting catwalks. These components of Phase II South are expected to require installation of the following steel piles:

• Thirty-four 36-in (91.4-cm) diameter temporary template piles (all template piles would subsequently be removed using vibratory methods);

• Forty-eight 36-in (91.4-cm) diameter permanent piles (15 of which would be installed above the high tide line); and

• Twenty-eight 48-in (121.9-cm) diameter permanent piles.

Additionally, during Phase II South, a tour boat return dock would be constructed to serve as a temporary tour boat moorage and as an access point to the onshore facilities for passengers returning from a commercial marine tour. These structures would also require the installation of the following steel piles:

• Twenty-three 36-in (91.4-cm) diameter temporary template piles (all template piles would subsequently be removed using vibratory methods); and

• Fifty-seven 36-in (91.4-cm) diameter permanent piles (nine of which would be installed above the high tide line).

Phase II North

In-water work for Phase II North consists of a multi-use harbor and a concrete boat launch. The multi-use harbor would consist of five connected floats, which would serve as a small boat harbor, seaplane base, and fuel dock for commercial tour boats and planes that use the site. The multi-use harbor would be accessed by a 170.7-m long approach trestle and a 30.5-m long transfer span. The concrete boat launch would require the development and installation of a pre-cast concrete plank and steel piles would be used to support a float for temporary moorage that would be positioned on top of the boat launch. These structures would require the installation of the following steel piles:

• Thirty 36-in (91.4-cm) diameter temporary template piles (all template piles would subsequently be removed using vibratory methods);

• Sixty 24-in (61-cm) diameter permanent piles;

• Forty-two 36-in (91.4-cm) diameter permanent piles (six of which would be installed above the high tide line); and

• Sixteen 24-in (61-cm) diameter permanent piles for the concrete boat launch.

Construction Equipment and Installation and Removal Approach

Turnagain proposes to utilize the following equipment for the installation and removal of piles to support the components and infrastructure development:

• A vibratory hammer (ICE 44B) with a static weight of 5,556.5 kg;

• A diesel impact hammer (Delmag D46) with maximum energy of 145,452.1 joules (J) of capability; and

• Three shaft drills:

1. NUMA Patriot 180 for 24-in (61-cm) piles;

2. MF34 for 36-in (91.4-cm) piles; and

3. Hyper 331 for 48-in (121.9-cm) piles.

All temporary template piles would be installed using a vibratory hammer and/or DTH driving then subsequently removed via vibratory methods. All permanent piles would be installed using any or all available methods of pile driving (
i.e.,
vibratory, impact, DTH), as dictated by engineering requirements and substrate conditions. The methodology used in Turnagain's application assumed that all three pile driving methods would be used for all permanent piles; however, not all three approaches may be necessary. In circumstances where all three methods are used, piles would first be vibrated into the seafloor substrate, then an impact hammer would be used to drive to tip elevation, and then a DTH hammer would be placed inside the piling and the shaft would be drilled into the bedrock. A summary of all piles proposed for removal and/or installation below the high tide line are included in tables 1-3. Take is not anticipated to occur from pile installation above the high tide line.

EN29JN26.001

EN29JN26.002

EN29JN26.003

Proposed mitigation, monitoring, and reporting measures are described in detail later in this document (please see Proposed Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

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

Table 4 lists all species or stocks for which take is likely 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 (
e.g.,
Carretta
et al.,
2026; Young
et al.,
2026). All values presented in table 4 are the most recent available at the time of publication and are available online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

EN29JN26.004

As indicated above, all 10 species (with 15 managed stocks) in table 4 temporally and spatially co-occur with the activity to the degree that take is likely to occur. All species that could potentially occur in the proposed

project area are included in table 10 of the application. While gray whales (
Eschrichtius robustus
), sperm whales (
Physeter macrocephalus
), and Pacific white-sided dolphins (
Lagenorhynchus obliquidens
) have been documented in the area, the temporal and/or spatial occurrence of these species is such that take is not expected to occur, and they are not discussed further. Gray whales and Pacific white-sided dolphins are considered to be very rare and sperm whales are considered to be rare in the project area. Take of these species has not been requested nor proposed to be authorized and these species are not considered further in this document.

In addition, the northern sea otter (
Enhydra lutris kenyoni
) can be found in Southeast Alaska; however, this species is managed by the U.S. Fish and Wildlife Service and is not considered further in this document.

Humpback whales are the most commonly observed baleen whale in Alaska and have been observed in Southeast Alaska in all months of the year (Baker
et al.,
1986). NMFS recognizes five stocks of humpback whales in the North Pacific: (1) the Central America/Southern Mexico-California-Oregon-Washington stock (found from Central America to the West Coast of the U.S. and includes the Central America DPS); (2) the Mainland Mexico-California-Oregon-Washington stock (found from Mexico to the West Coast of the U.S., Alaska, and Russia and includes the Mexico DPS); (3) the Hawaii stock (found from Hawaii to the West Coast of the U.S., Alaska, and Russia and includes the Hawaii DPS); (4) the Mexico-North Pacific stock (found from Mexico to the West Coast of the U.S. and includes the Mexico DPS); and (5) the Western North Pacific stock (found from Asia to Russia and Western Alaska/Bering Sea and includes the Western North Pacific DPS) (Young
et al.,
2026). In the project area, humpback whales are expected to be from the Hawaii stock and the Mexico-North Pacific stock. Humpback whales migrate to Southeast Alaska in spring to feed after months of fasting in equatorial breeding grounds in Hawaii and Mexico. Humpback whales found in the project area are predominantly members of the Hawaii DPS (98 percent probability in Southeast Alaska), which is not listed under the ESA; however, based on a comprehensive photo-identification study, members of the Mexico DPS, which is listed as threatened, have a small potential to occur in the project location (2 percent probability in Southeast Alaska) (Wade, 2021). Peak abundance of humpback whales in Southeast Alaska typically occurs during late summer to early fall. Most humpback whales begin returning to southern breeding grounds in fall or winter. However, due to temporal overlap between whales departing and returning, humpbacks can be found in Alaskan feeding grounds in every month of the year (Baker
et al.,
1985; Straley, 1990; Wynne and Witteveen, 2009). It is also common for some humpback whales to overwinter in areas of Southeast Alaska. It is thought that those humpbacks that remain in Southeast Alaska do so in response to the availability of winter schools of fish, such as herring (Straley, 1990).

Humpback whales are dependent on foraging resources in Southeast Alaska, and large portions of Southeast Alaska have been identified as biologically important areas (BIAs) for seasonal feeding due to the high density of animals, with the Lynn Canal and Stephens Passage a BIA for humpback whale feeding from April through October (Wild
et al.,
2023). In Stephens Passage, humpback whales are most often observed during seasons of high prey concentration, May through September (Witteveen
et al.,
2011); however, feeding humpback whales' presence in the Gulf of Alaska has also been correlated closely with peak abundance of Pacific herring (
Clupea pallasii
) during late fall and early winter. Most humpback whales migrate to other regions during winter to breed but over-wintering (non-breeding) humpback whales have been noted and may be increasingly common (Straley, 1990), and a few may skip migration altogether (Straley
et al.,
2018). Therefore, humpbacks may be present year-round in Stephens Passage, but are less common during the late winter and early spring. The project area is not located in or near designated critical habitat for threatened and endangered humpback whale DPSs.

Minke whales in Southeast Alaska are part of the Alaska stock (Muto
et al.,
2022). Dedicated surveys for cetaceans in Southeast Alaska found that minke whales were scattered throughout inland waters from Glacier Bay and Icy Strait to Clarence Strait, with small concentrations near the entrance of Glacier Bay. All sightings were of single minke whales, except for a single sighting of multiple minke whales. Surveys took place in spring, summer, and fall, and minke whales were present in low numbers in all seasons and years. No information appears to be available on the winter occurrence of minke whales in Southeast Alaska and Dahlheim
et al.
(2009) could not assess seasonality of minke whales' presence in the area due to low encounter rates; however, they were observed in Chatham Strait south of the project area.

Killer whales have been observed in all the world's oceans, but the highest densities occur in colder and more productive waters found at high latitudes. Killer whales occur along the entire Alaska coast, in British Columbia and Washington inland waterways, and along the outer coasts of Washington, Oregon, and California. There are three distinct ecotypes, or forms, of killer whales recognized: resident, transient, and offshore. The three ecotypes differ morphologically, ecologically, behaviorally, and genetically. In Southeast Alaska, two resident ecotypes (Alaska Resident and Northern Resident) range from the Aleutian Islands to Washington State and two transient populations (West Coast Transient and Gulf of Alaska, Aleutian Islands and Bering Sea Transient) are found from California to Southeast Alaska (Young
et al.,
2026; Myers
et al.,
2021). The Alaska Resident stock and the West Coast Transient stock are frequently seen in the project area while the Northern Resident stock and the Aleutian Islands and Bering Sea Transient stock are considered very rare in the project area.

Dall's porpoises are found throughout the North Pacific Ocean, from southern Japan to southern California and north to the Bering Sea. All Dall's porpoises in Alaska are members of the Alaska stock. This species can be found in offshore, inshore, and nearshore habitat, but prefers waters more than 183-m deep (Dahlheim
et al.,
2009; Jefferson, 2009). Dall's porpoises have been consistently observed in Lynn Canal, Stephens Passage, upper Chatham Strait, Frederick Sound, and Clarence Strait (Dalheim
et al.,
2000). Despite generalized water depth preferences, Dall's porpoises may occur in shallower waters. Moran
et al.
(2018) recently mapped Dall's porpoise distributions in bays, shallow water, and nearshore areas of Prince William Sound, habitats not typically utilized by this species. Jefferson
et al.
(2019) estimated the highest density of Dall's porpoise during summer months (31.6 individuals/100 km
2
).

Harbor porpoises from the Northern Southeast Alaska Inland Waters stock range from Cape Suckling to the Canada border (Muto
et al.,
2022). Harbor porpoises frequent primarily coastal waters in Southeast Alaska (Dalheim
et al.,
2009) and occur most frequently in waters less than 100-m deep (Hobbs and Waite, 2010). Harbor porpoises forage in waters less than 200-m deep on small pelagic schooling fish such as herring, cod, pollock, octopus, smelt, and

bottom-dwelling fish, occasionally feeding on squid and crustaceans (Bjørge and Tolley 2009; Wynne
et al.,
2011). Calving generally occurs from May to August, but can vary by region. Abundance data for harbor porpoises in Southeast Alaska were collected during 18 seasonal surveys spanning 22 years, from 1991 to 2012, and the density in Lynn Canal and Stephens Passage was estimated as 0.023 individuals/km
2
(Dahlheim
et al.,
2015). Zerbini
et al.
(2022) estimated harbor porpoise density in northern Southeast Alaska as 0.106 animals/km
2
.

California sea lions from the U.S. stock have been sighted in recent decades in Southeast Alaska and have been seen during all seasons but most often in spring (Valenzuela-Toro
et al.,
2023; Maniscalco
et al.,
2004). Male California sea lions disperse widely from their breeding rookeries in southern California to forage as far north as Canada (Carretta
et al.,
2022), with some individuals observed dispersing farther north. The U.S. stock of California sea lions have a wide range, typically from the border of the United States and Mexico. During the winter males commonly migrate to feeding grounds off California, Oregon, Washington, British Columbia and recently Southeast Alaska. There is an active unusual mortality event declared for the U.S. stock of California sea lions but this is mostly limited to southern California. Females and pups on the other hand stay close to breeding colonies until the pups have weened. The furthest north females have been observed is off the coast of Washington and Oregon during warm water years. California sea lions feed primarily offshore in coastal waters. California sea lion breeding areas are mostly in southern California and are not expected to spatially overlap with the project area. They have been observed co-located with Steller sea lions north of Douglas Island in Favorite Channel and Lynn Canal on Portland Island, Little Island, Benjamin Island, Faust Rock, and Poundstone Rock.

Northern fur seals occur from southern California north to the Bering Sea and west to the Sea of Okhotsk and Honshu Island, Japan. During the summer breeding season, most of the worldwide population is found on the Pribilof Islands (St. Paul Island and St. George Island) in the southern Bering Sea, with the remaining animals on rookeries in Russia, on Bogoslof Island in the southern Bering Sea, on San Miguel Island and the Farallon Islands in California (Muto
et al.,
2022). Northern fur seals feed on a variety of prey including, squid, walleye pollock, Pacific herring, and capelin (Diaz Gomez
et al.,
2015). While fur seals are rare in the project area, they have been spotted in this area during the winter. In January 2024, a fur seal was observed at the northern end of Lynn Canal for 7 days near the project site during the Skagway Ore Terminal Redevelopment project in Skagway, Alaska. Fur seals may only occur near the project area during their migration between the Pribilof Islands and California in the fall and spring. Since they are mostly solitary when out on the ocean, large groups are not expected near the project area.

Steller sea lions are found throughout the North Pacific Ocean, including coastal and inland waters from Russia (Kuril Islands and the Sea of Okhotsk), east to Alaska, and south to central California (Año Nuevo Island). Steller sea lions were listed as threatened range-wide under the ESA on November 26, 1990 (55 FR 49204, November 26, 1990); they were subsequently partitioned into the western and eastern DPSs, respectively, in 1997 (Allen and Angliss, 2010). The Eastern DPS remained classified as threatened (62 FR 24345, May 5, 1997) until it was delisted in November 2013, while the Western DPS (those individuals west of 144° W longitude or Cape Suckling, Alaska) was upgraded to endangered status following separation of the stocks, and it remains listed as endangered.

The majority of Steller sea lions that inhabit Southeast Alaska are part of the Eastern DPS; however, branded individuals from the Western DPS make regular movements across the 144° longitude boundary to the northern “mixing zone” haulouts and rookeries within Southeast Alaska (Jemison
et al.,
2013). While haulouts and rookeries in the northern portion of Southeast Alaska may be important areas for Western DPS animals, there continues to be little evidence that their regular range extends to the southern haulouts and rookeries in Southeast Alaska (Jemison
et al.,
2018). However, genetic data analyzed in Hastings
et al.
(2020) indicated that up to 1.4 percent of Steller sea lions near the project area may be members of the Western DPS, which NMFS recommends using in their 2020 guidance (Hastings
et al.,
2020; NMFS, 2020). There are several haulouts in Southeast Alaska but only one, Benjamin Island, has been documented near Stephens Passage in southern Lynn Canal. Local tour operators expressed that sea lions are frequently seen in the area and also frequently seen on a channel marker at the south end of Horse Island, located across Stephens Passage from the project area. The project area is not located in or near designated critical habitat for the Western DPS of Steller sea lions.

Harbor seals range from Baja California north along the west coasts of California, Oregon, Washington, British Columbia, and Southeast Alaska; west through the Gulf of Alaska, Prince William Sound, and the Aleutian Islands; and north in the Bering Sea to Cape Newenham and the Pribilof Islands. Harbor seals occur year-round in the inside passages of Southeast Alaska and are regularly sighted in Auke Bay. Harbor seals forage on fish and invertebrates (Orr
et al.,
2004) including capelin, eulachon, cod, pollock, flatfish, shrimp, octopus, and squid (Wynne, 2012). They are opportunistic feeders that forage in marine, estuarine, and occasionally freshwater habitat, adjusting their foraging behavior to take advantage of prey that are locally and seasonally abundant (Payne and Selzer, 1989). Research has demonstrated that harbor seals conduct both shallow and deep dives while foraging (Tollit
et al.,
1997), depending on prey availability. Harbor seals usually give birth to a single pup between May and mid-July; birthing locations are dispersed over several haulout sites and not confined to major rookeries (Klinkhart
et al.,
2008). Harbor seals haul out on rocks, reefs, beaches, and drifting glacial ice. They are non-migratory; their local movements are associated with tides, weather, season, food availability, and reproduction, as well as sex and age class (Swain
et al.,
1996; Lowry
et al.,
2001; Boveng
et al.,
2012). Harbor seals are commonly sighted in the waters of the inside passages throughout Southeast Alaska and there are two recorded haulouts near the project area at Horse Shoal (3.7 km away) and Scull Island (8.6 km away) where harbor seals are frequently seen (AFSC, 2024).

Northern elephant seals breed and give birth in California (U.S.) and Baja California (Mexico), primarily on offshore islands, from December to March (Stewart
et al.,
1993). Spatial segregation in foraging areas between males and females is evident from satellite tag data (Le Beouf
et al.,
2000). Males migrate to the Gulf of Alaska and western Aleutian Islands along the continental shelf to feed on benthic prey, while females migrate to pelagic areas in the Gulf of Alaska and the central North Pacific to feed on pelagic prey (Le Beouf
et al.,
2000). Breeding and important haulouts areas are not expected to spatially overlap with the project area but there has been an increase in sightings of around

Southeast Alaska in recent years, including in the Juneau area, with recent sightings near the project area.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of sound exposure, it is necessary to understand the frequency ranges marine mammals are able to hear. Because not all marine mammal species have equal hearing capabilities (
e.g.,
Southall
et al.,
2019; Erbe
et al.,
2025), NMFS divides marine mammals into hearing groups and identifies generalized hearing ranges for each group (table 5). For more information on how these hearing groups and ranges were derived, see the Updated Technical Guidance (NMFS, 2024).

EN29JN26.005

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 discusses how components of the specified activity may impact marine mammals and their habitat. The Estimated Take of Marine Mammals section 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 impact pile driving for installation, vibratory pile driving for installation and removal, and DTH systems. The effects of underwater noise from Turnagain's proposed activities have the potential to result in Level B harassment of marine mammals in the action area and, for some species/stocks as a result of certain proposed activities, Level A harassment.

The proposed activities include in the installation and/or removal of steel piles of varying diameters. There are a variety of types and degrees of effects to marine mammals, prey species, and habitat that could occur as a result of the proposed activities. Below we provide a brief description of the types of sound sources that would be generated by the project, the general impacts from these types of activities, and an analysis of the anticipated impacts on marine mammals from the project, 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 though exposure to sound include impact pile driving for installation, vibratory pile driving for removal and installation, and DTH. Impact hammers typically operate by repeatedly dropping and/or pushing a heavy piston onto a pile to drive the pile into substrate. Sound generated by impact hammers is impulsive, characterized by rapid rise times and high peak levels, a potentially injurious combination (Hastings and Popper, 2005). Vibratory hammers install piles by vibrating them and allowing the weight of the hammer to push them into substrate. Vibratory hammers typically produce less sound (
i.e.,
lower levels) than impact hammers. Peak sound pressure levels (SPLs) may be 180 dB or greater, but are generally 10-20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Oestman
et al.,
2009; California Department of Transportation, 2020). Sounds produced by vibratory hammers are non-impulsive; compared to sounds produced by impact hammers, the rise time is slower, reducing the probability and severity of injury, and the sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson
et al.,
2005).

DTH systems use a combination of percussive and drilling mechanisms to advance a hole into 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. A DTH system drills through bedrock using a rotating function like a standard drill, in concert with a hammering mechanism integrated into the system 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.

The sounds produced by the DTH system simultaneously contain both a continuous non-impulsive component from the drilling action and an

impulsive component from the hammering action. 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.

The likely or possible impacts of Turnagain's proposed activities on marine mammals could involve both non-acoustic and acoustic stressors. Potential non-acoustic stressors could result from the physical presence of the equipment and personnel; however, given the known pinniped haul-out sites are not in the immediate vicinity of the project area (located 3.7 and 8.6 km away from the project site), visual and other non-acoustic stressors would be limited, and any impacts to marine mammals are expected to primarily be acoustic in nature.

Potential Effects of Underwater Sound on Marine Mammals

The introduction of anthropogenic noise into the aquatic environment from impact pile driving, vibratory pile driving, and DTH is the primary means by which marine mammals may be harassed during the 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 sound from active acoustic sources can potentially result in one or more of the following: temporary or permanent hearing impairment, non-auditory physical or physiological effects, behavioral disturbance, stress, and masking (Richardson
et al.,
1995; Gordon
et al.,
2003; Nowacek
et al.,
2007; Southall
et al.,
2007; Götz
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, vibratory, and DTH driving are reasonably likely to result in such effects. Potential effects from impulsive sound sources can range in severity from effects such as behavioral disturbance or tactile perception to physical discomfort, slight injury of the internal organs and the auditory system, or mortality (Yelverton
et al.,
1973). Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to high level underwater sound or as a secondary effect of extreme behavioral reactions (
e.g.,
change in dive profile as a result of an avoidance reaction) caused by exposure to sound include neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage (Cox
et al.,
2006; Southall
et al.,
2007; Zimmer and Tyack, 2007; Tal
et al.,
2015). The proposed project activities considered here do not involve the use of devices, such as explosives or mid-frequency active sonar, that are associated with these types of effects.

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.,
2003; 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 Turnagain.

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 Turnagain proposes 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. 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 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
24
) in an accelerating fashion: at low exposures with lower SEL
24
, the amount of TTS is typically small and the growth curves have shallow slopes. At exposures with higher SEL
24
, 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. While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. For cetaceans, published data on the onset of TTS are limited to captive bottlenose dolphin (
Tursiops truncatus
), beluga whale (
Delphinapterus leucas
), harbor porpoise, and Yangtze finless porpoise (
Neophocoena asiaeorientalis
) (Southall
et al.,
2019). For pinnipeds in water, measurements of TTS are limited to harbor seals, elephant seals, bearded seals (
Erignathus barbatus
) and California sea lions (Kastak
et al.,
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 depends 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
24
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 to noise also has the potential to behaviorally disturb marine mammals response—in other words, not every response qualifies as behavioral disturbance, and for responses that do, those of a higher level, or accrued across

a longer duration, have the potential to affect foraging, reproduction, or survival. Behavioral disturbance may include a variety of effects, including subtle changes in behavior (
e.g.,
minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. 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 increase their haul out time, possibly to avoid in-water disturbance (Thorson and Reyff, 2006).

Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors (
e.g.,
species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (
e.g.,
Richardson
et al.,
1995; Wartzok
et al.,
2003; Southall
et al.,
2007, 2019; Weilgart, 2007; Archer
et al.,
2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison
et al.,
2012), and can vary depending on characteristics associated with the sound source (
e.g.,
whether it is moving or stationary, number of sources, distance from the source). 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.,
2003). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder
et al.,
2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure.

As noted 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.,
2003; 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). 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; 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). 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
et al.
(2016) reported significant effects on humpback whale foraging behavior in Stellwagen Bank in response to ship noise including slower descent rates, and fewer side-rolling events per dive with increasing ship 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; 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 re 1 μPa; SEL of a single strike (SEL
ss
): 127 dB re 1 μPa
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). Harbor porpoises, Atlantic white-sided dolphins (
Lagenorhynchus actusus
), 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; 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 stranding. 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.,
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 ship traffic in the Bay of Fundy was associated with decreased stress in North Atlantic right whales (
Eubalaena glacialis
). 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.

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 environments 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 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. The energy distribution of sound from vibratory pile driving 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 Turnagain's proposed activities will only occur intermittently, across an estimated total of 339 (not necessarily consecutive) days during the full 2-year authorization period covered by each IHA, if finalized, in a relatively small area focused around the proposed construction site. Thus, Turnagain'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 pinnipeds that are swimming or hauled out near the project site within the range of noise levels elevated above airborne acoustic harassment criteria. Although pinnipeds are known to haul-out regularly on man-made objects, we believe that incidents of take resulting solely from airborne sound are unlikely due to the proximity between the proposed project area and the known haul out sites (
e.g.,
3.7 km and 8.6 km away for harbor seals; 61 km for Steller sea lions). Cetaceans are not expected to be exposed to airborne sounds that would result in harassment as defined under the MMPA.

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

Potential Effects on Marine Mammal Habitat

Turnagain's proposed activities could have localized, temporary impacts on marine mammal habitat, including prey, by increasing in-water SPLs. Increased noise levels may affect the acoustic habitat (refer to masking discussion) and adversely affect marine mammal prey in the vicinity of near the project areas (see discussion below). During DTH, impact, and vibratory pile driving or removal, elevated underwater noise levels would ensonify the project areas where both fish 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 toon the individuals or populations.

In-Water Construction Effects on Potential Foraging Habitat

As previously mentioned, the project area in Southeast Alaska does not contain habitat of known importance other than being designated as a feeding BIA for humpback whales during the months of April through October (Wild
et al.,
2023). However, the designated area only represents a tiny segment of foraging habitat for humpback whales. Foraging BIAs for other species, such as the gray whale (second half of March through the first half of June) and sperm whale (April through September), do not spatially overlap with the project area and are found seaward in the Gulf of Alaska (Wild
et al.,
2023). No critical habitat is located within the project area and the project area is highly influenced by pre-existing and ongoing anthropogenic development and activities.

The total seafloor area likely to be impacted by Turnagain's activities is relatively small compared to the vast foraging area available habitat in Southeast Alaska. At best, the impact area provides marginal foraging habitat for marine mammals and fish. Furthermore, proposed pile driving for installation and removal at the project site would not be expected to obstruct the movement or migration of marine mammals.

A temporary and localized increase in turbidity near the seafloor would occur in the immediate area due to the area where piles are installed or removed. In general, turbidity associated with pile installation is localized to about a 7.6-m radius around the pile. The sediments of the project site would settle out rapidly when disturbed. Cetaceans are not expected to be close enough to the pile-driving areas to experience the effects of turbidity, and any pinnipeds could avoid localized turbid areas. Depending on the tidal stage, local strong currents are anticipated to disburse any additional suspended sediments produced by project activities at moderate to rapid rates. Therefore, we expect the impact from increased noise is turbidity levels to be discountable to marine mammals and do not discuss it further.

The potential for prey (
i.e.,
fish) to temporarily avoid the immediate area is also possible. The duration of fish and marine mammal avoidance of this area after pile driving 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 in the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity.

The proposed project will occur within the same footprint as existing marine infrastructure. The nearshore and intertidal habitat where the proposed project will occur is an area of relatively high marine vessel traffic. Most marine mammals do not generally use the area within the footprint of the project area. Temporary, intermittent, and short-term habitat alteration may result from increased noise levels during the proposed construction activities. Effects on marine mammals will be limited to temporary displacement from pile installation and removal noise, and effects on prey species will be similarly limited in time and space.

Temporary and localized reduction in water quality will occur as a result of in-water construction activities. Most of this effect would occur during the installation and removal of piles when seafloor sediments are disturbed. The installation and removal of piles would disturb seafloor 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.

Effects to turbidity and sedimentation are expected to be short-term, minor, and localized. Since there may be currents that are strong in the area, following the completion of sediment-disturbing activities, suspended sediments in the water column should dissipate and quickly return to background levels in all construction scenarios. Turbidity within the water column has the potential to reduce the level of oxygen in the water and irritate the gills of prey fish species in the proposed project area. However, turbidity plumes associated with the project would be temporary and localized, and fish in the proposed project area would be able to move away from and avoid the areas where plumes may occur. Therefore, it is expected that the impacts on prey fish species from turbidity, and therefore on marine mammals, would be minimal and temporary. In general, the area likely impacted by the proposed construction activities is relatively small compared to the available marine mammal habitat in Southeast Alaska.

Potential Effects on Prey

Sound may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species (
e.g.,
crustaceans, cephalopods, 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.,
Peña
et al.,
2013; Wardle
et al.,
2001; Jorgenson and Gyselman, 2009; Cott
et al.,
2012). More commonly, though, the impacts of noise on fishes are temporary.

SPLs of sufficient strength have been known to cause injury to fishes and fish mortality (summarized in Popper
et al.,
2014). However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen
et al.
(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).

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.,
2019). 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, rock hammering, and DTH excavation. Impact pile driving, vibratory pile driving, and DTH could 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. However, generally, the duration of impact pile driving would be limited to the final stage of installation (“proofing”) after the pile has been driven as close as practicable to the design depth with a vibratory driver (where necessary). In-water construction activities would only occur during daylight hours, allowing fish to forage and transit the project area in the evening.

Construction likely would have minimal permanent and temporary impacts on benthic invertebrate species, a marine mammal prey source. In addition, it should be noted that the area in question is low-quality habitat since it is already highly developed and experiences a high level of anthropogenic noise from normal operations and other vessel traffic.

There are several fish species near Juneau for which NMFS has identified Essential Fish Habitat (EFH), including: chinook salmon (

Oncorhynchus

tshawytscha

), chum salmon (
O. keta
), coho salmon (
O. kisutch
), pink salmon (
O. gorbuscha
), and sockeye salmon (
O. nerka
) in fresh and estuarine waters; and staghorn sculpin (
Leptocottus armatus
), sablefish (
Anoplopoma fimbria
), Pacific Ocean perch (
Sebastes alutus
), yelloweye rockfish (
S. ruberrimus
), shortraker rockfish (
S. borea
), rougheye rockfish (
S. aleutianus
), dusky rockfish (
S. ciliatus
), Pacific cod, starry flounder (
Platichthys stellatus
), yellowfin sole (
Pleuronectes asper
), and rock sole (
P. bilineatus
) (Federal Aviation Administration, 2005). Additionally there are various other “forage fish” in marine waters located near the project area. Many creeks and water bodies are presented in the area where these species made reside (
i.e.,
Duck Creek, Jordan Creek, Mendenhall River, Tidal Sloughs, Low Marsh, and High Marsh) (Federal Aviation Administration, 2005). Given the temporary nature of activities and the number of additional waterbodies in the area that present viable habitat, adverse effects on EFH in this area are not expected.

Potential Effects on Foraging Habitat

The proposed 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. 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 Turnagain's 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 Turnagain'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.

There are times of known seasonal marine mammal foraging in Southeast Alaska around fish processing/hatchery infrastructure or when fish are congregating, but the affected areas of Southeast Alaska are a small portion of the total foraging habitat available in the region. In general, effects on marine mammal prey species are expected to be minor and temporary due to the short timeframe of the project and the small project footprint.

Increased turbidity from construction activities can adversely affect forage fish and juvenile salmonid out-migratory routes in the project area. Both herring and salmon form a significant prey base for Steller sea lions, whereas herring is the primary prey species of humpback whales; both herring and salmon are components of the diet of many other marine mammal species that occur in the project area. Increased turbidity is expected to happen near construction activities. However, suspended sediments and particulates are expected to dissipate quickly within a single tidal cycle. Given the limited area affected and high tidal dilution rates, any effects on forage fish and salmon are expected to be minor or negligible. In addition, best management practices would be in effect, limiting the extent of turbidity to the immediate project area. Finally, exposure to turbid waters from construction activities is not expected to differ from the current exposure; fish of the disturbed area and marine mammals in the Southeast Alaska region are routinely exposed to substantial levels of suspended sediment from glacial sources.

In summary, given the temporary nature of the construction project and relatively small areas being affected, the DTH and pile driving installation and removal activities associated with the proposed action are not likely to have a permanent, adverse effect on any fish habitat or populations of fish species. The most likely impact to fishes at the project site would be temporary avoidance of the area. The most likely impact on fish from DTH and pile driving and removal activities at the project area would be temporary behavioral avoidance of the area. The duration of fish avoidance in this area after pile driving stops is unknown, but a rapid return to regular recruitment, distribution, and behavior is anticipated. Any behavioral avoidance by fish in disturbed areas would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity. Thus, we preliminarily conclude that the 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 the adverse effects on their populations.

Estimated Take of Marine Mammals

This section provides an estimate of the number of incidental takes proposed for authorization through the IHA, which will inform NMFS' consideration of “small numbers,” the negligible impact determinations, and impacts on subsistence uses.

Harassment is the only type of take expected to result from these activities. Except with respect to certain activities not pertinent here, section 3(18) of the MMPA defines “harassment” as any act of pursuit, torment, or annoyance, which (i) has the potential to injure a marine mammal or marine mammal stock in the wild (Level A harassment); or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering (Level B harassment).

Takes proposed for authorization would primarily be by Level B harassment, as use of the acoustic source/s (
i.e.,
impact pile driving, vibratory pile driving, and DTH drilling) 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, and phocids 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. 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).

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; Southall
et al.,
2021; Ellison
et al.,
2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS generally predicts that marine mammals are likely to be behaviorally harassed in a manner considered to be Level B harassment when exposed to underwater anthropogenic noise above root-mean-squared pressure received levels (RMS SPL) of 120 dB referenced to 1 microPascal (re 1 μPa) for continuous (
e.g.,
vibratory pile driving, drilling) and above RMS SPL 160 dB re 1 μPa for non-explosive impulsive (
e.g.,
seismic airguns) or intermittent (
e.g.,
scientific sonar) sources. Generally speaking, Level B harassment take estimates based on these behavioral harassment thresholds are expected to include any likely takes by TTS as, in most cases, the likelihood of TTS occurs at distances from the source less than those at which behavioral harassment is likely. TTS of a sufficient degree can manifest as behavioral harassment, as reduced hearing sensitivity and the potential reduced opportunities to detect important signals (conspecific communication, predators, prey) may result in changes in behavior patterns that would not otherwise occur.

Turnagain's proposed construction activities include the use of continuous (vibratory pile driving and DTH) and impulsive (impact pile driving and DTH) sources, and therefore, the RMS SPL thresholds of 120 and 160 dB re 1 μPa are applicable.

Level A Harassment

NMFS' Updated Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 3.0) (NMFS, 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). Turnagain's proposed activities includes the use of impulsive (impact pile driving and DTH) and non-impulsive (vibratory hammer and DTH) sources.

The 2024 Updated Technical Guidance criteria include both updated thresholds and updated weighting functions for each hearing group. The thresholds are provided in table 6. 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:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools.

BILLING CODE 3510-22-P

EN29JN26.006

Ensonified Area

Here, we describe operational and environmental parameters of the activity used to estimate the area ensonified above the acoustic thresholds, including source levels and transmission loss coefficient.

The sound field in the project area consists of existing background noise plus additional construction noise from the proposed project. Marine mammals are expected to be affected via sound generated by the primary components of the project (
i.e.,
impact, vibratory, DTH). The source levels assumed for both removal and installation activities are based on reviews of measurements of the same or similar types and dimensions available in the scientific literature and from similar coastal construction projects. The source levels for the piles and activities (
i.e.,
installation or removal and simultaneous pile driving scenarios) are presented in tables 7-8. A 5-dB reduction in source levels was applied to all 48-in proxy sound sources due to use of an unconfined bubble curtain during impact pile driving and DTH (see Proposed Mitigation section for further information).

EN29JN26.007

BILLING CODE 3510-22-C

EN29JN26.008

Transmission Loss (
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 seafloor composition and topography. The general formula for underwater
TL
is:

TL = B
×
Log10(R
1
/R
2
)
,

where:

TL
= transmission loss in dB,

B
= transmission loss coefficient,

R
1
= the distance of the modeled SPL from the driven pile, and

R
2
= the distance from the driven pile of the initial measurement.

This formula neglects loss due to scattering and absorption, which is assumed to be zero here. The degree to which underwater sound propagates away from a sound source depends on various factors, most notably the water

bathymetry and the presence or absence of reflective or absorptive conditions, including in-water structures and sediments. Spherical spreading occurs in a perfectly unobstructed (free-field) environment not limited by depth or water surface, resulting in a 6 dB reduction in sound level for each doubling of distance from the source (20*log[range]). Cylindrical spreading occurs in an environment in which sound propagation is bounded by the water surface and seafloor, resulting in a reduction of 3 dB in sound level for each doubling of distance from the source (10*log[range]). A practical spreading value of 15 is often used under conditions where water increases with depth as the receiver moves away from the shoreline, resulting in an expected propagation environment that would lie between spherical and cylindrical spreading loss conditions. Absent site-specific acoustical monitoring with differing measured
TL,
practical spreading is used. Site-specific
TL
data for Juneau is not available; therefore, the default coefficient of 15 is used to calculate the distances to the Level A and Level B harassment thresholds.

Assuming practicable spreading and other assumptions regarding the source characteristics and operational logistics (
e.g.,
source level, number of strikes per pile, number of piles per day), Turnagain calculated distances to the Level A harassment and Level B harassment thresholds and associated ensonified areas. Because an ensonified area associated with Level A harassment is more technically challenging to predict given the accounting for a cumulative energy component that changes over time, to assist applicants in assessing the potential for Level A harassment without the need for complex modeling, NMFS developed an optional User Spreadsheet tool to accompany the 2024 Updated Technical Guidance (see
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools
). This relatively simple tool can be used to calculate a Level A harassment isopleth distance for use in conjunction with marine mammal density or occurrence to help predict the amount of take that may occur incidental to an activity. 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 (
i.e.,
impact, vibratory, 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 are reported below in tables 9-11.

EN29JN26.009

EN29JN26.010

EN29JN26.011

Using the practical spreading model, NMFS determined that the underwater noise would yield the following calculated distances to the Level A harassment and Level B harassment

thresholds for marine mammals (tables 12-13).

EN29JN26.012

EN29JN26.013

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. Available information regarding marine mammal occurrence in the project area includes monitoring data, previous monitoring reports, and consultation with local researchers and marine professionals. Next, we describe how all of the information described above is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization. Occurrence probability estimates are based on approximations for each species and factor in historic data of occurrence, seasonality, and estimated group size in Stephens Passage. A summary of expected occurrence is shown in table 14 and group size is based on the best available published research for these species and their presence in the project area (see table 12 in the application for additional information).

EN29JN26.014

Minke whales are generally rare in Southeast Alaska, infrequently sighted in Stephens Passage, and are often observed as single individuals (Dahlheim
et al.,
2009). NMFS estimates that up to one group of one individual per month may occur within the Level A and Level B harassment zones.

Humpback whales found in the project areas are predominantly members of the Hawai'i DPS (98 percent probability), which is not listed under the ESA. However, based on a comprehensive photo-identification study, members of the Mexico DPS, which is listed as threatened under the ESA, have a small potential to occur (2 percent probability) (Wade, 2016). It is estimated that up to two groups of two individuals per day of either stock may occur, with a likelihood of no more than 1 group of two whales per week in the Level A harassment zone.

Killer whales occur along the entire coast of Alaska (Braham and Dahlheim, 1982), are often observed in inland waterways of Southeast Alaska, and four stocks may be present in the project area: 1) Alaska Resident; 2) Gulf of Alaska, Aleutian Islands, and Bering Sea Transient; 3) Northern Resident; and 4) West Coast Transient. Two groups of six

individuals per week from the resident stocks (Alaska Resident; Northern Resident) are expected to occur in the Level B harassment zone and one group of four individuals per week from the transient stocks (Gulf of Alaska, Aleutian Islands, and Bering Sea Transient; West Coast Transient) are expected to occur in the Level B harassment zone.

Dall's porpoises are frequently observed in Stephens Passage and NMFS estimates up to two groups of three individuals per week will occur in the Level B harassment zone and one group of three individuals per week will occur in the Level A harassment zone.

Harbor porpoises are observed almost daily during the summer near Colt and Horse Islands across Stephens Passage from the project site on Douglas Island. NMFS estimates up to two groups of two individuals per week will occur in the Level B harassment zone and one group of two individuals per week will occur in the Level A harassment zone.

Harbor seal are commonly seen on two haulouts near the project area: Horse Shoal approximately 3.7 km southwest of the project site and Scull Island approximately 8.6 km south of the project site. During a geotechnical study of the project site in September 2025, five harbor seals were recorded during 4 days of in-water work approximately 80-200 m from the proposed project location. NMFS estimates five groups of two individuals per day will occur in the Level B harassment zone and three groups of two individuals per week will occur in the Level A harassment zone.

Northern elephant seal males migrate from Baja California, Mexico, and California to the Gulf of Alaska and western Aleutian Islands along the continental shelf to feed on benthic prey, while females migrate to pelagic areas in the Gulf of Alaska and the central North Pacific to feed on pelagic prey (Le Beouf
et al.,
2000). NMFS estimates one group of one individual per month will occur in the Level B harassment zone and one group of one individual per month will occur in the Level A harassment zone.

Northern fur seals have been reported near Juneau in the winter and as far north as the northern end of Lynn Canal. Northern fur seals are rare in the project area but one lone animal was sighted swimming in the Gastineau Channel in 2019 and three were sighted in 2021 near Juneau. NMFS estimates one group of one individual per month will occur in the Level B harassment zone and one group of one individual per month will occur in the Level A harassment zone.

California sea lions are also rare in the project area but are known to co-locate with Steller sea lions at haulouts. During the winter males commonly migrate to feeding grounds off California, Oregon, Washington, British Columbia, and recently Southeast Alaska. NMFS estimates one group of one individual per month will occur in the Level B harassment zone and one group of one individual per month will occur in the Level A harassment zone.

Steller sea lions commonly occur in the project area and both the Western and Eastern DPSs may occur near Douglas Island, located in the Lynn Canal region delineated by Hastings
et al.
(2020). Based on these data, 1.4 percent of Steller sea lions are expected to be from the Western stock while 98.6 percent are expected to be from the Eastern stock, and it is estimated that up to five groups of one individual per day may occur, with a likelihood of no more than three groups per week in the Level A harassment zone.

Take Estimation

Here we describe how the information provided above is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization.

Based on the species-specific information, the expected occurrence (inclusive of group size and estimated frequency of presence) was multiplied by the number of days of each type of pile driving activities to determine the total take estimate. Turnagain does not yet have the operational details necessary to determine how many days of concurrent pile driving may occur, so group size, expected frequency of presence, and overall construction days (
i.e.,
assuming the maximum number of construction days as if no concurrent activities were planned) were used to estimate take incidental to that activity. Estimated take was calculated either daily or monthly, depending on the occurrence information available for each species, using the following formulas:

Estimated take (daily) = group size × groups per day × days of pile driving;
and

Estimated take (monthly) = group size × groups per month (i.e., 30-day period) × months of pile driving activity (i.e., number of days of pile driving activity/30 days))

The equation for daily estimated take was used for species whose occurrence was “common” and therefore had a daily occurrence estimate. The equation for monthly estimated take was used for all other species. Other factors, such as approximate group size, expected frequency of appearance, and overall number of construction days, were used in the calculation to determine the take proposed for authorization (table 15). While Turnagain primarily expects take by Level B harassment to occur, a small amount of take by Level A harassment is proposed for 9 species (11 stocks). Table 15 summarizes proposed amounts of take by both Level A and Level B harassment, as well as the percentage of each stock expected to be taken during both phases of the proposed activity.

BILLING CODE 3510-22-P

EN29JN26.015

BILLING CODE 3510-22-C
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 ITAs 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, as well as subsistence uses. 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 Turnagain in its adequate and complete application or are the result of subsequent coordination between NMFS and Turnagain. Turnagain 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, Turnagain would follow these general mitigation measures:

• Take proposed for authorization, by Level A and Level B harassment only, would be limited to the species and numbers listed in table 15. In-water piling activities would be required to be halted upon observation of either a species for which incidental take was not authorized or for a species for which incidental take has been authorized but the number of takes has been met, entering or is within the harassment zone, if the IHA is issued;

• The taking by serious injury or death of any of the species listed in table 15 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 amounts proposed for authorization, as listed in table 15, would be prohibited and would result in the modification, suspension, or revocation of the IHA, if issued;.

• Ensure that construction supervisors and crews, the marine mammal monitoring team, and relevant 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;

• Turnagain, construction supervisors and crews, PSOs, and relevant 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;

• Employ PSOs and establish monitoring locations as described in the Protected Species Monitoring and Mitigation Plan (PSMMP). Turnagain must monitor the project area to the maximum extent possible based on the required number of PSOs, required monitoring locations, and environmental conditions;

• Tur

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2026-13055. Public record. Not legal advice.