# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to U.S. Navy Maintenance and Pile Replacement Project in Puget Sound, Washington

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2024-07676

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** April 11, 2024
- **Citation:** 89 FR 25580

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XD681]
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to U.S. Navy Maintenance and Pile Replacement Project in Puget Sound, Washington

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 the United States Navy (Navy) for authorization to take marine mammals incidental to 2 years of construction activities associated with the Naval Facilities Engineering Command Northwest (NAVFAC NW) Maintenance and Pile Replacement (MPR) project in Puget Sound, Washington. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue two consecutive 1-year incidental harassment authorizations (IHAs) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-time, 1-year renewal that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorizations and agency responses will be summarized in the final notice of our decision.

DATES:

Comments and information must be received no later than May 13, 2024.

ADDRESSES:

Comments should be addressed to Jolie Harrison, Chief, Permits and Conservation Division, Office of Protected Resources, NMFS and should be submitted via email to
ITP.Fleming@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 above.

Instructions:
NMFS is not responsible for comments sent by any other method, to any other address or individual, or received after the end of the comment period. Comments, including all attachments, must not exceed a 25-megabyte file size. All comments received are a part of the public record and will generally be posted online at
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:

Kate Fleming, Office of Protected Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

The MMPA prohibits the “take” of marine mammals, with certain exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361
et seq.
) direct the Secretary of Commerce (as delegated to NMFS) to allow, upon request, the incidental, but not intentional, taking of small numbers of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region if certain findings are made and either regulations are proposed or, if the taking is limited to harassment, a notice of a proposed IHA is provided to the public for review.

Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s) and will not have an unmitigable adverse impact on the availability of the species or stock(s) for taking for subsistence uses (where relevant). Further, NMFS must prescribe the permissible methods of taking and other “means of effecting the least practicable adverse impact” on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stocks for taking for certain subsistence uses (referred to in shorthand as

“mitigation”); and requirements pertaining to the monitoring and reporting of the takings. The definitions of all applicable MMPA statutory terms cited above are included in the relevant sections below.

National Environmental Policy Act

To comply with the National Environmental Policy Act of 1969 (NEPA; 42 U.S.C. 4321
et seq.
) and NOAA Administrative Order (NAO) 216-6A, NMFS must review our proposed action (
i.e.,
the issuance of two consecutive 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.

We will review all comments submitted in response to this notice prior to concluding our NEPA process or making a final decision on the request for two consecutive IHAs.

Summary of Request

On October 5, 2023, NMFS received a request from the Navy for two consecutive 1-year IHAs to take marine mammals incidental to construction associated with the Navy's NAVFAC NW MPR project in Puget Sound, Washington. Following NMFS' review of the application, the Navy submitted a revised version on December 14, 2023, additional information on January 10, 2024, and the marine mammal monitoring plan on January 23, 2024. Final revisions to both the application and the marine mammal monitoring plan were provided on March 2, 2024. The application was deemed adequate and complete on February 27, 2024. The Navy's request is for take of 10 species of marine mammals by Level B harassment and, for harbor seal, Level B and Level A harassment. Neither the Navy nor NMFS expect serious injury or mortality to result from this activity. Therefore, IHAs are appropriate.

NMFS previously issued a regulation and associated Letters of Authorization to the Navy for related work (84 FR 15963, April 17, 2019;
https://www.fisheries.noaa.gov/action/incidental-take-authorization-us-navy-marine-structure-maintenance-and-pile-replacement-wa
). The Navy complied with all the requirements (
e.g.,
mitigation, monitoring, and reporting) of the previous LOAs, and information regarding their monitoring results may be found in the Effects of Specified Activities on Marine Mammals and Their Habitat.

Description of Proposed Activity

Overview

Maintaining existing wharfs and piers is vital to sustaining the Navy's mission and ensuring readiness. To ensure continuance of necessary missions at the four installations, the Navy must conduct annual maintenance and repair activities at existing marine waterfront structures, including removal and replacement of piles of various types and sizes. The Navy refers to this program as the Marine Structure MPR program.

The activities that have the potential to take marine mammals by Level A harassment and Level B harassment include installation and/or removal of timber, concrete, and steel piles by vibratory and impact pile driving and down-the hole (DTH) drilling. Construction would span the course of 2 years, with the first year beginning on July 15, 2024, and lasting through July 14, 2025. The second year of construction activities would begin July 15, 2025, and continue through July 14, 2026.

The Navy has requested the issuance of two consecutive IHAs in association with the two project years. Given the similarities in activities between project years, NMFS is issuing this single
Federal Register
notice to solicit public comments on the issuance of the two similar, but separate, IHAs.

Dates and Duration

The Navy anticipates that the planned NAVFAC NW MPR activities will occur over 2 years. The year 1 IHA would be valid from July 1, 2024-June 30, 2025, and the year 2 would span July 1, 2025-June 30, 2026. The specified activities would occur at any time during each project year, subject to existing time of year restrictions, or in-water work windows, designed to protect fish species listed under the U.S. Endangered Species Act (ESA). For Naval Base Kitsap (NBK) Bangor (located in Hood Canal), in-water work would occur from July 16 through January 15 each project year. At the remaining three facilities (located in Puget Sound), in-water work would occur from July 16 through February 15.

Days of pile driving at each site were based on the estimated work days using a slow production rate (
e.g.,
four-six piles per day for fender pile replacement). These conservative rates are the basis for estimates of total days at each facility each year (table 1, table 2). These totals include both extraction and installation of piles and represent a conservative estimate of pile driving days at each facility. In a real construction situation, pile driving production rates would be maximized when possible and actual daily production rates may be higher, resulting in fewer actual pile driving days.

Specific Geographic Region

The four installations are located within the inland waters of Washington State. One facility is located within Hood Canal, while the remainder are located within Puget Sound. See figure 1-1 of the Navy's application for a regional map and section 2 for full details regarding the specified geographical region. Puget Sound is one of the largest estuaries in the United States and is a place of great physical and ecological complexity and productivity. With nearly six million people (doubled since the 1960s), Puget Sound is also heavily influenced by human activity.

NBK Bangor serves as the Pacific homeport for the Navy's TRIDENT submarine squadron and other ships home-ported or moored at the installation and to maintain and operate administrative and personnel support facilities including security, berthing, messing, and recreational services. It is located on Hood Canal, a long, narrow, fjord-like basin of western Puget Sound (see figure 1-2 of the Navy's application). Oriented northeast to southwest, the portion of the canal from Admiralty Inlet to a large bend, called the Great Bend, at Skokomish, Washington, is 84 kilometers (km) (52 miles (mi)) long. East of the Great Bend, the canal extends an additional 24 km (15 mi) to Belfair. Throughout its 108-km (67 mi) length, the width of the canal varies from 1.6 to 3.2 km (1 to 2 mi) and exhibits strong depth/elevation gradients. Hood Canal is characterized by relatively steep sides and irregular seafloor topography. In northern Hood Canal, water depths in the center of the waterway near Admiralty Inlet vary between 91 and 128 meters (m) (300 and 420 feet (ft)). As the canal extends southwestward toward the Olympic Mountain Range and Thorndyke Bay, water depth decreases to approximately 49 m (160 ft) over a moraine deposit. This deposit forms a sill across the canal

in the vicinity of Thorndyke Bay, which limits seawater exchange with the rest of Puget Sound. The NBK Bangor waterfront occupies approximately 8 km (5 mi) of the shoreline within northern Hood Canal (1.7 percent of the entire Hood Canal coastline) and lies just south of the sill feature.

NBK Bremerton serves as the homeport for a nuclear aircraft carrier and other Navy vessels. It is located on the north side of Sinclair Inlet in southern Puget Sound (see figure 1-3 of the Navy's application). Sinclair Inlet is located off the main basin of Puget Sound and is about 6.9 km long and 1.9 km wide. The inlet is connected to the main basin through Port Orchard Narrows and Rich Passage. Another relatively narrow waterway, Port Washington Narrows, connects Sinclair Inlet to Dyes Inlet. In-water structures, shoreline fill, and erosion protection at NBK Bremerton have resulted in a shoreline geometry and character that is quite different from undisturbed shorelines in Puget Sound. Bathymetry near existing piers and in turning basins immediately offshore has been altered by significant dredging to accommodate aircraft carriers and other Navy vessels. Water depths range from 12 to 14 m (40 to 45 ft), increasing to 14 to 15 m (45 to 50 ft) in dredged berthing areas. West of the project sites, further into Sinclair Inlet, depths gradually decrease to less than 9 m (30 ft).

NBK Manchester provides bulk fuel and lubricant support to area Navy afloat and shore activities. It is located on Orchard Point, approximately 6.4 km (4 mi) due east of Bremerton. Please see figure 1-4 of the Navy's application. The installation is bounded by Clam Bay to the northwest, Rich Passage to the northeast, and Puget Sound to the east. NBK Manchester piers are located on the north side of Orchard Point and in a small embayment open on the south side of Orchard Point. In Clam Bay, the bathymetry is gently sloping with depths in the outer portions of the bay of approximately 5.5 m (18 ft) below mean lower low water (MLLW). Depths off Orchard Point drop off dramatically to 18 m (60 ft) below MLLW approximately 150 m (500 ft) from shore and 90 m (300 ft) below MLLW 1.6 km (1 m) offshore. Rich Passage is a shallow sill, less than 21 m (70 ft) deep.

Naval Station (NS) Everett provides homeport ship berthing, industrial support, and a Navy administrative center. It is located in Port Gardner Bay in Puget Sound's Whidbey Basin (see figure 1-5 of the Navy's application). To the west of the installation is the channelized mouth of the Snohomish River bounded by Jetty Island, which is composed of sediment from maintenance dredging and acts as a breakwater for the northwest area along the installation's waterfront. Jetty Island separates Port Gardner Bay and Possession Sound from the Snohomish River channel. The mouth of the Snohomish River channel is a historically industrialized area of highly modified shorelines and dredged waterways that forms a protected harbor within Port Gardner Bay. East of Jetty Island lies the Snohomish River estuary, consisting of a series of interconnected sloughs that flow through the lowlands east and north of the river's main channel. Water depths in Possession Sound range from about 9 m (30 ft) near the industrialized shoreline in Port Gardner to 180 m (600 ft) in mid-channel.

Detailed Description of the Specified Activity

The Navy plans to conduct maintenance and repair activities at marine waterfront structures at the four aforementioned installations within Puget Sound (Washington inland waters) and Hood Canal. Repairs would include replacing up to 150 structurally unsound piles with 164 concrete or steel piles over a 1-year period (July 2024 through July 2025) at NBK Bremerton and NBK Manchester using impact and vibratory pile driving and removal and DTH drilling; and replacing 130 structurally unsound piles over a 1-year period (July 2025-July 2026) at NBK Bremerton, NBK Bangor and NS Everett using impact and vibratory pile driving and removal.

Tables 1 and 2 provide a summary of pile types, sizes, and maximum numbers of piles at each installation to be replaced over the two 1-year MPR Program periods from July 2024-July 2025 and July 2025-July 2026, respectively. This estimate assumes all piles would be removed and replaced with new piles. However, existing piles may be repaired in place with no new piles installed and if replaced piles are larger than existing piles, typically fewer piles are needed. Therefore, estimates of replaced piles for each installation are a conservative overestimate. These estimates also include temporary (or “false work”) piles that may be required during construction. Actual numbers will depend on the number actually replaced and the size and type of new piles installed.

The MPR program includes pile repair, extraction, and installation, all of which may be accomplished through a variety of methods. However, only pile extraction and installation using vibratory and impact pile drivers and DTH drilling are expected to have the potential to result in incidental take of marine mammals. Pile repair methods include stubbing, wrapping, pile encapsulation, welding, or coating. These processes do not involve pile driving and are not expected to have the potential to result in incidental take of marine mammals. Pile removal may be accomplished via vibratory extraction or via mechanical methods such as cutting/chipping, clamshell removal, or direct pull. Four primary methods of pile installation would be used: water jetting, vibratory pile driving, impact pile driving, or DTH drilling. Noise levels produced through mechanical extraction activities and water jetting are not expected to exceed baseline levels produced by other routine activities and operations at the four facilities, and any elevated noise levels produced through these activities are expected to be intermittent, of short duration, and with low peak values. Therefore, only impact and vibratory pile driving, vibratory removal, and DTH drilling are carried forward for further analysis.

Vibratory hammers, which can be used to either install or extract a pile, contain a system of counter-rotating eccentric weights powered by hydraulic motors, and are designed in such a way that horizontal vibrations cancel out, while vertical vibrations are transmitted into the pile. The pile driving machine is lifted and positioned over the pile by means of an excavator or crane, and is fastened to the pile by a clamp and/or bolts. The vibrations produced cause liquefaction of the substrate surrounding the pile, enabling the pile to be extracted or driven into the ground using the weight of the pile plus the hammer. Impact hammers use a rising and falling piston to repeatedly strike a pile and drive it into the ground. DTH drilling is a common method used to drill holes through hard rock substrates. DTH drilling uses rotary cutting percussion action using a button bit. In DTH drilling, the drill pipe transmits the necessary feed force and rotation to the hammer and bit, along with the compressed air used to actuate the hammer and flush the cuttings.

Table 1—Pile Types and Maximum Anticipated Number To Be Replaced at Each Installation Between July 2024 and July 2025

Pile size/type
Method

Number of
piles

Estimated
piles per day

Days of
installation
or removal

NBK Bremerton (Pier C and Pier 5)

13-inch Timber
Removal, Vibratory or Pull
78
6 (up to 10)
30

24-in Concrete Octagonal
Installation, Impact
25
4

18-in x 18-inch square concrete
Installation, Impact
65
5

NBK Manchester (Fuel Pier)

26-in Steel
Removal, Pull or Cut
72
N/A
37

24-in Concrete
Installation, DTH or impact
74
1-2

Table 2—Pile Types and Maximum Anticipated Number To Be Replaced at Each Installation Between July 2025 and July 2026

Pile size/type
Method

Number of
piles

Estimated
piles per day

Days of
installation
or removal

NBK Bangor Marginal Wharf

36-inch Steel
Removal, Vibratory or Pull
78
4
36

Installation, Vibratory or Impact
78
4

NBK Bremerton (Pier F)

24-in Steel
Removal, Vibratory
48
1-6
24

Installation, Vibratory
48

NS Everett (Pier A)

12-in Steel
Removal, Vibratory or Cut
4
1-2
8

Installation, Vibratory or Impact
4
1-2

Between July 2024 and July 2025, the following activities are planned: (1) At NBK Bremerton, 25 13-inch (in) timber fender piles would be removed at Pier C using vibratory pile driving or pulling and replaced with 25 24-in concrete fender piles using impact pile driving. At the same installation, 53 13-in timber piles would be vibratory removed at Pier 5 and replaced with up to 65 18-in concrete piles using impact pile driving. Impact pile driving at Pier 5 may occur at the same time as vibratory pile driving at Pier C, though Pier 5 is shielded from Pier C pile driving sound by Dry Dock 6, which is a solid structure extending into Sinclair Inlet; and (2) At NBK Manchester a total of 72 26-in steel piles would be removed and replaced with 74 24-in concrete piles at the Fuel Pier. Concrete piles would be installed using DTH drilling in areas with bedrock while impact pile driving would be used if there is no bedrock.

Between July 2025 and July 2026, the following activities are planned: (1) Up to 78 steel fender piles (36-in) at NBK Bangor are anticipated to be removed by vibratory pile driving or cutting, and 78 steel fender piles (36-in) could be installed using vibratory pile driving with impact proofing at this same location; (2) A total of 48 24-in steel fender piles would be removed and replaced with 48 new 24-in steel fender piles using vibratory pile driving at NBK Bremerton, Pier F; and (3) At NS Everett a total of 4 12-in steel piles will be removed by vibratory pile driving or cutting and replaced with 4 12-in steel piles by vibratory or impact pile driving if necessary at Pier A.

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 3 lists all species or stocks for which take is expected and proposed to be authorized for both proposed IHAs, and summarizes information related to the population or stock, including regulatory status under the MMPA and 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 serious injury and mortality from anthropogenic sources are included here as gross indicators of the

status of the species or stocks and other threats.

Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Alaska and Pacific SARs. All values presented in table 3 are the most recent available at the time of publication (including from the draft 2023 SARs) and are available online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

Table 3—Marine Mammal Species
4
Likely To Be Affected by the Specified Activities

Common name
Scientific name
Stock

ESA/
MMPA status;
strategic

(Y/N)
1

Stock abundance

(CV, N
min
, most recent abundance survey)
2

PBR

Annual

M/SI
3

Order Artiodactyla—Cetacea—Mysticeti (baleen whales)

Family Eschrichtiidae:

Gray Whale

Eschrichtius robustus

Eastern N Pacific
-, -, N
26,960 (0.05, 25,849, 2016)
801
131

Family Balaenopteridae (rorquals):

Humpback Whale

Megaptera novaeangliae

Central America/Southern Mexico—CA/OR/WA
E, D, Y
1,494 (0.171, 1,284, 2021)
3.5
14.9

Mainland Mexico—CA/OR/WA
T, D, Y
3,477 (0.101, 3,185, 2018)
43
22

Hawai'i
-, -, N
11,278 (0.56, 7,265, 2020)
127
27.09

Minke Whale

Balaenoptera acutorostrata

CA/OR/WA
-, -, N
915 (0.792, 509, 2018)
4.1
0.19

Odontoceti (toothed whales, dolphins, and porpoises)

Family Delphinidae:

Killer Whale

Orcinus orca

Eastern North Pacific Southern Resident
E, D, Y
73 (N/A, 73, 2022)
0.13
0

West Coast Transient
-, -, N

349
5
(N/A, 349, 2018)

3.5
0.4

Family Phocoenidae (porpoises):

Dall's Porpoise

Phocoenoides dalli

CA/OR/WA
-, -, N
16,498 (0.61, 10,286, 2018)
99
≥0.66

Harbor Porpoise

Phocoena phocoena

Washington Inland Waters
-, -, N
11,233 (0.37, 8,308, 2015)
66
≥7.2

Order Carnivora—Pinnipedia

Family Otariidae (eared seals and sea lions):

CA Sea Lion

Zalophus californianus

U.S
-, -, N
257,606 (N/A, 233,515, 2014)
14,011
>321

Steller Sea Lion

Eumetopias jubatus

Eastern
-, -, N

36,308
6
(N/A, 36,308, 2022)

2,178
93.2

Family Phocidae (earless seals):

Harbor Seal

Phoca vitulina

Washington Inland Hood Canal
-, -, N
3,363 (0.16, 2,940, 2019)
88
2

Washington Northern Inland Waters
-, -, N
16,451 (0.07, 15,462, 2019)
928
40

Northern Elephant Seal

Mirounga angustirostris

CA Breeding
-, -, N
187,386 (N/A, 85,369, 2013)
5,122
13.7

1
ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.

2
NMFS marine mammal SARs online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region.
CV is coefficient of variation; N
min
is the minimum estimate of stock abundance.

3
These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (
e.g.,
commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range.

4
Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy (
https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/
).

5
Nest is based upon count of individuals identified from photo-ID catalogs in analysis of a subset of data from 1958-2018.

6
Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys. Estimates provided are for the U.S. only.

As indicated above, all 10 species (with 14 managed stocks) in table 3 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. All species that could potentially occur in the proposed project areas are included in table 3-1 of the application for two consecutive IHAs. While Pacific white-sided dolphin, bottlenose dolphin, long-beaked common dolphin, and Risso's dolphin have been documented in the Puget Sound, the temporal and/or spatial occurrence of these species is such that take is not expected to occur, and they are not discussed further beyond the explanation provided here. Additionally, the range of the southern Puget Sound stock of harbor seal does not overlap with the project area and the stock is not discussed further. These species are very rare in Puget Sound and are not expected to occur near any of the MPR installations.

In addition, the northern sea otter may be found in the Puget Sound area. However, northern sea otters are managed by the U.S. Fish and Wildlife Service and are not considered further in this document.

Gray Whale

Gray whales are observed in Washington inland waters in all months of the year, with peak numbers occurring from March through June (Calambokidis
et al.,
2010). Most whales sighted are part of a small regularly occurring group of 6 to 10 whales that use the northern Puget Sound as a springtime feeding area (Calambokidis
et al.,
2010; Calambokidis, 2017). Observed feeding areas are located in Saratoga Passage between Whidbey and Camano Islands including Crescent Harbor, and in Port Susan Bay located between Camano Island and the mainland north of Everett (Calambokidis
et al.,
2010). Gray whales that are not identified with the regularly occurring feeding group are occasionally sighted in Puget Sound. These whales are not associated with feeding areas and are often emaciated (WDFW, 2012).

In the waterways near NBK Bremerton (Rich Passage/Sinclair Inlet/Dyes Inlet/Agate Passage), 11 opportunistic sightings of gray whales were reported to the Orca Network (a public marine mammal sightings database) between 2003 and 2012. In October 2020, PSOs observed a gray whale near NBK Bangor during construction associated with a Pier Extension Project (DoN, 2021). PSOs were on site observing marine mammals for 99 days between July 2020 and January 2021 (DoN, 2021) and for 32 days between October 2021 and January 2022 (DoN, 2022). However, gray whales were not observed during monitoring efforts associated with other projects occurring at relevant Navy installations in Puget Sound. This includes two projects occurring at NBK Bangor: the Explosives Handling Wharf Pile Replacement Project (monitoring occurred on 14 days between August 2021 and October 2021) (Hamer Environmental, 2021), and the Service Pier B710 Pile Replacement Project (monitoring occurred on 4 days between December 2021 and January 2022) (Sandoval
et al.,
2022), and one project occurring at NBK Manchester in which PSOs monitored for 11 days between September and December 2021 for the Pier B213 Fender Replacement Project (Sandoval and Johnson, 2021).

There is a Biologically Important Area (BIA) for migrating gray whales in the inland waters of Puget Sound from January through July and October through December and for feeding gray whales between March and May (Calambokidis
et al.,
2015).

Between 2019 and 2023, there was an Unusual Mortality Event (UME) for gray whales occurring along the West Coast from Mexico through Alaska. While most of the strandings associated with this UME have been documented along Washington's Pacific coast, 14 gray whale strandings have been reported in inland waters between February and July, 2 of which were reported near NS Everett (May 2019 and April 2020); one at the mouth of Hood Canal (May 2019), and one near NBK Bremerton (March 2021). Additionally, a gray whale spent several weeks in Dyes Inlet near NBK Bremerton in April and May 2023 and subsequently stranded near Olympia, Washington in June of that year. Gray whales are rarely sighted in Hood Canal south of the Hood Canal Bridge, including a stranded whale at Belfair State Park (Orca Network, 2022).

Gray whales are expected to occur in the waters surrounding all four installations. However, gray whales are expected to occur primarily from March through June when in-water construction will not occur. Therefore, although some exposure to individual gray whales could occur at the four facilities, project timing will help to minimize potential exposures.

Humpback Whale

On September 8, 2016, NMFS divided the once single species into 14 distinct population segments (DPS) under the ESA, removed the species-level listing as endangered, and, in its place, listed four DPSs as endangered and one DPS as threatened (81 FR 62259, September 8, 2016). The remaining nine DPSs were not listed. There are four DPSs in the North Pacific, including Western North Pacific and Central America, which are listed as endangered, Mexico, which is listed as threatened, and Hawaii, which is not listed.

The 2022 Pacific SARs described a revised stock structure for humpback whales which modifies the previous stocks designated under the MMPA to align more closely with the ESA-designated DPSs (Caretta
et al.,
2023; Young
et al.,
2023). Specifically, the three previous North Pacific humpback whale stocks (Central and Western North Pacific stocks and a CA/OR/WA stock) were replaced by five stocks, largely corresponding with the ESA-designated DPSs. These include Western North Pacific and Hawaii stocks and a Central America/Southern Mexico-CA/OR/WA stock (which corresponds with the Central America DPS). The remaining two stocks, corresponding with the Mexico DPS, are the Mainland Mexico-CA/OR/WA and Mexico-North Pacific stocks (Caretta
et al.,
2023; Young
et al.,
2023). The former stock is expected to occur along the west coast from California to southern British Columbia, while the latter stock may occur across the Pacific, from northern British Columbia through the Gulf of Alaska and Aleutian Islands/Bering Sea region to Russia.

The Hawai'i stock consists of one demographically independent population (DIP)—Hawai'i—Southeast Alaska/Northern British Columbia DIP and one unit—Hawai'i—North Pacific unit, which may or may not be composed of multiple DIPs (Wade
et al.,
2021). The DIP and unit are managed as a single stock at this time, due to the lack of data available to separately assess them and lack of compelling conservation benefit to managing them separately (NMFS, 2023; NMFS, 2019; NMFS, 2022b). The DIP is delineated based on two strong lines of evidence: genetics and movement data (Wade
et al.,
2021). Whales in the Hawai'i—Southeast Alaska/Northern British Columbia DIP winter off Hawai'i and largely summer in Southeast Alaska and Northern British Columbia (Wade
et al.,
2021). The group of whales that migrate from Russia, western Alaska (Bering Sea and Aleutian Islands), and central Alaska (Gulf of Alaska excluding Southeast Alaska) to Hawai'i have been delineated as the Hawai'i-North Pacific unit (Wade
et al.,
2021). There are a small number of whales that migrate between Hawai'i and southern British Columbia/Washington, but current data and analyses do not provide a clear understanding of which unit these whales belong to (Wade
et al.,
2021) (Caretta
et al.,
2023; Young
et al.,
2023).

The Mexico—North Pacific unit is likely composed of multiple DIPs, based on movement data (Martien
et al.,
2021; Wade, 2021, Wade
et al.,
2021). However, because currently available data and analyses are not sufficient to delineate or assess DIPs within the unit, it was designated as a single stock (NMFS, 2023a; NMFS, 2019; NMFS, 2022c). Whales in this stock winter off Mexico and the Revillagigedo Archipelago and summer primarily in Alaska waters (Martien
et al.,
2021; Carretta
et al.,
2023; Young
et al.,
2023).

Within U.S. west coast waters, three current DPSs may occur: The Hawaii DPS (not listed), Mexico DPS (threatened), and Central America DPS (endangered). According to Wade
et al.
(2021), the probability that whales encountered in Washington waters are from a given DPS are as follows: Hawaii, 69 percent; Mexico (CA-OR-WA), 25 percent; Central America, 6 percent.

Humpback whales have been reported in the Puget Sound during every month in 2022 (Orca Network, 2023). Most humpback whale sightings reported since 2003 were in the main basin of Puget Sound with numerous sightings in the waters between Point No Point and Whidbey Island, Possession Sound, and southern Puget Sound in the vicinity of Point Defiance. Some of the reported sightings were in the vicinity of NS Everett and NBK Manchester. A few sightings of possible humpback whales were reported by Orca Network in the waters near NBK Bremerton and between January 2003 and December 2015. Humpback whales were sighted in the vicinity of Manette Bridge in Bremerton in March and May 2016, and May 2017 (Orca Network, 2017), and a carcass was found under a dock at NBK Bremerton in June 2016 (Cascadia Research, 2016).

In Hood Canal, single humpback whales were observed for several weeks in 2012 and in 2015 (Orca Network, 2022). Multiple sightings in Hood Canal were reported in June 2019, February through May 2020, and August 2021 (Orca Network, 2022). Prior to the 2012 sightings, there were no confirmed reports of humpback whales entering Hood Canal (Orca Network, 2022).

Humpback whales were not observed by protected species observers (PSOs) during monitoring completed for Navy construction projects at NBK Bangor (DoN, 2021; DoN, 2022; Hamer Environmental, 2021; Sandoval
et al.,
2022) and NBK Manchester (Sandoval and Johnson, 2021; Sandoval
et al.,
2022; Hamer Environmental, 2021). The number of humpback whales potentially present near any of the four naval installations over the project time period is expected to be low in any month.

Minke Whale

Sightings of minke whales in Puget Sound are infrequent, with approximately 14 opportunistic sightings recorded south of the Admiralty Inlet between 2005 and 2012, from March through October. In recent years (2022 and 2023), possible sightings of a single minke whale have been reported near NBK Bangor in September and October (the Orca Network 2022 and 2023), and in 2021 and 2022, a few minke whale sightings were reported south of Whidbey Island by the Pacific Whale Watch Association (Gless and Krieger, 2023). However, minke whales were not observed by PSOs during monitoring completed for Navy construction projects at NBK Bangor (DoN, 2021; DoN, 2022; Hamer Environmental, 2021; Sandoval
et al.,
2022) and NBK Manchester (Sandoval and Johnson, 2021; Sandoval
et al.,
2022; Hamer Environmental, 2021) and the number of minke whales potentially present near any of the four installations is expected to be very low in any month and even lower in winter months.

Killer Whale (Transient)

Groups of transient killer whales were observed for lengthy periods in Hood Canal in 2003 (59 days) and 2005 (172 days) (London, 2006), but were not observed again until 2016, when they were seen on a handful of days between March and May (including in Dabob Bay). Transient killer whales were observed by PSOs in December 2020 and December 2021 during construction at NBK Bangor (DoN, 2021; DoN, 2022). Transient killer whales have been seen infrequently near NBK Bremerton, including in Dyes Inlet and Sinclair Inlet (
e.g.,
sightings in 2010, 2013, 2015, 2022, and 2023) (Orca Network, 2023). Transient killer whales have occasionally been observed transiting through Rich Passage near NBK Manchester. In 2022, transient killer whales were observed in Possession Sound near NS Everett.

West Coast transient killer whales most often travel in small pods averaging four individuals (Baird and Dill, 1996); however, the most commonly observed group size in Puget Sound (waters east of Admiralty Inlet, including Hood Canal, through South Puget Sound and north to Skagit Bay) from 2004 to 2010 was 6 whales (Houghton
et al.,
2015). This is consistent with the mean group size of transient killer whales observed by PSOs during monitoring for year 1 of the service pier extension project at NBK Bangor in 2021 (DoN, 2021). Mean group size of killer whales observed at this site during year 2 was 5 (DoN, 2022). Transient killer whales were not observed by PSOs during monitoring completed for other Navy construction projects completed at NBK Bangor (Hamer Environmental, 2021; Sandoval
et al.,
2022) or NBK Manchester (Sandoval and Johnson, 2021; Sandoval
et al.,
2022; Hamer Environmental, 2021).

Killer Whale (Resident)

Southern Resident Killer Whales (SRKW) are expected to occur occasionally in the waters surrounding all of the installations except those in Hood Canal, where they have not been reported since 1995 (NMFS, 2006; 86 FR 41668, August 2, 2021). SRKW are rare near NBK Bremerton, with the last confirmed sighting in Dyes Inlet in 1997. Southern residents have been observed in Saratoga Passage and Possession Sound near NS Everett. SRKW were not observed by PSOs during construction activities occurring at NBK Manchester (Sandoval and Johnson, 2021) and NBK Bangor (DoN, 2021; DoN, 2022; Hamer Environmental, 2021; Sandoval
et al.,
2022).

The stock contains three pods (J, K, and L pods), with pod sizes ranging from approximately 16 (in K pod) to 34 (in L pod) individuals. Group sizes encountered can be smaller or larger if pods temporarily separate or join together.

Critical habitat for SRKW, designated pursuant to the ESA and revised in 2018 (80 FR 9366, March 5, 2018) includes three specific areas: (1) Summer core area in Haro Strait and waters around the San Juan Islands; (2) Puget Sound; and (3) Strait of Juan de Fuca. The primary constituent elements essential for conservation of the habitat are: (1) Water quality to support growth and development; (2) Prey species of sufficient quantity, quality, and availability to support individual growth, reproduction, and development, as well as overall population growth; and (3) Passage conditions to allow for migration, resting, and foraging. The Puget Sound segment of the designated critical habitat for SRKW is defined as the area south of the Deception Pass Bridge, west of the entrance to Admiralty Inlet, and north of the Hood Canal Bridge. Although the three naval installations that fall within this area are excluded from the area designated as Critical Habitat under the ESA, they do contain the aforementioned Primary Constituent Elements (PCEs). However, we note that water quality and habitat for prey species is generally degraded in the vicinity of these industrial environments relative to other areas contacting the PCEs that may be less impacted (see Effects of Specified Activities on Marine Mammals and Their Habitat section). SRKW have been observed in this area in all seasons but most occurrence here (especially the J pod) typically correlates with fall salmon runs (NMFS 2006).

Dall's Porpoise

Dall's porpoise are known to occur in Puget Sound, and have been sighted as far south as Carr Inlet in southern Puget Sound and as far north as Saratoga Passage, north of NS Everett (Nysewander
et al.,
2005; WDFW, 2008). Dall's porpoise could also occasionally occur in Hood Canal with the last observation in deeper water near NBK Bangor in 2008 (Tannenbaum
et al.,
2009). However, Dall's porpoise were not observed during vessel line-transect

surveys and other monitoring efforts completed in Hood Canal (including Dabob Bay) in 2011 (HDR, 2012). Dall's porpoises have not been documented in the Rich Passage to Agate Passage area in the vicinity of NBK Bremerton, but have been observed in Possession Sound near NS Everett (primarily during winter) (Nysewander
et al.,
2005; WDFW, 2008). Dall's porpoises could be present in waters in the vicinity of any of the installations considered here, and are considered more likely to occur during winter months than summer months in groups of up to 25 individuals. Dall's porpoise were not observed by PSOs during monitoring associated with construction activities at NBK Bangor (Hamer Environmental 2021, Sandoval
et al.,
2022; DoN, 2021; DoN 2022) and NBK Manchester (Sandoval and Johnson, 2021).

Harbor Porpoise

Sightings of harbor porpoise in Hood Canal north of the Hood Canal Bridge have increased in recent years (Evenson
et al.,
2016; Elliser
et al.,
2021; Rone
et al.,
2024). Across three seasons, Jefferson (2016) estimated 185 individuals in Hood Canal based on aerial surveys completed in 2013-2015, and less than a decade later, Rone's (2024) population estimates based on vessel based surveys completed in 2022-2023 in Hood Canal ranged from 308 individuals in the winter to 1,385 individuals in the fall. Mean group size of harbor porpoises for each survey season in the 2013-2016 aerial surveys was 1.7 (Smultea
et al.,
2017) and similarly, 1.6 individuals per group in Hood Canal during surveys completed in 2023 (Rone
et al.,
2024).

Information is available on harbor porpoise occurrence in Puget Sound (Navy, 2019; Smultea
et al.,
2022) and more recently some limited site-specific (within 500 meters) information is available for the Navy installations (DoN, 2021; DoN, 2022; Sandoval and Johnson, 2022).

PSOs associated with a service pier extension project at NBK Bangor monitored for 95 days between July 16, 2020 and January 13, 2021. Harbor porpoise were observed each month during the monitoring period, with peak numbers recorded in August. A total of 420 sightings of harbor porpoise groups were recorded during this time (DoN, 2021). The closest harbor porpoises came to the project site during pile driving operations was 75 m. Harbor porpoise were also observed during year 2 of this project, which took place on 32 days between October 19, 2021 and January 14, 2022. Groups of harbor porpoise were observed on 12 occasions in October, December and January (DoN, 2022); Sightings were estimated to be 8,000 m from the project site during pile driving operations. However, porpoise sightings were notably absent in a 21 square kilometers (km
2
) area adjacent to the NBK Bangor within the otherwise high-density region, during surveys completed to collect fine-scale marine mammal occurrence data in Hood Canal (Rone
et al.,
2024).

At NBK Manchester, a total of 17 harbor porpoise were detected by PSOs associated with a fender pile replacement project at Manchester Fuel Depot on 11 days between September 28, 2021 and December 10, 2021 (Sandoval and Johnson, 2022).

Finally, monitoring reports are not available for NS Everett, but according to the Navy's application, harbor porpoises have been observed infrequently at this installation. See IHA application).

California Sea Lion

California sea lions are typically present most of the year except for mid-June through July in Washington inland waters, with peak abundance between October and April (Navy, 2023). During summer months and associated breeding periods, the inland waters are not considered a high-use area by California sea lions, as they would be returning to rookeries in California waters. However, as described below, surveys at the naval installations indicate that a few individuals may remain year-round (Navy, 2023).

The Navy conducts surveys at its installations in Puget Sound that have sea lion haulouts. Specifically, California sea lion haul-outs occur at NBK Bangor, NBK Bremerton, and NS Everett (though California sea lions may haul out opportunistically at any location). California sea lions have been documented during shore-based surveys at NBK Bangor in Hood Canal since 2008 in all survey months, with as many as 320 individuals observed at one time (October 2018) hauled out on submarines at Delta Pier and on Port Security Barrier (PSB) floats (Navy, 2023). Additionally, California sea lions were observed consistently at NBK Bangor during Navy construction projects: 557 California Sea Lions were observed across 99 days between July 2020 and January 2021 (DoN, 2021); 57 were observed across 32 days between October 2021 and January 2022 (DoN, 2022); 44 California Sea Lions were observed across 14 days between August 2021 and October 2021 (Hamer Environmental, 2021); and 3 were observed across 4 days between December 2021 and January 2022, (Sandoval
et al.,
2022).

California sea lions have been documented on PSB floats during shore- and boat-based surveys at NBK Bremerton since 2010, with as many as 412 individuals hauled out at one time (October 2019) (Navy, 2023).

California sea lions have been documented during shore-based surveys at NS Everett from 2012 to 2022 in all survey months, with as many as 267 individuals hauled out at one time (April 2020) on PSB floats.

California sea lions haul out on floating platforms in Clam Bay approximately 0.5 mi (0.8 km) offshore from the Manchester Fuel Depot's finger pier, and approximately 13 km (8 mi) from NBK Bremerton. PSO's observed a total of 276 California Sea Lions at NBK Manchester across 11 monitoring days occurring between September and December 2021 (Sandoval and Johnson, 2021).

The Navy conducted surveys of sea lions on the floats from 2012 through 2016, and 2018 through 2022. In 2020, the surveys were expanded to include Orchard Rocks, a haulout approximately 0.8 mi (1.3 km) northeast of Manchester Fuel Depot that is available at lower tides. Between 2012 and 2016, California sea lions were observed in every survey month except July and August, with as many as 130 individuals present in one survey in October 2014. Aerial surveys were conducted by WDFW from March-April 2013, July-August 2013, November 2013, and February 2014. These surveys detected California sea lions on the floating platforms during all survey months except July, with up to 54 individuals present on one survey in November 2013. In 2018, the number of sea lions decreased corresponding to the removal of floats. Numbers subsequently increased following the reintroduction of floats in 2021. During this time, California sea lions were observed on the floating platforms during all survey months except July, with up to 212 individuals present on 1 survey in February 2022.

California sea lions are expected to be exposed to noise from project activities at NBK's Bangor, Bremerton, Manchester, and NS Everett because haul-outs are at these installations or nearby. Exposure is estimated to occur primarily from August through the end of the in-water work window in mid-January or mid-February.

Steller Sea Lion

Steller sea lions have been seasonally documented in shore-based surveys at NBK Bangor in Hood Canal since 2008

with a maximum of 21 individuals observed in November 2019 (Navy, 2023). Surveys at NBK Bangor indicate Steller sea lions begin arriving in September and depart by the end of May (Navy, 2023). Steller sea lions were not observed at NBK Bangor during construction occurring on 14 days between August and October 2021 (Hamer Environmental, 2021), on 4 construction days occurring between December and January 2022 (Sandoval, 2022), or on 32 construction days between October and January (DoN, 2022). However, 87 Steller sea lions were observed across 99 days between July and January 2021 (DoN, 2021).

Steller sea lions have not been detected during shore-based surveys at NBK Bremerton since the surveys were initiated in 2010 (Navy, 2023). A Steller sea lion was sighted on a float on the floating security barrier during a vessel survey in 2012 (Lance, 2012 personal communication) and others were detected during aerial surveys conducted by WDFW (Jeffries, 2000).

Steller sea lions haul out on floating platforms in Clam Bay approximately 0.5 mi (0.8 km) offshore from the NBK Manchester finger pier, and approximately 8 mi (13 km) from NBK Bremerton. The number of Steller sea lions in the vicinity of NBK Manchester is limited by the variable size and availability of floating platforms in Clam Bay. As discussed above, the Navy has conducted surveys of sea lions on the floats since November 2012; however, no surveys were conducted September 2013 through November 2013 and July 2017 through June 2018 (Navy, 2023). Steller sea lions were seen in all surveyed months except for June, July, and August with as many as 43 individuals present in September 2021.

Shore-based surveys conducted since July 2012 at NS Everett have rarely detected Steller sea lions. However, occasional observations have been reported from the PSB or in the Notch Basin, generally one at a time (Navy, 2023). Other than these detections on the installation's PSBs, the nearest known Steller sea lion haulout is 14 mi (23 km) away; therefore, Steller sea lions are expected to be a rare occurrence in waters off this installation during pile driving activities.

Harbor Seal

Harbor seals in Washington inland waters have been divided into three stocks: Hood Canal, Northern Inland Waters, and Southern Puget Sound. The range of the northern inland waters stock includes Puget Sound north of the Tacoma Narrows Bridge, the San Juan Islands, and the Strait of Juan de Fuca, while the southern Puget Sound stock range includes waters south of the Tacoma Narrows Bridge. Therefore, animals present at NBK Bremerton, NBK Manchester, and NS Everett are most likely to be from the northern inland waters stock, while those present at NBK Bangor are expected to be from the Hood Canal stock.

Harbor seals are expected to occur year-round at all installations with the greatest numbers expected at installations with nearby haulout sites. In Hood Canal, where NBK Bangor is located, known haulouts occur on the west side of Hood Canal at the mouth of the Dosewallips River and on the western and northern shorelines in Dabob Bay located approximately 8.1 mi (13 km) away. Vessel-based surveys conducted from 2007 to 2010 at NBK Bangor observed harbor seals in every month of surveys (Agness & Tannenbaum, 2009; Tannenbaum
et al.,
2009, 2011). Harbor seals were routinely seen during marine mammal monitoring for the Navy's recent construction projects at this site (Hamer Environmental, 2021; Sandoval
et al.,
2022; DoN, 2021; DoN, 2022). Small numbers of harbor seals have been documented hauling out opportunistically at NBK Bangor (
e.g.,
on the PSB floats, wavescreen at Carderock Pier, buoys, barges, marine vessels, and logs) and on man-made floating structures. The largest number of harbor seals observed in a single survey was 27 individuals in October 2018.

At NS Everett, Navy surveys were conducted regularly between 2012 and 2016, and again beginning in 2019, at which point surveys were expanded to include the entire East Waterway. The largest number of harbor seals observed in a single survey was 578 individuals in September 2019 (Navy, 2023). However, log rafts were removed from the East Waterway in the spring of 2022 and number of seals observed per survey has decreased. Harbor seals occupy the waters and haulout sites near NS Everett year-round. Harbor seal abundance is highest July through October. Mother pup pairs have been observed at NS Everett each summer since 2018, with a peak count of 96 pups observed in August 2021.

No haulouts have been identified at NBK Bremerton or Manchester. Single harbor seals have been observed swimming in these areas or hauled out on nearby rocks or on floats. The nearest documented haulouts to NBK Bremerton are across Sinclair Inlet, approximately 0.7 mi (1.1 km) away, and according to the Navy's application, is estimated to have less than 100 individuals (see IHA application). The nearest documented haulout to NBK Manchester is Orchard Rocks Conservation Area in Rich Passage, approximately 1.0 mi away. As discussed above, the Navy began surveying this area in June 2020, which has led to a dramatic increase in the number of harbor seals observed in proximity to Manchester Fuel Depot. A total of 25 harbor seals were observed by PSOs across 11 monitoring days occurring between September and December 2021 at this Naval installation (Sandoval and Johnson, 2021). The Navy has counted up to 153 harbor seals hauled-out and in the water near Orchard Rocks in June (Navy, 2023). Blakely Rocks is another known haulout in the vicinity of NBK Manchester, located approximately 3.5 mi away on the east side of Bainbridge Island. The haulout at Blakely Rocks is estimated to have less than 100 individuals (Jeffries, 2012 personal communication).

Northern Elephant Seal

No haul-outs occur in Puget Sound with the exception of individual elephant seals occasionally hauling out for two to four weeks to molt, usually during the spring and summer and typically on sandy beaches (Calambokidis and Baird, 1994). These animals are usually yearlings or subadults and their haul-out locations are unpredictable. One male subadult elephant seal was observed hauled out to molt at Manchester Fuel Depot in 2004 and a northern elephant seal was observed north of NBK Bangor in Hood Canal, from Kitsap Memorial Park in August 2020 (DoN, 2021). Northern elephant seals were not observed by PSOs during the Navy's other construction activities occurring at NBK Bangor (Hamer Environmental, 2021; Sandoval
et al.,
2022; DoN, 2021; DoN, 2022) or NBK Manchester (Sandoval and Johnson, 2021). Although regular haul-outs occur in the Strait of Juan de Fuca, the occurrence of elephant seals in Puget Sound is unpredictable and rare.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities (
e.g.,
Richardson
et al.,
1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall
et al.

(2007, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling,
etc.
). Note that no direct measurements of hearing ability have been successfully completed for mysticetes (
i.e.,
low-frequency cetaceans). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65 decibel (dB) threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall
et al.
(2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in table 4.

Table 4—Marine Mammal Hearing Groups
(NMFS, 2018)

Hearing group

Generalized
hearing range *

Low-frequency (LF) cetaceans (baleen whales)
7 Hz to 35 kHz.

Mid-frequency (MF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales)
150 Hz to 160 kHz.

High-frequency (HF) cetaceans (true porpoises,
Kogia,
river dolphins, Cephalorhynchid,
Lagenorhynchus cruciger
&
L. australis
)

275 Hz to 160 kHz.

Phocid pinnipeds (PW) (underwater) (true seals)
50 Hz to 86 kHz.

Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)
60 Hz to 39 kHz.

* Represents the generalized hearing range for the entire group as a composite (
i.e.,
all species within the group), where individual species' hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65 dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall
et al.,
2007) and PW pinniped (approximation).

The pinniped functional hearing group was modified from Southall
et al.
(2007) on the basis of data indicating that phocid species have consistently demonstrated an extended frequency range of hearing compared to otariids, especially in the higher frequency range (Hemilä
et al.,
2006; Kastelein
et al.,
2009; Reichmuth
et al.,
2013).

For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information.

Effects of Specified Activities on Marine Mammals and Their Habitat

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

Acoustic effects on marine mammals during the specified activity can occur from impact pile driving, and vibratory pile driving and removal in both years, and the use of DTH equipment in year 1 only. These effects may result in Level A or Level B harassment of marine mammals in the project area.

Description of Sound Sources

The marine soundscape is comprised of both ambient and anthropogenic sounds. Ambient sound is defined as the all-encompassing sound in a given place and is usually a composite of sound from many sources both near and far (American National Standards Institute (ANSI), 1995). The sound level of an area is defined by the total acoustical energy being generated by known and unknown sources. These sources may include physical (
e.g.,
waves, wind, precipitation, earthquakes, ice, atmospheric sound), biological (
e.g.,
sounds produced by marine mammals, fish, and invertebrates), and anthropogenic sound (
e.g.,
vessels, dredging, aircraft, construction).

The sum of the various natural and anthropogenic sound sources at any given location and time—which comprise “ambient” or “background” sound—depends not only on the source levels (as determined by current weather conditions and levels of biological and shipping activity) but also on the ability of sound to propagate through the environment. In turn, sound propagation is dependent on the spatially and temporally varying properties of the water column and sea floor, and is frequency-dependent. As a result of the dependence on a large number of varying factors, ambient sound levels can be expected to vary widely over both coarse and fine spatial and temporal scales. Sound levels at a given frequency and location can vary by 10 to 20 dB from day to day (Richardson
et al.,
1995). The result is that, depending on the source type and its intensity, sound from the specified activity may be a negligible addition to the local environment or could form a distinctive signal that may affect marine mammals.

In-water construction activities associated with the project would include impact pile driving, vibratory pile driving and removal, and use of DTH equipment (year 1 only). The sounds produced by these activities fall into one of two general sound types: Impulsive and non-impulsive. Impulsive sounds (
e.g.,
explosions, gunshots, sonic booms, impact pile driving) are typically transient, brief (less than 1 second), broadband, and consist of high peak sound pressure with rapid rise time and rapid decay (ANSI, 1986; National Institute of Occupational Safety and Health (NIOSH), 1998; NMFS, 2018). Non-impulsive sounds (
e.g.,
aircraft, machinery operations such as drilling or dredging, vibratory pile driving, and active sonar systems) can be broadband, narrowband or tonal, brief or prolonged (continuous or intermittent), and typically do not have the high peak sound pressure with rapid rise/decay time that impulsive sounds do (ANSI, 1995; NIOSH, 1998; NMFS, 2018). The distinction between these two sound types is important because they have differing potential to cause physical effects, particularly with regard to hearing (
e.g.,
Ward 1997 in Southall
et al.,
2007).

Three types of hammers would be used on this project: impact, vibratory, and DTH (year 1 only). Impact hammers

operate by repeatedly dropping and/or pushing a heavy piston onto a pile to drive the pile into the substrate. Sound generated by impact hammers is characterized by rapid rise times and high peak levels, a potentially injurious combination (Hastings and Popper, 2005). Vibratory hammers install piles by vibrating them and allowing the weight of the hammer to push them into the sediment. Vibratory hammers produce significantly less sound than impact hammers. Peak Sound Pressure Levels (SPLs) may be 180 dB or greater, but are generally 10 to 20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Oestman
et al.,
2009). Rise time is slower, reducing the probability and severity of injury, and sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson
et al.,
2005).

A DTH hammer is essentially a drill bit that drills through the bedrock using a rotating function like a normal drill, in concert with a hammering mechanism operated by a pneumatic (or sometimes hydraulic) component integrated into to the DTH hammer to increase speed of progress through the substrate (
i.e.,
it is similar to a “hammer drill” hand tool). The sounds produced by the DTH method contain both a continuous, non-impulsive component from the drilling action and an impulsive component from the hammering effect. Therefore, we treat DTH systems as both impulsive and continuous, non-impulsive sound source types simultaneously.

Acoustic Effects

The introduction of anthropogenic noise into the aquatic environment from pile driving and removal and DTH equipment is the primary means by which marine mammals may be harassed from the Navy's specified activities. In general, animals exposed to natural or anthropogenic sound may experience behavioral, physiological, and/or physical effects, ranging in magnitude from none to severe (Southall
et al.,
2007). Generally, exposure to pile driving and removal and DTH noise has the potential to result in behavioral reactions (
e.g.,
avoidance, temporary cessation of foraging and vocalizing, changes in dive behavior) and, in limited cases, auditory threshold shifts (TS). Exposure to anthropogenic noise can also lead to non-observable physiological responses such as an increase in stress hormones. Additional noise in a marine mammal's habitat can mask acoustic cues used by marine mammals to carry out daily functions such as communication and predator and prey detection. The effects of pile driving and removal and DTH noise on marine mammals are dependent on several factors, including but not limited to sound type (
e.g.,
impulsive vs. non-impulsive), the species, age and sex class (
e.g.,
adult male vs. mother with calf), duration of exposure, the distance between the pile and the animal, received levels, behavior at time of exposure, and previous history with exposure (Wartzok
et al.,
2003; Southall
et al.,
2007). Here we discuss physical auditory effects (TSs) followed by behavioral effects and potential impacts on habitat.

NMFS defines a noise-induced TS as a change, usually an increase, in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). The amount of TS is customarily expressed in dB. A TS can be permanent or temporary. As described in NMFS (2018), there are numerous factors to consider when examining the consequence of TS, including, but not limited to, the signal temporal pattern (
e.g.,
impulsive or non-impulsive), likelihood an individual would be exposed for a long enough duration or to a high enough level to induce a TS, the magnitude of the TS, time to recovery (seconds to minutes or hours to days), the frequency range of the exposure (
i.e.,
spectral content), the hearing and vocalization frequency range of the exposed species relative to the signal's frequency spectrum (
i.e.,
how animal uses sound within the frequency band of the signal;
e.g.,
Kastelein
et al.,
2014), and the overlap between the animal and the source (
e.g.,
spatial, temporal, and spectral).

Permanent Threshold Shift (PTS)
—NMFS defines PTS as a permanent, irreversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Available data from humans and other terrestrial mammals indicate that a 40 dB TS approximates PTS onset (Ward
et al.,
1958; Ward
et al.,
1959; Ward, 1960; Kryter
et al.,
1966; Miller, 1974; Henderson
et al.,
2008). PTS levels for marine mammals are estimates, because there are limited empirical data measuring PTS in marine mammals (
e.g.,
Kastak
et al.,
2008), largely due to the fact that, for various ethical reasons, experiments involving anthropogenic noise exposure at levels inducing PTS are not typically pursued or authorized (NMFS, 2018).

Temporary Threshold Shift (TTS)
—NMFS defines TTS as a temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Based on data from cetacean TTS measurements (Southall
et al.,
2007), a TTS of 6 dB is considered the minimum TS clearly larger than any day-to-day or session-to-session variation in a subject's normal hearing ability (Schlundt
et al.,
2000; Finneran
et al.,
2000; Finneran
et al.,
2002). As described in Finneran (2016), marine mammal studies have shown the amount of TTS increases with cumulative sound exposure level (SEL
cum
) in an accelerating fashion: At low exposures with lower SEL
cum,
the amount of TTS is typically small and the growth curves have shallow slopes. At exposures with higher SEL
cum,
the growth curves become steeper and approach linear relationships with the noise SEL.

Depending on the degree (elevation of threshold in dB), duration (
i.e.,
recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious (similar to those discussed in
Masking,
below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more serious impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall
et al.,
2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost.

Currently, TTS data only exist for four species of cetaceans (bottlenose dolphin (
Tursiops truncatus
), beluga whale (
Delphinapterus leucas
), harbor porpoise, and Yangtze finless porpoise (
Neophocoena asiaeorientalis
) and five species of pinnipeds exposed to a limited number of sound sources (
i.e.,
mostly tones and octave-band noise) in laboratory settings (Finneran, 2015). TTS was not observed in trained spotted (
Phoca largha
) and ringed (
Pusa hispida
) seals exposed to impulsive noise at levels matching previous predictions of TTS onset (Reichmuth
et al.,
2016). In general, harbor seals and

harbor porpoises have a lower TTS onset than other measured pinniped or cetacean species (Finneran, 2015). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species. No data are available on noise-induced hearing loss for mysticetes. For summaries of data on TTS in marine mammals or for further discussion of TTS onset thresholds, please see Southall
et al.
(2007), Finneran and Jenkins (2012), Finneran (2015), and table 5 in NMFS (2018).

Activities for this project include impact and vibratory pile driving, vibratory pile removal, and DTH drilling. There would likely be pauses in activities producing the sound during each day. Given these pauses and the fact that many marine mammals are likely moving through the project areas and not remaining for extended periods of time, the potential for TS declines.

Behavioral Effects
—Behavioral disturbance may include a variety of effects, including subtle changes in behavior (
e.g.,
minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Behavioral responses to sound are highly variable and context-specific, and any reactions depend on numerous intrinsic and extrinsic factors (
e.g.,
species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (
e.g.,
Richardson
et al.,
1995; Wartzok
et al.,
2003; Southall
et al.,
2007; Weilgart, 2007; Archer
et al.,
2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison
et al.,
2012), and can vary depending on characteristics associated with the sound source (
e.g.,
whether it is moving or stationary, number of sources, distance from the source). Please see Appendices B-C of Southall
et al.
(2007) for a review of studies involving marine mammal behavioral responses to sound.

Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok
et al.,
2003). 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). Animals are most likely to habituate to sounds that are predictable and unvarying. 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.

Available studies show wide variation in response to underwater sound; therefore, it is difficult to predict specifically how any given sound in a particular instance might affect marine mammals perceiving the signal. If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant (
e.g.,
Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 2005). However, there are broad categories of potential response, which we describe in greater detail here, that include alteration of dive behavior, alteration of foraging behavior, effects to breathing, interference with or alteration of vocalization, avoidance, and flight.

Changes in dive behavior can vary widely, and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive (
e.g.,
Frankel and Clark, 2000; Costa
et al.,
2003; Ng and Leung, 2003; Nowacek
et al.,
2004; Goldbogen
et al.,
2013). 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. 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; Melcón
et al.,
2012). In addition, behavioral state of the animal plays a role in the type and severity of a behavioral response, such as disruption to foraging (
e.g.,
Wensveen
et al.,
2017). An evaluation of whether foraging disruptions would be likely to incur fitness consequences considers temporal and spatial scale of the activity in the context of the available foraging habitat and, in more severe cases may necessitate consideration of 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 naturally varies with different behaviors, and variations in respiration 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 also have shown that species and signal characteristics are important factors in whether respiration rates are unaffected or change, 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.,
2005; Kastelein
et al.,
2006; Kastelein
et al.,
2018; Gailey
et al.,
2007; Isojunno
et al.,
2018).

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 (
Orcinus orca
) have been observed to increase the length of their songs (Miller
et al.,
2000; Fristrup
et al.,
2003; Foote
et al.,
2004), while 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; Rolland
et al.,
2012). In some cases, however, animals may cease or alter sound production in response to underwater sound (
e.g.,
Bowles
et al.,
1994; Castellote
et al.,
2012; Cerchio
et al.,
2014).

Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors, and is one of the most obvious manifestations of

disturbance in marine mammals (Richardson
et al.,
1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from airgun surveys (Malme
et al.,
1984). Often avoidance is temporary, and animals return to the area once the noise has ceased (
e.g.,
Bowles
et al.,
1994; Goold, 1996; Stone
et al.,
2000; Morton and Symonds, 2002; Gailey
et al.,
2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur (
e.g.,
Blackwell
et al.,
2004; Bejder
et al.,
2006; Teilmann
et al.,
2006).

A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response (
e.g.,
directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (Evans and England, 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response.

Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention (
i.e.,
when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been observed in marine mammals, but studies involving fish and terrestrial animals have shown that increased vigilance may substantially reduce feeding rates and efficiency (
e.g.,
Beauchamp and Livoreil, 1997; Fritz
et al.,
2002; Purser and Radford, 2011). In addition, chronic disturbance can cause population declines through reduction of fitness (
e.g.,
decline in body condition) and subsequent reduction in reproductive success, survival, or both (
e.g.,
Harrington and Veitch, 1992; Daan
et al.,
1996; Bradshaw
et al.,
1998).

Many animals perform vital functions, such as feeding, resting, traveling, and socializing, on a diel cycle (24-hour cycle). Disruption of such functions resulting from reactions to stressors such as sound exposure are more likely to be significant if they last more than one diel cycle or recur on subsequent days (Southall
et al.,
2007). Consequently, a behavioral response lasting less than 1 day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall
et al.,
2007). Note that there is a difference between multi-day substantive behavioral reactions and multi-day anthropogenic activities. For example, just because an activity lasts for multiple days does not necessarily mean that individual animals are either exposed to activity-related stressors for multiple days or, further, exposed in a manner resulting in sustained multi-day substantive behavioral responses.

To assess the strength of behavioral changes and responses to external sounds and SPLs associated with changes in behavior, Southall
et al.
(2007) developed and utilized a severity scale, which is a 10-point scale ranging from no effect (labeled 0), effects not likely to influence vital rates (low; labeled from 1 to 3), effects that could affect vital rates (moderate; labeled from 4 to 6), to effects that were thought likely to influence vital rates (high; labeled from seven to nine). Southall
et al.
(2021) updated the severity scale by integrating behavioral context (
i.e.,
survival, reproduction, and foraging) into severity assessment. For non-impulsive sounds (
i.e.,
similar to the sources used during the proposed action), data suggest that exposures of pinnipeds to sources between 90 and 140 dB (referenced to 1 micropascal (re 1 μPa)) do not elicit strong behavioral responses; no data were available for exposures at higher received levels for Southall
et al.
(2007) to include in the severity scale analysis. Reactions of harbor seals were the only available data for which the responses could be ranked on the severity scale. For reactions that were recorded, the majority (17 of 18 individuals/groups) were ranked on the severity scale as a 4 (defined as moderate change in movement, brief shift in group distribution, or moderate change in vocal behavior) or lower. The remaining response was ranked as a six (defined as minor or moderate avoidance of the sound source).

The Navy documented marine mammals during construction activities at NBK Manchester (September 28 and December 10, 2021) and NBK Bangor (2021 and 2022) during work that preceded these proposed IHAs as well as during the installation of a service pier. Harbor seals were consistently the most frequently observed marine mammal in the area observed by PSOs. During pile driving activities at these installations, harbor seals were most commonly observed typically traveling and swimming, though some behaviors recorded during pile driving activities indicated that harbor seals were aware of the construction, such as less foraging reported and looking at the construction site or startling. Likewise California sea lions were observed traveling and swimming during pile driving activities, but in a couple instances were observed porpoising or breaching. Harbor porpoises were observed traveling, milling, porpoising and a gray whale was observed slow and fast traveling and milling. At NBK Bangor, a total of three harbor seals were observed foraging, socializing, feeding (when fish kills were apparent) during impact pile driving. Behavior changes noted during pile driving included startle responses, splashing, swimming in circles, re-entering water after being hauled out and looking in all directions and swimming fast.

Stress responses
—An animal's perception of a threat may be sufficient to trigger stress responses consisting of some combination of behavioral responses, autonomic nervous system responses, neuroendocrine responses, or immune responses (
e.g.,
Seyle, 1950; Moberg, 2000). In many cases, an animal's first and sometimes most economical (in terms of energetic costs) response is behavioral avoidance of the potential stressor. Autonomic nervous system responses to stress typically involve changes in heart rate, blood pressure, and gastrointestinal activity. These responses have a relatively short duration and may or may not have a significant long-term effect on an animal's fitness. Neuroendocrine stress responses often involve the hypothalamus-pituitary-adrenal system. Virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction, altered metabolism, reduced immune competence, and behavioral disturbance (
e.g.,
Moberg, 1987; Blecha, 2000). Increases in the circulation of glucocorticoids are also equated with stress (Romano
et al.,
2004).

The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and “distress” is the cost of the response. During a stress response, an animal uses

glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose serious fitness consequences. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other functions. This state of distress will last until the animal replenishes its energetic reserves sufficient to restore normal function.

Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses are well-studied through controlled experiments and for both laboratory and free-ranging animals (
e.g.,
Holberton
et al.,
1996; Hood
et al.,
1998; Jessop
et al.,
2003; Krausman
et al.,
2004; Lankford
et al.,
2005). Stress responses due to exposure to anthropogenic sounds or other stressors and their effects on marine mammals have also been reviewed (Fair and Becker, 2000; Romano
et al.,
2002b) and, more rarely, studied in wild populations (
e.g.,
Romano
et al.,
2002a). For example, Rolland
et al.
(2012) found that noise reduction from reduced ship traffic in the Bay of Fundy was associated with decreased stress in North Atlantic right whales. These and other studies lead to a reasonable expectation that some marine mammals will experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress.” In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2003).

Auditory Masking
—Sound can disrupt behavior through masking, or interfering with, an animal's ability to detect, recognize, or discriminate between acoustic signals of interest (
e.g.,
those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson
et al.,
1995). Masking occurs when the receipt of a sound is interfered with by another coincident sound at similar frequencies and at similar or higher intensity, and may occur whether the sound is natural (
e.g.,
snapping shrimp, wind, waves, precipitation) or anthropogenic (
e.g.,
pile driving, shipping, sonar, seismic exploration) in origin. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest (
e.g.,
signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities (
e.g.,
sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions. Masking of natural sounds can result when human activities produce high levels of background sound at frequencies important to marine mammals. Conversely, if the background level of underwater sound is high (
e.g.,
on a day with strong wind and high waves), an anthropogenic sound source would not be detectable as far away as would be possible under quieter conditions and would itself be masked.

Airborne Acoustic Effects
—Pinnipeds that occur near the project site could be exposed to airborne sounds associated with pile driving and removal that have the potential to cause behavioral harassment, depending on their distance from pile driving activities. Cetaceans are not expected to be exposed to airborne sounds that would result in harassment as defined under the MMPA. 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 the acoustic criteria. We recognize that pinnipeds in the water could be exposed to airborne sound that may result in behavioral harassment when looking with their heads above water. Most likely, airborne sound would cause behavioral responses similar to those discussed above in relation to underwater sound. For instance, anthropogenic sound could cause hauled out pinnipeds to exhibit changes in their normal behavior, such as reduction in vocalizations, or cause them to temporarily abandon the area and move further from the source. However, these animals would likely previously have been `taken' because of exposure to underwater sound above the behavioral harassment thresholds, which are generally 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 additional incidental take resulting from airborne sound for pinnipeds is warranted, and airborne sound is not discussed further.

Anticipated Effects on Marine Mammal Habitat

The Navy's construction activities could have localized, temporary impacts on marine mammal habitat and their prey by increasing in-water sound pressure levels and slightly decreasing water quality. Increased noise levels may affect acoustic habitat (see masking discussion above) and adversely affect marine mammal prey in the vicinity of the project areas (see discussion below). During DTH, impact and vibratory pile driving or removal, elevated levels of underwater noise would ensonify a portion of Puget Sound (Year 1 and Year 2) and Hood Canal (Year 2 only) where both fishes and mammals occur and could affect foraging success. Additionally, marine mammals may avoid the area during construction, however, displacement due to noise is expected to be temporary and is not expected to result in long-term effects to the individuals or populations. Construction activities are of short duration and would likely have temporary impacts on marine mammal habitat through increases in underwater sound.

A temporary and localized increase in turbidity near the seafloor would occur in the immediate area surrounding the area where piles are installed and removed. In general, turbidity associated with the pile installation is localized to about 25-ft (7.6 m) radius around the pile (Everitt
et al.,
1980). Cetaceans are not expected to be close enough to the project pile driving areas to experience effects of turbidity, and pinnipeds could avoid localized areas of turbidity. Therefore, the impact from increased turbidity levels is expected to be minimal for marine mammals. Furthermore, pile driving and removal at the project site would not obstruct movements or migration of marine mammals.

In-Water Construction Effects on Potential Foraging Habitat
—The areas likely impacted by the project are relatively small compared to the available habitat in Puget Sound (Year 1 and Year 2) and Hood Canal (Year 2 only). The total seafloor area affected by pile installation and removal is a small area compared to the vast foraging area available to marine mammals in the area. At best, the impacted areas provide marginal foraging habitat for marine mammals and fishes. Furthermore, pile driving and removal at the project site would not obstruct long-term movements or migration of marine mammals.

Avoidance by potential prey (
i.e.,
fish or, in the case of transient killer whales, other marine mammals) of the immediate area due to the temporary loss of this foraging habitat 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 disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity.

Effects on Potential Prey
—Construction activities would produce continuous (
i.e.,
vibratory pile driving and DTH drilling) and intermittent (
i.e.,
impact driving and DTH drilling) sounds. Sound may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species (
e.g.,
crustaceans, cephalopods, fish, zooplankton). Marine mammal prey varies by species, season, and location. Here, we describe studies regarding the effects of noise on known marine mammal prey.

Fish utilize the soundscape and components of sound in their environment to perform important functions such as foraging, predator avoidance, mating, and spawning (
e.g.,
Zelick and Mann, 1999; Fay, 2009). Depending on their hearing anatomy and peripheral sensory structures, which vary among species, fishes hear sounds using pressure and particle motion sensitivity capabilities and detect the motion of surrounding water (Fay
et al.,
2008). The potential effects of noise on fishes depends on the overlapping frequency range, distance from the sound source, water depth of exposure, and species-specific hearing sensitivity, anatomy, and physiology. Key impacts to fishes may include behavioral responses, hearing damage, barotrauma (pressure-related injuries), and mortality.

Fish react to sounds that are especially strong and/or intermittent low-frequency sounds, 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 fish; several are based on studies in support of large, multiyear bridge construction projects (
e.g.,
Scholik and Yan, 2001; Scholik and Yan, 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.,
Pena
et al.,
2013; Wardle
et al.,
2001; Jorgenson and Gyselman, 2009).

SPLs of sufficient strength have been known to cause injury to fish and fish mortality. However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen
et al.
(2012a) showed that a TTS of 4 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.,
2012b; Casper
et al.,
2013).

The most likely impact to fishes from pile driving activities at the project area would be temporary behavioral avoidance of the area. The duration of fish avoidance of this area after pile driving stops is unknown, but a rapid return to normal recruitment, distribution, and behavior is anticipated. In general, impacts to marine mammal prey species are expected to be minor and temporary due to the expected short daily duration of individual pile driving events and the relatively small areas being affected. It is also not expected that the industrial environment of the Navy installations provides important fish habitat or harbors significant amount of forage fish.

The area likely impacted by the activities is relatively small compared to the available habitat in inland waters in the region. 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 Navy 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. Effects to habitat will not be discussed further in this document.

Estimated Take

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

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

Authorized takes would primarily be by Level B harassment, as use of the acoustic sources (
i.e.,
impact and vibratory pile driving and removal and DTH drilling) has the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for auditory injury (Level A harassment) to result, primarily for phocids because predicted auditory injury zones are larger than for mid-frequency cetacean species and/or otariids, and they can be difficult to detect. Auditory injury is unlikely to occur for mid, low, and high-frequency cetacean species and otariids. The proposed mitigation and monitoring measures are expected to minimize the severity of the taking to the extent practicable.

As described previously, no serious injury or mortality is anticipated or proposed to be authorized for this activity. Below we describe how the proposed take numbers are estimated.

For acoustic impacts, generally speaking, we estimate take by considering: (1) acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and (4) the number of days of activities. We note that while these factors can contribute to a basic calculation to provide an initial prediction of potential takes, additional information that can qualitatively inform take estimates is also sometimes available (
e.g.,
previous monitoring results or average group size). Below, we describe the factors considered here in more detail and present the proposed take estimates.

Acoustic Thresholds

NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur PTS of some degree (equated to Level A harassment).

Level B Harassment
—Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context (
e.g.,
frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment (
e.g.,
bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict (
e.g.,
Southall
et al.,
2007, 2021; Ellison
et al.,
2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS generally predicts that marine mammals are likely to be behaviorally harassed in a manner considered to be Level B harassment when exposed to underwater anthropogenic noise above root-mean-squared pressure received levels (c) of 120 dB (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.

The Navy's proposed activity includes the use of continuous (vibratory pile driving and removal and DTH drilling) and impulsive (impact pile driving and DTH drilling) sources, and therefore the RMS SPL thresholds of 120 and 160 dB re 1 μPa is applicable, respectively.

Level A harassment
—NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) (Technical Guidance, 2018) identifies dual criteria to assess auditory injury (Level A harassment) to five different marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). The Navy's proposed activity includes the use of impulsive (impact pile driving and DTH drilling) and non-impulsive (vibratory pile driving and removal) sources.

These thresholds are provided in the table below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS' 2018 Technical Guidance, which may be accessed at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

Table 5—Thresholds Identifying the Onset of Permanent Threshold Shift

Hearing group

PTS onset acoustic thresholds *
(received level)

Impulsive
Non-impulsive

Low-Frequency (LF) Cetaceans

Cell 1:

L
pk,flat
:
219 dB;
L
E,LF,24h
:
183 dB

Cell 2:

L
E,LF,24h
:
199 dB.

Mid-Frequency (MF) Cetaceans

Cell 3:

L
pk,flat
:
230 dB;
L
E,MF,24h
:
185 dB

Cell 4:

L
E,MF,24h
:
198 dB.

High-Frequency (HF) Cetaceans

Cell 5:

L
pk,flat
:
202 dB;
L
E,HF,24h
:
155 dB

Cell 6:

L
E,HF,24h
:
173 dB.

Phocid Pinnipeds (PW)(Underwater)

Cell 7:

L
pk,flat
:
218 dB;
L
E,PW,24h
:
185 dB

Cell 8:

L
E,PW,24h
:
201 dB.

Otariid Pinnipeds (OW)(Underwater)

Cell 9:

L
pk,flat
:
232 dB;
L
E,OW,24h
:
203 dB

Cell 10:

L
E,OW,24h
:
219 dB.

* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive sounds, these thresholds should also be considered.

Note:
Peak sound pressure (
L
pk
) has a reference value of 1 μPa, and SEL
cum
(
L
E
) has a reference value of 1µPa
2
s. In this table, thresholds are abbreviated to reflect ANSI standards (ANSI, 2013). However, peak sound pressure is defined by ANSI as incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript “flat” is being included to indicate peak sound pressure should be flat weighted or unweighted within the generalized hearing range. The subscript associated with SEL
cum
thresholds indicates the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The SEL
cum
thresholds could be exceeded in a multitude of ways (
i.e.,
varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be exceeded.

Ensonified Area

Here, we describe operational and environmental parameters of the activity that are used in estimating the area ensonified above the acoustic thresholds, including source levels and transmission loss (TL) coefficient.

The sound field in the project area is the existing background noise plus additional construction noise from the proposed project. Marine mammals are expected to be affected via sound generated by the primary components of the project (
i.e.,
pile driving and removal and DTH drilling).

The project includes vibratory pile installation and removal, impact pile driving, and DTH drilling in year 1 and vibratory pile installation and removal and impact pile driving in year 2. Source levels for these activities are based on reviews of measurements of the same or similar types and dimensions of piles available in the literature. Source levels for each pile size and activity each year are presented in table 6. Source levels for vibratory installation and removal of piles of the same diameter are assumed to be the same.

NMFS recommends treating DTH systems as both impulsive and continuous, non-impulsive sound source type simultaneously. Thus, impulsive thresholds are used to evaluate Level A harassment, and continuous thresholds are used to evaluate Level B harassment. With regards to DTH mono-hammers, NMFS recommends proxy levels for Level A harassment based on available data

regarding DTH systems of similar sized piles and holes (Heyvaert and Reyff, 2021) (table 1, table 7 and table 8 includes number of piles and duration each year; table 6 includes sound pressure and sound exposure levels for each pile type).

The Navy proposed to use bubble curtains when impact driving steel piles (relevant to Year 2 activities only). For the reasons described in the next paragraph, we assume here that use of the bubble curtain would result in a reduction of 8 dB from the assumed SPL (rms) and SPL (peak) source levels for these pile sizes, and reduce the applied source levels accordingly.

During the 2023 study at NBK Bremerton, the Navy conducted comparative measurements of source levels when impact driving steel piles with and without a bubble curtain. Underwater sound levels were measured at two locations during the installation of one 24-in diameter steel pile and four 36-in steel piles. The bubble curtain used during the measurements reduced median peak sound levels by between 8 and 12 dB, median RMS sound levels by 10 and 12 dB, and median single strike SEL sound levels by 7 and 8 dB. The analysis included in the proposed rule for the regulations preceding these IHAs (83 FR 9366, March 5, 2018) as well as results from the NBK Bangor Trident Support Facilities Explosive Handling Wharf study (Navy 2013), are consistent with these findings. While proper set-up and operation of the system is critical, and variability in performance should be expected, we believe that in the circumstances evaluated here an effective attenuation performance of 8 dB is a reasonable assumption.

Table 6—Estimates of Mean Underwater Sound Levels Generated During Vibratory and Impact Pile Installation, DTH Drilling, and Vibratory Pile Removal for Year 1 and Year 2

Pile driving method
Pile type
Pile size
dB RMS
dB Peak
dB SEL
Attenuation
Reference

Year 1

Impact
Concrete

18-in
24-in

170
174

184
188

159
164

N/A
N/A

Navy 2015.
Navy 2015.

Vibratory
Timber
13-in
161
N/A
N/A
N/A
Greenbusch Group, Inc. 2019.

DTH
Concrete
24-in
167
184
159
N/A
Heyvaert & Reyff 2021.

Year 2

Impact

Steel
1

12
36

177
194

192
211

167
181

−8 dB
1

−8 dB
1

Caltrans 2015, 2020.
Navy 2015b.

Vibratory

12
24
36

153
161
166

N/A
N/A
N/A

N/A
N/A
N/A

N/A
N/A
N/A

Navy 2015b.
Navy 2015b.
Navy 2015b.

Note:
dB peak = peak sound level; DTH = down-the-hole drilling; rms = root mean square; SEL = sound exposure level.

1
Values modeled for impact driving of 12-inch and 36-inch steel piles will be reduced by 8 dB for noise exposure modeling to account for attenuation from a bubble curtain

TL
is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source.
TL
parameters vary with frequency, temperature, sea conditions, current, source and receiver depth, water depth, water chemistry, and bottom composition and topography. The general formula for underwater
TL
is:

TL
=
B
* 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

Absent site-specific acoustical monitoring with differing measured TL, a practical spreading value of 15 is used as the TL coefficient in the above formula. Site-specific TL data for the Puget Sound are not available; therefore, the default coefficient of 15 is used to determine the distances to the Level A harassment and Level B harassment thresholds.

The ensonified area associated with Level A harassment is more technically challenging to predict due to the need to account for a duration component. Therefore, NMFS developed an optional User Spreadsheet tool to accompany the Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically overestimates of some degree, which may result in an overestimate of potential take by Level A harassment. However, this optional tool offers the best way to estimate isopleth distances when more sophisticated modeling methods are not available or practical. For stationary sources such as pile driving, the optional User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity, it would be expected to incur PTS. Inputs used in the optional User Spreadsheet tool, and the resulting estimated isopleths, are reported below.

Table 7—User Spreadsheet Inputs, Year 1

Vibratory
13-in Timber
Installation or removal
Impact
18-in Concrete
Installation
24-in Concrete
Installation
DTH
24-in Concrete
Installation

Spreadsheet Tab Used
A.1) Vibratory Pile Driving
E.1) Impact Pile Driving
E.1) Impact Pile Driving
E.2) DTH Drilling.

Source Level (SPL)
161 RMS
159 SEL
164 SEL
167 RMS, 159 SEL.

Transmission Loss Coefficient
15
15
15
15.

Weighting Factor Adjustment (kHz)
2.5
2
2
2.

Activity Duration per day (minutes)
90

80.

Strike Rate per second

12.

Number of strikes per pile

1,000
1,000

Number of piles per day
6
5
4
2.

Distance of sound pressure level measurement
10
10
10
10.

Table 8—User Spreadsheet Inputs, Year 2

Vibratory
12-in Steel
Installation or removal
24-in Steel
Installation or removal
36-in Steel
Installation or removal
Impact
12-in Steel; BC
Installation
36-in Steel; BC
Installation

Spreadsheet Tab Used
A.1) Vibratory Pile Driving
A.1) Vibratory Pile Driving
A.1) Vibratory Pile Driving
E.1) Impact Pile Driving
E.1) Impact Pile Driving.

Source Level (SPL)
153 RMS
161 RMS
166 RMS
167 SEL
181 SEL.

Transmission Loss Coefficient
15
15
15
15
15.

Weighting Factor Adjustment (kHz)
2.5
2.5
2.5
2
2.

Activity Duration per day (minutes)
30
90
133
N/A
N/A.

Number of strikes per pile
N/A
N/A
N/A
1,000
1,000.

Number of piles per day
2
6
4
2
4.

Distance of sound pressure level measurement
10
10
10
10
10.

BC = Bubble Curtain

Table 9—Level A Harassment and Level B Harassment Isopleths From Vibratory and Impact Pile Driving and DTH drilling

Pile type
Level A harassment isopleths (m)
LF
MF
HF
PW
OW

Level B
harassment
isopleth
(m)

Area of
harassment
zone

(km
2
)

Year 1

Vibratory

13-inch timber
8.9
<1
13.2
5.4
<1
5,412

16 km
2
.

Impact

18-inch concrete
73.3
2.6
87.4
39.3
2.9
46

0.007 km
2
.

24-inch concrete
136.2
4.8
162.2
72.9
5.3
86

0.02 km
2
.

DTH

24-inch concrete
374.1
13.3
445.6
200.2
14.6
13,594

75 km
2
.

Year 2

Vibratory

12-inch steel
1.3
<1
<1
<1
<1
1,585

8 km
2
.

24-inch steel
8.9
<1
13.2
5.4
<1
5,412

16 km
2
.

36-inch steel
25.1
2.2
37.0
15.2
1.1
11,659

31 km
2
.

Impact

12-inch steel
39.8
1.4
47.4
21.3
1.6
39.8

0.005 km
2
.

36-inch steel
542.1
19.3
645.8
290.1
21.1
541.2

0.92 km
2
.

Marine Mammal Occurrence

In this section we provide information about the occurrence of marine mammals, including density or other relevant information that will inform the take calculations.

Available information regarding marine mammal occurrence in the vicinity of the four installations includes density information aggregated in the Navy's Marine Mammal Species Density Database (NMSDD; Navy, 2019) or site-specific survey information from particular installations (
e.g.,
local pinniped counts). More recent density estimates for harbor porpoise are available in Smultea
et al.
(2017) and Rone
et al.,
(2024). First, for each installation we describe anticipated frequency of occurrence and the information deemed most appropriate for the exposure estimates. For all facilities, large whales (humpback whale, minke whale, and gray whale), killer whales (transient and resident), Dall's porpoise, and elephant seal are considered as occurring only rarely and unpredictably, on the basis of past sighting records. For these species, average group size is considered in concert with expected frequency of occurrence to develop the most realistic exposure estimate. Although certain species are not expected to occur at all at some facilities—for example, resident killer whales are not expected to occur in Hood Canal—the Navy has developed an overall take estimate and request for these species for each project year.

All species described above are considered as rare, unpredictably occurring species. A density-based analysis is used for harbor porpoise (table 10), while data from site-specific abundance surveys are used for California sea lion, Steller sea lion, and harbor seal at all installations. One exception is that for Steller sea lion at NBK Bremerton, a density-based analysis is used because local data have resulted in no observations of this species (Navy, 2023).

Table 10—Marine Mammal Densities

Species
Region

Density
(June-February)

Harbor porpoise
Hood Canal (Bangor)

1
0.81

East Whidbey Island (Everett)

2
0.75

Sinclair Inlet (Bremerton)

2
0.53

Vashon (Manchester)

2
0.25

Steller Sea Lion
Puget Sound—Fall/Winter

3
0.05

Sources:
1
Rone
et al.,
2024;
2
Smultea
et al.,
2017;
3
Navy, 2019.

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.

To quantitatively assess exposure of marine mammals to noise from pile driving activities, the Navy proposed three methods, to be used depending on the species' assumed spatial and temporal occurrence. For species with rare or infrequent occurrence at a given installation during the in-water work window, the likelihood of interaction was reviewed on the basis of past records of occurrence (described in Description of Marine Mammals in the Area of Specified Activities) and the potential maximum duration of work days at each installation, as well as total work days for all installations. Occurrence of the species in this category [
i.e.,
large whales, killer whales, elephant seal (all installations), and Dall's porpoise (Hood Canal only)] would not be anticipated to extend for multiple days. Except for SRKW, the probable duration of all rare, unpredictably occurring species is assumed to be two days, roughly equivalent to one transit in and out of a project site. In the case of SRKW, the probable duration is assumed to be one day only, as SRKW have not been observed near naval installations during work completed previously at these installations. The calculation for species with rare or infrequent occurrence is:

Exposure estimate = expected group size × probable duration

For species that occur regularly but for which site-specific abundance information is not available, density estimates (table 10) were used to determine the number of animals potentially exposed on any one day of pile driving or removal. The calculation for density-based analysis of species with regular occurrence is:

Exposure estimate = N (density) × Zone of Influence (ZOI, area) × days of pile driving

For remaining species, site-specific abundance information (
i.e.,
primarily the mean of monthly average counts per surveys completed between 2008 and 2022) was used. In cases where documented presence of a given pinniped species was variable throughout year and the mean of monthly average count (2008-2022) was ≥1, the mean of monthly maximum counts of surveys completed between 2008 and 2022 was used:

Exposure estimate = Abundance × days of pile driving

Large Whales
—For each species of large whale (
i.e.,
humpback whale, minke whale, and gray whale), we assume rare and infrequent occurrence at all installations. For all

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2024-07676. Public record. Not legal advice.