# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Port of San Francisco Mission Bay Ferry Landing Project in San Francisco Bay, California

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2026-06484

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** April 3, 2026
- **Citation:** 91 FR 16900

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XF443]
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Port of San Francisco Mission Bay Ferry Landing Project in San Francisco Bay, California

AGENCY:

National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce.

ACTION:

Notice; proposed incidental harassment authorization; request for comments on proposed authorization and possible renewal.

SUMMARY:

NMFS has received a request from the Port of San Francisco (PSF) for authorization to take marine mammals incidental to the Mission Bay Ferry Landing (MBFL) Project in San Francisco Bay (SFB), California (CA). Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an incidental harassment authorization (IHA) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on possible one-time, 1-year renewals for each IHA that could be issued under certain circumstances and if all requirements are met, as described in the Request for Public Comments section at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorization and agency responses will be summarized in the final notice of our decision.

DATES:

Comments and information must be received no later than May 4, 2026.

ADDRESSES:

Comments should be addressed to the Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service and should be submitted via email to
ITP.esch@noaa.gov.
Electronic copies of the application and supporting documents, as well as a list of the references cited in this document, may be obtained online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities.
In case of problems accessing these documents, please call the contact listed below.

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

Carter Esch, Office of Protected Resources, NMFS (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

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

Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s) and will not have an unmitigable adverse impact on the availability of the species or stock(s) for taking for subsistence uses (where relevant). Further, NMFS must prescribe the permissible methods of taking; other “means of effecting the least practicable adverse impact” on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stocks for taking for certain subsistence uses (referred to as “mitigation”); and requirements pertaining to the monitoring and reporting of the takings. The definitions of all applicable MMPA statutory terms used above are included in the relevant sections below (see also 16 U.S.C. 1362; 50 C.F.R 216.3, and 216.103).

National Environmental Policy Act

To comply with the National Environmental Policy Act of 1969 (NEPA; 42 U.S.C. 4321
et seq.
) and NOAA Administrative Order (NAO) 216-6A, NMFS must review our proposed action (
i.e.,
the issuance of an IHA) with respect to potential impacts on the human environment.

These actions are consistent with categories of activities identified in Categorical Exclusion B4 (IHAs with no anticipated serious injury or mortality) of the Companion Manual for NAO 216-6A, which do not individually or cumulatively have the potential for significant impacts on the quality of the human environment and for which we have not identified any extraordinary circumstances that would preclude this categorical exclusion. Accordingly, NMFS has preliminarily determined that the issuance of the proposed IHA qualifies to be categorically excluded from further NEPA review.

Summary of Request

On October 10, 2025, NMFS received a request from PSF for an IHA to take marine mammals incidental to vibratory pile driving and extraction, and down-the-hole (DTH) driving, necessary for construction of the MBFL Project within PSF's Southern Waterfront in the Mission Bay/Central Waterfront area.

NMFS previously issued an IHA to PSF to harass small numbers of marine mammals, by Level B harassment, incidental to similar activities, effective June 1, 2019, to May 31, 2020 (83 FR 53217, October 22, 2018). Following issuance of the original IHA, Project construction was significantly delayed due to the City of San Francisco's project resources and funding constraints. PSF then divided the Project construction sequencing into two phases. MBFL Phase 1 project elements, completed from June to November 2020, included only project activities incidental to which take of marine mammals was not anticipated (
i.e.,
demolition, dredging, and sand capping). Following a five-year construction delay, PSF is preparing to initiate construction of the remaining MBFL Phase 2 elements (
i.e.,
pile installation and extraction using vibratory methods and DTH driving). Since issuance of the 2018 IHA, PSF has

streamlined the project description to include a ferry landing only, rather than both ferry and water taxi landings. Therefore, the specified activities described in the 2025 IHA request include only a subset of those analyzed for the 2018 IHA, with minor changes to pile sizes and installation parameters.

Following NMFS' review of the application drafts and associated discussions, PSF iteratively submitted revised versions of the application on January 8, February 6, and February 23, 2026. The application was deemed adequate and complete on March 5, 2026.

PSF now proposes to construct a single-float, two-berth MBFL to provide ferry access to the SFB area. PSF is requesting an IHA to cover the period of June 1, 2026, to May 31, 2027. PSF's proposed activity includes vibratory pile driving, vibratory pile extraction, and DTH driving, which may result in the incidental take of marine mammals, by harassment only. PSF's request is for incidental take, by Level B harassment, of eight species of marine mammals. No Level A harassment is anticipated to occur, and none is proposed for authorization. Neither PSF nor NMFS expect serious injury or mortality to result from this activity and, therefore, an IHA is appropriate.

Description of Proposed Activity

Overview

PSF proposes to construct the MBFL, a single‐float, two‐berth ferry landing, in SFB, CA, within PSF's Southern Waterfront in the Mission Bay/Central Waterfront area. The MBFL will provide critical regional ferry service to and from the Mission Bay neighborhood, one of the fastest growing neighborhoods in San Francisco, as well as the Dogpatch, Potrero Hill, Pier 70, and the Central Waterfront neighborhoods. The MBFL will provide capability to berth two ferry boats simultaneously and it is estimated that the ferry landing will have the capacity to handle up to 6,000 passengers per day. The ferry landing is considered essential to alleviate current regional transportation overcrowding and provide transportation resiliency in the event of an earthquake, Bay Bridge failure, or other unplanned events. The ferry landing in-water construction activities that have the potential to take marine mammals include vibratory pile driving and extraction, and DTH driving. In total, PSF anticipates conducting 32 non-consecutive days of in-water construction with the potential to result in take of eight species of marine mammals, over a 46-day period between June 1 and November 30, 2026.

Dates and Duration

The proposed IHA would be valid for the statutory maximum of 1 year from the date of effectiveness. It will become effective upon written notification from the applicant to NMFS but not beginning later than 1 year from the date of issuance or extending beyond 2 years from the date of issuance. Although the IHA would be active for a period of 1 year, in-water pile installation and extraction activities are planned from June through November to protect sensitive life stages of endangered fish in the area. PSF plans to conduct in-water construction activities over the course of 46 days from June 1, 2026, through November 30, 2026, although only 32 of those days would include construction activities that may result in incidental harassment of marine mammals. This schedule is subject to change, however, as project delays may occur due to a number of factors (
e.g.,
poor weather, equipment availability constraints).

Pile installations would proceed sequentially (
i.e.,
no concurrent activities planned). PSF estimates an overall production rate of two to six piles per day, although this number would vary depending on the stage of construction. PSF anticipates that all vibratory pile driving and extraction and DTH driving would be limited to daylight hours.

Specified Geographical Region

The project is located in SFB within PSF's Southern Waterfront in the Mission Bay/Central Waterfront area. The specific geographic location for the project is provided in figure 1. The project site is approximately three kilometers (km) south of the San Francisco-Oakland Bay Bridge, on the western side of SFB in the Central Basin. The nearby waterfront is an active recreational and commercial port and shipyard. The Long Wharf is located in northern region of the central Bay, south of the eastern terminus of the Richmond-San Rafael Bridge (Figure 1). Water depth in the project area ranges from approximately 6 to 15 meters (m). The substrate is primarily Bay mud, however, sand or gravel may exist deeper into the substrate. The project area around Berth 1 is approximately 470 square kilometers (km
2
) in size. Ambient underwater noise in the vicinity of the project area is generated by shipping activity, ferry traffic, and sound generated by the Richmond Bridge piers. Underwater noise measurements in 2006 and from 2020 to 2022 found the ambient noise in the project area to exceed 120 decibels (dB) root-mean-squared (RMS). Ambient underwater noise levels at Long Wharf may vary with noise levels being higher at Berth 1, likely due to its closer proximity to the main shipping channel.

EN03AP26.000

Figure 1—MBFL Project Location in SFB, CA

Detailed Description of Specific Activity

PSF proposes to construct the MBFL, a single‐float, two‐berth ferry landing in Mission Bay, located in SFB, CA, within PSF's Southern Waterfront in the Mission Bay/Central Waterfront area. Table 1 provides a summary of in-water construction activities, including installation of octagonal concrete piles which would not require pile driving or DTH driving. PSF defines four components of the overall ferry landing structure:

Pier Bents 1 and 2
—includes vibratory pile driving installation of four permanent 48-in steel caisson sleeves, drilling inside each caisson sleeve to create space to accommodate the base of one 24-in octagonal concrete pile per caisson sleeve, crane-mediated placement of four concrete piles (one per sleeve), and grouting to secure the base of each concrete pile;

Pier Bents 3 to 7
—includes vibratory pile driving installation of 10 temporary 30-in steel caisson sleeves, drilling inside each caisson sleeve to create space to accommodate the base of a 24-in octagonal concrete pile per caisson sleeve, crane-mediated placement of ten concrete piles, grouting to secure the base of each concrete pile, and vibratory pile extraction of each 30-in steel caisson sleeve;

Float Guide Piles
—includes vibratory pile driving installation of six 36-in steel pipe piles to refusal, followed by DTH to the 20-ft (6.1-m) embedment depth; and

Donut Fender Piles
—includes vibratory pile driving installation of two 36-in steel pipe piles to refusal, followed by DTH to the 20-ft (6.1-m) embedment depth.

To ensure the piles are correctly positioned during construction of the ferry landing, the contractor may elect to utilize a temporary pile-driving template. PSF estimates that the template may be installed and moved up to 10 times during construction. Four 14-in steel H-piles would support the template. Each of the four H-piles would be driven to refusal with a vibratory pile driver (600 seconds/pile) every time the template is set up and extracted using the same vibratory piling methodology to release the template for subsequent use, for a combined total of 80 H-pile installations and extractions (installation and extraction of 4 H-piles x 10 template applications).

Table 1—Summary of PSF's Pile Installation Activities for the MBFL Project

Project element
Pile type

Pile
diameter
(inches)

Method

Duration and
strikes/second
(sec)

Pile events per day
Days
Total pile events

Pile driving template piles
H-Pile Steel (temporary)
14
Vibratory pile driving and extraction
600
8 (4 installed and 4 removed)
10
80 (40 installed and 40 removed).

Pier (Bents 1 & 2)
Steel Caisson (permanent)
48
Vibratory pile driving
900
1
4
4.

Octagonal Concrete

24

No pile driving or DTH

N/A

1

4

4
.

Pier (Bents 3 -7)
Steel Caisson (temporary)
30
Vibratory pile driving and extraction
900
2 (1 installed and 1 removed)
10
20 (10 installed and 10 removed).

Octagonal Concrete

24

No pile driving or DTH

N/A

1

10

10
.

Float Guide Piles
Steel Pipe (permanent)
36
Vibratory pile installation
1,200
1
6
6.

Donut Fender Piles

DTH driving
20 minutes (10/sec)
1
2
2.

* Activities in italics are not likely to incidentally harass marine mammals.

To aid in constructing Pier Bents, PSF would first install the template (using the approach described above) to support vibratory pile driving installation of each of four permanent 48-in (Bents 1 and 2) and 10 temporary 30-in (Bents 3 to 7) steel caisson sleeves. Once a given caisson sleeve is in place, sediment/soil/rock within the caisson would be drilled out using a Bauer BG18 rotary drill (similar) to create a rock socket (
i.e.,
a void in the substrate in which to seat the base of the pile). All drilled sediment/soil/rock will be collected for disposal and transported to an appropriate permitted facility. However, rotary drilling is not likely to result in incidental take of marine mammals, and we do not discuss it further. Using a crane, PSF would place/seat a 24‐in diameter concrete pile in each rock socket. After securing each concrete pile with grouting, PSF would remove the associated outer caisson sleeve and four temporary support H-piles. The 48-in caisson sleeves (n=4) would be permanent; thus, extraction only applies to the 30-in caisson sleeves (n=10). Figure 3 in the IHA application provides a depiction of this process.

Installation of the 36-in steel float and donut piles will require vibratory pile driving until refusal is reached (1,200 sec/pile), followed by DTH driving for approximately 20 minutes to achieve the target full 20 ft (6.1 m) embedment depth. PSF would utilize a noise attenuation system (
i.e.,
bubble curtain) during all DTH driving.

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

Description of Marine Mammals in the Area of Specified Activities

Sections 3 and 4 of the ITA 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 this information, and we refer the reader to these descriptions, instead of reprinting the information. Information regarding population trends and threats for the following species may be found in NMFS' Stock Assessment Reports (SARs;
https://www.fisherie.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 2 lists all species or stocks for which take is expected and proposed to be authorized for this activity and summarizes information related to the population or stock, including regulatory status under the MMPA and ESA and potential biological removal (PBR), where known. PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, which 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 (M/SI) from anthropogenic sources are included here as gross indicators of the status of the species or stocks and other threats.

Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Pacific and Alaska SARs. All values presented in table 2 are the most recent available at the time of publication (including from the draft 2024 SARs) and are available online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

Table 2—Status of Marine Mammal Species
1
Likely To Occur Near the Project Area

Common name
Scientific name
Stock

ESA/
MMPA
status;
strategic

(Y/N)
2

Stock abundance

(CV, N
min
, most recent

abundance survey)
3

PBR

Annual

M/SI
4

Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)

Family Eschrichtiidae:

Gray whale

Eschrichtius robustus

Eastern North Pacific
-/- ; N
25,960 (0.05, 25,849, 2016)
801
131

Superfamily Odontoceti (toothed whales, dolphins, and porpoises)

Family Delphinidae:

Bottlenose dolphin

Tursiops truncatus

California Coastal
-/- ; N
453 (0.06, 346, 2011)
2.7
> = 2

Family Phocoenidae (porpoises):

Harbor porpoise

Phocoena phocoena

San Francisco-Russian River
-/- ; N
7,777 (0.62, 4,811, 2017
73
> = 0.4

Order Carnivora—Superfamily Pinnipedia

California sea lion

Zalophus californianus

United States
-/- ; N
257,606 (N/A, 233,515, 2014)
14,011
>321

Steller sea lion

Eumetopias jubatus

Eastern North Pacific
-,-,N
36,308 (N/A, 36,308, 2022)
2,178
92.3

Northern fur seal

Callorhinus ursinus

California
-/- ; N
14,050 (n/a, 7,524, 2013)
451
1.8

Eastern North Pacific
-/- ; N
612,765 (0.2, 518,651, 2022)
11,151
296

Family Phocidae (earless seals):

Pacific harbor seal

Phoca vitulina richardii

California
-/- ; N
30,968 (n/a, 27,348, 2012)
1,641
43

Northern elephant seal

Mirounga angustirostris

California Breeding
-/- ; N
194,907 (N/A, 88,794, 2023)
5,328
11.2

1
Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy (
https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies
).

2
ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.

3
NMFS' marine mammal SARs can be found online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.
CV is the coefficient of variation; N
min
is the minimum estimate of stock abundance. In some cases, CV is not applicable.

4
These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (
e.g.,
commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range.

Very few marine mammal species occur consistently within SFB, and even fewer are likely to occur near the project area (
i.e.,
in the inner Bay) during the planned period of in-water construction (June-November). When cetacean sightings do occur, most tend to occur north of the project area, in the Central Bay (the area bound by the Golden Gate Bridge to the west, the Richmond Bridge to the north, and the San Francisco-Oakland Bay Bridge (SFOBB) to the south). The SFOBB, the southern boundary of the Central Bay, is approximately 1.5 miles (2.4 km) north of the project area. Only harbor seals, California sea lions, harbor porpoises, and bottlenose dolphins are sighted in SFB year-round; other marine mammal species sighted, although more infrequently, include the gray whale, humpback whale, northern elephant seal, Guadalupe fur seal, and northern fur seal. However, both the temporal and/or spatial occurrence of the humpback whale and Guadalupe fur seal is such that take is not expected to occur, and they are not discussed further beyond the explanation provided here.

Humpback whales are historically rare visitors to the interior of SFB. However, beginning in 2016, a seasonal (
i.e.,
April to November) influx of humpback whales occurred inside SFB near the Golden Gate Bridge (Keener 2017). Markiwitz
et al.
(2024) documented increased use of the portions of SFB near the Golden Gate strait as foraging habitat by humpback whales. Systematic land- and boat-based observations made during their 2016-2018 study period indicated that individual humpback whales moved into and out of SFB (
i.e.,
east and west of the Golden Gate Bridge) daily, on a timescale correlated with the tidal cycle, although individuals rarely ventured east of Alcatraz Island and never south of the SFOBB. PSF's project location is south of the documented foraging habitat, to the extent that neither NMFS nor PSF anticipates that planned construction activities would result in incidental taking of humpback whales. To ensure no take occurs, PSF proposes to shutdown construction activities should this species show up unexpectedly and approach the Level B harassment zone.

Although extremely rare, Guadalupe fur seals may range into the waters of northern California and the Pacific Northwest, potentially using the Farallon Islands (off central California) and Channel Islands (off southern California) as haul-out sites during these movements (Simon, 2016). However, Guadalupe fur seal occurrence in the vicinity of San Francisco is usually in the form of stranded juveniles (usually younger than 2 years old) with evidence of malnutrition, especially during El Niño events (NMFS 2017a). Because Guadalupe fur seals are so rare in the area, and sightings are associated with specific abnormal weather conditions, NMFS has determined that no Guadalupe fur seals are likely to occur in the project vicinity and, therefore, no take is expected to occur.

As indicated above, all eight species (with nine managed stocks) in table 2 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur.

Harbor Seal

Harbor seals are distributed from Baja California north to the Aleutian Islands of Alaska. Harbor seals do not make extensive pelagic migrations but may travel hundreds of km to find food or suitable breeding areas (Herder, 1986; Harvey and Goley, 2011; Carretta
et al.,
2023). Harbor seals are the most common marine mammal species observed in SFB and occur year-round, primarily observed hauled out on exposed rocky ledges and sloughs in the southern Bay. Harbor seals, central-place foragers (Orians and Pearson 1979) that tend to exhibit strong site fidelity within season and across years, forage close to haul-out sites, thus repeatedly visiting specific foraging areas (Grigg
et al.,
2012; Suryan and Harvey, 1998; Thompson
et al.,
1998). Harbor seals in SFB forage mainly within 7 mi (11.3 km of their primary haul-out site (Grigg
et al.,
2012), and often within just 1-3 mi (1-5 km; Torok 1994). The closest harbor seal haul-out site to the Project Area is Yerba Buena Island (YBI), approximately 3.3 mi (5.3 km) to the east of the Project Area. Although the YBI haul-out is not expected to be within the area of ensonification, it is likely that foraging seals from this location would be present in the water during construction.

Gray Whale

Gray whales are one of the most common whales along the California coast. A small number of whales, known as the Pacific Coast Feeding Group, are known to feed along the Pacific coast between Kodiak Island, AK and northern California, as well as in nearshore waters just outside of SFB (Carretta
et al.,
2022). The southward migration to winter breeding grounds occurs from December through February

while the northward migration to the feeding grounds takes place from February through May, peaking in March. Since 2019, it has become more common for gray whales on their northward migration, during the months of February and March, to enter SFB to feed (Bartlett, 2022). Although PSF would not initiate MBFL pile installation activities until June 1, well outside the northward migratory period, it is possible that a gray whale may enter the project area during pile driving activities.

In 2024, during monitoring required by an IHA for construction activities near the MBFL project site, Protected Species Observers (PSOs) observed gray whales more often than expected (Integral Consulting Inc., 2025a). The California Academy of Sciences and Marine Mammal Center reported an unusually high number of sightings in the SFB in 2025, with more than 30 individual gray whales confirmed via photo identification. By comparison, only six gray whales were sighted in SFB in 2024. Roughly one-third of the whales sighted in 2025 remained in SFB for at least 20 days; among these individuals, body condition ranged from normal to emaciated.

Bottlenose Dolphin

The common bottlenose dolphin is found in all oceans across the globe and is one of the most commonly observed marine mammal species in coastal waters and estuaries. Two genetically distinct stocks occur off the coast of California, the California coastal stock and the California/Oregon/Washington offshore stock. The range of the California coastal stock has been expanding north since an El Niño event in 1982 through 1983 (Hansen and Defran, 1990; Wells
et al.,
1990) and spans as far north as Sonoma County (Keener
et al.,
2023). From 2010 to 2018, a photo-identification monitoring study identified 84 distinctive individual bottlenose dolphins in SFB, likely belonging to the California coastal stock (Keener
et al.,
2023). This stock is highly transitory, shows little site fidelity, and individuals are highly mobile (Weller
et al.,
2016). Since 2008, coastal bottlenose dolphins have been observed regularly in SFB in proximity to the Golden Gate near the mouth of SFB, north of PSF's MBFL project site (Bay Nature, 2020). However, due to increased numbers of dolphins occurring in SFB, it is possible that a limited number of individuals may approach the project area during in-water construction activities.

Harbor Porpoise

Harbor porpoises typically occur in cool temperate to sub-polar waters less than 62.6 degrees Fahrenheit (17 degrees Celsius) (Read 1999) where prey aggregations are concentrated (Watts and Gaskin, 1985). In the eastern Pacific, harbor porpoises occur in coastal and inland waters from Point Conception, California to Alaska (Gaskin 1984). The non-migratory San Francisco-Russian River stock ranges from Pescadero to Point Arena, California, utilizes relatively shallow nearshore waters (<100 m), and feeds on small schooling fishes such as northern anchovy and Pacific herring which enter SFB (Caretta
et al.,
2022; Stern
et al.,
2017). Harbor porpoises tend to occur in small groups and are considered relatively cryptic animals.

Recently, observations of harbor porpoises within SFB have become more common (Duffy 2015; Stern
et al.,
2017; AECOM, 2021). Before 2008, harbor porpoises occurred primarily outside of SFB, although SFB has historically been considered habitat for harbor porpoises (Broughton, 1999). From 2011 to 2014, the Golden Gate Cetacean Research program conducted a visual count and identified 2,698 porpoise groups from the Golden Gate Bridge during 96 percent of their on-effort survey days (Stern
et al.,
2017). Harbor porpoise movements into SFB are linked to tidal cycles, with the greatest numbers of individuals sighted during high tide to ebb tide periods. Movements into SFB, which may serve as a foraging habitat, are likely influenced by prey availability (Duffy 2015; Stern
et al.,
2017). Although harbor porpoise sightings are generally concentrated in the vicinity of the Golden Gate Bridge and Angel Island, northwest of the project site (Keener, 2011), this species is occurring more frequently in SFB east of Angel Island and may approach the project area during pile driving activities.

California Sea Lion

California sea lions reside in the Eastern North Pacific Ocean in shallow coastal and estuarine waters. A common, abundant marine mammal, they are found throughout the U.S. west coast, generally within 10-miles of shore and are known to breed on the offshore islands of California from May through July (Heath and Perrin 2009). During the non-breeding season, adult and sub-adult males and juveniles migrate northward along the coast, to central and northern California, Oregon, Washington, and Vancouver Island (Jefferson
et al.,
1993). They return south the following spring (Lowry and Forney 2005; Heath and Perrin 2009). Females and some juveniles tend to remain closer to rookeries (Antonelis
et al.,
1990; Melin
et al.,
2008).

California sea lions occur within SFB-Delta in their highest numbers while migrating to and from their primary breeding areas on the Farallon and California Channel Islands, and when Pacific herring and salmon inhabit Bay-Delta waters spawn. or migrate to upriver spawning areas. They haul out on offshore rocks, sandy beaches, and onto floating docks, wharfs, vessels, and other man-made structures in SFB and coastal waters of the state.

In SFB, California sea lions have been observed at Angel Island and occupying the docks near Pier 39, which is the largest California sea lion haul‐out in SFB. A maximum of 1,706 sea lions were counted at Pier 39 in 2009. However, since then the population has averaged at about 50-300 depending upon the season (The Marine Mammal Center ((TMMC) 2017). This group of sea lions has decreased in size in recent years, coincident with a fluctuating decrease in the herring population in SFB. There are no known breeding sites within SFB. Their primary breeding site is in the Channel Islands (USACE 2011). The sea lions appear at Pier 39 after returning from the Channel Islands at the beginning of August (Bauer 1999). No other sea lion haul‐out sites have been identified in SFB and no pupping has been observed at the Pier 39 site or any other site in SFB under normal conditions (USACE 2011). Although there has been documentation of pupping on docks in SFB, this event was during a domoic acid event. The Port does not anticipate that any domoic events will occur during the project construction activities. The project site is approximately 4 miles away from Pier 39.

Although there is little information regarding the foraging behavior of the California sea lion in southern SFB, they have been observed foraging on a regular basis in the shipping channel south of YBI. Foraging grounds have also been identified for pinnipeds, including sea lions, between YBI and Treasure Island, as well as off the Tiburon Peninsula (California Department of Transportation (CALTRANS), 2006), 2006). The California sea lions that use the Pier 39 haul‐out site may be feeding on Pacific herring (
Clupea harengus
), northern anchovy, and other prey in the waters of SFB (CALTRANS, 2013a). In addition to the Pier 39 haul‐out, California sea lions haul out on buoys and similar structures throughout SFB. Although

mainly observed swimming off the San Francisco and Marin shorelines within SFB, California sea lions may occasionally enter the project area to forage.

Stellar Sea Lion

Steller sea lions are found along the North Pacific Rim from Japan to California. The eastern Pacific U.S. stock includes animals originating from rookeries east of Cape Suckling, Alaska, and ranges from approximately the Alaska-Canada border to California. Breeding and pupping occur from mid-May to mid-July. Females usually mate within two weeks of giving birth. Steller sea lions have a polygynous mating system in which only a small proportion of the males (
i.e.,
bulls) father most of the pups. Bulls are highly territorial during the breeding season, often aggressively guarding a rocky outcrop or area onshore. Although species' occurrence is rare in the project area, since 1993, a single adult male Steller sea lion has been observed using the nearby Pier 39 haul-out sites more than 30 times over 10 years, typically intermittently July through September, but as recently as March 2026.

Northern Elephant Seal

Northern elephant seals are found in the eastern and central North Pacific Ocean and range as far north as Alaska and as far south as Mexico, spending approximately 9 months per year at sea. The species breeds and pups from December through March in the Channel Islands of California or Baja California in Mexico, preferring sandy beaches or similar habitat (Stewart and Huber, 1993; Stewart
et al.,
1994; Carretta
et al.,
2022). The largest rookeries are on San Nicolas and San Miguel islands in the northern Channel Islands. Near SFB, elephant seals breed, molt, and haul out at Año Nuevo Island, the Farallon Islands, and Point Reyes National Seashore.

Elephant seals do not have any established haul out sites in the SFB, but occasional sightings have occurred. The most recent sighting was in 2012 on the beach at Clipper Cove on Treasure Island, when a healthy yearling elephant seal hauled out for a day. Approximately 100 juvenile northern elephant seals strand in SFB each year, including at YBI and Treasure Island (fewer than 10 strandings per year) (CALTRANS, 2018). Although visits to SFB are rare, it is possible that a few individuals could be present in the project area during construction activities.

Northern Fur Seal

Northern fur seals range from southern California north to the Bering Sea, and west to the Okhotsk Sea and Honshu Island, Japan in the west (Carretta
et al.,
2022). Most of the population breeds on the Pribilof Islands in the southern Bering Sea, although a small percentage of the population breed at San Miguel Island and the Farallon Islands off the coast of California. Northern fur seals show high site fidelity to breeding and rookery locations and may swim long distances for prey. Their diet is composed of small schooling fish such as walleye pollock, herring, hake, anchovy, and squid. Diet and population trends vary with environmental conditions, such as El Niño (Carretta
et al.,
2022). The California stock of northern fur seals forage in waters outside of SFB. Juvenile northern fur seals occasionally strand in SFB, especially during El Niño events (TMMC 2016). TMMC responds to approximately five northern fur seal strandings per year in SFB (TMMC, 2016). TMMC occasionally responds to stranded fur seals around YBI and Treasure Island. Although rarely observed in SFB, it is possible individuals may be present during construction activities but unlikely that the species will be exposed to construction activities.

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.
). Generalized hearing ranges were chosen based on the approximately 65-dB threshold from composite audiograms, previous analyses in NMFS (2018), and/or data from Southall
et al.
(2007) and Southall
et al.
(2019). We note that the names of two hearing groups and the generalized hearing ranges of all marine mammal hearing groups have been recently updated (NMFS, 2024) as reflected below in table 3.

Table 3—Marine Mammal Hearing Groups
[NMFS, 2024]

Hearing group
Generalized hearing range *

Low-frequency (LF) cetaceans (baleen whales)
7 Hz to 36 kHz.

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

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

200 Hz to 165 kHz.

Phocid pinnipeds (PW) (underwater) (true seals)
40 Hz to 90 kHz.

Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)
60 Hz to 68 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 may not be as broad. Generalized hearing range chosen based on ~65 dB threshold from composite audiogram, previous analysis in NMFS (2018), and/or data from Southall
et al,
2007, 2019). Additionally, animals are able to detect very loud sounds above and below that “generalized” hearing range.

For more details concerning these groups and associated generalized hearing ranges, please see (NMFS, 2024) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

This section includes a summary and 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 likely to adversely affect the species or stock through effects on annual rates of recruitment or survival.

There are a variety of types and degrees of effects on marine mammals and their habitat (including prey) that could occur as a result of the specified activities. Below, we provide a brief description of the types of sound generated by specified activities, the general impacts on marine mammals and their habitat from these types of activities, and a related project-specific analysis, with consideration of the proposed mitigation measures.

Description of Sound Sources for the Specified Activities

Activities associated with the project with the potential to incidentally take marine mammals though exposure to sound would include vibratory pile installation and extraction, and DTH driving. Vibratory hammers install piles by vibrating them and allowing the weight of the hammer to push them into the substrate. Vibratory hammers typically produce less sound (
i.e.,
lower sound pressure level (SPLs)) than impact hammers. Peak SPLs may be 180 dB or greater but are generally 10 to 20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Oestman
et al.,
2009; CALTRANS, 2015, 2020). Sounds produced by vibratory hammers are non-impulsive and, compared to sounds produced by impact hammers, have a slower rise time that reduces the probability and severity of injury, given the sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson
et al.,
2005).

DTH driving uses a combination of drilling and impact hammering mechanisms to advance development of a hole in rock, with or without simultaneously advancing a pile/casing into that hole. DTH excavation is accomplished by the efficient progression of a drill bit, rotated under pressure while simultaneously hammered by a specialized percussive hammer located within the drill string (
i.e.,
“behind” the bit), the combined forces moving the bit forward to fracture rock. Traditional impact and vibratory pile driving involve a hammer striking the top of the pile, causing the entire length of the submerged pile to radiate sound as a linear source. However, the DTH hammering mechanism is integrated into the drill itself, so the primary sound generation point is at the interface of the drill bit and the substrate (
i.e.,
rock) deep within the ground/seabed, radiating sound pressure more like a point rather than linear source. DTH systems often involve a single hammer (mono-hammer), but multi- or “cluster” hammer drills are also used widely. For construction of the MBFL, PSF anticipates that installation of the 36-in steel pipe piles to the full 20-ft (6.1-m) embedment depth will require DTH driving using a mono-hammer.

The sounds produced by the DTH driving methods simultaneously contain both a continuous non-impulsive component from the drilling action and an impulsive component from the hammering effect. Therefore, for purposes of evaluating Level A harassment and Level B harassment under the MMPA, NMFS treats DTH systems simultaneously as both impulsive (Level A harassment thresholds) and continuous, non-impulsive (Level B harassment thresholds) sound source types. While DTH impact hammering can, in general, result in Level A harassment of marine mammals, it is not expected for this project given the small zones produced by the proposed DTH driving (quantified in the Estimated Take of Marine Mammals section) coupled with proposed monitoring and shutdown measures (described in the Proposed Mitigation and Proposed Monitoring and Reporting sections) that would prevent animals from entering these small zones.

The likely or possible impacts of the proposed activities on marine mammals could result from both non-acoustic and acoustic stressors. Potential non-acoustic stressors include the physical presence of the equipment, vessels, and personnel; however, the closest known harbor seal (
i.e.,
YBI) and California sea lion (
i.e.,
Pier 39) haul-out sites are located approximately 3.3 mi (5.3 km) and 4.0 mi (6.4 km), respectively, from the MBFL location; thus, we expect that visual and other non-acoustic stressors would be limited. Should any animals approach the project site(s) closely enough to be harassed due to the presence of equipment or personnel, we expect they would have already traveled through the acoustic harassment zones for the specified in-water activities and, thus, would already be considered taken by acoustic impacts. Therefore, any impacts to marine mammals are expected to be primarily acoustic in nature.

Acoustic Effects

The introduction of anthropogenic noise into the aquatic environment from pile driving and extraction is the means by which marine mammals may be harassed by the specified activity. 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, 2019). In general, exposure to pile driving and extraction 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, an auditory threshold shift (TS). Exposure to anthropogenic noise can also lead to non-observable physiological responses such an increase in stress hormones. Additional noise in a marine mammal's habitat can mask acoustic cues used by marine mammals to carry out daily functions such as communication, and predator and prey detection. The effects of pile driving noise on marine mammals are dependent on several factors, including, but not limited to, sound type (
e.g.,
impulsive vs. non-impulsive), the species, age and sex class (
e.g.,
adult male vs. mom with calf), duration of exposure, the distance between the pile and the animal, received levels, behavior at time of exposure, and previous history with exposure (Wartzok
et al.,
2004; Southall
et al.
2007). Here, we discuss physical auditory effects (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, 2024). The amount of TS is customarily expressed in dB. A TS can be permanent or temporary. As described in NMFS (2018, 2024), there are numerous factors to consider when examining the consequence of TS, including, but not limited to, the signal temporal pattern (
e.g.,
impulsive or non- impulsive), likelihood an individual would be exposed for a long enough duration or to a high enough level to induce a TS, the magnitude of the TS, time to recovery (seconds to minutes or hours to days), the frequency range of the exposure (
i.e.,
spectral content), the hearing 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).

Auditory Injury (AUD INJ) and Permanent Threshold Shift (PTS)
—NMFS defines AUD INJ as “damage to the inner ear that can result in destruction of tissue . . . which may or may not result in PTS” (NMFS, 2024). 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, 2024). PTS does not generally affect more than a limited frequency range, and an animal that has incurred PTS has incurred some level of hearing loss at the relevant frequencies; typically, animals with PTS are not functionally deaf (Au and Hastings, 2008; Finneran, 2016). Available data from humans and other terrestrial mammals indicate that a 40-dB TS approximates PTS onset (see Ward
et al.
19
5
8, 1959, 1960; Kryter
et al.,
1966; Miller, 1974; Ahroon
et al.,
1996; Henderson
et al.,
2008). PTS levels for marine mammals are estimates; with the exception of a single study unintentionally inducing PTS in a harbor seal (Kastak
et al.,
2008), there are no empirical data measuring PTS in marine mammals. For various ethical reasons, experiments involving anthropogenic noise exposure at levels inducing PTS are not typically pursued or authorized (NMFS 2024, 2018).

Temporary Threshold Shift (TTS)
—TTS is a temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2024, 2018). Based on data from mammals ranging from discountable to serious (similar to those discussed in the Auditory Masking section, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non- critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more serious impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall
et al.,
2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost.

Many studies have examined noise- induced hearing loss in marine mammals (see Finneran (2015) and Southall
et al.
(2019) for summaries). TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 2013). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. For cetaceans, published data on the onset of TTS are limited to captive bottlenose dolphin, beluga whale, harbor porpoise, and Yangtze finless porpoise (
Neophocoena asiaeorientalis
) (Southall
et al.,
2019). For pinnipeds in water, measurements of TTS are limited to harbor seals, elephant seals, bearded seals (
Erignathus barbatus
) and California sea lions (Kastak
et al.,
1999, 2007; Kastelein
et al.,
2019b, 2019c, 2021, 2022a, 2022b; Reichmuth
et al.,
2019; Sills
et al.,
2020). TTS was not observed in spotted (
Phoca largha
) and ringed (
Pusa hispida
) seals exposed to single airgun impulse sounds at levels matching previous predictions of TTS onset (Reichmuth
et al.,
2016). These studies examine hearing thresholds measured in marine mammals before and after exposure to intense or long- duration sound exposures. The difference between the pre-exposure and post-exposure thresholds can be used to determine the amount of TS at various post-exposure times. The amount and onset of TTS depend on the exposure frequency. Sounds at low frequencies, well below the region of best sensitivity for a species or hearing group, are less hazardous than those at higher frequencies, near the region of best sensitivity (Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure levels are higher compared to those in the region of best sensitivity (
i.e.,
a low frequency noise would need to be louder to cause TTS onset when TTS exposure level is higher), as shown for harbor porpoises and harbor seals (Kastelein
et al.,
2019a, 2019c). Note that in general, harbor seals and harbor porpoises have a lower TTS onset than other measured pinniped or cetacean species (Finneran, 2015). In addition, TTS can accumulate across multiple exposures, but the resulting TTS will be less than the TTS from a single, continuous exposure with the same sound exposure level (SEL) (Mooney
et al.,
2009; Finneran
et al.,
2010; Kastelein
et al.,
2014, 2015). This means that TTS predictions based on the total, cumulative SEL will overestimate the amount of TTS from intermittent exposures, such as sonars and impulsive sources. Nachtigall
et al.
(2018) describe measurements of hearing sensitivity of multiple odontocete species (bottlenose dolphin, harbor porpoise, beluga, and false killer whale (
Pseudorca crassidens
)) when a relatively loud sound was preceded by a warning sound. These captive animals were shown to reduce hearing sensitivity when warned of an impending intense sound. Based on these experimental observations of captive animals, the authors suggest that wild animals may dampen their hearing during prolonged exposures or if conditioned to anticipate intense sounds. Another study showed that marine mammal TTS measurements (Southall
et al.,
2007, 2019), 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 (Finneran
et al.,
2000, 2002; Schlundt
et al.,
2000). As described in Finneran (2015), marine mammal studies have shown the amount of TTS increases with the 24-hour cumulative SEL (SEL
24
) in an accelerating fashion: at low exposures with lower SEL
24,
the amount of TTS is typically small and the growth curves have shallow slopes. At exposures with higher SEL
24
, the growth curves become steeper and approach linear relationships with the SEL.

Depending on the degree (elevation of threshold in dB), duration (
i.e.,
recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to more impactful (similar to those discussed in auditory masking, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more severe impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall
et al.,
2007), so we can infer that strategies exist for coping with this condition to

some degree, though likely not without cost.

Many studies have examined noise-induced hearing loss in marine mammals (see Finneran (2015) and Southall
et al.
(2019) for summaries). TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 2013). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS) (Finneran 2015). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. For cetaceans, published data on the onset of TTS are limited to captive bottlenose dolphin, beluga whale (
Delphinapterus leucas
), harbor porpoise, and Yangtze finless porpoise (
Neophocoena asiaeorientalis
) (Southall
et al.,
2019). For pinnipeds in water, measurements of TTS are limited to harbor seals, elephant seals, bearded seals (
Erignathus barbatus
) and California sea lions (Kastak
et al.,
1999, 2007; Kastelein
et al.,
2019b, 2019c, 2021, 2022a, 2022b; Reichmuth
et al.,
2019; Sills
et al.,
2020). TTS was not observed in spotted (
Phoca largha
) and ringed (
Pusa hispida
) seals exposed to single airgun impulse sounds at levels matching previous predictions of TTS onset (Reichmuth
et al.,
2016). These studies examine hearing thresholds measured in marine mammals before and after exposure to intense or long-duration sound exposures. The difference between the pre-exposure and post-exposure thresholds can be used to determine the amount of TS at various post-exposure times.

The amount and onset of TTS depend on the exposure frequency. Sounds below the region of best sensitivity for a species or hearing group are less hazardous than those near the region of best sensitivity (Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure levels are higher compared to those in the region of best sensitivity (
i.e.,
a low frequency noise would need to be louder to cause TTS onset when TTS exposure level is higher), as shown for harbor porpoises and harbor seals (Kastelein
et al.,
2019a, 2019c). Note that in general, harbor seals and harbor porpoises have a lower TTS onset than other measured pinniped or cetacean species (Finneran, 2015). In addition, TTS can accumulate across multiple exposures, but the resulting TTS will be less than the TTS from a single, continuous exposure with the same SEL (Mooney
et al.,
2009; Finneran
et al.,
2010; Kastelein
et al.,
2014, 2015). This means that TTS predictions based on the total SEL
24
will overestimate the amount of TTS from intermittent exposures, such as sonars and impulsive sources. Nachtigall
et al.
(2018) describe measurements of hearing sensitivity of multiple odontocete species (bottlenose dolphin, harbor porpoise, beluga, and false killer whale) when a relatively loud sound was preceded by a warning sound. These captive animals were shown to reduce hearing sensitivity when warned of an impending intense sound. Based on these experimental observations of captive animals, the authors suggest that wild animals may dampen their hearing during prolonged exposures or if conditioned to anticipate intense sounds. echolocating animals (including odontocetes) might have anatomical specializations that might allow for conditioned hearing reduction and filtering of low-frequency ambient noise, including increased stiffness and control of middle ear structures and placement of inner ear structures (Ketten
et al.,
2021). Data available on noise-induced hearing loss for mysticetes are currently lacking (NMFS, 2018). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species.

Relationships between TTS and PTS thresholds have not been studied in marine mammals, and there is no PTS data for cetaceans, but such relationships are assumed to be similar to those in humans and other terrestrial mammals. PTS typically occurs at exposure levels at least several decibels above that inducing mild TTS (
e.g.,
a 40-dB TS approximates PTS onset (Kryter
et al.,
1966; Miller, 1974), while a 6-dB TS approximates TTS onset (Southall
et al.,
2007, 2019). Based on data from terrestrial mammals, a precautionary assumption is that the PTS thresholds for impulsive sounds (such as impact pile driving pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and PTS cumulative SEL thresholds are 15 to 20 dB higher than TTS cumulative SEL thresholds (Southall
et al.,
2007, 2019). Given the higher level of sound or longer exposure duration necessary to cause PTS as compared with TTS, it is considerably less likely that PTS could occur.

Activities for this project include vibratory pile driving and vibratory extraction, and DTH driving. There would likely be pauses in activities producing the sound during each day. Given these pauses and the fact that many marine mammals are unlikely to remain in the project area for extended periods of time, the potential for TS declines.

Behavioral Harassment
—Exposure to noise from vibratory pile driving and vibratory extraction, and DTH driving, can also have the potential to behaviorally disturb marine mammals. Generally speaking, NMFS considers a behavioral disturbance that rises to the level of harassment under the MMPA a non-minor response—in other words, not every response qualifies as behavioral disturbance, and for responses that do, those of a higher level, or accrued across a longer duration, have the potential to affect foraging, reproduction, or survival. Behavioral disturbance may include a variety of effects, including subtle changes in behavior (
e.g.,
minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Behavioral responses may include changing durations of surfacing and dives, changing direction and/or speed; reducing/increasing vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); eliciting a visible startle response or aggressive behavior (such as tail/fin slapping or jaw clapping); avoidance of areas where sound sources are located. Pinnipeds may increase their haul out time, possibly to avoid in- water disturbance (Thorson and Reyff, 2006).

Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors (
e.g.,
species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (
e.g.,
Richardson
et al.,
1995; Wartzok
et al.,
2004; Southall
et al.,
2007, 2019; Weilgart, 2007; Archer
et al.,
2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison
et al.,
2012), and can vary depending on characteristics associated with the sound source (
e.g.,
whether it is moving or stationary, number of sources, distance from the source). In general, pinnipeds seem more tolerant of, or at least habituate more quickly to, potentially disturbing underwater sound than do cetaceans, and generally seem to be less responsive to exposure to industrial sound than most cetaceans. Please see Appendices B and C of Southall
et al.
(2007) and Gomez
et al.

(2016) for reviews of studies involving marine mammal behavioral responses to sound.

Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok
et al.,
2004). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder
et al.,
2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure.

As noted above, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals that are highly motivated to remain in an area for feeding (Richardson
et al.,
1995; Wartzok
et al.,
2004; National Research Council (NRC), 2005). Controlled experiments with captive marine mammals have shown pronounced behavioral reactions, including avoidance of loud sound sources (Ridgway
et al.,
1997; Finneran
et al.,
2003). Observed responses of wild marine mammals to loud pulsed sound sources (
e.g.,
seismic airguns) have been varied but often consist of avoidance behavior or other behavioral changes (Richardson
et al.,
1995; Morton and Symonds, 2002; Nowacek
et al.,
2007).

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

Changes in dive behavior can vary widely and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive (
e.g.,
Frankel and Clark, 2000; Costa
et al.,
2003; Ng and Leung, 2003; Nowacek
et al.,
2004; Goldbogen
et al.,
2013a, 2013b). Variations in dive behavior may reflect interruptions in biologically significant activities (
e.g.,
foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response.

Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators (
e.g.,
bubble nets or sediment plumes), or changes in dive behavior. However, acoustic and movement bio-logging tools have been used in some cases, to infer responses of feeding to anthropogenic noise. For example, Blair
et al.
(2016) reported significant effects on humpback whale foraging behavior in Stellwagen Bank in response to ship noise including slower descent rates, and fewer side-rolling events per dive with increasing ship nose. In addition, Wisniewska
et al.
(2018) reported that tagged harbor porpoises demonstrated fewer prey capture attempts when encountering occasional high-noise levels resulting from vessel noise as well as more vigorous fluking, interrupted foraging, and cessation of echolocation signals observed in response to some high-noise vessel passes.

In response to playbacks of vibratory pile driving sounds, captive bottlenose dolphins showed changes in target detection and number of clicks used for a trained echolocation task (Branstetter
et al.,
2018). Similarly, harbor porpoises trained to collect fish during playback of impact pile driving sounds also showed potential changes in behavior and task success, though individual differences were prevalent (Kastelein
et al.,
2019d). As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance (
e.g.,
Croll
et al.,
2001; Nowacek
et al.,
2004; Madsen
et al.,
2006; Yazvenko
et al.,
2007). A determination of whether foraging disruptions incur fitness consequences would require information on or estimates of the energetic requirements of the affected individuals and the relationships among prey availability, foraging effort and success, and the life history stage(s) of the animal.

Variations in respiration naturally vary with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in understanding species differences in the tolerance of underwater noise when determining the potential for impacts resulting from anthropogenic sound exposure (
e.g.,
Kastelein
et al.,
2001, 2005, 2006; Gailey
et al.,
2007). For example, harbor porpoises' respiration rate increased in response to pile driving sounds at and above a received broadband SPL of 136 dB (zero-peak SPL: 151 dB (re 1 mPa); SEL of a single strike: 127 dB re 1 mPa2-s) (Kastelein
et al.,
2013).

Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors and is one of the most obvious manifestations of disturbance in marine mammals (Richardson
et al.,
1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme
et al.,
1984). Avoidance may be short-term, with animals returning to the area once the noise has ceased (
e.g.,
Bowles
et al.,
1994; Goold, 1996; Stone
et al.,
2000; Morton and Symonds, 2002; Gailey
et al.,
2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur (
e.g.,
Blackwell
et al.,
2004; Bejder
et al.,
2006; Teilmann
et al.,
2006).

A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response (
e.g.,
directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and

Heithaus, 1996; Bowers
et al.,
2018). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (England
et al.,
2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response.

Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention (
i.e.,
when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been demonstrated for marine mammals, but studies involving fishes and terrestrial animals have shown that increased vigilance may substantially reduce feeding rates (
e.g.,
Beauchamp and Livoreil, 1997; Fritz
et al.,
2002; Purser and Radford, 2011). In addition, chronic disturbance can cause population declines through reduction of fitness (
e.g.,
decline in body condition) and subsequent reduction in reproductive success, survival, or both (
e.g.,
Harrington and Veitch, 1992; Daan
et al.,
1996; Bradshaw
et al.,
1998). However, Ridgway
et al.
(2006) reported that increased vigilance in bottlenose dolphins exposed to sound over a 5-day period did not cause any sleep deprivation or stress effects.

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

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 would experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress”. In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2003), however distress is an unlikely result of this project based on observations of marine mammals during previous, similar projects in the area.

Auditory Masking
—Since many marine mammals rely on sound to find prey, moderate social interactions, and facilitate mating (Tyack, 2008), noise from anthropogenic sound sources can interfere with these functions, but only if the noise spectrum overlaps with the hearing sensitivity of the receiving marine mammal (Southall
et al.,
2007; Clark
et al.,
2009; Hatch
et al.,
2012). Chronic exposure to excessive, though not high-intensity, noise could cause masking at particular frequencies for marine mammals that utilize sound for vital biological functions (Clark
et al.,
2009). Acoustic masking is when other noises such as from human sources interfere with an animal's ability to detect, recognize, or discriminate between acoustic signals of interest (
e.g.,
those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson
et al.,
1995; Erbe
et al.,
2016). Therefore, under certain circumstances, marine mammals whose acoustical sensors or environment are being severely masked could also be impaired from maximizing their performance fitness in survival and reproduction. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest (
e.g.,
signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities (
e.g.,
sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions (Hotchkin and Parks, 2013).

Marine mammals vocalize for different purposes and across multiple modes, such as whistling, echolocation click production, calling, and singing. Changes in vocalization behavior in response to anthropogenic noise can occur for any of these modes and may result from a need to compete with an increase in background noise or may reflect increased vigilance or a startle

response. For example, in the presence of potentially masking signals, humpback whales and killer whales have been observed to increase the length of their songs (Miller
et al.,
2000; Fristrup
et al.,
2003) or vocalizations (Foote
et al.,
2004), respectively, while North Atlantic right whales (
Eubalaena glacialis
) have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks
et al.,
2007). Fin whales have also been documented lowering the bandwidth, peak frequency, and center frequency of their vocalizations under increased levels of background noise from large vessels (Castellote
et al.,
2012). Other alterations to communication signals have also been observed. For example, gray whales, in response to playback experiments exposing them to vessel noise, have been observed increasing their vocalization rate and producing louder signals at times of increased outboard engine noise (Dahlheim and Castellote, 2016). Alternatively, animals may cease sound production during production of aversive signals (Bowles
et al.,
1994).

Under certain circumstances, marine mammals experiencing significant masking could also be impaired from maximizing their performance fitness in survival and reproduction. Therefore, when the coincident (masking) sound is human made, it may be considered harassment when disrupting or altering critical behaviors. It is important to distinguish TTS and PTS, which persist after the sound exposure, from masking, which occurs during the sound exposure. Because masking (without resulting in TS) is not associated with abnormal physiological function, it is not considered a physiological effect, but rather a potential behavioral effect (though not necessarily one that would be associated with harassment).

The frequency range of the potentially masking sound is important in determining any potential behavioral impacts. For example, low-frequency signals may have less effect on high- frequency echolocation sounds produced by odontocetes but are more likely to affect detection of mysticete communication calls and other potentially important natural sounds such as those produced by surf and some prey species. The masking of communication signals by anthropogenic noise may be considered as a reduction in the communication space of animals (
e.g.,
Clark
et al.,
2009) and may result in energetic or other costs as animals change their vocalization behavior (
e.g.,
Miller
et al.,
2000; Foote
et al.,
2004; Parks
et al.,
2007; Di Iorio and Clark, 2010; Holt
et al.,
2009). Masking can be reduced in situations where the signal and noise come from different directions (Richardson
et al.,
1995), through amplitude modulation of the signal, or through other compensatory behaviors (Hotchkin and Parks, 2013). Masking can be tested directly in captive species (
e.g.,
Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild (
e.g.,
Branstetter
et al.,
2013).

Marine mammals at or near the proposed project site may be exposed to anthropogenic noise which may be a source of masking. Vocalization changes may result from a need to compete with an increase in background noise and include increasing the source level, modifying the frequency, increasing the call repetition rate of vocalizations, or ceasing to vocalize in the presence of increased noise (Hotchkin and Parks, 2013). For example, in response to loud noise, beluga whales may shift the frequency of their echolocation clicks to prevent masking by anthropogenic noise (Eickmeier and Vallarta, 2022).

Masking occurs in the frequency band or bands that animals utilize and is more likely to occur in the presence of broadband, relatively continuous noise sources such as vibratory pile driving. Energy distribution of pile driving covers a broad frequency spectrum, and sound from pile driving would be within the audible range of pinnipeds and cetaceans present in the proposed action area. While some construction during the specified activities may mask some acoustic signals that are relevant to the daily behavior of marine mammals, the short-term duration and limited areas affected make it very unlikely that the fitness of individual marine mammals would be impacted.

Airborne Acoustic Effects
—Pinnipeds that may occur near the project site could be exposed to airborne sounds associated with construction activities that have the potential to cause behavioral harassment, depending on their distance from these activities. Airborne noise would primarily be an issue for pinnipeds that are swimming or hauled out near the project site within the range of noise levels elevated above airborne acoustic harassment criteria. There is also a possibility that an animal could surface in-water, but with head out, within the area in which airborne sound exceeds relevant thresholds and thereby be exposed to levels of airborne sound that we associate with harassment. However, as a result of the mitigation and monitoring measures and due to the infrequent occurrence of marine mammals in the area, takes by behavioral harassment resulting from airborne sounds that would result in harassment as defined under the MMPA are not expected.

Marine Mammal Habitat Effects

The proposed specified activities could have localized, temporary impacts on marine mammal habitat and their prey by increasing in-water SPLs and slightly decreasing water quality. Increased noise levels may affect acoustic habitat (see
Auditory Masking
discussion above) and adversely affect marine mammal prey in the vicinity of the project area (see discussion below). During in-water vibratory pile driving and vibratory extraction, and DTH driving, elevated levels of underwater noise would ensonify the project area where both fish and some mammals occur and could affect foraging success.

Water Quality
—Temporary and localized reduction in water quality would occur as a result of in-water construction activities. Most of this effect would occur during the installation and extraction of piles when bottom sediments are disturbed. The installation and extraction of piles would disturb bottom sediments and may cause a temporary increase in suspended sediment in the project area. During pile extraction, sediment attached to the pile moves vertically through the water column until gravitational forces cause it to slough off under its own weight. The small resulting sediment plume is expected to settle out of the water column within a few hours. Studies of the effects of turbid water on fish (marine mammal prey) suggest that concentrations of suspended sediment can reach thousands of milligrams per liter before an acute toxic reaction is expected (Burton, 1993).

Effects to turbidity and sedimentation are expected to be short-term, minor, and localized. Suspended sediments in the water column should dissipate and quickly return to background levels in all construction scenarios. Turbidity within the water column has the potential to reduce the level of oxygen in the water and irritate the gills of prey fish species in the proposed project area. However, turbidity plumes associated with the project would be temporary and localized, and fish in the proposed project area would be able to move away from and avoid the areas where plumes may occur. Therefore, it is expected that the impacts on prey fish species from turbidity, and therefore on

marine mammals, would be minimal and temporary. In general, the area likely impacted by the proposed construction activities is relatively small compared to the available marine mammal habitat in the area and does not include any areas of particular importance.

In-Water Construction Effects on Potential Prey
—Sound may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species (
e.g.,
crustaceans, cephalopods, fish, zooplankton). Marine mammal prey varies by species, season, and location and, for some, is not well documented. 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
et al.,
1999; Fay, 2009). Depending on their hearing anatomy and peripheral sensory structures, which vary among species, fishes hear sounds using pressure and particle motion sensitivity capabilities and detect the motion of surrounding water (Fay
et al.,
2008). The potential effects of noise on fish depend 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 which 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, although several are based on studies in support of large, multiyear bridge construction projects (
e.g.,
Scholik and Yan, 2001, 2002; Popper and Hastings, 2009). Several studies have demonstrated that impulse sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs (
e.g.,
Fewtrell and McCauley, 2012; Pearson
et al.,
1992; Skalski
et al.,
1992; Santulli
et al.,
1999; Paxton
et al.,
2017). However, some studies have shown no or slight reaction to impulse sounds (
e.g.,
Pena
et al.,
2013; Wardle
et al.,
2001; Jorgenson and Gyselman, 2009; Cott
et al.,
2012). More commonly, though, the impacts of noise on fish are temporary.

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 is likely restored when damaged cells are replaced with new cells. Halvorsen
et al.
(2012a) showed that a TTS of 4-6 dB was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long. Injury caused by barotrauma can range from slight to severe and can cause death and is most likely for fish with swim bladders. Barotrauma injuries have been documented during controlled exposure to impact pile driving (Halvorsen
et al.,
2012b; Casper
et al.,
2013).

The greatest potential impact to fishes during construction would occur during DTH driving, which has an impact hammer component. In-water construction activities would only occur during daylight hours, allowing fish to forage and transit the project area in the evening. Vibratory pile driving would possibly elicit behavioral reactions from fishes such as temporary avoidance of the area but is unlikely to cause injuries to fishes or have persistent effects on local fish populations. Construction also would have minimal permanent and temporary impacts on benthic invertebrate species, a marine mammal prey source. In addition, it should be noted that the area in question is low-quality habitat since it is already highly developed and experiences a high level of anthropogenic noise from normal operations and other vessel traffic. In general, any negative impacts on marine mammal prey species are expected to be minor and temporary.

Fish populations in the proposed project area that serve as marine mammal prey could be temporarily affected by noise from pile installation and extraction. The frequency range in which fishes generally perceive underwater sounds is 50 to 2,000 Hz, with peak sensitivities below 800 Hz (Popper and Hastings, 2009). Fish behavior or distribution may change, especially with strong and/or intermittent sounds that could harm fishes. High underwater SPLs have been documented to alter behavior, cause hearing loss, and injure or kill individual fish by causing serious internal injury (Hastings and Popper, 2005).

The most likely impact to fish from pile driving and extraction activities in the project area would be temporary behavioral avoidance of the area. The duration of fish avoidance of an 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.

In-Water Construction Effects on Potential Foraging Habitat
—The area likely impacted by the project is relatively small compared to the available habitat in the SFB area and does not include any biologically important areas (BIAs) or ESA-designated critical habitat. The total area affected by the project is small compared to the vast foraging area available to marine mammals in the area. Pile driving and extraction at the project site would not obstruct long-term movements or migration of marine mammals.

Avoidance by potential prey (
i.e.,
fish) 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.

In summary, given the short daily duration of sound associated with individual pile driving events and the relatively small areas being affected, pile driving activities associated with the proposed action are not likely to have a permanent adverse effect on any fish habitat, or populations of fish species. Any behavioral avoidance by fish of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity. Thus, we conclude that impacts of the specified activity are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species. Further, any impacts to marine mammal habitat are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations.

Estimated Take of Marine Mammals

This section provides an estimate of the number of incidental takes proposed for authorization through the IHA, which will inform 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 be by Level B harassment, as use of the acoustic sources (
i.e.,
vibratory installation and extraction, DTH driving) has the potential to result in disruption of behavioral patterns for individual marine mammals. Based on the nature of the activity and the anticipated effectiveness of the mitigation measures (
i.e.,
shutdown at the Level A harassment isopleth) discussed in detail below in the Proposed Mitigation section, Level A harassment is neither anticipated nor proposed to be authorized. As described previously, no serious injury or mortality is anticipated or proposed to be authorized for this activity. Below we describe how the proposed take numbers are estimated.

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

Acoustic Criteria

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

Level B Harassment
—Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context (
e.g.,
frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment (
e.g.,
bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict (
e.g.,
Southall
et al.,
2007, 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 RMS pressure received levels (RMS SPL) of 120 dB (referenced to 1 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, estimates of take by Level B harassment 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.

PSF's proposed construction activity includes the use of vibratory pile driving and extraction, and DTH driving, both of which are treated as continuous noise sources when evaluating the potential for Level B harassment; therefore, the RMS SPL thresholds of 120 dB re 1 μPa is applicable.

Level A Harassment
—NMFS' 2024 Updated Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 3.0) (Updated Technical Guidance, 2024) identifies dual criteria to assess AUD INJ (Level A harassment) to five different underwater marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive) (table 4). PSF's proposed activity includes the use of impulsive (DTH hammering component) and non-impulsive (vibratory pile driving and DTH drilling component) sources.

The 2024 Updated Technical Guidance criteria include both updated thresholds and updated weighting functions for each hearing group (table 4). These thresholds criteria are provided in the table below. The references, analysis, and methodology used in the development of the criteria thresholds, as well as the detailed description of the updated weighting functions, are described in NMFS' 2024 Updated Technical Guidance, which may be accessed at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools.

Table 4—Thresholds Identifying the Onset of AUD INJ

Hearing group

AUD INJ onset thresholds *
(received level)

Impulsive
Non-impulsive

Low-Frequency (LF) Cetaceans

Cell 1:

L
p,
0-pk,flat
:
222 dB;
L
E,
p,
LF,24h
:
183 dB

Cell 2:

L
E,
p,

LF,24h
:
197 dB.

High-Frequency (HF) Cetaceans

Cell 3:

L
p,
0-pk,flat
:
230 dB;
L
E,
p,
HF,24h
:
193 dB

Cell 4:

L
E,
p,

HF,24h
:
201 dB.

Very High-Frequency (VHF) Cetaceans

Cell 5:

L
p,
0-pk,flat
:
202 dB;
L
E,
p,
VHF,24h
:
159 dB

Cell 6:

L
E,
p,
VHF,24h
:
181 dB.

Phocid Pinnipeds (PW) (Underwater)

Cell 7:

L
p,
0-pk.flat
:
223 dB;
L
E,
p,
PW,24h
:
183 dB

Cell 8:

L
E,
p,
PW,24h
:
195 dB.

Otariid Pinnipeds (OW) (Underwater)

Cell 9:

L
p,
0-pk,flat
:
230 dB;
L
E,
p,
OW,24h
:
185 dB

Cell 10:

L
E,
p,
OW,24h
:
199 dB.

* Dual metric thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating AUD INJ onset. If a non-impulsive sound has the potential of exceeding the peak SPL thresholds associated with impulsive sounds, these thresholds are recommended for consideration.

Note:
Peak SPL (
L
p,
0-pk
) has a reference value of 1 µPa, and weighted cumulative SEL (
L
E,
p
) has a reference value of 1µPa
2
s. In this table, thresholds are abbreviated to be more reflective of International Organization (ISO) for Standardization standards (ISO 2017). The subscript “flat” is being included to indicate peak sound pressure are flat weighted or unweighted within the generalized hearing range of marine mammals (
i.e.,
7 Hz to 165 kHz). The subscript associated with cumulative SEL thresholds indicates the designated marine mammal auditory weighting function (LF, HF, and VHF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The weighted cumulative SEL 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 thresholds will be exceeded.

As discussed in the
Description of Sound Sources
section above, DTH systems have both continuous, non-impulsive, and impulsive components. When evaluating Level B harassment, NMFS recommends treating DTH as a continuous source and applying RMS SPL thresholds of 120 dB re 1 μPa. When evaluating Level A harassment, NMFS recommends treating DTH as an impulsive source, applying the thresholds in the second column of table 4.

NMFS (2022) guidance on DTH systems recommends source levels for DTH systems (
https://media.fisheries.noaa.gov/2022-11/PUBLIC%20DTH%20Basic%20Guidance_November%202022.pdf
). NMFS has applied those levels in our analysis (see table 5 for NMFS' proposed source levels) of potential acoustic impacts from DTH driving during PSF's installation of 36-in steel pipe piles.

Ensonified Area

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

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

The project includes vibratory pile installation and extraction and DTH driving. Source levels for these activities are based on reviews of measurements of the same or similar types and dimensions of pile available in the literature. Source levels for each pile size are presented in table 5. Source levels for vibratory installation and extraction of piles of the same diameter are assumed to be the same. PSF plans to use a bubble curtain for all DTH driving, and a 5-dB reduction in source level is assumed from those presented in table 5 for DTH driving.

Table 5—Source Levels for Proposed Activities

Project element
Pile type

Pile
diameter
(in)

Method

Duration
(seconds/pile)

Daily/total piling events
(including installation and extraction)

Source level (dB)
Peak
SEL
RMS

Pile driving template piles
H-pile steel (temporary)
14
Vibratory pile installation and extraction
600
8/80 (40 installed and 40 removed)
165
NA
150

Pier (Bents 1 & 2)
Steel Caisson (permanent)
48
Vibratory pile installation
900
1/4
NA
NA
170

Pier (Bents 3-7)
Steel Caisson (temporary)
30
Vibratory pile installation and extraction
900
2/20 (10 installed and 10 removed)
196
NA
159

Float Guide and Donut Fender Piles
Steel (permanent)
36
Vibratory pile installation
1,200
2/8
206
172
172

DTH driving
20 minutes (10 strikes per second)
2/8

1
194

164

1
174

1
PSF will deploy a bubble curtain during all DTH driving, which is expected to provide a 5-dB reduction from the source levels presented in table (SPL
peak
and SPL
rms
).

Transmission loss (TL) is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source in the acoustic field. 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 acoustic monitoring with differing measured
TL,
a practical spreading loss value of 15 is used as the
TL
coefficient in the above formula for nearshore environments. Site-specific
TL
data for the MBFL project site 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 TL model described above was used to calculate the expected noise propagation from vibratory pile driving and extraction, and DTH driving, using

representative source levels to estimate the harassment zones exceeding the noise criteria. The resulting distances to Level A harassment and Level B harassment isopleths are shown in table 6. The largest calculated distances to the Level B harassment isopleth would be produced during vibratory pile installation of 36-in steel pipe piles (29,286 m) and 48-in steel caisson sleeves (21,544 m), and DTH driving of 36-in steel pipe piles (39,811 m). However, when accounting for attenuation from landmass interference, the maximum radius of the Level B harassment zone is approximately 6,000 m (table 6).

The ensonified area associated with Level A harassment (AUD INJ) is more technically challenging to predict due to the need to account for a duration component. Therefore, NMFS developed an optional User Spreadsheet tool to accompany the 2024 Updated Technical Guidance that can be used to predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically going to be overestimates of some degree, which may result in an overestimate of potential take by Level A harassment (AUD INJ). 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 and DTH, the optional User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity, it would be expected to incur AUD INJ, which includes but is not limited to PTS.

PSF used NMFS' 2024 Updated Technical Guidance and optional User Spreadsheet to calculate the maximum distances to Level A harassment (AUD INJ onset) thresholds for all in-water construction activities (
i.e.,
vibratory installation and extraction, and DTH driving). Inputs used in the optional User Spreadsheet tool include values in table 1 (
e.g.,
number of piles per day, duration) and table 5 (
i.e.,
source levels). Sound source locations were chosen to model the greatest possible affected area from the representative notional pile location. The resulting estimated distances to Level A harassment threshold isopleths are reported below in table 6.

Table 6—Maximum Distances
1
to MMPA Harassment Threshold Isopleths

Project element
Pile type

Pile
diameter
(in)

Duration
(seconds/pile)

Method

Distance to Level A harassment (AUD INJ) isopleth
(meters)

Cetaceans
LF
HF
VHF
Pinnipeds
PW
OW

Distance to Level B harassment isopleth
1

(meters)

Pile driving template piles
H-pile steel (temporary)
14
600
Vibratory pile installation and extraction
4.4
1.7
3.6
5.7
1.9
2,154

Pier (Bents 1 & 2)
Steel Caisson (permanent)
48
900
Vibratory pile installation
23.1
8.9
18.9
29.8
10

2
21,554

Pier (Bents 3-7)
Steel Caisson (temporary)
30
900
Vibratory pile installation and extraction
4.3
1.6
3.5
5.5
1.9
3,981

Float Guide and Donut Fender Piles
Steel (permanent)
36
1,200
Vibratory pile installation
38.1
14.6
31.1
49
16.5

2
29,286

20 minutes (10 strikes per second)

DTH driving
3

282.2
36
436.8
250.7
93.5

2
39,811

1
The distances to Level B harassment isopleth were evaluated relative to the 120 dB SPL
rms
threshold for vibratory pile driving and DTH driving, based on its continuous component.

2
The harassment zones will be truncated due to the presence of intersecting landmasses, extending to a maximum of 6,000 m from the sound source during vibratory pile installation of 48-in steel caisson sleeves and both methods of installation (
i.e.,
vibratory pile driving and DTH driving) of 36-in steel pipe piles.

3
All distances calculated assuming 5 dB attenuation by a bubble curtain.

Marine Mammal Occurrence and Take Estimation

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

No systematic line transect surveys of marine mammals have been performed in SFB. Therefore, estimates of occurrence for each species were derived using the following datasets:

• 17 years of sighting data collected during the SFOBB construction project (CALTRANS, 2018);

• 5 years of sighting and stranding data from TMMC (NMFS, 2021b as cited by Integral Consulting Inc., 2025a)

• 5 years of sighting and stranding data from The California Academy of Sciences (CAS) (Integral Consulting Inc., 2025a); and

• Monitoring data collected in Spring 2025 over 11 days in Remedial Response Areas A and B (required by NMFS-issued IHA for the Piers 39 to 43
1/2
Sediment Remediation Project) (Integral Consulting Inc., 2025b).

Monitoring data collected by CALTRANS for the SFOBB project over 17 years can be used to approximate density of the observed species near PSF's project site. Care was taken to eliminate multiple observations of the same animal in the dataset, although this can be difficult and it is likely that the same individual may have been counted by observers multiple times on the same day. The amount of monitoring performed per year varied, depending on the frequency and duration of construction activities with the potential to affect marine mammals. During the 257 days of monitoring from 2000 through 2017 (including 15 days of baseline monitoring in 2003), CALTRANS observed a total of 1,029 harbor seals, 83 California sea lions, and 24 harbor porpoises in the vicinity of the SFOBB, with the number of harbor seals and harbor porpoises increasing significantly beginning in 2015. These observations included data from baseline, pre-, during, and post-pile driving, mechanical dismantling, onshore blasting, and offshore implosion activities.

The TMMC and CAS datasets report sightings of marine mammals found within SFB between September 2016 and September 2021. The sightings include those of stranded animals (that

were of confirmed species and associated with a confirmed location within SFB) whether they were living, dead (all stages of decomposition), floating, or stranded. The TMMC and CAS often have duplicate sightings in their databases due to how information is received from the public. As TMMC receives the most reports from the public, their dataset was treated as the primary source. Duplicates were removed from the CAS dataset and CAS sightings are reported separately. The age, sex, and reproductive condition of individuals of each species that may potentially be taken is difficult to estimate given the lack of information on the class distribution of these species within the project area and greater SFB. Below are estimates for each species potentially affected.

Depending on the distribution of sightings and granularity of data, different sources have been used to estimate the species-specific number of individuals expected to occur within SFB and, thus, potentially within the area ensonified by PSF's pile-installation activities.

Gray Whale

Gray whales may enter SFB in late winter/early spring or in the fall during their migrations and, in recent years, there have been an increased number of gray whales in the western and Central Bay (Integral Consulting Inc., 2025a). During construction in March-April 2025, multiple gray whales were observed in SFB (Integral Consulting Inc., 2025b). According to TMMC, in June 2025, 9 individual gray whales were observed over 14 days (TMMC, unpublished data). As such, PSF anticipates the potential for gray whale occurrence in the MBFL project's Level B harassment ensonified zones. Given these data, and the trends they indicate, PSF estimates that one gray whale could occur in the project area every other day (0.5 whales/day), and NMFS concurs with this approach.

Bottlenose Dolphin

Historically, observations of bottlenose dolphins have occurred west of Treasure Island and were concentrated along the nearshore area of San Francisco south to Redwood City. Since 2016, one individual has been regularly seen near the former Alameda Air Station, and five animals were regularly seen in the summer and fall of 2018 in the same location (Integral Consulting Inc., 2025a). In February 2019, an adult and juvenile were seen on two separate occasions northwest of the Oakland Inner Harbor, over 4 mi (6.4 km) from PSF's proposed project area (Integral Consulting Inc., 2025a). No bottlenose dolphins were observed during pre-construction monitoring in 2020 (Haase, 2021) or during construction in the spring of 2025 (Integral Consulting Inc., 2025b). Although bottlenose dolphins are relatively uncommon in SFB, NMFS conservatively assumes that one group of bottlenose dolphins will be present in the project area during the construction period. A group size is estimated to be five animals based on sightings of bottlenose dolphins in SFB (Integral Consulting Inc., 2025a).

Pacific Harbor Porpoise

Harbor porpoises are primarily seen near the Golden Gate Bridge, Marin County, and the city of San Francisco on the northwest side of SFB (Keener
et al.,
2012; Stern
et al.,
2017). CAS recorded 29 harbor porpoises (only 2 of which were alive) over the past 5 years, and
https://www.iNaturalist.org
recorded 11 harbor porpoises in SFB over the past 2 years. During 2020 monitoring, an individual harbor porpoise was seen near the project area on 2 of the 5 monitoring days (Haase, 2021), and a single harbor porpoise was observed within the Level B harassment zone during 11 days of monitoring in the spring of 2025 (Integral Consulting Inc., 2025b). Based on these data, PSF estimates that two harbor porpoises could occur within the MBFL project's Level B harassment zone per day, and NMFS concurs.

California Sea Lion

The Pier 39 K-Dock California sea lion haul-out site supports up to 1,701 individuals, with the highest abundance occurring from August through October. Pier 39 is the only regularly used sea lion haul-out site in the project vicinity, located approximately 3 mi (5 km) northwest of the MBFL project site. The Sea Lion Center at Pier 39 regularly counted sea lions at K-Dock from 1991 through 2018; from 2016 through 2018, the yearly average ranged from 89 to 229 animals per day; the average per day over all 3 years was 191. The maximum numbers of animals using the haul-out site in 2016, 2017, and 2018 were 707, 239, and 466 respectively; the average maximum per day over this period was 324. TMMC recorded 1,586 sea lions in SFB between September 2016 and September 2021. CAS recorded an additional 191 for a total of 1,777 over 5 years. Based on these data, PSF estimates that California sea lions could occur within the MBFL project's Level B harassment zone at a rate of 0.97 per day, and NMFS concurs with this approach.

Steller Sea Lion

Steller sea lions are rare in SFB. TMMC recorded four Steller sea lions in SFB from 2016 to 2021 (NMFS, 2021b), and CAS recorded no Steller sea lions over the same time frame (NMFS, 2021a). On rare occasions, Steller sea lions are seen on the Pier 39 K-Dock haul-out site (located approximately 3 miles (5 km) northwest of the MBFL site). An adult male was spotted there in May 2023 (Segura, 2023), and, in previous years, a single male Steller sea lion had been observed using the Pier 39 K-Dock haul-out site intermittently during July and August, and occasionally September (Integral Consulting Inc., 2025a). No Steller sea lions were observed during the 2020 or 2025 monitoring (Haase, 2021; Integral Consulting Inc., 2025b). Given the potential for Stellar sea lion occurrence at Pier 39, if only rarely, NMFS feels it is appropriate to assume one Steller sea lion may occur in PSF's proposed project area during the period of construction.

Northern Fur Seal

TMMC recorded 44 northern fur seals in SFB from 2016 to 2021 (NMFS, 2021b). CAS recorded an additional 3 for a total of 47 over 5 years (NMFS, 2021a), yielding a frequency of 0.03 northern fur seals per day, or approximately 10 northern fur seals per year. In the fall and winter, northern fur seals occasionally strand on YBI and Treasure Island (Integral Consulting Inc., 2025a), approximately 3.3 mi (5.3 km) from PSF's proposed project area. PSF assumes 10 northern fur seals could occur in the proposed project area and within the Level B harassment zone per year (
i.e.,
within the effective period of the proposed IHA), given the maximum potential sightings in San Franciso Bay averaged over a 5-year period is 10 individuals. NMFS concurs with this approach.

Northern Elephant Seal

TMMC recorded 903 northern elephant seals in SFB from 2016 to 2021 (NMFS, 2021b). The CAS reported an additional 6 northern elephant seals over the same timeframe (NMFS, 2021a), for a total of 909 seals, yielding an average of 0.5 northern elephant seals per day. No northern elephant seals were observed during monitoring efforts conducted in 2020 and 2025 (Haase, 2021; Integral Consulting Inc., 2025b). Based on these data, PSF assumed 0.5 elephant seals will occur in the proposed project area per day (
i.e.,
one elephant seal in the ensonified zone

every 2 days). NMFS concurs with this assumption.

Pacific Harbor Seal

Pacific harbor seals in SFB forage mainly within 7 mi (11.3 km) of their primary haul-out site (Grigg
et al.,
2012) and often within just 1-3 mi (1.6-4.8 km) (Torok, 1994). The only harbor seal haul-out site within 7 mi (11.3 km) of the project site is YBI, approximately 3.3 mi (5.3 km) northeast of the MBFL site. Given the large Level B harassment zone sizes predicted for vibratory installation of 48-in steel caisson sleeves (21,554 m) and 36-in steel pipe piles (29,286 m), and DTH driving of 36-in steel pipe piles (39,811 m), it is likely harbor seals foraging in the vicinity of the YBI would enter the ensonified area during pile installations.

The TMMC recorded 495 harbor seals in SFB between September 2016 and September 2021. CAS recorded an additional 34 for a total of 529 over the same period, yielding an average of 0.29 per day. CALTRANS has reported between zero and 188 harbor seals using the YBI haul-out site, depending on the year. PSF determined that an occurrence rate estimate for harbor seals based on the CALTRANS dataset (3.957 harbor seals per day) would be appropriate, given the large sample size, and NMFS concurs.

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 estimate take by Level B harassment for the gray whale, harbor porpoise, California sea lion, northern elephant seal, and harbor seal, the species-specific expected daily occurrence was multiplied by the estimated number of construction days for the entire project (n=46), which includes only 32 days of in-water construction with the potential for incidental take of marine mammals (see table 1) and an additional 14 days to support placement of the 24-in octagonal concrete piles, a process th

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2026-06484. Public record. Not legal advice.