# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Tillamook South Jetty Repairs in Tillamook Bay, Oregon

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2022-13605

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** June 27, 2022
- **Citation:** 87 FR 38116

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XC074]
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Tillamook South Jetty Repairs in Tillamook Bay, Oregon

AGENCY:

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

ACTION:

Notice; proposed incidental harassment authorizations; request for comments on proposed authorizations and possible renewals.

SUMMARY:

NMFS has received a request from the U.S. Army Corps of Engineers (USACE)—Portland District (Corps) for authorization to take marine mammals incidental to 2 years of activity associated with Tillamook South Jetty Repairs in Tillamook Bay, Oregon. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue two one-year incidental harassment authorizations (IHAs) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-time, one-year renewal for each IHA that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorization and agency responses will be summarized in the final notice of our decision.

DATES:

Comments and information must be received no later than July 27, 2022.

ADDRESSES:

Comments should be addressed to Jolie Harrison, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service and should be submitted via email to
ITP.renytysonmoore@noaa.gov.

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
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:

Reny Tyson Moore, Office of Protected Resources, NMFS, (301) 427-8401. Electronic copies of the application and supporting documents, as well as a list of the references cited in this document, may be obtained online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities.
In case of problems accessing these documents, please call the contact listed above.

SUPPLEMENTARY INFORMATION:

Background

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

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

The definitions of all applicable MMPA statutory terms cited above are included in the relevant sections below.

National Environmental Policy Act

To comply with the National Environmental Policy Act of 1969 (NEPA; 42 U.S.C. 4321
et seq.
) and NOAA Administrative Order (NAO) 216-6A, NMFS must review our proposed actions (
i.e.,
the issuance of two IHAs) 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 NOAA Administrative Order 216-6A, which do not individually or cumulatively have the potential for significant impacts on the quality of the human environment and for which we have not identified any extraordinary circumstances that would preclude this categorical exclusion. Accordingly, NMFS has preliminarily determined that the issuance of the proposed IHAs qualifies to be categorically excluded from further NEPA review.

We will review all comments submitted in response to this notice prior to concluding our NEPA process or making a final decision on the IHA requests.

Summary of Request

On February 11, 2022, NMFS received a request from the Corps for two one-year IHAs to take marine mammals incidental to repairs of the Tillamook South Jetty in Tillamook Bay, Oregon. The application was deemed adequate and complete on May 23, 2022. The Corps' request is for take of five species of marine mammals by Level B harassment and, for a subset of these species (
i.e.,
harbor seals (
Phoca vitulina richardii
), northern elephant seals (
Mirounga angustriostris
), and harbor porpoises (
Phocoena phocoena
)), take by Level A harassment. Neither the Corps nor NMFS expect serious injury or mortality to result from this activity and, therefore, IHAs are appropriate.

Description of Proposed Activity

Overview

The Corps constructed, and continues to maintain, two jetties at the entrance of Tillamook Bay, Oregon to provide reliable navigation into and out of the bay. A Major Maintenance Report (MMR) was completed in 2003 to evaluate wave damage to the jetties and provide design for necessary repairs. Some repairs to the North Jetty were completed in 2010, and further repairs to the North Jetty root and trunk began in January 2022. The Tillamook South Jetty Repairs Project (
i.e.,
the “proposed activities”) would complete critical repairs to the South Jetty, as described in the MMR, with a focus on rebuilding the South Jetty head. Work would consist of repairs to the existing structures within the original jetty footprints (
i.e.,
trunk repairs and the construction of a 100-foot cap to repair the South Jetty Head), with options to facilitate land- and water-based stone transport, storage, and placement operations. A temporary material offload facility (MOF), which would be approximately 15 meters (m) (50 feet (ft)) by 30 m (100 ft), would be constructed to transfer jetty rock from barges to shore at the South Jetty.

The two IHAs requested by the Corps would be associated with the construction (Year 1 IHA) and removal (Year 2 IHA) of the temporary MOF. Construction of the MOF would involve vibratory (preferred) and/or impact pile driving of up to 10 12-inch H piles, 24 24-inch timber or steel pipe piles, and 250 24-inch steel sheets (type NZ, AZ, PZ, or SCZ), and is anticipated to occur during the first year of the project (November 1, 2022 through October 31, 2023). Removal of the MOF would involve vibratory extraction of all installed piles and sheets and is anticipated to occur between November 1, 2024 and October 31, 2025. The Corps proposed work windows are between November and February and between July and August each year to adhere to terms and conditions outlined in the U.S. Fish and Wildlife Service (USFWS) Biological Opinion (BiOp) to minimize potential take of the Western snowy plover (WSP), currently listed as threatened under the Endangered Species Act (ESA). Sounds resulting from pile installation and removal from these proposed activities may result in the incidental take of marine mammals by Level A and Level B harassment.

Dates and Duration

Completion of the South Jetty repairs is anticipated to take multiple construction seasons. The primary in-water sound effects would be associated with construction (Year 1 IHA) and deconstruction (Year 2 IHA) of a MOF at Kincheloe Point. MOF construction/deconstruction would only occur during the aforementioned work windows and when weather conditions would not restrict watercraft operations or compromise crew safety. The Corps anticipates commencing work in the autumn of 2022. Construction of the

MOF is anticipated to take 20 to 23 days and to occur between November 1, 2022 and February 15, 2023 or between July 1, 2023 and August 31, 2023. Deconstruction of the MOF is estimated to take 13 days and is anticipated to occur between November 1, 2024 and February 15, 2025 or between July 1, 2025 and August 31, 2025. The Corps plans to conduct pile driving only during daylight hours (from sunrise to sunset).

Specific Geographic Region

Tillamook Bay is located on the Oregon Coast near the city of Garibaldi in Tillamook County, Oregon (Figure 1). The Bay is protected from the open ocean by shoals and a sandbar called the Bayocean Peninsula. It is generally very shallow, with depths ranging from 0.3 to 2.1 m (1 to 7 ft) throughout most of the Bay, but reaching depths of up to 10 m (32 ft) in the South, Main, and Bay City Channels. The sediment in Tillamook Bay consists primarily of sand or mud, and there are several sea grass beds present in the region. Tillamook Bay provides a safe harbor for the water-dependent economies of local and state entities. It is the third largest bay in Oregon and sustains significant biological and economic resources. The proposed activities would be located on the Bayocean Split, Tillamook County, Oregon (Tillamook Bay, River Mile 1; Section 18, 19, and 20 of Township 1N, Range 10W; Latitude: 45.565500, Longitude: −123.948983).

EN27JN22.001

The Port of Garibaldi is located approximately 3.2 kilometers (km) (2 miles (mi)) east of the entrance to Tillamook Bay and contains a lumber mill, seafood processing plants, marine repair shops, a commercial and charter fishing marina, and a public boat launch. The United States Coast Guard (USCG) Station Tillamook Bay is also located at the Port of Garibaldi; operations include towing vessels and assisting recreational and commercial boaters throughout the year with five search and rescue boats. The U.S. Highway 101 corridor is adjacent to Tillamook Bay, passing through the coastal cities of Bay City, Garibaldi, and Barview closest to the South Jetty (see Figure 1-1 in the Corps' application). The nearest residences to the proposed activity area are located in Barview, approximately 610 m (2,000 ft) away on the opposite side of the entrance channel.

Detailed Description of Specific Activity

The purpose of the proposed activities is to protect the structural integrity of the Tillamook South Jetty and to improve navigation conditions at the channel entrance through major maintenance repair activities. As with most jetties along the Oregon coast, the Tillamook South Jetty was constructed to facilitate safe navigation and support a more stable entrance channel at the mouth of Tillamook Bay. It was

constructed in phases between 1969 and 1979 to a final length of 2,046 m (8,025 ft). The South Jetty currently has a total length that is approximately 320 m (1,050 ft) shorter than the authorized footprint, and the head is severely damaged with an estimated recession rate of approximately 8.5 m (28 ft) per year. As with the Tillamook North Jetty, there has also been erosion of the jetty trunk. No repairs have occurred since the original construction. The 2003 MMR report and subsequent 2014 Corps inspection recommended several repair actions that are the basis for the proposed construction activities. Repair activities would consist of two main components at the South Jetty: trunk repairs and construction of a 30 m (100-ft) cap to repair the South Jetty head.

In addition to stone placement at the South Jetty head and trunk, related construction activities associated with these repairs, specifically the delivery and storage of new stone, include the construction of a temporary MOF near Kincheloe Point; channel dredging to maintain access to MOF; roadway improvements and possible turnouts along Bayocean Dike Road; and utilization of two upland staging and stockpiling areas: one primary staging area adjacent to the South Jetty trunk and a smaller staging area near the MOF. The Contractor will ultimately decide on the means and methods for construction, within these constraints and the conditions outlined in the proposed IHAs. Given uncertainty about which features will be implemented to facilitate site access, the Corps' application assumes a temporary MOF, which requires pile driving, would be constructed to accommodate barge operations. The proposed activities also include removal and site restoration for each of the temporary construction features upon project completion. As discussed in further detail below, NMFS assumes that take of marine mammals is likely to result only from pile driving activities conducted as part of the MOF construction/removal and not from activities related to the delivery, storage, or placement of jetty stone.

Construction Staging Areas

Jetty repairs and associated construction elements require areas for equipment and supply staging and storage, parking areas, access roads, scales, general yard requirements, and jetty stone stockpile areas. There would be one primary staging area adjacent to the South Jetty trunk and a smaller staging area near the MOF (Figure 1). Temporary erosion controls would be put in place before any alteration of the sites. An Erosion and Sediment Control Plan (ESCP) would outline facilities and Best Management Practices (BMPs) that would be implemented and installed prior to any ground-disturbing activities on the project site, including mobilization. These erosion controls would prevent pollution caused by surveying or construction operations and ensure sediment-laden water do not leave the project site, enter Tillamook Bay, or impact aquatic and terrestrial wildlife.

Ocean barging is anticipated to be the primary method of material and equipment transport; however, Bayocean Dike Road (Figure 1) would be used to access the staging areas and work sites. Prior to construction, the road would be improved to facilitate the necessary level of construction traffic. Specific details and locations of road improvement actions would depend on the condition of the road at the start of construction, however any improvements or alterations would avoid wetlands and waters of the U.S. to the maximum extent practicable. Roadway improvements would also avoid any locations identified as having significant cultural resources.

There are no known pinnipeds haul-outs on the sites proposed for these staging areas or near the proposed access roads (see Description of Marine Mammals in the Area of Specified Activities). Therefore, upland activities related to the development of the staging areas and access roads are not anticipated to impact any marine mammal species, and are not considered further in our analysis.

Temporary Material Offloading Facility

A temporary MOF is needed to transfer jetty rock from barges to shore at the South Jetty. The MOF would provide moorage for barges and a structure for crane support. The preferred location of the MOF is on the south side of Kincheloe Point, on the site of a former staging area (Figure 1). Detailed design of the MOF would be completed closer to the time of construction. The discussion below is based on general assumptions about likely design elements. These assumptions represent a conservative scenario for purposes of analysis.

The offloading platform could require the use of an anchor line moorage or dolphins. The platform would be approximately 15 m (50 ft) by 30 m (100 ft) and would be constructed using a sheet pile perimeter wall, installed using a vibratory hammer. A maximum of 24, 24-inch timber or steel piles would be installed as mooring dolphins, up to 10, 12-inch steel H-piles will be installed for support, and up to 250, 24-inch steel sheets (type NZ, AZ, PZ, or SCZ) would be driven for the perimeter wall. The maximum pile diameter would be 24 inches, and caps (or other deterrence devices) would be installed on each pile to discourage birds from perching. The platform would be constructed within the confines of the perimeter wall by filling in the area with backfill. The H-piles would be shoreward of installed sheets and most likely driven into the fill material with very little water, if any. A contractor would be limited by these general constraints, but the final MOF design would be per their discretion, largely based on site conditions, material availability, and cost. The MOF would be sited to avoid direct impacts to eelgrass during construction. In-water noise incidental to vibratory and impact pile driving of the MOF is anticipated to result in Level A harassment and/or Level B harassment.

Vibratory hammers are the preferred method of pile installation. However, impact driving may be required for steel pipe piles if vibratory means prove infeasible (impact pile driving would not be required for any other pile type). For any impact driving of steel piles, a confined bubble curtain will be used to reduce in-water sound. Pile driving to construct the MOF is anticipated to take 20 (vibratory installation methods only) to 23 (vibratory and impact installation methods) days over the course of a month (Table 1) and would occur under the first IHA (Year 1). Multiple piles would not be driven concurrently. Vibratory hammers would be used to remove the temporary MOF and is anticipated to take an additional 13 days over the course of a month (Table 1). Deconstruction would occur under the second IHA (Year 2).

Table 1—Summary of Pile Details and Estimated Effort Required for the Construction and Deconstruction of the Temporary MOF

Pile type
Size

Number of sheets/
piles

Vibratory
installation
duration per pile/sheet
(minutes)

Vibratory
removal
duration per pile/sheet
(minutes)

Potential impact strikes per pile, if needed

Production rate
(piles/day)

Installation
(vibratory)

Installation
(impact)

Removal
(vibratory)

Range of installation days anticipated
1

Vibratory only
Vibratory and impact

Range of
vibratory
removal days

anticipated
1

AZ Steel Sheet
2

24-inch
250
10
3

25

50
10-12
10-12
5-7

Timber or Steel Pile
24-inch
24
15
5
533
8
4
12
3-6
6-9
2-4

H-Pile
12-inch
10
10
3

10

10
1-2
1-2
1-2

Project totals
284
49.83 hours
16.17 hours

14-20
17-23
8-13

1
The minimum days of installation and removal are based on the expected production rates. The maximum days of installation and removal are estimated assuming built in contingency days, which have been added into the construction schedule, are needed.

2
Or comparable.

Dredging

In order to allow fully loaded barges to access the MOF, dredging would occur prior to the construction of the platform. Based on the conditions at the preferred MOF location, it is conservatively estimated that no more than 5,000 cubic yards of material would be dredged. The barge route from the main channel to the MOF will be sited to avoid potential adverse effects to eelgrass to the maximum extent practicable. The area dredged would include the area adjacent to the shore where the barge would be moored (see Figure 1-4 in the Corps' application). Sandy dredged material removed to facilitate barge access would be placed in the Primary Staging Area as indicated in Figure 1-3 in the Corps' application and used to fill depressions and create better habitat for WSP post construction.

The scope and duration of dredging would be limited to the minimum area and amount of time needed to achieve project purposes. Initial MOF dredging would take approximately one week to complete, and will occur between July 15 and March 15 to avoid the peak timing for juvenile coho salmon outmigration. Ongoing maintenance will occur as needed. Only mechanical dredging would be permissible, and dredges would be operated to limit dredge spillover.

The Corps will work to meet state water quality standards. To minimize water turbidity and the potential for entrainment of organisms during dredging for the MOF, the clamshell bucket or head of the dredge would remain on the bottom to the greatest extent possible and only be raised 1 m (3 ft) off the bottom when necessary for dredge operations. Turbidity levels will be monitored via visual observations to identify any adverse detectable change in water quality. A hand-held turbidity meter will be deployed and used during MOF dredging and fill activities. No more than 10 percent cumulative increase in natural stream turbidities may be allowed, as measured relative to a control point immediately upstream of the turbidity causing activity. However, limited duration activities necessary to address an emergency or to accommodate essential dredging, construction, or other legitimate activities and which cause the standard to be exceeded may occur provided all practicable turbidity control techniques have been applied. See Oregon Administrative Rules (OAR) 340-041-0036.

While dredging may produce underwater noise above the relevant harassment threshold (
i.e.,
between 150 and 180 dB; Clark
et al.,
2002; Miles
et al.,
1986), the noise produced by dredging is similar to other common on-and in-water industrial activities typically occurring in the area. Additionally, dredging will only occur in a relatively small and confined area of Tillamook Bay over a short duration of time (
i.e.,
5 days), limiting the potential for impacts. Therefore, incidental takes of marine mammals are not anticipated or proposed to be authorized for dredging activities, and this activity is not considered further in our analysis.

South Jetty Maintenance and Repairs

Significant repairs are proposed along the South Jetty, where the majority of work would occur from STA 70+00 westward. These stations are enumerated in 30 m (100-ft) increments such that STA 71+00 would be 30 m (100 ft) seaward from STA 70+00. Additional repairs to the jetty trunk between Stations 43+00 and 49+00 are also planned. The jetty cap will be from STA 77+00 to 77+75 to elevation + 5.5 m (18 ft) relative to North American Vertical Datum of 1988 (NAVD88). From the final head station centerline, the end of the jetty will be built out in a 6 m (20 ft) radius to elevation + 5.5 m (18 ft) NAVD88. The crest width of the jetty cap would be 12 m (40 ft). The crest width of the jetty trunk would be 9 m (30 ft) with a target crest elevation of + 5.5 m (18 ft) NAVD88. The average stone density would be approximately 180 pounds (lbs)/ft
3
, and the total quantity of stone required for the proposed activities is estimated at 31,000 cubic yards (~76,000 tons). Stone placement at the South Jetty would take just under 150 working days.

While placement of jetty stone could produce noise, NMFS has determined that sounds produced from this action would not exceed marine mammal thresholds beyond 10 m (33 ft) from the source in the water and beyond 100 m (328 ft) from the source in the air (86 FR 22151; April 27, 2021). There are no known pinniped haul-outs or other known important marine mammal habitats within the vicinity of the South Jetty (see Description of Marine Mammals in the Area of Specified Activities) limiting the potential for impacts from stone placement. Therefore, incidental takes of marine mammals are not anticipated or proposed to be authorized for jetty stone placement, and are not considered further in our analysis.

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

Description of Marine Mammals in the Area of Specified Activities

Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history of the potentially affected species. NMFS fully considered all of this information, and we refer the reader to these descriptions, incorporated here by reference, instead

of reprinting the information. Additional information regarding population trends and threats may be found in NMFS' Stock Assessment Reports (SARs;
www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments
) and more general information about these species (
e.g.,
physical and behavioral descriptions) may be found on NMFS' website (
https://www.fisheries.noaa.gov/find-species).

Table 2 lists all species or stocks for which take is expected and proposed to be authorized for these activities, and summarizes information related to the population or stock, including regulatory status under the MMPA and ESA and potential biological removal (PBR), where known. PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (as described in NMFS' SARs). While no serious injury or mortality is anticipated or authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species 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 SARs (
e.g.,
Carretta
et al.
2021) or Alaska SARs (
e.g.,
Muto et al. 2020). All values presented in Table 2 are the most recent available at the time of publication and are available in the 2020 SARs (Carretta
et al.
2021, Muto
et al.,
2020) and draft 2021 SARs (available online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports
).

Table 2—Species Likely Impacted by the Specified Activities

Common name
Scientific name
MMPA stock

ESA/MMPA status; strategic

(Y/N)
1

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

PBR

Annual M/SI
3

Superfamily Odontoceti (toothed whales, dolphins, and porpoises)

Family Phocoenidae (porpoises):

Harbor Porpoise

Phocoena phocoena

Northern OR/WA Coast
-,-, N
21,487 (0.44; 15,123; 2011)
151
≥3.0

Order Carnivora—Superfamily Pinnipedia

Family Otariidae (eared seals and sea lions):

California sea lion

Zalophus californianus

U.S.
-,-, N
257,606 (N/A.; 233,515; 2014)
14,011
>320

Steller sea lion

Eumetopias jubatus

Eastern
-,-, N
43,201 (N/A; 43,201; 2017)
2,592
112

Family Phocidae (earless seals):

Harbor seal

Phoca vitulina richardii

OR/CA Coastal
-, N
24,732 (0.12; N/A; 1999)
UND
10.6

Northern elephant seal

Mirounga angustirostris

California Breeding
-,-, N
187,386 (N/A; 85,369; 2013)
5,122
5.3

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

2
NMFS marine mammal stock assessment reports online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.
CV is coefficient of variation; N
min
is the minimum estimate of stock abundance. In some cases, CV is not applicable (N.A.).

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

As indicated above, all 5 species (with 5 managed stocks) in Table 2 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. All species (26 marine mammal species and 27 marine mammal stocks) that could potentially occur in the proposed survey areas are included in Table 3-3 of the Corps' application. The majority of the species listed in the Corps' table are unlikely to occur in the project vicinity. For example, numerous cetaceans (
i.e.,
sei whale,
Balaenoptera borealis borealis;
fin whale,
Balaenoptera physalus physalus;
Risso's dolphin,
Grampus griseus;
common bottlenose dolphin,
Tursiops truncatus truncatus;
striped dolphin,
Stenella coeruleoalba;
common dolphin,
Delphinus delphis;
short-finned pilot whale,
Globicephala macrorhynchus;
Baird's beaked whale,
Berardius bairdii;
Mesoplodont beaked whale,
Mesoplodon spp.;
Cuvier's beaked whale,
Ziphius cavirostris;
pygmy sperm whale,
Kogia breviceps;
dwarf sperm whale,
Kogia sima;
sperm whale,
Physeter macrocephalus
) are only encountered at the continental slope (>20 km/12 mi offshore) or in deeper waters offshore and would not be affected by construction activities. Other species may occur closer nearshore but are rare or infrequent seasonal inhabitants off the Oregon coast (
i.e.,
minke whale,
Balaenoptera acutorostrata scammoni;
Pacific white-sided dolphin,
Lagenorhynchus obliquidens;
Northern right-whale dolphin,
Lissodelphis borealis;
killer whale,
Orcinus orca
(“Eastern North Pacific Southern Resident Stock”); Dall's porpoise,
Phocoenoides dalli dalli
). Given these considerations, the temporary duration of potential pile driving, and noise isopleths that would not extend beyond the bay entrance (please see Estimated Take), there is no reasonable expectation for the proposed activities to affect the above species and they will not be addressed further.

While ten marine mammal species could occur in the vicinity of the proposed project activities (
i.e.,
harbor seals; Northern elephant seal; Steller sea lion; California sea lion; humpback whales,
Megaptera novaeangliae;
fin whales,
Balaenoptera physalus physalus;
gray whales,
Eschrichtius robustus;
blue whales,
Balaenoptera musculus musculus;
killer whales,
Orcinus orca;
and harbor porpoises), Tillamook Bay is relatively shallow and

noise resulting from the construction/deconstruction of the MOF would be limited to the interior waters of the bay and would not extend to coastal waters. Larger whales (
e.g.,
humpback whales, fin whales, gray whales, blue whales, killer whales) may transit the waters near the coastline but are unlikely inhabitants of Tillamook Bay itself. In reviewing OBIS-SEAMAP (2022) and records for all marine mammals recorded within a 16 km (10 mi) radius of Tillamook Bay, only humpback whales, gray whales, harbor porpoises, California sea lions, Steller sea lions, and harbor seals were commonly reported. Killer whales have only been seen on rare occasions (TinyFishTV, 2014; rempeetube, 2016; Corey.c, 2017), and Dall's porpoise (and northern right whale dolphins have been reported a bit further offshore (Halpin
et al.,
2009; OBIS-SEAMAP, 2022). Gray whales and humpback whales have been observed in the vicinity of Tillamook Bay, however, they are highly unlikely to enter the relatively shallow waters of Tillamook Bay and be subject to pile driving noise disturbance. Given these considerations, take of these species (
i.e.,
humpback whales, fin whales, gray whales, blue whales, killer whales) is not expected to occur, and they are not discussed further beyond the explanation provided here.

Harbor Porpoise

In the Pacific Ocean, harbor porpoise are found in coastal and inland waters from Point Conception, California to Alaska and across to Kamchatka and Japan (Gaskin, 1984). Six harbor porpoise stocks have been designated off California/Oregon/Washington, based on genetic analyses and density discontinuities identified from aerial surveys. While harbor porpoise are rare within Tillamook Bay, if present, animals likely belong to the Northern Oregon/Washington Coast stock, which is delimited from Cape Flattery, Washington (located approximately 320 km (198 mi) north of Tillamook Bay), to Lincoln City, Oregon (located approximately 68 km (42 mi) south of Tillamook Bay) (Carretta
et al.,
2022).

Entanglement is the primary cause of human-related injury and death for harbor porpoises, however, estimated fishery mortality and serious injury rates are well below PBR. Harbor porpoises are sensitive to disturbance by a variety of anthropogenic sound sources, and the limited range of several U.S. West Coast harbor porpoise stocks makes them particularly vulnerable to potential impacts (see overview in Forney
et al.,
2017).

Harbor porpoises on the Pacific Northwest coast of the United States are typically found in waters roughly 100-200 m (328-656 ft) deep (NOAA, 2013a; Holdman
et al.
2018). They occur along the Oregon coast year-around and may be slightly more abundant in summer and exhibit diel or tidal movement patterns related to prey availability (Holdman
et al.,
2018). Harbor porpoises have been detected within a 16 km (10 mi) radius of the Tillamook Bay entrance channel (Halpin
et al.,
2009; OBIS-SEAMAP, 2022), and they could potentially occur in the project vicinity during the proposed activities.

California Sea Lion

California sea lions are distributed along the North Pacific waters from central Mexico to southeast Alaska, with breeding areas restricted primarily to island areas off southern California (the Channel Islands), Baja California, and in the Gulf of California (Carretta
et al.,
2021). There are five genetically distinct geographic populations. The population seen in Oregon is the Pacific Temperate population (which comprises the U.S. stock managed by NMFS), which are commonly seen in Oregon from September through May (ODFW, 2015).

The occurrence of the California sea lion along the Oregon coast is seasonal with lowest abundance in Oregon in the summer months, from May to September, as they migrate south to the Channel Islands in California to breed. They are commonly found in Oregon haul-out sites from September to May and during this period, adult and subadult males have been observed in bays, estuaries, and offshore rocks along the Oregon coast. In fact, a few males have been reported in Oregon waters throughout the year (Mate, 1973). The population breeds in the California Channel Islands and most females and young pups remain in that region year-around (Mate, 1973).

The California sea lion stock has been growing steadily since the 1970s. The stock is estimated to be approximately 40 percent above its maximum net productivity level (MNPL = 183,481 animals), and it is therefore considered within the range of its optimum sustainable population (OSP) size (Laake
et al.,
2018). The stock is also near its estimated carrying capacity of 275,298 animals (Laake
et al.,
2018). However, there remain many threats to California sea lions including entanglement, intentional kills, harmful algal blooms, and climate change. For example, for each 1 degree Celsius increase in sea surface temperature (SST), the estimated odds of survival declined by 50 perfect for pups and yearlings, while negative SST anomalies resulted in higher survival estimates (DeLong
et al.,
2017). Such declines in survival are related to warm oceanographic conditions (
e.g.,
El Niño) that limit prey availability to pregnant and lactating females (DeLong
et al.,
2017). Changes in prey abundance and distribution have been linked to warm-water anomalies in the California Current that have impacted a wide range of marine taxa (Cavole
et al.,
2016), including California sea lions. For example, between 2013 and 2017, NOAA declared an unusual mortality event (UME) for California sea lions as high mortality of pup and juvenile age classes were documented during this time. NOAA identified changes in the availability of sea lion prey species, particularly sardines, as a contributing factor.

California sea lions may occur in the project vicinity, but there have been no confirmed sightings in Tillamook Bay (Halpin
et al.,
2009; OBIS-SEAMAP, 2022). The closest known haul out site is at Three Arch Rock, which is approximately 23 km (14 mi) south of the proposed site of the MOF.

Steller Sea lion

The Steller sea lion range extends along the Pacific Rim, from northern Japan to central California. For management purposes, Steller sea lions inhabiting U.S. waters have been divided into two DPS: the Western U.S. and the Eastern U.S. Steller sea lions encountered off the Oregon coast are part of the Eastern U.S. Stock, with rookeries in California, Oregon, Washington, Southeast Alaska, and British Columbia (Muto
et al.,
2021). The Western U.S. stock of Steller sea lions are listed as endangered under the ESA and depleted and strategic under the MMPA. The Eastern U.S. stock (including those living in Oregon) was de-listed in 2013 following a population growth from 18,040 in 1979 to 70,174 in 2010 (an estimated annual growth of 4.18 percent) (NMFS, 2013). A population growth model indicates the eastern stock of Steller sea lions increased at a rate of 4.25 percent per year (95 percent confidence intervals of 3.77-4.72 percent) between 1987 and 2017 based on an analysis of pup counts in California, Oregon, British Columbia, and Southeast Alaska (Muto
et al.,
2021). This stock is likely within its OSP; however, no determination of its status relative to OSP has been made (Muto
et al.,
2021).

Off the Oregon coast, Steller sea lions have been observed ashore from the Columbia River south to Rogue Reef and typically inhabit offshore rocks and

islands. There are seven major haul-out sites noted in Oregon during the breeding season, however, there are no known rookery sites near Tillamook Bay (Pitcher
et al.,
2007). The closest known haul out site is at Three Arch Rock, which is approximately 23 km (14 mi) south of the proposed site of the MOF. Steller sea lions have been detected in Tillamook Bay during marine mammal surveys (Pearson and Verts, 1970; Halpin
et al.,
2009; Ford
et al.,
2013) and may occur in the vicinity of the project.

Harbor Seal

Harbor seals inhabit coastal and estuarine waters off Baja California, north along the western coasts of the continental U.S., British Columbia, and Southeast Alaska, west through the Gulf of Alaska and Aleutian Islands, and in the Bering Sea north to Cape Newenham and the Pribilof Islands (Caretta
et al.,
2021). Within U.S. west coast waters, five stocks of harbor seals are recognized: (1) Southern Puget Sound (south of the Tacoma Narrows Bridge); (2) Washington Northern Inland Waters (including Puget Sound north of the Tacoma Narrows Bridge, the San Juan Islands, and the Strait of Juan de Fuca); (3) Hood Canal; (4) Oregon/Washington Coast; and (5) California. Seals potentially affected by this activity would be part of the Oregon/Washington Coast stock.

Harbor seals generally are non-migratory, with local movements associated with tides, weather, season, food availability, and reproduction (Scheffer and Slipp, 1944; Fisher, 1952; Bigg 1969, 1981). Harbor seals do not make extensive pelagic migrations, though some long distance movement of tagged animals in Alaska (900 km, 559 mi) and along the U.S. west coast (up to 550 km, 342 mi) have been recorded (Brown and Mate, 1983; Herder, 1986; Womble, 2012). Harbor seals have displayed strong fidelity to haulout sites (Pitcher and Calkins, 1979; Pitcher and McAllister, 1981).

Harbor seals were historically hunted in Oregon as a nuisance to fishermen, however, their numbers have steadily increased since the passage of the MMPA in 1972 (Harvey, 1987; Brown
et al.,
2005). While harbor seals are still subject to incidental take from commercial fisheries in the region, overall mortality is relatively low. However, the most recent abundance estimate available for this stock dates to 1999 (Carretta
et al.,
2021).

Harbor seals are one of the most abundant pinnipeds in Oregon and can typically be found in coastal marine and estuarine waters of the Oregon coast throughout the year. On land, they can be found on offshore rocks and islands, along shore, and on exposed flats in the estuary (Harvey, 1987). There is one haul-out site roughly 1.5 km (0.9 mi) east of the proposed MOF that has been historically noted in Tillamook Bay. This haul-out is located on an intertidal sand flat in the middle of the bay (See Figure 4-1 in the Corps' application) and highest utilization has been observed during the May/June reproductive season (B.E. Wright, personal communication, February 12, 2021; ODFW, 2022). This is consistent with other findings noting harbor seals being more abundant in Tillamook Bay during the summer pupping season (Brown and Mate, 1983). There is also evidence that animals may move between Netarts Bay, a prominent feeding site located approximately 15 km (9 mi) south of Tillamook Bay, and Tillamook Bay in the non-pupping season (Brown and Mate, 1983). Therefore, harbor seals are expected to occur in the vicinity of the project.

Northern Elephant Seal

The California Breeding Stock of Northern elephant seals breeds and gives birth in California and makes extended foraging trips to areas including coastal Oregon biannually during the fall and spring (Le Boeuf
et al.,
2000). While both males and females may transit areas off the Oregon coast, males seem to have focal forage areas near the continental shelf break while females typically move further offshore and feed opportunistically at numerous sites while in route (Le Beouf
et al.,
2000).

Populations of northern elephant seals in the U.S. and Mexico have recovered after being nearly hunted to extinction (Stewart
et al.,
1994). Northern elephant seals underwent a severe population bottleneck and loss of genetic diversity when the population was reduced to an estimated 10-30 individuals (Hoelzel
et al.,
2002). Although movement and genetic exchange continues between rookeries, most elephant seals return to natal rookeries when they start breeding (Huber
et al.,
1991). The California breeding population is now demographically isolated from the Baja California population. No international agreements exist for the joint management of this species by the U.S. and Mexico. The California breeding population is considered to be a separate stock (Carretta
et al.,
2022).

The population is currently susceptible to incidental take and injury from gillnet and trawl fisheries operating offshore, however, the human-caused mortality is still well below the estimated PBR level.

There have been no recorded sightings of northern elephant seals in the immediate vicinity of Tillamook Bay, however, there have been sightings toward Netarts Bay, located approximately 14 km (9 mi) south of the Tillamook South Jetty, and further offshore (Halpin
et al.,
2009; OBIS-SEAMAP, 2022). Therefore, northern elephant seals could transit the area.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities (
e.g.,
Richardson
et al.,
1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall
et al.
(2007, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc.). Note that no direct measurements of hearing ability have been successfully completed for mysticetes (
i.e.,
low-frequency cetaceans). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65 decibel (dB) threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall
et al.
(2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in Table 3.

Table 3—Marine Mammal Hearing Groups
[NMFS, 2018]

Hearing group
Generalized hearing range *

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

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

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

275 Hz to 160 kHz.

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

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

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

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

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

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

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

Acoustic effects on marine mammals during the specified activity can occur from impact and vibratory pile driving. The effects of underwater noise from the Corps' proposed activities have the potential to result in Level A and Level B harassment of marine mammals in the action area.

Description of Sound Sources

This section contains a brief technical background on sound, on the characteristics of certain sound types, and on metrics used in this proposal inasmuch as the information is relevant to the specified activity and to a discussion of the potential effects of the specified activity on marine mammals found later in this document. For general information on sound and its interaction with the marine environment, please see,
e.g.,
Au and Hastings (2008); Richardson
et al.
(1995); Urick (1983).

Sound travels in waves, the basic components of which are frequency, wavelength, velocity, and amplitude. Frequency is the number of pressure waves that pass by a reference point per unit of time and is measured in hertz (Hz) or cycles per second. Wavelength is the distance between two peaks or corresponding points of a sound wave (length of one cycle). Higher frequency sounds have shorter wavelengths than lower frequency sounds, and typically attenuate (decrease) more rapidly, except in certain cases in shallower water. Amplitude is the height of the sound pressure wave or the “loudness” of a sound and is typically described using the relative unit of the dB. A sound pressure level (SPL) in dB is described as the ratio between a measured pressure and a reference pressure (for underwater sound, this is 1 microPascal (μPa)), and is a logarithmic unit that accounts for large variations in amplitude; therefore, a relatively small change in dB corresponds to large changes in sound pressure. The source level represents the SPL referenced at a distance of 1 m from the source (referenced to 1 μPa), while the received level is the SPL at the listener's position (referenced to 1 μPa).

Root mean square (RMS) is the quadratic mean sound pressure over the duration of an impulse. RMS is calculated by squaring all of the sound amplitudes, averaging the squares, and then taking the square root of the average (Urick, 1983). RMS accounts for both positive and negative values; squaring the pressures makes all values positive so that they may be accounted for in the summation of pressure levels (Hastings and Popper, 2005). This measurement is often used in the context of discussing behavioral effects, in part because behavioral effects, which often result from auditory cues, may be better expressed through averaged units than by peak pressures.

Sound exposure level (SEL; represented as dB referenced to 1 micropascal squared per second (re 1 μPa
2
-s)) represents the total energy in a stated frequency band over a stated time interval or event, and considers both intensity and duration of exposure. The per-pulse SEL is calculated over the time window containing the entire pulse (
i.e.,
100 percent of the acoustic energy). SEL is a cumulative metric; it can be accumulated over a single pulse, or calculated over periods containing multiple pulses. Cumulative SEL (SELcum) represents the total energy accumulated by a receiver over a defined time window or during an event. Peak sound pressure (also referred to as zero-to-peak sound pressure or 0-pk) is the maximum instantaneous sound pressure measurable in the water at a specified distance from the source, and is represented in the same units as the RMS sound pressure.

When underwater objects vibrate or activity occurs, sound-pressure waves are created. These waves alternately compress and decompress the water as the sound wave travels. Underwater sound waves radiate in a manner similar to ripples on the surface of a pond and may be either directed in a beam or beams or may radiate in all directions (omnidirectional sources), as is the case for sound produced by the pile driving activity considered here. The compressions and decompressions associated with sound waves are detected as changes in pressure by aquatic life and man-made sound receptors such as hydrophones.

Even in the absence of sound from the specified activity, the underwater environment is typically loud due to

ambient sound, which is defined as the all-encompassing sound in a given place and is usually a composite of sound from many sources both near and far (ANSI, 1995). The sound level of a region is defined by the total acoustical energy being generated by known and unknown sources. These sources may include physical (
e.g.,
wind and waves, earthquakes, ice, atmospheric sound), biological (
e.g.,
sounds produced by marine mammals, fish, and invertebrates), and anthropogenic (
e.g.,
vessels, dredging, construction) sound. A number of sources contribute to ambient sound, including wind and waves, which are a main source of naturally occurring ambient sound for frequencies between 200 Hz and 50 kilohertz (kHz) (Mitson, 1995). In general, ambient sound levels tend to increase with increasing wind speed and wave height. Precipitation can become an important component of total sound at frequencies above 500 Hz, and possibly down to 100 Hz during quiet times. Marine mammals can contribute significantly to ambient sound levels, as can some fish and snapping shrimp. The frequency band for biological contributions is from approximately 12 Hz to over 100 kHz. Sources of ambient sound related to human activity include transportation (surface vessels), dredging and construction, oil and gas drilling and production, geophysical surveys, sonar, and explosions. Vessel noise typically dominates the total ambient sound for frequencies between 20 and 300 Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz and, if higher frequency sound levels are created, they attenuate rapidly.

A recent study of ambient ocean sound for Oregon's nearshore environment observed maximum and minimum levels of 136 dB re 1 μPa and 95 dB re 1 μPa, respectively, with an average level of 113 dB re 1 μPa over a period of one year (Haxel
et al.,
2011). This level could vary given the presence of different recreational and commercial vessels (
e.g.,
up to 150 dB for small fishing vessels (Hildebrand, 2005), up to 186 dB for large vessels, 81 to 166 dB for empty tugs and barges and up to 170 dB for loaded tugs and barges (Richardson
et al.,
1995) within the frequencies between 20 and 5000 Hz), or other factors (
e.g.,
wind and waves, traffic noise along adjacent roadways, aquatic animals, currents, etc.) as described above. No direct data on ambient noise levels within Tillamook Bay are available; however, in-water ambient noise levels are considered comparable to similar bays.

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

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

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

The likely or possible impacts of the Corps' proposed activities on marine mammals could involve both non-acoustic and acoustic stressors. Potential non-acoustic stressors could result from the physical presence of the equipment and personnel; however, given there are no known pinniped haul-out sites in the vicinity of the proposed site of the MOF construction/deconstruction, visual and other non-acoustic stressors would be limited, and any impacts to marine mammals are expected to primarily be acoustic in nature. Acoustic stressors include effects of heavy equipment operation during pile installation and removal.

Acoustic Impacts

The introduction of anthropogenic noise into the aquatic environment from pile driving and removal is the primary means by which marine mammals may be harassed from the Corps' specified activities. In general, animals exposed to natural or anthropogenic sound may experience physical and psychological effects, ranging in magnitude from none to severe (Southall
et al.,
2007, 2019). In general, exposure to pile driving noise has the potential to result in auditory threshold shifts and behavioral reactions (
e.g.,
avoidance, temporary cessation of foraging and vocalizing, changes in dive behavior). Exposure to anthropogenic noise can also lead to non-observable physiological responses such an increase in stress hormones. Additional noise in a marine mammal's habitat can mask acoustic cues used by marine mammals to carry out daily functions such as communication and predator and prey detection. The effects of pile driving 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 (threshold shifts)

followed by behavioral effects and potential impacts on habitat.

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

Permanent Threshold Shift (PTS)
—NMFS defines PTS as a permanent, irreversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Available data from humans and other terrestrial mammals indicate that a 40 dB threshold shift approximates PTS onset (see Ward
et al.,
1958, 1959; Ward, 1960; Kryter
et al.,
1966; Miller, 1974; Ahroon
et al.,
1996; Henderson
et al.,
2008). PTS levels for marine mammals are estimates, as with the exception of a single study unintentionally inducing PTS in a harbor seal (Kastak
et al.,
2008), there are no empirical data measuring PTS in marine mammals largely due to the fact that, for various ethical reasons, experiments involving anthropogenic noise exposure at levels inducing PTS are not typically pursued or authorized (NMFS, 2018).

Temporary Threshold Shift (TTS)
—A temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Based on data from cetacean TTS measurements (see Southall
et al.
2007), a TTS of 6 dB is considered the minimum threshold shift clearly larger than any day-to-day or session-to-session variation in a subject's normal hearing ability (Schlundt
et al.,
2000; Finneran
et al.,
2000, 2002). As described in Finneran (2015), marine mammal studies have shown the amount of TTS increases with SELcum in an accelerating fashion: at low exposures with lower SELcum, the amount of TTS is typically small and the growth curves have shallow slopes. At exposures with higher SELcum, the growth curves become steeper and approach linear relationships with the noise SEL.

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

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

TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 1985). 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. Currently, TTS data only exist for four species of cetaceans (bottlenose dolphin), beluga whale (
Delphinapterus leucas
), harbor porpoise, and Yangtze finless porpoise (
Neophocoena asiaeorientalis
)) and five species of pinnipeds exposed to a limited number of sound sources (
i.e.,
mostly tones and octave-band noise) in laboratory settings (Finneran, 2015). TTS was not observed in trained spotted (
Phoca largha
) and ringed (
Pusa hispida
) seals exposed to impulsive noise at levels matching previous predictions of TTS onset (Reichmuth
et al.,
2016). In general, harbor seals and harbor porpoises have a lower TTS onset than other measured pinniped or cetacean species (Finneran, 2015). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species. No data are available on noise-induced hearing loss for mysticetes. For summaries of data on TTS in marine mammals or for further discussion of TTS onset thresholds, please see Southall
et al.
(2007), Finneran and Jenkins (2012), Finneran (2015), and Table 5 in NMFS (2018).

Construction and deconstruction of the MOF, which is required to repair the Tillamook South Jetty, requires a combination of impact pile driving and vibratory pile driving. During this project, these activities will not occur at the same time and there will be pauses in activities producing the sound during each day. Given these pauses and that many marine mammals are likely moving through the project area and not remaining for extended periods of time, the potential for TTS declines.

Behavioral Harassment
—Exposure to noise from pile driving and removal also has the potential to behaviorally disturb marine mammals. Behavioral disturbance may include a variety of effects, including subtle changes in behavior (
e.g.,
minor or brief avoidance

of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Disturbance may result in changing durations of surfacing and dives, changing direction and/or speed; reducing/increasing vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); eliciting a visible startle response or aggressive behavior (such as tail/fin slapping or jaw clapping); avoidance of areas where sound sources are located. Pinnipeds may increase their haul out time, possibly to avoid in-water disturbance (Thorson and Reyff, 2006). Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors (
e.g.,
species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (
e.g.,
Richardson
et al.,
1995; Wartzok
et al.,
2003; Southall
et al.,
2007; Weilgart, 2007; Archer
et al.,
2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison
et al.,
2012), and can vary depending on characteristics associated with the sound source (
e.g.,
whether it is moving or stationary, number of sources, distance from the source). In general, pinnipeds seem more tolerant of, or at least habituate more quickly to, potentially disturbing underwater sound than do cetaceans, and generally seem to be less responsive to exposure to industrial sound than most cetaceans. Please see Appendices B and C of Southall
et al.
(2007) and Gomez
et al.
(2016) for reviews of studies involving marine mammal behavioral responses to sound.

Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok
et al.,
2003). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder
et al.,
2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure.

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

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

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

Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators (
e.g.,
bubble nets or sediment plumes), or changes in dive behavior. As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance (
e.g.,
Croll
et al.,
2001; Nowacek
et al.,
2004; Madsen
et al.,
2006; Yazvenko
et al.,
2007). A determination of whether foraging disruptions incur fitness consequences would require information on or estimates of the energetic requirements of the affected individuals and the relationship between prey availability, foraging effort and success, and the life history stage of the animal.

Variations in respiration naturally vary with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in understanding species differences in the tolerance of underwater noise when determining the potential for impacts resulting from anthropogenic sound exposure (
e.g.,
Kastelein
et al.,
2001, 2005, 2006; Gailey
et al.,
2007).

Marine mammals vocalize for different purposes and across multiple modes, such as whistling, echolocation click production, calling, and singing. Changes in vocalization behavior in response to anthropogenic noise can occur for any of these modes and may result from a need to compete with an increase in background noise or may reflect increased vigilance or a startle response. For example, in the presence of potentially masking signals, humpback whales and killer whales have been observed to increase the length of their songs (Miller
et al.,
2000; Fristrup
et al.,
2003; Foote
et al.,
2004), while right whales (
Eubalaena glacialis
) have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks
et al.,
2007). In some cases, animals may cease sound production during production of aversive signals (Bowles
et al.,
1994).

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

A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response (
e.g.,
directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996, Bowers
et al.,
2018). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (Evans and England, 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response.

Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention (
i.e.,
when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been demonstrated for marine mammals, but studies involving fish 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 five-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 one day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall
et al.,
2007). Note that there is a difference between multi-day substantive behavioral reactions and multi-day anthropogenic activities. For example, just because an activity lasts for multiple days does not necessarily mean that individual animals are either exposed to activity-related stressors for multiple days or, further, exposed in a manner resulting in sustained multi-day substantive behavioral responses.

Stress responses
—An animal's perception of a threat may be sufficient to trigger stress responses consisting of some combination of behavioral responses, autonomic nervous system responses, neuroendocrine responses, or immune responses (
e.g.,
Seyle, 1950; Moberg, 2000). In many cases, an animal's first and sometimes most economical (in terms of energetic costs) response is behavioral avoidance of the potential stressor. Autonomic nervous system responses to stress typically involve changes in heart rate, blood pressure, and gastrointestinal activity. These responses have a relatively short duration and may or may not have a significant long-term effect on an animal's fitness.

Neuroendocrine stress responses often involve the hypothalamus-pituitary-adrenal system. Virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction, altered metabolism, reduced immune competence, and behavioral disturbance (
e.g.,
Moberg, 1987; Blecha, 2000). Increases in the circulation of glucocorticoids are also equated with stress (Romano
et al.,
2004).

The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and “distress” is the cost of the response. During a stress response, an animal uses glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose serious fitness consequences. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other functions. This state of distress will last until the animal replenishes its energetic reserves sufficient to restore normal function.

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

Auditory Masking
—Since many marine mammals rely on sound to find prey, moderate social interactions, and facilitate mating (Tyack, 2008), noise from anthropogenic sound sources can interfere with these functions, but only if the noise spectrum overlaps with the hearing sensitivity of the marine mammal (Southall
et al.,
2007; Clark
et al.,
2009; Hatch
et al.,
2012). Chronic exposure to excessive, though not high-intensity, noise could cause masking at particular frequencies for marine mammals that utilize sound for vital biological functions (Clark
et al.,
2009). Acoustic masking is when other noises such as from human sources interfere

with an animal's ability to detect, recognize, or discriminate between acoustic signals of interest (
e.g.,
those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson
et al.,
1995; Erbe
et al.,
2016). Therefore, under certain circumstances, marine mammals whose acoustical sensors or environment are being severely masked could also be impaired from maximizing their performance fitness in survival and reproduction. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest (
e.g.,
signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities (
e.g.,
sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions.

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

The frequency range of the potentially masking sound is important in determining any potential behavioral impacts. For example, low-frequency signals may have less effect on high-frequency echolocation sounds produced by odontocetes but are more likely to affect detection of mysticete communication calls and other potentially important natural sounds such as those produced by surf and some prey species. The masking of communication signals by anthropogenic noise may be considered as a reduction in the communication space of animals (
e.g.,
Clark
et al.,
2009) and may result in energetic or other costs as animals change their vocalization behavior (
e.g.,
Miller
et al.,
2000; Foote
et al.,
2004; Parks
et al.,
2007; Di Iorio and Clark, 2009; Holt
et al.,
2009). Masking can be reduced in situations where the signal and noise come from different directions (Richardson
et al.,
1995), through amplitude modulation of the signal, or through other compensatory behaviors (Houser and Moore, 2014). Masking can be tested directly in captive species (
e.g.,
Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild (
e.g.,
Branstetter
et al.,
2013).

Marine mammals in Tillamook Bay are exposed to anthropogenic noise which may lead to some habituation, but is also a source of masking. Vocalization changes may result from a need to compete with an increase in background noise and include increasing the source level, modifying the frequency, increasing the call repetition rate of vocalizations, or ceasing to vocalize in the presence of increased noise (Hotchkin and Parks, 2013).

Masking is more likely to occur in the presence of broadband, relatively continuous noise sources. Energy distribution of pile driving covers a broad frequency spectrum, and sound from pile driving would be within the audible range of pinnipeds and cetaceans present in the proposed action area. While some pile driving during the Corps' activities may mask some acoustic signals that are relevant to the daily behavior of marine mammals, the short-term duration and limited areas affected make it very unlikely that survival would be affected.

Airborne Acoustic Effects
—Pinnipeds that occur near the project site could be exposed to airborne sounds associated with pile driving and removal 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 the acoustic criteria. However, given that the closest known haul outs are approximately 1.5 km (0.9 mi) away for harbor seals and approximately 23 km (14 mi) or greater for California sea lions, Steller sea lions, and northern elephant seals, the likelihood of pinnipeds being exposed to airborne noise over the short duration of intermittent pile driving and removal is low.

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

Marine Mammal Habitat Effects

The Corps' proposed activities would not result in permanent negative impacts to habitats used directly by marine mammals, but may have potential short-term impacts to food sources such as forage fish and may affect acoustic habitat (see masking discussion above). There are no known foraging hotspots or other ocean bottom structure of significant biological importance to marine mammals present in the marine waters of the project area. The Corps' proposed activities in Tillamook Bay could have localized, temporary impacts on marine mammal habitat and their prey by increasing in-water sound pressure levels and slightly decreasing water quality. During impact pile driving and vibratory pile driving or removal, elevated levels of underwater noise would ensonify a portion of Tillamook Bay where both fishes and mammals occur and could affect foraging success. Additionally, marine mammals may avoid the area during construction, however, displacement due to noise is expected to be temporary and is not expected to result in long-term effects to the individuals or populations. The proposed construction activities are of short duration and would likely have temporary impacts on marine mammal habitat through increases in underwater and airborne sound.

Pile installation/removal may temporarily increase turbidity resulting from suspended sediments. Any increases would be temporary, localized, and minimal. In general, turbidity associated with pile installation is localized to about a 7.6 m

(25 ft) radius around the pile (Everitt
et al.,
1980). Cetaceans and pinnipeds in Tillamook Bay are not expected to be close enough to the project pile driving areas to experience effects of turbidity; however, if they were they could avoid localized areas of turbidity. Therefore, the impact from increased turbidity levels is expected to minimal for marine mammals. Furthermore, pile driving and removal at the project site would not obstruct movements or migration of marine mammals.

Potential Pile Driving Effects on Prey
—Sound from pile driving may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species (
e.g.,
crustaceans, cephalopods, fish, zooplankton). Marine mammal prey varies by species, season, and location. Here, we describe studies regarding the effects of noise on known marine mammal prey.

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

Fish react to sounds that are especially strong and/or intermittent low-frequency sounds. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. The reaction of fish to noise depends on the physiological state of the fish, past exposures, motivation (
e.g.,
feeding, spawning, migration), and other environmental factors. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pile driving on fish; several are based on studies in support of large, multiyear bridge construction projects (
e.g.,
Scholik and Yan, 2001, 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 (summarized in Popper
et al.,
2014). However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen
et al.
(2012a) showed that a TTS of 4-6 dB was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long. Injury caused by barotrauma can range from slight to severe and can cause death, and is most likely for fish with swim bladders. Barotrauma injuries have been documented during controlled exposure to impact pile driving (Halvorsen
et al.,
2012b; Casper
et al.,
2013).

The most likely impact to fish from pile driving and removal activities at the project area would be temporary behavioral avoidance of the area. The duration of fish avoidance of this area after pile driving stops is unknown, but a rapid return to normal recruitment, distribution, and behavior is anticipated. In general, impacts to marine mammal prey species are expected to be minor and temporary due to the short timeframe of the project.

In summary, given the short daily duration of sound associated with individual pile driving and the small area being affected relative to available nearby habitat, 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 or other prey. 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

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

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

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

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

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

Acoustic Thresholds

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

Level B Harassment
—Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context (
e.g.,
frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment (
e.g.,
bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict (
e.g.,
Southall
et al.,
2007, 2021, Ellison
et al.,
2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS generally predicts that marine mammals are likely to be behaviorally harassed in a manner considered to be Level B harassment when exposed to underwater anthropogenic noise above root-mean-squared pressure received levels (RMS SPL) of 120 dB (referenced to 1 micropascal (re 1 μPa)) for continuous (
e.g.,
vibratory pile-driving, drilling) and above RMS SPL 160 dB re 1 μPa for non-explosive impulsive (
e.g.,
seismic airguns) or intermittent (
e.g.,
scientific sonar) sources.

The Corps' proposed activity includes the use of continuous (vibratory pile driving/removal) and impulsive (impact pile driving) sources, and therefore the RMS SPL thresholds of 120 and 160 dB re 1 μPa are applicable.

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

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

Table 4—Thresholds Identifying the Onset of Permanent Threshold Shift

Hearing group

PTS Onset Thresholds *
(received level)

Impulsive
Non-impulsive

Low-Frequency (LF) Cetaceans

Cell 1: L
p,
0-pk,flat
:
219 dB;
L
E,p,
LF,24h
:
1183 dB

Cell 2: L
E,p
, LF,24h
:
199 dB.

Mid-Frequency (MF) Cetaceans

Cell 3: L
p,
0-pk,flat
:
230 dB;
L
E,p,
MF,24h
:
1185 dB

Cell 4: L
E,p
, MF,24h
:
198 dB.

High-Frequency (HF) Cetaceans

Cell 5: L
p,
0-pk,flat
:
202 dB;
L
E,p
,HF,24h
:
155 dB

Cell 6: L
E,p,
HF,24h
:
173 dB.

Phocid Pinnipeds (PW) (Underwater)

Cell 7: L
p,
0-pk.flat
:
218 dB;
L
E,p
,PW,24h
:
1185 dB

Cell 8: L
E,p,
PW,24h
:
201 dB.

Otariid Pinnipeds (OW) (Underwater)

Cell 9: L
p,
0-pk,flat
:
232 dB;
L
E,p
,OW,24h
:
203 dB

Cell 10: L
E,p,
OW,24h
:
219 dB.

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

Note:
Peak sound pressure level (
L
p,
0-pk
) has a reference value of 1 µPa, and weighted cumulative sound exposure level (
L
E,p
) has a reference value of 1µPa
2
s. In this Table, thresholds are abbreviated to be more reflective of International Organization for Standardization standards (ISO 2017). The subscript “flat” is being included to indicate peak sound pressure are flat weighted or unweighted within the generalized hearing range of marine mammals (
i.e.,
7 Hz to 160 kHz). The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The weighted cumulative sound exposure level thresholds could be exceeded in a multitude of ways (
i.e.,
varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to indicate the conditions under which these thresholds will be exceeded.

Ensonified Area

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

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

Sound Source Levels of Proposed Activities
—The intensity of pile driving sounds is greatly influenced by factors such as the type of piles, hammers, and the physical environment in which the activity takes place. In order to calculate distances to the Level A harassment and Level B harassment sound thresholds for the methods and piles being used in this project, NMFS used empirical data from sound source verification (SSV) studies reported in Navy (2015) and CALTRANS (2020), to develop source levels for the various pile types, sizes and methods (Table 5). These proxies were chosen as they were obtained from SSV studies on piles of comparable types and sizes and/or in comparable environments (
e.g.,
they had comparable water depths). Note that these source levels represents the SPL referenced at a distance of 10 m from the source. It is conservatively assumed that the Corps will use steel instead of timber for the 24-inch pipe piles as the estimated proxy values for steel are louder than timber (
e.g.,
Greenbusch Group, 2018; 84 FR 61026, November 12, 2019). It is also conservatively assumed that vibratory removal will produce comparable levels of in-water noise as vibratory installation.

Table 5—Estimates of Underwater Sound Levels Generated During Vibratory and Impact Pile Installation, and Vibratory Pile Removal

Pile driving method
Pile description

Source level
(dB peak)

Source level
(dB RMS)

Source level
(dB SEL)

Reference

Impact (attenuated
1
)

24-inch steel pipe pile
198
184
173
CALTRANS (2020).

Vibratory (installation and removal; unattenuated)

24-inch steel pipe pile
24-inch AZ steel sheets

177

161
163

163

Navy (2015).
CALTRANS (2020).

12-inch steel H-piles
165
150
147
CALTRANS (2020).

1
The estimated SPLs for 24-inch steel pipes assume a 5 dB reduction resulting from the use of a confined bubble curtain system.

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

TL = B * log10 (R1/R2),

Where:

B = transmission loss coefficient (assumed to be 15)

R1 = the distance of the modeled SPL from the driven pile, and

R2 = the distance from the driven pile of the initial measurement.

This formula neglects loss due to scattering and absorption, which is assumed to be zero here. The degree to which underwater sound propagates away from a sound source is dependent on a variety of factors, most notably the water bathymetry and presence or absence of reflective or absorptive conditions including in-water structures and sediments. The recommended TL coefficient for most nearshore environments is the practical spreading value of 15. This value results in an expected propagation environment that would lie between spherical and cylindrical spreading loss conditions, which is the most appropriate assumption for the Corps' proposed construction activities in the absence of specific modelling. All Level B harassment isopleths are reported in Table 7 considering RMS SSLs for impact and vibratory pile driving, respectively.

Level A Harassment Zones
—The ensonified area associated with Level A harassment is more technically challenging to predict due to the need to account for a duration component. Therefore, NMFS developed an optional User Spreadsheet tool to accompany the Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically going to be overestimates of some degree, which may result in an overestimate of potential take by Level A harassment. However, this optional tool offers the best way to estimate isopleth distances when more sophisticated modeling methods are not available or practical. For stationary sources, such as vibratory and impact pile driving, the optional User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity, it would be expected to incur PTS. Inputs used in the optional User Spreadsheet tool, and the resulting estimated isopleths, are reported in Table 6.

Table 6—NMFS User Spreadsheet Inputs

Impact pile driving
installation

24-inch steel pipe pile
Vibratory pile driving
Installation
24-inch steel pipe pile
24-inch AZ steel sheets
12-inch steel H-piles
Removal
24-inch steel pipe pile
24-inch AZ steel sheets
12-inch steel H-piles

Spreadsheet Tab Used
E.1) Impact pile driving
A.1) Non-Impul, Stat, Cont
A.1) Non-Impul, Stat, Cont
A.1) Non-Impul, Stat, Cont
A.1) Non-Impul, Stat, Cont
A.1) Non-Impul, Stat, Cont
A.1) Non-Impul, Stat, Cont.

Source Level (SPL)
173 dB SEL
161 dB RMS
163 dB RMS
150 dB RMS
161 dB RMS
163 dB RMS
150 dB RMS.

Transmission Loss Coefficient
15
15
15
15
15
15
15.

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

Number of strikes per pile
533

Time to install/remove single pile (minutes)

15
10
10
5
3
3.

Piles per day
4
8
25
10
12
50
10.

Table 7—Distances to Level A Harassment, by Hearing Group, and Level B Harassment Thresholds per Pile Type and Pile Driving Method

Activity
Pile description
Piles per day
Level A harassment distance (m)
HF
PW
OW

Level A

harassment areas (km
2
) for all

hearing
groups

Level B

harassment distance (m) all hearing groups
1

Level B

harassment areas (km
2
) for all

hearing

groups
1

Impact Installation (attenuated)
2

24-inch steel pipe pile
4
424.5
190.7
13.8
<0.5
399
0.39

Vibratory Installation
24-inch steel pipe pile
8
16.0
6.6
0.5
<0.1
5,412
20.14

24-inch AZ steel sheets
14
35.5
14.6
1.0
<0.1
7,357
27.01

12-inch steel H-piles
10
2.6
1.1
0.1
<0.1
1,000
1.84

Vibratory Removal
24-inch steel pipe pile
12
10.1
4.2
0.3
<0.1
5,412
20.14

24-inch AZ steel sheets
50
25.3
10.4
0.7
<0.1
7,357
27.01

12-inch steel H-piles
10
1.2
0.5
0.0
<0.1
1,000
1.84

1
Harassment areas have been truncated where appropriate to account for land masses.

2
Distances to Level A harassment, by hearing group, for impact pile driving were calculated based on SEL source levels as they resulted in larger, thus more conservative, isopleths for calculating PTS onset than Peak source levels.

Marine Mammal Occurrence and Take Estimation

In this section we provide information about the occurrence of marine mammals, including density or other relevant information, that will inform the take calculations. We also describe how the information provided above is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization.

In most cases, recent marine mammal counts, density estimates, or abundance estimates were not available for Tillamook Bay. Thus, information regarding marine mammal occurrence from proximal data obtained from nearshore sightings and haul-out sites (
e.g.,
Three Arch Rock) is used to approximate local abundance in Tillamook Bay. When proximal count estimates were available (
i.e.,
for harbor seals, Steller sea lions, and California sea lions), the Corps derived density estimates with an assumption that surveys accounted for animals present in the entirety of Tillamook Bay, an area roughly 37 km
2
(Oregon Coastal Atlas, 2022). The Corps multiplied marine mammal densities by isopleth areas to estimate potential take associated with pile driving. Given that marine mammal densities are likely not uniform in Tillamook Bay, NMFS instead estimates potential take associated with pile driving for these and the other marine mammal species assuming maximum daily occurrence rates (based on the abovementioned nearby proximal count estimates) multiplied by the total number of action days estimated per activity. There may be 20 (vibratory pile driving only) to 23 (vibratory and impact pile driving) total days of noise exposure from pile driving during the Corps' proposed activities in Year 1 and 13 (vibratory removal only) total days of noise exposure from pile driving during the Corps' proposed activities in Year 2. Takes for Year one for all species except harbor porpoises (see below) are estimated assuming that both vibratory and impact pile driving will be necessary and thus the maximum number of days of action days are required (
i.e.,
23 days). Takes for Year two assume that 13 total action days are required. A summary of take proposed for authorization is available in Tables 8 and 9.

Harbor Porpoises

There were multiple occurrences of 1-2 harbor porpoises detected in the coastal waters just north of the Tillamook Bay entrance during June and July of 1990 (Halpin
et al.,
2009; Ford
et al.,
2013). More recently, aerial surveys have detected single animals near the Tillamook Bay entrance in October 2011 and September 2012 (Adams
et al.,
2014). Although there were no recorded harbor porpoise observations within Tillamook Bay itself, the species is somewhat cryptic and there is potentially low detection during aerial surveys. Thus, NMFS estimates the daily harbor porpoise abundance within Tillamook Bay to be 1 individual.

During Year 1, if impact pile driving is necessary for driving steel piles, the Level A harassment distance for this activity for harbor porpoises is larger than the Level B harassment distance (Table 7) and the proposed shutdown zone (see the Proposed Mitigation section). Therefore, the Corps proposed that all harbor porpoises in Tillamook Bay on days when impact pile driving occurs would be taken by Level A harassment. NMFS concurs with this estimate and proposes to authorize 9 instances of take by Level A harassment for harbor porpoises in Year 1 during construction of the MOF (1 harbor porpoise per day × 9 days of impact pile driving = 9 takes by Level A harassment).

During Year 1, if vibratory and impact pile driving is required, the Corps estimated that there could be 14 takes of harbor porpoises by Level B harassment (1 harbor porpoise per day × 12 days vibratory installing steel sheets = 12 takes by Level B harassment, and 1 harbor porpoise per day × 2 days vibratory installing H piles = 2 takes by Level B harassment, for a total of 14 takes by Level B harassment; Table 1). If only vibratory pile driving is required, the Corps estimated that 20 harbor porpoises may be taken by Level B harassment (1 harbor porpoise per day × 20 total action days; Table 1). Therefore, to be conservative, NMFS proposes to authorize 20 instances of take by Level B harassment for harbor porpoises (the maximum estimate of animals that may be taken by Level B harassment based on the two likely scenarios) in Year 1 during construction of the MOF.

During Year 2, the Corps requested and NMFS proposes to authorize 13 instances of take by Level B harassment for harbor porpoises during vibratory removal of the MOF (1 harbor porpoise per day × 13 total action days; Table 1). No Level A harassment is anticipated to occur or proposed to be authorized. Considering the small Level A harassment zones (Table 7) in comparison to the required shutdown zones (see the Proposed Mitigation section) it is unlikely that a harbor porpoise will enter and remain within the area between the Level A harassment zone and the shutdown zone for a duration long enough to be taken by Level A harassment.

California Sea Lions

The estimate for daily California sea lion abundance (n = 11) is based on coastal surveys conducted between 2002 and 2005 (Scordino, 2006). While pile driving will occur in winter or summer, the maximum number of animals detected during any month (
i.e.,
11 sea lions in April) at the Three Arch Rock haul out site, located approximately 23

km (14 mi) from the proposed site of the MOF, was used to estimate daily occurrence by the Corps. Given the distance of this haul out site from the proposed activities, the fact that pile driving is not expected to occur in April due to timing constrictions, and the low likelihood that all animals present at the Three Arch Rock would leave and enter Tillamook Bay on a single day; the Corps' estimated that approximately half of the individuals present at Three Arch Rock (6 California sea lions) could potentially enter Tillamook Bay during pile driving and be subject to acoustic harassment. NMFS concurs and estimates, based on the best available science, the daily California sea lion abundance within Tillamook Bay to be 6 individuals.

During Year 1, NMFS proposes to authorize 138 instances of take by Level B harassment for California sea lions during the construction of the MOF (6 California sea lions per day × 23 total action days required for impact and vibratory pile driving; Table 1). During Year 2, NMFS proposes to authorize 78 instances of take by Level B harassment for California sea lions during vibratory removal of the MOF (6 California sea lions per day × 13 total action days; Table 1). Under either scenario, Level A harassment is not anticipated or proposed to be authorized for Year 1 or Year 2. Considering the small Level A harassment zones (Table 1) in comparison to the required shutdown zones (see the Proposed Mitigation section) it is unlikely that a California sea lion will enter and remain within the area between the Level A harassment zone and the shutdown zone for a duration long enough to be taken by Level A harassment.

Steller Sea Lions

The Corps and NMFS are unaware of any recent data regarding Steller sea lion abundance near Tillamook Bay. Therefore, seasonal Steller sea lion abundance was estimated based on the maximum number of animals detected (n = 38 for between November and February, and n = 58 between July and August) at the Three Arch Rock haul out site during coastal surveys between 2002 and 2005 (Scordino, 2006). Given that this haul out site is roughly 23 km (14 mi) away from the proposed MOF, the Corps conservatively estimated that half of the individuals present at Three Arch Rock (19 Steller sea lions between November and February, and 29 Steller sea lions between July and August) could potentially disperse throughout Tillamook Bay during pile driving and be subject to harassment from the proposed activities. For the purposes of our take estimation, NMFS conservatively assumes that the daily Steller sea lion abundance in Tillamook Bay is equivalent to the largest seasonal abundance that the Corps estimated would be present (
i.e.,
we assume that 29 individual Steller sea lions would be present each day in Tillamook Bay).

During Year 1, NMFS proposes to authorize 667 instances of take by Level B harassment for Steller sea lions during the construction of the MOF (29 Steller sea lions per day × 23 total action days required for impact and vibratory pile driving; Table 1). During Year 2, NMFS proposes to authorize 377 instances of take by Level B harassment for Steller sea lions during vibratory removal of the MOF (6 Steller sea lions per day × 13 total action days; Table 1). Under either scenario, Level A harassment is not anticipated or proposed to be authorized for Year 1 or Year 2. The Level A harassment zones (Table 1) are smaller than the required shutdown zones (see the Proposed Mitigation section), therefore it is unlikely that a Steller sea lion will enter and remain within the area between the Level A harassment zone and the shutdown zone for a duration long enough to be taken by Level A harassment.

Harbor Seals

The latest (May 2014) pinniped aerial surveys conducted by the Oregon Department of Fish and Wildlife (ODFW, 2022) estimated 220 harbor seals (pups and non-pups combined) within Tillamook Bay (B.E. Wright, personal communication, February 12, 2021). After applying the Huber
et al.
(2001) correction factor of 1.53, used to account for likely imperfect detection during surveys, the adjusted number of harbor seals that may have been present Tillamook Bay during the 2014 surveys is approximately 337 individuals. However, that estimate likely overestimates the number of harbor seals present in the non-pupping season. Therefore, the Corps used calculations from monthly surveys of Tillamook Bay haul out sites between 1978 and 1981 carried out by Brown and Mate (1983) to estimate the average proportion of animals present during the Nov—Feb and Jul—Aug proposed construction windows (relative to counts observed in May). Accounting for these proportions (0.67 and 1.2, respectively), the Corps estimated that the 337 harbor seals likely present in May 2014 would have equated to an average abundance of 226 harbor seals between November and February and 404 harbor seals between July and August. For the purposes of our take estimation, NMFS conservatively assumes that the daily harbor seal abundance in Tillamook Bay is equivalent to the largest seasonal abundance that the Corps estimated would be present (
i.e.,
we assume that 404 individual harbor seals would be present each day in Tillamook Bay).

During Year 1, NMFS estimates that 9,292 total instances of take for harbor seal

[Text truncated at 120,000 characters. The full text is on the page linked above.]

---

Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2022-13605. Public record. Not legal advice.