# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to U.S. Army Corps of Engineers Miller Sands Island, Rice Island, and Cottonwood Island Pile Dike Repairs Projects on the Lower Columbia River in Oregon and Washington

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2026-08153

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** April 27, 2026
- **Citation:** 91 FR 22498

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XF657]
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to U.S. Army Corps of Engineers Miller Sands Island, Rice Island, and Cottonwood Island Pile Dike Repairs Projects on the Lower Columbia River in Oregon and Washington

AGENCY:

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

ACTION:

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

SUMMARY:

NMFS has received a request from U.S. Army Corps of Engineers (USACE) for authorization to take marine mammals incidental to the Miller Sands-Rice Island Pile Dike Repairs Project (MSRI Project) and Cottonwood Island Pile Dike Replacement Project (CI Project) on the lower Columbia River (LCR) in Oregon and Washington. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue two incidental harassment authorizations (IHAs) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on possible one-time, 1-year renewals that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorizations and agency responses will be summarized in the final notice of our decision.

DATES:

Comments and information must be received no later than May 27, 2026.

ADDRESSES:

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

copies of the application and supporting documents, as well as a list of the references cited in this document, may be obtained online at:
https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act/incidental-take-authorizations-construction-activities.
In case of problems accessing these documents, please call the contact listed below.

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

FOR FURTHER INFORMATION CONTACT:

Austin Demarest, Office of Protected Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

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

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

National Environmental Policy Act

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

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

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 April 10, 2025, and May 9, 2025, NMFS received requests from USACE for two IHAs to take marine mammals incidental to pile driving (installation and removal) associated with construction to replace pile dikes at Miller Sands-Rice Island and Cottonwood Island on the lower Columbia River in Oregon and Washington. Following NMFS' review of each original application and multiple revised versions, USACE submitted revised versions for the MSRI Project and CI Project on March 9, 2026, and March 12, 2026, respectively. NMFS subsequently deemed the applications complete on March 26, 2026. USACE's request for the MSRI Project is for take of harbor porpoises, Steller sea lions, California sea lions, and harbor seals, by Level B harassment, and for a subset of these species, by Level A harassment. For the CI Project, USACE's request is for take of Steller sea lions, California sea lions, and harbor seals, by Level A and Level B harassment. Neither USACE nor NMFS expect serious injury or mortality to result from this activity and, therefore, IHAs are appropriate.

Description of Proposed Activity

Overview

The USACE proposes repairing and replacing pile dikes for two separate projects at different locations on the lower Columbia River (LCR). The projects would restore flood control, prevent erosion, maintain safe vessel passage, and reduce the frequency and need of maintenance dredging in the LCR. The USACE MSRI Project would repair and replace three existing pile dikes between river mile (RM) 23 and RM 25 near Altoona, Washington. The project includes removing debris and degraded timber piles, enhancing or extending enrockment which would replace three existing timber pile dikes, and connecting two of these three pile dikes together (connector). After enrockment is in place, eight steel Aid to Navigation (ATON) piles would be installed along the enrockment to mark the new pile dikes and pile dike connector. In-water construction is anticipated over 4 months between November 2026 through February 2027 in Wahkiakum County, Washington, and Clatsop County, Oregon.

The USACE CI Project would repair or replace 10 existing pile dikes between RM 68 and RM 71 in the LCR, southeast and directly upstream of Longview, Washington in Cowlitz County. The project would include construction of new shore attachments for 5 pile dikes, installing new steel marker piles at 10 pile dikes, enhancing or extending enrockment in place of existing pile dikes, and construction of up to 3 material offload facilities on Cottonwood Island. Construction for the CI Project is expected to occur over 4 months from November 2026 through February 2027. Activities from both projects that have the potential to result in Level A harassment and Level B harassment of marine mammals from underwater sound production include impact and vibratory pile installation and vibratory pile removal.

Dates and Duration

Each of these proposed IHAs would be valid for the statutory maximum of 1 year from the date of effectiveness. They would become effective upon written notification from the applicant to NMFS, but not beginning later than 1 year from the date of issuance or extending beyond 2 years from the date of issuance.

The MSRI Project is scheduled to span 5 months, with pile driving being restricted to a 4-month window between

November 2026 and March 2027. Debris and pile removal would require approximately 15 days, while pile installation would take approximately 8 days; construction days may be non-consecutive.

The CI Project is scheduled to occur over 4 months, from November 2026 through February 2027. Permanent and temporary pile installation or removal would take approximately 66 non-consecutive days. Activities for both projects would occur during daylight hours, specifically from 30 minutes before civil dawn to 30 minutes after civil dusk.

Specific Geographic Region

The LCR flows 146 miles (mi) or 235 kilometers (km) from Bonneville Dam to the Pacific Ocean. This reach of the river features a deep-draft shipping channel supporting major ports and connects major cities and towns in Oregon and Washington to the Pacific Ocean. The LCR serves as an important migratory corridor for salmonids, sturgeon, and eulachon (
Thaleichthys pacificus
) as they transition freshwater and marine life stages, while providing foraging opportunities for pinnipeds and other wildlife.

The Miller Rice pile dike system consists of seven Pile Dolphins (PDs) located between Miller Sands Island and Rice Island, extending from RM 22.75 to RM 24.63 in Wahkiakum County, Washington, and Clatsop County, Oregon (figure 1). The structures are identified by their RM location: PDs 22.75, 23.07, 23.39, 23.67, 23.71, 23.81, and 24.63. The MSRI Project would replace three of these PDs (
i.e.,
23.71, 23.81, and 24.63) which are situated approximately 13.5 km upstream and east of Astoria, Oregon, along the Federal Navigation Channel. The area experiences frequent vessel traffic, including recreational boats, tugboats, and large cargo vessels, which all contribute to the in-air and underwater acoustic environment.

The CI Project construction area is located between RM 68 and RM 71 of the LCR in Cowlitz County, Washington (figure 2). A total of 10 PDs would be replaced along Cottonwood Island in the Columbia River at RM 68.35, 68.57, 68.79, 69.01, 69.25, 69.51, 69.79, 70.07, 71.17, and 71.51. The project site is approximately 3.5 km upstream and southeast of Longview, Washington, directly south of the Cowlitz River confluence with the Columbia River. The CI Project area is situated within a highly industrialized area, and experiences frequent recreational and commercial vessel traffic, which all contribute to the in-air and underwater acoustic environment.

BILLING CODE 3510-22-P

EN27AP26.075

Figure 1—USACE Miller Sands-Rice Island Dike Repairs Project Site Map

EN27AP26.076

Figure 2—USACE Cottonwood Island Dike Repairs Project Site Map

BILLING CODE 3510-22-C
Detailed Description of the Specified Activity

The MSRI Project and the CI Project are needed to manage sediments, direct flow, provide bank protection, reduce the frequency and need of dredging, and to improve navigability within the LCR Federal Navigation Channel (FNC). The present-day pile dike system was built from 1917 through 1923 and from 1933 through 1939. After decades of deferred maintenance and repairs, the LCR pile dike system no longer functions as initially designed. Therefore, both of these proposed projects would replace degraded pile dikes and improve vessel navigability within sections of the FNC in the Columbia River.

The MSRI Project involves five construction activities:

1. Removing debris behind existing pile dikes.

2. Removing degraded timber piles, spreaders, and hardware.

3. Enhancing enrockment at three PDs (23.71, 23.81, and 24.63) by mechanically placing rock on the prior PD footprint and connecting enrockment between PD 23.71 and PD 23.81.

4. Installing eight new isolated ATON piles.

5. Site access and staging.

Debris removal and disposal would be followed by mechanical removal by direct pull methods or breaking existing timber piles at the mudline; therefore, vibratory pile extraction would not be necessary. Rock would be transported by barge and placed at each dike location using a crane or long-arm excavator with a clamshell bucket, orange peel grapple, or excavator bucket. Rocks (ranging from 50 to 1,000 pounds [22 to 454 kilograms]) would be lowered below the water's surface and released directly above the existing substrate. Rock placement would occur during the in-water work window (November-February), as well as in September and October.

After rock placement, eight new 24-inch steel pipe ATON piles would be installed to mark each PD and the PD connector. Vibratory hammers would be used to drive ATON piles to the point of refusal and then an impact hammer would be used to ensure that the piles are seated in the substrate. Impact and vibratory pile installation would occur over 8 days and sound produced from these activities has the potential to result in incidental take of marine mammals by Level A and Level B harassment. Activities 1, 2, 3, and 5 are not expected to cause take of marine mammals because these activities do not produce sound with characteristics likely to result in marine mammal harassment and are thus not discussed further.

Table 1—MSRI Project Pile Installation Summary

Method
Pile size, material

Pile type
and location

Piles/day
(min-max)

Time
(minutes) or
(strikes/pile)

Number
of piles

Min
duration
(days)

Max
duration

Vibratory
24-inch steel pipe
ATON-PD 23.71
1-8
12
2
1
2

Impact

(225)

Vibratory
24-inch steel pipe
ATON/Enrockment between PD 23.71 and PD 23.81

12
1

1

Impact

(225)

Vibratory
24-inch steel pipe
ATON/PD 23.81

12
2

2

Impact

(225)

Vibratory
24-inch steel pipe
ATON/24.63

12
3

3

Impact

(225)

Totals

8
1
8

The Cottonwood Project involves 5 construction activities:

1. Construction and removal of Material Offload Facilities (MOF).

2. Removal of 162 existing timber piles.

3. Installation of 114 new 12-inch timber piles offset from the original 5 PDs at RM 68.35, 69.01, 69.51, 69.76, and 70.7.

4. Installation of 17 steel pipe ATON piles between 10.75-24-inches in diameter.

5. Adding rock around the new piles for scour protection.

All materials associated with the CI Project would initially be transported by barges and tugboats to the construction site, which would be anchored in place with spuds. The MOF piles would be installed with a vibratory hammer and consist of 18 24-inch steel pipe piles and 100 24-inch steel sheet piles. A maximum of three MOFs can be built over 21 days and then removed over 10.5 days using vibratory methods. Existing damaged piles would be removed by vertical pull or by breaking them off at the mudline.

New piles would be installed using a vibratory hammer to the point of refusal and then an impact hammer would be used to ensure piles are seated in the substrate. Both timber and steel ATON piles can be installed on the same day, but only one pile at a time, with a maximum of 8 piles per day. Pile installation would occur over approximately 34 days.

All project activities, except for PD 68.35, would take place anytime during the in-water work window from November 2026 to February 2027. Work on PD 68.35 would be restricted to November due to its close proximity (200 meters (m)) to a seasonal pinniped haulout site. Activities 1, 3, and 4, which involve pile installation and removal with vibratory and impact hammers, and sound produced from these activities has the potential to result in incidental take of marine mammals by Level A and Level B harassment. Activities 2 and 5 are not expected to cause take of marine mammals because these activities do not produce sound with characteristics likely to result in marine mammal harassment and are thus not discussed further.

Table 2—CI Project Pile Installation and Removal Summary

Method
Pile size, material

Pile type and/or
location

Time/pile
(minutes),
(strikes/pile)

Number
of piles

Max
piles/day

Min
duration
(days)

Expected
duration
(days)

Installation

Vibratory
10.75-12-inch steel pipe
ATON
12
11
4
2.75
11

Impact

4.5 (225)

Vibratory
16-inch steel pipe
ATON
12
4
3
1.5
4

Impact

4.5 (225)

Vibratory
24-inch steel pipe
ATON
12
2
1
2
2

Impact

4.5 (225)

Vibratory
12-inch timber pole
PD 68.35
8
14
8
1.8
2

Impact

4.5 (225)

Vibratory
12-inch timber pole
PD 69.01
8
14
8
1.8
2

Impact

4.5 (225)

Vibratory
12-inch timber pole
PD 69.51
8
18
8
2.3
3

Impact

4.5 (225)

Vibratory
12-inch timber pole
PD 69.76
8
35
8
4.4
5

Impact

4.5 (225)

Vibratory
12-inch timber pole
PD 70.7
8
33
8
4.1
5

Impact

4.5 (225)

Vibratory
24-inch steel pipe
MOF 1
12
18
8
2.25
3

Vibratory
24-inch steel sheet
MOF 1
10
100
25
4
4

Vibratory
24-inch steel pipe
MOF 2
12
18
8
2.25
3

Vibratory
24-inch steel sheet
MOF 2
10
100
25
4
4

Vibratory
24-inch steel pipe
MOF 3
12
18
8
2.25
3

Vibratory
24-inch steel sheet
MOF 3
10
100
25
4
4

Total Duration of Pile Installation (days)
39.4
55

MOF Removal

Vibratory
24-inch steel pipe
MOF 1
12
18
8
2.25
3

Vibratory
24-inch steel sheet
MOF 1
3
100
200
0.5
0.5

Vibratory
24-inch steel pipe
MOF 2
12
18
8
2.25
3

Vibratory
24-inch steel sheet
MOF 2
3
100
200
0.5
0.5

Vibratory
24-inch steel pipe
MOF 3
12
18
8
2.25
3

Vibratory
24-inch steel sheet
MOF 3
3
100
200
0.5
0.5

Total Duration of Pile Removal (days)
8.25
10.5

Total Duration of Pile Driving and Removal (days)
47.65
65.5

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

Description of Marine Mammals in the Area of Specified Activities

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

Table 3 lists all four species and stocks for which take is expected and proposed to be authorized for the MSRI Project and a subset of three species (California sea lion, Steller sea lion, and harbor seal) for which take is expected and proposed to be authorized the CI Project. Tables 3 summarizes information related to the population or stock, including regulatory status under the MMPA and Endangered Species Act (ESA) and potential biological removal (PBR), where known. PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (as described in NMFS' SARs). While no serious injury or mortality is anticipated or proposed to be authorized here, PBR and annual serious injury and mortality (M/SI) from anthropogenic sources are included here as gross indicators of the status of the species or stocks and other threats.

Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Alaska and Pacific SARs. All values presented in table 3 are the most recent available at the time of publication (including from the draft 2024 SARs) and are available online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

Table 3—Species
1
With Estimated Take From the Specified Activities

Common name
Scientific name
Stock

ESA/
MMPA
status;
strategic

(Y/N)
2

Stock
abundance

(CV, N
min
, most recent abundance

survey)
3

PBR

Annual

M/SI
4

Odontoceti (toothed whales, dolphins, and porpoises)

Family Delphinidae:

Family Phocoenidae (porpoises):

Harbor Porpoise
5

Phocoena phocoena

Northern OR/WA Coast
-, -, N
22,074 (0.391, 16,068, 2022)
161
≥3.2

Order Carnivora—Pinnipedia

Family Otariidae (eared seals and sea lions):

CA Sea Lion

Zalophus californianus

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

Steller Sea Lion

Eumetopias jubatus

Eastern
-, -, N

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

2,178
93.2

Family Phocidae (earless seals):

Harbor Seal

Phoca vitulina

OR/WA Coastal
-, -, N

22,549 (UNK, 19,561, 2022)
7

UND
8

10.6

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

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

3
NMFS marine mammal stock assessment reports online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region.
CV is coefficient of variation; N
min
is the minimum estimate of stock abundance.

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

5
Incidental take of harbor porpoises is not expected or proposed for authorization for the CI Project.

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

7
Most recent SAR does not include an abundance estimate for this stock. These data are for the Washington coast and thus underestimate the size of the OR/WA Coastal stock; estimates are from Pearson
et al.
2024.

8
UND means undetermined.

As indicated above, all four species (with four managed stocks) of marine mammals in table 3 spatially and temporally co-occur to the degree that take is reasonably likely to occur in the proposed MSRI Project area. However, California sea lions, Steller sea lions, and harbor seals could spatially co-occur within the CI Project area to the degree that take is reasonably likely to occur.

While gray whales, humpback whales, killer whales, and northern elephant seals have been reported in the LCR, the temporal or spatial occurrence of these species is such that take is not expected to occur, and they are not discussed further beyond the explanation provided here. Gray whales, humpback whales, and killer whales have been documented in the LCR, but sightings of these animals have primarily been at RM 11 and below, and sightings above this area are considered rare (no sightings in recent years) within both project areas. Northern elephant seals have been documented within the LCR but all reported sightings of these species within the project areas are over 40 years old and all recent sightings have occurred below RM 11 in the Columbia River. Therefore, take of these species is not expected nor proposed to be authorized and these species are not considered further in this document.

Harbor Porpoise

In the eastern North Pacific Ocean, harbor porpoises are found in coastal and inland waters from Point Barrow, along the Alaskan coast, and down the west coast of North America to Point Conception, California. Harbor porpoises are known to occur year-round in the inland trans-boundary waters of Washington and British Columbia, Canada and along the Oregon/Washington coast.

Harbor porpoise movement along west coast of the United States is relatively restricted and they do not move extensively between California, Oregon, and Washington (Calambokidis and Barlow, 1991). The Northern Oregon/Washington Coast stock of harbor porpoises ranges from Lincoln City, Oregon, to Cape Flattery, Washington and the stock commonly occurs in the Columbia River Estuary (Carretta
et al.,
2020). Their nearshore abundance peaks with anchovy presence, which is generally June through October. In 2024, three harbor porpoises were documented over 33 days of marine mammal monitoring for year 2 of USACE's East and West Sand Island Pile Dike Repairs Project at RM 4. Considering the spatial and temporal distribution, harbor porpoises could occur in the MRSI Project area but are not unexpected to occur in the CI Project area.

California Sea Lion

California sea lions are found along the west coast from the southern tip of Baja California to southeast Alaska. They breed mainly on offshore islands from Southern California's Channel Islands south to Mexico. Non-breeding males often roam north in spring foraging for food. Since the mid-1980s, increasing numbers of California sea lions have been documented feeding on fish along the Washington coast and—more recently—in the Columbia River as far upstream as Bonneville Dam, at RM 146. However, the total number of California sea lions observed at Bonneville Dam has been in decline, ranging from 195 individuals in 2015 to 24 individuals in 2021, and 50 individuals in 2023 (Braun
et al.,
2024).

In recent years, California sea lions have been reported below Bonneville Dam (RM 146) feeding on returning white sturgeon (
Acipenser transmontanus
) and adult salmonids (Braun
et al.,
2024). California sea lions have been observed hauling out at East Mooring Basin in Astoria, Oregon, city docks in Rainier, Oregon, and the Cowlitz River mouth in Longview, Washington (Oregon Department of Fish and Wildlife [ODFW], 2024). Considering the spatial and temporal distribution, California sea lions are expected to occur in both the MSRI and CI Project areas.

Steller Sea Lion

Steller sea lions that occur in the LCR, including the project vicinity, are members of the eastern Distinct Population Segment (DPS), ranging from Southeast Alaska to central California, including both Oregon and Washington (Jeffries
et al.,
2000; Scordino, 2006; NMFS, 2013). In Washington, Steller sea lions occur mainly along the outer coast from the Columbia River to Cape Flattery (Jeffries
et al.,
2000). The eastern DPS of Steller sea lions has historically bred on rookeries located in Southeast Alaska, British Columbia, Oregon, and California. However, within the last several years, a new rookery has become established on the outer Washington coast at the Carroll Island and Sea Lion Rock complex (Muto
et al.,
2019).

Steller sea lions have also been observed at the base of Bonneville Dam (RM 146) in recent years, feeding on white sturgeon (
Acipenser transmontanus
) and salmonids (Braun
et al.,
2024). Steller sea lions have been observed hauling out at the South Jetty at the mouth of the Columbia River, city docks in Rainier, OR, and the Cowlitz River mouth in Longview, WA (ODFW, 2024). Considering the spatial and temporal distribution, Steller sea lions

are expected to occur in both the MSRI and CI Project areas.

Harbor Seal

Harbor seals are the most common, widely distributed marine mammal found in Washington and Oregon marine waters and are frequently observed in the nearshore marine environment. The Oregon/Washington Coastal Stock was most recently estimated at 22,549 harbor seals in 2024 (Pearson
et al.,
2024). Harbor seals use hundreds of sites to rest or haulout along coastal and inland waters, including intertidal sand bars and mudflats in estuaries; intertidal rocks and reefs; sandy, cobble, and rocky beaches; islands; and log booms, docks, and floats in all marine areas of the state (Harvey 1987; Jeffries
et al.,
2003).

Harbor seals in this population are typically non-migratory and reside year-round in the Columbia River and generally remain in the same area throughout the year for breeding and feeding. Pupping seasons in coastal estuaries vary geographically; in the Columbia River, Willapa Bay, and Grays Harbor, pups are born from mid-April through June (Jeffries
et al.,
2003). Harbor seals in the Columbia River do exhibit some seasonal movement upriver, including into or through both of USACE's proposed project areas, to follow winter and spring runs of Pacific eulachon and outmigrating juvenile salmon (
Oncorhynchus spp.
), and they are observed regularly in the Columbia River including the action areas. Within the lower Columbia River, they tend to congregate to feed at the mouths of tributary rivers, including the Cowlitz and Kalama rivers (RMs 68 and 73, respectively). Washington Department of Fish and Wildlife's (WDFW's) atlas of seal and sea lion haulout sites (Jeffries
et al.,
2000) identifies shoals near the confluence of the Cowlitz and Columbia rivers, one of which is located 200 m from the CI Project site, as a documented haulout site. Additionally, ODFW has documented harbor seals hauled out near the MSRI Project area at Taylor Sands Island, around Green Island, and in Grays Bay during the months of May through June (Edwards, personal communication, 2023). Therefore, harbor seals could enter both of USACE's proposed project areas during in-water construction.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities (
e.g.,
Richardson
et al.,
1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall
et al.
(2007; 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling,
etc.
). Generalized hearing ranges were chosen based on the ~65 decibel (dB) threshold from composite audiograms, previous analyses in NMFS (2018), and/or data from Southall
et al.
(2007, 2019). We note that the names of two hearing groups and the generalized hearing ranges of all marine mammal hearing groups have been recently updated (NMFS, 2024) as reflected below in table 4.

Table 4—Marine Mammal Hearing Groups
[NMFS, 2024]

Hearing group

Generalized
hearing
range *

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

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

Very High-frequency (VHF) cetaceans

(true porpoises,
Kogia,
river dolphins, Cephalorhynchid,
Lagenorhynchus cruciger
&
L. australis
)

200 Hz to 165 kHz.

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

Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)
60 Hz to 68 kHz.

* Represents the generalized hearing range for the entire group as a composite (
i.e.,
all species within the group), where individual species' hearing ranges may not be as broad. Generalized hearing range chosen based on approximately 65 dB threshold from composite audiogram, previous analysis in NMFS (2018), and/or data from Southall
et al.
(2007, 2019). Additionally, animals are able to detect very loud sounds above and below that “generalized” hearing range.

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

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

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

Acoustic effects on marine mammal during the specified activities for the MSRI Project and CI Project could occur from impact pile driving and vibratory pile driving and removal. The effects of underwater noise from USACE's proposed activities have the potential to result in Level A and Level B harassment of marine mammals in the proposed action areas.

Description of Sound Sources

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

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

In-water construction associated with the proposed projects would include impact 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; National Institute for Occupational Safety and Health (NIOSH), 1998; ANSI, 2005; 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).

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

The likely or possible impacts of the USACE's proposed activities on marine mammals could involve both non-acoustic and acoustic stressors. Potential non-acoustic stressors could result from the physical presence of the equipment, vessel, and personnel; however, we expect that any animals that approach the project sites close enough to be harassed due to the presence of equipment or personnel would be within the Level B harassment zones from pile driving would already be subject to harassment from the in-water activities. Therefore, any impacts to marine mammals are expected to primarily be acoustic in nature. Acoustic stressors would be generated by heavy equipment operation during pile installation and removal (
i.e.,
impact and vibratory pile driving and removal).

Potential Effects of Underwater Sound on Marine Mammals

The introduction of anthropogenic noise into the aquatic environment from impact and vibratory pile driving and removal is the primary means by which marine mammals may be harassed from the USACE's specified activities. Anthropogenic sounds cover a broad range of frequencies and sound levels and can have a range of highly variable impacts on marine life from none or minor to potentially severe responses depending on received levels, duration of exposure, behavioral context, and various other factors. Broadly, underwater sound from active acoustic sources, such as those in the Projects, can potentially result in one or more of the following: temporary or permanent hearing impairment, non-auditory physical or physiological effects, behavioral disturbance, stress, and masking (Richardson
et al.,
1995; Gordon
et al.,
2003; Nowacek
et al.,
2007; Southall
et al.,
2007; Götz
et al.,
2009).

We describe the more severe effects of certain non-auditory physical or physiological effects only briefly as we do not expect that use of pile driving hammers (impact and vibratory) is reasonably likely to result in such effects (see below for further discussion). Potential effects from impulsive sound sources can range in severity from effects such as behavioral disturbance or tactile perception to physical discomfort, slight injury of the internal organs and the auditory system, or mortality (Yelverton
et al.,
1973). Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to high level underwater sound or as a secondary effect of extreme behavioral reactions (
e.g.,
change in dive profile as a result of an avoidance reaction) caused by exposure to sound include neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage (Cox
et al.,
2006; Southall
et al.,
2007; Zimmer and Tyack, 2007; Tal
et al.,
2015). Each project's activities considered here do not involve the use of devices such as explosives or mid-frequency tactical sonar that are associated with these types of effects.

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). Exposure to anthropogenic 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). It 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 degree of effect of an acoustic exposure on marine mammals is dependent on several factors, including, but not limited to, sound type (
e.g.,
impulsive vs. non-impulsive), signal characteristics, the species, age and sex class (
e.g.,
adult male vs. mom with calf), duration of exposure, the distance between the noise source and the animal, received levels, behavioral state at time of exposure, and previous history with exposure (Wartzok
et al.,
2004; Southall
et al.,
2007). In general, sudden, high-intensity sounds can cause hearing loss as can longer exposures to lower-intensity sounds. Moreover, any temporary or permanent loss of hearing, if it occurs at all, will occur almost exclusively for noise within an animal's hearing range. We describe below the specific manifestations of acoustic effects that may occur based on each of the activities proposed by the USACE.

Richardson
et al.
(1995) described zones of increasing intensity of effect that might be expected to occur in relation to distance from a source and assuming that the signal is within an animal's hearing range. First (at the greatest distance) is the area within which the acoustic signal would be audible (potentially perceived) to the animal but not strong enough to elicit any overt behavioral or physiological response. The next zone (closer to the receiving animal) corresponds with the area where the signal is audible to the animal and of sufficient intensity to elicit behavioral or physiological responsiveness. The third is a zone within which, for signals of high intensity, the received level is sufficient to potentially cause discomfort or tissue damage to auditory or other systems. Overlaying these zones to a certain extent is the area within which masking

(
i.e.,
when a sound interferes with or masks the ability of an animal to detect a signal of interest that is above the absolute hearing threshold) may occur; the masking zone may be highly variable in size.

Below, we provide additional details regarding potential impacts on marine mammals and their habitat from noise in general, starting with hearing impairment, as well as from the specific activities the USACE plans to conduct, to the degree it is available.

Auditory Injury (AUD INJ)
—NMFS defines auditory injury as “damage to the inner ear that can result in destruction of tissue . . . which may or may not result in permanent threshold shifts (PTS)” (NMFS, 2024). NMFS defines PTS as a permanent, irreversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2024). PTS does not generally affect more than a limited frequency range, and an animal that has incurred PTS has incurred some level of hearing loss at the relevant frequencies; typically, animals with PTS are not functionally deaf (Au and Hastings, 2008; Finneran, 2016). Available data from humans and other terrestrial mammals indicate that a 40-dB threshold shift approximates PTS onset (see Ward
et al.,
1958, 1959, 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)—
TTS is a temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Based on data from cetacean TTS measurements (Southall
et al.,
2007, 2019), a TTS of 6 dB is considered the minimum Threshold Shift (TS) clearly larger than any day-to-day or session-to-session variation in a subject's normal hearing ability (Schlundt
et al.,
2000; Finneran
et al.,
2000, 2002). As described in Finneran (2015), marine mammal studies have shown the amount of TTS increases with cumulative sound exposure level (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 a time when communication is critical for successful mother/calf interactions could have more serious impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall
et al.,
2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost.

Many studies have examined noise-induced hearing loss in marine mammals (see Finneran (2015) and Southall
et al.
(2019) for summaries). TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 2013). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. For pinnipeds in water, measurements of TTS are limited to harbor seals, elephant seals (
Mirounga angustirostris
), bearded seals (
Erignathus barbatus
) and California sea lions (Kastak
et al.,
1999, 2007; Kastelein
et al.,
2019b, 2019c, 2021, 2022a, 2022b; Reichmuth
et al.,
2019; Sills
et al.,
2020). These studies examined hearing thresholds measured in marine mammals before and after exposure to intense or long-duration sound exposures. The difference between the pre-exposure and post-exposure thresholds can be used to determine the amount of TS at various post-exposure times.

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

Relationships between TTS and PTS thresholds have not been studied in marine mammals, 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 dBs above that inducing mild TTS (
e.g.,
a 40-dB TS approximates PTS onset (Kryter
et al.,
1966; Miller, 1974), while a 6-dB TS approximates TTS onset (Southall
et al.,
2007, 2019). Based on

data from terrestrial mammals, a precautionary assumption is that the PTS thresholds for impulsive sounds (such as impact pile driving pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and PTS SELcum thresholds are 15 to 20 dB higher than TTS SELcum thresholds (Southall
et al.,
2007, 2019). Given the higher level of sound or longer exposure duration necessary to cause PTS as compared with TTS, it is considerably less likely that PTS could occur.

Pile dike repairs for the MSRI and CI Projects would require impact pile driving and vibratory pile driving and removal. Construction activities for each project would occur independently under separate authorizations. For each project, only one method of pile installation or removal would occur at a time, although multiple pile driving methods may be used on the same day. Pile driving associated with each project is not expected to be constant and pauses in the activities producing sounds are likely. Given these pauses and that many marine mammals would be transiting through the project areas and not remaining for extended periods of time, the potential for TS declines. For California sea lions, Steller sea lions, and harbor seals, animals are expected to remain in the CI project area, particularly around haulout site 24, which is a sand bar where the Cowlitz River and Carrols Channel meet with the mainstem Columbia River. California sea lions and Steller sea lions could also remain near the CI Project area as they transit to and from haulout site 24, and other structures near the Rainier, Oregon waterfront. Animals swimming with heads underwater would be exposed to pile driving noise throughout a day on multiple days, increasing risk of TS. However, we also expect these individuals to remain out of the water on haulouts for extended durations which reduces risk of TS.

Behavioral Harassment
—Exposure to noise from pile driving and removal also have the potential to behaviorally disturb marine mammals. 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).

Disturbance may result in changing durations of surfacing and dives, number of blows per surfacing, or moving direction and/or speed; reduced/increased vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); visible startle response or aggressive behavior (such as tail/fluke slapping or jaw clapping); avoidance of areas where sound sources are located. Pinnipeds may increase their haul out time, possibly to avoid in-water disturbance (Thorson and Reyff, 2006). Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors (
e.g.,
species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (
e.g.,
Richardson
et al.,
1995; Wartzok
et al.,
2004; Southall
et al.,
2007, 2021; Weilgart, 2007; Archer
et al.,
2010). Behavioral reactions can vary not only among individuals but also within exposures of an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison
et al.,
2012, Southall
et al.,
2021), 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 too, potentially disturbing underwater sound than do cetaceans, and generally seem to be less responsive to exposure to industrial sound than most cetaceans. For a review of the studies involving marine mammal behavioral responses to sound, see Southall
et al.,
2007; Gomez
et al.,
2016; and Southall
et al.,
2021 reviews.

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 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.

Airborne Acoustic Effects
—Pinnipeds that occur near the project sites 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 the activities. Cetaceans are not expected to be exposed to airborne sounds that would result in harassment as defined under the MMPA.

Airborne noise would primarily be an issue for pinnipeds that are swimming or hauled out near the project sites within the range of noise levels elevated above the airborne acoustic harassment criteria. We recognize that pinnipeds in the water could be exposed to airborne sound that may result in behavioral harassment when swimming with their heads above water. Most likely, airborne sounds 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.

Stress Response
—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, 2005), however distress is an unlikely result of these projects based on observations of marine mammals during previous, similar construction projects in the LCR.

Auditory Masking
—Sound can disrupt behavior through masking, or interfering with, an animal's ability to detect, recognize, or discriminate between acoustic signals of interest (
e.g.,
those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson
et al.,
1995; Erbe
et al.,
2016). Masking occurs when the receipt of a sound is interfered with by another coincident sound at similar frequencies and at similar or higher intensity and may occur whether the sound is natural (
e.g.,
snapping shrimp, wind, waves, precipitation) or anthropogenic (
e.g.,
shipping, sonar, seismic exploration, pile driving) in origin. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest (
e.g.,
signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities (
e.g.,
sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions. Masking of natural sounds can result when human activities produce high levels of background sound at frequencies important to marine mammals. Conversely, if the background level of underwater sound is high (
e.g.,
on a day with strong wind and high waves), an anthropogenic sound source would not be detectable as far away as would be possible under quieter conditions and would itself be masked.

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).

Masking affects both senders and receivers of acoustic signals and can potentially have long-term chronic effects on marine mammals at the population level as well as at the individual level. Low-frequency ambient sound levels have increased by as much as 20 dB (more than three times in terms of SPL) in the world's ocean from pre-industrial periods, with most of the increase from distant commercial shipping (Hildebrand, 2009). All anthropogenic sound sources, but especially chronic and lower-frequency signals (
e.g.,
from vessel traffic), contribute to elevated ambient sound levels, thus intensifying masking. The MSRI and CI Projects are located in areas with routine vessel traffic from recreational and commercial vessels; therefore, background sound levels are generally already elevated.

Marine Mammal Habitat Effects

Proposed construction for the MSRI and CI Projects could have localized, temporary impacts on marine mammal habitat, including prey, by increasing in-water SPLs and slightly decreasing water quality. Increased noise levels may affect acoustic habitat (see Auditory Masking) and adversely affect marine mammal prey in the vicinity of the project area (see discussion below). During impact and vibratory pile driving or removal, elevated levels of underwater noise would ensonify the project areas where both fish and mammals occur and could affect foraging success. Additionally, marine

mammals may avoid the areas 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. Each project would be relatively short in duration and would likely only have temporary impacts on marine mammal habitat through increases in underwater and airborne sound.

Water Quality
—In-water pile driving activities would also cause short-term effects on water quality due to increased turbidity. Temporary and localized increase in turbidity near the riverbed would occur in the immediate area surrounding where piles are installed or removed and where rock placement occurs due benthic sediment disturbance. In general, turbidity associated with pile installation is localized to about a 25 ft (7.6 m) radius around the pile (Everitt
et al.,
1980). The sediments of the project sites would settle out of the water column rapidly when disturbed. Local currents and tides are anticipated to disburse any additional suspended sediments produced by each of the project's activities at moderate to rapid rates depending on river current or tidal stage. Studies of the effects of turbid water on fish (marine mammal prey) suggest that concentrations of suspended sediment can reach thousands of milligrams per liter before an acute toxic reaction is expected (Burton, 1993).

Effects from turbidity and sedimentation are expected to be short-term, minor, and localized. Suspended solids in the water column should dissipate and quickly return to background levels in all construction scenarios. Turbidity within the water column has the potential to reduce the level of oxygen in the water and irritate the gills of prey fish species in each of the proposed project's areas. However, suspended sediment associated with the project would be temporary and localized, and fish in the proposed project area would be able to move away from and avoid the areas where plumes may occur. Therefore, it is expected that the impacts on prey fish species from turbidity, and therefore on marine mammals, would be minimal and temporary. In general, the areas likely impacted by the proposed construction activities are relatively small compared to the total available marine mammal habitat in the LCR in Oregon and Washington. Therefore, we expect the impact from increased turbidity levels to be discountable to marine mammals and do not discuss it further.

In-water Effects on Potential Foraging Habitat
—The proposed activities would not result in permanent impacts to habitats used directly by marine mammals and only negligible increases in vessel traffic are expected in either location as a result of the specified activities. The areas likely impacted by the proposed actions are relatively small compared to the total available habitat in the LCR in Oregon and Washington. Each of the proposed project areas are highly influenced by anthropogenic activities and provide limited foraging habitat for marine mammals. The total riverbed area affected by pile driving and rock placement activities is small compared to the vast foraging areas available to marine mammals both upstream and downstream the construction sites in the LCR. At best, the area impacted provide marginal foraging habitat for marine mammals and fishes. Furthermore, pile driving, pile removal and rock placement would not obstruct movements or migration of marine mammals.

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

Fish react to sounds which are especially strong and/or intermittent low-frequency sounds, and behavioral responses such as flight or avoidance are the most likely effects. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. The reaction of fish to noise depends on the physiological state of the fish, past exposures, motivation (
e.g.,
feeding, spawning, migration), and other environmental factors. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pile driving on fish, several of which are based on studies in support of large, multi-year bridge construction projects (
e.g.,
Scholik and Yan, 2001; Popper and Hastings, 2009). Many 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.,
Pearson
et al.,
1992; Skalski
et al.,
1992; Santulli
et al.,
1999; Fewtrell and McCauley, 2012; Paxton
et al.,
2017). In response to pile driving, Pacific sardines (
Sardinops sagax
) and northern anchovies (
Engraulis mordax
) may exhibit an immediate startle response to individual strikes but return to “normal” pre-strike behavior following the conclusion of pile driving with no evidence of injury as a result (see NAVFAC, 2014). However, some studies have shown no or slight reaction to impulse sounds (
e.g.,
Wardle
et al.,
2001; Popper
et al.,
2005; Jorgenson and Gyselman, 2009; Peña
et al.,
2013).

SPLs of sufficient strength have been known to cause injury to fish and fish mortality. However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function is likely restored when damaged cells are replaced with new cells. Halvorsen
et al.
(2012b) 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.,
2012a; Casper
et al.,
2013) and the greatest potential effect on fish during the proposed project would occur during impact pile driving. Impact pile driving for each of the proposed USACE construction projects would constitute a small proportion of total in-water construction time. For the MSRI Project, impact driving would be limited to 6 minutes per pile; consequently, installing all eight piles in a single day would result in a maximum of 48 minutes of impact noise. Similarly, the CI Project would require only 4.5 minutes of impact driving per pile, resulting in a total daily duration of just 36 minutes if eight piles are installed. In-water construction would be restricted to daylight hours (defined as 30 minutes before sunrise to 30 minutes after sunset) which would allow fish to forage and transit the area undisturbed

at night. While vibratory pile driving may elicit temporary behavioral avoidance, it is unlikely to cause injury or have persistent effects on local populations. Furthermore, all installation would occur within USACE and USFWS-designated work windows from November 1, 2026, through February 28, 2027, to minimize exposure for migrating ESA-listed fish species. Notably, the MSRI and CI Project areas already experience significant anthropogenic noise from regular vessel traffic, with the CI Project area subject to additional noise from industrial activities.

The most likely impact to fishes from impact and vibratory pile driving and removal in project areas would be temporary behavioral avoidance of the area. The duration of fish avoidance of the area after pile driving stops is unknown but a rapid return to normal recruitment, distribution, and behavior is anticipated. There are times of known seasonal marine mammal foraging when fish are aggregating but the impacted areas are small portions of the total foraging habitats available in the LCR. In general, impacts to marine mammal prey species are expected to be minor and temporary. Further, it is anticipated that preparation activities for pile driving (
i.e.,
positioning of the pile or hammer) and upon initial startup of devices would cause fish to move away from the affected area where injuries may occur. Therefore, relatively small portions of the proposed project area would be affected for short periods of time, and the potential for effects on fish to occur would be temporary and limited to the duration of sound‐generating activities.

Construction activities, in the form of increased turbidity, also have the potential to adversely affect forage fish in the project area. As discussed earlier, increased turbidity is expected to occur in the immediate vicinity (approximately 25 ft (7.6 m) or less) of construction activities (Everitt
et al.,
1980). However, suspended solids are expected to dissipate quickly within a single tidal cycle. Given the limited area affected and high tidal dilution rates, any effects on forage fish are expected to be minor or negligible. In addition, best management practices would be in effect to limit the extent of turbidity to the immediate project areas. Finally, turbidity levels resulting from construction activities are expected to remain within the range of baseline conditions. Fish and marine mammals in these regions are frequently exposed to significant suspended sediment loads from winter storm runoff, as well as other natural and anthropogenic sources.

In summary, given the short daily duration of sound associated with pile driving and removal the relatively small areas being affected, pile driving and removal activities associated with the proposed projects are not likely to have a permanent adverse effect on any fish habitat, or populations of fish species. Thus, we conclude that impacts of the specified activity are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species. Further, any impacts to marine mammal habitat are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations.

Estimated Take of Marine Mammals

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

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

Authorized takes would primarily be by Level B harassment (in the form of behavioral disturbance and temporary threshold shift (TTS)), as use of the acoustic sources (
i.e.,
vibratory, and impact pile driving; and vibratory pile 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), primarily affecting harbor seals, Steller sea lions, and California sea lions because of their prevalence in project areas, nearby haulouts, and predicted AUD INJ zones are relatively larger than for other hearing groups. The proposed mitigation and monitoring measures are expected to minimize the severity of the taking to the extent practicable.

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

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

Acoustic Criteria

NMFS recommends the use of acoustic criteria that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur AUD INJ of some degree (equated to Level A harassment). Criteria for AUD INJ, and hearing group categories are available in NMFS' Updated Technical Guidance (NMFS 2024) and are reflected below in the Level A harassment section.

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

anthropogenic noise above root-mean-squared pressure received levels (RMS SPL) of 120 dB (referenced to 1 micropascal (re 1 μPa)) for continuous (
e.g.,
vibratory pile driving, drilling) and above RMS SPL 160 dB re 1 μPa for non-explosive impulsive (
e.g.,
seismic airguns) or intermittent (
e.g.,
scientific sonar) sources. Generally speaking, Level B harassment take estimates based on these behavioral harassment thresholds are expected to include any likely takes by TTS as, in most cases, the likelihood of TTS occurs at distances from the source less than those at which behavioral harassment is likely. TTS of a sufficient degree can manifest as behavioral harassment, as reduced hearing sensitivity and the potential reduced opportunities to detect important signals (conspecific communication, predators, prey) may result in changes in behavior patterns that would not otherwise occur.

The USACE's proposed activities include the use of continuous (vibratory hammer) and impulsive (impact hammer) sources, and therefore the RMS SPL thresholds of 120 and 160 dB re 1 μPa are applicable.

Level A harassment
—NMFS' Updated Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 3.0) (Updated Technical Guidance, 2024) identifies dual criteria to assess AUD INJ (Level A harassment) to five different underwater marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). The USACEs' proposed activities include the use of impulsive (impact hammer) and non-impulsive (vibratory hammer) sources.

The 2024 Updated Technical Guidance criteria include both updated thresholds and updated weighting functions for each hearing group. The thresholds are provided in table 5 below. The references, analysis, and methodology used in the development of the criteria are described in NMFS' 2024 Updated Technical Guidance, which may be accessed at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools.

Table 5—Thresholds Identifying the Onset of Auditory Injury

Hearing group

AUD INJ onset acoustic thresholds *
(received level)

Impulsive
Non-impulsive

Low-Frequency (LF) Cetaceans

Cell 1: L
pk,flat
:
222 dB;
L
E,LF,24h
:
183 dB

Cell 2: L
E, LF,24h
:
197 dB.

High-Frequency (HF) Cetaceans

Cell 3: L
pk,flat
:
230 dB;
L
E,HF,24h
:
193 dB

Cell 4: L
E, HF,24h
:
201 dB.

Very High-Frequency (VHF) Cetaceans

Cell 5: L
pk,flat
:
202 dB;
L
E,VHF,24h
:
159 dB

Cell 6: L
E,VHF,24h
:
181 dB.

Phocid Pinnipeds (PW) (Underwater)

Cell 7: L
pk,flat
:
223 dB;
L
E,PW,24h
:
183 dB

Cell 8: L
E,PW,24h
:
195 dB.

Otariid Pinnipeds (OW) (Underwater)

Cell 9: L
pk,flat
:
230 dB;
L
E,OW,24h
:
185 dB

Cell 10: L
E,OW,24h
:
199 dB.

* Dual metric criteria for impulsive sounds: Use whichever criteria results in the larger isopleth for calculating AUD INJ onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level criteria associated with impulsive sounds, the PK SPL criteria are recommended for consideration for non-impulsive sources.

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 1 μPa
2
s. In this table, criteria are abbreviated to be more reflective of International Organization for Standardization standards (ISO, 2017). The subscript “flat” is being included to indicate peak sound pressure are flat weighted or unweighted within the generalized hearing range of marine mammals underwater (
i.e.,
7 hertz (Hz) to 165 kHz). The subscript associated with cumulative sound exposure level criteria indicates the designated marine mammal auditory weighting function (LF, HF, and VHF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The weighted cumulative sound exposure level criteria could be exceeded in a multitude of ways (
i.e.,
varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to indicate the conditions under which these criteria will be exceeded.

Ensonified Area

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

In order to calculate distances to the Level A and Level B harassment thresholds for the methods and piles being used in these projects, NMFS used proxy source levels for the piles that were identified from the literature. Vibratory and impact pile driving of steel pipe, timber, and steel sheet piles for the MSRI and CI Projects were based on the summary of data for each pile material and type provided by Caltrans (2020, 2015). Table 6 shows the source levels used for calculating harassment zones for impact driving as well as vibratory pile driving and removal for the MSRI and CI Projects. The source levels used were the most suitable due to similar pile sizes, pile driving, and pile removal methods.

Table 6—Estimated Unattenuated Underwater Sound Pressure Level Associated With Vibratory and Impact Pile Driving for the CI Project

Pile type
Method
Source for proxy values used
SPLs or SEL at 10 meters distance

Average
Peak SPL,
dB re 1 μPa

Average
RMS SPL,
dB re 1 μPa

Average
SEL, dB
re 1 μPa2-sec

MSRI Project

24-inch Steel pipe
Vibratory Installation
Caltrans (2020)
194
157
NA

24-inch Steel pipe
Impact installation
Caltrans (2015)
203
190
177

CI Project

10-12-inch Steel pipe
Vibratory Installation
Caltrans (2015)
171
155
NA

10-12-inch steel pipe
Impact Installation
Caltrans (2015, 2020)
192
177
167

16-inch Steel pipe
Vibratory Installation
Caltrans (2020)
196
158
NA

16-inch Steel pipe
Impact Installation
Caltrans (2020)
200
185
175

20-24-inch Steel pipe
Impact Installation
Caltrans (2015)
203
190
177

24-inch Steel pipe
Vibratory Installation
Caltrans (2020)
194
157
NA

24-inch AZ Steel sheet
Vibratory Installation and Removal
Caltrans (2020)
175
160
NA

12-16-inch Timber
Vibratory Installation
Caltrans (2020)
NA
162
NA

12-14-inch Timber
Impact installation
Caltrans (2020)
180
170
160

SPL = Sound Pressure Levels; SEL = Sound Exposure Level; RMS = root mean square; dB re 1 μPa = decibels referenced to 1 micropascal; dB re 1 μPa2 -sec = decibels referenced to 1 micropascal squared second; NA = not applicable. All SPLs and SELs are unattenuated.

Level B Harassment Zones

Transmission loss (TL) is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source until the source becomes indistinguishable from ambient sound. TL parameters vary with frequency, temperature, river 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:

TL = transmission loss in dB

B = transmission loss coefficient; for practical spreading equals 15

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

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

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 USACE's proposed activities in the absence of specific modeling. The spreadsheet inputs for pile size, type, and installation method for each project are included in tables 7 and 8. The estimated Level B harassment zones for USACE's proposed activities are shown in tables 9 and 10 for the MSRI and CI Projects, 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 2024 Updated Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically going to be overestimates of some degree, which may result in an overestimate of potential take by Level A harassment. However, this optional tool offers the best way to estimate isopleth distances when more sophisticated modeling methods are not available or practical. For stationary sources such as impact and vibratory 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 AUD INJ. Inputs used in the optional User Spreadsheet tool, and the resulting estimated isopleths, are reported below.

Table 7—NMFS User Spreadsheet Inputs for the MSRI Project

Pile size and material
Spreadsheet tab used

Source level
(SPL)

Weighting
factor
adjustment

Transmission
loss
coefficient

Activity
duration
(minutes),
or
(strikes/pile)

Number
of piles
per day

Distance of
sound
pressure
level
measurement
(m)

Vibratory pile driving

24-inch steel
A.1) Vibratory Pile Driving
157 dB RMS
2.5
15
12
8
10

Impact pile driving

a

24-inch steel
E.1) Impact Pile Driving
190 dB RMS, 177 dB SEL, 203 dB PK
2
15
(225)
8
10

a
5 dB of attenuation was applied to impact driving to account for noise reduction from bubble curtains.

Table 8—NMFS User Spreadsheet Inputs for the CI Project

Pile size and material
Spreadsheet tab used

Source level
(SPL)

Weighting
factor
adjustment

Transmission
loss
coefficient

Activity
duration
(minutes)
or
(strikes/pile)

Number
of piles
per day

Distance of
sound
pressure
level
measurement
(m)

Vibratory pile driving

10.75-12-inch steel pipe
A.1) Vibratory Pile Driving
155 dB RMS
2.5
15
12
4
10

16-inch steel pipe

158 dB RMS
2.5
15
18
3
10

24-inch steel pipe (ATON)

157 dB RMS
2.5
15
12
1
10

12-inch timber pole

162 dB RMS
2.5
15
8
8
10

24-inch steel pipe (MOF)

157 dB RMS
2.5
15
12
8
10

24-inch Steel Sheet (MOF)

160 dB RMS
2.5
15
10
25
10

Vibratory pile removal

24-inch steel pipe (MOF)
A.1) Vibratory Pile Driving
157 dB RMS
2.5
15
12
8
10

24-inch Steel Sheet (MOF)

160 dB RMS
2,5
15
3
200
10

Impact Pile driving

a

10.75-12-inch steel pipe
E.1) Impact Pile Driving
177 dB RMS, 167 dB SEL, 200 dB PK
2
15
(225)
4
10

16-inch steel pipe

185 dB RMS, 175 dB SEL, 200 dB PK
2
15
(225)
3
10

24-inch steel pipe (ATON)

190 dB RMS, 177 dB SEL, 203 dB PK
2
15
(225)
8
10

12-inch timber pole

170 dB RMS, 160 dB SEL, 180 dB PK
2
15
(225)
8
10

a
5 dB of attenuation was applied to impact driving to account for noise reduction from bubble curtains.

Table 9—Projected Distances to Level A Harassment and Level B Harassment Isopleths (
m
) by Marine Mammal Hearing Groups for Vibratory and Impact Installation of Piles for the MSRI Project

Pile size and material

Level A harassment distance
(m)

LF cetaceans
HF cetaceans
VHF cetaceans
PW
OW

Level B
harassment
distance
(m)

Vibratory pile driving

24-inch steel pipe
7
3
6
9
3
2,929

Impact pile driving

a

24-inch steel pipe
272
34
421
242
90
464

a
5 dB of attenuation was applied to impact driving to account for noise reduction from bubble curtains.

Table 10—Projected Distances to Level A Harassment and Level B Harassment Isopleths (
m
) by Marine Mammal Hearing Groups for the Vibratory Installation or Removal and Impact Installation

Pile size and material

Level A harassment distance
(m)

LF cetaceans
HF cetaceans
VHF cetaceans
PW
OW

Level B
harassment
distance
(m)

Vibratory pile driving

10.75-12-inch steel pipe
3
1
3
4
2
2,154

16-inch steel pipe
4
2
3
5
2
3,415

24-inch steel pipe (ATON)
2
1
1
2
1
2,929

12-inch timber
15
6
12
19
6
6,310

24-inch steel pipe (MOF)
a

7
3
6
9
3
2,929

24-inch Steel Sheet (MOF)
a

21
8
19
17
26
4,642

Impact pile driving

b

10.75-12-inch steel pipe
37
5
57
33
12
63

16-inch steel pipe
104
13
161
93
35
215

24-inch steel pipe (ATON)
68
9
105
60
23
464

12-inch timber
20
3
31
18
7
22

a
indicates piles would be installed and removed.

b
5 dB of attenuation was applied to impact driving to account for noise reduction from bubble curtains.

Marine Mammal Occurrence

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

For all species, the best available scientific data was considered to estimate occurrence for both proposed projects.

For the MSRI Project, incidental take is expected to occur for harbor seals, California lions, Steller sea lions and harbor porpoises. Occurrence of harbor porpoises for the MSRI Project was derived from a monitoring report for the USACE Sand Island Pile Dike Replacement Project, located at RM 4 in the LCR. During the 15 days of monitoring for that project, seven individual harbor porpoises were observed (Hammer Environmental L.P., 2020). Based on these observations, USACE estimates that two harbor porpoises may enter Level B Harassment zones during the 8 days of pile driving for the MRSI Project. NMFS concurs with this approach because although harbor porpoises are generally uncommon in project area, they could potentially occur.

Initially, USACE estimated harbor seal take based on densities derived from ODFW and WDFW surveys as well as personal communication with state biologists. Upon review, NMFS determined that the ODFW data for harbor seals and California sea lions were either outside of the proposed project area or represented months of peak abundance for these species which do not align with the MSRI Project's in-water work window. Similarly, the initial California sea lion and Steller sea lion densities were based on a single count 40 RM upstream of the project site, which NMFS deemed unrepresentative of the MSRI Project area.

For the CI Project, incidental take is expected to occur for harbor seals, California sea lions, and Steller sea lions. Initially, USACE estimated harbor seal take based on the maximum number of animals observed on haulout sites 24 and 25 in 2000 (WDFW, 2000). NMFS determined these data were outdated, as they were over 26 years old. For California sea lions and Steller sea lions, USACE initially estimated take based on single count of animals at haulout sites 24 A, B, and C, as well as pinnipeds counts at Bonneville Dam, located 70 RM upstream (Edwards, personal communication, 2023, and Braun
et. al.,
2024). NMFS does not agree with this approach because historical data, single counts, and data from Bonneville Dam is unlikely to accurately reflect current occurrence of pinnipeds at the CI Project area. Consequently, NMFS proposed, and USACE accepted, revised methodologies for estimating take for both the MSRI and CI Projects using more recent and geographically relevant data described below.

EN27AP26.077

Figure 3—Pinniped Haulouts Near the CI Project Area

Previously, NMFS inquired about current marine mammal signings data from the ODFW in the WDFW in October 2024 for the Interstate Bridge Replacement Project (90 FR 40492, August 19, 2025). These agencies provided information about the relative use of haulout areas and the seasonality of pinniped presence in the Columbia and Willamette Rivers. This data indicated that peak seasonal presence occurred between the months of February through May, though sea lions are often present at Bonneville Dam in other months.

In November 2024, NMFS received unpublished 2012-2020 pinniped abundance monitoring data for the LCR from ODFW in collaboration with the Columbia River Inter-Tribal Fish Commission (CRITFC), and ODFW pinniped monitoring data for 2021-2024 from haulout sites in Columbia, Willamette, and Kalama Rivers. CRITFC data were taken via boat-based surveys of known pinniped haulouts along the LCR and the ODFW monitoring data were taken via boat and aerial drone surveys in the Columbia, Willamette, and Kalama Rivers at known haulout sites (Brown, M., Personal communication, 2024). Each of these data sets presented pinnipeds as a guild, not separated by species.

NMFS analyzed CRITFC datasets for Zone 4 of the Columbia River Estuary, spanning from Astoria, Oregon river kilometer RM 12 to the upper end of the estuary RM 41. Although the MSRI Project is expected to occur between December and February, CRITFC data were only available from February through May. These data show a seasonal increase in pinniped abundance starting in February, with a wide range of annual variability. Given the project's brief 8-day duration, it is possible that all in-water work could be concentrated at the end of the work window when pinniped density is highest. To account for this and for the variability in pinniped sightings between years, NMFS utilized the monthly 75th percentile of February and March occurrence data pooled, which were used in take calculations and are presented in table 11. This methodology ensures that take of pinnipeds reflects this seasonal trend, specifically accounting for the higher abundance observed in late February when all construction for the MSRI Project could potentially occur.

Table 11—Pinniped Occurrence for the Columbia River Between Astoria, OR and the Upper End of the Columbia River Estuary

Month

Monthly
average

Monthly
75th Percentile

Average
for
February
and
March

75th
Percentile for February
and
March

February
10.5
14.3
70.5
79.2

March
85.5
89.3

While the CI Project area (RM 68-72) falls within CRITFC Survey Zone 3, NMFS believes that the ODFW monitoring data from 2021 through 2024 provides a more scientifically precise representation of pinniped occurrence

in the immediate vicinity (Brown, M., Personal communication, 2024). This dataset captures seasonal variation between January through May, showing an increase in occurrence that peaks between February and March. To ensure take estimates accurately reflect seasonal variability during the CI Project's November through December pile driving window, NNMFS condensed the monitoring data using the following approach:

•
Averaging Methodology:
Monthly counts were compiled to calculate monthly and 2-month pooled averages (
e.g.,
January/February, and February/March) to capture peak seasonal occurrence.

•
November/December Proxy:
Because specific monitoring data were unavailable for these months, the January monthly average was used as a surrogate.

•
January Adjustment:
The January/February pooled average was applied to January project activities to account for increasing seasonal occurrence.

•
February Adjustment:
The February/March pooled average was applied to February project activities to ensure estimates account for the late-season peak in occurrence.

The resulting values in table 12 were applied to the Level A formula for the CI Project below.

Table 12—Pinniped Occurrence for the Cowlitz/Rainier Haulouts Used in Take Estimation

Construction Month

Guild
average

Observation
month(s)
(moving average(s))

November
138
January (one-month).

December
138
January (one-month).

January
148
January and February (two-months).

February
298.15
February and March (two-months).

Take Estimation

Here we describe how the information provided above is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization. Because recent monitoring data obtained from CRITFC, ODFW, and WDFW often do not differentiate between pinniped species, NMFS calculated occurrence rates for the three expected pinniped species as a combined guild.

The predicted isopleths in table 13 differ from those presented in the original applications because the application's Level A harassment isopleths were modeled without a bubble curtain. In this proposed authorization, NMFS applied a 5 dB noise attenuation factor to account for USACE's use of bubble curtains during impact pile driving.

Not all animals within the MSRI and CI Project areas are expected to be exposed to noise levels exceeding the threshold for Level A harassment. NMFS concurs with USACE's proposal to estimate Level A harassment based on the proportion of the largest pile-driving isopleth (impact or vibratory) for each pile size relative to the average river width at the construction site (Table 13).

Table 13—Proportion of Eposure By Activity For Transiting Pinnipeds, Total Days of Pile Installation, and Average Days of Pile Installation Each Month for the MSRI and CI Projects

Installation method
a

Pile type

Predicted
largest
isopleth
(m)

Average
channel
width
(m)

Proportion of
channel width
ensonified

Total
days of
pile driving

Days of pile
installation
per month

MSRI Project

Attenuated Impact Installation
b

24-inch Steel Pipe
242
9,918
0.026
8
2

CI Project

Unattenuated vibratory installation
12-inch timber piles
19
969
0.020
17
4.25

Attenuated impact installation
b

10 to 12-inch steel pipe piles
33
811.4
0.041
11
2.75

Attenuated impact installation
b

16-inch steel pipe piles
93
862
0.108
4
1

Attenuated impact installation
b

24-inch steel pipe
60
762
0.079
2
0.5

a
Only the largest harassment zone (impact or vibratory installation) per pile size was included because both methods would occur on the same day and take was calculated with the largest of the two zones.

b
5 dB of attenuation was applied to impact driving to account for noise reduction from bubble curtains.

MSRI Project: Take Calculation Methods

NMFS used the following formula to calculate take by Level A harassment for pinnipeds as a guild for the MSRI Project:

Level A harassment= (Largest predicted Level A harassment isopleth (m)/Average river channel width (m)) × Total days of pile driving × 75th percentile of 2-month pinniped occurrence (February and March)

For the MSRI Project, the largest Level A harassment isopleth would occur during impact pile driving of 24-inch steel pipe piles. After applying the 5 dB attenuation for bubble curtain use, the largest Level A harassment isopleth for

the pinniped guild is 242 m. Dividing this by the average channel width results in an isopleth ratio of 0.026 (table 13).

To calculate the take estimate, this ratio (0.026) was multiplied by the total duration of pile driving (8 days) and the 75th percentile of pinniped occurrence for February and March (79.6 animals per day) from CRITFC Zone 4 surveys. This results in a rounded estimate of 17 takes by Level A harassment. Accordingly, NMFS proposes to authorize 17 takes of pinnipeds by Level A harassment for the MSRI Project, presented as a guild (tables 14 and 15).

NMFS used the following formula to calculate take by Level B harassment for the MSRI Project:

Level B harassment = ((total days of pile driving × 75th percentile of 2-month pinniped occurrence (February and March))—Calculated Level A harassment)

Take by Level B harassment was calculated by multiplying the 8 days of pile driving for 24-inch steel pipe piles by the 75th percentile of pooled March/February occurrence (79.6), equating to 634 total pinniped takes by Level B harassment. After subtracting the 17 takes by Level A harassment, the result is 617 estimated takes by Level B harassment. Thus, NMFS proposes to authorize 617 takes by Level B harassment of pinnipeds presented as a guild (tables 14 and 15).

Table 14—Estimated Take by Level A Harassment and Level B Harassment Proposed for Authorization for Pinnipeds as a Guild for the MSRI Project

Pile type
(installation or removal method)

Estimated
take
November
through
December

Total

Level A harassment

24-inch steel pipe (impact)
16.8
17

Level B harassment

Total Level B harassment−Level A harassment

24-inch steel pipe (impact)
633.6
617

Table 15—Proposed take of Marine Mammals by Level A and Level B Harassment and Percent of Each Stock Expected Take for the MSRI Project

Species
Stock
Proposed Take—MSRI Project

Level A
harassment

Level B
harassment

Percentage of stock
a

Harbor Porpoise
Northern OR/WA Coast
0
2
<1

California Sea Lion
U.S
17
617
<1

Steller Sea Lion
Eastern

1.7

Harbor Seal
OR/WA Coastal

2.8
b

a
NMFS conservatively assumes that all proposed estimated takes could come from a single stock due to the inability to distinguish between species detected during surveys. In reality, takes would occur to all three stocks and the percentages shown are thus overestimates.

b
The SAR lists the abundance for this stock as unknown; Pearson
et al.,
2024 report an estimate of 22,549, which we used in this analysis.

CI Project: Take Calculation Methods

NMFS used the following formula to calculate take by Level A harassment per pile size/type for the CI project:

Level A harassment (per pile size/type) = (Largest predicted Level A harassment isopleth (m)/Average river channel width (m)) × Average pile driving days per month × Monthly or pooled 2-month average pinniped occurrence

For all pile sizes, except 12-inch timber piles, the largest predicted Level A harassment isopleth occurs during impact pile driving. The average river channel width represents the mean of all pile installation locations (PDs) corresponding to each specific pile size and type. The average pile driving days is the total number of days per pile type divided by four, as the in-water work window spans 4 months (December through February) (table 13). USACE assumed that each pile type would be driven on separate days. Estimates for each pile size were summed to determine the total takes by Level A harassment for the CI Project (table 16).

NMFS used the following formula to calculate take by Level B harassment for the CI Project:

Level B harassment (per pile size/type) = (Average monthly pile driving days x Monthly or pooled 2-month average of pinniped occurrence)—Calculated take by Level A harassment

The total Level B harassment for the CI Project was calculated by summing the estimates for all pile sizes/types and then subtracting the total estimated takes by Level A harassment (table 16). Total takes proposed for authorization by Level A and Level B harassment are presented in table 17.

Table 16—Take by Level A and Level B Harassment of Pinnipeds as a Guild for Each Pile Size and Total Take for the CI Project

Pile type
(installation or removal method)

November
December
January
February

Total
(rounded)

Level A harassment

Installation

12-inch timber pole (vibratory)
11.5
11.5
12.3
24.8
247

10-12-inch steel pipe (impact)
15.4
15.4
16.6
33.3

16-inch steel pipe (impact)
14.9
14.9
16
32.2

24-inch steel pipe (impact)
5.4
5.4
5.8
11.7

Level B harassment

Installation)

Total (rounded)

12-inch timber pole (vibratory)
586.5
586.5
629
1,267.1
11,578

10-12-inch steel pipe (impact)
379.5
379.5
407
819.9

16-inch steel pipe (impact)
138
138
148
298.2

24-inch steel pipe (impact)
a

69
69
74
149.1

24-inch steel pipe (vibratory)
b

310.5
310.5
333
670.8

24-inch steel sheet (vibratory)
b

414
414
444
894.5

Removal

24-inch steel pipe (vibratory)
b

310.5
310.5
333
670.8

24-inch steel sheet (vibratory)
b

51.75
51.75
55.5
111.8

a
Indicates permanent Aid to Navigation (ATON) piles.

b
Indicates temporary Material Offload Facility (MOF) pile.

Table 17—Proposed take of Marine Mammals by Level A and Level B Harassment and Percent of Each Stock Expected Take for the CI Project

Species
Stock
Proposed Take

Level A
harassment

Level B
harassment

Percentage of Stock
a

California Sea Lion
U.S
247
11,758
4.6

Steller Sea Lion
Eastern

32.6

Harbor Seal
b

OR/WA Coastal

52.44

a
NMFS conservatively assumes that all proposed estimated takes could come from a single stock due to the inability to distinguish between species detected during surveys. In reality, takes would occur to all three stocks and likely to the same individuals over subsequent days, and the percentages shown are thus overestimates.

b
The SAR lists the abundance for this stock as unknown; Pearson
et al.,
2024 report an estimate of 22,549, which we used in this analysis.

Proposed Mitigation

In order to issue an IHA under section 101(a)(5)(D) of the MMPA, NMFS must set forth the permissible methods of taking pursuant to the activity, and other means of effecting the least practicable impact on the species or stock and its habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stock for taking for certain subsistence uses (latter not applicable for this action). NMFS regulations require applicants for incidental take authorizations to include information about the availability and feasibility (economic and technological) of equipment, methods, and manner of conducting the activity or other means of effecting the least practicable adverse impact upon the affected species or stocks, and their habitat (50 CFR 216.104(a)(11)).

In evaluating how mitigation may or may not be appropriate to ensure the least practicable adverse impact on species or stocks and their habitat, as well as subsistence uses where applicable, NMFS considers two primary factors:

(1) The manner in which, and the degree to which, the successful implementation of the measure(s) is expected to reduce impacts to marine mammals, marine mammal species or stocks, and their habitat. This considers the nature of the potential adverse impact being mitigated (likelihood, scope, range). It further considers the likelihood that the measure will be effective if implemented (probability of accomplishing the mitigating result if implemented as planned), the likelihood of effective implementation (probability implemented as planned), and;

(2) The practicability of the measures for applicant implementation, which may consider such things as cost, impact on operations.

The mitigation requirements described in the following were proposed by USACE in its adequate and complete applications or are the result of subsequent coordination between NMFS and USACE. USACE has agreed that all of the mitigation measures are practicable. NMFS has fully reviewed the specified activities and the mitigation measures to determine if the mitigation measures would result in the least practicable adverse impact on marine mammals and their habitat, as

required by the MMPA, and has determined the proposed measures are appropriate. NMFS describes these below as proposed mitigation requirements and has included them in the proposed IHAs.

In addition to the measures described later in this section, the USACE would follow these general mitigation measures:

• Authorized take, by Level A and Level B harassment only, would be limited to the species and numbers listed in tables 15 and 17. Construction activities must be halted upon observation of either a species for which incidental take is not authorized or a species for which incidental take has been authorized but the authorized number of takes has been met, entering or is within the harassment zone.

• The taking by serious injury or death of any of the species listed in table 16 or any taking of any other species of marine mammal would be prohibited and would result in the modification, suspension, or revocation of the IHAs, if issued. Any taking exceeding the authorized amounts listed in tables 15 and 17 would be prohibited and would result in the modification, suspension, or revocation of the IHAs, if issued.

• Ensure that construction supervisors and crews, the marine mammal monitoring team, and relevant USACE staff are trained prior to the start of all construction activities, so that responsibilities, communication procedures, marine mammal monitoring protocol, and operational procedures are clearly understood. New personnel joining during the projects must be trained prior to commencing work;

• The USACE, construction supervisors and crews, protected species observers (PSOs), and relevant USACE staff must avoid direct physical interaction with marine mammals during construction activity. If a marine mammal comes within 10 meters of such activity, operations must cease and vessels must reduce speed to the minimum level required to maintain steerage and safe working conditions, as necessary to avoid direct physical interaction;

• Employ PSOs and establish monitoring locations as described in Section 5 of the IHAs and the USACE's Marine Mammal Monitoring and Mitigation Plans (see chapter 10 and chapter 13 of the USACE MSRI and CI Project applications, respectively). The USACE must monitor the project area to the maximum extent possible based on the required number of PSOs, required monitoring locations, and environmental conditions.

Additionally, the following mitigation measures apply to the USACE's in-water construction activities at both the MSRI and CI project locations:

Establishment of Shutdown Zones

The USACE would establish shutdown zones with radial distances as identified in tables 18 and 19 for all construction activities. The purpose of a shutdown zone is generally to define an area within which shutdown of the activity would occur upon sighting of a marine mammal (or in anticipation of an animal entering the defined area). If a marine mammal enters or is observed within the shutdown zones indicated in tables 18 and 19, pile driving must be delayed or halted. Operations may only resume once the animal is visually confirmed outside the zone or 15 minutes have passed without a re-detection.

Construction supervisors and crews, PSOs, and relevant USACE staff must avoid direct physical interaction with marine mammals during construction activities. If marine mammals come within 10 m of such activity, operations must cease, to avoid direct interaction. If an activity is delayed or halted due to the presence of a marine mammal, the activity may not commence or resume until either the animal has voluntarily exited and been visually confirmed beyond the shutdown zone indicated in tables 18 and 19 or 15 minutes have passed without re-detection of the animal.

Finally, construction activities must be halted upon observation of a species for which incidental take is not authorized or a species for which incidental take has been authorized but the authorized number of takes has been met entering or within any shutdown zone. If a marine mammal species not covered under these IHAs enters a shutdown zone, all in-water activities would cease until the animal leaves the zone or has not been observed for at least 15 minutes. Pile driving may proceed if the unauthorized species is observed leaving the clearance and shutdown zone or if 15 minutes have passed since the last observation.

Table 18—Proposed Shutdown Zones During MSRI Project Activities

Pile type, size, and method or activity

Shutdown zone
(m)

VHF cetaceans
PW
OW

24-inch Steel Pipe, Vibratory Installation
50

24-inch Steel Pipe, Impact Installation.
Barge Movement and Rock or Pile Placement

10

Table 19—Proposed Shutdown Zones During CI Project Activities

Pile type, size, and method or Activity

Shutdown zones
(m)

PW
OW

10-12, 16, and 24 Steel Pipe Piles, Impact Installation
60

12-inch Timber Pole Pile, Vibratory and Impact Installation
40

10-12, 16, and 24-inch Steel Pipe Piles, and 24-inch Steel Sheet Piles, Vibratory Installation or Removal
20

Terrestrial Work at PD 68.35
60

Barge Movement and Rock or Pile Placement
10

Pre- and Post-Activity Monitoring

Monitoring would take place before, during, and 30 minutes after any pile driving or pile removal activities (
i.e.,
pre-start clearance monitoring). In addition, monitoring for 30 minutes would take place whenever a break in the specified activity (
i.e.,
impact pile driving, vibratory pile driving) of 30 minutes or longer occurs. Pre-start clearance monitoring would be conducted during periods of visibility sufficient for the lead PSO to determine that the shutdown zones indicated in tables 18 and 19 are clear of marine mammals. Pile driving may commence following 30 minutes of observation when the determination is made that the shutdown zones are clear of marine mammals. If pile driving is delayed or halted due to the presence of a marine mammal, the activities would not commence or resume until either the animal has voluntarily left and been visually confirmed beyond the shutdown zones or 15 minutes have passed without re-detection of the animal.

Soft Start Procedures for Impact Driving

Soft-start procedures are used to provide additional protection to marine mammals by providing warning and/or giving marine mammals a chance to leave the area prior to an impact hammer operating at full capacity. The USACE would use soft start techniques when impact pile driving. Soft start procedures require contractors to provide an initial set of three strikes at reduced energy, followed by a 30-second waiting period, then two subsequent reduced- energy strike sets. A soft start would be implemented at the start of each day's impact pile driving and at any time following cessation of impact pile driving for a period of 30 minutes or longer.

Bubble Curtain

A bubble curtain would be employed during impact installation or proofing of timber or steel piles, unless the piles are driven in the dry, or water is less than 3 ft (0.9 m) in depth. A bubble curtain would not be required during vibratory pile driving. At minimum, the bubble curtain must distribute air bubbles around 100 percent of the piling perimeter for the full depth of the water column. The lowest bubble ring would be in contact with the substrate for the full circumference of the ring. The weights attached to the bottom ring would ensure 100 percent substrate contact. No parts of the ring or other objects would prevent full substrate contact. Air flow to the bubblers must be balanced around the circumference of the pile.

Based on our evaluation of the applicant's proposed measures, NMFS has preliminarily determined that the proposed mitigation measures provide the means of effecting the least practicable impact on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance. NMFS conducted an independent evaluation of the proposed measures, and has preliminarily determined for each of the proposed IHAs that the proposed mitigation measures provide the means of effecting the least practicable impact on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance.

Proposed Monitoring and Reporting

In order to issue an IHA f

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2026-08153. Public record. Not legal advice.