# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Ferry Berth Improvements in Tongass Narrows in Ketchikan, Alaska

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2022-02035

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** February 2, 2022
- **Citation:** 87 FR 5980

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XB709]
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Ferry Berth Improvements in Tongass Narrows in Ketchikan, Alaska

AGENCY:

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

ACTION:

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

SUMMARY:

NMFS has received a request from the Alaska Department of Transportation and Public Facilities (ADOT) for an Incidental Harassment Authorization (IHA) to take marine mammals incidental to the construction of four ferry berth facilities in Tongass Narrows in Ketchikan, Alaska: The Gravina Airport Ferry Layup Facility, the Gravina Freight Facility, the Revilla New Ferry Berth, and the Gravina Island Shuttle Ferry Berth Facility. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an IHA to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-time, one-year renewal that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorizations and agency responses will be summarized in the final notice of our decision.

DATES:

Comments and information must be received no later than March 4, 2022.

ADDRESSES:

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

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

FOR FURTHER INFORMATION CONTACT:

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

SUPPLEMENTARY INFORMATION:

Background

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

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

National Environmental Policy Act

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

Summary of Request

On August 19, 2021, NMFS received a request from the ADOT for an IHA to take marine mammals incidental to the construction of two ferry berth facilities in Tongass Narrows in Ketchikan, Alaska: The Gravina Airport Ferry Layup Facility and the Gravina Freight Facility. On December 17, 2021 we received a revised request that included additional work components associated with the Revilla New Ferry Berth and Upland Improvements and the New Gravina Island Shuttle Ferry Berth and Related Terminal Improvements in the same region. The application was deemed adequate and complete on January 4, 2022. ADOT's request is for take of a small number of eight species of marine mammals, by Level B harassment and Level A harassment. Of those eight species, five (Steller sea lion (
Eumetopias jubatus
), harbor seal (
Phoca vitulina richardii
), harbor porpoise (
Phocoena phocoena
), Dall's porpoise (
Phocoenoides dalli
) and minke whale (
Balaenoptera acutorostrata
)) may also be taken by Level A harassment. Neither the ADOT nor NMFS expects serious injury or mortality to result from this activity and, therefore, an IHA is appropriate.

NMFS previously issued two consecutive IHAs and a Renewal IHA to ADOT for this work (85 FR 673, January 7, 2020; 86 FR 23938, May 05, 2021).

ADOT complied with all the requirements (
e.g.,
mitigation, monitoring, and reporting) of the previous IHAs and information regarding their monitoring results may be found in the Description of Marine Mammals in the Area of Specified Activities and Marine Mammal Occurrence and Take Calculation and Estimation sections. An IHA for the first phase of construction of the Ketchikan-Gravina Access Project was issued to ADOT on December 20, 2019 (85 FR 673, January 7, 2020). Complete construction of two of those components, the Revilla New Ferry Berth and Upland Improvements and Gravina Island Shuttle Ferry Berth Facility/Related Terminal Improvements, did not occur within the timeframe authorized by the Phase 1 IHA and will not be finished before the expiration of the subsequent one-year renewal (86 FR 23938, May 05, 2021). Therefore, ADOT is requesting a new IHA for incidental take associated with the continued marine construction of these facilities. This proposed IHA would be valid for one year.

Description of Proposed Activity

Overview

ADOT is making improvements to existing ferry berths and constructing new ferry berths on Gravina Island and Revillagigedo (Revilla) Island in Tongass Narrows, near Ketchikan in southeast Alaska (Figure 1). These ferry facilities provide the only public access between the city of Ketchikan, AK on Revilla Island, and the Ketchikan International Airport on Gravina Island (Figure 1). The project's proposed activities that have the potential to take marine mammals, by Level A harassment and Level B harassment, include vibratory and impact pile driving, down-the-hole (DTH) operations for pile installation (rock socketing of piles and tension anchors to secure piles), and vibratory pile removal. The marine construction associated with the proposed activities is planned to occur over 91 non-consecutive days over one year beginning March 2022.

Improvement and construction of facilities is important to provide reliable access to the airport and facilitate growth and development in the region. Some of the existing ferry facilities are aging and periodically out-of-service for repairs or maintenance, and this project would provide redundant ferry berths to increase reliability. Ketchikan is Alaska's fifth largest city, with a population of approximately 8,125 (DCCED 2017), and has numerous marine facilities including fishing infrastructure, cruise and ferry terminals, and shipyards.

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Dates and Duration

In-water construction is scheduled to begin on March 1, 2022, upon expiration of the current Phase I IHA (86 FR 23938; May 5, 2021). ADOT anticipates that construction would occur during daylight hours only with in-water construction occurring 6 days per week. ADOT anticipates that the project would require approximately 91 days of pile installation and removal

over the course of 7 or 8 months. Although it is anticipated that the project would be completed sooner, ADOT requests that the IHA be valid for a full year, from March 1, 2022 to February 28, 2023, to accommodate scheduling unknowns or delays.

ADOT plans to implement the Essential Fish Habitat (EFH) Conservation Recommendations developed by NMFS. No in-water work would occur between March 1 and June 15 for three project components: The Revilla New Ferry Berth and Upland Improvements, Gravina Airport Ferry Layup Facility, and Revilla Refurbish Existing Ferry Berth Facility.

Specific Geographic Region

The proposed construction project is located in Ketchikan, Alaska (Figure 1). Improvements to the Gravina Airport Ferry Layup Facility construction would occur in the same location as the existing layup dock facility. The new Gravina Freight Facility would be constructed in the same location as the existing barge offload facility. The New Gravina Island Shuttle Ferry Berth construction would occur slightly North of the Airport Ferry Layup Facility. Improvements and construction on Revilla Island would occur approximately 4 kilometers (km; 2.5 miles (mi)) north of downtown Ketchikan. The new Revilla Island Airport Shuttle Ferry Berth would be constructed immediately adjacent to the existing Revilla Island Ferry Berth.

Tongass Narrows is an approximately 13-mile-long, north-south-oriented marine channel situated between Revilla Island to the east and Gravina Island to the west. In the vicinity of the proposed project, Tongass Narrows is as little as 300 meters (m; 984 feet; ft) wide. Tongass Narrows is generally characterized by strong tidal currents and by steep bedrock or coarse gravel-cobble-boulder shoreline. Lower intertidal and shallow subtidal areas are often sandy or mixed gravel, sand, and shell, with varied amounts of silt. At other areas, however, such as at rocky points and along the northwestern shore of Pennock Island (which is located in the south end of Tongass Narrows, between Gravina and Revilla Islands), bedrock slopes steeply to subtidal depths. Subtidal habitats are a mix of bedrock outcrops or ledges, boulder-cobble slopes, and, where lower slopes permit, sandy gravel bottoms, often mixed with significant amounts of shell debris, similar to intertidal habitats.

Several small natural coves and areas protected by constructed breakwaters provide wave and current protection for marine habitats with sand or gravel bottoms with some areas of eelgrass (
Zostera marina
) beds. Extensive areas of riprap bank protection and fill occur along the northeastern shoreline of the City of Ketchikan. Construction of numerous buildings and docks on pilings over the intertidal and shallow subtidal zone has significantly modified the shorelines in these areas. Shoreline protection activities have similarly modified approximately 1 mile of the shoreline of Gravina Island in the vicinity of the airport and airport ferry terminal.

Water depths reach approximately 49 m (160 ft) in the middle of the Tongass Narrows between the airport and town, but generally do not exceed 18 m (60 ft) where piles would be installed. The channel bottom slopes at about 2:1 (horizontal: vertical) from opposite shores. Geological conditions in the vicinity of the project were recently evaluated (CH2M 2018). The substrate consists of approximately 18 to 23 m (60 to 75 ft) of very loose to very dense granular deltaic or alluvial sand and gravel. At approximately 18 to 23 m (60 to 75 ft) below the mudline, the substrate transitions to phyllite bedrock (CH2M 2018). Pile installation would occur in waters ranging in depth from less than 1 m (3.3 ft) nearshore to approximately 20 m (66 ft), depending on the structure and location.

Ongoing vessel activities throughout Tongass Narrows, land-based industrial and commercial activities, and regular aircraft operations result in elevated in-air and underwater sound conditions in the project area that increase with proximity to the proposed project component sites. Sound levels likely vary seasonally, with elevated levels during summer when the tourism and fishing industries are at their peaks.

Detailed Description of Specific Activity

Planned construction includes the installation and continued construction of new ferry facilities and the renovation of existing structures. As stated above, the four proposed construction components include: The Gravina Airport Ferry Layup Facility, the Gravina Freight Facility, the Revilla New Ferry Berth and Upland Improvements, and the New Gravina Island Shuttle Ferry Berth and Related Terminal Improvements. ADOT anticipates that work may occur at multiple sites concurrently, and that two hammers or DTH equipment could be used concurrently (discussed further in the Estimated Take section).

Gravina Airport Ferry Layup Facility

The new ferry layup dock and transfer bridge would support layup and maintenance of the airport ferry system. The current layup dock at the Gravina Airport Ferry Layup Facility is in disrepair and needs to be replaced. ADOT would remove the existing 265-ft (80.1-m)-long floating dock, mooring structures, and transfer bridge and construct a new 250-ft by 85-ft (76.2 m by 25.9 m) concrete or steel floating dock in its place. The floating dock would be restrained by two side-restraint float dolphins and three corner/mid-restraint float dolphins. A new 20-ft by 140-ft (6.1 m by 42.6 m) steel transfer bridge would provide access to the floating dock. It would be necessary to remove, relocate, and replenish the existing rock slope, demolish the existing concrete abutment, and construct a new pile-supported bridge abutment. The Gravina Airport Ferry Layup Facility construction and Gravina Freight Facility construction is anticipated to require a total of 47 days of in-water pile installation and removal.

Gravina Freight Facility

The new Gravina Freight Facility, located approximately 100 m from the Gravina Airport Ferry Layup Facility (Figure 1), would be constructed in the same location as the existing barge offload facility. This facility would provide improved access to Gravina Island for highway loads that cannot be accommodated by the shuttle ferry. The existing ramp would be widened and re-graded both above and below the high tide line. A new concrete plank or asphalt pavement ramp would be constructed in its place. Five breasting dolphins and one mooring dolphin would be constructed to support barge docking and would include pedestrian walkways for access by personnel. In addition, two new pile-supported mooring structures would be constructed above the high tide line. As stated above, the Gravina Airport Ferry Layup Facility construction and Gravina Freight Facility construction is anticipated to require a total of 47 days of in-water pile installation and removal.

Revilla New Ferry Berth and Upland Improvements

The new Revilla Island airport shuttle ferry berth is the only project component that would occur on Revilla Island, and is currently under construction immediately adjacent to the existing Revilla Island Ferry Berth (Figure 1). The new ferry berth consists of a 7,400 square ft (ft
2
; 687.4 m
2
) pile-supported approach trestle at the shore side of the ferry terminal and a 1,500 ft
2
(139.4 m) pile-supported approach

trestle extension located landside and north of the new approach trestle. A 25-ft by 142-ft (7.6 m by 43.2 m) steel transfer bridge with vehicle traffic lane and separated pedestrian walkway extends from the trestle to a new 2,200 ft
2
(204.3 m
2
) steel float and apron. The steel float is supported by three guide pile dolphins. A bulkhead retaining wall is being constructed at the transition from uplands to the approach trestle. Two new stern berth dolphins with fixed hanging fenders and three new floating fender dolphins are being constructed to moor vessels. The new apron would be supported by three new guide pile dolphins. Water depths at the dolphins reach approximately 60 ft (18.2 m).

While construction on the Revilla New Ferry Berth is already underway, ADOT anticipates that it would not be complete before ADOT's current IHA (86 FR 23938; May 5, 2021) expires. Therefore, ADOT has requested take associated with the portion of the project that it anticipates may remain, which consists of installation of up to five tension anchors.

Upland improvements associated with the Revilla New Ferry Berth include reconstruction of terminal facilities, installation of utilities, and construction of improvements to existing staging/parking areas. Upland improvements are not anticipated to harass marine mammals, and therefore, are not discussed further in this document.

Gravina Island Shuttle Ferry Berth and Related Terminal Improvements

The new Gravina Island Airport Shuttle Ferry Berth is currently under construction (86 FR 23938; May 5, 2021) immediately adjacent to the existing Gravina Island Ferry Berth (Figure 1). The new facility consists of an approximately 7,000 ft
2
(650.3 m
2
) pile-supported approach trestle at the shore side of the ferry terminal. A 25-ft by 142-ft (7.6 m by 43.2 m) steel transfer bridge with vehicle traffic lane and separated pedestrian walkway leads to a new 2,200 ft
2
(204.3 m
2
) steel float and apron. The steel float is supported by three new guide pile dolphins. Ferry berthing is supported by two new stern berth dolphins and three new floating fender dolphins. To support the new facility, a new bulkhead retaining wall is being constructed between the existing ferry berth and the new approach trestle. A new fill slope measuring approximately 21,200 ft
2
(1,969.5 m
2
) is being constructed west of the approach trestle. Upland improvements include widening of the ferry approach road, retrofits to the existing pedestrian walkway, installation of utilities, and construction of a new employee access walkway. Due to unforeseen construction delays encountered during the Phase 1 IHA construction period, ADOT anticipates that construction on the Gravina Island Shuttle Ferry Berth would not be completed before the expiration of the current IHA (86 FR 23938; May 5, 2021). Therefore, ADOT has requested take associated with the portion of the project that it anticipates may remain, which consists of up to 35 piles (both plumb and battered), 17-21 rock sockets, 28 tension anchors, and up to 4 micropile anchors (Table 1).

Across the four project sites, three methods of pile installation are anticipated. These include vibratory and impact hammers, use of DTH systems to make holes for rock sockets and tension and micropile anchors at some locations (Figure 1-3 of ADOT's IHA Application). Installation of steel piles through the sediment layer would be accomplished using vibratory or impact methods. Depending on the location, the pile would be advanced to refusal at bedrock. Where sediments are deep and rock socketing or anchoring (described below) is not required, the final approximately 10 ft (3 m) of driving would be conducted using an impact hammer so that the structural capacity of the pile embedment can be verified or proofed. Proofing is expected to require approximately 50 strikes over 15 minutes. Where sediments are shallow, an impact hammer would be used to seat the piles into competent bedrock before a DTH system is used to create holes for the rock sockets and/or tension anchors. The pile installation methods used would depend on sediment depth and conditions at each pile location.

Rock sockets are holes made in the bedrock where overlying sediments are too shallow to adequately secure the bottom portion of a pile using other methods. Rock sockets are constructed utilizing a DTH device which uses both rotary and percussion-type drill action. These devices consist of a drill bit that drills through the bedrock using both rotary and pulse impact mechanisms. This breaks up the rock to allow removal of the fragments, creating a hole that allows for insertion of the pile. The socket holes are just large enough for the pile to fit down in to provide lateral strength for the pile. The pile is usually advanced at the same time that drilling occurs (the bit has a flexible tip that can be retracted and pulled back up through the center of a pile). Rock socket holes would be up to 15 ft (4.6 m) into the bedrock. Drill cuttings are expelled from the top of the pile using compressed air and/or other fluids. It is estimated that use of DTH for rock sockets into the bedrock would take approximately 4-8 hours per pile. Some piles would be seated in rock sockets as well as anchored with tension anchors.

Tension anchors are comprised of a threaded steel rod grouted into the bedrock strata at a specified depth below the pile tip. The rod is tested and anchored to the top of the pile to resist uplift forces in the associated structure. Tension anchors are installed within piles that are DTH drilled or hammered into the bedrock below the elevation of the pile tip, after the pile has been driven through the sediment layer to refusal. A 6- or 8-inch-diameter steel pipe casing is inserted inside the larger-diameter production pile. A DTH hammer and bit is inserted into the casing, and a 6- to 8-inch-diameter hole is made into bedrock. The typical depth of the hole varies, but 20-30 ft (6.1-9.1 m) is common to meet engineering needs. Rock fragments would be removed through the top of the casing with compressed air. A steel rebar rod is then grouted into the drilled hole and affixed to the top of the pile.

Micropiles have a casing diameter of approximately 3 to 10 in. A DTH hammer device is used to create a hole in a manner identical to the rock sockets as described above. The micropile casing is inserted to depth and a steel reinforcement bar is inserted in the casing, and then grout is pumped into the casing. The construction of the Gravina Island Shuttle Ferry Berth could potentially utilize up to four micropiles. Because both tension anchors and micropiles require drilling an 8-inch-diameter hole, they are discussed together throughout this document.

Vibratory methods would also be used to remove temporary steel pipe piles. These proposed activities and the noise they produce have the potential to take marine mammals, by Level A harassment and Level B harassment of marine mammals.

Each of the project components would include installation of steel pipe piles that are 20, 24, or 30 inches in diameter (Table 1). Temporary piles would be installed and removed with a vibratory hammer. Some permanent piles would be battered (
i.e.,
installed at an angle). Approximately 50 impact strikes would be required for proofing each permanent pile, requiring approximately 15 minutes of active impact hammering per pile.

The estimated average installation rate for the project is one to one and a half permanent or two temporary pipe piles per day (Table 1). On some days,

more or fewer piles or partial piles may be installed. It would likely not be possible to install an individual permanent pile to refusal with a vibratory hammer, use DTH methods for the rock socket, impact proof, and install the tension anchor on the same day. The construction crew may use a single installation method for multiple piles on a single day or find other efficiencies to increase production; the anticipated ranges of possible values are provided in Table 1. The estimated removal rate for temporary piles is two steel pipe piles per day. On some days, more or fewer piles may be removed. It is estimated that the 40 temporary piles would be removed in 36 days.

In sum, approximately 91 days of pile installation and removal are anticipated (Table 1), and of the 102 piles which ADOT anticipates it will install, 40 of them will be installed and removed (for a total of 142 pile installations and removals).

Above-water work would consist of the installation of a concrete float, a transfer bridge and transition ramp, dock-mounted fenders, and utility lines. A utility and storage building would be constructed on top of the concrete float. No in-water noise is anticipated in association with above-water and upland construction activities, and no associated take of marine mammals is anticipated from the noise or visual disturbance. Therefore, above-water and upland construction activities are not discussed further in this document.

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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. Additional information regarding population trends and threats may be found in NMFS's 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's website (
https://www.fisheries.noaa.gov/find-species
).

Table 2 lists all species or stocks for which take is expected and proposed to be authorized for this specified activity, and summarizes information related to the population or stock, including regulatory status under the MMPA and Endangered Species Act (ESA) and potential biological removal (PBR), where known. For taxonomy, we follow Committee on Taxonomy (2021). 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's SARs). While no mortality is anticipated or authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species and other threats.

Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS's 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's U.S. Alaska SARs (
e.g.,
Muto
et al.
2021). All values presented in Table 2 are the most recent available at the time of publication and are available in the draft 2021 SARs (Muto
et al.
2021; available online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports
).

Table 2—Marine Mammal Species or Stocks for Which Take Is Expected and Proposed To Be Authorized

Common name
Scientific name

MMPA
stock

ESA/MMPA status;
strategic

(Y/N)
1

Stock abundance Nbest,

(CV; N
min
; most recent

abundance survey)
2

PBR

Annual

M/SI
3

Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)

Family Balaenidae:

Humpback whale

Megaptera novaeangliae

Central North Pacific
E, D, Y
10,103 (0.3; 7,890; 2006)
83
26

Minke whale

Balaenoptera acutorostrata

Alaska
-, N
N.A.(See SAR; N.A.; see SAR)
UND
0

Order Cetartiodactyla—Cetacea—Superfamily Odontoceti (toothed whales, dolphins, and porpoises)

Family Delphinidae:

Killer whale

Orcinus orca

Alaska Resident
-, N
2,347 (N.A.; 2,347; 2012)
24
1

West Coast Transient
-, N
349 (N.A, 349; 2018)
3.5
0.4

Northern Resident
-, N
302 (N.A.; 302; 2018
2.2
0.2

Pacific white-sided dolphin

Lagenorhynchus obliquidens

North Pacific
-,-; N
26,880 (N.A.; N.A.; 1990)
UND
0

Family Phocoenidae

Harbor porpoise

Phocoena phocoena

Southeast Alaska
-, Y
See SAR (see SAR; see SAR; 2012)
See SAR
34

Dall's porpoise

Phocoenoides dalli

Alaska
-, N
See SAR (see SAR; see SAR; 2015)
See SAR
37

Order Carnivora—Superfamily Pinnipedia

Family Otariidae (eared seals and sea lions):

Steller sea lion

Eumetopias jubatus

Eastern U.S.
-,-, N
43,201 (see SAR; 43,201; 2017)
2,592
112

Family Phocidae (earless seals)

Harbor seal

Phoca vitulina richardii

Clarence Strait
-, N
27,659 (See SAE; 24,854; 2015)
746
40

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

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

3
These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury (M/SI) 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.

All species that could potentially occur in the proposed survey areas are included in Table 3-1 of the IHA application. However, the spatial occurrence of gray whale and fin whale is such that take is not expected to

occur, and they are not discussed further beyond the explanation provided here. Gray whales have not been reported by any local experts or recorded in monitoring reports and it would be extremely unlikely for a gray whale to enter Tongass Narrows or the small portions of Revillagigedo Channel this project would impact. Similarly for fin whale, sightings have not been reported and it would be unlikely for a fin whale to enter the project area as they are generally associated with deeper, more offshore waters. The remaining eight species (with 10 managed stocks) in Table 2 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur, and we have proposed authorizing it.

Humpback Whale

Humpback whales are found throughout Southeast Alaska in a variety of marine environments, including open-ocean, near-shore waters, and areas with strong tidal currents (Dahlheim
et al.
2009). Most humpback whales are migratory and spend winters in the breeding grounds off either Hawaii or Mexico. Humpback whales generally arrive in Southeast Alaska in March and return to their wintering grounds in November. Some humpback whales depart late or arrive early to feeding grounds, and therefore the species occurs in Southeast Alaska year-round (Straley 1990; Straley
et al.
2018). Current threats to humpback whales include vessel strikes, spills, climate change, and commercial fishing operations (Muto
et al.
2021).

Humpback whales worldwide were designated as “endangered” under the Endangered Species Conservation Act in 1970, and were listed under the ESA at its inception in 1973. However, on September 8, 2016, NMFS published a final decision that changed the status of humpback whales under the ESA (81 FR 62259), effective October 11, 2016. The decision recognized the existence of 14 DPSs based on distinct breeding areas in tropical and temperate waters. Five of the 14 DPSs were classified under the ESA (4 endangered and 1 threatened), while the other 9 DPSs were delisted. Humpback whales found in the project area are predominantly members of the Hawaii DPS, which is not listed under the ESA. However, based on a comprehensive photo-identification study, members of the Mexico DPS, which is listed as threatened, are known to occur in Southeast Alaska. Members of different DPSs are known to intermix on feeding grounds; therefore, all waters off the coast of Alaska should be considered to have ESA-listed humpback whales. Approximately 2 percent of all humpback whales in Southeast Alaska and northern British Columbia are members of the Mexico DPS, while all others are members of the Hawaii DPS (Wade
et al.
2021).

The DPSs of humpback whales that were identified through the ESA listing process do not necessarily equate to the existing MMPA stocks. The stock delineations of humpback whales under the MMPA are currently under review. Until this review is complete, NMFS considers humpback whales in Southeast Alaska to be part of the Central North Pacific stock, with a status of endangered under the ESA and designations of strategic and depleted under the MMPA (Muto
et al.
2021).

Southeast Alaska is considered a biologically important area for feeding humpback whales between March and May (Ellison
et al.
2012), though not currently designated as critical habitat (86 FR 21082; April 21, 2021). Most humpback whales migrate to other regions during the winter to breed, but rare events of over-wintering humpbacks have been noted, and may be attributable to staggered migration (Straley, 1990; Straley
et al.
2018). It is thought that those humpbacks that remain in Southeast Alaska do so in response to the availability of winter schools of fish prey, which primarily includes overwintering herring (Straley
et al.
2018). In Alaska, humpback whales filter feed on tiny crustaceans, plankton, and small fish such as walleye pollock, Pacific sand lance, herring, eulachon, and capelin (Witteveen
et al.
2012). It is common to observe groups of humpback whales cooperatively bubble feeding. Group sizes in Southeast Alaska generally range from one to four individuals (Dahlheim
et al.
2009).

No systematic studies have documented humpback whale abundance near Ketchikan. Anecdotal information (See Section 4 of IHA Application) suggests that this species is present in low numbers year-round in Tongass Narrows, with the highest abundance during summer and fall. Anecdotal reports suggest that humpback whales are seen only once or twice per month, while more recently it has been suggested that the occurrence is more regular, such as once per week on average, and more seasonal. Humpbacks observed in Tongass Narrows are generally alone or in groups of one to three individuals. Most humpback whales depart Alaska for their breeding grounds in October and November, and return in March and April. In August 2017, a group of six individuals was observed passing through Tongass Narrows several times per day, for several days in a row. Local residents reported that such high abundance is common in August and September. NMFS reported that in 2018 airport ferry personnel observed a lone humpback whale in the area every few days for several months and a group of two humpback whales every other week (Muto
et al.
2019).

In the Biological Opinion for this project, NMFS assumed the occurrence of humpback whales in the project area to be one two individuals twice per week, year-round. The assumption was based on differences in abundance throughout the year, recent observations of larger groups of whales present during summer, and a higher than average frequency of occurrence in recent months.

The City of Ketchikan (COK) Rock Pinnacle project, which was located approximately 4 km southeast of the proposed project site, reported one humpback whale sighting of one individual during the project (December 2019 through January 2020) (Sitkiewicz 2020). During the Ward Cove Cruise Ship Dock Construction, located approximately 5 km northwest of the proposed project site, protected species observers (PSOs) observed 28 sightings of humpbacks on eighteen days of in water work that occurred between February and September 2020, with at least one humpback being recorded every month. A total of 42 individuals were recorded and group sizes ranged from solo whales to pods of up to six (Power Systems & Supplies of Alaska 2020). Humpbacks were recorded in each month of construction, with the most individuals (10) being recorded in May, 2020.

Humpback whales were sighted on 17 days out of 88 days of monitoring in Tongass Narrows in 2020 and 2021 (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). There were no sightings in January or February, but humpback whales were observed each month from October to December 2020 and May to June 2021 (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). There was only 1 day in June in which humpback whales were observed, but on that day there were four groups of whales—three pairs and one group of four (DOT&PF 2021d). In other months, humpback whale sightings were mostly individual animals and occasionally pairs. During November 2020, a single known individual (by fluke pattern) was observed repeatedly, accounting for 14 of the 26 sighting events that month (DOT&PF 2020). During monitoring, humpback whales were observed on average once a week.

Minke Whale

Minke whales are found throughout the northern hemisphere in polar, temperate, and tropical waters. The population status of minke whales is considered stable throughout most of their range. Historically, commercial whaling reduced the population size of this species, but given their small size, they were never a primary target of whaling and did not experience the severe population declines as did larger cetaceans.

The International Whaling Commission has identified a less concentrated stock throughout the eastern Pacific. NOAA further splits this stock between Alaska whales and resident whales of California, Oregon, and Washington (Muto
et al.,
2021). Minke whales are found in all Alaska waters. There are no population estimates for minke whales in Alaska. Surveys in Southeast Alaska have consistently identified individuals throughout inland waters in low numbers (Dahlheim
et al.
2009).

Minke whales in Southeast Alaska are part of the Alaska stock (Muto
et al.
2021). Dedicated surveys for cetaceans in Southeast Alaska found that minke whales were scattered throughout inland waters from Glacier Bay and Icy Strait to Clarence Strait, with small concentrations near the entrance of Glacier Bay (Dahlheim
et al.
2009). All sightings were of single minke whales, except for a single sighting of multiple minke whales. Surveys took place in spring, summer, and fall, and minke whales were present in low numbers in all seasons and years. No information appears to be available on the winter occurrence of minke whales in Southeast Alaska.

In Alaska, the minke whale diet consists primarily of euphausiids and walleye pollock. Minke whales are generally found in shallow, coastal waters within 200 m of shore (Zerbini
et al.
2006) and are almost always solitary or in small groups of 2 to 3. In Alaska, seasonal movements are associated with feeding areas that are generally located at the edge of the pack ice (NMFS 2014).

There are no known occurrences of minke whales within the project area. Since their ranges extend into the project area and they have been observed in southeast Alaska, including in Clarence Strait (Dahlheim
et al.,
2009), it is possible the species could occur near the project area. During the surveys by Dalheim
et al.
(2009), all but one encounter was with a single whale and, although infrequent, minke whales were observed during all seasons surveyed (spring, summer and fall). No minke whales where reported during the COK Rock Pinnacle Blasting Project (Sitkiewicz 2020). During marine mammal monitoring of Tongass Narrows in 2020 and 2021, there were no minke whales observed on 88 days of observations across 7 months (October 2020-February 2021; May-June 2021) (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Future observations of minke whale in the project area are expected to be rare.

Killer Whale

Killer whales have been observed in all the world's oceans, but the highest densities occur in colder and more productive waters found at high latitudes (NMFS 2016). Killer whales occur along the entire Alaska coast, in British Columbia and Washington inland waterways, and along the outer coasts of Washington, Oregon, and California (NMFS 2016).

Based on data regarding association patterns, acoustics, movements, and genetic differences, eight killer whale stocks are now recognized within the Pacific U.S. Exclusive Economic Zone. This proposed IHA considers only the Eastern North Pacific Alaska Resident stock (Alaska Resident stock), Eastern North Pacific Northern Resident stock (Northern Resident stock), and West Coast Transient stock, because all other stocks occur outside the geographic area under consideration (Muto
et al.,
2021).

There are three distinct ecotypes, or forms, of killer whales recognized: Resident, Transient, and Offshore. The three ecotypes differ morphologically, ecologically, behaviorally, and genetically. Surveys between 1991 and 2007 encountered resident killer whales during all seasons throughout Southeast Alaska. Both residents and transients were common in a variety of habitats and all major waterways, including protected bays and inlets. There does not appear to be strong seasonal variation in abundance or distribution of killer whales, but there was substantial variability between years during this study (Dahlheim
et al.,
2009). Spatial distribution has been shown to vary among the different ecotypes, with resident and, to a lesser extent, transient killer whales more commonly observed along the continental shelf, and offshore killer whales more commonly observed in pelagic waters (Rice
et al.,
2021).

No systematic studies of killer whales have been conducted in or around Tongass Narrows. Killer whales have been observed in Tongass Narrows year-round and are most common during the summer Chinook salmon run (May-July). During the Chinook salmon run, Ketchikan residents have reported pods of 20-30 whales and during the 2016/2017 winter a pod of 5 whales was observed in Tongass Narrows (84 FR 36891; July 30, 2019). Typical pod sizes observed within the project vicinity range from 1 to 10 animals and the frequency of killer whales passing through the action area is estimated to be once per month (Frietag 2017). Anecdotal reports suggest that large pods of killer whales (as many as 80 individuals, but generally between 25 and 40 individuals) are not uncommon in May, June, and July when the king salmon are running. During the rest of the year, killer whales occur irregularly in pods of 6 to 12 or more individuals. Large pods would be indicative of the Alaska resident population, which travels and hunts in large social groups.

Transient killer whales are often found in long-term stable social units (pods) of 1 to 16 whales. Average pod sizes in Southeast Alaska were 6.0 in spring, 5.0 in summer, and 3.9 in fall. Pod sizes of transient whales are generally smaller than those of resident social groups. Resident killer whales occur in larger pods, ranging from 7 to 70 whales that are seen in association with one another more than 50 percent of the time (Dahlheim
et al.,
2009; NMFS 2016b). In Southeast Alaska, resident killer whale mean pod size was approximately 21.5 in spring, 32.3 in summer, and 19.3 in fall (Dahlheim
et al.,
2009).

Although killer whales may occur in large numbers, they generally form large pods and would incur fewer work stoppages than their numbers suggest. Killer whales tend to transit through Tongass Narrows, and do not linger in the project area.

Marine mammal observations in Tongass Narrows during 2020 and 2021 support an estimate of approximately one group of killer whales a month in the project area. During 7 months of monitoring (October 2020-February 2021; May-June 2021), there were five killer whale sightings in 4 months (November, February, May, June) totaling 22 animals and sightings occurred on 5 out of 88 days of monitoring (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Pod sizes ranged from two to eight animals (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). During the COK's monitoring for the Rock Pinnacle Removal project in December 2019 and January 2020, no killer whales were observed (Sitkiewicz 2020). Over 8 months of monitoring at the Ward Cove Cruise Ship Dock in 2020, killer whales were only observed on two days in March (Power Systems

and Supplies of Alaska, 2020). These observations included a sighting of one pod of two killer whales and a second pod of five individuals travelling through the project area.

Pacific White-Sided Dolphin

Pacific white-sided dolphins are a pelagic species inhabiting temperate waters of the North Pacific Ocean and along the coasts of California, Oregon, Washington, and Alaska (Muto
et al.,
2021). Despite their distribution mostly in deep, offshore waters, they may also be found over the continental shelf and near shore waters, including inland waters of Southeast Alaska (Ferrero and Walker 1996). The North Pacific stock is found within the project area. The Pacific white-sided dolphin is distributed throughout the temperate North Pacific Ocean, north of Baja California to Alaska's southern coastline and Aleutian Islands. The North Pacific Stock ranges from Canada into Alaska (Muto
et al.,
2021).

Pacific white-sided dolphins prey on squid and small schooling fish such as capelin, sardines, and herring (Morton 2006). They are known to work in groups to herd schools of fish and can dive underwater for up to 6 minutes to feed (Morton 2006). Group sizes have been reported to range from 40 to over 1,000 animals, but groups of between 10 and 100 individuals (Stacey and Baird 1991) occur most commonly. Seasonal movements of Pacific white-sided dolphins are not well understood, but there is evidence of both north-south seasonal movement (Leatherwood
et al.
1984) and inshore-offshore seasonal movement (Stacey and Baird 1991).

Scientific studies and data are lacking relative to the presence or abundance of Pacific white-sided dolphins in or near Tongass Narrows. Although they generally prefer deeper and more-offshore waters, anecdotal reports suggest that Pacific white-sided dolphins have previously been observed in Tongass Narrows, although they have not been observed entering Tongass Narrows or nearby inter-island waterways in 15-20 years.

Pacific white-sided dolphins are rare in the inside passageways of Southeast Alaska. Most observations occur off the outer coast or in inland waterways near entrances to the open ocean. According to Muto
et al.
(2018), aerial surveys in 1997 sighted one group of 164 Pacific white-sided dolphins in Dixon entrance to the south of Tongass Narrows. Surveys in April and May from 1991 to 1993 identified Pacific white-sided dolphins in Revillagigedo Channel, Behm Canal, and Clarence Strait (Dahlheim and Towell 1994). These areas are contiguous with the open ocean waters of Dixon Entrance. Dalheim
et al.
(2009) frequently encountered Pacific white-sided dolphin in Clarence Strait with significant differences in mean group size and rare enough encounters to limit the seasonality investigation to a qualitative note that spring featured the highest number of animals observed. These observations were noted most typically in open strait environments, near the open ocean. Mean group size was over 20, with no recorded winter observations nor observations made in the Nichols Passage or Behm Canal, located on either side of the Tongass Narrows. Though generally preferring more pelagic, open-water environments, Pacific white-sided dolphin could be present within the action area during the construction period. This observational data, combined with anecdotal information, indicates there is a rare, however, slight potential for Pacific white-sided dolphins to occur in the project area.

During marine mammal monitoring of Tongass Narrows in 2020 and 2021, no Pacific white-sided dolphins were observed on 88 days of observations across 7 months (October 2020-February 2021; May-June 2021), which supports the anecdotal evidence that sightings of this species are rare (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). There were also no sightings of Pacific white-sided dolphins during the COK Rock Pinnacle Blasting Project during monitoring surveys conducted in December 2019 and January 2020 (Sitkiewicz 2020) or during monitoring surveys conducted between February and September 2020 as part of the Ward Cove Cruise Ship Dock (Power Systems and Supplies of Alaska, 2020).

Harbor Porpoise

In the eastern North Pacific Ocean, the harbor porpoise ranges from Point Barrow, along the Alaska coast, and down the west coast of North America to Point Conception, California. In Alaska, harbor porpoises are currently divided into three stocks, based primarily on geography: The Bering Sea stock, the Southeast Alaska stock, and the Gulf of Alaska stock. The Southeast Alaska stock ranges from Cape Suckling to the Canadian border (Muto
et al.
2021). Harbor porpoises frequent primarily coastal waters in Southeast Alaska (Dahlheim
et al.
2009) and occur most frequently in waters less than 100 m (328 ft) deep (Hobbs and Waite 2010; Dahlheim
et al.
2015).

Abundance data for harbor porpoises in Southeast Alaska were collected during 18 seasonal surveys spanning 22 years, from 1991 to 2012 (Dahlheim
et al.
2015). The project area and Tongass Narrows fall within the Clarence Strait to Ketchikan region, as identified by this study for the survey effort. Harbor porpoise densities in this region in summer were low, ranging from 0.01 to 0.02 harbor porpoises/km
2
.

Studies of harbor porpoises reported no evidence of seasonal changes in distribution for the inland waters of Southeast Alaska (Dahlheim
et al.
2009). Their small overall size, lack of a visible blow, low dorsal fins and overall low profile, and short surfacing time make them difficult to observe (Dahlheim
et al.
2015), likely reducing identification and reporting of this species, and these estimates therefore may be low.

Calving occurs from May to August; however, this can vary by region. Harbor porpoises are often found traveling alone, or in small groups less than 10 individuals (Schmale 2008). According to aerial surveys of harbor porpoise abundance in Alaska conducted in 1991-1993, mean group size in Southeast Alaska was calculated to be 1.2 animals (Dahlheim
et al.
2000).

Anecdotal reports (see Section 3 of the IHA Application) specific to Tongass Narrows indicate that harbor porpoises are rarely observed in the project area, and actual sightings are less common than those suggested by Dahlheim
et al.
(2015). Harbor porpoises prefer shallower waters (Dahlheim
et al.
2015) and generally are not attracted to areas with elevated levels of vessel activity and noise such as Tongass Narrows. Harbor porpoises are expected to be present in the project area only a few times per year. Freitag (2017 as cited in 83 FR 22009; May 11, 2018) observed harbor porpoises in Tongass Narrows zero to one time per month and NMFS (83 FR 22009; May 11, 2018) has estimated that one group of harbor porpoises would enter Tongass Narrows each month.

Harbor porpoises were sighted on 3 days of in-water work during monitoring associated with the Ward Cove Cruise Ship Dock, with three sightings of 15 individuals sighted in March and April, 2020 (Power Systems and Supplies of Alaska, 2020). Solo individuals and pods of up to 10 were identified as swimming and travelling 2,500 m to 2,800 m from in-water work. During marine mammal monitoring of Tongass Narrows in 2020 and 2021, no harbor porpoises were observed on 88 days of observations across 7 months (October 2020-February 2021; May-June 2021), which supports the anecdotal evidence that harbor porpoise sightings are rare (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Marine mammal

monitoring associated with the COK Rock Pinnacle Removal project also did not observe any harbor porpoise during surveys conducted in December 2019 and January 2020 (Sitkiewicz 2020).

Dall's Porpoise

Dall's porpoises are found throughout the North Pacific, from southern Japan to southern California north to the Bering Sea. Dall's porpoises are not listed as endangered or threatened under the ESA. All Dall's porpoises in Alaska are members of the Alaska stock, and those off California, Oregon, and Washington are part of a separate stock. This species can be found in offshore, inshore, and nearshore habitat, but prefer waters more than 600 ft (180 m) deep (Jefferson 2009).

No systematic studies of Dall's porpoise abundance or distribution have occurred in Tongass Narrows; however, surveys for cetaceans throughout Southeast Alaska were conducted between 1991 and 2007 (Dahlheim
et al.
2009). The species is generally found in waters in excess of 600 ft (183 m) deep (Dahlheim
et al.
2009, Jefferson 2009), which do not occur in Tongass Narrows. Jefferson
et al.
(2019) presents historical survey data showing few sightings in the Ketchikan area, and based on these occurrence patterns, concludes that Dall's porpoise rarely come into narrow waterways, like Tongass Narrows. Anecdotal reports suggest that Dall's porpoises are found northwest of Ketchikan near the Guard Islands, where waters are deeper, as well as in deeper waters to the southeast of Tongass Narrows. Should Dall's porpoises occur in the project area, they would likely be present in March or April, given past observations in the region. Despite generalized water depth preferences, Dall's porpoises may occur in shallower waters. This species has a tendency to bow-ride with vessels and may occur in the project area incidentally a few times per year.

The mean group size in Southeast Alaska is estimated at approximately three individuals (Dahlheim
et al.
2009; Jefferson 2019). However, in the Ketchikan vicinity, Dall's porpoises are reported to typically occur in groups of 10-15 animals, with an estimated maximum group size of 20 animals (Freitag 2017, 83 FR 37473; August 1, 2018).

Dall's porpoises were positively identified on 2 days of in-water work during monitoring associated with the Ward Cove Cruise Ship Dock (Power Systems and Supplies of Alaska, 2020). A pod of three and a pod of five were recorded travelling at least 3,000 m from the construction site in April and May, respectively. During marine mammal monitoring of Tongass Narrows in 2020 and 2021, there were sightings of Dall's porpoises on 2 out of 88 days of observations across 7 months (October 2020-February 2021; May-June 2021)—once in November 2020 and once in February 2021. The pod sighted in November contained six animals; the pod observed in February had 10. Based on this recent data, there is no known pattern to their attendance in the project area, but they do occur rarely (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d).

Steller Sea Lion

Steller sea lions were listed as threatened range-wide under the ESA on November 26, 1990 (55 FR 49204). Steller sea lions were subsequently partitioned into the western and eastern DPSs (and MMPA stocks) in 1997 (62 FR 24345; May 5, 1997). The eastern DPS remained classified as threatened until it was delisted in November 2013. The current minimum abundance estimate for the eastern DPS of Steller sea lions is 43,201 individuals (Muto
et al.
2021). The western DPS (those individuals west of 144° W longitude or Cape Suckling, Alaska) was upgraded to endangered status following separation of the DPSs, and it remains endangered today. There is regular movement of both DPSs across this 144° W longitude boundary (Jemison
et al.
2013), however, due to the distance from this DPS boundary, it is likely that only eastern DPS Steller sea lions are present in the project area. Therefore, animals potentially affected by the project are assumed to be part of the eastern DPS.

There are several mapped and regularly monitored long-term Steller sea lion haulouts surrounding Ketchikan, such as West Rocks (36 miles/58 km) or Nose Point (37 miles/60 km), but none are known to occur within Tongass Narrows (Fritz
et al.
2015). The nearest known Steller sea lion haulout is located approximately 20 miles (58 km) west/northwest of Ketchikan on Grindall Island (Figure 4-1 in application). Summer counts of adult and juvenile sea lions at this haulout since 2000 have averaged approximately 191 individuals, with a range from 6 in 2009 to 378 in 2008. Only two winter surveys of this haulout have occurred. In March 1993, a total of 239 individuals were recorded, and in December 1994, a total of 211 individuals were recorded. No sea lion pups have been observed at this haulout during surveys. Although this is a limited and dated sample, it suggests that abundance may be consistent year-round at the Grindall Island haulout.

No systematic studies of sea lion abundance or distribution have occurred in Tongass Narrows. Anecdotal reports suggest that Steller sea lions may be found in Tongass Narrows year-round, with an increase in abundance from March to early May during the herring spawning season, and another increase in late summer associated with salmon runs. Overall sea lion presence in Tongass Narrows tends to be lower in summer than in winter (FHWA 2017). During summer, Steller sea lions may aggregate outside the project area, at rookery and haulout sites. Monitoring during construction of the Ketchikan Ferry Terminal in summer (July 16 through August 17, 2016) did not record any Steller sea lions (ADOT&PF 2015); however, monitoring during construction of the Ward Cove Dock, located approximately 6 km northwest of the Project site, recorded 181 individual sea lions on 44 days between February and September 2020 (Power Systems & Supplies of Alaska, 2020). Most sightings occurred in February (45 sightings of 88 sea lions) and March (34 sightings of 45 sea lions); the fewest number of sightings were observed in May (1 sighting of 1 sea lion) (Power Systems & Supplies of Alaska, 2020). Sightings were of single individuals, pairs, and herds of up to 10 individuals.

Sea lions are known to transit through Tongass Narrows while pursuing prey. Steller sea lions are also known to follow fishing vessels, and may congregate in small numbers at seafood processing facilities and hatcheries or at the mouths of rivers and creeks containing hatcheries, where large numbers of salmon congregate in late summer. Three seafood processing facilities are located east of the proposed berth location on Revilla Island, and two salmon hatcheries operated by the Alaska Department of Fish & Game (ADF&G) are located east of the project area. Steller sea lions may aggregate near the mouth of Ketchikan Creek, where a hatchery upstream supports a summer salmon run. The Creek mouth is more than 4 km (2.5 mi) from both ferry berth sites, and is positioned behind the cruise ship terminal and within the small boat harbor. In addition to these locations, anecdotal information from a local kayaking company suggests that there are Steller sea lions present at Gravina Point, near the southwest entrance to Tongass Narrows.

A total of 181 Steller sea lions were sighted on 44 separate days during all months of Ward Cove Cruise Ship Dock construction (February through September, 2020) (Power Systems and

Supplies of Alaska, 2020). Most sightings occurred in February and March and the fewest sightings were in May. Sightings were of single individuals, pairs, and herds of up to 10 individuals.

The DOT&PF implemented a marine mammal monitoring program in Tongass Narrows for recent previous construction components of the Tongass Narrows Project (84 FR 34134; July 17, 2019). Monitoring took place from October 2020 through February 2021 and May through June 2021, and results indicated that Steller sea lion numbers were highest in January and February (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Steller sea lions were observed in the Tongass Narrows Project area on 49 of 88 days between October 2020 and June 2021 (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). They were observed in every month that observations took place (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Over the course of the 7 months of monitoring, there were 77 sightings of 92 individual animals (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Sightings of Steller sea lions were most frequent in January and February and least common in May and June (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Sightings were primarily of single animals, but animals were also present in pairs and groups up to five sea lions (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). This is consistent with Freitag (2017 as cited in 83 FR 22009; May 11, 2018), though groups of up to 80 individuals have been observed (HDR, Inc. 2003). On average over the course of a year, Steller sea lions occur in Tongass Narrows approximately three or four times per week (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d).

Harbor Seal

Harbor seals range from Baja California north along the west coasts of Washington, Oregon, California, British Columbia, and Southeast Alaska; west through the Gulf of Alaska, Prince William Sound, and the Aleutian Islands; and north in the Bering Sea to Cape Newenham and the Pribilof Islands. In 2010, harbor seals in Alaska were partitioned into 12 separate stocks based largely on genetic structure (Allen and Angliss 2010). Harbor seals in Tongass Narrows are recognized as part of the Clarence Strait stock. Distribution of the Clarence Strait stock ranges from the east coast of Prince of Wales Island from Cape Chacon north through Clarence Strait to Point Baker and along the east coast of Mitkof and Kupreanof Islands north to Bay Point, including Ernest Sound, Behm Canal, and Pearse Canal (Muto
et al.
2021). The latest stock assessment analysis indicates that the current 8-year estimate of the Clarence Strait population trend is +138 seals per year, with a probability that the stock is decreasing of 0.413 (Muto
et al.
2021). Harbor seals haul out on rocks, reefs, beaches, and drifting glacial ice, and feed in marine, estuarine, and occasionally fresh waters. Harbor seals are generally non-migratory, with local movements associated with such factors as tides, weather, season, food availability, and reproduction (Muto,
et al.
2021).

No systematic studies of harbor seal abundance or distribution have occurred in Tongass Narrows. Aerial surveys conducted in August 2011 did not record any harbor seal haulouts in Tongass Narrows, but several haulouts were located on the outer shores of Gravina Island (London
et al.
2015). There is no known harbor seal haulout in Tongass Narrows although seals have been observed hauled out on docks in Ketchikan Harbor. The closest listed haulout is located off the tip of Gravina Island, approximately 8 km (5 mi) northwest of Ward Cove (AFSC 2018).

Anecdotal observations indicate that harbor seals are common in Tongass Narrows, although no data exist to quantify abundance. Two salmon hatcheries operated by ADF&G are located east of the project area. Like Steller sea lions, harbor seals may aggregate near the mouth of Ketchikan Creek when salmon are running in summer. The creek mouth is more than 4 km (2.5 mi) from the project component sites, and is positioned behind both the cruise ship terminal and within the small boat harbor. In the project area, they tend to be more abundant during spring, summer and fall months when salmon are present in Ward Creek. Anecdotal evidence indicates that harbor seals typically occur in groups of 1-3 animals in Ward Cove (Spokely 2019). They were not observed in Tongass Narrows during a combined 63.5 hours of marine mammal monitoring that took place in 2001 and 2016 (OSSA 2001, Turnagain 2016). The COK conducted pinnacle rock blasting in December 2019 and January 2020 near the vicinity of the proposed project and recorded a total of 21 harbor seal sightings of 24 individuals over 76.2 hours of pre- and post-blast monitoring (Sitkiewicz 2020).

Harbor seals were sighted during every month of construction (February through September, 2020) associated with the Ward Cove Cruise Ship Dock, with most sightings in February and March and the fewest in July (Power Systems and Supplies of Alaska, 2020). There were 247 sighting events of 271 individuals. Sighting events were of solo individuals, pairs, and the occasional group of three.

Marine mammal monitoring occurred near the project site from October 2020 to February 2021 and resumed in May 2021 during Phase 1 of the previously issued IHA (85 FR 673; January 7, 2020). Harbor seals were observed in the Tongass Narrows Project area in every month in which observations took place, except during October 2020 when only 3 days of monitoring occurred (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Harbor seals were sighted on 68 days out of 88 days of monitoring (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). They were mostly sightings of single animals, but animals were also present in pairs and groups up to five seals (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d). Sightings of harbor seals were consistent over the course of 7 months of intermittent monitoring; they were observed 5 to 6 days per week on average (DOT&PF 2020, 2021a, 2021b, 2021c, 2021d).

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. Current data indicate that 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) recommended that marine mammals be divided into functional hearing groups based on directly measured or estimated hearing ranges on the basis of available behavioral response data, audiograms derived using auditory evoked potential techniques, anatomical modeling, and other data. Note that no direct measurements of hearing ability have been successfully completed for mysticetes (
i.e.,
low-frequency cetaceans). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65 decibel (dB) threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall
et al.
(2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in Table 3.

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

Hearing group
Generalized hearing range*

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

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

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

275 Hz to 160 kHz.

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

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

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

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

For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information. Eight marine mammal species (six cetacean and two pinniped (one otariid and one phocid) species) have the reasonable potential to co-occur with the proposed survey activities. Please refer to Table 2. Of the cetacean species that may be present, two are classified as low-frequency cetaceans (
i.e.,
all mysticete species), two are classified as mid-frequency cetaceans (
i.e.,
all delphinid and ziphiid species and the sperm whale), and two are classified as high-frequency cetaceans (
i.e.,
harbor porpoise, Dall's porpoise and
Kogia spp.
).

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

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

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

Description of Sound Sources

The marine soundscape is comprised of both ambient and anthropogenic sounds. Ambient sound is defined as the all-encompassing sound in a given place and is usually a composite of sound from many sources both near and far (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 activity may be a negligible addition to the local environment or could form a distinctive signal that may affect marine mammals.

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

Three types of hammers would be used on this project: Impact, vibratory, and DTH. Impact hammers operate by repeatedly dropping and/or pushing a heavy piston onto a pile to drive the pile into the substrate. Sound generated by impact hammers is characterized by rapid rise times and high peak levels, a potentially injurious combination (Hastings and Popper 2005). Vibratory hammers install piles by vibrating them and allowing the weight of the hammer to push them into the sediment. Vibratory hammers produce significantly less sound than impact hammers. Peak Sound Pressure Levels (SPLs) may be 180 dB or greater, but are generally 10 to 20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Oestman
et al.

2009). Rise time is slower, reducing the probability and severity of injury, and sound energy is distributed over a greater amount of time (Nedwell and Edwards 2002; Carlson
et al.
2005).

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

The likely or possible impacts of ADOT's proposed activity on marine mammals could involve both non-acoustic and acoustic stressors. Potential non-acoustic stressors could result from the physical presence of the equipment and personnel; however, any impacts to marine mammals are expected to primarily be acoustic in nature. Acoustic stressors include effects of heavy equipment operation during pile installation and removal and use of DTH.

Acoustic Impacts

The introduction of anthropogenic noise into the aquatic environment from pile driving and removal and DTH is the primary means by which marine mammals may be harassed from ADOT's specified activity. In general, animals exposed to natural or anthropogenic sound may experience physical and psychological effects, ranging in magnitude from none to severe (Southall
et al.
2007, 2019). In general, exposure to pile driving and DTH noise has the potential to result in auditory threshold shifts and behavioral reactions (
e.g.,
avoidance, temporary cessation of foraging and vocalizing, changes in dive behavior). Exposure to anthropogenic noise can also lead to non-observable physiological responses such an increase in stress hormones. Additional noise in a marine mammal's habitat can mask acoustic cues used by marine mammals to carry out daily functions such as communication and predator and prey detection. The effects of pile driving and DTH noise on marine mammals are dependent on several factors, including, but not limited to, sound type (
e.g.,
impulsive vs. non-impulsive), the species, age and sex class (
e.g.,
adult male vs. mom with calf), duration of exposure, the distance between the pile and the animal, received levels, behavior at time of exposure, and previous history with exposure (Wartzok
et al.
2004; Southall
et al.
2007). Here we discuss physical auditory effects (threshold shifts) followed by behavioral effects and potential impacts on habitat.

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

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

Temporary Threshold Shift (TTS)—A temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS 2018). Based on data from cetacean TTS measurements (see Southall
et al.
2007), a TTS of 6 dB is considered the minimum threshold shift clearly larger than any day-to-day or session-to-session variation in a subject's normal hearing ability (Schlundt
et al.
2000; Finneran
et al.
2000, 2002). As described in Finneran (2015), marine mammal studies have shown the amount of TTS increases with 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 time when communication is critical for successful mother/calf interactions could have more serious impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall
et al.
2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost.

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

mammal TTS data come from a limited number of individuals within these species. No data are available on noise-induced hearing loss for mysticetes. For summaries of data on TTS in marine mammals or for further discussion of TTS onset thresholds, please see Southall
et al.
(2007), Finneran and Jenkins (2012), Finneran (2015), and Table 5 in NMFS (2018).

Installing piles requires a combination of impact pile driving, vibratory pile driving, and DTH. For the project, these activities may occur at the same time (up to two hammers of any combination of hammer/drill type), though such an occurrence is anticipated to be infrequent and for short durations on any given day, given that pile installation and removal occurs intermittently to allow for adjusting piles and measuring and documenting progress. Therefore, there would likely be pauses in activities producing the sound during each day. Given these pauses and that many marine mammals are likely moving through the project area and not remaining for extended periods of time, the potential for TS declines.

Behavioral Harassment
—Exposure to noise from pile driving and removal and DTH also has 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.
2003; Southall
et al.
2007; Weilgart 2007; Archer
et al.
2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison
et al.
2012), and can vary depending on characteristics associated with the sound source (
e.g.,
whether it is moving or stationary, number of sources, distance from the source). In general, pinnipeds seem more tolerant of, or at least habituate more quickly to, potentially disturbing underwater sound than do cetaceans, and generally seem to be less responsive to exposure to industrial sound than most cetaceans. Please see Appendices B and C of Southall
et al.
(2007) for a review of studies involving marine mammal behavioral responses to sound.

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

In 2016, ADOT documented observations of marine mammals during construction activities (
i.e.,
pile driving and DTH) at the Kodiak Ferry Dock (ABR 2016) in the Gulf of Alaska. In the marine mammal monitoring report for that project, 1,281 Steller sea lions were observed within the estimated Level B harassment zone during pile driving or DTH (
i.e.,
documented as potential take by Level B harassment). Of these, 19 individuals demonstrated an alert behavior, 7 were fleeing, and 19 swam away from the project site. All other animals (98 percent) were engaged in activities such as milling, foraging, or fighting and did not change their behavior. In addition, two sea lions approached within 20 m of active vibratory pile driving activities. Three harbor seals were observed within the disturbance zone during pile driving activities; none of them displayed disturbance behaviors. Fifteen killer whales and three harbor porpoise were also observed within the Level B harassment zone during pile driving. The killer whales were travelling or milling while all harbor porpoises were travelling. No signs of disturbance were noted for either of these species. Given the similarities in species, activities, and habitat, we expect similar behavioral responses of marine mammals to the ADOT's specified activity. That is, disturbance, if any, is likely to be temporary and localized (
e.g.,
small area movements). Monitoring reports from other recent pile driving and DTH projects in Alaska have observed similar behaviors, for example, the Biorka Island Dock Replacement Project (
https://www.fisheries.noaa.gov/action/incidental-take-authorization-faa-biorka-island-dock-replacement-project-sitka-ak
).

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

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

The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and

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

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

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

Airborne Acoustic Effects
—Pinnipeds that occur near the project site could be exposed to airborne sounds associated with pile driving and removal and DTH that have the potential to cause behavioral harassment, depending on their distance from these activities. Cetaceans are not expected to be exposed to airborne sounds that would result in harassment as defined under the MMPA.

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

Marine Mammal Habitat Effects

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

The area likely impacted by the project includes much of Tongass Narrows, but overall this area is relatively small compared to the available habitat in the surrounding area including Revillagigedo Channel, Behm Canal, and Clarence Strait. Pile installation/removal and DTH may temporarily increase turbidity resulting from suspended sediments. Any increases would be temporary, localized, and minimal. In general, turbidity associated with pile installation is localized to about a 25-ft radius around the pile (Everitt
et al.
1980). Cetaceans are not expected to be close enough to the project pile driving areas to experience effects of turbidity, and pinnipeds could avoid localized areas of turbidity. Therefore, the impact from increased turbidity levels is expected to minimal for marine mammals. Furthermore, pile driving and removal at the project site would not obstruct movements or migration of marine mammals.

In-water Construction Effects on Potential Prey
—Construction activities

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

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

Fish react to sounds that are especially strong and/or intermittent low-frequency sounds. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. The reaction of fish to noise depends on the physiological state of the fish, past exposures, motivation (
e.g.,
feeding, spawning, migration), and other environmental factors. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pile driving on fish; several are based on studies in support of large, multiyear bridge construction projects (
e.g.,
Scholik and Yan 2001, 2002; Popper and Hastings 2009). Several studies have demonstrated that impulse sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs (
e.g.,
Fewtrell and McCauley, 2012; Pearson
et al.
1992; Skalski
et al.
1992; Santulli
et al.
1999; Paxton
et al.
2017). However, some studies have shown no or slight reaction to impulse sounds (
e.g.,
Pena
et al.
2013; Wardle
et al.
2001; Jorgenson and Gyselman, 2009; Cott
et al.
2012).

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

The most likely impact to fish from pile driving and removal and DTH activities at the project area would be temporary behavioral avoidance of the area. The duration of fish avoidance of this area after pile driving stops is unknown, but a rapid return to normal recruitment, distribution and behavior is anticipated. Any behavioral avoidance by fish of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity in Revillagigedo Channel, Behm Canal, and Clarence Strait. Additionally, the City of Ketchikan within Tongass Narrows has a busy industrial water front, and human impact lessens the value of the area as foraging habitat. There are times of known seasonal marine mammal foraging in Tongass Narrows around fish processing/hatchery infrastructure or when fish are congregating, but the impacted areas of Tongass Narrows are a small portion of the total foraging habitat available in the region. In general, impacts to marine mammal prey species are expected to be minor and temporary due to the short timeframe of the project.

Construction activities, in the form of increased turbidity, have the potential to adversely affect eulachon, herring, and juvenile salmonid outmigratory routes in the project area. Salmon and forage fish, like eulachon and herring, form a significant prey base for Steller sea lions and are major components of the diet of many other marine mammal species that occur in the project area. Increased turbidity is expected to occur only in the immediate vicinity of construction activities and to dissipate quickly with tidal cycles. Given the limited area affected and high tidal dilution rates any effects on fish are expected to be minor.

Additionally, the presence of transient killer whales means some marine mammal species are also possible prey (harbor seals, harbor porpoises). ADOT's pile driving, pile removal and DTH activities are expected to result in limited instances of take by Level B and Level A harassment on these smaller marine mammals. That, as well as the fact that ADOT is impacting a small portion of the total available marine mammal habitat means that there would be minimal impact on these marine mammals as prey.

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

Estimated Take

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

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

Authorized takes would primarily be by Level B harassment, as use of the acoustic sources (
i.e.,
impact and vibratory pile driving and DTH) have the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for auditory injury (Level A harassment) to result, primarily for mysticetes, high frequency species and phocids because predicted auditory injury zones are larger than for mid-frequency species and otariids. Auditory injury is unlikely to occur for mid-frequency species and otariids. The proposed mitigation and monitoring

measures are expected to minimize the severity of such taking to the extent practicable.

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

Generally speaking, we estimate take by considering: (1) Acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and, (4) and the number of days of activities. We note that while these basic factors can contribute to a basic calculation to provide an initial prediction of 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 estimate.

Acoustic Thresholds

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

Level B Harassment for non-explosive sources
—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 (
e.g.,
frequency, predictability, duty cycle), the environment (
e.g.,
bathymetry), and the receiving animals (hearing, motivation, experience, demography, behavioral context) and can be difficult to predict (Southall
et al.
2007, Ellison
et al.
2012). Based on what the available science indicates and the practical need to use a threshold based on a factor that is both predictable and measurable for most activities, NMFS uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS predicts that marine mammals are likely to be behaviorally harassed in a manner we consider Level B harassment when exposed to underwater anthropogenic noise above received levels of 120 dB re 1 microPascal (μPa) (root mean square (rms)) for continuous (
e.g.,
vibratory pile-driving, DTH) and above 160 dB re 1 μPa (rms) for non-explosive impulsive (
e.g.,
seismic airguns) or intermittent (
e.g.,
scientific sonar) sources. This take estimation includes disruption of behavioral patterns resulting directly in response to noise exposure (
e.g.,
avoidance), as well as that resulting indirectly from associated impacts such as TTS or masking. ADOT's proposed activity includes the use of continuous (vibratory pile driving/removal and DTH) and impulsive (impact pile driving and DTH) sources, and therefore both the 120 and 160 dB re 1 μPa (rms) thresholds are applicable.

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

These thresholds are provided in Table 4 below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS 2018 Technical Guidance, which may be accessed at
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

Table 4—Thresholds Identifying the Onset of Permanent Threshold Shift

Hearing group

PTS onset acoustic thresholds *
(received level)

Impulsive
Non-impulsive

Low-Frequency (LF) Cetaceans

Cell 1:

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

Cell 2:

L
E,LF,24h
:
199 dB.

Mid-Frequency (MF) Cetaceans

Cell 3:

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

Cell 4:

L
E,MF,24h
:
198 dB.

High-Frequency (HF) Cetaceans

Cell 5:

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

Cell 6:

L
E,HF,24h
:
173 dB.

Phocid Pinnipeds (PW) (Underwater)

Cell 7:

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

Cell 8:

L
E,PW,24h
:
201 dB.

Otariid Pinnipeds (OW) (Underwater)

Cell 9:

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

Cell 10:

L
E,OW,24h
:
219 dB.

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

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

Ensonified Area

Here, we describe operational and environmental parameters of the activity that will feed into identifying the area ensonified above the acoustic thresholds, which include source levels and transmission loss coefficient.

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

In order to calculate distances to the Level A harassment and Level B harassment sound thresholds for the methods and piles being used in this project, NMFS used acoustic monitoring data from other locations to develop source levels for the various pile types,

sizes and methods (Table 5). Note that piles of differing sizes have different sound source levels (SSLs).

Empirical data from recent ADOT sound source verification (SSV) studies at Ketchikan were used to estimate SSLs for vibratory and impact driving of 30-inch steel pipe piles (Denes
et al.
2016). Data from Ketchikan was used because of its proximity to this proposed project in Tongass Narrows. However, the use of data from Alaska sites was not appropriate in all instances. Details are described below.

For vibratory driving of 24-inch steel piles, data from a Navy pile driving project in the Puget Sound, WA was reviewed (Navy 2015). From this review, ADOT determined the Navy's suggested source value of 161 dB rms was an appropriate proxy source value, and NMFS concurs. Because the source value of smaller piles of the same general type (steel in this case) are not expected to exceed a larger pile, the same 161 dB rms source value was used for 20-inch steel piles. This assumption conforms with source values presented in Navy (2015) for a project using 16-inch steel piles at Naval Base Kitsap in Bangor, WA.

ADOT used source values of 177 dB SEL and 190 dB rms for impact driving of 24-inch and 20-inch steel piles. These values were determined based on summary values presented in Caltrans (2015) for impact driving of 24-inch steel piles. NMFS concurs that the same source value was an acceptable proxy for impact driving of 20-inch steel piles.

Sound pressure levels in the water column resulting from DTH are not well studied. Because DTH hole creation includes both impulsive and continuous components, NMFS guidance currently recommends that it be treated as a continuous sound for Level B calculations and as an impulsive sound for Level A calculations (Table 11). In the absence of data specific to different hole sizes, current NMFS guidance recommends that calculation of Level B zones for DTH use the same continuous SSL of 167 dB SEL for all hole sizes (Heyvaert and Reyff 2021). Recommended SSLs for 30-inch and 24-inch holes as well as 8-inch holes for tension anchors and micropiles for use in the calculation of Level A harassment thresholds are provided by current NMFS guidance and in Table 5.

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

Method and pile type
Vibratory hammer

SSL at 10 m
dB rms

Literature source

30-inch steel piles
162

Denes
et al.
2016.

24-inch steel piles
161
Navy 2015.

20-inch steel piles
161
Navy 2015.

DTH of rock sockets and tension anchors
dB rms

All pile diameters
167
Heyvaert and Reyff 2021.

DTH of rock sockets and tension anchors
dB SELss
dB peak

30-inch rock socket
164
194

Reyff and Heyvaert 2019; Reyff 2020; Denes
et al.
2016.

24-inch rock socket
159
184
Heyvaert and Reyff 2021.

8-inch tension anchor/micropile
144
170
Reyff 2020.

Impact hammer
dB rms
dB SEL
dB peak

30-inch steel piles
195
181
209

Denes
et al.
2016.

24-inch steel piles
190
177
203
Caltrans 2015.

20-inch steel piles
190
177
202
Caltrans 2015.

Note:
It is assumed that noise levels during pile installation and removal are similar. SEL = sound exposure level; dB peak = peak sound level; rms = root mean square.

Simultaneous use of two impact, vibratory, or DTH hammers, or any combination of those equipment, could occur. Such occurrences are anticipated to be infrequent, would be for short durations on any given day, and ADOT anticipates that no more than two hammers would be operated concurrently. Simultaneous use of two hammers or DTH systems could occur at the same project site, or at two different, but nearby project sites. Simultaneous use of hammers could result in increased SPLs and harassment zone sizes given the proximity of the component driving sites and the physical rules of decibel addition. ADOT anticipates that concurrent use of two hammers producing continuous noise could occur on 44 days, which is half the anticipated number of days of construction (91 days) and represents complete overlap between the two contracts and/or represents use of two hammers by a single contractor. Although it is unlikely that overlap would be complete, ADOT anticipates, and NMFS concurs, this scenario represents the potential worst case scenario, given that a more accurate estimate is not possible, and concurrent operation of hammers would be incidental. Given that the use of more than one hammer for pile installation on the same day (whether simultaneous or not) would increase the number of piles installed per day, this would be anticipated to result in a reduction of the total number of days of pile installation. Table 6 shows how potential scenarios would reduce the total number of pile driving days and weeks. However, as described in the
Marine Mammal Occurrence and Take Calculation and Estimation
section below, ADOT has conservatively calculated take with the assumption that pile driving would occur on all 91 days.

Table 6—Calculated Reduction of Pile Driving Days Based on Percentage of Project Days With Two Hammers in Use

Percent overlap

Days of
overlap

Days of work
completed
during
overlap
(2 hammers)

Remaining
days of work
with single
hammer

Total number
of days
of work

Weeks
of work

0
0.0
0.0
91.0
91.0
15.2

10
9.1
18.2
72.8
81.9
13.7

20
18.2
36.4
54.6
72.8
12.1

30
27.3
54.6
36.4
63.7
10.6

40
36.4
72.8
18.2
54.6
9.1

50
45.5
91.0
0.0
45.5
7.6

NMFS (2018b) handles overlapping sound fields created by the use of more than one hammer differently for impulsive (impact hammer and Level A harassment zones for drilling with a DTH hammer) and continuous sound sources (vibratory hammer and Level B harassment zones for drilling with a DTH hammer; Table 7) and differently for impulsive sources with rapid impulse rates of multiple strikes per second (DTH) and slow impulse rates (impact hammering) (NMFS 2021). It is unlikely that the two impact hammers would strike at the same instant, and therefore, the SPLs would not be adjusted regardless of the distance between impact hammers. In this case, each impact hammer would be considered to have its own independent Level A harassment and Level B harassment zones.

When two DTH hammers operate simultaneously their continuous sound components overlap completely in time. When the Level B isopleth of one DTH sound source encompasses the isopleth of another DTH sound source, the sources are considered additive and combined using the following rules (Table 7). The method described below was based on one created by Washington State Department of Transportation (WSDOT) and has been updated and modified by NMFS (WSDOT 2020). For addition of two simultaneous DTH hammers, the difference between the two SSLs is calculated, and if that difference is between 0 and 1 dB, 3 dB are added to the higher SSL; if difference is between 2 or 3 dB, 2 dB are added to the highest SSL; if the difference is between 4 to 9 dB, 1 dB is added to the highest SSL; and with differences of 10 or more decibels, there is no addition.

When two continuous noise sources, such as vibratory hammers, have overlapping sound fields, there is potential for higher sound levels than for non-overlapping sources.

When two or more vibratory hammers are used simultaneously, and the isopleth of one sound source encompasses the isopleth of another sound source, the sources are considered additive and source levels are combined using the rules in Table 7, similar to described above for DTH.

Table 7—Rules for Combining Sound Source Levels Generated During Pile Installation

Hammer types
Difference in SSL
Level A zones
Level B zones

Vibratory, Impact
Any
Use impact zones
Use largest zone.

Impact, Imp

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2022-02035. Public record. Not legal advice.