# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Homer Harbor System Four Float Replacement Project
**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 City of Homer (Homer) for authorization to take marine mammals incidental to the Homer Harbor System Four Float Replacement Project in Homer, AK. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an incidental harassment authorization (IHA) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-time, 1-year renewal that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorization and agency responses will be summarized in the final notice of our decision.
**DATES:**
Comments and information must be received no later than May 4, 2026.
**ADDRESSES:**
Comments should be addressed to Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service and should be submitted via email to *[email protected].* Electronic copies of the application and supporting documents, as well as a list of the references cited in this document, may be obtained online at: *https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities.* In case of problems accessing these documents, please call the contact listed below.
*Instructions:* NMFS is not responsible for comments sent by any other method, to any other address or individual, or received after the end of the comment period. Comments, including all attachments, must not exceed a 25-megabyte file size. All comments received are a part of the public record and will generally be posted online at *https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act* without change. All personal identifying information ( *e.g.,* name, address) voluntarily submitted by the commenter may be publicly accessible. Do not submit confidential business information or otherwise sensitive or protected information.
**FOR FURTHER INFORMATION CONTACT:**
Craig Cockrell, Office of Protected Resources, NMFS, (301) 427-8401.
**SUPPLEMENTARY INFORMATION:**
**Background**
The MMPA prohibits the “take” of marine mammals, with certain exceptions. Section 101(a)(5)(D) of the MMPA (16 U.S.C. 1361 *et seq.* ) directs the Secretary of Commerce (as delegated to NMFS) to allow, upon request, the incidental, but not intentional, taking of small numbers of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region if certain findings are made and either regulations are proposed or, if the taking is limited to harassment, a notice of a proposed IHA is provided to the public for review.
Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s) and will not have an unmitigable adverse impact on the availability of the species or stock(s) for taking for subsistence uses (where relevant). Further, NMFS must prescribe the permissible methods of taking; other “means of effecting the least practicable adverse impact” on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stocks for taking for certain subsistence uses (referred to as “mitigation”); and requirements pertaining to the monitoring and reporting of the takings. The definitions of all applicable MMPA statutory terms used above are included in the relevant sections below ( *see also* 16 U.S.C. 1362; 50 CFR 216.3 and 216.103).
**National Environmental Policy Act**
To comply with the National Environmental Policy Act of 1969 (NEPA; 42 U.S.C. 4321 *et seq.* ) and NOAA Administrative Order (NAO) 216-6A, NMFS must review our proposed action ( *i.e.,* the issuance of an IHA) with respect to potential impacts on the human environment.
This action is consistent with categories of activities identified in Categorical Exclusion B4 (IHAs with no anticipated serious injury or mortality) of the Companion Manual for NAO 216-6A, which do not individually or cumulatively have the potential for significant impacts on the quality of the human environment and for which we have not identified any extraordinary circumstances that would preclude this categorical exclusion. Accordingly, NMFS has preliminarily determined that the issuance of the proposed IHA qualifies to be categorically excluded from further NEPA review.
**Summary of Request**
On November 13, 2025, NMFS received a request from Homer for an IHA to take marine mammals incidental to the construction of the Homer Harbor System Four Float Replacement Project in Homer, AK. Following NMFS' review of the application, Homer submitted a revised version on February 11, 2026. The application was deemed adequate and complete on February 24, 2026. Homer's request is for take of six species of marine mammals, by Level B harassment and, for harbor seals, Level A harassment. Neither Homer nor NMFS expect serious injury or mortality to result from this activity and, therefore, an IHA is appropriate.
**Description of Proposed Activity**
**Overview**
The purpose of the project is to repair and make improvements, including the expansion of the current footprint of the dock system of the Homer Small Boat Harbor. The location provides safe harbor for boats of various sizes in the city of Homer. Takes of marine mammals by Level A and Level B harassment are expected to occur due to impact and vibratory pile driving and removal. The project would occur at the entrance of Kachemak Bay which is located in off of a sandbar directly south of Homer, AK. It is expected to take up to 75 non-consecutive days to complete the pile driving and removal activities.
**Dates and Duration**
The proposed IHA would be valid for the statutory maximum of 1 year from the date of effectiveness. It will become effective upon written notification from the applicant to NMFS, but not beginning later than 1 year from the date of issuance or extending beyond 2 years from the date of issuance. Construction activities are expected to occur over a 1-year period from August 2027 through July 2028. It is anticipated that the pile driving work would take 75 non-consecutive days.
**Specific Geographic Region**
The project area is located within the Homer Small Boat Harbor, within Kachemak Bay in Southcentral Alaska (figure 1). Kachemak Bay is approximately 64 kilometers (km) long and empties into the lower Cook Inlet. The bay is approximately 35 km wide at the mouth and narrows to approximately 5 km wide at the end. The Homer Small Boat Harbor is located near the end of Homer Spit, which extends 7 km into the mouth of Kachemak Bay. Kachemak Bay is between 3 and 137 m deep in the project area outside of Homer Harbor.
**Figure 1—Homer Small Boat Harbor Project Area**
**Detailed Description of the Specified Activity**
Homer proposes to replace the gangway at Ramp Six and most of Float System Four at the Homer Small Boat Harbor. In-water construction activities associated with the project would include impact pile driving and vibratory pile driving and removal. Pile removal may also be completed using a “dead pull” method, where a pile is tethered to a crane and is removed directly. Impact hammers operate by repeatedly dropping a heavy piston onto a pile to drive the pile into the substrate. Vibratory hammers install piles by vibrating them and allowing the weight of the hammer to push them into the sediment.
The new dock system would be constructed in two units, unit one and unit two to repair failing components of the dock system and expand the footprint of the current dock configuration (see figure 7 and 8 in Homer's application). During the construction of unit one Homer would remove 56 steel and timber piles and install 76 steel piles of various sizes. During the construction of unit two Homer would remove 46 steel and timber piles and install 57 steel piles of various sizes (table 1). Twenty-eight 16 inch (in) (41 centimeters (cm)) temporary steel piles would only be used when needed and would not be driven to support the installation of every permanent pile. Homer does not know the location and number of the temporary piles in advance. Therefore, Homer is estimating, based on similar previous projects, that temporary piles would be installed in proportion to the number of permanent piles in each unit. Unit 1 contains 57 percent of the permanent piles, and it is assumed that 57 percent of temporary piles (16 piles) would be installed and removed in unit one. Unit two would include 43 percent of temporary piles (12 piles) would be installed and removed. Dead pull methods would not have impacts on marine mammals; however, we assume that all pile removal is conducted using vibratory hammer.
| Pile diameter and construction unit | Number of piles |
| --- | --- |
| | |
| 12.75-in steel pipe piles (unit one) | 8 |
| 16-in steel pipe piles (unit one) | 42 |
| 18-in steel pipe piles (unit one) | 26 |
| 12.75-in steel pipe piles (unit two) | 6 |
| 16-in steel pipe piles (unit two) | 28 |
| 18-in steel pipe piles (unit two) | 3 |
| 24-in steel pipe piles (unit two) | 20 |
| | |
| 12-in timber piles (unit one) | 16 |
| 12.75-in steel pipe piles (unit one) | 23 |
| 16-in steel pipe piles (unit one) | 17 |
| 12-in timber piles (unit two) | 20 |
| 12.75-in steel pipe piles (unit two) | 17 |
| 16-in steel pipe piles (unit two) | 9 |
Above water construction would include the installation of components on the new floats such as mooring cleats and bullrails, electrical lines and power/light pedestals, fire suppression lines and hydrants, water lines, and a new sewer remote pumping station and safety equipment such as fire extinguishers, life rings, and safety ladders. This above-water work is not expected to result in incidental take of marine mammals. Noise generated above the water would not be transmitted into the water and there are no major pinniped haulouts located near the project area, therefore airborne noise is therefore not considered further in this document.
Proposed mitigation, monitoring, and reporting measures are described in detail later in this document (please see Proposed Mitigation and Proposed Monitoring and Reporting).
**Description of Marine Mammals in the Area of Specified Activities**
Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history of the potentially affected species. NMFS fully considered all of this information, and we refer the reader to these descriptions, instead of reprinting the information. Additional information regarding population trends and threats may be found in NMFS' Stock Assessment Reports (SARs; *https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments* ) and more general information about these species ( *e.g.,* physical and behavioral descriptions) may be found on NMFS' website ( *https://www.fisheries.noaa.gov/find-species).*
Table 2 lists all species or stocks for which take is expected and proposed to be authorized for this activity and summarizes information related to the population or stock, including regulatory status under the MMPA and Endangered Species Act (ESA) and potential biological removal (PBR), where known. PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (as described in NMFS' SARs). While no serious injury or mortality is anticipated or proposed to be authorized here, PBR and annual mortality and serious injury (M/SI) from anthropogenic sources are included here as gross indicators of the status of the species or stocks and other threats.
Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Alaska SARs. All values presented in table 2 are the most recent available at the time of publication (including from the draft 2024 SARs) and are available online at: *https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.*
| Common name | Scientific name | Stock | ESA/ | Stock abundance | PBR | Annual |
| --- | --- | --- | --- | --- | --- | --- |
| | | | | | | |
| | | | | | | |
| Humpback whale | | Hawai'i | -,-, N | 11,278 (0.56, 7,265, 2020) | 127 | 27.09 |
| | | Mexico-North Pacific | T, D, Y | N/A (N/A, N/A, 2006) | UND | 0.57 |
| | | | | | | |
| | | | | | | |
| Killer whale | | Eastern North Pacific Alaska Resident | -, -, N | 1,920 (N/A, 1,920, 2019) | 19 | 1.3 |
| | | Eastern North Pacific Gulf of Alaska, Aleutian Islands and Bering Sea Transient | -, -, N | 587 (N/A, 587, 2012) | 5.9 | 0.8 |
| | | | | | | |
| Harbor porpoise | | Gulf of Alaska | -, -, Y | 31,046 (0.21, N/A, 1998) | UND | 72 |
| Dall's Porpoise | | Alaska | -, -, N | UND (UND, UND, 2015) | UND | 37 |
| | | | | | | |
| | | | | | | |
| Steller Sea Lion | | Western DPS | E, D, Y | 49,837 (N/A, 49,837, 2022) | 299 | 267 |
| | | | | | | |
| Harbor Seal | | Cook Inlet/Shelikof Strait | -, -, N | 28,411 (N/A, 26,907, 2018) | 807 | 107 |
As indicated above, all six species (with eight managed stocks) in table 2 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. While gray whale ( *Eschrichtius robustus* ), fin whale ( *Balaenoptera physalus* ), minke whale ( *Balaenoptera acutorostrata* ), beluga whale ( *Delphinapterus leucas* ), Pacific white-sided dolphin ( *Lagenorhynchus obliquidens* ), and northern fur seals ( *Callorhinus ursinus* ) have been documented in the area in the past, the temporal and/or spatial occurrence of these species is such that take is not expected to occur, and they are not discussed further beyond the explanation provided here. Based on the applicants research these species have not used the entrance of the Kachemak Bay and the surrounding waters for a number of years. Although the entrance of the Kachemak Bay is a designated critical habitat and a small and resident population biologically important area (BIA) for Cook Inlet beluga whale, sightings of beluga whale in the area have not occurred since 2001. Therefore, take of these species is not expected to occur.
**Humpback Whale**
Two stocks of humpback whales could be found in the project area. These include the Hawai'i Stock (not ESA-listed) and the Mexico-North Pacific Stock (ESA-threatened). Humpback whales are encountered regularly in lower Cook Inlet, including Kachemak Bay. Since there are multiple sightings of humpback whales every year, they are considered frequent in the project area.
Within the project area, most humpback whales (89 percent) are likely to be from the Hawaii DPS, approximately 11 percent are likely to be from the threatened Mexico DPS.
**Killer Whale**
Two stocks of killer whales could occur in the project area. These include the Eastern North Pacific Alaska Resident stock and the Gulf of Alaska/Aleutian Islands/Bering Sea Transient stock. Killer whales have been sighted near Homer and Port Graham in lower Cook Inlet (Shelden *et al.,* 2022, Shelden *et al.,* 2003, Rugh *et al.,* 2005). Resident killer whales from pods often sighted near Kenai Fjords National Park and in Prince William Sound have been occasionally photographed in lower Cook Inlet (Shelden *et al.,* 2003). The availability of salmon influences when resident killer whales are more likely to be sighted in Cook Inlet. Killer whales were observed in Kachemak and English Bay three times during aerial surveys conducted between 1993 and 2004 (Rugh *et al.,* 2005).
**Harbor Porpoise**
The harbor porpoise frequents nearshore waters and coastal embayments throughout their range, including bays, harbors, estuaries, and fjords less than 198 meters (m) deep (NMFS 2022). A review of marine mammal sighting databases (iNaturalist 2025, OBIS 2025), indicates that harbor porpoises are infrequently observed throughout Kachemak Bay during spring, summer, and fall. Anecdotal observations also report infrequent sightings of harbor porpoises year-round in the vicinity of the project area (SolsticeAK 2025).
**Dall's Porpoise**
Although Dall's porpoises generally prefer open water, they are known to frequent nearshore habitats and areas of shallow water and therefore may be found in Kachemak Bay (Moran *et al.,* 2018). A review of marine mammal sighting databases indicates that Dall's porpoises are infrequently observed throughout Kachemak Bay during summer (iNaturalist 2025). This is corroborated by anecdotal observations reporting infrequent sightings in the vicinity of the project area (SolsticeAK 2025).
**Steller Sea Lion**
Steller sea lions were partitioned into the western and eastern distinct population segments (DPSs) in 1997 (62 FR 24345, May 5, 1997). The western DPS (those individuals west of the 144° W longitude or Cape Suckling, Alaska) was also upgraded to endangered status during the separation of the DPSs on May 5, 1997. Only individuals from the western DPS are present in the project area. A review of marine mammal sighting databases indicates that Steller sea lions are infrequently recorded in Kachemak Bay during spring, summer, and fall (iNaturalist 2025) and anecdotal reports suggest they are occasionally observed near the project area, primarily outside the harbor and during summer and fall (SolsticeAK 2025). There are no Steller sea lion haulouts or rookeries in Kachemak Bay.
**Harbor Seal**
Harbor seals are common in the project area and are frequently observed within the Homer Small Boat Harbor. A review of marine mammal sighting databases indicates that harbor seals are commonly recorded in Kachemak Bay year-round (iNaturalist 2025). Anecdotal reports suggest they are observed almost daily near the project area (SolsticeAK 2025). There are no haulouts located within the vicinity of the project area that would be affected by the construction activities.
**Marine Mammal Hearing**
Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities ( *e.g.,* Richardson *et al.,* 1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall *et al.* (2007; 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, *etc.* ). Generalized hearing ranges were chosen based on the 65 decibel (dB) threshold from composite audiograms, previous analyses in NMFS (2018), and/or data from Southall *et al.* (2007) and Southall *et al.* (2019). We note that the names of two hearing groups and the generalized hearing ranges of all marine mammal hearing groups have been recently updated (NMFS, 2024) as reflected below in table 3.
| Hearing group | Generalized hearing range * |
| --- | --- |
| Low-frequency (LF) cetaceans (baleen whales) | 7 Hz to 36 kHz. |
| High-frequency (HF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales) | 150 Hz to 160 kHz. |
| Very High-frequency (VHF) cetaceans (true porpoises,
river dolphins, Cephalorhynchid,
&
) | 200 Hz to 165 kHz. |
| Phocid pinnipeds (PW) (underwater) (true seals) | 40 Hz to 90 kHz. |
| Otariid pinnipeds (OW) (underwater) (sea lions and fur seals) | 60 Hz to 68 kHz. |
For more detail concerning these groups and associated frequency ranges, please see NMFS (2024) for a review of available information.
**Potential Effects of Specified Activities on Marine Mammals and Their Habitat**
This section provides a discussion of the ways in which components of the specified activity may impact marine mammals and their habitat. The Estimated Take of Marine Mammals section later in this document includes a quantitative analysis of the number of individuals that are expected to be taken by this activity. The Negligible Impact Analysis and Determination section considers the content of this section, the Estimated Take of Marine Mammals section, and the Proposed Mitigation section, to draw conclusions regarding the likely impacts of these activities on the reproductive success or survivorship of individuals and whether those impacts are reasonably expected to, or reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.
Acoustic effects on marine mammals during the specified activities are expected to potentially occur from vibratory pile installation and removal and impact pile driving. The effects of underwater noise from Homer's proposed activities have the potential to result in Level B harassment of marine mammals in the action area and, for harbor seals as a result of certain activities, Level A harassment.
There are a variety of types and degrees of effects on marine mammals and their habitat (including prey) that could occur as a result of the specified activities. Below we provide a brief description of the types of sound generated by specified activities, the general impacts on marine mammals and their habitat from these types of activities, and a related project-specific analysis with consideration of the proposed mitigation measures.
**Description of Sound Sources for the Specified Activities**
Activities associated with the project that have the potential to incidentally take marine mammals though exposure to sound include both vibratory and impact hammers.
Impact hammers typically 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 impulsive, characterized by rapid rise times and high peak sound pressure 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 substrate, and extract piles by using vibration to break the sediment friction and allow a crane to pull the piles out. Vibratory hammers typically produce less sound ( *i.e.,* lower sound pressure levels) 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; California Department of Transportation (CALTRANS), 2015, 2020). Sounds produced by vibratory hammers are non-impulsive; compared to sounds produced by impact hammers, they have a slower rise time, reducing the probability and severity of injury, and the sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson *et al.,* 2005).
**Potential Effects of Underwater Sound on Marine Mammals**
The introduction of anthropogenic noise into the aquatic environment from impact and vibratory hammers is the primary means by which marine mammals may be harassed from the Homer's specified activity. Anthropogenic sounds cover a broad range of frequencies and sound levels and can have a range of highly variable impacts on marine life from none or minor to potentially severe responses depending on received levels, duration of exposure, behavioral context, and various other factors. Broadly, underwater sound from active acoustic sources, such as those in the Project, can potentially result in one or more of the following: temporary or permanent hearing impairment, non-auditory physical or physiological effects, behavioral disturbance, stress, and masking (Richardson *et al.,* 1995; Gordon *et al.,* 2003; Nowacek *et al.,* 2007; Southall *et al.,* 2007; Götz *et al.,* 2009).
We describe the more severe effects of certain non-auditory physical or physiological effects only briefly as we do not expect that the use of impact and vibratory hammers are reasonably likely to result in such effects (see below for further discussion). Potential effects from impulsive sound sources can range in severity from effects such as behavioral disturbance or tactile perception to physical discomfort, slight injury of the internal organs and the auditory system, or mortality (Yelverton *et al.,* 1973). Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to high level underwater sound or as a secondary effect of extreme behavioral reactions ( *e.g.,* change in dive profile as a result of an avoidance reaction) caused by exposure to sound include neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage (Cox * et al.,* 2006; Southall *et al.,* 2007; Zimmer and Tyack, 2007; Tal *et al.,* 2015). The Project activities considered here do not involve the use of devices such as explosives or mid-frequency tactical sonar that are associated with these types of effects.
The degree of effect of an acoustic exposure on marine mammals is dependent on several factors, including, but not limited to, sound type ( *e.g.,* impulsive vs. non-impulsive), signal characteristics, the species, age and sex class ( *e.g.,* adult male vs. mom with calf), duration of exposure, the distance between the noise source and the animal, received levels, behavioral state at time of exposure, and previous history with exposure (Wartzok *et al.,* 2004; Southall *et al.,* 2007). In general, sudden, high-intensity sounds can cause hearing loss as can longer exposures to lower-intensity sounds. Moreover, any temporary or permanent loss of hearing, if it occurs at all, will occur almost exclusively for noise within an animal's hearing range. We describe below the specific manifestations of acoustic effects that may occur based on the activities proposed by Homer.
Richardson *et al.* (1995) described zones of increasing intensity of effect that might be expected to occur in relation to distance from a source and assuming that the signal is within an animal's hearing range. First (at the greatest distance) is the area within which the acoustic signal would be audible (potentially perceived) to the animal but not strong enough to elicit any overt behavioral or physiological response. The next zone (closer to the receiving animal) corresponds with the area where the signal is audible to the animal and of sufficient intensity to elicit behavioral or physiological responsiveness. The third is a zone within which, for signals of high intensity, the received level is sufficient to potentially cause discomfort or tissue damage to auditory or other systems. Overlaying these zones to a certain extent is the area within which masking ( *i.e.,* when a sound interferes with or masks the ability of an animal to detect a signal of interest that is above the absolute hearing threshold) may occur; the masking zone may be highly variable in size.
Below, we provide additional details regarding potential impacts on marine mammals and their habitat from noise in general, starting with hearing impairment, as well as from the specific activities Homer plans to conduct, to the degree it is available.
**Hearing Threshold Shifts**
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, 2024). The amount of threshold shift is customarily expressed in dB. A TS can be permanent or temporary. As described in NMFS (2018, 2024) there are numerous factors to consider when examining the consequence of TS, including, but not limited to, the signal temporal pattern ( *e.g.,* impulsive or non-impulsive), likelihood an individual would be exposed for a long enough duration or to a high enough level to induce a TS, the magnitude of the TS, time to recovery (seconds to minutes or hours to days), the frequency range of the exposure ( *i.e.,* spectral content), the hearing frequency range of the exposed species relative to the signal's frequency spectrum ( *i.e.,* how animal uses sound within the frequency band of the signal; *e.g.,* Kastelein *et al.,* 2014), and the overlap between the animal and the source ( *e.g.,* spatial, temporal, and spectral).
**Auditory Injury (AUD INJ)**
NMFS (2024) defines AUD INJ as damage to the inner ear that can result in destruction of tissue, such as the loss of cochlear neuron synapses or auditory neuropathy (Houser 2021; Finneran 2024). AUD INJ may or may not result in a permanent threshold shift (PTS). PTS is subsequently defined as a permanent, irreversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2024). PTS does not generally affect more than a limited frequency range, and an animal that has incurred PTS has some level of hearing loss at the relevant frequencies; typically, animals with PTS or other AUD INJ are not functionally deaf (Au and Hastings, 2008; Finneran, 2016). Available data from humans and other terrestrial mammals indicate that a 40-dB threshold shift approximates AUD INJ onset (see Ward *et al.,* 1958, 1959; Ward, 1960; Kryter *et al.,* 1966; Miller, 1974; Ahroon *et al.,* 1996; Henderson *et al.,* 2008). AUD INJ 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 AUD INJ in marine mammals largely due to the fact that, for various ethical reasons, experiments involving anthropogenic noise exposure at levels inducing AUD INJ are not typically pursued or authorized (NMFS, 2024).
**Temporary Threshold Shift (TTS)**
TTS is a temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2024), and is not considered an AUD INJ. Based on data from marine mammal TTS measurements (see Southall *et al.,* 2007, 2019), 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 (Finneran *et al.,* 2000, 2002; Schlundt *et al.,* 2000). As described in Finneran (2015), marine mammal studies have shown the amount of TTS increases with the 24-hour cumulative sound exposure level (SEL <sub>24</sub> ) in an accelerating fashion: at low exposures with lower SEL <sub>24</sub> , the amount of TTS is typically small and the growth curves have shallow slopes. At exposures with higher SEL <sub>24</sub> , the growth curves become steeper and approach linear relationships with the sound exposure level (SEL).
Depending on the degree (elevation of threshold in dB), duration ( *i.e.,* recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to more impactful (similar to those discussed in auditory masking, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more severe impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall *et al.,* 2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost.
Many studies have examined noise-induced hearing loss in marine mammals (see Finneran (2015) and Southall *et al.* (2019) for summaries). TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 2013). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS) (Finneran, 2015). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. For cetaceans, published data on the onset of TTS are limited to captive bottlenose dolphin ( *Tursiops truncatus* ), beluga whale, harbor porpoise, and Yangtze finless porpoise ( *Neophocoena asiaeorientalis* ) (Southall *et al.,* 2019). For pinnipeds in water, measurements of TTS are limited to harbor seals, elephant seals ( *Mirounga angustirostris* ), bearded seals ( *Erignathus barbatus* ) and California sea lions ( *Zalophus californianus* ) (Kastak *et al.,* 1999, 2007; Kastelein *et al.,* 2019b, 2019c, 2021, 2022a, 2022b; Reichmuth *et al.,* 2019; Sills *et al.,* 2020). TTS was not observed in spotted ( *Phoca largha* ) and ringed ( *Pusa hispida* ) seals exposed to single airgun impulse sounds at levels matching previous predictions of TTS onset (Reichmuth *et al.,* 2016). These studies examine hearing thresholds measured in marine mammals before and after exposure to intense or long-duration sound exposures. The difference between the pre-exposure and post-exposure thresholds can be used to determine the amount of threshold shift at various post-exposure times.
The amount and onset of TTS depends on the exposure frequency. Sounds below the region of best sensitivity for a species or hearing group are less hazardous than those near the region of best sensitivity (Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure levels are higher compared to those in the region of best sensitivity ( *i.e.,* a low frequency noise would need to be louder to cause TTS onset when TTS exposure level is higher), as shown for harbor porpoises and harbor seals (Kastelein *et al.,* 2019a, 2019c). Note that in general, harbor seals and harbor porpoises have a lower TTS onset than other measured pinniped or cetacean species (Finneran, 2015). In addition, TTS can accumulate across multiple exposures, but the resulting TTS will be less than the TTS from a single, continuous exposure with the same SEL (Mooney *et al.,* 2009; Finneran *et al.,* 2010; Kastelein *et al.,* 2014, 2015). This means that TTS predictions based on the total, SEL <sub>24</sub> will overestimate the amount of TTS from intermittent exposures, such as sonars and impulsive sources. Nachtigall *et al.* (2018) describe measurements of hearing sensitivity of multiple odontocete species (bottlenose dolphin, harbor porpoise, beluga, and false killer whale ( *Pseudorca crassidens* )) when a relatively loud sound was preceded by a warning sound. These captive animals were shown to reduce hearing sensitivity when warned of an impending intense sound. Based on these experimental observations of captive animals, the authors suggest that wild animals may dampen their hearing during prolonged exposures or if conditioned to anticipate intense sounds. Another study showed that echolocating animals (including odontocetes) might have anatomical specializations that might allow for conditioned hearing reduction and filtering of low-frequency ambient noise, including increased stiffness and control of middle ear structures and placement of inner ear structures (Ketten *et al.,* 2021). Data available on noise-induced hearing loss for mysticetes are currently lacking (NMFS, 2024). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species.
Relationships between TTS and AUD INJ thresholds have not been studied in marine mammals, and there are no measured PTS data for cetaceans, but such relationships are assumed to be similar to those in humans and other terrestrial mammals. AUD INJ typically occurs at exposure levels at least several dB above that inducing mild TTS ( *e.g.,* a 40-dB threshold shift approximates AUD INJ onset (Kryter *et al.,* 1966; Miller, 1974), while a 6-dB threshold shift approximates TTS onset (Southall *et al.,* 2007, 2019). Based on data from terrestrial mammals, a precautionary assumption is that the AUD INJ thresholds for impulsive sounds (such as impact pile driving pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and AUD INJ cumulative sound exposure level thresholds are 15 to 20 dB higher than TTS cumulative sound exposure level thresholds (Southall *et al.,* 2007, 2019). Given the higher level of sound or longer exposure duration necessary to cause AUD INJ as compared with TTS, it is considerably less likely that AUD INJ could occur.
**Behavioral Effects**
Exposure to noise also has the potential to behaviorally disturb marine mammals to a level that rises to the definition of harassment under the MMPA. Generally speaking, NMFS considers a behavioral disturbance that rises to the level of harassment under the MMPA a non-minor response—in other words, not every response qualifies as behavioral disturbance, and for responses that do, those of a higher level, or accrued across a longer duration, have the potential to affect foraging, reproduction, or survival. Behavioral disturbance may include a variety of effects, including subtle changes in behavior ( *e.g.,* minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Behavioral responses may include changing durations of surfacing and dives, changing direction and/or speed; reducing/increasing vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); eliciting a visible startle response or aggressive behavior (such as tail/fin slapping or jaw clapping); and avoidance of areas where sound sources are located. In addition, pinnipeds may increase their haul out time, possibly to avoid in-water disturbance (Thorson and Reyff, 2006).
Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors ( *e.g.,* species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors ( *e.g.,* Richardson *et al.,* 1995; Wartzok *et al.,* 2004; Southall *et al.,* 2007, 2019; Weilgart, 2007; Archer *et al.,* 2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison *et al.,* 2012), and can vary depending on characteristics associated with the sound source ( *e.g.,* whether it is moving or stationary, number of sources, distance from the source). In general, pinnipeds seem more tolerant of, or at least habituate more quickly to, potentially disturbing underwater sound than do cetaceans, and generally seem to be less responsive to exposure to industrial sound than most cetaceans. Please see Appendices B and C of Southall *et al.* (2007) and Gomez *et al.* (2016) for reviews of studies involving marine mammal behavioral responses to sound.
Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok *et al.,* 2004). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder *et al.,* 2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure.
As noted above, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals that are highly motivated to remain in an area for feeding (Richardson *et al.,* 1995; Wartzok *et al.,* 2004; National Research Council (NRC), 2005). Controlled experiments with captive marine mammals have shown pronounced behavioral reactions, including avoidance of loud sound sources (Ridgway *et al.,* 1997; Finneran *et al.,* 2003). Observed responses of wild marine mammals to loud pulsed sound sources ( *e.g.,* seismic airguns) have been varied but often consist of avoidance behavior or other behavioral changes (Richardson *et al.,* 1995; Morton and Symonds, 2002; Nowacek *et al.,* 2007).
Available studies show wide variation in response to underwater sound; therefore, it is difficult to predict specifically how any given sound in a particular instance might affect marine mammals perceiving the signal ( *e.g.,* Erbe *et al.,* 2019). 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. If a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant ( *e.g.,* Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 2005). However, there are broad categories of potential response, which we describe in greater detail here, that include alteration of dive behavior, alteration of foraging behavior, effects to breathing, interference with or alteration of vocalization, avoidance, and flight.
**Avoidance and Displacement**
Changes in dive behavior can vary widely and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive ( *e.g.,* Frankel and Clark, 2000; Costa *et al.,* 2003; Ng and Leung, 2003; Nowacek *et al.,* 2004; Goldbogen *et al.,* 2013a, 2013b; Blair *et al.,* 2016). Variations in dive behavior may reflect interruptions in biologically significant activities ( *e.g.,* foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response.
Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators ( *e.g.,* bubble nets or sediment plumes), or changes in dive behavior. Acoustic and movement bio-logging tools also have been used in some cases to infer responses to anthropogenic noise. 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.
Respiration rates vary naturally with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in understanding species differences in the tolerance of underwater noise when determining the potential for impacts resulting from anthropogenic sound exposure ( *e.g.,* Kastelein *et al.,* 2001; 2005; 2006; Gailey *et al.,* 2007). For example, harbor porpoise respiration rates increased in response to pile driving sounds at and above a received broadband SPL of 136 dB (zero-peak SPL: 151 dB re 1 μPa; SEL of a single strike (SEL <sub>ss</sub> ): 127 dB re 1 μPa <sup>2</sup> -s) (Kastelein *et al.,* 2013).
Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors, and is one of the most obvious manifestations of disturbance in marine mammals (Richardson *et al.,* 1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme *et al.,* 1984). Avoidance may be short-term, with animals returning to the area once the noise has ceased ( *e.g.,* Bowles *et al.,* 1994; Goold, 1996; Stone *et al.,* 2000; Morton and Symonds, 2002; Gailey *et al.,* 2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur ( *e.g.,* Blackwell *et al.,* 2004; Bejder *et al.,* 2006; Teilmann *et al.,* 2006).
A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response ( *e.g.,* directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996; Bowers *et al.,* 2018). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (England *et al.,* 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response.
Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention ( *i.e.,* when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been demonstrated for marine mammals, but studies involving fishes and terrestrial animals have shown that increased vigilance may substantially reduce feeding rates ( *e.g.,* Beauchamp and Livoreil, 1997; Fritz *et al.,* 2002; Purser and Radford, 2011). In addition, chronic disturbance can cause population declines through reduction of fitness ( *e.g.,* decline in body condition) and subsequent reduction in reproductive success, survival, or both ( *e.g.,* Harrington and Veitch, 1992; Daan *et al.,* 1996; Bradshaw *et al.,* 1998). However, Ridgway *et al.* (2006) reported that increased vigilance in bottlenose dolphins exposed to sound over a 5-day period did not cause any sleep deprivation or stress effects.
Many animals perform vital functions, such as feeding, resting, traveling, and socializing, on a diel cycle (24-hour cycle). Disruption of such functions resulting from reactions to stressors such as sound exposure are more likely to be significant if they last more than one diel cycle or recur on subsequent days (Southall *et al.,* 2007). Consequently, a behavioral response lasting less than one day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall *et al.,* 2007). Note that there is a difference between multi-day substantive ( *i.e.,* meaningful) behavioral reactions and multi-day anthropogenic activities. For example, just because an activity lasts for multiple days does not necessarily mean that individual animals are either exposed to activity-related stressors for multiple days or, further, exposed in a manner resulting in sustained multi-day substantive behavioral responses.
**Physiological 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.,* Selye, 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; Ayres *et al.,* 2012; Yang *et al.,* 2022). 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. In addition, Lemos *et al.* (2022) observed a correlation between higher levels of fecal glucocorticoid metabolite concentrations (indicative of a stress response) and vessel traffic in gray whales. Yang *et al.* (2022) studied behavioral and physiological responses in captive bottlenose dolphins exposed to playbacks of “pile-driving-like” impulsive sounds, finding significant changes in cortisol and other physiological indicators but only minor behavioral changes. These and other studies lead to a reasonable expectation that some marine mammals will experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress.” In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2005), however distress is an unlikely result of this project based on observations of marine mammals during previous, similar construction projects.
**Auditory Masking**
Since many marine mammals rely on sound to find prey, moderate social interactions, and facilitate mating (Tyack, 2008), noise from anthropogenic sound sources can interfere with these functions, but only if the noise spectrum overlaps with the hearing sensitivity of the receiving marine mammal (Southall *et al.,* 2007; Clark *et al.,* 2009; Hatch *et al.,* 2012). Chronic exposure to excessive, though not high-intensity, noise could cause masking at particular frequencies for marine mammals that utilize sound for vital biological functions (Clark *et al.,* 2009). Acoustic masking is when other noises such as from human sources interfere with an animal's ability to detect, recognize, or discriminate between acoustic signals of interest ( *e.g.,* those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson *et al.,* 1995; Erbe *et al.,* 2016). Therefore, under certain circumstances, marine mammals whose acoustical sensors or environment are being severely masked could also be impaired from maximizing their performance fitness in survival and reproduction. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest ( *e.g.,* signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities ( *e.g.,* sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions (Hotchkin and Parks, 2013).
Marine mammals vocalize for different purposes and across multiple modes, such as whistling, echolocation click production, calling, and singing. Changes in vocalization behavior in response to anthropogenic noise can occur for any of these modes and may result from a need to compete with an increase in background noise or may reflect increased vigilance or a startle response. For example, in the presence of potentially masking signals, humpback whales and killer whales have been observed to increase the length of their songs (Miller *et al.,* 2000; Fristrup *et al.,* 2003) or vocalizations (Foote *et al.,* 2004), respectively, while North Atlantic right whales ( *Eubalaena glacialis* ) have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks *et al.,* 2007). Fin whales have also been documented lowering the bandwidth, peak frequency, and center frequency of their vocalizations under increased levels of background noise from large vessels (Castellote *et al.,* 2012). Other alterations to communication signals have also been observed. For example, gray whales, in response to playback experiments exposing them to vessel noise, have been observed increasing their vocalization rate and producing louder signals at times of increased outboard engine noise (Dahlheim and Castellote, 2016). Alternatively, in some cases, animals may cease sound production during production of aversive signals (Bowles *et al.,* 1994, Wisniewska *et al.,* 2018).
Under certain circumstances, marine mammals experiencing significant masking could also be impaired from maximizing their performance fitness in survival and reproduction. Therefore, when the coincident (masking) sound is human-made, it may be considered harassment when disrupting or altering critical behaviors. It is important to distinguish TTS and PTS, which persist after the sound exposure, from masking, which occurs during the sound exposure. Because masking (without resulting in TS) is not associated with abnormal physiological function, it is not considered a physiological effect, but rather a potential behavioral effect (though not necessarily one that would be associated with harassment).
The frequency range of the potentially masking sound is important in determining any potential behavioral impacts. For example, low-frequency signals may have less effect on high-frequency echolocation sounds produced by odontocetes but are more likely to affect detection of mysticete communication calls and other potentially important natural sounds such as those produced by surf and some prey species. The masking of communication signals by anthropogenic noise may be considered as a reduction in the communication space of animals ( *e.g.,* Clark *et al.,* 2009) and may result in energetic or other costs as animals change their vocalization behavior ( *e.g.,* Miller *et al.,* 2000; Foote *et al.,* 2004; Parks *et al.,* 2007; Di Iorio and Clark, 2010; Holt *et al.,* 2009). Masking can be reduced in situations where the signal and noise come from different directions (Richardson *et al.,* 1995), through amplitude modulation of the signal, or through other compensatory behaviors, including modifications of the acoustic properties of the signal or the signaling behavior (Hotchkin and Parks, 2013). Masking can be tested directly in captive species ( *e.g.,* Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild ( *e.g.,* Branstetter *et al.,* 2013).
Masking occurs in the frequency band that the animals utilize, and is more likely to occur in the presence of broadband, relatively continuous noise sources such as vibratory hammers. Energy distribution of construction sound covers a broad frequency spectrum, and is anticipated to be within the audible range of marine mammals present in the proposed action area. Since noises generated from the proposed construction activities are mostly concentrated at low frequencies (< 2 kHz), these activities likely have less effect on mid-frequency echolocation sounds produced by odontocetes (toothed whales). However, lower frequency noises are more likely to affect detection of communication calls and other potentially important natural sounds such as surf and prey noise. Low-frequency noise may also affect communication signals when they occur near the frequency band for noise and thus reduce the communication space of animals ( *e.g.,* Clark *et al.,* 2009) and cause increased stress levels ( *e.g.,* Holt *et al.,* 2009). Unlike TS, masking, which can occur over large temporal and spatial scales, can potentially affect the species at population, community, or even ecosystem levels, in addition to individual levels. Masking affects both senders and receivers of the signals, and at higher levels for longer durations, could have long-term chronic effects on marine mammal species and populations. However, the noise generated by the Homer's proposed activities will only occur intermittently, across an estimated 75 days during the authorization period in a relatively small area focused around the proposed construction site. Thus, while the Homer's proposed activities may mask some acoustic signals that are relevant to the daily behavior of marine mammals, the short-term duration and limited areas affected make it very unlikely that the fitness of individual marine mammals would be impacted.
**Potential Effects on Marine Mammal Habitat**
The Homer's proposed activities could have localized, temporary impacts on marine mammal habitat, including prey, by increasing in-water SPLs. Increased noise levels may affect acoustic habitat and adversely affect marine mammal prey in the vicinity of the project areas (see discussion below). Elevated levels of underwater noise would ensonify the project areas where both fishes and mammals occur and could affect foraging success. Additionally, marine mammals may avoid the area during the proposed construction activities; however, displacement due to noise is expected to be temporary and is not expected to result in long-term effects to the individuals or populations.
The total area likely impacted by the Homer's activities is relatively small compared to the available habitat in the Kachemak Bay, AK. Avoidance by potential prey ( *i.e.,* fish) of the immediate area due to increased noise is possible. The duration of fish and marine mammal avoidance of this area after the in-water construction stops is unknown, but a rapid return to normal recruitment, distribution, and behavior is anticipated. Any behavioral avoidance by fish or marine mammals of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity.
The proposed project would occur within the same footprint as existing marine infrastructure. The nearshore and intertidal habitat where the proposed project would occur is an area of relatively high marine vessel traffic. Most marine mammals do not generally use the area within the footprint of the project area. Temporary, intermittent, and short-term habitat alteration may result from increased noise levels during the proposed construction activities. Effects on marine mammal habitat would be limited to pile installation and removal noise, and effects on prey species would be similarly limited in time and space.
**Water Quality**
Temporary and localized reduction in water quality would occur as a result of in-water construction activities. Most of this effect would occur during the installation and removal of piles when bottom sediments are disturbed. The installation and removal of piles would disturb bottom sediments and may cause a temporary increase in suspended sediment in the project area. During pile extraction, sediment attached to the pile moves vertically through the water column until gravitational forces cause it to slough off under its own weight. The small resulting sediment plume is expected to settle out of the water column within a few hours. Studies of the effects of turbid water on fish (marine mammal prey) suggest that concentrations of suspended sediment can reach thousands of milligrams per liter before an acute toxic reaction is expected (Burton, 1993).
Since the currents are so strong in the area, following the completion of sediment-disturbing activities, suspended sediments in the water column should dissipate and quickly return to background levels in all construction scenarios. Turbidity within the water column has the potential to reduce the level of oxygen in the water and irritate the gills of prey fish species in the proposed project area. However, turbidity plumes associated with the project would be temporary and localized, and fish in the proposed project area would be able to move away from and avoid the areas where plumes may occur. Therefore, it is expected that the impacts on prey fish species from turbidity, and therefore on marine mammals, would be minimal and temporary. In general, the area likely impacted by the proposed construction activities is relatively small compared to the available marine mammal habitat in the Homer Harbor System Four Float Replacement Project.
**Potential Effects on Prey**
Sound may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species ( *e.g.,* crustaceans, cephalopods, fishes, zooplankton). Marine mammal prey varies by species, season, and location and, for some, is not well documented. Studies regarding the effects of noise on known marine mammal prey are described here.
Fishes utilize the soundscape and components of sound in their environment to perform important functions such as foraging, predator avoidance, mating, and spawning ( *e.g.,* Zelick *et al.,* 1999; Fay, 2009). Depending on their hearing anatomy and peripheral sensory structures, which vary among species, fishes hear sounds using pressure and particle motion sensitivity capabilities and detect the motion of surrounding water (Fay *et al.,* 2008). The potential effects of noise on fishes depends on the overlapping frequency range, distance from the sound source, water depth of exposure, and species-specific hearing sensitivity, anatomy, and physiology. Key impacts to fishes may include behavioral responses, hearing damage, barotrauma (pressure-related injuries), and mortality.
Fish react to sounds that are especially strong and/or intermittent low-frequency sounds, and behavioral responses such as flight or avoidance are the most likely effects. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. The reaction of fish to noise depends on the physiological state of the fish, past exposures, motivation ( *e.g.,* feeding, spawning, migration), and other environmental factors. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pile driving on fishes ( *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.,* Peña *et al.,* 2013; Wardle *et al.,* 2001; Jorgenson and Gyselman, 2009; Cott *et al.,* 2012). More commonly, though, the impacts of noise on fishes are temporary.
SPLs of sufficient strength have been known to cause injury to fishes and fish mortality (summarized in Popper *et al.,* 2014). However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen *et al.* (2012b) showed that a TTS of 4 to 6 dB was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long. Injury caused by barotrauma can range from slight to severe and can cause death, and is most likely for fish with swim bladders. Barotrauma injuries have been documented during controlled exposure to impact pile driving (Halvorsen *et al.,* 2012a; Casper *et al.,* 2013, 2017).
Fish populations in the proposed project area that serve as marine mammal prey could be temporarily affected by noise from pile installation and removal. The frequency range in which fishes generally perceive underwater sounds is 50 to 2,000 Hz, with peak sensitivities below 800 Hz (Popper and Hastings, 2009). Fish behavior or distribution may change, especially with strong and/or intermittent sounds that could harm fishes. High underwater SPLs have been documented to alter behavior, cause hearing loss, and injure or kill individual fish by causing serious internal injury (Hastings and Popper, 2005).
Zooplankton is a food source for several marine mammal species, as well as a food source for fish that are then preyed upon by marine mammals. Population effects on zooplankton could have indirect effects on marine mammals. Data are limited on the effects of underwater sound on zooplankton species, particularly sound from construction (Erbe *et al.,* 2019). Popper and Hastings (2009) reviewed information on the effects of human-generated sound and concluded that no substantive data are available on whether the sound levels from pile driving, seismic activity, or any human-made sound would have physiological effects on invertebrates. Any such effects would be limited to the area very near (1 to 5 m) the sound source and would result in no population effects because of the relatively small area affected at any one time and the reproductive strategy of most zooplankton species (short generation, high fecundity, and very high natural mortality). No adverse impact on zooplankton populations is expected to occur from the specified activity due, in part, to large reproductive capacities and naturally high levels of predation and mortality of these populations. Any mortalities or impacts that might occur would be negligible.
The greatest potential impact to marine mammal prey during construction would occur during impact pile driving. However, the duration of impact pile driving would be limited to two piles and to the final stage of installation (“proofing”) after the pile has been driven as close as practicable to the design depth with a vibratory driver. In-water construction activities would only occur during daylight hours, allowing fish to forage and transit the project area in the evening. Vibratory pile driving would possibly elicit behavioral reactions from fishes such as temporary avoidance of the area but is unlikely to cause injuries to fishes or have persistent effects on local fish populations. Construction also would have minimal permanent and temporary impacts on benthic invertebrate species, a marine mammal prey source. In addition, it should be noted that the area in question is low-quality habitat since it is already highly developed and experiences a high level of anthropogenic noise from normal operations and other vessel traffic.
**Potential Effects on Foraging Habitat**
The Homer Harbor System Four Float Replacement Project is not expected to result in any habitat-related effects that could cause significant or long-term negative consequences for individual marine mammals or their populations, since installation and removal of in-water piles would be temporary and intermittent. The total seafloor area affected by pile installation and removal is a very small area compared to the vast foraging area available to marine mammals outside this project area. The area impacted by the project is relatively small compared to the available habitat just outside the project area, and there are no areas of particular importance that would be impacted by this project. Any behavioral avoidance by fish of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity. As described in the preceding, the potential for the Homer's construction to affect the availability of prey to marine mammals or to meaningfully impact the quality of physical or acoustic habitat is considered to be insignificant. Therefore, impacts of the project are not likely to have adverse effects on marine mammal foraging habitat in the proposed project area.
In summary, given the relatively small areas being affected, as well as the temporary and mostly transitory nature of the proposed construction activities, any adverse effects from the Homer's activities on prey habitat or prey populations are expected to be minor and temporary. The most likely impact to fishes at the project site would be temporary avoidance of the area. Any behavioral avoidance by fish of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity. Thus, we conclude that impacts of the specified activities are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species. Further, any impacts to marine mammal habitat are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations.
**Estimated Take of Marine Mammals**
This section provides an estimate of the number of incidental takes proposed for authorization through the IHA, which will inform NMFS' consideration of “small numbers,” the negligible impact determinations, and impacts on subsistence uses.
Harassment is the only type of take expected to result from these activities. Except with respect to certain activities not pertinent here, section 3(18) of the MMPA defines “harassment” as any act of pursuit, torment, or annoyance, which (i) has the potential to injure a marine mammal or marine mammal stock in the wild (Level A harassment); or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering (Level B harassment).
Authorized takes would primarily be by Level B harassment, as use of the construction equipment ( *i.e.,* impact and vibratory hammers) has the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for auditory injury (AUD INJ) (Level A harassment) to result, primarily for harbor seals because predicted AUD INJ zones are larger and this species may be present in the project area. AUD INJ is unlikely to occur for all other species where take is proposed due to in-water sound not leaving the confines of the harbor. The proposed mitigation and monitoring measures are expected to minimize the severity of the taking to the extent practicable.
As described previously, no serious injury or mortality is anticipated or proposed to be authorized for this activity. Below we describe how the proposed take numbers are estimated.
For acoustic impacts, generally speaking, we estimate take by considering: (1) acoustic criteria above which NMFS believes there is some reasonable potential for marine mammals to be behaviorally harassed or incur some degree of AUD INJ; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and, (4) the number of days of activities. We note that while these factors can contribute to a basic calculation to provide an initial prediction of potential takes, additional information that can qualitatively inform take estimates is also sometimes available ( *e.g.,* previous monitoring results or average group size). Below, we describe the factors considered here in more detail and present the proposed take estimates.
**Acoustic Criteria**
NMFS recommends the use of acoustic criteria that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur AUD INJ of some degree (equated to Level A harassment).
*Level B Harassment* —Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context ( *e.g.,* frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment ( *e.g.,* bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict ( *e.g.,* Southall *et al.,* 2007; Southall *et al.,* 2021; Ellison *et al.,* 2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS generally predicts that marine mammals are likely to be behaviorally harassed in a manner considered to be Level B harassment when exposed to underwater anthropogenic noise above root-mean-squared sound pressure levels (RMS SPL) of 120 dB (referenced to 1 micropascal (re 1 μPa)) for continuous ( *e.g.,* vibratory pile driving, drilling) and above RMS SPL 160 dB re 1 μPa for non-explosive impulsive ( *e.g.,* seismic airguns) or intermittent ( *e.g.,* scientific sonar) sources. Generally speaking, Level B harassment take estimates based on these behavioral harassment thresholds are expected to include any likely takes by TTS as, in most cases, the likelihood of TTS occurs at distances from the source less than those at which behavioral harassment is likely. TTS of a sufficient degree can manifest as behavioral harassment, as reduced hearing sensitivity and the potential reduced opportunities to detect important signals (conspecific communication, predators, prey) may result in changes in behavior patterns that would not otherwise occur.
Homer's proposed activity includes the use of continuous (vibratory hammers) and impulsive (impact hammers) sources, and therefore the RMS SPL thresholds of 120 and 160 dB re 1 μPa, respectively, are applicable.
*Level A harassment* —NMFS' Updated Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 3.0) (Updated Technical Guidance, 2024) identifies dual criteria to assess AUD INJ (Level A harassment) to five different underwater marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). Homer's proposed activity includes the use of impulsive (impact hammers) and non-impulsive (vibratory hammers) sources.
The 2024 Updated Technical Guidance criteria include both updated thresholds and updated weighting functions for each hearing group. The thresholds are provided in the table below. The references, analysis, and methodology used in the development of the criteria are described in NMFS' 2024 Updated Technical Guidance, which may be accessed at: *https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools.*
| Hearing group | AUD INJ onset acoustic thresholds * | Impulsive | Non-impulsive |
| --- | --- | --- | --- |
| Low-Frequency (LF) Cetaceans | 222 dB;
183 dB | 197 dB. | |
| High-Frequency (HF) Cetaceans | 230 dB;
193 dB | 201 dB. | |
| Very High-Frequency (VHF) Cetaceans | 202 dB;
159 dB | 181 dB. | |
| Phocid Pinnipeds (PW) (Underwater) | 223 dB;
183 dB | 195 dB. | |
| Otariid Pinnipeds (OW) (Underwater) | 230 dB;
185 dB | 199 dB. | |
**Ensonified Area**
Here, we describe operational and environmental parameters of the activity that are used in estimating the area ensonified above the acoustic thresholds, including source levels and transmission loss coefficient.
The sound field in the project area is the existing background noise plus additional construction noise from the proposed project. Marine mammals are expected to be affected via sound generated by the primary components of the project ( *i.e.,* vibratory pile removal, vibratory pile driving, and impact pile driving). The source levels assumed for both removal and installation activities are based on reviews of measurements of piles of the same or similar types and dimensions available in the scientific literature and from similar coastal construction projects. The source level for the piles and activities ( *i.e.,* installation or removal) are presented in table 5.
| | | | | |
| --- | --- | --- | --- | --- |
| Activity | Proxy sound source level at 10 m | Reference | | |
| 12-in timber piles | 162 | Caltrans 2020. | | |
| 12.75-in steel piles | 163 | NMFS 2023. | | |
| 16-in steel piles. | | | | |
| 18-in steel piles. | | | | |
| 24-in steel piles. | | | | |
| Impact pile driving | dB SEL | dB RMS | dB Peak | |
| In-air; all pile sizes | | 109 | | NAVFAC SW 2020. |
| 18-in steel piles | 175 | 185 | 200 | Caltrans 2020. |
Transmission loss (TL) is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source. TL parameters vary with frequency, temperature, sea conditions, current, source and receiver depth, water depth, water chemistry, bottom composition, and topography. The general formula for underwater TL is:
TL = B * Log <sub>10</sub> (R <sub>1</sub> /R <sub>2</sub> ),
Where:
TL = transmission loss in dB
B = transmission loss coefficient; for practical spreading equals 15
R <sub>1</sub> = the distance of the modeled SPL from the driven pile, and
R <sub>2</sub> = the distance from the driven pile of the initial measurement.
This formula neglects loss due to scattering and absorption, which is assumed to be zero here. The degree to which underwater sound propagates away from a sound source depends on various factors, most notably the water bathymetry and the presence or absence of reflective or absorptive conditions, including in-water structures and sediments. Spherical spreading occurs in a perfectly unobstructed (free-field) environment not limited by depth or water surface, resulting in a 6 dB reduction in sound level for each doubling of distance from the source (20*log[range]). Cylindrical spreading occurs in an environment in which sound propagation is bounded by the water surface and sea bottom, resulting in a reduction of 3 dB in sound level for each doubling of distance from the source (10*log[range]). A practical spreading value of 15 is often used in shallow-water coastal conditions, such as those found in the NBPL and NBSD projects. In these environments, sound waves repeatedly reflect off the surface and bottom, reflecting an expected propagation environment between spherical and cylindrical spreading-loss conditions. Therefore, the default coefficient of 15 is used to calculate distances to the Level A harassment and Level B harassment thresholds.
Assuming practicable spreading and other assumptions regarding the source characteristics and operational logistics ( *e.g.,* source level, number of strikes per pile, number of piles per day), Homer calculated distances to the Level A harassment and Level B harassment thresholds and associated ensonified areas. Because an ensonified area associated with Level A harassment is more technically challenging to predict given the accounting for a cumulative energy component that changes over time, to assist applicants in assessing the potential for Level A harassment without the need for complex modeling, NMFS developed an optional User Spreadsheet tool to accompany the 2024 Updated Technical Guidance (see *https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools* ). This relatively simple tool can be used to calculate a Level A harassment isopleth distance for use in conjunction with marine mammal density or occurrence data to predict the amount of take that may occur incidental to an activity. We note that, because of some of the assumptions in the methods underlying this spreadsheet tool, we anticipate that the resulting isopleths would typically be overestimates, which may lead to an overestimate of potential exposures from Level A harassment. However, this optional tool offers a practical alternative for estimating isopleth distances when more sophisticated modeling methods are unavailable or are impractical. For stationary sources such as impact or vibratory pile driving and removal, the optional User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity within 24 hours, it would be expected to incur AUD INJ. Inputs used in the optional User Spreadsheet tool are contained within table 6.
| | Existing pile removal | 12-in | 12.75-in | 16-in | Temporary pile | 16-in | 16-in | Permanent pile installation | 12.75-in | 16-in | 18-in | 24-in |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Pile Material | Timber | Steel | Steel | Steel | Steel | Steel | Steel | Steel | Steel | | | |
| Total Number of Piles | 36 | 40 | 26 | 28 | 28 | 14 | 70 | 29 | 20 | | | |
| | | | | | | | | | | | | |
| Max # of Piles Vibrated per Day | 20 | 20 | 20 | 2 | 2 | 10 | 10 | 10 | 10 | | | |
| Vibratory Time per Pile (mins) | 10 | 10 | 10 | 10 | 10 | 15 | 15 | 20 | 30 | | | |
| Estimated Number of Days | 4 | 4 | 3 | 14 | 14 | 4 | 18 | 8 | 5 | | | |
| Vibratory Time Total (mins) | 360 | 400 | 260 | 280 | 280 | 210 | 1,050 | 580 | 600 | | | |
| | | | | | | | | | | | | |
| Number of Piles | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | | | |
| Max # of Piles Impacted per Day | | | | | | | | 2 | | | | |
| Number of Strikes per Pile | | | | | | | | 240 | | | | |
| Number of Days | | | | | | | | 1 | | | | |
Using the practical spreading model and source assumptions identified in table 5 and the user spreadsheet inputs in table 6, Homer calculated, and NMFS has carried forward into this analysis the distances to the Level A harassment and Level B harassment thresholds for marine mammals of this project (table 7). It should be noted that the Level B harassment zones during the construction of unit two of the project presented in the table below result in a narrow beam of sound outside the harbor entrance. In past IHAs, NMFS had determined that take from similar narrow harassment zones may not result in take of marine mammals given that many animals pass through the area in a short amount of time. Here NMFS does expect take of a limited number of marine mammals during the construction of unit two based on the analysis provided by the applicant.
| Pile size and material | Activity | Calculated distances for acoustic thresholds in M | Level A | LF cetaceans | HF cetaceans | VHF cetaceans | Phocids | Otariids | Level B |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| | | | | | | | | | |
| 12-in timber | Existing pile removal | 24.0 | 9.2 | 19.6 | 30.9 | 10.4 | 6,309.6 | | |
| 12.75-in steel | Existing pile removal | 28.0 | 10.7 | 22.9 | 36.0 | 12.1 | 7,356.4 | | |
| | Permanent pile installation | 23.1 | 8.9 | 18.9 | 29.7 | 10.0 | 7,356.4 | | |
| 16-in steel | Existing pile removal | 28.0 | 10.7 | 22.9 | 36.0 | 12.1 | 7,356.4 | | |
| | Temporary pile installation | 6.0 | 2.3 | 4.9 | 7.8 | 2.6 | 7,356.4 | | |
| | Temporary pile removal | 6.0 | 2.3 | 4.9 | 7.8 | 2.6 | 7,356.4 | | |
| | Permanent pile installation | 23.1 | 8.9 | 18.9 | 29.7 | 10.0 | 7,356.4 | | |
| 18-in steel | Permanent pile installation | 28.0 | 10.7 | 22.9 | 36.0 | 12.1 | 7,356.4 | | |
| 24-in steel | Permanent pile installation | 36.7 | 14.1 | 29.9 | 47.2 | 15.9 | 7,356.4 | | |
| | | | | | | | | | |
| 18-in steel | Permanent pile installation | 178.6 | 22.8 | 276.4 | 158.7 | 59.2 | 464.2 | | |
**Marine Mammal Occurrence**
In this section we provide information about the occurrence of marine mammals, including density or other relevant information which will inform the take calculations.
The applicant used survey data from the Cook Inlet Beluga Whale surveys over several years to estimate average group sizes for all of the marine mammal species where take is proposed outside the harbor (Sheldon *et al.,* 2013, 2015, 2017, 2022; Sheldon and Wade 2019). Average group sizes from within the harbor were derived by local observations (SolsticeAK 2025). The frequency of occurrence ( *e.g.,* monthly or daily) was determined by local observations within and outside the Homer Small Boat Harbor. Humpback whales and killer whales are expected to frequent the area four times a month. Dall's porpoise, harbor porpoise, and Steller sea lions are less frequent, only occurring once a month. Harbor seals are the most common marine mammal expected to be present daily during the project. Both Steller sea lions and harbor seals are the only marine mammals expected to occur within and outside the harbor and take could occur during both unit one and unit two. All other species are expected to occur outside the harbor and would only be taken during the construction of unit two. The table below summarizes the average group sizes calculated from the Cook Inlet Beluga Whale survey for each species where take is proposed.
| Species | Group size within harbor | Group size outside harbor |
| --- | --- | --- |
| Humpback whale | N/A | 2 |
| Killer whale | N/A | 7 |
| Dall's porpoise | N/A | 3 |
| Harbor porpoise | N/A | 3 |
| Harbor seal | 2 (9
) | 12 |
| Steller sea lion | 1 | 5 |
**Take Estimation**
Here we describe how the information provided above is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization.
To calculate the estimated take that may occur incidental to the Homer Small Boat Harbor project, the applicant used the following methods below, and NMFS has carried them forward in the analysis below. Each estimate of take was rounded up to the highest whole number. Homer used the following equation to estimate exposures during each unit of construction:
Occurrence by day or times per month × average group size of marine mammal species × days of activity on a given unit
For example for humpback whales take by Level B harassment is only expected during construction of unit two. The following equation was used to estimate the incidental take of humpbacks:
4 groups per month × 2 whales per group × 32 days in unit 2/30 days per month = 9 humpback whale takes by Level B harassment
Additional information related to the take calculations for each marine mammal species by construction unit and construction method ( *i.e.,* vibratory and impact) can be found in section 6.1 of Homer's application. It is expected that in the project area incidental take of humpback whales would be split between both the Hawaii stock and the Mexico-North Pacific stock by 89 percent and 11 percent respectively (Wade 2021). NMFS estimates that incidental take from both stocks of killer whales present in the project area could occur at an equal probability from either stock. The total incidental take by Level A and Level B harassment proposed for authorization under this IHA can be found in table 9.
| Species | Stock (N
) | Level A | Level B | Total | Stock | Percent |
| --- | --- | --- | --- | --- | --- | --- |
| Humpback Whale | Hawaii | 0 | 8 | 8 | 11,278 | <0.1 |
| | Mexico North Pacific | 0 | 1 | 1 | 918 | 0.1 |
| Killer Whale | ENP Alaska Resident | 0 | 30 | 30 | 1,920 | 1.6 |
| | ENP Gulf of Alaska, Aleutian Islands, and Bering Sea | 0 | | | 587 | 5.1 |
| Dall's Porpoise | Alaska | 0 | 4 | 4 | 13,110 | <0.1 |
| Harbor Porpoise | Gulf of Alaska | 0 | 4 | 4 | 31,046 | <0.1 |
| Harbor Seal | Cook Inlet/Shelikof Strait | 9 | 854 | 863 | 28,411 | 3.0 |
| Steller Sea Lion | Western DPS | 0 | 8 | 8 | 49,837 | <0.1 |
**Proposed Mitigation**
In order to issue an IHA under section 101(a)(5)(D) of the MMPA, NMFS must set forth the permissible methods of taking pursuant to the activity, and other means of effecting the least practicable impact on the species or stock and its habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance. NMFS regulations require applicants for incidental take authorizations to include information about the availability and feasibility (economic and technological) of equipment, methods, and manner of conducting the activity or other means of effecting the least practicable adverse impact upon the affected species or stocks, and their habitat (50 CFR 216.104(a)(11)).
In evaluating how mitigation may or may not be appropriate to ensure the least practicable adverse impact on species or stocks and their habitat, as well as subsistence uses where applicable, NMFS considers two primary factors:
(1) The manner in which, and the degree to which, the successful implementation of the measure(s) is expected to reduce impacts to marine mammals, marine mammal species or stocks, and their habitat. This considers the nature of the potential adverse impact being mitigated (likelihood, scope, range). It further considers the likelihood that the measure will be effective if implemented (probability of accomplishing the mitigating result if implemented as planned), the likelihood of effective implementation (probability implemented as planned); and
(2) The practicability of the measures for applicant implementation, which may consider such things as cost, impact on operations.
The mitigation requirements described in the following were proposed by Homer in its adequate and complete application. Homer has agreed that all of the mitigation measures are practicable. NMFS has fully reviewed the specified activities and the mitigation measures to determine if the mitigation measures would result in the least practicable adverse impact on marine mammals and their habitat, as required by the MMPA, and has determined the proposed measures are appropriate. NMFS describes these below as proposed mitigation requirements, and has included them in the proposed IHA.
*Establishment of Shutdown Zones* —Homer would establish shutdown zones with radial distances as identified in table 10 for all construction activities. The purpose of a shutdown zone is generally to define an area within which shutdown of the activity would occur upon sighting of a marine mammal (or in anticipation of an animal entering the defined area). If a marine mammal is observed entering or within the shutdown zones indicated in table 10, pile driving activity must be delayed or halted. If pile driving is delayed or halted due to the presence of a marine mammal, the activity may not commence or resume until either the animal has voluntarily exited and been visually confirmed beyond the shutdown zones or 15 minutes have passed without re-detection of the animal. If a marine mammal comes within or approaches the shutdown zone indicated in table 10, such operations must cease. Shutdown zones would vary based on the activity type and marine mammal hearing group.
| Pile size and material | Activity | Distance (m) to Level A shutdown zones | LF | HF | VHF | PW | OW |
| --- | --- | --- | --- | --- | --- | --- | --- |
| | | | | | | | |
| 12-in timber | Existing pile removal | 25 | 10 | 20 | 35 | 15 | |
| 12.75-in steel | Existing pile removal | 30 | 15 | 25 | 40 | 15 | |
| | Permanent pile installation | 25 | 10 | 20 | 30 | 10 | |
| 16-in steel | Existing pile removal | 30 | 15 | 25 | 40 | 15 | |
| | Temporary pile installation | 10 | 10 | 10 | 10 | 10 | |
| | Temporary pile removal | 10 | 10 | 10 | 10 | 10 | |
| | Permanent pile installation | 25 | 10 | 20 | 30 | 10 | |
| 18-in steel | Permanent pile installation | 30 | 15 | 25 | 40 | 15 | |
| 24-in steel | Permanent pile installation | 40 | 15 | 30 | 50 | 20 | |
| | | | | | | | |
| 18-in steel | Permanent pile installation | 180 | 25 | 280 | 50 | 60 | |
*Monitoring the Level B Harassment Zones* —Homer has identified the Level B harassment zones for each proposed activity. These zones provide utility for observing by establishing monitoring protocols for areas adjacent to the shutdown zones. The Level B harassment zones enable observers to be aware of and communicate the presence of marine mammals in the project area outside the shutdown zone and thus prepare for a potential cessation of activity should the animal enter the shutdown zone. Protected Species Observers (PSOs) would monitor the entire area to the extent practicable defined in tables 11.
| Pile size and material | Activity | Level B |
| --- | --- | --- |
| | | |
| 12-in timber | Existing pile removal | 6,310 |
| 12.75-in steel | Existing pile removal | 7,360 |
| | Permanent pile installation | 7,360 |
| 16-in steel | Existing pile removal | 7,360 |
| | Temporary pile installation | 7,360 |
| | Temporary pile removal | 7,360 |
| | Permanent pile installation | 7,360 |
| 18-in steel | Permanent pile installation | 7,360 |
| 24-in steel | Permanent pile installation | 7,360 |
| | | |
| 18-in steel | Permanent pile installation | 470 |
*Pre- and Post-Activity Monitoring* —Monitoring would take place from 30 minutes prior to initiation of pile driving activity ( *i.e.,* pre-start clearance monitoring) through 30 minutes post-completion of pile driving activity. In addition, monitoring for 30 minutes would take place whenever a break in the specified activity ( *i.e.,* impact pile driving or vibratory pile driving) of 30 minutes or longer occurs. Pre-start clearance monitoring would be conducted during periods of visibility sufficient for the lead PSO to determine that the shutdown zones indicated in table 10 are clear of marine mammals. Pile driving may commence following 30 minutes of observation when the determination is made that the shutdown zones are clear of marine mammals.
*Soft Start* —Homer would use soft-start techniques when impact pile driving. Soft-start requires contractors to provide an initial set of three strikes at reduced energy, followed by a 30-second waiting period, then two subsequent reduced-energy strike sets. A soft-start would be implemented at the start of each day's impact pile driving and at any time following cessation of impact pile driving for a period of 30 minutes or longer. Soft-start procedures are used to provide additional protection to marine mammals by providing a warning and/or giving marine mammals a chance to leave the area prior to the hammer operating at full capacity.
In summary, based on our evaluation of the Homer's proposed mitigation measures for the Homer Small Boat Harbor project, NMFS has preliminarily determined that the proposed mitigation measures provide the means of effecting the least practicable impact on the affected species or stocks and their habitat, with particular focus on rookeries, mating grounds, and similar areas of significance.
**Proposed Monitoring and Reporting**
In order to issue an IHA for an activity, section 101(a)(5)(D) of the MMPA states that NMFS must set forth requirements pertaining to the monitoring and reporting of such taking. The MMPA implementing regulations at 50 CFR 216.104(a)(13) indicate that requests for authorizations must include the suggested means of accomplishing the necessary monitoring and reporting that will result in increased knowledge of the species and of the level of taking or impacts on populations of marine mammals that are expected to be present while conducting the activities. Effective reporting is critical both to compliance as well as ensuring that the most value is obtained from the required monitoring.
Monitoring and reporting requirements prescribed by NMFS should contribute to improved understanding of one or more of the following:
• Occurrence of marine mammal species or stocks in the area in which take is anticipated ( *e.g.,* presence, abundance, distribution, density);
• Nature, scope, or context of likely marine mammal exposure to potential stressors/impacts (individual or cumulative, acute or chronic), through better understanding of: (1) action or environment ( *e.g.,* source characterization, propagation, ambient noise); (2) affected species ( *e.g.,* life history, dive patterns); (3) co-occurrence of marine mammal species with the activity; or (4) biological or behavioral context of exposure ( *e.g.,* age, calving or feeding areas);
• Individual marine mammal responses (behavioral or physiological) to acoustic stressors (acute, chronic, or cumulative), other stressors, or cumulative impacts from multiple stressors;
• How anticipated responses to stressors impact either: (1) long-term fitness and survival of individual marine mammals; or (2) populations, species, or stocks;
• Effects on marine mammal habitat ( *e.g.,* marine mammal prey species, acoustic habitat, or other important physical components of marine mammal habitat); and
• Mitigation and monitoring effectiveness.
The monitoring and reporting requirements described in the following were proposed by Homer in its adequate and complete application. Homer has agreed to the requirements. NMFS describes these below as requirements and has included them in the proposed IHA.
Homer would abide by all monitoring and reporting measures contained within the IHA, if issued, and their Protected Species Monitoring Plans (see NMFS' website at *https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities* ). NMFS describes these below as requirements and has included them in the proposed IHA.
**Visual Monitoring**
All PSOs must be NMFS-approved and have no other assigned tasks during monitoring periods. Homer would have between one and three PSOs actively monitoring on-site at all times during pile-driving activities. Where a team of three or more PSOs is required, a lead observer or monitoring coordinator would be designated. The lead PSO would be required to have prior experience working as a PSO during a NMFS-issued ITA or Letter of Concurrence. PSOs would be placed in locations as specified in the marine mammal monitoring plan.
**Reporting**
Homer would be required to submit a draft report(s) on all construction activities and marine mammal monitoring results to NMFS within 90 days of the completion of monitoring, or 60 days prior to the requested issuance of any subsequent IHAs or similar activity at the same location, whichever comes first. The information required to be collected and reported to NMFS is included in the draft IHA available at *https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities.* In summary, the report would include, but not be limited to, information regarding activities that occurred, marine mammal sighting data, and whether mitigative actions were taken or could not be taken. Homer would also be required to submit reports on any observed injured or dead marine mammals. If the death or injury was clearly caused by the specified activity, Homer would immediately cease the specified activities until NMFS is able to review the circumstances of the incident and determine what, if any, additional measures are appropriate to ensure compliance with the terms of the IHA. Homer would not resume its activities until notified by NMFS.
*Reporting Injured or Dead Marine Mammals —* In the event that personnel involved in Homer's activities discover an injured or dead marine mammal, Homer would report the incident to the NMFS Office of Protected Resources ( *[email protected], [email protected]* ) and to the Alaska Regional Stranding Coordinator as soon as feasible. If the death or injury was clearly caused by the specified activity, the Homer would immediately cease the specified activities until NMFS is able to review the circumstances of the incident and determine what, if any, additional measures are appropriate to ensure compliance with the IHA. Homer would not resume their activities until notified by NMFS. The report would include the following information:
• Description of the incident;
• Environmental conditions ( *e.g.,* Beaufort sea state, visibility);
• Description of all marine mammal observations in the 24 hours preceding the incident;
• Photographs or video footage of the animal(s) (if equipment is available).
• Time, date, and location (latitude/longitude) of the first discovery (and updated location information if known and applicable);
• Species identification (if known) or description of the animal(s) involved;
• Condition of the animal(s) (including carcass condition if the animal is dead);
• Observed behaviors of the animal(s), if alive; and
• General circumstances under which the animal was discovered.
Specific proposed mitigation, monitoring, and reporting requirements can be found in the draft IHAs found at *https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities.*
**Negligible Impact Analysis and Determination**
NMFS has defined negligible impact as an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival (50 CFR 216.103). A negligible impact finding is based on the lack of likely adverse effects on annual rates of recruitment or survival ( *i.e.,* population-level effects). An estimate of the number of takes alone is not enough information on which to base an impact determination. In addition to considering estimates of the number of marine mammals that might be “taken” through harassment, NMFS considers other factors, such as the likely nature of any impacts or responses ( *e.g.,* intensity, duration), the context of any impacts or responses ( *e.g.,* critical reproductive time or location, foraging impacts affecting energetics), as well as effects on habitat, and the likely effectiveness of the mitigation. We also assess the number, intensity, and context of estimated takes by evaluating this information relative to population status. Consistent with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, September 29, 1989), the impacts from other past and ongoing anthropogenic activities are incorporated into this analysis via their impacts on the baseline ( *e.g.,* as reflected in the regulatory status of the species, population size and growth rate where known, ongoing sources of human-caused mortality, or ambient noise levels).
To avoid repetition, the discussion of our analysis applies to all the species listed in table 9, given that the anticipated effects of this activity on these different marine mammal stocks are expected to be similar. Where there are meaningful differences between species or stocks, or groups of species, in anticipated individual responses to activities, impact of expected take on the population due to differences in population status, or impacts on habitat, they are described independently in the analysis below.
Pile driving and removal activities associated with the project as outlined previously, have the potential to disturb or displace marine mammals. Specifically, the specified activities may result in take, in the form of Level A harassment and Level B harassment from underwater sounds generated from pile driving and removal. Potential takes could occur if individuals of these species are present in zones ensonified above the thresholds for Level A or Level B harassment identified above when these activities are underway.
Take by Level A and Level B harassment would be due to potential behavioral disturbance, TTS, and PTS. No serious injury or mortality is anticipated or proposed for authorization given the nature of the activity and measures designed to minimize the possibility of injury to marine mammals. Take by Level A harassment is only anticipated for harbor seals. Impacts to affected individuals of harbor seals are not expected to result in population-level impacts. The potential for harassment is minimized through the construction method ( *i.e.* use of direct pull removal or vibratory methods to the extent practical) and the implementation of the planned mitigation measures (see Proposed Mitigation section).
In addition to the expected effects resulting from Level B harassment, we anticipate that harbor porpoises, Steller sea lions, and harbor seals may sustain some limited Level A harassment in the form of auditory injury. However, animals in these locations that experience PTS would likely only receive slight PTS, *i.e.,* minor degradation of hearing capabilities within regions of hearing that align most completely with the energy produced by pile driving, *i.e.,* the low-frequency region below 2 kHz, not severe hearing impairment or impairment in the regions of greatest hearing sensitivity. If hearing impairment occurs, it is most likely that the affected animal would lose a few decibels in its hearing sensitivity, which in most cases is not likely to meaningfully affect its ability to forage and communicate with conspecifics. As described above, we expect that marine mammals would be likely to move away from a sound source that represents an aversive stimulus, especially at levels that would be expected to result in PTS, given sufficient notice through use of soft start.
The project also is not expected to have significant adverse effects on affected marine mammals' habitat. The project activities would not modify existing marine mammal habitat for a significant amount of time. The activities may cause some fish or invertebrates to leave the area of disturbance, thus temporarily impacting marine mammals' foraging opportunities in a limited portion of the foraging range; but, because of the short duration of the activities, the relatively small area of the habitat that may be affected, and the availability of nearby habitat of similar or higher value, the impacts to marine mammal habitat are not expected to cause significant or long-term negative consequences. There are no known haulouts for Steller sea lions or harbor seals within the project area. Repeated exposures of individuals to this pile driving activity could cause Level A and Level B harassment but are unlikely to considerably disrupt foraging behavior or result in significant decrease in fitness, reproduction, or survival for the affected individuals.
In summary and as described above, the following factors primarily support our preliminary determination that the impacts resulting from this activity are not expected to adversely affect any of the species or stocks through effects on annual rates of recruitment or survival:
• No serious injury or mortality is anticipated or authorized;
• Any Level A harassment (AUD INJ) is anticipated to be slight AUD INJ ( *i.e.,* of a few decibels) within the lower frequencies associated with pile driving and not encompassing a species' full hearing range;
• The anticipated incidents of Level B harassment would consist of, at worst, temporary modifications in behavior that would not result in fitness impacts on individuals;
• The area affected by the specified activity is very small relative to the overall habitat ranges of all species, does not include any rookeries, does not include ESA-designated critical habitat, and does not include any BIAs;
• Effects on species that serve as prey for marine mammals from the activities are expected to be short-term and, therefore, any associated impacts on marine mammal feeding are not expected to result in significant or long-term consequences for individuals, or to accrue adverse impacts on their populations;
• The project area is located in a highly active harbor; therefore, species are likely acclimated to anthropogenic activities and behavioral reactions are expected to be minor (if at all); and
• The proposed mitigation measures, such as soft-starts, and shutdowns, are expected to reduce the effects of the specified activity to the least practicable adverse impact level.
Based on the analysis contained herein of the likely effects of the specified activity on marine mammals and their habitat, and taking into consideration the implementation of the proposed monitoring and mitigation measures, NMFS preliminarily finds that the total marine mammal take from the proposed activity will have a negligible impact on all affected marine mammal species or stocks.
**Small Numbers**
As noted previously, only take of small numbers of marine mammals may be authorized under section 101(a)(5)(A) and (D) of the MMPA for specified activities other than military readiness activities. The MMPA does not define small numbers and so, in practice, where estimated numbers are available, NMFS compares the number of individuals taken to the most appropriate estimation of abundance of the relevant species or stock in our determination of whether an authorization is limited to small numbers of marine mammals. When the predicted number of individuals to be taken is fewer than one-third of the species or stock abundance, the take is considered to be of small numbers (see 86 FR 5322, January 19, 2021). Additionally, other qualitative factors may be considered in the analysis, such as the temporal or spatial scale of the activities.
Table 9 demonstrates the number of animals that could be exposed to the received noise levels that could cause harassment for the proposed work in Homer, AK. Our analysis shows that less than 5.1 percent of each affected stock could be taken by harassment. The numbers of animals proposed to be taken for these stocks would be considered small relative to the relevant stock's abundances, even if each estimated taking occurred to a new individual, an extremely unlikely scenario.
Based on the analysis contained herein of the proposed activity (including the proposed mitigation and monitoring measures) and the anticipated take of marine mammals, NMFS preliminarily finds that small numbers of marine mammals would be taken relative to the population size of the affected species or stocks.
**Unmitigable Adverse Impact Analysis and Determination**
In order to issue an IHA, NMFS must find that the specified activity will not have an “unmitigable adverse impact” on the subsistence uses of the affected marine mammal species or stocks by Alaskan Natives. NMFS has defined “unmitigable adverse impact” in 50 CFR 216.103 as an impact resulting from the specified activity: (1) That is likely to reduce the availability of the species to a level insufficient for a harvest to meet subsistence needs by: (i) Causing the marine mammals to abandon or avoid hunting areas; (ii) Directly displacing subsistence users; or (iii) Placing physical barriers between the marine mammals and the subsistence hunters; and (2) That cannot be sufficiently mitigated by other measures to increase the availability of marine mammals to allow subsistence needs to be met.
There have been no harvest of marine mammals in the Homer area since 2014. The project area has never been used for subsistence hunts by the surrounding communities of Seldovia Village Tribe, the Native Village of Port Graham, the Native Village of Nanwalek (also known as English Bay), and Ninilchik Village. Given the lack of overlap with current subsistence hunting areas and the proposed project area there are no relevant subsistence uses of marine mammals adversely impacted by this action. The proposed project is not likely to adversely impact the availability of any marine mammal species or stocks that are commonly used for subsistence purposes or to impact subsistence harvest of marine mammals in the region.
Based on the description of the specified activity, the measures described to minimize adverse effects on the availability of marine mammals for subsistence purposes, and the proposed mitigation and monitoring measures, NMFS has preliminarily determined that there will not be an unmitigable adverse impact on subsistence uses from Homer's proposed activities.
**Endangered Species Act**
Section 7(a)(2) of the ESA of 1973 (16 U.S.C. 1531 *et seq.* ) requires that each Federal agency ensures that any action it authorizes, funds, or carries out is not likely to jeopardize the continued existence of any endangered or threatened species or result in the destruction or adverse modification of designated critical habitat. To ensure ESA compliance for the issuance of incidental take authorizations, NMFS Office of Protected Resources (OPR) consults internally whenever we propose to authorize take for ESA-listed species, in this case with the NMFS Alaska Regional Office (AKRO).
NMFS is proposing to authorize take of Mexico-North Pacific DPS of humpback whales and the Western DPS of Steller sea lions, which are listed under the ESA.
OPR has requested initiation of section 7 consultation with the AKRO for the issuance of this IHA. NMFS will conclude the ESA consultation prior to reaching a determination regarding the proposed issuance of the authorization.
**Proposed Authorization**
As a result of these preliminary determinations, NMFS proposes to issue an IHA to Homer for conducting construction of the Homer Harbor System Four Float Replacement Project in Homer, AK, provided the previously mentioned mitigation, monitoring, and reporting requirements are incorporated. A draft of the proposed IHA can be found at: *https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities.*
**Request for Public Comments**
We request comment on our analyses, the proposed authorization, and any other aspect of this notice of proposed IHA for the proposed construction of the Homer Harbor System Four Float Replacement Project in Homer, AK. We also request comment on the potential renewal of this proposed IHA as described in the paragraph below. Please include with your comments any supporting data or literature citations to help inform decisions on the request for this IHA or a subsequent renewal IHA.
On a case-by-case basis, NMFS may issue a one-time, 1-year renewal IHA following notice to the public providing an additional 15 days for public comments when (1) up to another year of identical or nearly identical activities as described in the Description of Proposed Activity section of this notice is planned or (2) the activities as described in the Description of Proposed Activity section of this notice would not be completed by the time the IHA expires and a renewal would allow for completion of the activities beyond that described in the *Dates and Duration* section of this notice, provided all of the following conditions are met:
• A request for renewal is received no later than 60 days prior to the needed renewal IHA effective date (recognizing that the renewal IHA expiration date cannot extend beyond 1 year from expiration of the initial IHA).
• The request for renewal must include the following:
1. An explanation that the activities to be conducted under the requested renewal IHA are identical to the activities analyzed under the initial IHA, are a subset of the activities, or include changes so minor ( *e.g.,* reduction in pile size) that the changes do not affect the previous analyses, mitigation and monitoring requirements, or take estimates (with the exception of reducing the type or amount of take).
2. A preliminary monitoring report showing the results of the required monitoring to date and an explanation showing that the monitoring results do not indicate impacts of a scale or nature not previously analyzed or authorized.
Upon review of the request for renewal, the status of the affected species or stocks, and any other pertinent information, NMFS determines that there are no more than minor changes in the activities, the mitigation and monitoring measures will remain the same and appropriate, and the findings in the initial IHA remain valid.
Dated: March 31, 2026.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries Service.