2024-15012. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Gary Paxton Industrial Park Vessel Haulout Project in Sitka, Alaska
Table 1—Pile Types, Installation Methods, and Durations
Pile size/type Method Number of piles Duration per pile (min) Strikes per pile Max piles per day Days of installation or removal Haulout Pier Support Pile 36-in Steel Pipe Pile Vibratory Installation 20 60 N/A 2 20 Impact Installation N/A 2,000 2 Haulout Pier Batter Pile 36-in Steel Pipe Pile Vibratory Installation 4 120 N/A 2 10 Impact Installation N/A 3,000 2 Haulout Pier Fender Pile 24-in Steel Pipe Pile Vibratory Installation 6 30 N/A 4 6 Template Pile 24-in Steel Pipe Pile Vibratory Installation and Removal 52 20 N/A 8 26 Expanded Uplands
Uplands expansion would facilitate the construction of the pile-supported 150-ton capacity haulout piers. Expanded uplands would be constructed with armor rock, shot rock borrow (bulk fill), and crushed aggregate base course. Bulk fill would be placed directly on the existing ground surface. When possible, materials would be placed in the dry during low tidal conditions, however, initial fill operations are planned to continue regardless of the level of tide. The bulk fill material would be delivered to the project site by trucks which would end-dump the material into on-site stockpiles for spreading. Bulk fill placement and spreading would be accomplished by track-mounted excavator, bulldozer, or motor grader. Above Mean Low Low Water, material would be placed in lifts of specified thickness. Each lift of material would be compacted with a vibratory drum roller compactor; all compaction operations would be performed when the tide is below the elevation of the work. As each lift of bulk fill material is placed, armor rock would be concurrently placed to protect the embankments from erosion during construction. As with the bulk fill materials, armor rock would be delivered to the project site by trucks and end-dumped into on-site stockpiles. Armor rock would be individually handled, manipulated, and placed on the bulk fill side slopes by a track-mounted excavator, or crane.
A layer of base course would be placed atop the expanded uplands area and compacted, using similar methods to the placement of bulk fill materials.
Stormwater Improvements
Stormwater improvements consisting of storm drain catch basins, utility holes, and associated piping would be installed to control stormwater within the expanded uplands. The uplands would be graded to facilitate stormwater drainage towards the catch basins installed in various locations throughout the site.
Vessel Washdown Pad and Utility Building
A permanent vessel washdown pad would be installed adjacent to the expanded uplands. A heated piping system would be incorporated into the concrete pad and the washdown pad would be equipped with drainage for vessel wash water. The drainage system would collect wash water used for vessel cleaning in a catch basin incorporated into the washdown pad and send it to a storm filter system containing a grit chamber for filtration of the effluent. All wash water would be discharged into the Sitka municipal sewer.
A 960-ft2 utility building would be installed on-site, adjacent to the vessel washdown pad, which would house the water treatment equipment and hydronic boilers for the heat piping system.
Proposed mitigation, monitoring, and reporting measures are described in detail later in this document (see Proposed Mitigation and Proposed Monitoring and Reporting section).
Description of Marine Mammals in the Area of Specified Activities
Sections 3 and 4 of CBS's 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 serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species or stocks and other threats.
Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Alaska and Pacific SARs. All values presented in table 2 are the most recent available at the time of publication (including from the draft 2023 SARs) and are available online at: https://www.fisheries.noaa.gov/ national/marine-mammal-protection/marine-mammal-stock-assessments.
Table 2—Marine Mammal Species 1 Likely To Occur Near the Project Area That May Be Taken by CBS's Activities
Common name Scientific name Stock ESA/ MMPA status; strategic (Y/N) 2 Stock abundance (CV, N min , most recent abundance survey) 3 PBR Annual M/SI 4 Order Artiodactyla—Cetacea—Mysticeti (baleen whales) Family Eschrichtiidae: Gray Whale Eschrichtius robustus Eastern N Pacific -, -, N 26,960 (0.05, 25,849, 2016) 801 131 Family Balaenopteridae (rorquals): Humpback Whale Megaptera novaeangliae 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) 5 UND 0.57 Family Delphinidae: Killer Whale Orcinus orca Eastern North Pacific Alaska Resident -, -, N 1,920 (N/A, 1,920, 2019) 6 19 1.3 Eastern North Pacific Gulf of Alaska, Aleutian Islands and Bering Sea Transient -, -, N 587 (N/A, 587, 2012) 6 5.9 0.8 Eastern Northern Pacific Northern Resident -, -, N 302 (N/A, 302, 2018) 6 2.2 0.2 West Coast Transient -, -, N 349 (N/A, 349, 2018) 6 3.5 0.4 Pacific White-Sided Dolphin Lagenorhynchus obliquidens N Pacific -, -, N 26,880 (N/A, N/A, 1990) UND 0 Family Phocoenidae (porpoises): Harbor Porpoise Phocoena phocoena Yakutat/Southeast Alaska Offshore Waters -, -, N N/A (N/A, N/A, 1997) 7 UND 22.2 Order Carnivora—Pinnipedia Family Otariidae (eared seals and sea lions): CA Sea Lion Zalophus californianus U.S -, -, N 257,606 (N/A, 233,515, 2014) 14,011 >321 Northern Fur Seal Callorhinus ursinus Eastern Pacific -, D, Y 626,618 (0.2, 530,376, 2019) 11,403 373 Steller Sea Lion Eumetopias jubatus Western E, D, Y 49,837 (N/A, 49,837, 2022) 8 299 267 Eastern -, -, N 36,308 (N/A, 36,308, 2022) 9 2,178 93.2 Family Phocidae (earless seals): Harbor Seal Phoca vitulina Sitka/Chatham Strait -, -, N 13,289 (N/A, 11,883, 2015) 356 77 1 Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy ( https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies; Committee on Taxonomy, 2022). 2 ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock. 3 NMFS marine mammal SARs online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region.CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable [explain if this is the case]. 4 These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined ( e.g., commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases. 5 Abundance estimates are based upon data collected more than 8 years ago and, therefore, current estimates are considered unknown. 6 Nest is based upon counts of individuals identified from photo-ID catalogs. 7 New stock split from Southeast Alaska stock. 8 Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys. Estimates provided are for the U.S. only. The overall Nmin is 73,211 and overall PBR is 439. 9 Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys. Estimates provided are for the U.S. only. As indicated above, all 9 species (with 14 managed stocks) in table 2 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. All species that could potentially occur in the proposed project areas are included in table 1 of the IHA application. Sperm whale, fin whale, North Pacific right whale, minke whale, and Dall's porpoise are other marine mammals that occur in the greater southeast Alaska area, but they are unlikely to be encountered at the Gary Paxton Industrial Park and thus are not addressed further in this notice.
In addition, the northern sea otter may be found in Sawmill Cove. However, northern sea otter are managed by the U.S. Fish and Wildlife Service and are not considered further in this document.
Gray Whale
The migration pattern of gray whales appears to follow a route along the western coast of Southeast Alaska, traveling northward from British Columbia through Hecate Strait and Dixon Entrance, passing the west coast of Baranof Island from late March to May and then return south in October and November (Jones et al., 1984; Ford et al., 2013). Gray whales are generally solitary, traveling alone or in small groups (NMFS, 2022b).
Historically, sightings of gray whales within Sitka Sound were common during the spring herring spawn; however, unusually large numbers of gray whales have been documented in western Sitka Sound near Kruzof Island since 2014 and 2015 [Alaska Department of Fish & Game (ADF&G), 2023; Wild et al., 2023]. It is unclear what has triggered this increase, but researchers believe it may be due to reduced prey availability in other parts of their range. Historical maps show that herring spawn in the eastern channel and Silver Bay in some years (ADF&G, 2023b). Additional historical records from 1964 to 2011 indicate that herring spawn in the Sitka Sound vicinity approximately every 1-3 years (Sill and Lemons, 2019). The most recent report of herring spawning in Sawmill Cove that NMFS is aware of occurred in 2011 (ADF&G, 2023b).
Records of gray whales in the Global Biodiversity Information Facility (GBIF) show 69 sightings reported by the public within and immediately offshore of Sitka Sound in the past 20 years (GBIF, 2023a). Spanning from 1995 to 2000, weekly land-based surveys of marine mammals from Sitka's Whale Park, located at the entrance to Silver Bay, were completed between September and May (Straley and Pendell, 2017). Across 190 hours of monitoring, three gray whales were observed in November. During recent marine mammal surveys associated with construction projects near the project area in Sitka Sound and in Silver Bay, no gray whales were sighted [Turnagain Marine Construction (TMC), 2017; CBS, 2019; Solstice, 2023].
Humpback Whale
Humpback whales congregate in Sitka Sound in the spring to feed on spawning herring (Wild et al., 2023) and again in September through December to feed on more diverse forage (Straley et al., 2018; Wild et al., 2023). During the summer, both herring and humpback whales disperse throughout Sitka Sound and away from the project area (Straley, 2017 pers comm. in Solstice, 2017).
During weekly surveys completed at Sitka's Whale Park between 1995 and 2000, Humpback whales were frequently observed in groups of one to four at a rate of 2.18 individuals per day, with peak sightings in November and December (Straley and Pendell, 2017). Similar group sizes were documented during studies assessing the potential influence of humpback whales on wintering pacific herring populations, completed in the fall (Straley et al., 2018). Groups of 25-30 whales were occasionally recorded in areas outside Silver Bay in the Eastern Channel (Straley and Pendell, 2017). During construction of the Gary Paxton Industrial Park Multipurpose Dock Project in 2017, humpback whales were typically observed in group sizes of two (TMC, 2017. PSOs reported humpbacks whales most frequently between 1,800-2,000 m away, but distances recorded ranged from 500 m to 5,000 m (TMC, 2017).
During monitoring in June 2019 for the O'Connell Bridge Lightering Float Pile Replacement Project (CBS, 2019) within Crescent Bay and the Eastern Channel, no humpback whales observed. Observations during the offshore geotechnical investigation for this project resulted in four sightings of nine total humpback whales during 80 hours of drilling operations between September 20 and 29, 2023. Sightings consisted of one to four whales travelling, foraging, and swimming throughout Silver Bay and into Herring Cove (Solstice, 2023).
Humpback whales in the project area are predominantly of the Hawaii Distinct Population Segment (DPS), which is not ESA-listed. However, based on a comprehensive photo-identification study, individuals from the Mexico DPS, which is listed as threatened, are known to occur in Southeast Alaska. Individuals of different DPSs are known to intermix on feeding grounds; therefore, all waters off the coast of Alaska should be considered to have ESA-listed humpback whales. Approximately 2 percent of all humpback whales in Southeast Alaska and northern British Columbia are of the Mexico DPS, while all others are of the Hawaii DPS (NMFS, 2021).
Killer Whale
Killer whales have been observed in all oceans and seas of the world, but the highest densities occur in colder and more productive waters found at high latitudes. Killer whales are found throughout the North Pacific, and occur along the entire Alaska coast, in British Columbia and Washington inland waterways, and along the outer coasts of Washington, Oregon, and California.
Of the eight recognized killer whale stocks, only the Alaska resident; Northern resident; Gulf of Alaska, Aleutian Islands, and Bering Sea Transient (Gulf of Alaska transient); and the West coast transient stocks are considered in this application because other stocks occur outside the geographic area under consideration. It is estimated that the majority of killer whales in the project area would be from the Alaska Resident stock, (60.7 percent), followed by the Gulf of Alaska, Aleutian Islands, and Bering Sea stock (18.6 percent), then the West Coast Transient (11.1 percent) and finally the Northern Residents stock (9.6 percent) (Young et al., 2023). The probability of occurrence is estimated by dividing the population of each stock by their combined total population.
Records of killer whales in the GBIF show 84 sightings reported by the public within and immediately outside of Sitka Sound in the past 20 years. During weekly surveys at Whale Park in Sitka between 1995 and 2000, killer whales were “unpredictably” observed in groups of four to eight at a rate of 0.22 individuals per day, with all sightings most frequent in fall and spring (Straley and Pendell, 2017). During recent marine mammal surveys associated with construction projects near the project area in Sitka Sound and in Silver Bay, no killer whales were sighted (TMC, 2017; CBS, 2019; Solstice, 2023).
Pacific White-Sided Dolphin
Pacific white-sided dolphins typically inhabit the open ocean and coastal waters away from shore (NMFS, 2022b). Pacific white-sided dolphins are rare in the inside passageways of Southeast Alaska. Most observations occur off the outer coast or in inland waterways near entrances to the open ocean. However, there are records of pacific white sided dolphins observations in protected inland waters of British Columbia since at least the late 1980s (Morton, 2000; Ashe, 2015) It is thought that Pacific white-sided dolphins could be experiencing a poleward shift in their distribution in response to climate change (Salvadeo et al., 2010; Rone et al., 2017).
During weekly surveys completed at Sitka's Whale Park between 1995 and 2000, Pacific white sided dolphin were rarely observed in groups of around four at a rate of 0.02 individuals per day, with all recorded sightings in February (Straley and Pendell, 2017).
Recent construction monitoring reports of monitoring in Sitka Sound and in Silver Bay show no occurrence of Pacific white-sided dolphins in the project area (TMC, 2017; CBS, 2019; Solstice, 2023).
Harbor Porpoise
The harbor porpoise inhabits temperate, subarctic, and arctic waters. In the eastern North Pacific, harbor porpoises range from Point Barrow, Alaska, to Point Conception, California. Harbor porpoise primarily frequent coastal waters and occur most frequently in waters less than 100 m deep (Hobbs and Waite, 2010). They may occasionally be found in deeper offshore waters.
Harbor porpoise frequent nearshore waters, but are not common in the project vicinity. During weekly surveys completed at Sitka's Whale Park between 1995 and 2000, harbor porpoises were infrequently observed in groups of about five to eight at a rate of 0.09 individuals per day, with peak sightings in fall and late spring (Straley and Pendell, 2017). During recent marine mammal surveys associated with construction projects near the project area in Sitka Sound and in Silver Bay, no harbor porpoise were sighted (TMC, 2017; CBS, 2019; Solstice, 2023).
California Sea Lion
California sea lions live in coastal waters and on beaches, docks, buoys, and jetties. During the winter, male California sea lions commonly migrate to feeding grounds typically off California, Oregon, Washington, British Columbia, and recently and more rarely, in southeast Alaska (Woodford 2020). Females and pups typically stay close to breeding colonies until the pups have weened (NMFS 2022b). California sea lions are occasionally sighted across the Gulf of Alaska north to the Pribilof Islands during all seasons of the year (Maniscalco et al. 2004).
No research or monitoring reports have indicated sightings of California Sea Lions in the project area (Straley and Pendell, 2017; TMC, 2017; CBS, 2019; Solstice, 2023). However, records of California sea lions in the GBIF show 22 sightings reported by the public within and immediately offshore of Sitka Sound in the past 20 years, suggesting a rare possibility of occurrence.
Northern Fur Seal
Northern fur seals are typically found in offshore waters outside of the breeding season, although females and young males may be found closer to shore as they move to southern waters. In Southeast Alaska and British Columbia, they are known to occasionally haul out at sea lion rookeries (Carretta et al., 2022; Committee on Endangered Wildlife in Canada (COSEWIC), 2010).
Northern fur seals are considered rare in the project area. Only four sightings were included GBIF records within Sitka Sound and nearby offshore waters in the past 20 years, largely from agency surveys reported in Ocean Biodiversity Information System-Spatial Ecology Analysis of Megavertebrate Populations (GBIF, 2023a). Additionally, during weekly surveys at Whale Park in Sitka between 1995 and 2000, no occurrences of northern fur seals were reported (Straley and Pendell, 2017), nor were they documented during monitoring completed for recent construction Sitka Sound and in Silver Bay show (TMC, 2017; CBS, 2019; Solstice, 2023). However, a female northern fur seal pup was reported swimming “erratically” near the shore in Sitka in January 2023 before being transported to the Alaska Sea Life Center for medical treatment (McKenney, 2023).
Steller Sea Lion
The majority of Steller sea lions that inhabit Southeast Alaska are part of the eastern DPS; however, branded individuals from the western DPS make regular movements across the 144° longitude boundary to the northern “mixing zone” haulouts and rookeries within southeast Alaska (Jemison et al., 2013). While haulouts and rookeries in the northern portion of Southeast Alaska may be important areas for western DPS animals, there continues to be little evidence that their regular range extends to the southern haulouts and rookeries in Southeast Alaska (Jemison et al., 2018). However, genetic data analyzed in Hastings et al. (2020) indicated that up to 1.2 percent of Steller sea lions near the project area may be members of the western DPS.
Steller sea lions are common within Sitka Sound and are likely to be found within the project area year-round. Steller sea lions were observed every month of monitoring (September to May) conducted at Whale Park between 1995 and 2000 (Straley and Pendell, 2017). Typical group sizes ranged from 1-2 (though sometimes over 100) at a rate of 3.46 individuals per day, with peak sightings in November, January, and February.
In 2017, during construction of the Gary Paxton Industrial Park Multipurpose Dock Project in the same area, an average of more than six Steller sea lions per day were observed during 22 days of in-water construction per day in October and November. Mean group sizes recorded were two individuals. During approximately 30 hours of monitoring in June 2019 for the O'Connell Bridge Lightering Float Pile Replacement Project, a total of 42 Steller sea lions were observed within Crescent Bay and the Eastern Channel in group sizes of 1 to 3 individuals. Several of these individuals were recorded as approaching or leaving Silver Bay (CBS, 2019). Finally, observations during the offshore geotechnical investigation for this project resulted in 79 sightings of 99 total Steller sea lions during 80 hours of drilling operations between September 20 and 29, 2023. Sightings generally consisted of one to three sea lions swimming largely within Sawmill Cove (Solstice, 2023). PSOs observed Steller sea lions at distances ranging between 30 m to as far as 700 m from the project site, with 10 percent of individuals coming within less than 60 m of the project site, and over a third of sightings occurring between 60 m and 130 m Solstice, 2023).
The project action area does not overlap Steller sea lion critical habitat. The Biorka Island haulout is the closest designated critical habitat and is well over 25 km southwest of the project area. There are no known haulouts within the project area.
Harbor Seal
Harbor seals are common in the inside waters of southeastern Alaska, including within the vicinity of the project area. The species were observed during most months of monitoring (September through May) from data collected at Whale Park between 1995 and 2000, except in December and May (Straley and Pendell, 2017). Harbor seals were frequently observed in groups of one to two. Harbor seals were also commonly observed during recent construction projects completed in the area, in similar group sizes (one to two) (TMS, 2017; CBS, 2019; Solstice, 2023). Similar to Steller sea lions, harbor seals may linger in the project area for multiple days. However, no designated haulouts are within close proximity.
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.). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65-decibel (dB) threshold from the normalized composite audiograms, with the exception for lower limits for low- frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall et al. (2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in table 3.
Table 3—Marine Mammal Hearing Groups
[NMFS, 2018]
Hearing group Generalized hearing range * Low-frequency (LF) cetaceans (baleen whales) 7 Hz to 35 kHz. Mid-frequency (MF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales) 150 Hz to 160 kHz. High-frequency (HF) cetaceans (true porpoises, Kogia, river dolphins, Cephalorhynchids, Lagenorhynchus cruciger & L. australis) 275 Hz to 160 kHz. Phocid pinnipeds (PW) (underwater) (true seals) 50 Hz to 86 kHz. Otariid pinnipeds (OW) (underwater) (sea lions and fur seals) 60 Hz to 39 kHz. * Represents the generalized hearing range for the entire group as a composite ( i.e., all species within the group), where individual species' hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65-dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall et al., 2007) and PW pinniped (approximation). The pinniped functional hearing group was modified from Southall et al. (2007) on the basis of data indicating that phocid species have consistently demonstrated an extended frequency range of hearing compared to otariids, especially in the higher frequency range (Hemilä et al., 2006; Kastelein et al., 2009; Reichmuth et al., 2013). This division between phocid and otariid pinnipeds is now reflected in the updated hearing groups proposed in Southall et al. 2019.
For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information.
Potential Effects of Specified Activities on Marine Mammals and Their Habitat
This section 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.
Description of Sound Sources
The marine soundscape is comprised of both ambient and anthropogenic sounds. Ambient sound is defined as the all-encompassing sound in a given place and is usually a composite of sound from many sources both near and far [American National Standards Institute (ANSI), 1995]. The sound level of an area is defined by the total acoustical energy being generated by known and unknown sources. These sources may include physical ( e.g., waves, wind, precipitation, earthquakes, ice, atmospheric sound), biological ( e.g., sounds produced by marine mammals, fish, and invertebrates), and anthropogenic sound ( e.g., vessels, dredging, aircraft, construction).
The sum of the various natural and anthropogenic sound sources at any given location and time—which comprise “ambient” or “background” sound—depends not only on the source levels (as determined by current weather conditions and levels of biological and shipping activity) but also on the ability of sound to propagate through the environment. In turn, sound propagation is dependent on the spatially and temporally varying properties of the water column and sea floor, and is frequency-dependent. As a result of the dependence on a large number of varying factors, ambient sound levels can be expected to vary widely over both coarse and fine spatial and temporal scales. Sound levels at a given frequency and location can vary by 10-20 dB from day to day (Richardson et al., 1995). The result is that, depending on the source type and its intensity, sound from the specified activity may be a negligible addition to the local environment or could form a distinctive signal that may affect marine mammals.
In-water construction activities associated with the project would include impact and vibratory pile driving and removal. The sounds produced by these activities fall into one of two general sound types: impulsive and non-impulsive. Impulsive sounds ( e.g., explosions, gunshots, sonic booms, impact pile driving) are typically transient, brief (less than 1 second), broadband, and consist of high peak sound pressure with rapid rise time and rapid decay (ANSI, 1986; National Institute of Occupational Safety and Health (NIOSH), 1998; NMFS, 2018). Non-impulsive sounds ( e.g., aircraft, machinery operations such as drilling or dredging, vibratory pile driving, and active sonar systems) can be broadband, narrowband or tonal, brief or prolonged (continuous or intermittent), and typically do not have the high peak sound pressure with rapid rise/decay time that impulsive sounds do (ANSI, 1995; NIOSH, 1998; NMFS, 2018). The distinction between these two sound types is important because they have differing potential to cause physical effects, particularly with regard to hearing ( e.g., Ward, 1997, in Southall et al., 2007).
Two types of hammers would be used on this project: impact and vibratory. Impact hammers operate by repeatedly dropping a heavy piston onto a pile to drive the pile into the substrate. Sound generated by impact hammers is characterized by rapid rise times and high peak levels, a potentially injurious combination (Hastings and Popper, 2005). Vibratory hammers install piles by vibrating them and allowing the weight of the hammer to push them into the sediment. Vibratory hammers produce significantly less sound than impact hammers. Peak sound pressure levels (SPLs) may be 180 dB or greater, but are generally 10 to 20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Oestman et al., 2009). Rise time is slower, reducing the probability and severity of injury, and sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson et al., 2005).
The likely or possible impacts of CBS's proposed activity on marine mammals could involve both non-acoustic and acoustic stressors. Potential non-acoustic stressors could result from the physical presence of equipment and personnel; however, any impacts to marine mammals are expected to be primarily acoustic in nature. Acoustic stressors include effects of heavy equipment operation during pile installation and removal.
Acoustic Effects
The introduction of anthropogenic noise into the aquatic environment from pile driving and removal is the means by which marine mammals may be harassed from CBS's specified activity. In general, animals exposed to natural or anthropogenic sound may experience behavioral, physiological, and/or physical effects, ranging in magnitude from none to severe (Southall et al., 2007, 2019). In general, exposure to pile driving noise has the potential to result in behavioral reactions ( e.g., avoidance, temporary cessation of foraging and vocalizing, changes in dive behavior) and, in limited cases, an auditory threshold shift (TS). Exposure to anthropogenic noise can also lead to non-observable physiological responses such an increase in stress hormones. Additional noise in a marine mammal's habitat can mask acoustic cues used by marine mammals to carry out daily functions such as communication and predator and prey detection. The effects of pile driving noise on marine mammals are dependent on several factors, including, but not limited to, sound type ( e.g., impulsive vs. non-impulsive), the species, age and sex class ( e.g., adult male vs. mom with calf), duration of exposure, the distance between the pile and the animal, received levels, behavior at time of exposure, and previous history with exposure (Wartzok et al., 2004; Southall et al., 2007). Here we discuss physical auditory effects (TSs) followed by behavioral effects and potential impacts on habitat.
NMFS defines a noise-induced TS as a change, usually an increase, in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). The amount of TS is customarily expressed in dB. A TS can be permanent or temporary. As described in NMFS (2018), there are numerous factors to consider when examining the consequence of TS, including, but not limited to, the signal temporal pattern ( e.g., impulsive or non-impulsive), likelihood an individual would be exposed for a long enough duration or to a high enough level to induce a TS, the magnitude of the TS, time to recovery (seconds to minutes or hours to days), the frequency range of the exposure ( i.e., spectral content), the hearing and vocalization frequency range of the exposed species relative to the signal's frequency spectrum ( i.e., how animal uses sound within the frequency band of the signal; e.g., Kastelein et al., 2014), and the overlap between the animal and the source ( e.g., spatial, temporal, and spectral).
Permanent Threshold Shift (PTS) —NMFS defines PTS as a permanent, irreversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Available data from humans and other terrestrial mammals indicate that a 40-dB TS approximates PTS onset (Ward et al., 1958, 1959; Ward 1960; Kryter et al., 1966; Miller, 1974; Ahroon et al., 1996; Henderson et al., 2008). PTS levels for marine mammals are estimates, as with the exception of a single study unintentionally inducing PTS in a harbor seal (Kastak et al., 2008), there are no empirical data measuring PTS in marine mammals largely due to the fact that, for various ethical reasons, experiments involving anthropogenic noise exposure at levels inducing PTS are not typically pursued or authorized (NMFS, 2018).
Temporary Threshold Shift (TTS) —A temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Based on data from cetacean TTS measurements (Southall et al., 2007), a TTS of 6 dB is considered the minimum TS clearly larger than any day-to-day or session-to-session variation in a subject's normal hearing ability (Schlundt et al., 2000; Finneran et al., 2000, 2002). As described in Finneran (2015), marine mammal studies have shown the amount of TTS increases with cumulative sound exposure level (SELcum) in an accelerating fashion: At low exposures with lower SELcum, the amount of TTS is typically small and the growth curves have shallow slopes. At exposures with higher SELcum, the growth curves become steeper and approach linear relationships with the noise SEL.
Depending on the degree (elevation of threshold in dB), duration ( i.e., recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious (similar to those discussed in Masking, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more serious impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall et al., 2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost.
Many studies have examined noise-induced hearing loss in marine mammals (see Finneran (2015) and Southall et al. (2019) for summaries). TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 2013). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. For cetaceans, published data on the onset of TTS are limited to captive bottlenose dolphin ( 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 at low frequencies, well below the region of best sensitivity for a species or hearing group, are less hazardous than those at higher frequencies, near the region of best sensitivity (Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure levels are higher compared to those in the region of best sensitivity ( i.e., a low frequency noise would need to be louder to cause TTS onset when TTS exposure level is higher), as shown for harbor porpoises and harbor seals (Kastelein et al., 2019a, 2019c). Note that in general, harbor seals and harbor porpoises have a lower TTS onset than other measured pinniped or cetacean species (Finneran, 2015). In addition, TTS can accumulate across multiple exposures, but the resulting TTS will be less than the TTS from a single, continuous exposure with the same SEL (Mooney et al., 2009; Finneran et al., 2010; Kastelein et al., 2014, 2015). This means that TTS predictions based on the total, cumulative SEL will overestimate the amount of TTS from intermittent exposures, such as sonars and impulsive sources. Nachtigall et al. (2018) describe measurements of hearing sensitivity of multiple odontocete species (bottlenose dolphin, harbor porpoise, beluga, and false killer whale ( Pseudorca crassidens)) when a relatively loud sound was preceded by a warning sound. These captive animals were shown to reduce hearing sensitivity when warned of an impending intense sound. Based on these experimental observations of captive animals, the authors suggest that wild animals may dampen their hearing during prolonged exposures or if conditioned to anticipate intense sounds. Another study showed that echolocating animals (including odontocetes) might have anatomical specializations that might allow for conditioned hearing reduction and filtering of low-frequency ambient noise, including increased stiffness and control of middle ear structures and placement of inner ear structures (Ketten et al., 2021). Data available on noise-induced hearing loss for mysticetes are currently lacking (NMFS, 2018). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species.
Relationships between TTS and PTS thresholds have not been studied in marine mammals, and there is no PTS data for cetaceans, but such relationships are assumed to be similar to those in humans and other terrestrial mammals. PTS typically occurs at exposure levels at least several decibels above that inducing mild TTS ( e.g., a 40-dB threshold shift approximates PTS 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 PTS thresholds for impulsive sounds (such as impact pile driving pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and PTS cumulative 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 PTS as compared with TTS, it is considerably less likely that PTS could occur.
Activities for this project include impact and vibratory pile driving and removal. There would likely be pauses in activities producing the sound during each day. Given these pauses and the fact that many marine mammals are likely moving through the project areas and not remaining for extended periods of time, the potential for TS declines.
Behavioral Harassment —Exposure to noise from pile driving also has the potential to behaviorally disturb marine mammals. Generally speaking, NMFS considers a behavioral disturbance that rises to the level of harassment under the MMPA a non-minor response—in other words, not every response qualifies as behavioral disturbance, and for responses that do, those of a higher level, or accrued across a longer duration, have the potential to affect foraging, reproduction, or survival. Behavioral disturbance may include a variety of effects, including subtle changes in behavior ( e.g., minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Behavioral responses may include changing durations of surfacing and dives, changing direction and/or speed; reducing/increasing vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); eliciting a visible startle response or aggressive behavior (such as tail/fin slapping or jaw clapping); avoidance of areas where sound sources are located. Pinnipeds may increase their haul out time, possibly to avoid in-water disturbance (Thorson and Reyff, 2006). Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors ( e.g., species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors ( e.g., Richardson et al., 1995; Wartzok et al., 2004; Southall et al., 2007, 2019; Weilgart, 2007; Archer et al., 2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison et al., 2012), and can vary depending on characteristics associated with the sound source ( e.g., whether it is moving or stationary, number of sources, distance from the source). In general, pinnipeds seem more tolerant of, or at least habituate more quickly to, potentially disturbing underwater sound than do cetaceans, and generally seem to be less responsive to exposure to industrial sound than most cetaceans. Please see Appendices B and C of Southall et al. (2007) and Gomez et al. (2016) for reviews of studies involving marine mammal behavioral responses to sound.
Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok et al., 2004). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder et al., 2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure.
As noted above, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals that are highly motivated to remain in an area for feeding (Richardson et al., 1995; Wartzok et al., 2004; National Research Council (NRC), 2005). Controlled experiments with captive marine mammals have showed pronounced behavioral reactions, including avoidance of loud sound sources (Ridgway et al., 1997; Finneran et al., 2003). Observed responses of wild marine mammals to loud pulsed sound sources ( e.g., seismic airguns) have been varied but often consist of avoidance behavior or other behavioral changes (Richardson et al., 1995; Morton and Symonds, 2002; Nowacek et al., 2007).
Available studies show wide variation in response to underwater sound; therefore, it is difficult to predict specifically how any given sound in a particular instance might affect marine mammals perceiving the signal. If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant ( e.g., Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 2005). However, there are broad categories of potential response, which we describe in greater detail here, that include alteration of dive behavior, alteration of foraging behavior, effects to breathing, interference with or alteration of vocalization, avoidance, and flight.
Changes in dive behavior can vary widely and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive ( e.g., Frankel and Clark, 2000; Costa et al., 2003; Ng and Leung, 2003; Nowacek et al., 2004; Goldbogen et al., 2013a, 2013b). Variations in dive behavior may reflect interruptions in biologically significant activities ( e.g., foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response.
Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators ( e.g., bubble nets or sediment plumes), or changes in dive behavior. As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance ( e.g., Croll et al., 2001; Nowacek et al., 2004; Madsen et al., 2006; Yazvenko et al., 2007). A determination of whether foraging disruptions incur fitness consequences would require information on or estimates of the energetic requirements of the affected individuals and the relationship between prey availability, foraging effort and success, and the life history stage of the animal.
Variations in respiration naturally vary with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in understanding species differences in the tolerance of underwater noise when determining the potential for impacts resulting from anthropogenic sound exposure ( e.g., Kastelein et al., 2001, 2005, 2006; Gailey et al., 2007). For example, harbor porpoise' respiration rate increased in response to pile driving sounds at and above a received broadband SPL of 136 dB (zero-peak SPL: 151 dB re 1 μPa; SEL of a single strike: 127 dB re 1 μPa2 -s) (Kastelein et al., 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). In some cases, animals may cease sound production during production of aversive signals (Bowles et al., 1994).
Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors, and is one of the most obvious manifestations of disturbance in marine mammals (Richardson et al., 1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme et al., 1984). Avoidance may be short-term, with animals returning to the area once the noise has ceased ( e.g., Bowles et al., 1994; Goold, 1996; Stone et al., 2000; Morton and Symonds, 2002; Gailey et al., 2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur ( e.g., Blackwell et al., 2004; Bejder et al., 2006; Teilmann et al., 2006).
A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response ( e.g., directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996; Bowers et al., 2018). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (England et al., 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response.
Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention ( i.e., when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been demonstrated for marine mammals, but studies involving fishes and terrestrial animals have shown that increased vigilance may substantially reduce feeding rates ( e.g., Beauchamp and Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In addition, chronic disturbance can cause population declines through reduction of fitness ( e.g., decline in body condition) and subsequent reduction in reproductive success, survival, or both ( e.g., Harrington and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, Ridgway et al. (2006) reported that increased vigilance in bottlenose dolphins exposed to sound over a 5-day period did not cause any sleep deprivation or stress effects.
Many animals perform vital functions, such as feeding, resting, traveling, and socializing, on a diel cycle (24-hour cycle). Disruption of such functions resulting from reactions to stressors such as sound exposure are more likely to be significant if they last more than one diel cycle or recur on subsequent days (Southall et al., 2007). Consequently, a behavioral response lasting less than 1 day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall et al., 2007). Note that there is a difference between multi-day substantive ( i.e., meaningful) behavioral reactions and multi-day anthropogenic activities. For example, just because an activity lasts for multiple days does not necessarily mean that individual animals are either exposed to activity-related stressors for multiple days or, further, exposed in a manner resulting in sustained multi-day substantive behavioral responses.
During a dock replacement project completed at this site in 2017, monitors observed marine mammals during construction activities ( i.e., vibratory or impact installation 30-in and 48-in steel piles; and vibratory removal of 16-in wood piles) on 22 days between October 9 and November 9 (TMC, 2017). In most cases behaviors were not reported, but there is some information to indicate that during pile driving a Steller sea lion was observed feeding, and humpback whales were observed moving through the project area to the mouth of the bay or to the inner bay. We expect similar behavioral responses of marine mammals to CBS's specified activity for this proposed project. That is, disturbance, if any, is likely to be temporary and localized ( e.g., small area movements).
Stress Responses —An animal's perception of a threat may be sufficient to trigger stress responses consisting of some combination of behavioral responses, autonomic nervous system responses, neuroendocrine responses, or immune responses ( e.g., Seyle, 1950; Moberg, 2000). In many cases, an animal's first and sometimes most economical (in terms of energetic costs) response is behavioral avoidance of the potential stressor. Autonomic nervous system responses to stress typically involve changes in heart rate, blood pressure, and gastrointestinal activity. These responses have a relatively short duration and may or may not have a significant long-term effect on an animal's fitness.
Neuroendocrine stress responses often involve the hypothalamus-pituitary-adrenal system. Virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction, altered metabolism, reduced immune competence, and behavioral disturbance ( e.g., Moberg, 1987; Blecha, 2000). Increases in the circulation of glucocorticoids are also equated with stress (Romano et al., 2004).
The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and “distress” is the cost of the response. During a stress response, an animal uses glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose serious fitness consequences. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other functions. This state of distress will last until the animal replenishes its energetic reserves sufficient to restore normal function.
Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses are well-studied through controlled experiments and for both laboratory and free-ranging animals ( e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003; Krausman et al., 2004; Lankford et al., 2005). Stress responses due to exposure to anthropogenic sounds or other stressors and their effects on marine mammals have also been reviewed (Fair and Becker, 2000; Romano et al., 2002b) and, more rarely, studied in wild populations ( e.g., Romano et al., 2002a). For example, Rolland et al. (2012) found that noise reduction from reduced ship traffic in the Bay of Fundy was associated with decreased stress in North Atlantic right whales. These and other studies lead to a reasonable expectation that some marine mammals will experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress.” In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2003), however distress is an unlikely result of this project based on observations of marine mammals during previous, similar projects in the area.
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).
Under certain circumstances, marine mammals experiencing significant masking could also be impaired from maximizing their performance fitness in survival and reproduction. Therefore, when the coincident (masking) sound is human-made, it may be considered harassment when disrupting or altering critical behaviors. It is important to distinguish TTS and PTS, which persist after the sound exposure, from masking, which occurs during the sound exposure. Because masking (without resulting in TS) is not associated with abnormal physiological function, it is not considered a physiological effect, but rather a potential behavioral effect (though not necessarily one that would be associated with harassment).
The frequency range of the potentially masking sound is important in determining any potential behavioral impacts. For example, low-frequency signals may have less effect on high-frequency echolocation sounds produced by odontocetes but are more likely to affect detection of mysticete communication calls and other potentially important natural sounds such as those produced by surf and some prey species. The masking of communication signals by anthropogenic noise may be considered as a reduction in the communication space of animals ( e.g., Clark et al., 2009) and may result in energetic or other costs as animals change their vocalization behavior ( e.g., Miller et al., 2000; Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2010; Holt et al., 2009). Masking can be reduced in situations where the signal and noise come from different directions (Richardson et al., 1995), through amplitude modulation of the signal, or through other compensatory behaviors (Hotchkin and Parks, 2013). Masking can be tested directly in captive species ( e.g., Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild ( e.g., Branstetter et al., 2013).
Marine mammals at or near the proposed CBS project site may be exposed to anthropogenic noise which may be a source of masking. Vocalization changes may result from a need to compete with an increase in background noise and include increasing the source level, modifying the frequency, increasing the call repetition rate of vocalizations, or ceasing to vocalize in the presence of increased noise (Hotchkin and Parks, 2013). For example, in response to loud noise, beluga whales may shift the frequency of their echolocation clicks to prevent masking by anthropogenic noise (Tyack, 2000; Eickmeier and Vallarta, 2022).
Masking is more likely to occur in the presence of broadband, relatively continuous noise sources such as vibratory pile driving. Energy distribution of pile driving covers a broad frequency spectrum, and sound from pile driving would be within the audible range of pinnipeds and cetaceans present in the proposed action area. While some construction during the CBS's activities may mask some acoustic signals that are relevant to the daily behavior of marine mammals, the short-term duration and limited areas affected make it very unlikely that the fitness of individual marine mammals would be impacted.
Airborne Acoustic Effects —Airborne noise would primarily be an issue for pinnipeds that are swimming or hauled out near the project site within the range of noise levels elevated above the acoustic criteria. We recognize that pinnipeds in the water could be exposed to airborne sound that may result in behavioral harassment when looking with their heads above water. Most likely, airborne sound would cause behavioral responses similar to those discussed above in relation to underwater sound. For instance, anthropogenic sound could cause hauled-out pinnipeds to exhibit changes in their normal behavior, such as reduction in vocalizations, or cause them to temporarily abandon the area and move further from the source. However, these animals would previously have been “taken” because of exposure to underwater sound above the behavioral harassment thresholds, which are in all cases larger than those associated with airborne sound. Thus, the behavioral harassment of these animals is already accounted for in these estimates of potential take. Therefore, we do not believe that authorization of incidental take resulting from airborne sound for pinnipeds is warranted, and airborne sound is not discussed further. Cetaceans are not expected to be exposed to airborne sounds that would result in harassment as defined under the MMPA.
Marine Mammal Habitat Effects
The project would occur in an active marine commercial and industrial area. The new facility will consist primarily of new structures though an existing boat ramp will be filled. Construction activities at the Gary Paxton Industrial Park could have localized, temporary impacts on marine mammal habitat and their prey by increasing in-water SPLs and slightly decreasing water quality. Increased noise levels may affect acoustic habitat (see Masking discussion above) and adversely affect marine mammal prey in the vicinity of the project area (see discussion below). During vibratory and impact pile driving, elevated levels of underwater noise would ensonify a portion of Eastern Channel and Silver Bay, where both fish and mammals occur and could affect foraging success.
Construction activities are of short duration and would likely have temporary impacts on marine mammal habitat through increases in underwater and airborne sound. These sounds would not be detectable at the nearest known Steller sea lion and harbor sea haulouts, which are well beyond the maximum distance of predicted in-air acoustical disturbance.
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 removal, sediment attached to the pile moves vertically through the water column until gravitational forces cause it to slough off under its own weight. The small resulting sediment plume is expected to settle out of the water column within a few hours. Studies of the effects of turbid water on fish (marine mammal prey) suggest that concentrations of suspended sediment can reach thousands of milligrams per liter before an acute toxic reaction is expected (Burton, 1993).
Effects to turbidity and sedimentation are expected to be short-term, minor, and localized. Suspended sediments in the water column should dissipate and quickly return to background levels in all construction scenarios. Turbidity within the water column has the potential to reduce the level of oxygen in the water and irritate the gills of prey fish species in the proposed project area. However, turbidity plumes associated with the project would be temporary and localized, and fish in the proposed project area would be able to move away from and avoid the areas where plumes may occur. Therefore, it is expected that the impacts on prey fish species from turbidity, and therefore on marine mammals, would be minimal and temporary. In general, the area likely impacted by the proposed construction activities is relatively small compared to the available marine mammal habitat in Silver Bay, and does not include any areas of particular importance.
In-Water Construction Effects on Potential Prey —Sound may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species ( e.g., crustaceans, cephalopods, fish, zooplankton). Marine mammal prey varies by species, season, and location and, for some, is not well documented. Here, we describe studies regarding the effects of noise on known marine mammal prey.
Fish utilize the soundscape and components of sound in their environment to perform important functions such as foraging, predator avoidance, mating, and spawning ( e.g., Zelick et al., 1999; Fay, 2009). Depending on their hearing anatomy and peripheral sensory structures, which vary among species, fishes hear sounds using pressure and particle motion sensitivity capabilities and detect the motion of surrounding water (Fay et al., 2008). The potential effects of noise on fishes depends on the overlapping frequency range, distance from the sound source, water depth of exposure, and species-specific hearing sensitivity, anatomy, and physiology. Key impacts to fishes may include behavioral responses, hearing damage, barotrauma (pressure-related injuries), and mortality.
Fish react to sounds which are especially strong and/or intermittent low-frequency sounds, and behavioral responses such as flight or avoidance are the most likely effects. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. The reaction of fish to noise depends on the physiological state of the fish, past exposures, motivation ( e.g., feeding, spawning, migration), and other environmental factors. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pile driving on fish, although several are based on studies in support of large, multiyear bridge construction projects ( e.g., Scholik and Yan, 2001, 2002; Popper and Hastings, 2009). Several studies have demonstrated that impulse sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs ( e.g., Fewtrell and McCauley, 2012; Pearson et al., 1992; Skalski et al., 1992; Santulli et al., 1999; Paxton et al., 2017). However, some studies have shown no or slight reaction to impulse sounds ( e.g., Pena et al., 2013; Wardle et al., 2001; Jorgenson and Gyselman, 2009; Cott et al., 2012). More commonly, though, the impacts of noise on fish are temporary.
SPLs of sufficient strength have been known to cause injury to fish and fish mortality. However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen et al. (2012a) showed that a TTS of 4-6 dB was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long. Injury caused by barotrauma can range from slight to severe and can cause death, and is most likely for fish with swim bladders. Barotrauma injuries have been documented during controlled exposure to impact pile driving (Halvorsen et al., 2012b; Casper et al., 2013).
The greatest potential impact to fishes during construction would occur during impact pile installation of 24-in and 36-in steel pipe piles, which is estimated to occur on up to 30 days for a maximum of 6,000 strikes per day. In-water construction activities would only occur during daylight hours, allowing fish to forage and transit the project area in the evening. Vibratory pile driving would possibly elicit behavioral reactions from fishes such as temporary avoidance of the area but is unlikely to cause injuries to fishes or have persistent effects on local fish populations. Construction also would have minimal permanent and temporary impacts on benthic invertebrate species, a marine mammal prey source. In addition, it should be noted that the area in question is low-quality habitat since it is already highly developed and experiences a high level of anthropogenic noise from normal operations and other vessel traffic. In general, any negative impacts on marine mammal prey species are expected to be minor and temporary.
Fish populations in the proposed project area that serve as marine mammal prey could be temporarily affected by noise from pile installation and 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).
The most likely impact to fish from pile driving activities in the project area would be temporary behavioral avoidance of the area. The duration of fish avoidance of an area after pile driving stops is unknown, but a rapid return to normal recruitment, distribution and behavior is anticipated. In general, impacts to marine mammal prey species are expected to be minor and temporary due to the expected short daily duration of individual pile driving events.
In-Water Construction Effects on Potential Foraging Habitat —The areas likely impacted by the project are relatively small compared to the available habitat in adjacent Sitka Sound and does not include any BIAs or ESA-designated critical habitat. The total seafloor area affected by pile installation and removal and the new dock footprints is a small area compared to the vast foraging area available to marine mammals in the area. Pile driving and removal at the project site would not obstruct long-term movements or migration of marine mammals.
Avoidance by potential prey ( i.e., fish or, in the case of transient killer whales, other marine mammals) of the immediate area due to the temporary loss of this foraging habitat is also possible. The duration of fish and marine mammal avoidance of this area after pile driving stops is unknown, but a rapid return to normal recruitment, distribution, and behavior is anticipated. 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.
In summary, given the short daily duration of sound associated with individual pile driving events and the relatively small areas being affected, pile driving activities associated with the proposed action are not likely to have a permanent adverse effect on any fish habitat, or populations of fish species. Any behavioral avoidance by fish of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity. Thus, we conclude that impacts of the specified activity are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species. Further, any impacts to marine mammal habitat are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations.
Estimated Take of Marine Mammals
This section provides an estimate of the number of incidental takes proposed for authorization through the IHA, which will inform NMFS' consideration of “small numbers,” 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 acoustic sources ( i.e., pile driving) has the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for auditory injury (Level A harassment) to result, primarily for mysticetes, high frequency species and phocids because predicted auditory injury zones are larger than for mid-frequency species and otariids. Auditory injury is unlikely to occur for other groups except Steller sea lions because this species is expected to commonly occur in close proximity to the project area. The proposed mitigation and monitoring measures are expected to minimize the severity of the taking to the extent practicable.
As described previously, no serious injury or mortality is anticipated or proposed to be authorized for this activity. Below we describe how the proposed take numbers are estimated.
For acoustic impacts, generally speaking, we estimate take by considering: (1) acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and, (4) the number of days of activities. We note that while these factors can contribute to a basic calculation to provide an initial prediction of potential takes, additional information that can qualitatively inform take estimates is also sometimes available ( e.g., previous monitoring results or average group size). Below, we describe the factors considered here in more detail and present the proposed take estimates.
Acoustic Thresholds
NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur PTS of some degree (equated to Level A harassment).
Level B Harassment —Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context ( e.g., frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment ( e.g., bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict ( e.g., Southall et al., 2007, 2021; Ellison et al., 2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS generally predicts that marine mammals are likely to be behaviorally harassed in a manner considered to be Level B harassment when exposed to underwater anthropogenic noise above root-mean-squared pressure received levels (RMS SPL) of 120 dB (referenced to 1 micropascal (re 1 μPa)) for continuous ( e.g., vibratory pile driving, drilling) and above RMS SPL 160 dB re 1 μPa for non-explosive impulsive ( e.g., seismic airguns) or intermittent ( e.g., scientific sonar) sources. 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.
CBS's proposed activity includes the use of continuous (vibratory pile driving) and impulsive (impact pile driving) sources, and therefore the RMS SPL thresholds of 120 and 160 dB re 1 μPa is/are applicable.
Level A harassment —NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) (Technical Guidance, 2018) identifies dual criteria to assess auditory injury (Level A harassment) to five different marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). CBS's proposed activity includes the use of impulsive (impact pile driving) and non-impulsive (continuous pile driving) sources.
These thresholds are provided in the table below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS' 2018 Technical Guidance, which may be accessed at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.
Table 4—Thresholds Identifying the Onset of PTS
Hearing group PTS onset acoustic thresholds * (received level) Impulsive Non-impulsive Low-Frequency (LF) Cetaceans Cell 1: Lpk,flat : 219 dB; LE,LF,24h : 183 dB Cell 2: LE,LF,24h : 199 dB. Mid-Frequency (MF) Cetaceans Cell 3: Lpk,flat : 230 dB; LE,MF,24h : 185 dB Cell 4: LE,MF,24h : 198 dB. High-Frequency (HF) Cetaceans Cell 5: Lpk,flat : 202 dB; LE,HF,24h : 155 dB Cell 6: LE,HF,24h : 173 dB. Phocid Pinnipeds (PW) (Underwater) Cell 7: Lpk,flat : 218 dB; LE,PW,24h : 185 dB Cell 8: LE,PW,24h : 201 dB. Otariid Pinnipeds (OW) (Underwater) Cell 9: Lpk,flat : 232 dB; LE,OW,24h : 203 dB Cell 10: LE,OW,24h : 219 dB. * Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive sounds, these thresholds should also be considered. Note: Peak sound pressure ( Lpk ) has a reference value of 1 μPa, and cumulative sound exposure level ( LE ) has a reference value of 1μPa2 s. In this table, thresholds are abbreviated to reflect ANSI standards (ANSI, 2013). However, peak sound pressure is defined by ANSI as incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript “flat” is being included to indicate peak sound pressure should be flat weighted or unweighted within the generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could be exceeded in a multitude of ways ( i.e., varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be exceeded. Ensonified Area
Here, we describe operational and environmental parameters of the activity that are used in estimating the area ensonified above the acoustic thresholds, including source levels and transmission loss coefficient.
The sound field in the project area is the existing background noise plus additional construction noise from the proposed project. Marine mammals are expected to be affected via sound generated by the primary components of the project ( i.e., pile driving and removal).
The project includes vibratory pile installation and removal, and impact pile driving. Source levels for these activities are based on reviews of measurements of the same or similar types and dimensions of piles available in the literature. Source levels for each pile size and activity each year are presented in table 5. Source levels for vibratory installation and removal of piles of the same diameter are assumed to be the same.
Table 5—Estimates of Mean Underwater Sound Levels * Generated During Vibratory and Impact Pile Installation and Vibratory Pile Removal
Pile driving method Pile type Pile size (in.) dB RMS dB peak dB SEL Reference Impact Steel Pipe Support Pile Steel Pipe Batter Pile 36 193 210 183 Caltrans 2015, 2020. Vibratory Installation and Extraction Steel Pipe Support Steel Pipe Batter 36 166 N/A N/A NMFS 2023 Calculations. Steel Pipe Fender Steel Pipe Template 24 163 N/A N/A NMFS 2023 Calculations. Note: dB peak = peak sound level; rms = root mean square; SEL = sound exposure level. * All sound levels are referenced at 10 m. TL is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source. TL parameters vary with frequency, temperature, sea conditions, current, source and receiver depth, water depth, water chemistry, and bottom composition and topography. The general formula for underwater TL is:
TL = B × Log10 ( R1 / R2),
where
TL = transmission loss in dB
B = transmission loss coefficient
R1 = the distance of the modeled SPL from the driven pile, and
R2 = the distance from the driven pile of the initial measurement
Absent site-specific acoustical monitoring with differing measured TL, a practical spreading value of 15 is used as the TL coefficient in the above formula. Site-specific TL data for the Sitka Sound are not available; therefore, the default coefficient of 15 is used to determine the distances to the Level A harassment and Level B harassment thresholds.
The ensonified area associated with Level A harassment is more technically challenging to predict due to the need to account for a duration component. Therefore, NMFS developed an optional User Spreadsheet tool to accompany the Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically going to be overestimates of some degree, which may result in an overestimate of potential take by Level A harassment. However, this optional tool offers the best way to estimate isopleth distances when more sophisticated modeling methods are not available or practical. For stationary sources such as pile driving, the optional User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity, it would be expected to incur PTS. Inputs used in the optional User Spreadsheet tool, and the resulting estimated isopleths, are reported below.
Table 6—User Spreadsheet Inputs
Vibratory Impact 36-in haulout pier support pile 36-in haulout pier batter pile 24-in haulout pier fender pile 24-in template pile 36-in haulout pier support pile 36-in haulout pier batter pile Installation Installation or removal Installation Spreadsheet Tab Used A.1) Vibratory Pile Driving E.1) Impact Pile Driving Source Level (SPL) 166 RMS 163 RMS 183 SEL Transmission Loss Coefficient 15 Weighting Factor Adjustment (kHz) 2.5 2 Activity Duration per day (minutes) 60 120 30 20 Number of strikes per pile 2,000 3,000 Number of piles per day 2 4 8 Distance of sound pressure level measurement 10 Table 7—Level A Harassment and Level B Harassment Isopleths and Associated Areas From Vibratory and Impact Pile Driving and Vibratory Removal
Pile size/type Method Level A harassment: isopleths (m), areas (km2 ) Level B harassment: isopleth (m). areas (km2 ) LF MF HF PW OW Haulout Pier Support Pile 36-in steel pipe pile Vibratory Installation 23.4, ( 0.006) 2.1, ( 0.001) 34.5, ( 0.009) 14.2, ( 0.004) 1.0, ( 0.001) 11,659, ( 9.41) Impact Installation 2,516, ( 3.13) 89.5, ( 0.022) 2,997, ( 3.64) 1,347, ( 1.49) 98, ( 0.024) 1,585, ( 1.94) Haulout Pier Batter Pile 36-in Steel Pipe Pile Vibratory Installation 37.1, ( 0.010) 3.3, ( 0.003) 54.8, ( 0.013) 22.5, ( 0.006) 1.6, ( 0.001) 11,659, ( 9.41) Impact Installation 3,297, (3.97) 117.3, ( 0.029) 3,928, ( 4.64) 1,765, ( 2.24) 128, ( 0.032) 1,585, ( 1.94) Haulout Pier Fender Pile 24-in Steel Pipe Pile Vibratory Installation 14.7, ( 0.004) 1.3, ( 0.001) 21.8, ( 0.006) 9.0, ( 0.003) 0.6, ( 0.001) 7,356, ( 7.61) Template Pile 24-in Steel Pipe Pile Vibratory Installation and Removal 17.9, ( 0.005) 1.6, ( 0.001) 26.4, ( 0.008) 10.9, ( 0.003) 0.8, ( 0.001) 7,356, ( 7.61) Marine Mammal Occurrence and Take Estimation
In this section we provide information about the occurrence of marine mammals, including density or other relevant information which will inform the take calculations.
Additionally, we describe how the occurrence information is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization. Available information regarding marine mammal occurrence in the vicinity of the project area includes site-specific and nearby survey information and historic data sets. Prior data sets consulted included: (1) Protected Species Observer (PSO) monitoring completed at the project site on 8 days between September 20 and 29, 2023 during the geotechnical investigation preceding this project (Solstice, 2023), (2) PSO monitoring completed at the project site on 22 days between October and November 2017 during the Multipurpose Dock Project (TMC, 2017), (3) PSO monitoring completed at O'Connell Bridge (approximately 7 km to the east of the project site) on 4 days in June 2019 (CBS, 2019); (4) Land-based surveys conducted at Sitka's Whale Park completed weekly between September and May 1995-2000 (Straley and Pendell (2017)); and, (5) data available on the GBIF (see IHA application for further details).
To estimate take, CBS referred to the above referenced data sets to estimate takes per day for each species and multiplied this factor by the total number of construction days. NMFS finds it more appropriate to describe the take estimate inputs according to a daily occurrence probability in which groups per day and group size are estimated for each species and multiplied by the number of days of each type of pile driving activity. The equation used to estimate take by Level B harassment for all species is:
Exposure Estimate = group size × groups per day × days of pile driving activity.
CBS proposes to implement shutdown zones for mid-frequency cetaceans and otariids (except Steller sea lions) that meet or exceed the Level A harassment isopleths for all activities. For phocids, high frequency cetaceans, and low-frequency cetaceans, the calculated Level A harassment zones exceed the proposed shutdown zones during impact installation of 36-in steel piles, planned to occur on 30 construction days. Because the best available abundance estimates for these species cover the general region of Sitka Sound and Silver Bay, estimates of take by Level A harassment were based on the maximum predicted Level B isopleth for each pile type, typically from vibratory pile driving. In the absence of density data, best available monitoring data for the general area were used to estimate take by Level A harassment. Specifically, to calculate estimated take by Level A harassment for these species, we proportionally compared, by hearing group, the portion of the largest Level A harassment area (km2 ) that exceeds the planned shutdown zone area (km2 ) to the area (km2 ) of the largest Level B harassment zone across that pile type (typically from vibratory pile driving). This ratio was then multiplied by the group size, daily sightings, and number of construction days, according to the following equation:
Take by Level A harassment = Level A harassment area (km2 )/Level B harassment area (km2 ) × group size × groups per day × days of pile driving.
For Steller sea lions, during impact pile driving of 24-in and 36-in steel pipe piles, the shutdown zone would be established at 60 m rather than the larger Level A harassment isopleths (100 m and 130 m, respectively) due to practicability; local monitoring data suggests that Steller sea lions frequently occur within close proximity of the project site. The method described above did not produce an estimate of take by Level A harassment consistent with the best available data for this species at the project location. Therefore, recent monitoring data collected at this site (Solstice, 2023), were used as the basis of calculating take by Level A harassment. The proportion of Steller sea lions detected between 60 m and 130 m was multiplied by group size, number of daily sightings, and multiplied by the number of construction days when impact pile driving is proposed according to this equation:
Take by Level A harassment = group size × groups per day × days of impact pile driving activity x proportion of Steller sea lions observed occurring between 60-130 m during geotechnical drilling.
Proposed take estimates were rounded up to the nearest whole number in table 8.
Gray Whale
CBS requested take by Level B harassment of 31 gray whales, based on an estimated 1 gray whale every 2 days for 62 construction days. However, during weekly surveys conducted from September to May between 1995 and 2000, gray whales were infrequently observed in groups of three from Whale Park. As such, NMFS finds it more appropriate to propose to authorize 1 group of 3 gray whales every 14 construction days (62/14 construction days = 4.4 2-week construction week periods), resulting in 14 takes by Level B harassment (1 group × 3 gray whales × 4.4 construction periods = 13.2 takes by Level B harassment).
The proposed shutdown zone exceeds the calculated Level A harassment zone except during impact pile driving of 36-in steel piles (support and battered), estimated across 30 construction days. As such, it is possible that gray whales may occur in the Level A harassment zone and stay long enough to incur PTS before exiting. For 36-in support piles, the ratio of the Level A harassment area (km2 ) that exceeds the shutdown zone to the maximum predicted Level B harassment area (km2 ) is 0.06. This activity is estimated to take place on 20 construction days. For 36-in batter piles, the ratio of the Level A harassment area (km2 ) that exceeds the shutdown zone to the Level B harassment area is 0.16. This activity is estimated to take place on 10 construction days. As such, 3 takes by Level A harassment are estimated [(0.06 × 4.4 construction periods × 1 group × 3 gray whales) + (0.16 × 4.4 construction periods × 1 group × 3 gray whales) = 2.9 takes by Level A harassment].
Any individuals exposed to the higher levels associated with the potential for PTS closer to the source might also be behaviorally disturbed, however, for the purposes of quantifying take we do not count those exposures of one individual as a take by both Level A harassment take and Level B harassment. Therefore, takes by Level B harassment calculated as described above were further modified to deduct the proposed amount of take by Level A harassment. Therefore, NMFS proposes to authorize 3 takes by Level A harassment and 11 takes by Level B harassment for gray whale, for a total of 14 takes. When allocating take across stocks, take estimates are rounded up to the nearest whole number.
Humpback Whale
CBS requested take by Level B harassment of 248 humpback whales, based on an estimated 4 humpback whales occurring every 1 construction day for 62 construction days. NMFS concurs with this take estimate, acknowledging that two groups of two humpback whales occurring each construction day is reasonable based on previous monitoring data (2 groups × 2 humpback whales × 62 construction days = 248 takes by Level B harassment of humpback whale).
The proposed shutdown zone exceeds the calculated Level A harassment zone except during impact pile driving of 36-in steel piles (support and battered), estimated across 30 construction days. As such, it is possible that humpback whales may occur in the Level A harassment zone and stay long enough to incur PTS before exiting. For 36-in support piles, the ratio of the Level A harassment area (km2 ) that exceeds the shutdown zone to the maximum predicted Level B harassment area (km2 ) is 0.06. This activity is estimated to take place on 20 construction days. For 36-in batter piles, the ratio of the Level A harassment area (km2 ) that exceeds the shutdown zone to the Level B harassment area is 0.16. This activity is estimated to take place on 10 construction days. As such, 12 takes by Level A harassment are estimated [(0.06 × 20 construction days × 2 groups × 2 humpback whales) + (0.16 × 10 construction days × 2 groups × 2 humpback whales) = 11.2 takes by Level A harassment].
Any individuals exposed to the higher levels associated with the potential for PTS closer to the source might also be behaviorally disturbed, however, for the purposes of quantifying take we do not count those exposures of one individual as a take by both Level A harassment take and Level B harassment. Therefore, takes by Level B harassment calculated as described above were further modified to deduct the proposed amount of take by Level A harassment. Therefore, NMFS proposes to authorize 12 takes by Level A harassment and 236 takes by Level B harassment for humpback whale, for a total of 248 takes. When allocating take across stocks, take estimates are rounded up to the nearest whole number.
Killer Whale
CBS requested take by Level B harassment of 32 killer whales, based on an estimated 1 killer whale occurring every 2 construction days for 62 construction days. However, because killer whales were unpredictably observed from Whale Park in groups of 4-8 during weekly surveys conducted from September to May between 1995 and 2000, NMFS finds it more appropriate to propose to authorize 1 group of 8 killer whales every 7 construction days (62/7 construction days = 8.9 construction weeks), resulting in 71 takes by Level B harassment (1 group × 8 killer whales × 8.9 construction weeks = 71 takes by Level B harassment). No takes by Level A harassment were requested or are proposed for authorization.
Pacific White-Sided Dolphin
CBS requested take by Level B harassment of 16 Pacific white-sided dolphin, based on an estimated 1 Pacific white-sided dolphin occurring every 4 construction days for 62 construction days. However, Pacific white-sided dolphin were rarely observed from Whale Park in groups of four during weekly surveys conducted from September to May between 1995 and 2000. As such, NMFS finds it more appropriate to propose to authorize 1 group of 4 Pacific white-sided dolphin every 14 construction days (62/14 = 4.4 2-week construction periods), resulting in 18 takes by Level B harassment (1 group × 4 Pacific white-sided dolphin × construction 4.4 periods = 17.6 takes by Level B harassment). No takes by Level A harassment are requested or proposed for authorization.
Harbor Porpoise
CBS requested take by Level B harassment of 16 harbor porpoise, based on an estimated 1 harbor porpoise occurring every 4 construction days for 62 construction days. However, harbor porpoise were rarely observed from Whale Park in groups of five during weekly surveys conducted from September to May between 1995 and 2000. As such, NMFS finds it more appropriate to propose to authorize 1 group of 5 harbor porpoise every 14 construction days (62/14 construction days = 4.4 2-week construction week periods), resulting in 22 takes by Level B harassment (1 group × 5 harbor porpoises × 4.4 construction periods = 22 takes by Level B harassment).
During impact pile driving of 36-in steel piles, estimated across 30 construction days, the expected Level A harassment zone is larger than the planned shutdown zone (see Figure 1 of the Marine Mammal Mitigation and Monitoring Plan). As such, it is possible that harbor porpoise may enter the Level A harassment zone and stay long enough to incur PTS before exiting. For 36-in support piles, the ratio of the Level A harassment area (km2 ) that exceeds the shutdown zone to the maximum predicted Level B harassment area (km2 ) is 0.38. This activity is estimated to take place on 20 construction days (20 construction days/14 days = 1.43 2-week construction periods). For 36-in batter piles, the ratio of the portion of the Level A harassment area that exceeds the shutdown zone area (km2 ) to the maximum predicted Level B harassment area is 0.48. This activity is estimated to take place on 10 construction days (10 construction days/14 days = 0.71 2-week construction periods). As such, five takes by Level A harassment are estimated [(0.38 × 1 group × 5 harbor porpoise × 1.43 2-week construction periods) + (0.48 × 1 group × 5 harbor porpoises × 0.71 2-week construction periods) = 4.4 takes by Level A harassment].
Any individuals exposed to the higher levels associated with the potential for PTS closer to the source might also be behaviorally disturbed; however, for the purposes of quantifying take we do not count those exposures of one individual as a take by both Level A harassment and Level B harassment. Therefore, NMFS proposes to authorize 5 takes by Level A harassment and 17 takes by Level B harassment for harbor porpoise, for a total of 22 takes.
Steller Sea Lion
CBS requested take by Level B harassment of 496 Steller sea lions, based on an estimated 8 Steller sea lions occurring every 1 construction day for 62 construction days. NMFS concurs with this take estimate, acknowledging that four groups of two Steller sea lions occurring each construction day is reasonable based on previous monitoring data (2 groups × 4 Steller sea lion × 62 construction days = 496 takes by Level B harassment of Steller sea lion).
During impact pile driving of 36-in steel piles, estimated across 30 construction days, the expected Level A harassment zone is larger than the proposed shutdown zone. As such, it is possible that Steller sea lion may enter the Level A harassment zone and stay long enough to incur PTS before exiting. For 36-in support piles, the ratio of the Level A harassment area that exceeds the planned shutdown zone (km2 ) to the maximum predicted Level B harassment area (km2 ) for is 0.001. This activity is estimated to take place on 20 construction days. For 36-in batter piles, the ratio of the Level A harassment area (km2 ) to the maximum predicted Level B harassment area is 0.002. This activity is estimated to take place on 10 construction days. As such, one take by Level A harassment was estimated [(0.001 × 20 construction days × 2 groups × 4 Steller sea lion × 20 construction days) + (0.002 × 10 construction days × 2 groups × 4 Steller sea lion × 10 construction days) = 0.32 takes by Level A harassment].
However, the 0.32 takes by Level A harassment estimated using the method described above does not likely reflect the occurrence of Steller sea lion in the project area. Based on monitoring data collected during geotechnical survey conducted to inform this IHA application, Steller sea lions are expected to disproportionally occur within close proximity to the project site. Approximately 37 percent of Steller sea lions documented during that survey were observed between 60 m and 130 m, which corresponds to the Level A zones during impact pile driving of 36-in piles. These scenarios may occur on up to 30 construction days. Therefore 89 additional takes by Level A harassment are proposed for authorization (2 groups of 4 Steller sea lion × 30 construction days × 0.37 = 89 takes by Level A harassment).
Any individuals exposed to the higher levels associated with the potential for PTS closer to the source might also be behaviorally disturbed, however, for the purposes of quantifying take we do not count those exposures of one individual as a take by both Level A and Level B harassment. Therefore takes by Level B harassment calculated as described above are further modified to deduct the proposed amount of take by Level A harassment. Therefore, NMFS proposes to authorize 89 takes by Level A harassment and 407 takes by Level B harassment for Steller sea lion, for a total of 496 takes.
California Sea Lion
CBS requested take by Level B harassment of five California sea lions, based on an estimated one California sea lion occurring every month that construction is planned (October to March = 5 months) to account for the unlikely but small possibility that California sea lion could occur in the project area. However, NMFS finds it more appropriate to estimate take by Level B harassment according to proposed duration of in-water work (62 construction days/30 days in 1 month = 2.06 construction months). As such, NMFS proposes to authorize take by Level B harassment of three California sea lion (1 group × 1 California sea lion × 2.06 construction months = 2.06 takes by Level B harassment of California sea lion). No takes by Level A harassment are requested or proposed for authorization.
Northern Fur Seal
CBS requested take by Level B harassment of five northern fur seals, based on an estimated one northern fur seal occurring every month that construction is planned (October—March = 5 months) to account for the unlikely but small possibility that northern fur seals could occur in the project area. However, NMFS finds it more appropriate to estimate take by Level B harassment according to proposed duration of in-water work (62 construction days/30 days in 1 month = 2.06 months). As such, NMFS proposes to authorize take by Level B harassment of three northern fur seals (1 group × 1 northern fur seal × 2.06 construction months = 2.06 takes by Level B harassment of northern fur seal). No takes by Level A harassment are requested or proposed for authorization.
Harbor Seal
CBS requested take by Level B harassment of 124 harbor seals, based on an estimated 2 harbor seals occurring every 2 construction days for 62 construction days. However, because harbor seals are frequently documented in the project area, NMFS finds it more appropriate to propose to authorize 186 takes by Level B harassment of harbor seal, based on the maximum groups size of 3 documented at the project site in 2017 (1 group × 3 harbor seal × 62 construction days = 186 takes by Level B harassment).
During impact pile driving of 36-in steel piles, estimated across 30 construction days, the expected Level A harassment zone is larger than the planned shutdown zone. As such, it is possible that harbor seal may enter the Level A harassment zone and stay long enough to incur PTS before exiting. For 36-in support piles, the ratio of the Level A harassment area (km2 ) that exceeds the planned shutdown zone to the Level B harassment area (km2 ) is 0.16. This activity is estimated to take place on 20 construction days. For 36-in batter piles, the ratio of the Level A harassment area that exceeds the shutdown zone area (km2 ) to the maximum predicted Level B harassment area is 0.23 (km2 ). This activity is estimated to take place on 10 construction days. As such, 34 takes by Level A harassment are estimated [(0.16 × 20 construction days × 1 group × 3 harbor seals × 20 construction days) + (0.23 × 10 construction days × 1 group × 3 harbor seals) = 33.2 takes by Level A harassment].
Any individuals exposed to the higher levels associated with the potential for PTS closer to the source might also be behaviorally disturbed, however, for the purposes of quantifying take we do not count those exposures of one individual as a take by both Level A harassment take and Level B harassment. Therefore takes by Level B harassment calculated as described above are further modified to deduct the proposed amount of take by Level A harassment. Therefore, NMFS proposes to authorize 34 takes by Level A harassment and 152 takes by Level B harassment for harbor seal, for a total of 186 takes.
The total proposed take authorization for all species is summarized in table 8 below. Take by Level A harassment is proposed for a total of 3 incidents for gray whale, 11 incidents for humpback whale, 5 incidents for harbor porpoise, 6 instances for Steller sea lion, and 34 incidents for harbor seal.
Table 8—Proposed Take by Stock and Harassment Type and as a Percentage of Stock Abundance
Species Stock Proposed authorized take 1 Proposed take as a percentage of stock abundance Level B harassment Level A harassment Gray Whale Eastern N Pacific 11 3 <1 Mexico—North Pacific 5 1 <1 Humpback Whale 2 Hawai'i 231 11 <1 Killer Whale 3 ENP Alaska Resident 44 0 2.3 ENP Northern Resident 7 0 14.2 ENP Gulf of Alaska, Aleutian Islands, and Bering Sea 14 0 2.4 West Coast Transient 8 0 2.3 Pacific white-sided dolphin North Pacific 18 0 <1 Harbor Porpoise Yakutat/Southeast Alaska Offshore Waters 17 5 (4 ) Steller sea lion 5 Western DPS 5 1 <1 Eastern DPS 402 88 1.3 California sea lion United States 3 0 <1 Northern fur seal Eastern Pacific 3 0 <1 Harbor Seal Sitka/Chatham Strait 152 34 1.4 1 When allocating take across stocks, take estimates are rounded up to the nearest whole number. 2 2 percent of take by Level A and Level B harassment of humpback whales are allocated to the Mexico DPS according to NMFS, 2021 3 Take by level B harassment of killer whale is allocated across stocks according to the proportion of the stock compared to total number of animals in all four stocks that could occur in the project area: Alaska Residents, 60.7 percent; Northern Residents, 9.6 percent; Gulf of Alaska, Aleutian Islands, and Bering Sea: 18.6 percent; West Coast Transient, 11.1 percent. 4 A reliable abundance estimate for this stock is currently unavailable. 5 1.2 percent take by Level A and Level B harassment of Steller sea lions are allocated to the Western DPS according to Hastings et al. (2020). Proposed Mitigation
In order to issue an IHA under section 101(a)(5)(D) of the MMPA, NMFS must set forth the permissible methods of taking pursuant to the activity, and other means of effecting the least practicable impact on the species or stock and its habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stock for taking for certain subsistence uses (latter not applicable for this action). NMFS regulations require applicants for incidental take authorizations to include information about the availability and feasibility (economic and technological) of equipment, methods, and manner of conducting the activity or other means of effecting the least practicable adverse impact upon the affected species or stocks, and their habitat (50 CFR 216.104(a)(11)).
In evaluating how mitigation may or may not be appropriate to ensure the least practicable adverse impact on species or stocks and their habitat, as well as subsistence uses where applicable, NMFS considers two primary factors:
(1) The manner in which, and the degree to which, the successful implementation of the measure(s) is expected to reduce impacts to marine mammals, marine mammal species or stocks, and their habitat, as well as subsistence uses. 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, and impact on operations.
Mitigation for Marine Mammals and Their Habitat
Shutdown Zones —For all pile driving activities, CBS proposes to implement shutdowns within designated zones. 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). Shutdown zones vary based on the activity type and marine mammal hearing group (table 9). In most cases, the shutdown zones are based on the estimated Level A harassment isopleth distances for each hearing group. However, in cases where it would be challenging to detect marine mammals at the Level A harassment isopleth ( e.g., for phocids, high frequency cetaceans, and low frequency cetaceans during impact pile driving) and/or frequent shutdowns would create practicability concerns ( e.g., Steller sea lions during impact pile driving), smaller shutdown zones have been proposed (table 9).
Construction supervisors and crews, Protected Species Observers (PSOs), and relevant CBS staff must avoid direct physical interaction with marine mammals during construction activity. If a marine mammal comes within 10 m of such activity, operations must cease and vessels must reduce speed to the minimum level required to maintain steerage and safe working conditions, as necessary to avoid direct physical interaction. If an activity is delayed or halted due to the presence of a marine mammal, the activity may not commence or resume until either the animal has voluntarily exited and been visually confirmed beyond the shutdown zone indicated in table 9, or 15 minutes have passed without re-detection of the animal.
Finally, construction activities must be halted upon observation of a species for which incidental take is not authorized or a species for which incidental take has been authorized but the authorized number of takes has been met entering or within any harassment zone. If a marine mammal species not covered under this IHA enters a harassment zone, all in-water activities will cease until the animal leaves the zone or has not been observed for at least 15 minutes, and NMFS would be notified about species and precautions taken. Pile driving will proceed if the unauthorized species is observed leaving the harassment zone or if 15 minutes have passed since the last observation.
Table 9—Proposed Shutdown Zones
Pile size/type Method Shutdown zones (m) LF MF HF PW OW Steller sea lion Other OW Haulout Pier Support Pile 36-in Steel Pipe Pile Vibratory Installation 30 10 40 20 10 10 Impact Installation 2,000 90 300 130 60 100 Haulout Pier Batter Pile 36-in Steel Pipe Pile Vibratory Installation 40 10 60 30 10 10 Impact Installation 2,000 120 300 130 60 130 Haulout Pier Fender Pile 24-in Steel Pipe Pile Vibratory Installation 20 10 30 10 10 10 Template Pile 24-in Steel Pipe Pile Vibratory Installation and removal 20 10 30 20 10 10
Document Information
- Published:
- 07/09/2024
- Department:
- National Oceanic and Atmospheric Administration
- Entry Type:
- Notice
- Action:
- Notice; proposed incidental harassment authorization; request for comments on proposed authorization and possible renewal.
- Document Number:
- 2024-15012
- Dates:
- Comments and information must be received no later than August 8, 2024.
- Pages:
- 56317-56341 (25 pages)
- Docket Numbers:
- RTID 0648-XD855
- PDF File:
- 2024-15012.pdf