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Federal Register / Vol. 86, No. 122 / Tuesday, June 29, 2021 / Notices 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.
Exposure to loud sounds with 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 46 dB
was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long. Injury caused by barotrauma can range from slight to severe and can cause death, and is most likely for fish with swim bladders.
Barotrauma injuries have been documented during controlled exposure to impact pile driving Halvorsen et al., 2012b; Casper et al., 2013.
The most likely impact to fish from pile driving activities at the project areas 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 and the relatively small areas being affected.
The following essential fish habitat EFH species may occur in the project area during at least one phase of their lifestage: Chum Salmon Oncorhynchus keta, Pink Salmon O. gorbuscha, Coho Salmon O. kisutch, Sockeye Salmon O. nerka, and Chinook Salmon O.
tshawytscha. Three creeks flowing into Port Chester are known to contain salmonids: Hemlock Creek, Trout Lake Creek, and Melanson Lake outflow Giefer and Blossom 2020; however,
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adverse effects on EFH in this area are not expected.
The area impacted by the project is relatively small compared to the available habitat and does not include habitat of particular importance relative to available habitat overall. Any behavioral avoidance by fish of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity. As described in the preceding, the potential for the AKDOT&PFs construction to affect the availability of prey to marine mammals or to meaningfully impact the quality of physical or acoustic habitat is considered to be insignificant. Effects to habitat will not be discussed further in this document.
Estimated Take This section provides an estimate of the number of incidental takes proposed for authorization through this IHA, which will inform both NMFS
consideration of small numbers and the negligible impact determination.
Except with respect to certain activities not pertinent here, section 318 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.
Take of marine mammals incidental to the AKDOT&PFs pile driving and removal activities as well as during DTH could occur as a result of Level B
harassment only. Below we describe how the potential take is estimated. As described previously, no mortality is anticipated or proposed to be authorized for this activity. Below we describe how the take is estimated.
Generally speaking, we estimate take by considering: 1 Acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; 2 the area or volume of water that will be ensonified above these levels in a day; 3 the density or occurrence of marine mammals within these ensonified areas;
and, 4 and the number of days of activities. We note that while these basic factors can contribute to a basic calculation to provide an initial prediction of takes, additional information that can qualitatively
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inform take estimates is also sometimes available e.g., previous monitoring results or average group size. Below, we describe the factors considered here in more detail and present the proposed take estimate.
Acoustic Thresholds Using the best available science, NMFS has developed 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 HarassmentThough significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source e.g., frequency, predictability, duty cycle, the environment e.g., bathymetry, and the receiving animals hearing, motivation, experience, demography, behavioral context and can be difficult to predict Southall et al., 2007, Ellison et al., 2012. Based on what the available science indicates and the practical need to use a threshold based on a factor that is both predictable and measurable for most activities, NMFS
uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS
predicts that marine mammals are likely to be behaviorally harassed in a manner we consider Level B harassment when exposed to underwater anthropogenic noise above received levels of 120 dB re 1 mPa rms for continuous e.g., vibratory pile driving and DTH and above 160 dB re 1 mPa rms for impulsive sources e.g., impact pile driving. The AKDOT&PFs proposed activity includes the use of continuous vibratory pile driving, DTH and impulsive impact pile driving sources, and therefore the 120 and 160 dB re 1
mPa rms are applicable.
Level A harassmentNMFS
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. The technical guidance identifies the received levels, or thresholds, above which individual marine mammals are predicted to experience changes in their hearing sensitivity for all underwater anthropogenic sound sources, and reflects the best available science on the
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