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Federal Register / Vol. 86, No. 195 / Wednesday, October 13, 2021 / Proposed Rules
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available to marine mammals in the surrounding area.
Avoidance by potential prey i.e., fish of the immediate area due to the temporary loss of this foraging habitat is also possible. The duration of fish avoidance of this area after pile driving stops is unknown, but we anticipate a rapid return to normal recruitment, distribution and behavior. Any behavioral avoidance by fish of the disturbed area would still leave large areas of fish and marine mammal foraging habitat in the nearby vicinity in the project area.
Effects on Potential Prey Sound may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species e.g., fish. Marine mammal prey varies by species, season, and location. Here, we describe studies regarding the effects of noise on known marine mammal prey.
Fish utilize the soundscape and components of sound in their environment to perform important functions such as foraging, predator avoidance, mating, and spawning e.g., Zelick 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
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impulse sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs e.g., Fewtrell and McCauley, 2012; Pearson et al. 1992; Skalski et al.
1992; Santulli et al. 1999; Paxton et al.
2017. However, some studies have shown no or slight reaction to impulse sounds e.g., Pena et al. 2013; Wardle et al. 2001; Jorgenson and Gyselman, 2009;
Cott et al. 2012.
SPLs of sufficient strength have been known to cause injury to fish and fish mortality. However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen et al. 2012a showed that a TTS of 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.
The area impacted by the project is relatively small compared to the available habitat in the remainder of the project area and surrounding waters, and there are no areas of particular importance that would be impacted by this project. Any behavioral avoidance by fish of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity. As described in the preceding paragraphs, the potential for the Navys 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.
Estimated Take This section provides an estimate of the number of incidental takes proposed for authorization, which will inform both NMFS consideration of small numbers and the negligible impact determination.
Harassment is the only type of take expected to result from these activities.
Except with respect to certain activities
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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.
Authorized takes would be by Level A
and B harassment, in the form of disruption of behavioral patterns and potential TTS and PTS for individual marine mammals resulting from exposure to pile driving and removal.
As described previously, no serious injury or 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 the number of days of activities.
We note that while these factors can contribute to a basic calculation to provide an initial prediction of takes, additional information that can qualitatively inform take estimates is also sometimes available e.g., previous monitoring results or average group size. Below, we describe the factors considered here in more detail and present the proposed take estimate.
Acoustic Thresholds NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed equated to Level B harassment or to incur PTS of some degree equated to Level A harassment.
Level B 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
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