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Federal Register / Vol. 86, No. 122 / Tuesday, June 29, 2021 / Notices
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, 2009; 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 Houser and Moore, 2014. Masking can be tested directly in captive species e.g., Erbe, 2008, but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild e.g., Branstetter et al., 2013.
Masking affects both senders and receivers of acoustic signals and can potentially have long-term chronic effects on marine mammals at the population level as well as at the individual level. Low-frequency ambient sound levels have increased by as much as 20 dB more than three times in terms of SPL in the worlds ocean from pre-industrial periods, with most of the increase from distant commercial shipping Hildebrand, 2009. All anthropogenic sound sources, but especially chronic and lower-frequency signals e.g., from vessel traffic, contribute to elevated ambient sound levels, thus intensifying masking.
Potential Effects of the AKDOT&PFs ActivityAs described previously, the AKDOT&PF proposes to conduct pile driving, including impact and vibratory driving inclusive of DTH. The effects of pile driving on marine mammals are dependent on several factors, including the size, type, and depth of the animal;
the depth, intensity, and duration of the pile driving sound; the depth of the water column; the substrate of the habitat; the standoff distance between the pile and the animal; and the sound propagation properties of the environment. With both types, it is likely that the pile driving could result in temporary, short-term changes in an animals typical behavioral patterns and/or avoidance of the affected area.
These behavioral changes may include Richardson et al., 1995: Changing durations of surfacing and dives, number of blows per surfacing, or
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moving direction and/or speed;
reduced/increased vocal activities;
changing/cessation of certain behavioral activities such as socializing or feeding; visible startle response or aggressive behavior such as tail/fluke slapping or jaw clapping; avoidance of areas where sound sources are located;
and/or flight responses.
The biological significance of many of these behavioral disturbances is difficult to predict, even if the detected disturbances appear minor, and the consequences of behavioral modification could be expected to be biologically significant if the change affects growth, survival, or reproduction. However, significant behavioral modifications that could lead to effects on growth, survival, or reproduction, such as drastic changes in diving/surfacing patterns or significant habitat abandonment are extremely unlikely to result from this activity or in this area i.e., shallow waters in modified industrial areas.
Whether impact or vibratory driving, sound sources would be active for relatively short durations, with little potential for masking. Also, the frequencies output by pile driving activity are lower than those used by most species expected to be regularly present for communication or echolocation. We expect insignificant impacts from masking, and any masking event that could possibly rise to Level B harassment under the MMPA would occur concurrently within the zones of behavioral harassment already estimated for vibratory and impact pile driving, and which have already been taken into account in the exposure analysis.
Anticipated Effects on Marine Mammal Habitat The proposed activities would not result in permanent impacts to habitats used directly by marine mammals. The project would occur within the same footprint as existing marine infrastructure. The nearshore and intertidal habitat where the project would occur is an area of relatively high marine vessel traffic. Most marine mammals do not generally use the area within the footprint of the project area.
The proposed activities may have potential short-term impacts to food sources such as forage fish. The proposed activities could also affect acoustic habitat see masking discussion above, but meaningful impacts are unlikely. There are no known foraging hotspots, or other ocean bottom structures of significant biological importance to marine mammals present in the marine waters in the vicinity of
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the project area. Therefore, the main impact issue associated with the proposed activity would be temporarily elevated sound levels and the associated direct effects on marine mammals, as discussed previously. The most likely impact to marine mammal habitat occurs from pile driving effects on likely marine mammal prey i.e., fish near where the piles are installed. Impacts to the immediate substrate during installation and removal of piles are anticipated, but these would be limited to minor, temporary suspension of sediments, which could impact water quality and visibility for a short amount of time, but which would not be expected to have any effects on individual marine mammals or the prey for marine mammals. Impacts to substrate are therefore not discussed further.
Effects to PreySound 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.

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