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Federal Register / Vol. 86, No. 23 / Friday, February 5, 2021 / Notices
been demonstrated for marine mammals, but studies involving fish 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 fiveday period did not cause any sleep deprivation or stress effects.
Many animals perform vital functions, such as feeding, resting, traveling, and socializing, on a diel cycle 24-hour cycle. Disruption of such functions resulting from reactions to stressors such as sound exposure are more likely to be significant if they last more than one diel cycle or recur on subsequent days Southall et al., 2007.
Consequently, a behavioral response lasting less than one day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival Southall et al., 2007. Note that there is a difference between multi-day substantive 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.
Stress ResponsesAn animals 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 animals 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 animals fitness.
Neuroendocrine stress responses often involve the hypothalamus-pituitaryadrenal system. Virtually all neuroendocrine functions that are affected by stressincluding immune competence, reproduction, metabolism,
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and behaviorare 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.
Auditory MaskingSound can disrupt behavior through masking, or interfering with, an animals 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. Masking occurs when
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the receipt of a sound is interfered with by another coincident sound at similar frequencies and at similar or higher intensity, and may occur whether the sound is natural e.g., snapping shrimp, wind, waves, precipitation or anthropogenic e.g., shipping, sonar, seismic exploration in origin. 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 animals 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.
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 man-made, it may be considered harassment if disrupting behavioral patterns. 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.
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 highfrequency 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, 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
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