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Federal Register / Vol. 86, No. 171 / Wednesday, September 8, 2021 / Proposed Rules 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 projects in the area.

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Auditory Masking Sound 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 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, aircraft, sonar 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 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.

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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 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. 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.
Anticipated Effects on Marine Mammal Habitat The only direct habitat modification associated with the proposed activity is the restoration of the existing light station structures. Indirect effects of the activities on nearby feeding or haulout habitat are not expected. Increased noise levels are not likely to affect acoustic habitat or adversely affect marine mammal prey in the vicinity of the project area because source levels are low, transient, well away from the water, and do not readily transmit into the water. The Society would remove all waste, discarded materials and equipment from the island after each visit. Thus, NMFS does not expect that the proposed activity would have any effects on marine mammal habitat and
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NMFS expects that there will be no longor short-term physical impacts to pinniped habitat on NWSR.
Estimated Take This section provides an estimate of the number of incidental takes proposed for authorization through this rulemaking, 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 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 B
harassment only, in the form of disruption of behavioral patterns for individual marine mammals resulting from exposure to helicopter operations and lighthouse maintenance activities.
Based on the nature of the activity, Level A harassment is neither anticipated nor proposed to be authorized. As discussed earlier, behavioral Level B harassment is limited to movement and flushing, defined by the disturbance scale of pinniped responses to in-air sources to determine take Table 2. Furthermore, no mortality is anticipated or proposed to be authorized for this activity. Below we describe how the take is estimated.
Marine Mammal Occurrence In this section we provide the information about the presence, density, or group dynamics of marine mammals that will inform the take calculations.
The Societys monitoring efforts reported zero marine mammals present on NWSR, in 2010. Furthermore, operations were not conducted in the years 2013 through 2016; thus, monitoring was not conducted. No visits occurred in 2020. Visits have occurred in all other years since 2010.
Steller sea lions were first reported during restoration trips conducted in April 9 and November 350, with a maximum of 155/day of 2011 St.
George Reef Lighthouse Preservation Society SGRLPS 2011. Zero observations of Steller sea lions were reported during the one 2012 restoration trip and three 2017 trips conducted
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