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Federal Register / Vol. 86, No. 134 / Friday, July 16, 2021 / Proposed Rules
or feeding, or avoidance that also would be expected to continue for the duration of an exposure. The Navy then compiled the available data indicating the received sound levels and distances from the sources when those responses have occurred to predict how many instances of Level B harassment by behavioral disturbance occur in a day.
Take estimates alone do not provide information regarding the potential fitness or other biological consequences of the reactions on the affected individuals. NMFS therefore considers the available activity-specific, environmental, and species-specific information to determine the likely nature of the modeled behavioral responses and the potential fitness consequences for affected individuals.
In the range of potential behavioral effects that might be expected to be part of a response that qualifies as an instance of Level B harassment by behavioral disturbance which by nature of the way it is modeled/counted, occurs within one day, the less severe end might include exposure to comparatively lower levels of a sound, at a detectably greater distance from the animal, for a few or several minutes. A
less severe exposure of this nature could result in a behavioral response such as avoiding an area that an animal would otherwise have chosen to move through or feed in for some amount of time or breaking off one or a few feeding bouts.
More severe effects could occur when the animal gets close enough to the source to receive a comparatively higher level, or is exposed intermittently to different sources throughout a day. Such effects might result in an animal having a more severe flight response and leaving a larger area for a day or more or potentially losing feeding opportunities for a day. However, such severe behavioral effects are expected to occur infrequently.
The majority of Level B harassment takes are expected to be in the form of milder responses i.e., lower-level exposures that still rise to the level of take of a generally shorter duration. We anticipate more severe effects from takes when animals are exposed to higher received levels or at closer proximity to the source. However, depending on the context of an exposure e.g., depth, distance, if an animal is engaged in important behavior such as feeding, a behavioral response can vary across species and individuals within a species. Specifically, given a range of behavioral responses that may be classified as Level B harassment, to the degree that higher received levels are expected to result in more severe behavioral responses, only a smaller
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percentage of the anticipated Level B
harassment from Navy activities would be expected to potentially result in more severe responses see the Group and Species-Specific Analyses section below for more detailed information. To fully understand the likely impacts of the predicted/authorized take on an individual i.e., what is the likelihood or degree of fitness impacts, one must look closely at the available contextual information, such as the duration of likely exposures and the likely severity of the exposures e.g., whether they will occur for a longer duration over sequential days or the comparative sound level that will be received.
Ellison et al. 2012 and Moore and Barlow 2013, among others, emphasize the importance of context e.g., behavioral state of the animals, distance from the sound source in evaluating behavioral responses of marine mammals to acoustic sources.
Diel Cycle Many animals perform vital functions, such as feeding, resting, traveling, and socializing on a diel cycle 24-hour cycle. Behavioral reactions to noise exposure, when taking place in a biologically important context, such as disruption of critical life functions, displacement, or avoidance of important habitat, are more likely to be significant if they last more than one diel cycle or recur on subsequent days Southall et al., 2007. For example, Henderson et al.
2016 found that ongoing smaller scale events had little to no impact on foraging dives for Blainvilles beaked whale, while multi-day training events may decrease foraging behavior for Blainvilles beaked whale ManzanoRoth et al., 2016. There are very few multi-day training events proposed for PMSR.
Durations of Navy activities utilizing explosives vary and are fully described in Appendix A PMSR Scenarios Descriptions of the 2020 PMSR DEIS/
OEIS. The PMSR has activity occurring daily, but tests range from just a single missile launch or multiple launches, or may only be a captive carry where no munitions are air launched but the test is to determine the aircrafts ability to function properly with a missile on board, to a single or dual target launch from SNI, or a CSSQT where the ships capability is tested by how it performs with a multiple weapons systems against a target. Also, while some tests are planned well in advance, some portions of or the entire test may be cancelled due to weather or atmospheric conditions, sea state, a particular system or support infrastructure dysfunction, or many other factors. Most proposed
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explosive detonation events are scheduled to occur over a short duration one to a few hours; however, the explosive detonation component of the activity only lasts for seconds. Although explosive detonation events may sometimes be conducted in the same general areas repeatedly, because of their short duration and the fact that they are in the open ocean and animals can easily move away, it is similarly unlikely that animals would be exposed for long, continuous amounts of time, or demonstrate sustained behavioral responses. All of these factors make it unlikely that individuals would be exposed to the exercise for extended periods or on consecutive days.
Assessing the Number of Individuals Taken and the Likelihood of Repeated Takes As described previously, Navy modeling uses the best available science to predict the instances of exposure above certain acoustic thresholds, which are quantified as harassment takes. However, these numbers from the model do not identify whether and when the enumerated instances occur to the same individual marine mammal on different days, or how any such repeated takes may impact those individuals. One method that NMFS can use to help better understand the overall scope of the impacts is to compare the total instances of take against the abundance of that species or stock if applicable. For example, if there are 100 estimated harassment takes in a population of 100, one can assume either that every individual will be exposed above acoustic thresholds in no more than one day, or that some smaller number will be exposed in one day but a few individuals will be exposed multiple days within a year and a few not exposed at all. However, in this proposed rule the percentage of takes relative to abundance is under five percent for all species and in most cases less than one percent, meaning that it is less likely that individuals of most species will be taken multiple times, although we note that pinnipeds that haul out regularly in areas where activities are regularly conducted are more likely to be taken on multiple days.
Temporary Threshold Shift NMFS and the Navy have estimated that some species and stocks of marine mammals may sustain some level of TTS from explosive detonations. In general, TTS can last from a few minutes to days, be of varying degree, and occur across various frequency bandwidths, all of which determine the
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