Voglio sapere a riguardo di…

jbell on DSKJLSW7X2PROD with PROPOSALS2

Federal Register / Vol. 86, No. 134 / Friday, July 16, 2021 / Proposed Rules severity of the impacts on the affected individual, which can range from minor to more severe. Explosives are generally referenced as broadband because of the various frequencies. Table 31 indicates the number of takes by TTS that may be incurred by different species from exposure to explosives. The TTS
sustained by an animal is primarily classified by three characteristics:
1. FrequencyAvailable data of midfrequency hearing specialists exposed to midor high-frequency sounds; Southall et al., 2007 suggest that most TTS
occurs in the frequency range of the source up to one octave higher than the source with the maximum TTS at 12
octave above. TTS from explosives would be broadband.
2. Degree of the shift i.e., by how many dB the sensitivity of the hearing is reducedGenerally, both the degree of TTS and the duration of TTS will be greater if the marine mammal is exposed to a higher level of energy which would occur when the peak dB level is higher or the duration is longer. The threshold for the onset of TTS was discussed previously in this proposed rule. An animal would have to approach closer to the source or remain in the vicinity of the sound source appreciably longer to increase the received SEL. The sound resulting from an explosive detonation is considered an impulsive sound and shares important qualities i.e., short duration and fast rise time with other impulsive sounds such as those produced by air guns. Given the anticipated duration and levels of sound exposure, we would not expect marine mammals to incur more than relatively low levels of TTS i.e., single digits of sensitivity loss.
3. Duration of TTS recovery time In the TTS laboratory studies as discussed in the Potential Effects of Specified Activities on Marine Mammals and their Habitat section of the proposed rule, some using exposures of almost an hour in duration or up to 217 SEL, almost all individuals recovered within 1 day or less, often in minutes, although in one study Finneran et al., 2007 recovery took 4
days. For the same reasons discussed in the Preliminary Analysis and Negligible Impact DeterminationDiel Cycle section, and because of the short distance animals would need to be from the sound source, it is unlikely that animals would be exposed to the levels necessary to induce TTS in subsequent time periods such that their recovery is impeded.
The TTS takes would be the result of exposure to explosive detonations broad-band. As described above, we expect the majority of these takes to be
VerDate Sep<11>2014

17:54 Jul 15, 2021

Jkt 253001

in the form of mild single-digit, shortterm minutes to hours TTS. This means that for one time a year, for several minutes, a taken individual will have slightly diminished hearing sensitivity slightly more than natural variation, but nowhere near total deafness. The expected results of any one of these small number of mild TTS
occurrences could be that 1 it does not overlap signals that are pertinent to that animal in the given time period, 2 it overlaps parts of signals that are important to the animal, but not in a manner that impairs interpretation, or 3 it reduces detectability of an important signal to a small degree for a short amount of timein which case the animal may be aware and be able to compensate but there may be slight energetic cost, or the animal may have some reduced opportunities e.g., to detect prey or reduced capabilities to react with maximum effectiveness e.g., to detect a predator or navigate optimally. However, given the small number of times that any individual might incur TTS, the low degree of TTS
and the short anticipated duration, and the low likelihood that one of these instances would occur across a time period in which the specific TTS
overlapped the entirety of a critical signal, it is unlikely that TTS of the nature expected to result from the Navy activities would result in behavioral changes or other impacts that would impact any individuals of any hearing sensitivity reproduction or survival.
Auditory Masking or Communication Impairment The ultimate potential impacts of masking on an individual if it were to occur are similar to those discussed for TTS, but an important difference is that masking only occurs during the time of the signal, versus TTS, which continues beyond the duration of the signal.
Fundamentally, masking is referred to as a chronic effect because one of the key potential harmful components of masking is its durationthe fact that an animal would have reduced ability to hear or interpret critical cues becomes much more likely to cause a problem the longer it is occurring. Also inherent in the concept of masking is the fact that the potential for the effect is only present during the times that the animal and the source are in close enough proximity for the effect to occur and further, this time period would need to coincide with a time that the animal was utilizing sounds at the masked frequency. As our analysis has indicated, because of the sound sources primarily involved in this rule, we do not expect the exposures with the
PO 00000

Frm 00047

Fmt 4701

Sfmt 4702

37835

potential for masking to be of a long duration. Masking is fundamentally more of a concern at lower frequencies, because low frequency signals propagate significantly further than higher frequencies and because they are more likely to overlap both the narrower lowfrequency calls of mysticetes, as well as many non-communication cues, such as sounds from fish and invertebrate prey and geologic sounds that inform navigation. Masking is also more of a concern from continuous sources versus intermittent where there is no quiet time between a sound source within which auditory signals can be detected and interpreted. Explosions introduce low-frequency, broadband sounds into the environment, which could momentarily mask hearing thresholds in animals that are nearby, although sounds from explosions last for only a few seconds at most. Masking due to these short duration detonations would not be significant. Activities that have multiple, repeated detonations, such as some naval gunfire activities, could result in masking for mysticetes near the target impact area over the duration of the event. Effects of masking are only present when the sound from the explosion is present, and the effect is over the moment the sound is no longer detectable. Therefore, short-term exposure to the predominantly intermittent explosions are not expected to result in a meaningful amount of masking. For the reasons described here, any limited masking that could potentially occur from explosives would be minor and short-term and intermittent. Long-term consequences from physiological stress due to the sound of explosives would not be expected. In conclusion, masking is more likely to occur in the presence of broadband, relatively continuous noise sources such as from vessels; however, the duration of temporal and spatial overlap with any individual animal and the spatially separated sources that the Navy uses would not be expected to result in more than short-term, low impact masking that would not affect reproduction or survival of individuals.
Auditory Injury Permanent Threshold Shift Table 31 indicates the number of individuals of each species for which Level A harassment in the form of PTS
resulting from exposure to or explosives is estimated to occur. The number of individuals to potentially incur PTS
annually from explosives for each species ranges from 0 to 49 49 is for Dalls porpoise, but is more typically 0
or 1. As described previously, no
E:FRFM16JYP2.SGM

16JYP2