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Federal Register / Vol. 86, No. 134 / Friday, July 16, 2021 / Proposed Rules Porpoise Dalls PorpoiseThis section builds on the broader odontocete discussion above and brings together the discussion of the different types and amounts of take that Dalls porpoise are likely to incur, the applicable mitigation, and the status of the species to support the negligible impact determinations for each species.
Some Level A harassment by PTS is anticipated annually 49 takes, see Table 31.
In Table 31 above, we indicate the total annual numbers of take by Level A
and Level B harassment for Dalls porpoise, and a number indicating the instances of total take as a percentage of the abundance within the PMSR Study Area. Note also that, for Dalls porpoise and all odontocetes, the abundance within the PMSR Study Area represents only a portion of the species abundance.
As discussed above, the majority of takes by Level B harassment by behavioral disturbance of odontocetes, and thereby Dalls porpoise, is expected to be in the form of low to moderate severity of a shorter duration. As discussed earlier in this section, we anticipate more severe effects from takes when animals are exposed to higher received levels or for longer durations.
Occasional milder Level B harassment by behavioral disturbance, as is expected here, is unlikely to cause longterm consequences for either individual animals or populations.
We note that Dalls porpoise, as HFsensitive species, have a lower PTS
threshold than all other groups and therefore are generally likely to experience larger amounts of TTS and PTS. NMFS accordingly has evaluated slightly higher numbers of take for these species than most odontocetes some of which would have zero takes of TTS/
PTS. Therefore, even though the number of TTS and PTS takes are higher than for other odontocetes, any TTS or PTS is expected to be at a low to moderate level and for all of the reasons described above, TTS and PTS takes are not expected to impact reproduction or survival of any individual.
Dalls porpoise are not listed under the ESA, and there are no known biologically important areas identified for these species in the PMSR Study Area. The CA/OR/WA stock is found in the PMSR Study Area. There is no information on trends for this species within the PMSR Study Area. Dalls porpoise will benefit from the mitigation measures described earlier in the Proposed Mitigation Measures section.
Regarding the magnitude of Level B
harassment takes TTS and behavioral disruption, the number of estimated
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total instances of take compared to the abundance is less than 3 percent for Dall porpoise in the PMSR Study Area Table 31. Regarding the severity of those individual Level B harassment takes by behavioral disruption, we have explained that the duration of any exposure is expected to be between seconds and minutes i.e., relatively short duration. Regarding the severity of TTS takes, they are expected to be low to moderate level, of short duration, and mostly not in a frequency band that would be expected to interfere with communication and, therefore, the associated lost opportunities and capabilities are not at a level that will impact reproduction or survival. Dalls porpoise could be taken by a small amount of PTS annually, of likely low to moderate severity as described previously. A small permanent loss of hearing sensitivity PTS may include some degree of energetic costs for compensating or may mean some small loss of opportunities or detection capabilities, but at the expected degree the estimated takes by Level A
harassment takes by PTS for Dalls porpoise are unlikely to impact behaviors, opportunities, or detection capabilities to a degree that will interfere with reproductive success or survival of any individuals, let alone affect annual rates of recruitment or survival.
Altogether, Dalls porpoise are not listed under the ESA and there are no known population trends for the CA/
OR/WA stock. Our analysis suggests that a small portion of the stock will be taken, and disturbed at a low to moderate level, with those individuals likely not disturbed on more than one day or so a year. No serious injury or mortality is anticipated or proposed for authorization. The low magnitude and low to moderate severity of harassment effects is not expected to result in impacts on the reproduction or survival of any individuals, let alone have impacts on annual rates of recruitment or survival. Therefore, the total take will not adversely affect this species through impacts on annual rates of recruitment or survival. Some individuals are estimated to be taken by PTS of likely low to moderate severity. A small permanent loss of hearing sensitivity PTS may include some degree of energetic costs for compensating or may mean some small loss of opportunities or detection capabilities, but at the expected scale the estimated takes by Level A harassment by PTS are unlikely to impact behaviors, opportunities, or detection capabilities to a degree that would interfere with reproductive
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success or survival of any individuals, let alone affect annual rates of recruitment or survival. For these reasons, we have preliminarily determined, in consideration of all of the effects of the Navys activities combined, that the proposed take will have a negligible impact on Dalls porpoise.
Small Whales and DolphinsThis section builds on the broader discussion above and brings together the discussion of the different types and amounts of take that different small whale and dolphin species are likely to incur, the applicable mitigation, and the status of the species to support the negligible impact determinations for each species.
In Table 31 above, we indicate for each species the total annual numbers of take by Level A and Level B harassment for dolphins and small whales, and a number indicating the instances of total take as a percentage of abundance in the PMSR Study Area. Note also that, for dolphins and small whales, the abundance within the PMSR Study Area represents only a portion of the respective species abundance.
The majority of takes by Level B
harassment are expected to be in the form of low severity of a shorter duration. Occasional milder Level B
harassment by behavioral disturbance, as is expected here, is unlikely to cause long-term consequences for either individual animals or populations that have any effect on reproduction or survival. Limited Level A harassment PTS is anticipated and proposed for six species Long and short-beaked common dolphins, bottlenose dolphin, Rissos dolphin, Pacific white-sided dolphin, and Northern right whale dolphin.
Research and observations show that if delphinids are exposed to sounds they may react in a number of ways depending on their experience with the sound source and what activity they are engaged in at the time of the acoustic exposure. Delphinids may not react at all until the sound source is approaching within a few hundred meters, such as with a ship with hullmounted sonar, to within a few kilometers, depending on the environmental conditions and species.
Some dolphin species the more surfacedwelling taxatypically those with dolphin in the common name, such as bottlenose dolphins, spotted dolphins, spinner dolphins, roughtoothed dolphins, etc., but not Rissos dolphins, especially those residing in more industrialized or busy areas, have demonstrated more tolerance for disturbance and loud sounds and many of these species are known to approach
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