NMFS Biological Opinion on U.S. Navy training ... - Govsupport.us

FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013
levels between 140 and 195 dB. No monk seals would be exposed to received levels greater than 195 dB associated
with these other training activities.
Of the 171 instances in which <strong>NMFS</strong>’ exposure models identified Hawai’ian monk seals that might be exposed to
mid-frequency active sonar at received levels between 140 and 195 dB, about 100 of those instances would involve
exposures at received levels between 140 and 150 dB and 49 other instances would involve exposures at received
levels between 150 and 160 dB. The balance of the exposures would occur at received levels greater than 160 dB. In
three instances, Hawai’ian monk seals might be exposed at received levels sufficient to temporarily cause noiseinduced
hearing loss.
The information available does not allow us to assess the probable responses of Hawai’ian monk seals after they are
exposed to mid-frequency active sonar transmissions. In the past, we have assumed the Hawai’ian monk seals do not
seem likely to respond to those transmissions because the sonar that would be used during the anti-submarine
warfare exercises transmits at frequencies below hearing thresholds for Hawai’ian monk seals. However, the U.S.
Navy has concluded that at least one of these monk seals might accumulate acoustic energy sufficient to produce a
temporary shift in its hearing sensitivity. Although this is an important conclusion, it does not allow us to assess the
potential fitness consequences of the noise-induced loss in hearing sensitivity because we do not know the
magnitude of the loss in hearing sensitivity (a 3 dB loss in sensitivity versus a 10 dB loss in sensitivity), how long
the animal might be impaired (for example, does the animal recover in minutes, hours, or days), or the frequency
range affected by the loss (that is, what environmental cues might the animal fail to detect).
At a minimum, we would assume that a Hawai’ian monk seal that experienced a loss in hearing sensitivity would be
aware of the impairment and would experience a stress response as a result. We assume that, like the whales
discussed previously, monk seals are likely to try to avoid being exposed to vessel traffic, active sonar, and soundproducing
exercises such as gunnery exercises or sink exercises. We do not have the information necessary to
determine which of the many sounds associated with an exercise is likely to trigger avoidance behavior in Hawai’ian
monk seals (for example, engine noise, helicopter rotors, ordnance discharges, explosions, or some combination of
these), but these relatively shy animals are likely to avoid the general area in which an exercise would occur by
remaining close to a shoreline or on a beach. This avoidance will not prevent monk seals from being exposed to
received levels of active sonar or explosions, but it would prevent monk seals from being exposed at received levels
that would injure a monk seal, cause them physiological distress,or alter their reproductive success.
As discussed in the Environmental Baseline section of this <strong>Opinion</strong>, Hawaiian monk seals have been exposed to U.S.
Navy training activities in the Hawai'i Range Complex, including vessel traffic, aircraft traffic, active sonar, and
underwater detonations, for more than a generation. Although we do not know if more monk seals might have used
the action area or the reproductive success of monk seals in the Hawai'i Range Complex would be higher absent their
exposure to these activities, the rate at which Hawaiian monk seals occur in the Main Hawai'ian Islands suggests that
monk seals numbers in the action area continue to increases despite exposure to earlier training regimes. Although
the U.S. Navy proposes to increase the frequency of some of these activities, we do not believe those increases are
likely to affect the rate at which monk seal counts in the Main Hawai'ian Islands are increasing.
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