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
Based on the information available, and given the speeds at which Navy vessels operate during the activities they
proposed to conduct in the Hawai'i Range Complex, the protective measures the Navy proposes to employ during an
exercise, and the probable avoidance responses of those animals upon exposure, we think it is highly unlikely that
large whales would routinely accumulate acoustic energy sufficient to cause noise-induced loss of hearing
sensitivity. At the ship speeds involved, collisions would present a greater risk than noise-induced hearing loss; as
we have discussed previously, the Navy’s protective measures, which are designed to detect large whales (and other
objects) in their path to protect the ships from being damaged during a collision, are also likely to prevent large
whales from being exposed to received levels sufficient to cause hearing losses.
5.3.3.2 Acoustic Masking
Marine mammals use acoustic signals for a variety of purposes that differ among species, but include communication
between individuals, navigation, foraging, reproduction, and learning about their environment (Erbe and Farmer
2000, Tyack 2000). Masking, or auditory interference, generally occurs when sounds in the environment are louder
than and of a similar frequency to, auditory signals an animal is trying to receive. Masking, therefore, is a phenomenon
that affects animals that are trying to receive acoustic information about their environment, including sounds
from other members of their species, predators, prey, and sounds that allow them to orient in their environment (the
responses of animals sending acoustic signals are addressed in the next subsection). Masking these acoustic signals
can disturb the behavior of individual animals, groups of animals, or entire populations (Box M of Figure 3
illustrates the potential consequences of acoustic masking).
Richardson et al. (1995b) argued that the maximum radius of influence of an industrial noise (including broadband
low frequency sound transmission) on a marine mammal is the distance from the source to the point at which the
noise can barely be heard. This range is determined by either the hearing sensitivity of the animal or the background
noise level present. Industrial masking is most likely to affect some species’ ability to detect communication calls
and natural sounds (i.e., vocalizations from other members of its species, surf noise, prey noise, etc.; Richardson et
al. 1995).
Sperm whales have been observed to frequently stop echolocating in the presence of underwater pulses produced by
echosounders and submarine sonar (Watkins and Schevill 1975; Watkins et al. 1985). They also stop vocalizing for
brief periods when codas are being produced by other individuals, perhaps because they can hear better when not
vocalizing themselves (Goold and Jones 1995). Sperm whales have moved out of areas after the start of air gun
seismic testing (Davis et al. 1995). Seismic air guns produce loud, broadband, impulsive noise (source levels are son
the order of 250 dB) with “shots” every 15 seconds, 240 shots per hour, 24 hours per day during active tests.
Because they spend large amounts of time at depth and use low frequency sound sperm whales are likely to be
susceptible to low frequency sound in the ocean (Croll et al 1999). Furthermore, because of their apparent role as
important predators of mesopelagic squid and fish, changes in their abundance could affect the distribution and
abundance of other marine species.
The echolocation calls of toothed whales are subject to masking by high frequency sound. Human data indicate low
frequency sound can mask high frequency sounds (i.e., upward masking). Studies on captive odontocetes by Au et
al. (1974, 1985, 1993) indicate that some species may use various processes to reduce masking effects (e.g.,
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