Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technologies Corporation
are especially sensitive to vessel noise when the vessel is heading directly
toward the whale.
Generally similar although less detailed observations have been reported
for a variety of other baleen whale species (Richardson et al. 1983, 1989).
2.4.3 Seismic exploration
Marine seismic exploration under open water conditions produces impulsive
underwater sounds with source levels that greatly exceed those of other
routine activities.associated with offshore oil and gas exploration and
development.
Pinnipeds--Reactions of pinnipeds to impulsive seismic noise have not
been studied. Several species of pinnipeds are known to habituate to strong
underwater noises, sometimes impulsive, that are often used in attempts to
deter seals and sea lions from feeding on fish in nets or fish farms (e.g.
Mate and Harvey 1987). More specific information is available about the
reactions of ringed seals to on-ice seismic exploration via the Vibroseis
technique, which uses strong frequency-sweeps rather than impulsive sounds.
Vibroseis operations in winter and spring can cause localized movements of
ringed seals away from seismic lines. However, this effect is detectable only
within a short distance, possibly about 150 m (Kelly et al. 1986), even though
Vibroseis noise can be measured in ringed seal lairs at distances up to about
2-6 km (Holliday et al. 1984).
Toothed Whales--Reactions of toothed whales to seismic noise also have
not been studied systematically. The apparent ineffectiveness of small
explosive charges in scaring white whales from an Alaskan salmon river (Fish
and Vania 1971) may indicate a low degree of sensitivity to low-frequency
impulsive noise. Hearing sensitivity of toothed whales is best at frequencies
of several thousand Hertz (Awbrey et al. 1988), whereas almost all of the
energy in seismic pulses is at frequencies below 500 Hz. Thus, it is possible
that toothed whales are relatively insensitive .to seismic pulses.
Baleen Whales--The behavior of several species of baleen whales exposed
to seismic pulses has been observed opportunistically, and reactions of
bowhead, gray and humpback whales to seismic pulses have been studied during
controlled experiments. -
Migrating gray whales showed definite avoidance reactions and other
behavioral changes when exposed to seismic pulses with received levels exceeding
about 160 dB re 1 uPa. The received levels at which lo%, 50% and 90% of
the whales exhibited avoidance were estimated to be 164, 170 and 180 dB. Such
levels were estimated to occur 3.6, 2.5 and 1.2 km broadside from an airgun
array operating off the California coast. (Reaction distances could be
greater in the Bering Sea and especially the Beaufort Sea because sound
attenuates less rapidly with increasing distance in those areas than off
California--Miles et al. 1987.) Less consistent and less dramatic reactions
were suspected to occur at received levels of 140-160 dB, which would occur
considerably farther away (Malme et al. 1983, 1984). Results of less
extensive tests on gray whales summering in the Bering Sea gave results