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

Report No. 6945
BBN Systems and Technologies Corporation
seemed to be ignored. However, whales that had been exposed repeatedly to
whale-watching vessels sometimes approached those vessels. On the other hand,
whales often moved,away in response to strong or rapidly-changing vessel
noise. Avoidance reactions were especially strong when a boat was directly
approaching (Watkins 1986). All of these phenomena have also been documented
by other workers studying various species of baleen whales.
Reactions of gray whales to vessels have been described by several
workers, but very- little information has been reported (even indirectly) about
the sound levels to which they do and do not react. Migrating gray whales
have been reported to begin to exhibit avoidance when vessels approach within
200-300 m (Wyrick 1954). Summering gray whales may avoid ships that approach
within 350-550 m (Bogoslovskaya et al. 1981). Jones and Swartz (1986) found
that wintering gray whales tend to become less sensitive to boats as the
winter progresses, presumably reflecting a habituation process. They and
other workers also have documented an increasing tendency for gray whales to
approach rather than flee from vessels in recent years. On the other hand,
gray whales ceassd using one wintering lagoon for a number of years when ship
traffic was especially intense there, and returned in later years after ship
traffic had abated (Bryant et al. 1984).
Humpback whales summering in waters of southeast Alaska often swim away
when vessels approach within 2-4 km, and tend to dive when vessels are within
2 km (Baker et al. 1983). Sound levels received by the whales during those
observations were determined by Malme et al. (1982) and Miles and Malme
(1983). Dean et al. (1985) also found evidence that avoidance and other
behavioral changes were common when vessels were underway within several
kilometers of summering humpbacks. However, humpbacks sometimes show little
or no obvious reaction even when vessels are much closer than the typical
reaction distances reported by Baker et al. and Dean et al. Humpbacks are
less likely to react overtly when actively feeding than when resting or
engaged in other activities (Krieger and Wing 1986). Thus, no single
"response thresholdI1 can be defined that will apply to all humpbacks off
southeast Alaska. Reactions of humpbacks wintering in Hawaiian waters to
boats have been studied (e.g. Bauer and Herman 1986), but little information
is available about the reaction distances or the sound levels that cause
reactions in winter.
Reactions of bowhead whales to boats have been determined by experiments
as well as opportunistic observations (Richardson et al. 1985a,b; Koski andc .
Johnson 1987). Bowheads occasionally occur within a few hundred meters of oil
industry and other vessels. However, exper.iments have shown that bowheads
normally begin to swim rapidly away when vessels approach within 2-4 km.
Reactions at even greater distances apparently occur in some situations (Koski
and Johnson 1987). In one disturbance test where noise levels were measured
directly, the noise level 4 km away from the vessel, the approximate distance
at which bowheads began reacting, was only 84 dB re 1 uPa in the 1/3-octave
band of strongest noise; that level was only 6 dB above the background ambient
level in that band (Miles et al. 1987, p 225-231). However, bowheads tolerate
higher vessel noise levels in some situations (Koski and Johnson 1987).. They