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

Report No. 6945
BBN Systems and Technologies Corporation
Bowhead whales circled by an Islander twin-engine aircraft often reacted
when it was at or below 305 m altitude (1000 ft), infrequently reacted when it
was at 457 m, and rarely did so when it was at or above 610 m (Richardson et
al. 1985a,b). Underwater sound levels'produced by this aircraft circling at
various altitudes were reported by Greene (1985). Bowhead sensitivity to
aircraft seemed to vary depending on the activity of the whales and on the
water depth. Whales that were actively Involved in feeding or social
interactions were less sensitive to the aircraft than were those not actively
engaged in one of these activities. For a given aircraft altitude, bowhead
whales seemed to be more sensitive when the water depth was shallow than when
it was deep, possibly because of the known tendency for underwater noise from
an aircraft to propagate farther to the side in shallow than deep water (Urick
1972; Greene 1985).
The sensitivity of gray whales to aircraft noise also varies with whale
activity (Ljungblad et al. 1983, 1987). Migrating gray whales approached by a
UH-IN (Bell 212) helicopter have been reported to react to most approaches at
altitudes below 250 m, some approaches at 305-365 m, and to none of the
approaches at >425 m (SRA 1988). Underwater sounds produced by a Bell 212
passing overhead at various altitudes were recorded and measured by Greene
(1985). Malme et al. (1983, 1984) tested the reactions of migrating gray
whales to playbacks of that recording of Bell 212 sounds, repeated at an
average rate of 3 simulat$d helicopter passes per minute. They found that 50%
of the whales exhibited avoidance responses when the received helicopter noise
level was 120 dB re 1 pPa.
Based on these studies of bowhead and gray whales, plus less detailed
observations of other baleen whales, it is apparent that baleen whales often
react to aircraft overflights by hasty dives, turns, or other behaviors.
Sensitivity seems to depend on the activities and situations of the whales.
There is no indication that single or occasional aircraft overflights cause
long-term displacement of whales.
2.4.2 Ships and boats
Many authors have commented on the reactions or lack of reactions of
marine mammals (especially cetaceans) to ships and boats (reviewed by
Richardson et al. 1989). Most of these reports are anecdotal and lack both
experimental control and measurements of received sound levels. Observations
made from the disturbing vessel itself are difficult to interpret, since some
animals react far enough away such that their detectability is affected by the
presence of the ship. Also, as in the case of reactions to aircraft, it is
usually uncertain whether the animals responded to the noise, sight, or other
stimuli associated with the vessel. The following summary emphasizes the few
studies where more specific information was obtained.
Pinnipeds--Very few quantitative data have been reported on sensitivity
of pinnipeds to vess.els. Reaction distances of walruses hauled out on ice or
land to various types of boats have been reported. Reaction distances varied
widely depending on vessel type, whether the direction of approach was upwind
or downwind, group composition, and whether or not the animals had been
subjected to hunting recently (Fay et al. 1986; Richardson et al. 1989).