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

Report No. 6945
BBN,Systems and Technologies Corporation
After such an incident, they may return to the haul out site within a few
minutes, or may remain away for several hours or until the next day. In a
small minority of the observations that have been reported, pups have been
injured or killed by trampling when pinnipeds rushed into the sea, or as a
result of abandonment after such incidents. In a study of harbor seals,
Johnson (1977) found that light aircraft flying overhead at altitudes below
120 m (400 ft) nearly always caused seals to vacate the haul-out beaches;
reactions to aircraft at 120-305 m altitude were more variable . Osborn ( 1985)
found that aircraft flying below 150 m altitude over the same species caused
alert reactions and, in a minority of cases, rapid movement into the water.
California sea lions and elephant seals may be less sensitive. than harbor
seals (Bowles and Stewart 1980). The sensitivity of walruses to aircraft
varies widely (e.g., Fay et al. 1986), but walruses that are hauled out often
become alert or move into the water when aircraft approach within 1-14 km at
altitudes varying from 150 to 1500 m (Salter 1979). Among the other Alaskan
species, Steller sea lions, fur seals, ringed seals, spotted seals and bearded
seals often react to aircraft, but specific response thresholds have not been
reported (Johnson et al. 1989; Richardson et al. 1989).
In general, pinnipeds hauled out on land or ice react to airborne sound
from aircraft by becoming alert and, in many cases, by rushing into the
water. They tend to be more sensitive to low-flying than to high-flying
aircraft, to aircraft that are nearly overhead vs. those far to the side, and
to abruptly changing sounds than to steady sounds. There are some indications
that reactions to helicopters may be more severe than those to fixed-wing
aircraft at similar distances. However, the lack of data on sound exposure
levels makes these reports difficult to evaluate and impossible to quantify.
Sensitivity apparently can vary according to stage of the breeding cycle.
Partial habituation probably occurs under some conditions.
All available data on reactions of pinnipeds to aircraft involve animals
that are hauled out. There are no specific data on reactions of pinnipeds at
the surface of the water or underwater to noise from passing aircraft.
Toothed Whales--Toothed whales exposed to close approaches by aircraft
sometimes dive abruptly or swim away from the aircraft track. Aside from the
difficulty in being sure whether these behaviors were really attributable to
the aircraft, we are not aware of any attempts to measure or estimate the
received levels of aircraft noise that elicited these responses. Several
workers have reported behavioral reactions of white whales to aircraft and
helicopters flying overhead at altitudes ranging up to 500 m (e.g., Bel'kovich
1960). However, in other situations some workers have reported no detectable
reaction to aircraft at altitudes as low as 150 m (Fraker and Fraker 1979).
Data on reactions of other species of toothed whales to aircraft are even more
meagre. Sperm whales reportedly showed no obvious reaction to a light twin
engined aircraft circling overhead at 152 m altitude (Gambell 1968). Beaked
whales seem to be especially sensitive to aircraft (Doh1 et al. 1983).
Baleen Whales--Reactions of bowhead and gray whales to aircraft and/or
certain aircraft noises have been examined more systematically, and additional
anecdotal evidence is available for certain other species.