ASA 126th Meeting Denver 1993 October 4-8

4pAB1. Variability in behavioral reaction thresholds of bowhead whales to man-made underwater sounds.

W. John Richardson

LGL Ltd., Environmental Research Associates, 22 Fisher St., P.O.B. 280, King City, ON L0G 1K0, Canada

Charles R. Greene, Jr.

Greeneridge Sciences, Inc., Santa Barbara, CA 93110

Reactions of bowhead whales, Balaena mysticetus, to actual and simulated oil industry activities were studied in the Beaufort Sea during spring, summer, or autumn from 1980 to 1991. Received levels of oil industry noise that elicited behavioral reactions varied widely, depending partly on the source and characteristics of noise, the activity of whales when exposed, and the physical situation (all levels in dB re: 1 (mu)Pa, 20--1000-Hz band). Reactions to increasing noise levels from approaching boats occurred at received levels as low as 90 dB. In summer, roughly half the bowheads showed avoidance when the received level of steady drillship or dredge noise was about 115 or 20-dB above ambient. Results in spring were similar, but some bowheads tolerated received levels of drilling sound up to 135+ dB if the only available migration route through ice required close approach to a sound projector. In contrast, repetitive pulses from airgun arrays elicited avoidance only at received levels exceeding 150--180 dB (although weaker pulses may elicit subtle behavioral changes). Besides the variability among sound types and situations, there is much whale-to-whale variation in any one situation. No single received level criterion is appropriate to all situations. [Work supported by Minerals Management Service.]