The influence of sound propagation conditions on the behavioral response of whales to underwater industrial noise

Abstract

Results of recent studies involving gray, humpback, and bowhead whales show that whales tend to avoid areas with high underwater noise levels. Data obtained from whale behavioral observations during controlled exposure to representative industrial noise sources permit determination of the probability of avoidance Pa of the source region as a function of the noise level Ln. The zone of influence of a source may be defined as the region where Pa > 0.5. While the Ln required to produce this degree of avoidance has been found to depend on whale species and source type, some generalizations may be made. For low-frequency continuous noise, 50% of the whales exposed have been observed to avoid regions where the overall Ln is higher than 115 to 125 dB (re: 1 μPa). Sound transmission conditions at a specific site determine the distance from the source, where Ln falls below the Pa = 0.5 criterion level. The zone of influence thus has been found to vary considerably for the test sites investigated. For example, a drillship operating at a test site off the Alaskan Beaufort coast has an estimated zone of influence radius of 4 km, but, off the coast of California, the estimated zone of influence radius is reduced to 1 km. [Work sponsored by the Minerals Management Service.]