Prediction of potential disturbance of baleen whales by low‐frequency acoustic transients

High‐energy, low‐frequency sound sources are useful tools for geophysical surveying, submarine detection, and long distance acoustic tomography. These sources produce impulsive, narrow‐band and swept‐tonal signals at high levels in the oceanic environment. This study was made to estimate the received level‐time duration characteristics of acoustic transients that can potentially influence baleen whale behavior, the species of particular concern. Findings of acoustic disturbance studies show that continuous sound levels ≥120 dB re: 1 μPa produces ≥50% avoidance by gray and bowhead whales. However, for impulsive airgun sounds of duration ≤0.5 s, effective pulse levels 30 to 50 dB higher are required to produce 50% avoidance for the same species. Little information is available on whale response to intermediate sound durations representative of some sonar and tomography source operations. Consequently, the literature on human response to acoustic transients was examined for response prediction methodologies suitable for application to whale acoustic response. Similarities were found that support the application of a modified equivalent level (L_eq) metric. The exposure level–time duration characteristics obtained from this analysis are preliminary estimates. The predictions should be tested using data obtained in the oceanic environment using representative sources, signals, and whales. [Work supported by the U.S. Navy.]