Midfrequency sound propagation in beaked whale environments

Abstract

Recent mass strandings of beaked whales (Ziphiidae, Cetacea) coinciding with the use of midfrequency range (1–10 kHz) active sonar have caused speculation about the potentially adverse effects of these sound sources. Particular questions of the research and regulatory communities concern whether beaked whale sensitivity to midfrequency sound exposure is influenced by oceanographic characteristics present at the time of the mass stranding events. This study investigated the interaction between beaked whale habitat characteristics and the nature of a midfrequency signal by analyzing the oceanographic factors affecting underwater acoustic propagation. Three types of model sites were selected from five specific geographical locations where beaked whales have been regularly recorded or where a mass stranding event has been reported. A ray-trace acoustic propagation model was used to generate transmission loss for a 3-kHz signal over a representative 60-km transect at each locality. Model outputs visually demonstrated how the combination of site/event-specific oceanographic characteristics affects the sound propagation of a moving source. A parametric sensitivity comparison and statistical analysis were conducted to identify influential factors between environmental parameters, source depth, and the resulting transmission loss. Major findings of this study as well as future research direction are discussed. [Research supported by NAVSEA.]