Assessing the effects of mid-frequency sonar on cetaceans in Southern California

Mid-frequency active sonar (MFA) is regularly used during naval exercises to provide an acoustic image of subsurface features, including natural and anthropogenic targets. Because MFA is often operated at high intensities, its sounds can be heard for thousands of square kilometers. MFA signal characteristics can vary considerably over its frequency band, 1-10 kHz, which coincidently happens to be in the audible band for most, if not all, marine mammal species. Over the past decade, correlations have been found between MFA and anomalous mass standings of beaked whales (Cox et al., 2006). However, the mechanisms by which MFA affects beaked whales are not well understood.