Using passive acoustics to monitor the presence of marine mammals during Naval exercises

About

During 2008 and 2009, we were able to passive acoustically monitor marine mammals in the presence of U.S. Navy anti-submarine warfare training exercises using mid-frequency tactical sonar. The exercises were conducted in the potential sites of the proposed east coast Undersea Warfare Training Range (USWTR). As part of the monitoring effort for these exercises, up to nine bottom-mounted passive acoustic recorders were deployed in Onslow Bay and Jacksonville USWTR sites. The recorders sampled continuously at 32 kHz and 2 kHz for approximate three weeks. We analyzed these acoustic recordings for marine mammal vocalizations and sonar activity using spectrogram correlation detector. The recordings contain hundreds of odontocete vocalizations, including pilot whales (Globicephala sp.) and sperm whales (Physeter macrocephalus), occurring before during and after the sonar events. A review of a subsample of the acoustic data revealed several instances of unidentified odontocetes apparently mimicking sonar signals with frequency modulated whistles of similar frequencies. Ongoing and future efforts will include deploying the recorders at the Jacksonville site in a tighter configuration and synchronizing them in time to localize vocalizations. This effort will provide insight on the proximity and movement of marine mammals in conjunction with Navy exercises occurring in area. These recorders yield important information about the presence and vocal activity of odontocetes during these naval exercises.