The US Navy has been collecting data on the presence of marine mammals in conjunction with Navy exercises involving active sonar activity. During July 2008, the US Navy performed antisubmarine warfare training exercises in Onslow Bay, North Carolina, using midfrequency active sonar (1–10 kHz). The exercises were conducted in one of the potential sites of the proposed east coast Undersea Warfare Training Range (USWTR). As part of the monitoring effort for these exercises, five bottom-mounted passive acoustic recorders were deployed in Onslow Bay. The recordings contain hundreds of odontocete vocalizations, including Globicephala sp. (pilot whales) and Physeter macrocephalus (sperm whales), occurring before, during, and after the sonar events.

Balaenoptera acutorostrata (minke whale) is a small and elusive baleen whale that is rarely sighted in the tropical waters of the North Pacific Ocean. During winter and spring, complex sounds called ”boings” are frequently detected around the Hawaiian Islands and other Pacific island regions (Norris et al. 2009 ; Thompson and Friedl 1982 ) . Although boings were described over 45 years ago (Wenz 1964 ) , they were not attributed to minke whales until very recently (Rankin and Barlow 2005 ) . Sightings of Balaenoptera acutorostrata are uncommon in tropical and subtropical waters; however, boings are frequently detected around the Hawaiian Islands using seafloor hydrophones and from hydrophone arrays towed from research vessels. Even today, very little is known about acoustic behaviors and ecology of Balaenoptera acutorostrata. The long-term objective of this research effort is to improve our understanding of the acoustic ecology and behavior of Balaenoptera acutorostrata in their breeding habitat.