Passive Autonomous Acoustic Monitoring of Marine Mammals with Seagliders

The U.S. Navy’s use of tactical mid-frequency active sonar has been linked to marine mammal strandings and fatalities (NMFS 2001). These events have generated legal challenges to the Navy’s peacetime use of mid-frequency sonar, and have limited the Navy’s at-sea anti-submarine warfare training time. Beaked whales may be particularly sensitive to mid-frequency sonar. A mobile, persistent surveillance system that could detect, classify and localize beaked whales will help resolve the conflict between the Navy’s need for realistic training of mid-frequency sonar operators and the Navy’s desire to protect marine mammal populations worldwide. Underwater gliders equipped with appropriate acoustic sensors, processing, and detection systems – “passive acoustic monitoring (PAM) gliders” – may offer a partial solution to the problem. The acoustically-equipped SeagliderTM from the Applied Physics Laboratory of the University of Washington (APL-UW) is one such platform. A Seaglider can travel about 20 km/day through the water for a period of weeks to months, dive from the surface to 1000 m and back in a few hours, and use two-way satellite (Iridium) telemetry for data and command transfer. This makes it potentially highly useful for the long-term goal of this project, mitigating impacts of Navy operations on marine mammals.