Three‐dimensional passive acoustic tracking of sperm whale behavior with widely separated vertical arrays in the Gulf of Alaska

The Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) was started in 2002 to study the increasing depredation encounters between sperm whales and longline fishermen near Sitka, Alaska. In 2005, the acoustic component of the study included passive acoustic data from four autonomous recorders attached to the anchor lines of two longlines spaced 3 miles apart, essentially turning them into temporary vertical arrays and allowing the monitoring of sperm whale vocal activity during fishing operations. Although the use of multipath arrival information from recorded sperm whale clicks has been a standard procedure for range‐depth tracking, with the added knowledge of azimuthally dependent bathymetry relative to an array, a three‐dimensional track of whale motion can be obtained from the same multipath information. The evolution of multipath arrival patterns is matched to range‐, depth‐, and azimuth‐dependent modeled arrival patterns to generate an estimate of whale motion. The use of an acoustic propagation model can also account for all waveguide physics such as interaction with range‐dependent bathymetry and ray refraction. Acoustic tracking results concurrent with whale encounters will be presented and compared to visual sightings.