Acoustic observations of longline depredation by sperm whales

Sperm whales have learned to take sablefish off longline gear in the Gulf of Alaska. Over the past two years the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) has collected biopsy and photo‐ID data concerning longline depredation, via collaboration with local fishermen in Sitka, AK. In 2004, in collaboration with SEASWAP, sets of autonomous acoustic recorders were attached to the anchor lines of several longline deployments, effectively converting the fishing gear into a vertical acoustic array deployed 200 m beneath the surface. The fishing vessels then left the area, leaving the acoustic instruments behind to monitor the region. Several hours later, typically the next morning, each vessel would return and begin hauling in the gear, a procedure that was also recorded by the instruments. In May 2004 an interaction of two sperm whales with the F/V Cobra was recorded. It was found that the animals started producing sounds within 20 min of the longline recovery and continued being extremely vocally active throughout the recovery. Acoustic multipath was exploited to estimate the range and depth of the whales. [Work sponsored by the North Pacific Research Board.]