Cues, creaks, and decoys: Using underwater acoustics to study sperm whale interactions with the Alaskan black cod longline fishery

For decades off SE Alaska, sperm whales have located longlining fishing vessels and removed, or “depredated,” black cod from the hauls. In 2004, the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) began deploying passive acoustic recorders on longline fishing gear in order to identify acoustic cues that may alert whales to fishing activity. It was found that when hauling, longlining vessels generate distinctive cavitation sounds, which served to attract whales to the haul site. The combined use of underwater recorders and video cameras also confirmed that sperm whales generated “creak/buzz” sounds while depredating, even under good visual conditions. By deploying recorders with federal sablefish surveys over two years, a high correlation was found between sperm whale creak rate detections and visual evidence for depredation. Thus passive acoustics is now being used as a low-cost, remote sensing method to quantify depredation activity in the presence and absence of various deterrents. Two recent developments will be discussed in detail: the development and field testing of acoustic “decoys” as a potential means of attracting animals away from locations of actual fishing activity, and the use of “TadPro” cameras to provide combined visual and acoustic observations of longline deployments. [Work supported by NPRB, NOAA, and BBC.]