False killer whale (Pseudorca crassidens) echolocation and acoustic disruption : implications for longline bycatch and depredation

Author Posting. © The Authors, 2009. This article is posted here by permission of NRC Research Press for personal use, not for redistribution. The definitive version was published in Canadian Journal of Zoology 87 (2009): 726-733, doi:10.1139/Z09-061.False killer whales (Pseudorca crassidens (Owen, 1846)) depredate fish caught by the North Pacific pelagic longline fishery, resulting in loss of target species catch and the whales themselves becoming bycaught. This incidental take of false killer whales exceeds sustainable levels. In an effort to address a potential solution to reducing this depredation and bycatch, we tested an acoustic device designed to deter false killer whales from approaching longlines by reducing the whales’ echolocation performance capabilities. The device produced a series of complex, broadband signals (1–250 kHz) at high intensity levels (up to 182 dB). In the experiment, a trained false killer whale was asked to detect a target in the presence or absence of the acoustic device. Baseline performance capabilities were 95% correct responses. Initially, the device reduced the whale’s echolocation performance to chance levels. However, subsequent sessions demonstrated improvement in echolocation performance up to 85%. This improvement was likely a result of behaviorally adapting to the task and a decrease in the source level of the echolocation “disruptor”. The results underscore the challenges in using acoustic devices to reduce depredation and bycatch, and demonstrate the need for concern regarding anthropogenic noise levels and effects on odontocete echolocation capabilities.We gratefully acknowledge the Western Pacific Regional Fishery Management Council for their encouragement and funding of the project, as well as Rick van Lent and Wouter van Dam of SaveWave for lending us the Long-line Saver. Additional funding came from Robert Gisiner of the US Office of Naval Research for research grant No. N00014.05.1.07.38 to P.N