Acoustic systems to mitigate predation on tuna longline hooked fish by large marine animals - an Australian perspective of the global problem

• Main Authors: McPherson, Geoff, Turner, Phil, McPherson, Craig, Cato, Douglas
• Format: Conference Object
• Language: unknown
• Published: 2003
• Subjects: Killer Whale
• Online Access: https://researchonline.jcu.edu.au/10284/1/10284_McPherson_et_al_2003.pdf

Marine mammal (e.g. false killer whale) predation on Coral Sea longline catch threatens the viability of the fisher through direct removal of bait and fish from lines, or predator induced non-biting behaviour of the tuna species. Predation may be a learned response, and appears to be getting worse. Accidental mammal hookups on the gear are rare. An acoustic strategy is being developed to mitigate predation. Echlocation may be the dominant acoustic component of terminal stage predation. Acoustic devices are being modified to record the time of onset of stage predation. To assess the effectiveness of the acoustic (and mechanical) mitigation devices, a three-dimensional acoustic tracking system has been developed to prototype status in order to locate mammals around fishing gear. MATLAB is used to locate acoustic sources using time-of-arrival-differences between hydrophone pairs. The planned mitigation devices must meet animal ethics standards. Trials with synthetic data have demonstrated that an array of mixed hydrophone geometry (2 hardwired hydrophones and 2 sonobuoy hydrophones) would locate acoustic sources within volumes of water of approximately 500 cubic metres, compared to volumes of water of >7,000 cubic metres that exist between fish hooked on branchlines 50 m apart. Field trials are planned for October-November 2002.