Acoustic investigation of bycatch mitigation pingers

Pingers have been used on shark nets set along Queensland's beaches since 1992. Due to an increase in whale entanglements in 2009, new pingers (Fumunda F3 whale pingers and F10 dolphin pingers) were deployed between July and August 2010. Subsequently updated research on the use of these pingers was needed. For this study, the acoustic characteristics of pingers used on shark nets in Queensland Australia were measured and used to model sound propagation, estimate over what range marine mammals could detect the pingers, monitor ambient noise and to make recommendations on pinger deployment to the Queensland Shark Control Program (QSCP). The results of the sound propagation study indicate that the tones were a few hundred Hz less (2.6-2.8 Hz for F3 and 9.4-9.6 Hz for F10) than indicated. All pingers emitted multiple harmonics and fundamental tones. The power spectrum density levels varied up to 20 dB from angle to angle and pinger to pinger. The 1st harmonic of F3s was audible to all marine mammals over the longest ranges. Only 2 of the 6 tested pingers reached the manufacturer's listed audible range of 1-5 km. During testing, the ranges depended on the individual pinger and angle of the pinger toward the mammal. When animals travel alongside the net, a number of pingers should be set in a series. Based on the current configuration of 3-4 pingers per net of 200 m, humpback whales would hear all of the pingers at any location along the net but dolphins would hear only 1-2 pingers. When animals swim straight at the net, maximum pinger spacing would need to be based on the animals swim speed. The current net/pinger configuration is adequate for humpback whales, dugongs and dolphins swimming at normal travelling speeds. The current pinger spacing is insufficient for dolphins swimming straight at the net at high speeds.