A field test of acoustic deterrent devices used to reduce interactions between bottlenose dolphins and a coastal gillnet fishery

Bottlenose dolphins (Tursiops truncatus) interact frequently with gillnet fisheries throughout their range. These interactions, which include the depredation of captured fish, can have deleterious impacts on both dolphins and fishermen. Acoustic deterrent devices have been proposed as one means of reducing the frequency and severity of these interactions. We studied interactions between bottlenose dolphins and a gillnet fishery for Spanish mackerel (Scomberomorus maculatus) in North Carolina, USA and investigated the effect of SaveWave® acoustic deterrent devices on target fish catch and the frequency and nature of interactions with bottlenose dolphins. We made observations from commercial vessels and conducted focal visual and acoustic follows of dolphins from a research vessel. We examined the effects of SaveWave® devices on fish catches and dolphin behavior by comparing sets with functioning (active) devices and non-functioning (control) devices. In 2003, we collected baseline data on catch and dolphin behavior from 136 gillnet sets; during 2004 and 2005 we monitored 151 gillnet sets (83 with active devices, 68 with control devices). Fish catches were significantly lower when dolphins were observed interacting with gillnets. SaveWave® status (active versus control) did not affect fish catch, but dolphins were less likely to interact with and more likely to echolocate around gillnets equipped with active SaveWaves® than gillnets with control SaveWaves®. Despite these encouraging findings, SaveWave® devices were not sufficiently durable to be deployed effectively in this fishery.