To ping or not to ping: the use of active acoustic devices in mitigating interactions between small cetaceans and gillnet fisheries

Abstract

Active sound emitters ('pingers') are used in several gillnet fisheries to reduce bycatch of small cetaceans, and/or to reduce depredation by dolphins. Here, we review studies conducted to determine how effective these devices may be as management tools. Significant reductions in bycatch of harbour porpoise Phocoena phocoena, franciscana Pontoporia blainvillei, common Delphinus delphis and striped dolphin Stenella coeruleoalba, and beaked whales as a group have been demonstrated. For harbour porpoise this result has been replicated in 14 controlled experiments in North America and Europe, and appears to be due to porpoises avoiding the area ensonified by pingers. Two gillnet fisheries (California-Oregon driftnet fishery for swordfish; New England groundfish fishery) with mandatory pinger use have been studied for over a decade. Bycatch rates of dolphins/porpoises have fallen by 50 to 60%, and there is no evidence of bycatch increasing over time due to habituation. In both fisheries, bycatch rates were significantly higher in nets sparsely equipped with pingers or in which pingers had failed, than in nets without any pingers at all. Studies of pinger use to reduce depredation by bottlenose dolphins Tursiops truncatus generally show small and inconsistent improvements in fish catches and somewhat reduced net damage. Dolphin bycatch in these fisheries is rare, but still occurs in nets with pingers. Taken together, these studies suggest that the most promising candidates for bycatch reduction via pinger use will be gillnet fisheries in developed countries in which the bycaught cetaceans are generally neophobic species with large home ranges. We offer a set of lessons learned from the last decade of bycatch management.KEY WORDS: Gillnet · Bycatch · Dolphin · Porpoise · Pinger · Acoustic devices Resale or republication not permitted without written consent of the publisher Contribution to the Theme Section 'Techniques for reducing bycatch of marine mammals in gillnets'

Disentangling the causes of protected‐species bycatch in gillnet fisheries

“…It has been noted, for example, that despite observed 90% reductions in bycatch rates of porpoises associated with the use of pingers in scientifically designed trials, longer term efficacy in commercial fisheries can be lower as fishers' enthusiasm for the added workload (such as battery changing) diminishes (Dawson et al 2012). For bycatch mitigation measures to work in practice, rather than in controlled experiments, they must be easy to assimilate into normal fishing practices and effective long term compliance also requires the fishing community to be convinced of their utility (Poonian et al 2009).…”

“…A more detailed description of each factor and the evidence for correlation with bycatch rates is available as a bibliography in Supplementary Material. (Dawson et al 2012), but this is given no more weight in our table than a single study that has shown that some bird bycatch can be reduced with the use of acoustic deterrents (Melvin et al 1999a). …”

“…Acoustic deterrence has been trialed and tested many times with positive results in relation to cetacean bycatch (Dawson et al 2012), but only once for seabirds (Melvin et al 1999b), whose sub-surface hearing abilities are poorly understood. Clearly, if acoustic deterrent measures are successfully used for cetaceans, their effects on other groups should be explored in more detail.…”

Technical Measures in Order to Decrease Interactions Between Dolphins and Fishermen: Pingers

“…Therefore, using pingers in these areas may cause considerable issues (Franse, 2005). In their review, Dawson et al, (2013) indicated that the permenant use of pingers in adequate habitats may cause displacement of dolphins from their important habitats especially for species which have small home ranges. On the other hand, considering the fact that pinger signals from the entire Danish gillnet fleet could potentially cover <1% of the porpoises' habitat, displacement does not seem to be a trouble.…”

Acoustic alarms elicit only subtle responses in the behaviour of tropical coastal dolphins in Queensland, Australia

“…Dawson et al 2013, this Theme Section): (1) controlled experiments in commercial gillnet fisheries (e.g. Bordino et al 2002, Barlow & Cameron 2003; (2) observations of bycatch rates in fisheries in which pingers are used as part of a mitigation strategy (e.g.…”