Acoustic methods of reducing or eliminating marine mammal-fishery interactions: do they work?

Although a great deal of effort has been directed toward attempts to use sound to reduce o r eliminate marine mammal incidental capture in fisheries and predation on fish, there is little evidence of the effectiveness of such methods in solving marine mammal-fishery conflicts. Passive methods of increasing a net's reflectivity are hypothesized to result in lowered marine mammal bycatch rates, by making it easier for the animals to detect and avoid nets. However, so far, substantial decreases in cetacean bycatch have not been demonstrated, either from comparisons of catch rates in commercial fisheries or from observational studies of deterrence. The goal of active acoustic methods is the production of sound to warn the animals of the gear, or to cause them to leave the area. Various attempts have been made to use active methods to deter pinnipeds from areas of fishing activity (generally to avoid predation on the fish), and to warn cetaceans of the presence of a net (to reduce incidental catch). Net alarms have greatly reduced large whale entrapment in fish traps in Canadian waters, but despite extensive testing, have generally not shown similar success in reducing small cetacean bycatch in a number of gillnet fisheries. Overall, most attempts to use sound to reduce or eliminate marine mammal-fishery interactions have been based upon trial and error, with few controlled scientific experiments, making evaluation of the effectiveness of these methods difficult. Much more basic research on marine mammal echolocation behavior and on behavioral interactions between marine mammals and fisheries needs to be done before substantial success using acoustic methods can be expected.