FINGERS, PORPOISES AND POWER - UNCERTAINTIES WITH USING FINGERS TO REDUCE BY CATCH OF SMALL CETACEANS

Incidental mortality in gillnets is probably the most serious global t hreat to dolphin and porpoise populations. In 1994, a well-designed st udy demonstrated a 92% reduction in bycatch of harbour porpoises in si nk gillnets equipped with acoustic pingers. This result has not yet be en fully replicated; in the New Hampshire area where the experiment wa s conducted or elsewhere. Statistical po,ver analyses indicate that su ch studies are feasible only in areas of high entanglement rate. Curre ntly unanswered research questions include whether the 1994 results ca n be replicated, whether habituation might decrease effectiveness over time, and what the mechanism of deterrence is. Practical constraints include the size, cost and battery life of current pingers, and whethe r their rue could be monitored cost-effectively. Front a management pe rspective, even if the effectiveness of pingers is confirmed, widespre ad incorporation of them into gillnets may not alone be sufficient to meet the requirements of the US Marine Mammal Protection Act. For this reason scientists, managers and fishers must continue to explore othe r options, including time/area closures and encouragement of more sele ctive fishing methods. (C) 1998 Elsevier Science Ltd. All rights reser ved.