Chapter II — Species of Special Concern 



Table 3. Estimates of harbor porpoise bycatch in sink gillnet flsheries in the Bay of Fundy (Canada), Gulf 

 of Maine (U.S.), and off the U.S. mid-Atlantic states, 1990-1998' 



' Numbers in parentheses are ranges of the 95 percent confidence interval where available. 



^ D. Palka. 1997. Gulf of Maine Harbor Porpoise By-catch. Prepared for the Gulf of Maine Harbor Porpoise Take Reduction Team 



Meeting, December 16-17, 1997. National Marine Fisheries Service, Woods Hole, Massachusetts. Estimate for 1997 provided 



by National Marine Fisheries Service as unpublished data. 

 ' E. A. Trippel. 1998. Harbour Porpoise By-Catch in the Lower Bay of Fundy Gillnet Fishery. DFO Maritime Regional Fisheries 



Status Report 98/7E. Canadian Department of Fisheries and Oceans, Dartmouth, Nova Scotia. 

 * D. Palka. 1997. Mid-Atlantic Harbor Porpoise By-Catch and Gear Characteristics. Prepared for the Gulf of Maine Harbor 



Porpoise Take Reduction Team Meeting, December 16-17, 1997. National Marine Fisheries Service, Woods Hole, Massachusetts. 



Estimate for 1997 provided by National Marine Fisheries Service as unpublished data. 



In addition, the Service has encouraged New 

 England gillnetters to use acoustic deterrent devices 

 called pingers. Attached to gillnets at intervals along 

 their length, pingers emit periodic sound pulses 

 intended to keep harbor porpoises away from nets. 

 Experiments indicate that, in at least some areas, 

 pingers can reduce harbor porpoise bycatch rates by 

 90 percent or more when properly deployed and 

 maintained. It is not clear whether these devices 

 annoy and repel porpoises or simply alert them to the 

 presence of nets. Nor is it clear precisely what sound 

 characteristics elicit the avoidance response. Time- 

 area management zones to prohibit gillnet fishing or 

 require that nets be equipped with pingers have been 

 the principal approaches to date for reducing harbor 

 porpoise bycatch off New England. 



Measures to reduce bycatch off mid-Atlantic 

 states, first adopted by the Service late in 1998, will 

 go into effect during the winter and spring 1999 

 fishing seasons. Thus, their effectiveness is currently 



unknown. As discussed below, initial bycatch reduc- 

 tion measures for this area involve time-area fishing 

 closures, net design requirements, and limits on the 

 amount of gear that can be fished. There are no 

 provisions for using pingers in the mid- Atlantic area. 



Recent actions to reduce harbor porpoise bycatch 

 have been guided by the 1994 amendments to the 

 Marine Mammal Protection Act that established a new 

 regime for managing marine mammal-fishery interac- 

 tions. In part, the approach requires the Service to 

 calculate a potential biological removal level for each 

 marine mammal stock in U.S. waters. The potential 

 biological removal level is an estimate of the number 

 of animals that can be removed from a marine mam- 

 mal stock annually (not including natural mortality), 

 while ensuring that the stock will increase toward or 

 remain at its optimum sustainable population level. 

 For Gulf of Maine harbor porpoises, the Service has 

 calculated the potential biological removal level to be 

 483 harbor porpoises per year. 



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