Mitigation of harbour porpoise (Phocoena phocoena) by-catch in the gillnetfishery in the lower Bay of Fundy

Demersal gill nets equipped with acoustic alarms reduced harbour porpoise ( Phocoena phocoena) by-catch rates by 77% over those without alarms in the S wallowtail area of the lower Bay of Fundy during field testing in August 19 96 (68% reduction) and 1997 (85% reduction) (both years combined, three har bour porpoises in 249 alarmed nets versus 14 harbour porpoises in 267 nonal armed nets). The alarms spaced 100 m apart along the net floatline produced a 0.3-s pulse at 10-12 kHz every 4 s at a level of 133-145 dB re 1 mu Pa a t 1 m. In conditions of no rain and low wind (Sea State 0-2) the alarms wer e presumed to be clearly audible to harbour porpoises at ranges of 0.1-0.6 km. Catch rates of Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), and pollock (Pollachius virens) were not significantly different i n alarmed and nonalarmed nets (except in one season when pollock were caugh t in lower numbers in alarmed nets). Harbour porpoise by-catch and herring movements may be linked. During years of low herring abundance, we also obs erved low harbour porpoise entanglement rates.