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

Abstract

Demersal gill nets equipped with acoustic alarms reduced harbour porpoise (Phocoena phocoena) by-catch rates by 77% over those without alarms in the Swallowtail area of the lower Bay of Fundy during field testing in August 1996 (68% reduction) and 1997 (85% reduction) (both years combined, three harbour porpoises in 249 alarmed nets versus 14 harbour porpoises in 267 nonalarmed 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 µPa at 1 m. In conditions of no rain and low wind (Sea State 0-2) the alarms were 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 in alarmed and nonalarmed nets (except in one season when pollock were caught in lower numbers in alarmed nets). Harbour porpoise by-catch and herring movements may be linked. During years of low herring abundance, we also observed low harbour porpoise entanglement rates.

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

“…Although in many studies (Trippel et al, 1999;Gearin et al, 2000, Culik et al, 2001, Wilson and Dill, 2002, it is proved that pingers do not negatively effect the catch rate of target species, Kraus et al (Kraus et al, 1997), asserted that pingers cause reduction in target catch rate in a study performed on Atlantic herring ( Clupea harengus ).…”

A Framework for Monitoring and Assessing Socioeconomics and Governance of Large Marine Ecosystems1 1First published by Sutinen et al. in 2000: NOAA Technical Memorandum, NMFS-NE-158 (under contract # ENN F7 00378)

“…The estimated harbor porpoise bycatch in 1986 was 94-116 and in 1989 it was 130 (Trippel et al 1996). The Canadian gillnet fishery occurs mostly in the western portion of the Bay of Fundy during the summer and early autumn months, when the density of harbor porpoises is highest.…”

“…More recently, an observer program implemented in the summer of 1993 provided a total bycatch estimate of 424 harbor porpoises (± 1 SE: 200-648) from 62 observed trips, (approximately 11.3% coverage of the Bay of Fundy trips) (Trippel et al 1996).…”

“…The bycatch was estimated to be 101 harbor porpoises (95% confidence limit: 80-122), and the fishing fleet consisted of 28 vessels (Trippel et al 1996).…”

“…Approximately 30% of these observed trips used pingered nets. The estimated bycatch was 87 harbor porpoises (Trippel et al 1996). No confidence interval was computed due to lack of coverage in the Wolves fishing grounds.…”