Research Document - 2004/066

Harbour Porpoise Bycatch Estimates For Newfoundland’s 2002 Nearshore Cod Fishery

By Lawson, J., S. Benjamins, G. Stenson

Abstract

Despite reduced fishing effort in a number of north Atlantic fisheries following commercial collapse, concerns remain about levels of direct mortality, primarily through incidental catches in fishing gear, of harbour porpoise (Phocoena phocoena). Although harbour porpoise bycatch is known to occur in a number of nearshore fisheries along the coast of Newfoundland, there are few defendable, quantified estimates. This report briefly describes the level and distribution of the Atlantic cod gillnet fishery in the nearshore of Newfoundland in 2002, a period when the fishery was severely reduced. Based on several sources of data (bycatch rates derived using different methods of reporting; groundfish landings and net days as measures of effort, with either individual fishers or fishing trips as the sampling units) we estimate the potential number of incidental catches of harbour porpoises in this fishery in 2002. Confidence intervals were estimated using resampling techniques.

Estimates of bycatch of small cetaceans in 2002, virtually all of which are harbour porpoises, varied greatly (from 1,324 to 12,649 animals in the nearshore cod fishery, depending upon the calculation method used). Most of these were caught in the third quarter of the year (July – September) along the south coast, although porpoise bycatch was also reported in the second and fourth quarters. Confidence limits were large due to variation in the reported bycatch rates among individual fishers and geographic areas. Given its lower data variability and fewer assumptions required during analysis, we have greater confidence in the cetacean bycatch estimates based on net days as a measure of effort, during fishing trips (rather than effort per fisher). Thus we conclude that it is most likely that approximately 1,500 to 3,000 harbour porpoises were incidentally caught for the nearshore cod gillnet fishery in Newfoundland in 2002. The 95 percentile range values around the derived estimates are wide (ranging from 126 to 5,605 for this type of approximation).

Several strategies could be implemented to better monitor small cetacean bycatch. Porpoise population estimates are required before we can determine if such mortality is sustainable.

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