CSIRO Marine and Atmospheric Research
Past Seminars

Solutions to Seabird Bycatch in Alaska's Demersal Longline Fisheries

Seabird mortalities occur in longline fisheries as seabirds feed on sinking baits when the gear is deployed. In Alaska, USA, takes exceeding 6 short-tailed albatross within a 2-year period (4 in the groundfish fishery and 2 in the Pacific halibut fishery) could interrupt or close a $250 million demersal longline fishery. In order to develop Alaska specific and fleet specific solutions to the incidental take of short-tails and other seabirds, we compared a suite of seabird bycatch mitigation strategies over 2 years (1999 and 2000) in 2 major Alaska demersal longline fisheries: the Gulf of Alaska /Aleutian Island fishery for sablefish and halibut and the Bering Sea catcher-processor longline fishery for Pacific cod. Key features of this program were an industry-agency-academic collaboration and a comprehensive approach - measures of seabird abundance and behavior, and gear sink rates, as well as catch rates of all species. Our goal was to identify mitigation techniques that significantly reduced seabird bycatch with no loss of target catch or increase in the bycatch of other organisms.

Among all deterrents tested, paired streamer lines proved to be the most comprehensive solution. Paired streamer lines successfully reduced seabird bycatch in all years, regions, and fleets (88% to 100% relative to controls with no deterrent), despite the fact that we saw orders of magnitude variation in bycatch across years and in the case of the sablefish fishery, among regions. Most significantly, this success came with no consequence to catch rates of target-fish or the rate of capture of other bycatch species, thus satisfying our primary goal. Single streamer lines were slightly less effective than paired streamer lines, reducing seabird bycatch by 96 percent and 71 percent in the sablefish and cod fisheries, respectively. Although adding weight to the gear in both fisheries significantly reduced seabird bycatch relative to a control of no deterrent (37% for the sablefish fishery, 76% for the cod fishery), the addition of weight to the groundline in both fisheries provided no improvement in the already high bycatch reduction of paired streamer lines. The Mustad lineshooter tested in the 1999 cod fishery was the only deterrent that significantly increased the rate of seabird bycatch. Although the Mustad lining tube significantly reduced bycatch to levels similar to adding weight to the groundlines, performance was variable. Based on these results, paired and single streamer lines, deployed according to a prescribed performance standard, will soon be required mitigation in these Alaska fisheries.