Performance of Side-setting Method as a Mitigation Measure for Reducing Incidental Catch of Seabirds on a Large-sized Pelagic Longline Vessel

摘要

Experiments on the side-setting method (setting longline from the side of a vessel) in alarge-sized pelagic longline vessel (54m, 450GRT) were conducted in the western North Pacific, April-June, 2007 to evaluate its performance as a mitigation measurefor reducing seabird bycatch. Two sets of line setting equipment were installed on the port side of the foredeck (36.5m ahead of the stern; side-setting) and on the end of the stern deck (stern-setting). Experimental fishing operations were conducted alternating the two setting styles. The side-setting increased1.2 times greater initial sinking rates of baited hooks (0 -5m in depth), compared to the stern-setting. The side-setting method suppressed bait-taking behavior of Laysan and black-footed albatrosses {Phoebastria immutabilis and P. nigripes) close to zero level The high seabird bycatch avoidance effects of the side-setting were related to improved sinking rates of baited hooks, greater depth of baited hooks at the vessels stern due to advancedlocation of casting points, and threatening effect of the vessels hull. However, risks of line trouble were observed in the side-setting. These results demonstrate the potential of side-setting method in reducing seabird bycatch, but the safety of fishing operation, resistance to rough sea condition, and economical cost of deck modification should be evaluated carefully before introducing the side-setting method to commercial fishing fleet