Summary
The most difficult seabirds in the world to deter from baited hooks are white-chinned petrels, grey petrels and the shearwaters. A fundamental principle of seabird-friendly longlines is that they commence sinking immediately upon deployment and sink fast. Longlines with integrated weight (IW; 50 g/m lead beads woven into line fabric) clear the water surface immediately, sink with a linear profile (negligible lofting in propeller turbulence) and sink to 20 m depth 2.5 times faster than unweighted (UW) lines (0.25 m/s versus 0.1 m/s). Experiments were conducted in October/November in 2002 and 2003 on two freezer longliners in the New Zealand ling (demersal) longline fishery to determine effectiveness of IW longlines and a single streamer line as seabird deterrent. During the experiments the vessels were followed by up to 1,400 white-chinned petrels and 400 sooty shearwaters, as well as Salvin¡¯s, white-capped, Buller¡¯s, wandering and royal albatrosses. Dives on both types of longlines by white-chins and shearwaters were often intense. In 2002 81 white-chinned petrels and one sooty shearwater were caught on UW lines, compared to one white-chinned petrel on IW - a difference of 98%. In 2003 UW lines caught 46 white-chinned petrels and 38 sooty shearwaters, whereas IW lines caught three white-chinned petrels and 15 sooty shearwaters. Reductions in mortality were 93% and 64% for white-chinned petrels and sooty shearwaters, respectively. No albatrosses were caught in either year. The results suggest that gear that commences sinking immediately when set and at ¡Ý0.25 m/s will greatly reduce seabird mortality in demersal longline fisheries worldwide.