Fast sinking (integrated weight) longlines reduce mortality of white-chinned petrels ( Procellaria aequinoctialis) and sooty shearwaters ( Puffinus griseus) in demersal longline fisheries

Abstract

Longline fisheries have been responsible for the deaths of large numbers of seabirds worldwide. Two of the most difficult seabird species to deter from baited hooks are the white-chinned petrel ( Procellaria aequinoctialis) and sooty shearwater ( Puffinus griseus). Longlines with integrated weight (IW) sink faster than normal, unweighted (UW), longlines and have the potential to reduce the numbers of these species killed. The relative differences in the number of white-chinned petrels and sooty shearwaters killed on UW longlines and IW longlines containing 50 g/m beaded lead core were investigated in 2002 and 2003 in the New Zealand ling ( Genypterus blacodes) autoline fishery. Effects on catch rates of target and non-target fish species, and operational aspects of the use of IW gear, were also assessed. A single bird scaring streamer line was deployed on all sets of longlines. In 2002 and 2003, compared to UW lines IW lines reduced mortality of white-chinned petrels by 98.7% and 93.5%, respectively. In 2003 IW lines reduced sooty shearwater mortality by 60.5%. Catch rates of white-chinned petrels (including on sets when no fatalities were recorded) by IW gear were low: 0.005/1000 hooks (UW: 0.4) and 0.01/1000 hooks (UW: 0.17) in 2002 and 2003, respectively. Equivalent rates for sooty shearwaters in 2003 were 0.06/1000 hooks by IW and 0.13/1000 hooks by UW. No albatrosses were caught on either line type in 2002; in 2003 a single Salvin’s albatross ( Thalassarche salvini) was caught on UW gear. Both the number of ling and the mean masses of ling caught in 2003 by IW (mass: 189.3; CL 95% 162.7–220.3 kg/1000 hooks) and UW (200.6; CL 95% 178.2–225.9 kg/1000 hooks) longlines were similar statistically. Use of IW longlines and streamer lines in autoline fisheries should yield major conservation benefits to seabirds interacting with these fisheries worldwide.