Trawling regime influences longline seabird bycatch in the Mediterranean: new insights from a small-scale fishery

Unintended mortality in longlines emerged in the early 1990s as one of the most important threats for pelagic seabirds worldwide. Most of the studies were focused on highly developed industrial fisheries, overlooking bycatch in small-scale artisanal fisheries. However, bycatch in smallscale fisheries might have negative effects similar to those of industrial fisheries when they overlap with hotspot areas of top predators. Moreover, different types of fishing gear coexist in the same oceanographic area, particularly in highly exploited marine ecosystems such as the western Mediterranean. We quantify for the first time the influence of trawling regime on Cory's shearwater Calonectris diomedea bycatch in the western Mediterranean longline artisanal fishery. The availability of trawling discards has substantial influence on the foraging and breeding ecology of many seabirds, and trawling inactivity may drive shearwaters to seek alternative food resources, such as baits used in longline fishing. Based on our previous knowledge of the system, we also tested other variables affecting bycatch over 8 yr (1998 to 2005). Within this 2-fishery framework, we found that trawling regime, longline fishing time and breeding stage were key factors explaining shearwater attendance to longline vessels, but mainly trawling regime and fishing time increased the incidental capture of Cory's shearwaters. More specifically, during the pre-breeding and chick-rearing periods, bycatch dramatically increased during sunrise sets in the absence of trawling activity. Importantly, this study indicates the need for an integrated multi-fisheries management approach for the conservation of seabirds and highlights the necessity of banning longline fishing during periods of trawling inactivity.