Summary
Chile is a fishery country with important artisanal and industrial longline fleets during the last 30 year. Main fishing resources in southern Chile are Patagonian toothfish, Ling and Austral hake. All these fisheries are suspected to have high seabird mortality. The assessment of these fleets showed differential seabird bycatch levels for the artisanal and industrial fisheries. In the Austral hake artisanal fishery the seabird bycatch was 0.011 birds per 1000 hooks (BPUE) in 166,911 hooks observed (total effort=435,649 in one full season). Similarly, in the Patagonian toothfish artisanal fishery the estimated BPUE was 0.038 (N=131 sets, 104,500 hooks observed). In both cases abundance and diversity of albatrosses and petrels observed around the boats was high. The explanation of such low rates of incidental mortality are related with the use of drops lines and vertical setting of the longline, that in all the cases have a sink rate over 0.25 m/seg. By contrast, the industrial Patagonian toothfish fishery south to 47ºS, that fish using the Spanish longline system, had a mean BPUE of 0.371, being the BBA the most killed bird (Bootstrap model: mean=1522 birds/year; 95% CI=1033-2255). A GLM model showed that the main explanatory factors were the area (proximity to breeding islands), month and period of the day. Seabird bycatch were highly seasonal, concentrated mainly from October to December. Finally we discuss the potential impact that these fisheries seems to have had on the Gonzalo Island (Diego Ramirez) population, under the light of the fishing effort apply from 1987 to 2002.