Sources of bycatch of loggerhead sea turtles in the western Mediterranean other than drifting longlines

Abstract

Abstract Álvarez de Quevedo, I., Cardona, L., De Haro, A., Pubill, E., and Aguilar, A. 2010. Sources of bycatch of loggerhead sea turtles in the western Mediterranean other than drifting longlines. – ICES Journal of Marine Science, 67: 677–685. A survey, including questionnaires to fishers and observers on board fishing vessels, was conducted to assess turtle bycatch in the waters off Catalonia (northeastern Spain), a region inhabited mainly by loggerhead sea turtles (Caretta caretta) from the highly endangered eastern Mediterranean rookeries. Observer reports confirmed that the data produced by the interviewees were reliable, so interview results were used to estimate turtle bycatch. The number of turtles caught monthly per vessel was estimated at 0.01 for bottom longlines, 0.02 for trammelnets, 0.07 for bottom trawling, and 1.2 for drifting longlines. From these values, 481 (95% CI: 472–491) turtles were estimated to be taken annually as bycatch by the whole fleet. Bottom trawling and trammelnets were the most widely used fishing gears (33 and 31% of the total 11 237 fishing months), but most turtles were caught either by bottom trawlers (249; 95% CI 83–415) or by drifting longlines (124; 95% CI: 40–199). Ivlev's electivity index revealed that bottom trawler bycatch was higher than expected in areas with a wide continental shelf. Given the heavy turtle mortality associated with bottom trawling and the fact that, in southern Catalonia, the fleet mainly takes turtles from western Mediterranean rookeries, it is suggested that the fishery be regulated through winter fishing restrictions, reducing the number of bottom trawlers working in the area, reducing the time the net is in the water to prevent turtle suffocation, or being obliged to use turtle excluder devices.