Mitigation strategies for the reduction of sea turtle bycatch in the Mediterranean bottom trawl fisheries.

Incidental catch is the major threat to the survival of loggerhead turtles (Caretta caretta) in the Mediterranean. In this basin more than 100,000 turtles are estimated to be caught annually due to fishing practices. The mortality due to fishing capture (10-50% depending on fishing gear) can be considered as the main reason for sea turtle decline in this basin. Nevertheless, present knowledge about the interaction of sea turtles with fishing gears and the possible mitigation measures are still insufficiently studied. Successful strategies for sea turtles conservation mainly involve the knowledge of species biology and ecology, the identification of possible areas of interaction between turtles and fishing activities and finally the introduction of mitigation measures, such as gear modification through Bycatch Reducer Devices (BRDs). In this chapter two options adopted in the Adriatic Sea (central Mediterranean Sea) for sea turtle conservation have been described. The first is a theoretical approach based on developing models that can predict the identification of areas and periods at high risk of trawl-turtle interaction. Two set of data represented by telemetry data from tagged sea turtles and bottom trawl track from vessel monitoring systems (VMSs) were combined to provide an interaction index enabling prediction of potential trawl-turtle interaction hotspots and periods. The risk-analysis methodology here developed provides key information to design and implement management strategies, and it might have a worldwide application, considering that Vessel Monitoring System is actually in force in several countries. Once the areas and periods of possible trawl-turtle interaction have been identified, the effect of a flexible Turtle Excluder Device (TED) on the catching efficiency and performance of a commercial bottom trawl was tested in a gear comparison study in a Mediterranean coastal multispecies bottom trawl fishery. Considering fishermen reticence to change the gear traditionally used, determining the optimal gear configuration to minimise the loss of commercial catch and avoid turtle captures, was the main issue of the study. Experimental sea cruises showed that the device affected neither technical performances of the gear (horizontal and vertical net opening and door spread) nor fuel consumption during fishing activities. Sorting of the catch into commercial, discard and debris (e.g. rocks, timber, marine litter) fractions demonstrated that TED use did not affect catch efficiency, since the catch of the major commercial species did not exhibit appreciable differences, whereas debris was strongly reduced when the TED was in use. Underwater video camera recordings documented that fish caught in the net swam through the grid and easily reached the codend, missing the TED escape opening. Easy storage and improved catch retention compared with previous devices tested in this area make the flexible TED a practical and valuable solution to reduce turtle bycatch in the coastal Mediterranean demersal fisheries. In conclusion, the synergy of the two approaches described, can be considered as a reliable mitigation strategy in Mediterranean sea turtle conservation.