Traplines: A Promising Modification to Reduce Sea Turtle Bycatch in Swordfish Longlines

Fisheries bycatch is a major threat to sea turtles, and drifting longlines are among the most impactful gears worldwide; however, existing mitigation measures vary in effectiveness and may involve trade-offs with commercial catch volumes. Traplines are a new hookless terminal gear recently adopted in some pelagic longline fisheries, but their conservation value for sea turtles has not been assessed yet. We compared traplines and conventional J-hooks in 23 pelagic longline sets conducted by a single vessel in the central Mediterranean targeting swordfish. Within each set, hooks and traplines were deployed alternately along the same drifting longline, allowing paired comparison under identical conditions. Across all sets, 40,800 hooks and 6850 traplines were deployed. Hooks caught 127 loggerhead turtles (Caretta caretta) and 9711 kg of commercial fish, whereas traplines caught 1 turtle and 6580 kg of fish. Turtle and fish catch rates were significantly lower and higher for traplines, respectively. Conservation efficiency relative to economic performance was assessed as turtles caught per kilogram of fish, and this ratio was significantly lower for traplines. These preliminary results provide the first empirical evidence that traplines can nearly eliminate sea turtle bycatch while still producing substantial fish catches, at least under the environmental and technical conditions of this study. We encourage further research in a variety of contexts to assess the broader value of traplines for sea turtle conservation.