Effects of small (13/0) circle hooks on loggerhead sea turtle bycatch in a small-scale, italian pelagic longline fishery

Incidental catches by pelagic longline fisheries are recognized as serious threats to the loggerhead sea turtle, Caretta caretta (Linnaeus, 1758). In the present study, we assessed the effects of small (13/0) circle hooks on the catches of C. caretta in a small-scale, pelagic longline fishery off the southern coast of Ionian Calabria (southern Italy). Experiments were conducted on a commercial fishing vessel using circle hooks (Mustad 13/0, n = 2320) alternated with J-hooks (Mustad No. 4, n = 2322) along 13 longline sets. The mean catch per unit of effort (CPU E) of the target species Thunnus thynnus (Linnaeus, 1758) (n = 30) per fishing set and its mean body size did not differ significantly between the two hook types. No significant differences emerged in the sea turtle CPU E for each hook type; however, there was a significant reduction in mean body size with circle hooks due to a decrease in the catch rate of large juvenile loggerhead turtles. Although more data are necessary to obtain a comprehensive picture, the widespread adoption of 13/0 circle hooks has the potential for benefitting large juveniles and nesting adult sea turtles. Our data also suggest that adoption of 13/0 circle hooks would not adversely impact the economic viability of the fishery.