Reducing sea turtle interactions in the Hawaii-based longline swordfish fishery

The reduction of sea turtle mortality in fisheries may contribute to recovering populations. To reduce turtle interactions, regulations for the Hawaii-based longline swordfish fishery required vessels to switch from using a J-shaped hook with squid bait to a wider circle-shaped hook with fish bait. Analyses of observer data showed that, following the introduction of the regulations, significant and large reductions in sea turtle and shark capture rates occurred without compromising target species catches. Capture rates of leatherback and loggerhead turtles significantly declined by 83% and 90%, respectively. The swordfish catch rate significantly increased by 16%. However, combined tuna species and combined mahimahi, opah, and wahoo catch rates significantly declined by 50% and 34%, respectively. The shark catch rate significantly declined by 36%, highlighting the potential for the use of fish instead of squid for bait to contribute to addressing concerns over the sustainability of current levels of shark exploitation. There was also a highly significant reduction in the proportion of turtles that swallowed hooks (versus being hooked in the mouth or body or entangled) and a highly significant increase in the proportion of caught turtles that were released after removal of all terminal tackle, which may increase the likelihood of turtles surviving the interaction. A quarter of turtle captures were in clusters (>1 turtle caught per set and consecutive sets with turtle captures), which is substantially higher than predicted by chance if the events were independent. This suggests that turtles aggregate at foraging grounds and that instituting methods to avoid real-time turtle bycatch hotspots may further reduce turtle interactions. There was no significant correlation between turtle and swordfish catch rates (vessels with high swordfish CPUE do not necessarily have high turtle CPUE), indicating that there may be a fishing practice or gear design causing some vessels to have low turtle catch rates without compromising swordfish catch rates.