Abstract
Objective We sought to evaluate the effectiveness of "weak hooks" in reducing the bycatch of Bluefin Tuna Thunnus thynnus in the U.S. Gulf of America (also known as Gulf of Mexico) pelagic longline fishery while maintaining catch rates and size distributions of the primary target species, Yellowfin Tuna T. albacares.Methods A total of 416 experimental pelagic longline sets were conducted aboard commercial vessels in the Gulf of America. Two treatments were compared: a 4.00-mm-diameter circle hook (control) and a custom-made 3.65-mm-diameter circle hook (weak), which were deployed in an alternating fashion. Fish catches and sizes were recorded for each hook type, and catch rates and size distributions were compared statistically. A hook straightening metric was paired with fish fork length for 888 control hooks and 863 weak hooks that caught Yellowfin Tuna. Hook time recorders and time depth recorders were used to estimate escape times for animals that bent weak hooks.Results No significant differences were observed in catch rates between hook types for any of the captured species except Bluefin Tuna, whose catch rates were 46% lower on weak hooks. No differences in size frequency distributions were observed for Yellowfin Tuna between hook types, but larger Bluefin Tuna were caught less frequently on weak hooks. Hook gap widening increased with fish size and was over twice as pronounced for weak hooks compared to control hooks. Approximately 50% of escaped animals that bent weak hooks escaped within 5 min.Conclusions Weak hooks effectively reduced the bycatch of large Bluefin Tuna without significantly affecting the catch rates or size distributions of the primary target species or other encountered species. The increased likelihood of hook straightening on weak hooks suggests a mechanism for selective release of larger Bluefin Tuna, and escape data indicate rapid release for many animals. These results support the use of weak hooks as a tool for reducing bycatch of large Bluefin Tuna and promoting more sustainable fisheries.
Commercial fisheries that target Yellowfin Tuna and Swordfish also capture fish species/sizes that are illegal to retain or have no economic value. We found that using a weaker hook than the industry standard reduced the catch of Bluefin Tuna without reducing the target catch.