Relationship Between Hook Type and Hooking Location in Sea Turtles Incidentally Captured in the United States Atlantic Pelagic Longline Fishery

Abstract

Because incidental capture in pelagic longline fishing gear potentially kills or injures thousands of sea turtles annually, solutions to reduce the frequency and mortality rate of these interactions are critical conservation priorities. Understanding factors that affect post-hooking mortality rates remains an important component to evaluating the population-level impact of these interactions. Post-release mortality may be dependent upon the nature of the interaction (hooking location and/or entanglement) and amount of gear remaining at release. Hooking location can impact the ability of the crew to remove gear, as deeply ingested hooks cannot be removed safely. We examined the effects of hook type (circle vs J-hooks), offset (degrees), and other factors on hooking location in leatherback, Dermochelys coriacea (Vandelli, 1761), and loggerhead, Caretta caretta (linnaeus, 1758), sea turtles incidentally captured from 2000 to 2010 using fishery observer data. Significant differences in hooking location in loggerheads were observed between offset J-hooks and non-offset and 10° offset circle hooks; loggerheads were most often mouth/beak hooked with circle hooks, whereas most had swallowed offset J-hooks. Greater offsets appear to increase the frequency of deeply ingested hooks. Leatherback sea turtles were predominately externally hooked regardless of hook type, but mouth hookings occurred significantly more often on non-offset (0°) circle and J-hooks than on 10° offset circle hooks. When combined with outreach and education on careful release protocols, the use of circle hooks may increase post-interaction survival by modifying hooking location and facilitating maximum gear removal.