Hooks and sea turtles: a veterinarian's perspective

Six out of seven species of marine turtles are endangered, with longline bycatch considered one of the main causes for the decrease of their populations. Recently, the use of large circle hooks has been shown to reduce the impact of longline fishing on sea turtles, both decreasing the number of sea turtles captured, and shifting the number of hookings to the mouth, as opposed to other anatomical locations. However, little is known about the true post-release mortality of captured turtles in relation to hook location and associated lesions, essential information to adequately determine gear impacts. Here i discuss, from a veterinarian's point of view, the lesions caused by hooks in different locations in captured sea turtles, and their possible effects, combining information gathered from personal experience, long-term studies on captive sea turtles, post-mortem analysis of stranded sea turtles, and results of satellite tagging studies. Although hooks in the mouth are generally considered low risk, there are sensitive structures in this area, such as the glottis or the jaw joint, which should be carefully considered. On the other hand, the esophagus has a strong muscular wall and is somewhat resistant to lesions, unless the hook lodges close to the heart or large blood vessels. Lines left trailing are by far the most dangerous part of the gear, and have very high chance of causing mortality. Adequate training of fishermen by experienced researchers is essential to reduce sea turtle mortality, and more research is urgently needed to confirm the effectiveness of circle hooks.