Methods for mitigating sea turtle bycatch in longline fisheries: a meta-analysis

Among the various species affected by bycatch, sea turtles are particularly vulnerable due to their low population numbers. Although many methods have been developed to mitigate sea turtle bycatch in longline fisheries, the extent to which these methods reduce the probability of sea turtle bycatch remains unclear. We performed a meta-analysis of 21 publications which included control experiments in longline fisheries comparing the use of mitigation methods to no mitigation methods for the same target species. The results indicate that the use of circle hooks, circle hooks with a wire appendage, fish bait, blue-white lights, and stingray-like bait can mitigate sea turtle bycatch (only circle hooks and fish bait were used in fishing operations). The remaining two types (blue-white lights and stingray-like bait) affected the catch of the target species and did not have the prospect of practical application. We also found that most mitigation measures did not significantly affect the catch of the target species, and some studies did not assess the catch of target species. Setting Hookpod-mini on branch lines and dyeing bait with colors are alternative mitigation methods. However, most of these methods are ineffective or inefficient in mitigating sea turtle bycatch or even unsuitable for applying to actual operations. Our study also identified two ways to mitigate turtle bycatch by affecting their senses (i.e., effective chemical deterrents and auditory systems), which may be promising research directions for the future.