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Fisheries can profoundly affect bycatch species with 'slow' life history traits. Managing bait type offers one tool to control species selectivity. Different species and sizes of marine predators have different prey, and hence bait, preferences. This preference is a function of a bait's chemical, visual, acoustic and textural characteristics and size, and for seabirds the effect on hook sink rate is also important. We conducted a global meta-analysis of existing estimates of the relative risk of capture on different pelagic longline baits. We applied a Bayesian random effects meta-analytic regression modelling approach to estimate overall expected bait-specific catch rates. For blue shark and marine turtles, there were 34% (95% HDI: 4–59%) and 60% (95% HDI: 44–76%) significantly lower relative risks of capture on forage fish bait than squid bait, respectively. Overall estimates of bait-specific relative risk were not significantly different for seven other assessed taxa. The lack of a significant overall estimate of relative capture risk for pelagic shark species combined but significant effect for blue sharks suggests there is species-specific variability in bait-specific catch risk within this group. A qualitative literature review suggests that tunas and istiophorid billfishes may have higher catch rates on squid than fish bait, which conflicts with reducing marine turtle and blue shark catch rates. The findings from this synthesis of quantitative and qualitative evidence support identifying economically viable bycatch management measures with acceptable tradeoffs when multispecies conflicts are unavoidable, and highlight research priorities for global pelagic longline fisheries. [ABSTRACT FROM AUTHOR]

Bycatch in pelagic longline fisheries is one of the most serious threats to some sea turtle populations. Hook shape, hook minimum width and bait type have been the focus of research and management measures to mitigate problematic bycatch of vulnerable taxa. To assess the current state of knowledge and progress over the past decade, we reviewed findings on the effects of hook and bait type on pelagic longline sea turtle catch rates, anatomical hooking position and at-vessel mortality. Fish versus squid for bait lowered catch rates of leatherback sea turtles ( Dermochelys coriacea) and individual species of hard shelled turtles. Fish bait also reduced hard-shelled turtle deep hooking. Wider circle hooks reduced both leatherback and hard-shelled turtle catch rates relative to narrower J and tuna hooks, and reduced the proportion of caught hard-shelled turtles that were deeply hooked. Wider circle hooks with fish bait reduced leatherback and hard-shelled turtle catch rates relative to narrower J and tuna hooks with squid bait. Wider versus narrower circle hooks reduced hard-shelled sea turtle catch rates and deep hooking. The mechanisms for hook and bait type effects on turtle interactions are reviewed. Research designed to assess single factor effects is needed, in particular for hook shape and minimum width, and for hook and bait effects on anatomical hooking position and survival rates. Fishery-specific and holistic assessments are needed to account for variability between fisheries in a bycatch mitigation method's commercial viability, relative risks to affected populations and possible conflicting effects on vulnerable taxa. [ABSTRACT FROM AUTHOR]