Reducing by-catch of sea turtles in pelagic longline fisheries, in concert with activities to reduce other anthropogenic sources of mortality, may contribute to the recovery of marine turtle populations. Here, we review research on strategies to reduce sea turtle by-catch. Due to the state of management regimes in most longline fisheries, strategies to reduce turtle interactions must not only be effective but also must be commercially viable. Because most research has been initiated only recently, many results are not yet peer-reviewed, published or readily accessible. Moreover, most experiments have small sample sizes and have been conducted over only a few seasons in a small number of fisheries; many study designs preclude drawing conclusions about the independent effect of single factors on turtle by-catch and target catch rates; and few studies consider effects on other by-catch species. In the US North Atlantic longline swordfish fishery, 4.9-cm wide circle hooks with fish bait significantly reduced sea turtle by-catch rates and the proportion of hard-shell turtles that swallowed hooks vs. being hooked in the mouth compared to 4.0-cm wide J hooks with squid bait without compromising commercial viability for some target species. But these large circle hooks might not be effective or economically viable in other longline fisheries. The effectiveness and commercial viability of a turtle avoidance strategy may be fishery-specific, depending on the size and species of turtles and target fish and other differences between fleets. Testing of turtle avoidance methods in individual fleets may therefore be necessary. It is a priority to conduct trials in longline fleets that set gear shallow, those overlapping the most threatened turtle populations and fleets overlapping high densities of turtles such as those fishing near breeding colonies. In addition to trials using large 4.9-cm wide circle hooks in place of smaller J and Japan tuna hooks, other fishing strategies are under assessment. These include: (i) using small circle hooks (£ 4.6-cm narrowest width) in place of smaller J and Japan tuna hooks; (ii) setting gear below turtle-abundant depths; (iii) single hooking fish bait vs. multiple hook threading; (iv) reducing gear soak time and retrieval during daytime; and (v) avoiding by-catch hotspots through fleet communication programmes and area and seasonal closures.

Bycatch in pelagic longline fisheries threatens the viability of some seabird populations and reduces fishing efficiency. The mass of a branchline fishing weight and its distance from the hook significantly explain seabird catch risk during setting and hauling. We surveyed Hawaii tuna longline fishers to obtain their perspectives on the practicality, safety and economic viability of alternative designs which place weights adjacent to hooks instead of conventional designs with weighted swivels attached 0.6 m from the hook. We conducted experimental fishing to explore the commercial viability of a combination weighted swivel attached to the eye of the hook. We used a Bayesian random effects meta-analytic regression modeling approach to estimate pooled expected species-specific log relative risk of capture on conventional, as opposed to experimental, branchlines. There were significant decreases in catch rates on experimental branchlines of 54% (95% highest posterior density interval [HDI]: 34.3 to 73.8) for retained species and 28% (95% HDI: -7.5 to 93.3) for discarded species. For about 10% of experimental weighted hooks, the point of the hook tangled on the swivel, likely contributing to lower catch rates and making it more difficult for crew to coil branchlines. We identify possible factors explaining why the experimental gear reduced catch rates. The study demonstrates the benefits of stakeholder scoping to determine bycatch mitigation options with the highest promise for practicality, economic viability and safety, as well as benefits of conducting a pilot study to assess commercial viability to determine if a full experiment to assess bycatch mitigation efficacy is warranted.