Reducing sea turtle by‐catch in pelagic longline fisheries

Abstract

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 Because most research has been initiated only recently, many results are not yet peer-reviewed, published or readily accessible.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.

Predicting overfishing and extinction threats in multispecies fisheries

“…However, such "weak-stock management" can cause faster-growing populations to be underexploited, which lowers profits and decreases food supplies (56). Trade-offs between conservation and yield could be mitigated by improving the species selectivity of fishing technologies (7,36). Measurements of T and V/V key can be used to set selectivity goals and monitor progress.…”

Informing Marine Protected Area Designation and Management for Nesting Olive Ridley Sea Turtles Using Satellite Tracking

“…Bottom set gillnets, which are widely used by artisanal fisheries in Central Africa (Metcalfe et al, 2015b(Metcalfe et al, , 2016, pose a direct threat to sea turtles resting on the bottom and studies have highlighted the depth at which fishing occurs can influence the bycatch rates of sea turtles (Polovina et al, 2003;Gilman et al, 2006). Outside of the MPA, the estuary has been designated for community fishing activities; management plans may consider seasonal fishing restrictions during the internesting period, particularly for bottom-set fishing gear, which restricts turtles' ability to breathe at the surface.…”

Impacts of fisheries bycatch on marine turtle populations worldwide: toward conservation and research priorities

“…For example, several RMUs that interact with longline gear in the Northwest Atlantic Ocean and North Pacific Ocean fell into this category, which could reflect the substantial efforts in these regions to monitor and reduce turtle bycatch through on-board observer programs and the implementation and compliance of several mitigation measures, including changes to hooks, bait, and spatiotemporal distribution of fishing effort , Gilman et al 2006, Howell et al 2008. Regionally focused analyses of bycatch patterns over time in response to mitigation efforts would shed light on this possibility, although the ''snapshot'' nature of the bycatch studies makes such analyses challenging.…”