Reducing sea turtle by-catch in pelagic longline fisheries

By Eric Gilman, Erika A. Zollett, S. Beverly, H. Nakano, K. Davis, D. Shiode, P. Dalzell, Irene Kinan. 2006

246 citations recorded by the source corpus.

Reducingby-catchofseaturtlesinpelagiclonglinefisheries,inconcertwithactivitiesto 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. Becausemostresearchhasbeeninitiatedonlyrecently,manyresultsarenotyet peer-reviewed, publishedor readily accessible. Moreover, mostexperiments havesmall 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 effectofsinglefactorsonturtleby-catchandtargetcatchrates;andfewstudiesconsider 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 commercialviabilityofaturtleavoidancestrategymaybefishery-specific,dependingon thesizeandspeciesofturtlesandtargetfishandotherdifferencesbetweenfleets. 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 circlehooksinplaceofsmallerJandJapantunahooks,otherfishingstrategiesareunder 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.

Subfields: Global and Planetary Change, Nature and Landscape Conservation, Parasitology

View Paper: https://www.semanticscholar.org/paper/e48d72a7d9a1e921cc8267a1e6e9068552b29cf1

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Citations in the corpus

Circle hook effectiveness for the mitigation of sea turtle bycatch and capture of target species in a Brazilian pelagic longline fishery (2010, background): “Several measures to mitigate the incidental capture of sea turtles in pelagic longline fisheries have been proposed or implemented in different fisheries (Gilman et al., 2006; Werner et al., 2006).”
Impacts of fisheries bycatch on marine turtle populations worldwide: toward conservation and research priorities (2013, background): “…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 (Watson et al. 2005, Gilman et al. 2006, Howell et al. 2008).”
Shark catch in a pelagic longline fishery: Comparison of circle and tuna hooks (2006, background): “Catch rates did not differ significantly between the three hook types on either vessel (P = 0.48 and 0.43, two-way ANOVA).”
Reducing green turtle bycatch in small-scale fisheries using illuminated gillnets: the cost of saving a sea turtle (2016, background): “In contrast, the development of bycatch mitigation measures for gillnets, one of the most ubiquitous gear types, has been relatively slow (Melvin et al. 1999, Gilman et al. 2006).”
Effects of eliminating shallow hooks from tuna longline sets on target and non-target species in the Hawaii-based pelagic tuna fishery (2009, background): “Due to public scrutiny and their wide notoriety, longline interactions with sea turtles, birds and sharks often receive intense focus (Molony, 2005; Gilman et al., 2005, 2006; Watson et al., 2005).”
A review of marine mammal, sea turtle and seabird bycatch in USA fisheries and the role of policy in shaping management (2009, background): “Circle hooks have been shown to be effective at reducing sea turtle bycatch [86–88].”
Do circle hooks reduce the mortality of sea turtles in pelagic longlines? A review of recent experiments (2007, methodology): “Consideration was given to the commercial viability of potential mitigation measures ( Gilman et al., 2006 ) and the experiments were conceived, designed and conducted with the direct involvement of commercial fishermen.”
An overview of loggerhead sea turtle (Caretta caretta) bycatch and technical mitigation measures in the Mediterranean Sea (2010, background): “There is growing evidence that circle hooks tend to be located mostly externally in the jaw or mouth as opposed to deeper hooking (Watson et al. 2005; Gilman et al. 2006, 2007 ; R ead2007).”
Sea turtle by‐catch in the Mediterranean (2011, background): “Another technical solution is to place the hooks deeper in the water column (Gilman et al. 2006), because in open waters where the sea bottom is out of reach, loggerhead turtles rarely dive deeper than 100 m and they spend most of their time at less than 40 m (Polovina et al.”
Are we working towards global research priorities for management and conservation of sea turtles (2016, background): “…of bycatch mitigation — typically through changes in fishing gear — has been the focus of more critical research effort than any other interventions (Gilman et al. 2006, 2007, 2010, Read 2007, Alessandro & Antonello 2010, Bostwick et al. 2014, Senko et al. 2014b, Ortiz et al. 2016, Peckham et…”
Large-scale experiment shows that nylon leaders reduce shark bycatch and benefit pelagic longline fishers (2008, background): “Measures o reduce sea turtle interactions and mortality include large cirle hooks and the deep setting of longlines (Watson et al., 2004, 005; Gilman et al., 2006; Watson and Kerstetter, 2006).”
Incidental catch of sea turtles by the Brazilian pelagic longline fishery (2008, methodology): “This research, which parallels research by other countries on the same topic (Gilman et al., 2006), aims for the employment by the longline fleet of fishing gear less threatening to sea turtles; the experiments which have been performed by longliners based in Santos and Itajai operating to the…”
Estimating the odds of survival and identifying mitigation opportunities for common bycatch in pelagic longline fisheries (2009, background): “Because bycatch mitigation measures will likely be more readily accepted in commercial fisheries if modifications do not decrease the value of landed catch (e.g., Gilman et al., 2006a; Read, 2007), we estimated the effects of fishing variables on landed catch.”