Reducing sea turtle interactions in the Hawaii-based longline swordfish fishery

By Eric Gilman, D. Kobayashi, T. Swenarton, P. Dalzell, Irene Kinan-Kelly. 2007

205 citations recorded by the source corpus.

The reduction of sea turtle mortality in fisheries may contribute to recovering populations. To reduce turtle interactions, regulations for the Hawaii-based longline swordfish fishery required vessels to switch from using a J-shaped hook with squid bait to a wider circle-shaped hook with fish bait. Analyses of observer data showed that, following the introduction of the regulations, significant and large reductions in sea turtle and shark capture rates occurred without compromising target species catches. Capture rates of leatherback and loggerhead turtles significantly declined by 83% and 90%, respectively. The swordfish catch rate significantly increased by 16%. However, combined tuna species and combined mahimahi, opah, and wahoo catch rates significantly declined by 50% and 34%, respectively. The shark catch rate significantly declined by 36%, highlighting the potential for the use of fish instead of squid for bait to contribute to addressing concerns over the sustainability of current levels of shark exploitation. There was also a highly significant reduction in the proportion of turtles that swallowed hooks (versus being hooked in the mouth or body or entangled) and a highly significant increase in the proportion of caught turtles that were released after removal of all terminal tackle, which may increase the likelihood of turtles surviving the interaction. A quarter of turtle captures were in clusters (>1 turtle caught per set and consecutive sets with turtle captures), which is substantially higher than predicted by chance if the events were independent. This suggests that turtles aggregate at foraging grounds and that instituting methods to avoid real-time turtle bycatch hotspots may further reduce turtle interactions. There was no significant correlation between turtle and swordfish catch rates (vessels with high swordfish CPUE do not necessarily have high turtle CPUE), indicating that there may be a fishing practice or gear design causing some vessels to have low turtle catch rates without compromising swordfish catch rates.

Subfields: Ecology, Nature and Landscape Conservation

View Paper: https://www.semanticscholar.org/paper/132ba97288ec2ca9bb60d75e3f2c4686142f5e98

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Citations in the corpus

Estimating the odds of survival and identifying mitigation opportunities for common bycatch in pelagic longline fisheries (2009, background): “Unlike Watson et al. (2005), Brazner and McMillan (2008), Gilman et al. (2007) and the studies reviewed by Gilman et al. (2006a) and Read (2007), we found no conservation benefit for loggerhead turtles – one of the bycatch species for which conservation benefits were expected.”
Circle hook effectiveness for the mitigation of sea turtle bycatch and capture of target species in a Brazilian pelagic longline fishery (2010, background): “1%, respectively), similar to other findings (Gilman et al., 2007).”
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…”
Postrelease survival, vertical and horizontal movements, and thermal habitats of five species of pelagic sharks in the central Pacific Ocean (2011, methodology): “…introduced in 2004 to reduce sea turtle bycatch in the Hawaii-based shallow-set (nighttime) commercial longline fishery targeting swordfish (Gilman et al., 2007; Walsh et al., 2009), we began using 16/0 and 18/0 circle hooks (no offset), and Pacific saury (sanma, Cololabis saira) as bait.”
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; Read 2007).”
Sound, chemical, and light detection in sea turtles and pelagic fishes: sensory-based approaches to bycatch reduction in longline fisheries (2008, result): “Similar results were obtained when 18/0 circle hooks were incorporated into the Hawaiian swordfish fleet (Gilman et al. 2007).”