Shark interactions in pelagic longline fisheries

Imperial College London, Silwood Park Campus, Manor House, Buckhurst Road, Ascot SL5 7PY, UK
Marine Policy (Impact Factor: 2.62). 01/2008; 32(1):1-18. DOI: 10.1016/j.marpol.2007.05.001
Source: RePEc


Substantial ecological, economic and social problems result from shark interactions in pelagic longline fisheries. Improved understanding of industry attitudes and practices towards shark interactions assists with managing these problems. Information on fisher knowledge and new strategies for shark avoidance may benefit sharks and fishers. A study of 12 pelagic longline fisheries from eight countries shows that incentives to avoid sharks vary along a continuum, based on whether sharks represent an economic disadvantage or advantage. Shark avoidance practices are limited, including avoiding certain areas, moving when shark interaction rates are high, using fish instead of squid for bait and deeper setting. Some conventionally employed fishing gear and methods used to target non-shark species contribute to shark avoidance. Shark repellents hold promise; more research and development is needed. Development of specifically designed equipment to discard sharks could improve shark post release survival prospects, reduce gear loss and improve crew safety. With expanding exploitation of sharks for fins and meat, improved data collection, monitoring and precautionary shark management measures are needed to ensure that shark fishing mortality levels are sustainable.

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Available from: Eric L Gilman
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    • "A few studies found that leader material significantly affected elasmobranch catch rates, and wire leaders (steel traces) have been banned in some longline fisheries (e.g., Australia, Cook Islands, Fiji, Marshall Islands, Palau, Samoa, South Africa) with an explicit or implicit aim of reducing shark fishing mortality (Branstetter and Musick 1993; Yokota et al. 2006; Ward et al. 2008; Afonso et al. 2012; Clarke 2013; Gilman et al. 2013c, In Press). It is unclear, however, what effect leader material has on catch rates of other vulnerable taxa, and under what circumstances using monofilament instead of more durable leader materials (wire, multifilament nylon [polyamide]) results in lower elasmobranch fishing mortality (Ward et al. 2008; Gilman et al. 2008b, 2013b; Clarke et al. 2014). In addition to the limited understanding of the single effects of these four factors on elasmobranchs, there is likewise limited understanding of possible interacting effects (Gilman 2011; Gilman et al. 2008b, 2012; Afonso et al. 2012; Epperly et al. 2012; Hannan et al. 2013; Clarke et al. 2014). "
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    ABSTRACT: Elasmobranch mortality in pelagic longline fisheries poses a risk to some populations, alters the distribution of abundance between sympatric competitors, changing ecosystem structure, processes and stability. Individual and synergistic effects on elasmobranch catch and survival from pelagic longline gear factors, including methods prescribed to mitigate bycatch of other vulnerable taxa, were determined. Overall relative risk of higher circle vs. J-shaped hook shark catch rates conditioned on potentially informative moderators, from 30 studies, was estimated using an inverse-precision weighted mixed-effects meta-regression modeling approach. Sharks had a 1.20 times (95% CI: 1.03-1.39) significantly higher pooled relative risk of capture on circle hooks, with two significant moderators. The pooled relative risk estimate of ray circle hook catch from 15 studies was not significant (RR=1.22, 95% CI: 0.89-1.66) with no significant moderators. From a literature review, wire leaders had higher shark catch and haulback mortality than monofilament. Interacting effects of hook, bait and leader affect shark catch rates: hook shape and width and bait type determine hooking position and ability to sever monofilament leaders. Circle hooks increased elasmobranch catch but reduced haulback mortality and deep hooking relative to J-shaped hooks of the same or narrower width. Using fish vs. squid for bait increased shark catch and deep hooking. Pelagic stingray (Pteroplatytrygon violacea) catch and mortality were lower on wider hooks. Using circle instead of J-shaped hooks and fish instead of squid for bait, while benefitting sea turtles, odontocetes and possibly seabirds, exacerbates elasmobranch catch and injury, therefore warranting fishery-specific assessments to determine relative risks.
    Full-text · Article · Dec 2015 · Fish and Fisheries
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    • "Because most species of sharks have low reproductive potential they are well-equiped to sustain heavy fishing pressure and recovery times from overfishing are prolonged (Walker, 1998; Cortes, 2008; Smith et al., 2008). At the same time overexploitation and habitat degradation are main threats to elasmobranch populations (Prince, 2002; Gilman et al., 2008). Elasmobranchs, considered as commercial species, are generally caught by bottom trawl as by-catch in the Mediterranean Sea (Serena & Abella, 1999; Bertrand et al., 2000; Vacchi & Notarbartolo di Sciara, 2000). "
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    ABSTRACT: Total biomass, species composition, depth distribution, seasonal distribution and abundance of elasmobranchs were examined by commercial bottom trawls between 2009 and 2010 from Iskenderun Bay, Turkish coast of the northeastern Mediterranean. From 52 bottom trawl surveys, it was estimated that elasmobranchs represented 23% (190.1 of total fish biomass (840.8 in Iskenderun Bay. Dasyatis pastinaca, Gymnura altavela, Raja clavata and Rhinobatos spp. (Rhinobatos rhinobatos and Glaucostegus cemiculus) showed high occurrence and represented each between 11.10 and 38.46% of the whole elasmobranch biomass. The other species, Dipturus oxyrinchus, Raja miraletus, Torpedo marmorata and Torpedo torpedo, represented each between 0.12 and 2.82% of the total elasmobranchs biomass. Shark species, Mustelus mustelus, Scyliorhinus stellaris, Scyliorhinus canicula, Galeus melastomus and Squatina squatina, represented each between 0.45 and 1.7% of the whole elasmobranchs biomass. When seasonal distribution was examined, total catch of fish were 32.38, 23.24, 10.71 and 33.65%, of which elasmobranchs species constitute 24.11, 34.12, 20.42 and 21.34% in autumn, winter, spring and summer respectively. Single or sporadic captures were also recorded for Isurus oxyrinchus, Carcharhinus plumbeus, Carcharhinus altimus, Oxynotus centrina, Raja radula, Rhinoptera marginata and Pteromylaeus bovinus.
    Full-text · Article · Jul 2015 · Cahiers de Biologie Marine
    • "However, several authors have mentioned that the efficiency of such gear modifications is not only taxon-specific, but also depends on the specificities of the fleets and fisheries (e.g. Gilman et al., 2008; Read, 2007), and as such thorough experimental studies should be developed and implemented to test the efficiency of such gear modifications in each particular fishery (Gilman et al., 2012). The Portuguese pelagic longline fishery targeting swordfish in the Atlantic Ocean began in the 1970s, with only minor changes being incorporated in the last decade. "
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    ABSTRACT: The incidental bycatch of sea turtle in tuna and swordfish fisheries is currently recognized as one of the major threats to the populations of these species. Therefore a number of mitigation measures have been tested, particularly for longline fisheries targeting swordfish. As mitigation measures may also affect the fish catches, it is important to quantify these impacts both at the ecological and socio-economic levels. Between August 2008 and December 2011, a total of 202 experimental pelagic longline sets were carried out in the Tropical Northeast Atlantic Ocean. The combination J-hook baited with squid (traditionally used by the fishery) was compared against two circle hooks (one non-offset and one with 10° offset) and mackerel bait. Catches per unit effort (CPUE) were calculated and compared between the different hook style and bait combinations for all target, bycatch and discarded fish species. In addition, a GLM (generalized linear model) was applied for swordfish Xiphias gladius and blue shark Prionace glauca (two main target species) and bigeye thresher Alopias superciliosus (most discarded species). The swordfish catches were negatively affected when changing from the traditional gear (J-style hooks baited with squid) to one of the experimental combinations, with the bait type having a stronger influence than the hook style on this reduction. However, the overall target species CPUE and the value of the retained catch (VPUE, value per unit of effort) were not significantly affected, due to an increase on the blue shark CPUE. Furthermore, the hook style and the bait type did not seem to influence the at-haulback mortality rates of most discarded species, which were highly species-specific. Given the apparent lack of impact on the overall value of the retained catch, the use of circle hooks baited with mackerel on this particular fishery and region would be highly beneficial for sea turtle conservation, without affecting the economic viability of the fishery.
    No preview · Article · Apr 2015 · Fisheries Research
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