By-catch in a tropical shrimp fishery: are TEDs effective in excluding rays?

    Onderzoeksoutput: Hoofdstuk in Boek/Rapport/CongresprocedureC3: Congres abstract

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    Tropical shrimp trawling generally produces significant amounts of by-catch, including endangered marine species. To avoid incidental capture of marine turtles, Turtle Excluder Devices (TEDs) are now widespread. TEDs are effective in avoiding turtle by-catch and theoretically exclude all organisms large enough not to pass in between the TED’s vertical bars. Rays (Batoidea; Chondrichthyes: Elasmobranchii) are particular in this respect, because even large sized individuals might pass through a TED as a result of their flattened body shape. Several ray species are listed as threatened and they are very vulnerable to fishing mortality due to their life-history characteristics. By-catch of rays in tropical shrimp trawling is thus highly undesirable.
    The current study assessed the potential of TEDs in reducing ray by-catch in the seabob shrimp (Xiphopenaeus kroyeri) fishery in Suriname. Sixty-five catch-comparison hauls were conducted, comparing ray by-catch in trawls fitted with TEDs (test-net) and without TEDs (control-net). Overall, catch rate of rays was reduced by 36% in the test-net. Rays caught in the test-net were on average 21% smaller than those in the control-net meaning larger ones were indeed able to escape, while smaller individuals passed through the TED, ending up in the codend. As such, TEDs were most efficient in excluding Dasyatis geijskesi, the largest ray species, while no significant reduction was observed for the small-sized Urotrygon microphalmum. A GLMM was fitted to calculate exclusion-at-size for the two most abundant species. Exclusion of Dasyatis guttata reached 100% for individuals over 50cm (body width), while Gymnura micrura only approached 80% exclusion even for the largest individuals (70cm). Nevertheless, small sized (<40cm) rays were most common in the catch composition of the control-net. TEDs are thus inappropriate to fully protect ray populations in seabob shrimping grounds off Suriname. To reduce by-catch of small-sized rays, other net adaptations have to be tested.
    Oorspronkelijke taalEngels
    Titel ICES Symposium: Effects of fishing on benthic fauna, habitatand ecosystem function : June 16-19, Tromso, Norway
    Publicatiedatum2014
    PublicatiestatusGepubliceerd - 2014

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