Study

A cross-taxa assessment of pelagic longline by-catch mitigation measures: conflicts and mutual benefits to elasmobranchs

  • Published source details Gilman E., Chaloupka M., Swimmer Y. & Piovano S. (2016) A cross-taxa assessment of pelagic longline by-catch mitigation measures: conflicts and mutual benefits to elasmobranchs. Fish and Fisheries, 17, 748-784.

Actions

This study is summarised as evidence for the following.

Action Category

Modify longline configuration

Action Link
Marine Fish Conservation

Use a different bait type

Action Link
Marine Fish Conservation

Use a different hook type

Action Link
Marine Fish Conservation
  1. Modify longline configuration

    A review of 41 worldwide studies in 2016 of various methods to reduce unwanted shark and ray (Elasmobranchii) catches in pelagic longline fisheries (Gilman et al. 2016) found that modifying the configuration of longlines by using monofilament leader lines (to attach the hooks) instead of wire reduced the number of unwanted elasmobranchs caught, and survival at retrieval varied between species. Catch rates of elasmobranchs were lower for seven of 10 unwanted elasmobranch species using monofilament leader lines rather than wire, and higher for three species. Survival at gear retrieval was higher on monofilament leader lines for two of three species and lower for one compared to wire lines. The study performed a meta-analysis of 41 studies globally on the effects of different hook and bait types in pelagic longline fisheries on unwanted elasmobranch catch rates and survival.

    (Summarised by: Leo Clarke)

  2. Use a different bait type

    A systematic review in 2016 of 41 studies of pelagic longline fisheries worldwide (Gilman et al. 2016) found that changing bait type (using fish instead of squid), did not typically reduce the number of unwanted sharks and rays (Elasmobranchii) caught, or the incidence of deep-hooking injury associated with higher mortality, and did not increase survival at gear retrieval. Data were reported as graphical analyses (see review). When using fish instead of squid for bait, catch rates of sharks and rays were higher for seven of nine unwanted elasmobranch species, and lower for two species. Fish bait increased the incidence of deep-hooking injury in one of one unwanted species compared to squid bait. In addition, wider circle hooks baited with fish bait caught more of three of four species and fewer of one of four species, compared to narrow hooks (of all designs). The study performed a meta-analysis of 41 studies globally on the effects of different hook and bait types in pelagic longline fisheries on unwanted elasmobranch catch rates, survival and deep-hooking injury (see original paper for full search methods).

    (Summarised by: Leo Clarke)

  3. Use a different hook type

    A systematic review in 2016 of 40 studies assessing actions to reduce unwanted catch in pelagic longline fisheries worldwide (Gilman et al. 2016) found that using circle hooks instead of J-style hooks did not typically reduce the number of unwanted sharks and rays (Elasmobranchii) caught, but they did increase survival rate and reduce the incidence of deep-hooking. All data were reported as graphical analyses – see original paper. Catch rates were higher on circle hooks than J hooks for four of five species and lower for one species Survival rates at gear retrieval were higher on circle hooks than J hooks for three of three species. Using wider circle hooks rather than narrow J hooks increased catch rates of five of nine and reduced catch rates of four of nine species, whilst survival rates at gear retrieval were higher for five of six species and lower for one of six. The proportion of deep-hooked individuals (leading to higher fishing mortality) was lower on wider circle hooks than narrow J hooks for six of six species. In addition, wider hooks (of all designs) increased catch rates in one case and decreased them in another, compared to narrow hooks, and increased survival at gear retrieval. Wider circle hooks baited with fish bait caught more of three of four species and fewer of one of four species, compared to narrow hooks (of all designs). All data were reported as ratios of the number of findings with a significant increase or decrease. A meta-analysis was done of 40 studies in global locations on the effects of different hook and bait types on unwanted shark/ray catch rates, survival and deep-hooking injury, in pelagic longline fisheries.

    (Summarised by: Leo Clarke)

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