Study

Shark bycatch and mortality and hook bite-offs in pelagic longlines: Interactions between hook types and leader materials

  • Published source details Afonso A.S., Santiago R., Hazin H. & Hazin F.H.V. (2012) Shark bycatch and mortality and hook bite-offs in pelagic longlines: Interactions between hook types and leader materials. Fisheries Research, 131, 9-14

Actions

This study is summarised as evidence for the following.

Action Category

Modify longline configuration

Action Link
Marine Fish Conservation
  1. Modify longline configuration

    A replicated, controlled study in 2011 in an area of pelagic water in the southwestern Atlantic Ocean off Brazil (Afonso et al. 2012) found that modifying the configuration of tuna fishery longlines by using a nylon tether instead of a steel wire tether to suspend the hooks reduced the overall capture of unwanted sharks, but also reduced shark survival. Catch rates of all sharks combined were lower on nylon tethers than steel, irrespective of hook type (nylon: 4 sharks/1,000 hooks, steel: 8 sharks/1,000 hooks). However, if hooks that were bitten off were included (assumed to be by sharks) no effect of tether type was found (nylon: 8–12 sharks/1,000 hooks, steel: 8 sharks/1,000 hooks) and almost all occurred on nylon tethers. On nylon tethers only 34% of the shark catch (n=56) was alive compared to 54% (n=86) on steel tethers. Data were collected in January 2011 from 17 longline set deployments on a commercial fishing vessel. Longlines were made of nylon monofilament (3.5 mm diameter) and 90 km length. Each set had 1,000 hooks (total 17,000 hooks), randomly arranged with either nylon or stainless steel tethers and circle or J shaped hooks, baited with squid Illex sp.

    (Summarised by: Chris Barrett/Natasha Taylor)

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