Study

Permanent magnets reduce bycatch of benthic sharks in an ocean trap fishery

  • Published source details Richards R.J., Raoult V., Powter D.M. & Gaston T.F. (2018) Permanent magnets reduce bycatch of benthic sharks in an ocean trap fishery. Fisheries Research, 208, 16-21.

Actions

This study is summarised as evidence for the following.

Action Category

Attach an electropositive deterrent to fishing gear

Action Link
Marine Fish Conservation

Modify fishing trap/pot configuration

Action Link
Marine Fish Conservation
  1. Attach an electropositive deterrent to fishing gear

    A replicated, controlled study in 2013–2014 in three areas of sandy seabed in the South Pacific Ocean off the coast of New South Wales, Australia (Richards et al. 2018) found that traps fitted with magnets caught fewer unwanted sharks and rays (Elasmobranchii), and more of the commercially targeted species snapper Pagrus auratus, compared to conventional traps or traps fitted with non-magnetic material. Catch rates of sharks and rays were lower in traps with magnets (0.2 ind./trap) compared to standard traps (0.3 ind./trap) and traps with non-magnetic material (0.3 ind./trap). Target catches of snapper were highest in traps with magnets (magnets: 1.1 kg/trap, standard: 0.8 kg/trap, non-magnetic: 0.98 kg/trap). In addition, the presence of sharks and rays in traps reduced target snapper catches by 38%. Between December 2013 and August 2014, a total of 1,015 traps of three different designs were set in three areas of sandy seabed at 5–102 m depth. The fish traps had a wooden frame 180 x 120 x 80 cm covered in 50 mm wire mesh with a 100 x 60 mm escape panel at the rear. Each trap design had three funnel entrances (290 x 540 mm outer and 60 x 270 mm inner) which had either four magnets (75 x 13 x 16 mm) attached to each funnel, four non-magnetic bars of the same size attached to each funnel, or no change to the standard trap.

    (Summarised by: Leo Clarke)

  2. Modify fishing trap/pot configuration

    A replicated, controlled study in 2013–2014 in three areas of sandy seabed in the Tasman Sea off the coast of New South Wales, Australia (Richards et al. 2018) found that modified traps fitted with permanent magnets reduced the catches of unwanted sharks and rays (Elasmobranchii), compared to conventional traps with no magnets or traps fitted with non-magnetic material. Catch rates of sharks/rays in traps with magnets were lower (0.2/trap) than traps with no magnets (0.3/trap) and traps with non-magnetic material (0.3/trap). Commercial target snapper Pagrus auratus catches were higher in traps with magnets (1.1 kg/trap) than without magnets (0.8 kg/trap) and 1.0 kg/trap in traps with non-magnetic material. In addition, the presence of sharks/rays in traps reduced commercial target snapper catches by 34% (1.5 vs 2.3 kg/trap). Between December 2013 and August 2014, a total of 1,015 traps of three different designs were set in three areas of sandy seabed at 5–102 m depth. Traps had a wooden frame (180 × 120 × 80 cm) covered in 50 mm wire mesh with a 100 × 60 mm escape panel at the rear. Each trap design had three funnel entrances, either with or without four magnets (75 × 13 × 16 mm) or with four non-magnetic bars (same size as magnetic) attached to each funnel.

    (Summarised by: Leo Clarke)

Output references
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