Study

Reducing sea turtle interactions in the Hawaii-based longline swordfish fishery

  • Published source details Gilman E., Kobayashi D., Swenarton T., Brothers N., Dalzell P. & Kinan-Kelly I. (2007) Reducing sea turtle interactions in the Hawaii-based longline swordfish fishery. Biological Conservation, 139, 19-28.

Actions

This study is summarised as evidence for the following.

Action Category

Use circle hooks instead of J-hooks

Action Link
Reptile Conservation

Use a different bait type: Sea turtles

Action Link
Reptile Conservation
  1. Use circle hooks instead of J-hooks

    A before-and-after study in 1994–2006 in pelagic waters off the coast of Hawaii, USA (Gilman et al. 2007) found that fish-baited circle hooks reduced unwanted catch of sea turtles compared to squid-baited J-hooks in a swordfish Xiphias gladius longline fishery. Capture rates of leatherback Dermochelys coriacea reduced by 83% (0.006 turtles/1,000 hooks) and loggerhead Caretta caretta turtles by 90% (0.012 turtles/1,000 hooks) when fish-baited circle hooks were used compared to squid-baited J-hooks (leatherback: 0.03 turtles/1,000 hooks, loggerhead: 0.13 turtles/1,000 hooks). Mortality rates were similar whether circle (35 of 35 turtles survived) or J-hooks (180 of 182 survived) were used. Fewer turtles were deeply hooked when circle hooks were used (leatherback: 0%, hard-shell: 22%) compared to J-hooks (10%, 60%). Target swordfish catch increased by 16% after circle hooks were introduced, but tuna (Scombridae spp.), mahi mahi Coryphaena spp., opah Lampris spp. and wahoo Acanthocybium solandri catch reduced by 34–50% (see paper for details). Catch data from the US National Marine Fisheries Service observer programme were compared from before and after regulations were introduced requiring the use of 10° offset 18/0 circle hooks with fish bait in a pelagic swordfish longline fishery. Prior to the regulations, 9/0 J-hooks with squid bait were used. ‘Before’ data used was from 1994–2002 (120 observed trips of 1,631 sets with 1,282,748 J hooks deployed) and ‘after’ data was from 2004–2006 (164 observed trips of 2,631 sets with 2,150,674 hooks deployed).

    (Summarised by: Maggie Watson, Katie Sainsbury)

  2. Use a different bait type: Sea turtles

    A before-and-after study in 1994–2006 in pelagic waters off the coast of Hawaii, USA (Gilman et al. 2007) found fish-baited circle hooks reduced unwanted catch of sea turtles compared to squid-baited J-hooks in a swordfish Xiphias gladius longline fishery. Capture rates of leatherback turtles Dermochelys coriacea reduced by 83% (0.006 turtles/1,000 hooks) and loggerhead turtles Caretta caretta by 90% (0.012 turtles/1,000 hooks) when fish-baited circle hooks were used compared to squid-baited J-hooks (leatherback: 0.03 turtles/1,000 hooks, loggerhead: 0.13 turtles/1,000 hooks). Mortality rates were similar whether fish-baited circle or squid-baited J hooks were used (circle: 35 of 35 turtles survived, J: 180 of 182). Fewer turtles were deeply hooked when fish-baited circle hooks were used (leatherback: 0%, hard-shell: 22%) compared to squid-baited J hooks (10%, 60%). Swordfish catch increased by 16% after fish-baited circle hooks were introduced, but tuna (Scombridae), mahi mahi Coryphaena spp, opah Lampris spp. and wahoo Acanthocybium solandri catch reduced by 34–50% (see paper for details). Catch data from the US National Marine Fisheries Service observer programme were compared from before and after regulations were introduced requiring the use of 10° offset 18/0 circle hooks with fish bait in a pelagic swordfish longline fishery. Prior to the regulations, 9/0 J hooks with squid bait were used. ‘Before’ data used was from 1994–2002 (120 observed trips of 1,631 sets with 1,282,748 J hooks deployed) and ‘after’ data was from 2004–2006 (164 observed trips of 2,631 sets with 2,150,674 hooks deployed).

    (Summarised by: Maggie Watson, Katie Sainsbury)

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