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)

Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 21

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.


Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust