Study

Comparing the effects of offset and non-offset circle hooks on catch rates of fish and sea turtles in a shallow longline fishery

  • Published source details Swimmer Y., Arauz R., Wang J., Suter J., Musyl M., Bolaños A. & López A. (2010) Comparing the effects of offset and non-offset circle hooks on catch rates of fish and sea turtles in a shallow longline fishery. Aquatic Conservation: Marine and Freshwater Ecosystems, 20, 445-451.

Actions

This study is summarised as evidence for the following.

Action Category

Use non-offset hooks

Action Link
Reptile Conservation

Use a different hook type

Action Link
Marine Fish Conservation
  1. Use non-offset hooks

    A replicated, paired study in 2004–2006 in pelagic waters in the Gulf of Papagayo, Costa Rica (Swimmer et al. 2010) found that using non-offset circle hooks did not reduce unwanted catch rates of sea turtles compared to offset circle hooks in a shallow-set longline fishery. Catch rates of olive ridley Lepidochelys olivacea and green Chelonia mydas sea turtles were similar when non-offset circle hooks were used (olive ridley: 19.1 turtles/1,000 hooks, green: 0.3) compared to offset circle hooks (18.9, 0.4). Catch rates of commercially-targeted dolphinfish Coryphaena spp. were similar between hook types (non-offset: 53.1 fish/1,000 hooks, offset: 51.3). Circle hooks (size: 14/0) with and without a 10ᵒ offset point relative to the shaft of the hook were tested during six fishing trips with 42 shallow-set longline deployments (33,876 total hooks, 800 hooks/day) in November–March, 2004–2006. Hook types were alternated along each longline. Humboldt squid Dosidicus gigas was used as bait (approximately 50 x 50 x 250 mm sized pieces). Lines were deployed in the mornings and hauled in after 12 hours. Sea turtle catch was monitored by onboard observers.

    (Summarised by: Katie Sainsbury)

  2. Use a different hook type

    A replicated, controlled study in 2004–2006 in pelagic waters in the Gulf of Papagayo, Pacific Ocean, Costa Rica (Swimmer et al. 2010) found that using a different circle hook type (offset) in a longline fishery targeting dolphinfish Coryphaena hippurus did not reduce the incidental capture of pelagic stingray Pteroplatytrygon violacea or silky shark Carcharinus falciformis, compared to conventional non-offset circle hooks. Incidental catch was similar with offset and non-offset hooks for stingray (6.1 vs 4.7 ind/line) and silky shark (1.8 vs 2.5 ind/line). Eleven species of bony fish were also caught incidentally, for which catches were higher on offset hooks compared to non-offset hooks for seven species, lower for two and similar for two (see original paper for species individual data, not tested statistically). Data were collected from fishing trips between November and March 2004–2006, deploying longlines with offset (by 10°) and non-offset circle hook types (size 14/0) set alternately along 7 m lines attached to the main monofilament fishing line. All trips used Humboldt squid Dosidcus gigas as bait to target dolphinfish. Lines were deployed in the morning and soaked for 12 hours. All species caught/hook type were recorded. Data from 33,876 hooks across six trips were included in the analysis.

    (Summarised by: Natasha Taylor)

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