Use non-offset hooks

Overall effectiveness category Awaiting assessment
Number of studies: 2
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Effectiveness

not assessed
Certainty

not assessed
Harms

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Calculating overall effectiveness category

Background information and definitions

The hook points on non-offset hooks lie along the same plane as the hook shaft, whereas the points on offset hooks are bent sideways and out of alignment with the hook shaft (usually within 25ᵒ). As a result, offset hooks may be more likely to catch turtles in the mouth or on the body than non-off set hooks.

Studies in this action specifically test whether non-offset hooks are more, or less likely to catch sea turtles than offset hooks. For studies that compare using different types of circle hooks to different types of J-hooks, see: Use circle hooks instead of J-hooks.

See Use non-ringed hooks and Use larger hooks for studies that specifically test the effect of using these variations in hook design. See also See also Modify number of hooks between floats on longlines.

Study locations

Key messages

Two studies evaluated the effects of using non-offset hooks on reptile populations. One study was off the Pacific coast of Costa Rica and one was in the north-east Atlantic.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Survival (1 study): One replicated, controlled, paired study in the north-east Atlantic Ocean found that mortality of leatherback turtles was similar when caught with non-offset hooks or offset hooks.

BEHAVIOUR (0 STUDIES)

OTHER (2 STUDIES)

Unwanted catch (2 studies): One of two replicated, paired studies (including one controlled study) off the Pacific coast of Costa Rica and in the north-east Atlantic found that non-offset circle hooks caught a similar number of olive ridley and green turtles compared to offset circle hooks in a shallow-set longline fishery. The other study found that non-offset G-style circle hooks caught fewer leatherback and hard-shell turtles compared to offset Gt-style circle hooks or offset J-hooks in a longline swordfish fishery.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

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.
Study and other actions tested
Referenced paper
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.
A replicated, controlled, paired study in 2008–2011 in pelagic waters in the north-east Atlantic Ocean (Coelho et al. 2015) found that using non-offset circle hooks instead of offset J-hooks in a longline swordfish Xiphias gladius fishery reduced unwanted catch of sea turtles. Unwanted sea turtle catch was reduced with non-offset G-style circle hooks (leatherback turtles Dermochelys coriacea: 0.3–0.5 turtles/1,000 hooks; hard-shell sea turtles [Cheloniidae spp.]: 0.1), but not offset Gt-style circle hooks (leatherback turtles: 0.7–0.8 turtles/1,000 hooks; hard-shell turtles: 0.1–0.2), compared to traditional offset J-hooks (leatherback turtles: 0.9–1.0 turtles/1,000 hooks; hard-shell turtles: 0.2–0.4). Mortality and hooking location of leatherback turtles was similar between hook types (see paper for details). In August 2008–December 2011, a commercial vessel carried out 202 overnight longline fishing deployments (lines: 55 nm long with 5 branchlines, deployed 20–50 m deep, lit by green lights). Whole squid (Illex spp.) or mackerel (Scomber spp.) were used as bait (one type of bait/line deployment). Three hook styles: 10° offset J-hooks traditionally used in the fishery; non-offset G-style circle hooks; and 10° offset Gt-style circle hooks were alternated every 70–80 hooks along the line in a randomized start order (254,520 total hooks deployed with 42,420 of each hook/bait combination). Unwanted catch was counted and released.
Study and other actions tested
Referenced paper
Coelho R., Santos M.N., Fernandez-Carvalho J. & Amorim S. (2015) Effects of hook and bait in a tropical northeast Atlantic pelagic longline fishery: Part I-Incidental sea turtle bycatch. Fisheries Research, 164, 302-311.

Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Reptile Conservation

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