Effects of 17/0 circle hooks and bait on sea turtles bycatch in a Southern Atlantic swordfish longline fishery

Published source details Santos M.N., Coelho R., Fernandez-Carvalho J. & Amorim S. (2013) Effects of 17/0 circle hooks and bait on sea turtles bycatch in a Southern Atlantic swordfish longline fishery. Aquatic Conservation: Marine and Freshwater Ecosystems, 23, 732-744.
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This study is summarised as evidence for the following.

	Action	Category
	Use a different bait type: Sea turtles Action Link
	Use circle hooks instead of J-hooks Action Link

Use a different bait type: Sea turtles

A replicated, controlled study in 2008–2012 in pelagic waters in the Southern Atlantic (Santos et al. 2013) found that using mackerel Scomber spp. bait reduced unwanted catch of loggerhead turtles Caretta caretta and leatherback turtles Dermochelys coriacea compared to using squid Illex spp., but when squid bait was used, unwanted catch rates depended on the hook type used. Unwanted turtle catch was lower when mackerel bait was used regardless of hook type (non-offset circle: 0.2 turtles/1,000 hooks; offset circle: 0.2; J-hook: 0.3), compared to squid bait. The number of turtles caught by squid bait varied with hook type (non-offset circle hooks: 0.7 turtles/1000 hooks; offset circle hooks: 0.6 turtles; J-hooks 1.7). This pattern was observed for both leatherback and loggerhead turtle species (see paper for details). Overall turtle mortality rates were similar regardless of whether squid (146/228 individuals alive) or mackerel (40/58 individuals alive) was used as bait. Three hook types baited with either squid or mackerel were used alternately on a commercial longline fishing vessel: traditional J-hook (size: 9/0) and two circle hooks (a non-offset and a 10ᵒ offset, both sized: 17/0; 148,800 total hooks/type). In total 310 longline deployments (1,440 hooks/deployment; 446,400 total hooks, lines set to 20–50 m depths) were carried out overnight in October 2008–February 2012. One bait type was used in each deployment. Turtle catch was monitored by onboard observers.

(Summarised by: Katie Sainsbury)
Use circle hooks instead of J-hooks

A controlled study in 2008–2012 in pelagic waters in the Southern Atlantic (Santos et al. 2013) found that using circle hooks reduced unwanted catch of loggerhead Caretta caretta and leatherback Dermochelys coriacea turtles compared to using J-hooks when using squid Illex spp. instead of fish Scomber spp. bait. When squid was used as bait, the catch of all turtles was lower when using non-offset circle hooks (0.7 turtles/1,000 hooks) and offset circle hooks (0.6 turtles/1,000 hooks) compared to J-hooks (1.7 turtles/1,000 hooks). Total turtle catch was similar when mackerel bait was used (non-offset circle: 0.2 turtles/1,000 hooks; offset circle: 0.2 turtles/1,000 hooks; J-hook: 0.3 turtles/1,000 hooks). This pattern was observed for both leatherback and loggerhead turtles (see original paper for details). Overall turtle survival was higher when offset circle hooks were used (49 of 59, 83% of individuals alive) compared to non-offset circle hooks (38 of 72, 53% of individuals alive) or J-hooks (99 of 155, 64% of individuals alive). This pattern was observed for loggerhead turtles, but leatherback turtle survival was similar between hook types (see original paper for details). Three hook types baited with either squid or mackerel were used alternately on a commercial longline fishing vessel: traditional J-hook (size: 9/0) and two circle hooks (a non-offset and a 10ᵒ offset, both sized: 17/0; 148,800 total hooks/type). In total 310 longline deployments (1,440 hooks/deployment; 446,400 total hooks, lines set to 20–50 m depths) were carried out overnight in October 2008–February 2012. One bait type was used in each deployment. Turtle catch was monitored by onboard observers.

(Summarised by: Katie Sainsbury)