Sea turtle bycatch mitigation in U.S. longline fisheries

Published source details Swimmer Y., Gutierrez A., Bigelow K., Barceló C., Schroeder B., Keene K., Shattenkirk K. & Foster D.G. (2017) Sea turtle bycatch mitigation in U.S. longline fisheries. Frontiers in Marine Science, 4, 260.
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This study is summarised as evidence for the following.

	Action	Category
	Modify number of hooks between floats on longlines Action Link
	Reduce duration of time fishing gear is in the water Action Link
	Deploy fishing gear at different depths Action Link
	Add lights to fishing gear Action Link
	Use a different bait type: Sea turtles Action Link
	Use circle hooks instead of J-hooks Action Link

Modify number of hooks between floats on longlines

A replicated study in 1992–2015 in pelagic longline fisheries in the Atlantic and North Pacific (Swimmer et al. 2017) found that using fewer hooks between floats on a longline did not reduce turtle by-catch in the Pacific but had mixed effects in the Atlantic depending on the species. All data presented as statistical model results. In the Pacific, by-catch of leatherback Dermochelys coriacea and loggerhead Caretta caretta turtles was not affected by the number of hooks between floats. In the Atlantic, the chance of catching leatherback turtles was lower with fewer hooks between floats, whereas loggerheads were less likely to be caught when there were fewer (<3 hooks) or more (>5 hooks) hooks between floats (see paper for details). Pelagic Observer Program data from (1992–2015) was used to determine the number of turtles caught/1,000 hooks, and variation in the number of hooks between floats (majority were 3–5 or 4–5 hooks/float) was used to test its effect on bycatch.

(Summarised by: William Morgan)
Reduce duration of time fishing gear is in the water

A replicated study in 1992–2015 in pelagic longline fisheries in the Atlantic and North Pacific (Swimmer et al. 2017) found that the amount of time longlines were in the water did not affect that number of leatherback Dermochelys coriacea and loggerhead Caretta caretta turtles caught as bycatch. The amount of time lines were in the water did not affect the chance of catching turtles (data presented as statistical model results) over the range of durations surveyed (around 8–12 hours). Duration was measured as the time between the line being set and when it was hauled in and varied between around 8–12 hours. Pelagic Observer Program data from (1992–2015) was used to determine the number of turtles caught/1,000 hooks, and variation in the amount of time lines were deployed for was used to test its effect on bycatch.

(Summarised by: William Morgan)
Deploy fishing gear at different depths

A replicated study in 1992–2015 in pelagic longline fisheries in the Atlantic (Swimmer et al. 2017) found that longlines with deeper hooks caught fewer loggerhead turtles Caretta caretta, but bycatch of leatherbacks Dermochelys coriacea was not affected by hook depth. The chance of catching loggerheads was lower when hooks were around 22 m deep or more (data presented as statistical model results), but leatherback catch was unaffected by hook depth. Maximum hook depth was calculated by adding up the length of the floatline, branchline and dropline. Pelagic Observer Program data from (1992–2015) was used to determine the number of turtles caught/1,000 hooks. Variation in practices relating to hook depth was used to test its effect on bycatch.

(Summarised by: William Morgan)
Add lights to fishing gear

A replicated study in 1992–2015 in pelagic longline fisheries in the Atlantic and North Pacific (Swimmer et al. 2017) found that using more light sticks on longlines resulted in a higher chance of catching loggerhead turtles Caretta caretta but had no impact on leatherbacks Dermochelys coriacea (data reported as statistical model results). Pelagic Observer Program data from (1992–2015) was used to determine the number of turtles caught/1,000 hooks, and variation in the number of light sticks/hook (average of 0.4–0.9 sticks/hook) was used to test its effect on bycatch.

(Summarised by: William Morgan)
Use a different bait type: Sea turtles

A replicated, before-and-after study in pelagic longline fisheries in the Atlantic and North Pacific (Swimmer et al. 2017) found that using fish bait resulted in less leatherback Dermochelys coriacea and loggerhead Caretta caretta turtle bycatch compared to when squid bait was used. The number of turtles caught on longlines was lower in the Atlantic when fish bait was used (leatherback: 0–6% chance with circle hooks, 13% with J hooks; Loggerhead: 0–5% with circle hooks, 9% with J hooks) compared to squid bait (leatherback: 9% with circle hooks, 20% with J hooks; Loggerhead: 11% with circle hooks, 18% with J hooks). The same was true in the Pacific (loggerhead: circle hook: 1% with fish, 2% with squid; j hook: 5% with fish, 13% with squid). Following the introduction of regulations on bait and hooks, overall turtle bycatch was reduced in both the Atlantic (leatherback: 40% reduction; loggerhead: 61% reduction) and Pacific (leatherback: 84% reduction; loggerhead 95% reduction). Fisheries were closed in 2001 and re-opened with regulations regarding bait (fish or squid) and hook type (circle or J hooks) (see paper for details). Pelagic Observer Program data from before (1992–2001) and after (2004–2015) regulations was used to determine the number of turtles caught/1,000 hooks.

(Summarised by: William Morgan)
Use circle hooks instead of J-hooks

A replicated, before-and-after study in 1992–2015 in pelagic longline fisheries in the Atlantic and North Pacific (Swimmer et al. 2017) found that using circle hooks on longlines resulted in less leatherback Dermochelys coriacea and loggerhead Caretta caretta bycatch compared to when J-hooks were used. The chance of catching turtles on longlines was lower in the Atlantic when circle hooks were used (leatherback: 0–6% chance with fish bait (species not provided), 9% with squid bait (species not provided); loggerhead: 0–5% with fish bait, 11% with squid bait) compared to J-hooks (leatherback: 13% with fish bait, 20% with squid bait; loggerhead: 9% with fish bait, 18% with squid bait). The same was true in the Pacific (leatherback - circle hook: <1% vs. J-hook: 1%; loggerhead: circle hook: 1% with fish, 2% with squid vs. J-hook: 5% with fish, 13% with squid). Following the introduction of regulations on bait and hooks, overall bycatch was reduced in both the Atlantic (leatherback: 40% reduction; loggerhead: 61% reduction) and Pacific (leatherback: 84% reduction; loggerhead 95% reduction). Fisheries were closed in 2001 and re-opened with regulations regarding bait (fish or squid) and hook type (circle or J-hooks) (see paper for details). Pelagic Observer Program data from before (1992–2001) and after (2004–2015) regulations was used to determine the number of turtles caught/1,000 hooks.

(Summarised by: William Morgan)