Reduce duration of time fishing gear is in the water

Overall effectiveness category Awaiting assessment
Number of studies: 2
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Effectiveness

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not assessed
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Background information and definitions

Reducing the length of time that the gear is left in the water (‘soak time’) reduces the opportunity for aquatic reptiles to become entangled in fishing gear. It may also reduce mortality rates, because when reptiles become entangled they are unable to reach the surface to replenish oxygen levels and so may drown.

Study locations

Key messages

Two studies evaluated the effects on reptile populations of reducing the duration of time fishing gear is in the water. One study was in the Gulf of Gabès (Tunisia) and one was in the Atlantic and North Pacific.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Survival (1 study): One randomized study in the Gulf of Gabès found that retrieving longlines immediately resulted in fewer loggerhead turtles dying compared to when line retrieval was delayed.

BEHAVIOUR (0 STUDIES)

OTHER (2 STUDIES)

Unwanted catch (2 studies): One randomized study in the Gulf of Gabès and one replicated study in the Atlantic and North Pacific found that the amount of time that longlines were in the water for did not affect the number of loggerhead turtles or leatherback and loggerhead turtles caught.

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 randomized study in 2007–2008 on the sea bottom in the Gulf of Gabès, Tunisia (Echwikhi et al. 2012) found that reducing the time longlines were in the water did not reduce the rate of unwanted catch of loggerhead turtles Caretta caretta in a bottom longline fishery, but did reduce the mortality rate of turtles caught. A similar number of turtles were caught when lines were retrieved immediately (immediate retrieval: 0.18 turtles/1,000 hooks) or left in the water for longer periods (1–2 hour soak: 0.34 turtles/1,000 hooks; >2 hours soak: 0.49 turtles/1,000 hooks; 16 turtles in total). Mortality rates of turtles caught accidentally were lower when bottom longlines were retrieved immediately (0/3 turtles died) compared to when longlines were retrieved after 1–2 hours (2/6 turtles died) or after more than 2 hours (5/7 turtles died). Turtle data was collected by onboard observers in 38 bottom longline deployments during 20 randomly selected fishing trips (1–3 deployments/trip) in July–September 2007–2008. Longline deployments consisted of a 10–12 km longline anchored to the seabed with 1 m long branchlines with hooks (48,020 total hooks deployed). Frozen Sardinella Sardinella aurita or common cuttlefish Sepia officinalis were used as bait. Longline deployments took place at any time of day and lines were retrieved either immediately, after 1–2 hours, or after >2 hours.
Study and other actions tested
Referenced paper
Echwikhi K., Jribi I., Bradai M.N. & Bouain A. (2012) Interactions of loggerhead turtle with bottom longline fishery in the Gulf of Gabès, Tunisia. Journal of the Marine Biological Association of the United Kingdom, 92, 853-858.
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.
Study and other actions tested
Referenced paper
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.

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

Related Actions

Actions	Effectiveness	Studies	Category
Reduce duration of time fishing gear is in the water Action Link	Awaiting assessment	2	Synopsis Link
Set commercial catch quotas Action Link	No evidence found (no assessment)	0	Synopsis Link
Limit the number of fishing vessels or fishing days in an area Action Link	No evidence found (no assessment)	0	Synopsis Link