Release accidentally caught (‘bycatch’) reptiles

Overall effectiveness category Awaiting assessment
Number of studies: 3
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Background information and definitions

After reptiles have become caught in nets or traps, or hooked on lines, it may be possible to rehabilitate and release individuals depending on the extent or severity of any injuries incurred. Ideally rehabilitation and releases would follow established best practice guidelines to maximise survival rates and ensure each individual is sufficiently healthy prior to release.

For studies that test different methods for safely releasing accidentally captured reptiles, see also Establish handling and release procedures for accidentally captured or entangled (‘bycatch’) reptiles. For studies where injured reptiles were rehabilitated prior to release, see Species management – Rehabilitate and release injured or accidentally caught individuals.

Study locations

Key messages

Three studies evaluated the effects on reptile populations of releasing accidentally caught reptiles. One study was in each of the Caribbean Sea, Costa Rica and the Republic of Korea.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (2 STUDIES)

Survival (2 studies): One replicated study in the Caribbean Sea found that from a released group of green turtles that included some accidentally caught and some head-started individuals, some survived for at least several months in the wild. One replicated study in the Republic of Korea found that green turtles caught in pound nets all survived for at least two weeks to a year after release.

BEHAVIOUR (1 STUDY)

Behaviour change (1 study): One controlled study off the Pacific coast of Costa Rica found that the behaviour of longline-caught sea turtles following release was broadly similar to free-swimming turtles.

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 study in 1967–1974 in pelagic waters in the Caribbean Sea near Bermuda (Burnett-Herkes 1974) found that some accidentally-caught immature and some head-started green turtles Chelonia mydas survived at least several months in the wild. In total, 16 of 108 released accidentally-caught or head-started immature green turtles were recaptured. Nine turtles were recovered within 10 months, other recaptured turtles had spent up to 27 months in the wild. Most turtles were recaptured a few hundred metres to 14 km away from their point of release, except for one head-started turtle that was recaptured 2,315 km away from the release site after 10 months. In 1967–1971, eighty-nine green turtles were head-started in Costa Rica and released after approximately two years on the north and south coasts of Bermuda. In addition, 19 wild-born immature green turtles caught accidentally by local fisherman were tagged and released as part of the same programme.
Study and other actions tested
Referenced paper
Burnett-Herkes J. (1974) Returns of green sea turtles (Chelonia mydas Linnaeus) tagged at Bermuda. Biological Conservation, 6, 307-308.
A controlled study in 2001–2003 in pelagic waters on the Pacific coast of Costa Rica (Swimmer et al. 2006) found that sea turtles released back into the water after becoming caught on longline hooks travelled similar distances and dived to similar depths compared to free-swimming turtles. Longline-caught turtles travelled similar total distances (117–520 nautical miles) and distances each day (5 nautical miles/day) compared to free-swimming turtles (total distance: 50–443 nautical miles; 5 nautical miles/day). Longline-caught turtles made similar depth daily maximum dives (81–408 m) compared to free-swimming turtles (84–264 m). Longline-caught turtles made more deeper daytime dives than free-swimming turtles, which were more likely to make deeper dives at night (no statistical tests carried out, see original paper for details). None of the longline-caught turtles died during the study; one free-swimming turtle mortality occurred. In total nine olive ridley turtles Lepidochelys olivacea and one green turtle Chelonia mydas caught by fishermen were monitored using radio tags in November 2001–August 2003. Hooks were removed from the turtle’s jaw or mouth (except for one individual, see paper for details) and turtles were released. At the same time, five free-swimming olive ridley turtles were collected by the boat, radio-tagged and released for behavioural comparisons. On average, tags remained on line-caught turtles and free-swimming turtles for 54 and 60 days respectively.
Study and other actions tested
Referenced paper
Swimmer Y., Arauz R., McCracken M., McNaughton L., Ballestero J., Musyl M., Bigelow K. & Brill R. (2006) Diving behavior and delayed mortality of olive ridley sea turtles Lepidochelys olivacea after their release from longline fishing gear. Marine Ecology Progress Series, 323, 253-261.
A replicated study in 2015–2017 in three coastal sites of Jeju Island, the Republic of Korea (Jang et al. 2018) found that after releasing green turtles Chelonia mydas that were caught in pound nets near the capture site, all eight turtles survived. Turtles survived for at least 17–314 days and moved 36–1,393 km after being released. Five turtles stayed close to Jeju island and moved 36–581 km; one travelled west toward China and moved 514 km and two travelled east towards Japan and moved 489 and 1,393 km. In August 2015–September 2016, eight healthy turtles (7 juveniles, 1 adult) that were caught accidentally in pound nets (approximate size 25 x 15 x 10 m) were fitted with satellite transmitters before being released near the capture site. Transmitters were attached to the carapace using polyester resin and fiberglass cloth. Turtles were tracked for 17–314 days, with a maximum of one location/individual/day retained for analysis.
Study and other actions tested
Referenced paper
Jang S., Balazs G.H., Parker D.M., Kim B.Y., Kim M.Y., Ng C.K.Y. & Kim T.W. (2018) Movements of green turtles (Chelonia mydas) rescued from pound nets near Jeju Island, Republic of Korea. Chelonian Conservation and Biology, 17, 236-244.

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
Release accidentally caught (‘bycatch’) reptiles Action Link	Awaiting assessment	3	Synopsis Link
Modify fishing gear to reduce reptile mortality in the event of unwanted catch Action Link	Awaiting assessment	1	Synopsis Link
Establish handling and release procedures for accidentally captured or entangled (‘bycatch’) reptiles Action Link	Awaiting assessment	1	Synopsis Link