Release captive-bred reptiles into the wild: Sea turtles

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

Captive breeding is normally used to provide individuals that can then be released into the wild (often called ‘reintroduction’) to either re-establish a population that has been lost, or to augment an existing population (‘restocking’).

Release techniques vary considerably, from ‘hard releases’ involving the simple release of individuals into the wild to ‘soft releases’ which involve a variety of adaptation and acclimatisation techniques before release, or post-release feeding and care.

This action includes studies describing the effects of release programmes for captive-bred reptiles that do not specifically test the effectiveness of specific release techniques. For studies that compare specific release techniques see Use holding pens or enclosures at release site prior to release of captive-bred reptiles; Use holding pens or enclosures at release site prior to release of wild reptiles and Release reptiles into burrows.

Due to the number of studies found, this action has been split by species group, though no studies were found for amphisbaenians. See here for: Tortoises, terrapins, side-necked & softshell turtles; Snakes & lizards; Crocodilians or Tuatara.

Study locations

Key messages

Three studies evaluated the effects of releasing captive-bred sea turtles into the wild. Two studies were in the Gulf of Mexico and one was in the Caribbean.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (3 STUDIES)

Reproductive success (1 study): One replicated study in the Caribbean found that eight of over 30,000 captive-bred green turtles released into the wild (around 15,000 reared to one year or more in captivity) were observed nesting and two produced clutches of >100 eggs with hatching success of 63% and 88%.
Survival (3 studies): Three replicated studies in the Gulf of Mexico and the Caribbean reported that following releases of captive-bred Kemp's ridley turtles and green turtles into the wild, 120–606 of 22,000–30,000 turtles survived for 1–19 years after release.
Condition (1 study): One replicated study in the Gulf of Mexico found that captive-bred Kemp's ridley turtles released into the wild grew by 19–59 cm over 1–9 years.

BEHAVIOUR (0 STUDIES)

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 1978–1992 at several sites on the Texan coast of the Gulf of Mexico, USA (Caillouet et al. 1995; same experimental set-up as Caillouet et al. 1995) found that some released captive-bred and reared Kemp's ridley turtles Lepidochelys kempii survived up to 9 years in the wild. Of the 22,608 turtles released, more than 117 were recaptured in the Gulf of Mexico and adjacent bays 1–9 years after release. Recaptured turtles grew by 19–59 cm (straight carapace length) over a period of 1–9 years. In 1978–1992, a total of 22,608 turtles were released into the Gulf of Mexico or adjacent bays, including 18,790 yearlings. Of these yearlings, 18,174 (97%) were released into the Gulf of Mexico, and 616 (3%) into adjacent bays. Turtles were recaptured on an ad-hoc basis by a sea turtle stranding and salvage network and commercial or recreational fishers.
Study and other actions tested
Referenced paper
Caillouet Jr C.W., Fontaine C., Manzella-Tirpak S.A. & Williams T.D. (1995) Growth of head-started Kemp's Ridley sea turtles (Lepidochelys kempii) following release. Chelonian Conservation and Biology, 1, 231-234.
A replicated study in 1978–1993 at 13 sites on the Mexican, Texan and Floridian coasts of the Gulf of Mexico (Caillouet et al. 1995; same experimental set-up as Caillouet et al. 1995) found that following large scale releases of captive-bred yearling Kemp’s ridley turtles Lepidochelys kempii, some individuals survived and were recaptured 1–10 years after release. At least 606 turtles survived and were recaptured 1–2 years after release, and at least 59 survived and were recaptured 3–10 years after release. In 1978–1992, a total of 22,255 yearling turtles were released at 13 locations, with 197 released in Campeche, Mexico; 3,268 in west Florida, USA; and 18,174 in Texas, USA. Turtles were recaptured on an ad-hoc basis by a sea turtle stranding and salvage network and commercial or recreational fishers.
Study and other actions tested
Referenced paper
Caillouet Jr C.W., Fontaine C.T., Manzella-Tirpak S.A. & Shaver D. (1995) Survival of head-started Kep's Ridely sea turtles (Lepidochelys kempii) released into the Gulf of Mexico or adjacent bays. Chelonian Conservation and Biology, 1, 285-292.
A replicated study from 1980–2005 in the Cayman Islands and wider Caribbean (Bell et al. 2005) found that some released captive-bred and reared green turtles Chelonia mydas were recaptured as adults throughout the Caribbean, and some were observed successfully nesting. A total of 392 tagged animals were recaptured at intervals of six months to 19 years after release. Of these, 160 were recaptured in the Cayman Island and 232 from elsewhere (2 from Belize, 176 from Cuba, 8 from Honduras, 1 from Mexico, 38 from Nicaragua, 2 from Panama, 4 from USA and 1 from Venezuela). Eight turtles were observed nesting, and two individuals produced clutches of 112 and 110 eggs, with hatching success of 63% and 88%. Rearing occurred at the Cayman Turtle Farm: a commercial turtle meat operation that raised green turtles from captive adults and released excess turtles in to the wild. Eggs were laid on an artificial beach, incubated in a hatchery and then hatchlings reared in groups. Between 1980 and 2001, turtles were released (16,422 hatchlings, 14,347 yearlings and 65 turtles of 19–77 months old) during October–November. Approximately 80% of all turtles released were tagged using a variety of methods (notching, flipper tags and living tags). Recapture information came from intentional and accidental capture by fisheries throughout the Caribbean, stranding networks in the USA, an active recapture effort in 1994 (Cayman Islands) and observations of nesting females.
Study and other actions tested
Referenced paper
Bell C. D. L., Parsons J., Austin T. J., Broderick A. C., Ebanks-Petrie G. & Godley B. J. (2005) Some of them came home: the Cayman Turtle Farm headstarting project for the green turtle Chelonia mydas. Oryx, 39, 137-148.

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?

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This Action forms part of the Action Synopsis:

Reptile Conservation

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Breed reptiles in captivity: Snakes – Elapids Action Link	Awaiting assessment	4	Synopsis Link
Alter incubation temperatures to achieve optimal/desired sex ratio: Sea turtles Action Link	Awaiting assessment	1	Synopsis Link
Release captive-bred reptiles into the wild: Tortoises, terrapins, side-necked & softshell turtles Action Link	Awaiting assessment	14	Synopsis Link