Release captive-bred reptiles into the wild: Tuatara

Overall effectiveness category Awaiting assessment
Number of studies: 2
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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: Sea turtles; Tortoises, terrapins, side-necked & softshell turtles; Snakes & lizards or Crocodilians.

Study locations

Key messages

Two studies evaluated the effects of releasing captive-bred tuatara into the wild. One study was in New Zealand and one was a global review.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Abundance (1 study): One global review found that when using recruitment to the adult population as a measure of success, 32% of reptile translocations/releases (releases of captive individuals were 7% of total projects) were successful.
Condition (1 study): One study in New Zealand found that tuatara reared close to the release site had higher growth, but similar body condition compared to individuals reared in a warmer climate.

BEHAVIOUR (1 STUDY)

Behaviour change (1 studies): One study in New Zealand found that tuatara reared close to the release site had similar home range sizes and post-release dispersal compared to individuals reared in a warmer climate.

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 review of worldwide reptile translocation projects during 1991–2006 (Germano & Bishop 2009) found that a third of the projects, that included some releases of captive-bred animals, were considered successful with substantial recruitment to the adult population. Of the 47 translocation projects reviewed (39 species), 32% were successful, 28% failed and long-term success was uncertain for the remaining 40%. Projects that translocated animals due to human-wildlife conflicts failed more often (63% of 8 projects) than those for conservation purposes (15% of 38) and those for research purposes (50% of 5). Success was independent of the life-stage translocated/released, number of animals released and geographic region (see paper for details). Releases of captive-bred animals made up 7% of the projects, and individuals involved were adults in 75% of cases, juveniles and sub-adults in 64% of cases and eggs in 4% of cases. The most common reported cause of failure was homing and migration with the second most common reported cause being insufficient numbers, human collection and food/nutrient limitation all equally reported. Success was defined as evidence of substantial recruitment to the adult population during monitoring over a period at least as long as it takes the species to reach maturity.
Study and other actions tested
Referenced paper
Germano J.M. & Bishop P.J. (2009) Suitability of amphibians and reptiles for translocation. Conservation Biology, 23, 7-15.
A study in 2012–2013 in regenerating temperate forest in South Island, New Zealand (Jarvie et al. 2015) found that most released captive-reared tuatara Sphenodon punctatus survived at least 9 months after being released into a predator-free fenced enclosure with artificial burrows. After 3–5 months, all tuatara captive-reared locally (100%) and almost all tuatara captive-reared to the north of the release site (96%) survived. After 9–11 months, survival rates of tuatara reared north of the release site (70%) were higher than and locally-reared and released tuatara (67%, results were not statistically tested). Growth rates of locally-reared tuatara (0.05 mm/day) were faster than those reared away from the release site (0.04 mm/day). Changes in body condition, post-release dispersal and home range sizes were similar between locally-reared and distant-reared tuatara (see original paper for details). Juvenile tuatara (41 individuals) originating from the same wild population were released into a reserve in November–December 2012: captive-reared locally to the release site (13 individuals), and captive-reared 480 km north of the release site in a warmer climate (28 individuals). Captive-reared tuatara were hatched from artificially incubated eggs and reared until 4–6 years old. The reserve was surrounded by predator-resistant fencing and mammalian predators were mostly eradicated by 2008. Artificial burrows were buried in the release area. Tuatara were monitored by radio-tracking for 5 months (6 locally-reared, 10 north-reared individuals) and recapture surveys (all tuatara were PIT tagged) for up to 27 months after release.
Study and other actions tested
Referenced paper
Jarvie S., Senior A.M., Adolph S.C., Seddon P.J. & Cree A. (2015) Captive rearing affects growth but not survival in translocated juvenile tuatara. Journal of Zoology, 297, 184-193.

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

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