Release captive-bred Mallorcan midwife toads

Overall effectiveness category Trade-off between benefit and harms
Number of studies: 4
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How is the evidence assessed?

Effectiveness

68%
Certainty

58%
Harms

20%

Calculating overall effectiveness category

Study locations

Key messages

Three studies (including one replicated study and one review) in Mallorca found that captive-bred midwife toads released as tadpoles, toadlets or adults established breeding populations at 38%, 80% or 100% of sites.
One randomized, replicated, controlled study in the UK found that predator defences were maintained, but genetic diversity reduced in a captive-bred reintroduced population.

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 release programmes for captive-bred Mallorcan midwife toads Alytes muletensis in Mallorca (Bloxam & Tonge 1995) found that breeding populations were established at three of the eight release sites. Four of the other sites had calling males that were expected to breed by the end of 1994. Captive-bred toads, from three institutions, were released on eight occasions starting in 1989.
Study and other actions tested
Referenced paper
Bloxam Q.M.C. & Tonge S.J. (1995) Amphibians: suitable candidates for breeding-release programmes. Biodiversity and Conservation, 4, 636-644.
A before-and-after study in 1985–2002 in Mallorca (Román 2003) found that captive-bred Mallorcan midwife toads Alytes muletensis released as larvae and adults established breeding populations at 12 of 15 sites. Between four and 721 larvae were counted per site in 2001 and 4,000–5,000 were counted at one site in 2002. Two of the three populations failed because of predation by viperine snakes Natrix maura. From 1985, captive breeding was undertaken by a number of national and international centres. Adults (0–387/site) and larvae (0–227) were released at 15 sites over one to nine years in 1985–1997. Populations were surveyed in 2001.
Study and other actions tested
Referenced paper
Román A. (2003) The ferreret, the management of a critically ill species. Munibe (Suplemento), 16, 90-99.
A randomized, replicated, controlled study in captivity the UK (Kraaijeveld-Smit et al. 2006) found that predator defences were maintained in a captive-bred reintroduced population of Mallorcan midwife toads Alytes muletensis, but genetic diversity was reduced. There was no significant difference in morphological responses to predators in a population that had been captive-bred for 3–8 generations and released in a predator-free pond and the ancestral natural population. Tail length, lower tail fin shape and development did not differ. In terms of genetic diversity, although heterozygosity was similar between populations, the reintroduced population had lower allelic richness. Forty-eight tadpoles from the natural and reintroduced population (with the same ancestry) were captured. Treatments were: chemical cues from viperine snakes Natrix maura or green frogs Rana perezi or a control. Tadpoles were measured each 15 days. DNA was analysed.
Study and other actions tested
Referenced paper
Kraaijeveld-Smit F.J.L., Griffiths R.A., Moore R.D. & Beebee T.J.C. (2006) Captive breeding and the fitness of reintroduced species: a test of the responses to predators in a threatened amphibian. Journal of Applied Ecology, 43, 360-365.
A replicated study in 1989–2001 in Mallorca (Griffiths, García & Oliver 2008) found that released captive-bred Mallorcan midwife toads Alytes muletensis established stable and in some cases increasing, breeding populations at all 18 release sites. Seventy-six captive-bred tadpoles were released at two sites in 1989. Toadlets and tadpoles were then released on an annual basis up to 1997 and less regularly until 2001. Toads were screened for disease before release. Tadpoles were counted annually at the 18 release sites.
Study and other actions tested
Referenced paper
Griffiths R.A., Garcia G. & Oliver J. (2008) Re-introduction of the Mallorcan midwife toad, Mallorca, Spain. Pages 54-57 in: Global Re-introduction Perspectives: 2008. Re-introduction case-studies from around the globe. IUCN/SSC Re-introduction Specialist Group, Abu Dhabi.

Please cite as:

Smith, R.K., Meredith, H. & Sutherland, W.J. (2020) Amphibian Conservation. Pages 9-64 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

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This Action forms part of the Action Synopsis:

Amphibian Conservation

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