Re-introduction of the Mallorcan midwife toad, Mallorca, Spain

Summary

The Mallorcan midwife toad (Alytes muletensis), known only from Pleistocene fossils until live tadpoles were rediscovered in 1980, survives in gorges of Mallorca's Serra de Tramuntana mountains and today comprises about 34 populations, 16 original wild ones plus 18 established through re-introduction. Jersey Zoo began captive breeding in 1985 from eight wild-collected founders, supplemented by 12 more in 1987, achieving first captive breeding in 1988, with breeding colonies later established at other European institutions while the Balearic Island government retained formal ownership of all animals. Following site assessment by Mallorca's conservation authority, 76 tadpoles were released at two sites in 1989, with releases of tadpoles and toadlets continuing annually through 1997 and then less frequently until 2001; further re-introductions were paused pending disease and genetic research as global amphibian disease concerns grew. Microsatellite analysis completed in 2006 found wild populations retained high genetic diversity despite isolation between gorges, and no fitness loss after up to eight generations of captive breeding, though chytridiomycosis screening added in 2005 subsequently found the fungus in four populations without yet visibly affecting their breeding success. Annual tadpole censuses show breeding populations established at all 18 re-introduction sites through 2001, with wild populations stable or increasing; the toad also breeds successfully in specially constructed artificial livestock cisterns. The project rated itself Highly Successful, noting it is the only amphibian downgraded from Critically Endangered to Vulnerable in the 2004 Global Amphibian Assessment, with the species' geographic range effectively doubled.