The survival of captive-born animals in restoration programmes – Case study of the endangered European mink Mustela lutreola

As part of a conservation initiative, captive-bred individuals of the endangered European mink Mustela lutreola were released to a Baltic island ‘sanctuary’, Hiiumaa Island (Estonia), and their survival was monitored over eight years. Altogether, 54 released mink were equipped with radio-collars between 2000 and 2003 and their survival and causes of death were studied as a function of sex, age, housing conditions before release and number of generations in captivity. Mortality was greatest (∼ 50%) during 1–1.5 months following release. The survival of males was significantly higher than that of females (25% decline in 21 days, and 10 days, for males and females, respectively). Releasing pregnant females appeared to be an unsuccessful strategy. There was no evidence that the number of generations for which the lineage of the released individuals had been bred in captivity had any effect on survival. The main cause of death was other carnivores and raptors, although this broad categorization may conceal a diversity of fatal scenarios.We recommend for the future that the European mink being prepared for release should be maintained in large naturalistic enclosures beforehand, that a preponderance of females should be released, and that the indications that younger animals make better candidates for release should be investigated.