Do American mink kill European mink? Cautionary message for future recovery efforts

An experimental release of the European mink (Mustela lutreola) was carried out in the Salburua wetland in North Spain between 2008 and 2010. A partial removal of feral American mink (Neovison vison) was done preceding the release. The survival and the cause of death of each of 27 captive-bred minks were studied during five months after release. Only 22 % of the minks (N=6) survived during whole radio-tracking period. Predation was the most significant cause of mortality (76 %, N=16). Seven European minks (33 % of mortality) were killed by another mink-size carnivore-the causes of death of these individuals were of particular interest to clarify possible impact of a few remained American mink to released European mink. We used three criteria to identify the exact causes of death of these seven minks: 1. Comparison of the distances of bite marks with the inter-canine distances of small carnivores, 2. Site descriptions and signs of predators and 3. Density of carnivores within the study area. None of the criteria taken separately allowed the complete identification of the predator species. Summing up the results of all three criteria, a male American mink was found to be the most likely predator of at least six released European minks (29 % of overall mortality and 38 % of predated minks). Our results show that the presence of American mink, even if the number is estimated to be low, may seriously limit the success of reinforcement or reintroduction of the European mink.