Verbreitung und Ökologie des Minks - Mustela vison Schreber, 1777 (Carnivora, Mustelidae) - in Sachsen-Anhalt

Abstract

Zschille, J.; Heidecke, D.; Stubbe, M.: Distribution and ecology of feral American mink Mustela vison Schreber, 1777 (Carnivora, Mustelidae) in Saxony-Anhalt (Germany). - Hercynia N.F. 37 (2004): 103–126.The feral American Mink (Mustela vison) - a native species of North America - was introduced in Europe and Asia in the early 20th century for fur breeding. During the years, many animals escape fur farms or were released into the wild. Therefore, free-living populations have been established also in Germany, especially in the eastern part. But there are only a few investigations about the influence of this carnivorous newcomer on the indigenous biocoenosis. A questionnaire was handed out to different people (hunter, forester, angler and voluntary coworkers of nature conservation) in Saxony-Anhalt in order to locate the current range of feral mink in the study area. As the established screen map shows, the mink could be verified mainly in the great river meadow areas (Elbe and Mulde) in the eastern part of Saxony-Anhalt. In this area we registered also many observations of juveniles. But there also were some mink-records in the Helme-Unstrut-region and the Saale-Elster-region. These results confirm a preference of this species to water bank habitats. Altmark, Harz and Harzvorland are regions without many evidence of mink. The delayed colonisation in these areas is probably caused by suboptimal habitats, poor in water systems. Nevertheless, there also can be estimated a colonisation of all nearby natural lakes and rivers within the years to come. Furthermore, 113 mink carcasses were collected in the study area during a period from 11/1999 to 3/2002. They either were caught or found already dead. Stomach contents and reproduction status were analysed, the age of the minks was determined by counting the cementum annuli of canines and biometrical datas were taken. Measures of body, skull and organs confirm a typical sexual dimorphism of mink. The results of the stomach analysis (food biomass) demonstrate, that fishes (38 %), small mammals (23 %) and birds (23 %) represent the main prey groups, whereas amphibians (8 %), crustaceans (7 %), insects (<1 %) and molluscs (<1 %) play a secondary role in the diet of investigated animals. That opportune diet of the feral mink corresponds to another similar investigations in Europe. The potential mean litter size, derived from the number of placental scars, was 5,5 juveniles per female. But not all investigated adult females took part in reproduction, so this is a first indicate of intern regulation of population density. The age class distribution of the investigated minks is characterised by a low portion of juveniles (28 %), a comparatively high average age and a maximum age of eight years. These results are first indications of stable mink populations with relative high density and with tendency of expansion, at least in habitat with good quality like the river meadow areas. Altogether a strongly negative ecological impact of feral mink on native prey populations could not be found. But other studies indicate, that there is a negative impact, specially on water bird populations. Thus, there is urgent demand for research on this subject.