Do Otters and Mink Compete for Access to Foraging Sites? a Winter Case Study in the Mazurian Lakeland, Poland

Abstract

The distribution of otter and American mink tracks in the Mazurian Lakeland during winter, characterised by low temperatures and thick ice cover, was used to analyse competition between the two species for access to the limited area of foraging sites. The study was carried out in February and March, 2006 and comprised 12 lakes and sections of three rivers and two canals. Tracking was conducted along a total of 98.25 km of the shoreline, which was divided into 393 study sections, 250-m-long each. Otter tracks were recorded at all the lakes and canals under study and at two rivers. Mink tracks were recorded along all the watercourses and on eleven lakes. The otter was recorded in 25.9% of the sections, whereas American mink in 28.8% of the sections. Co-occurrence of the otter and mink was observed in 8.8% of the sections. In sections with unfrozen stretches (12.3% of all the study sections), the frequency of otter and mink tracks was significantly higher than in totally frozen sections. Co-occurrence of the otter and mink was found in 28.3% of the sections with access to open water. In unfrozen sections the frequency of co-occurrence of the two species was four times higher than in totally frozen sections. Only 20% of the sections with air holes were not visited by any of the two species. The study showed that during periods of low temperatures, when accessibility to open water and aquatic prey was limited, both species clearly preferred those parts of the water bodies where unfrozen places remained. A high rate of co-occurrence of the two species in such places indicates mutual tolerance between the otter and mink in the sections offering aquatic food resources.