The American mink, Mustela vison: its management and interactions with two native mustelids, the European polecat, M putorius, and the Eurasian otter, Lutra lutra

• Main Author: Harrington, Lauren A.
• Published: University of Oxford 2007
• Subjects: 591.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491517

Established in the UK for over 35 years, the alien, invasive American mink, Mustela vison, has had serious impacts on the country's native biodiversity. Mink predation is one of the factors responsible for the near extinction of the water vole in the UK. The first aim of this study was to assess the feasibility of removing American mink with a view to protecting water voles in the UK. Previous modelling work identified an optimal strategy for removing American mink. I designed a large-scale field experiment to test the effectiveness of this strategy. Although trapping proved effective in reducing the relative abundance of mink, the specific model strategy tested was insufficient for the protection of small populations of newly released captive-bred water voles over the summer and a more flexible, reactive approach was necessary. Over-winter survival of released water voles was achieved with fouf months (or less) mink trapping per year. I suggest that the reactive approach adopted was vital to this success. In Belarus, American mink appear to displace female polecats from riparian habitats. A second aim of my work was to investigate spatial overlap between these two species in the UK to assess the potential impact of mink on the recovery of polecats (a native species of conservation concern). I detected limited inter-specific spatial overlap, similar in extent to that found between intra-specific neighbours. I hypothesise that there is incomplete habitat partitioning between the two species and that temporal partitioning enables avoidance of inter-specific neighbours within overlap areas. I suggest that the presence of mink wiII not hinder the recovery of the polecat, but that they may affect' the carrying capacity of the landscape. Eurasian otters (also currently recovering nationally in the UK) are larger than American mink, and out-compete them through inter-specific aggression. The third aim of my research was to further investigate the relationships between these two species. I compared the relative abundance, diet, space use and activity patterns of mink on the River Thames, Oxfordshire, UK, in the 1990s (in the absence of otters) with that of mink at the same site in the 2000s (in the presence of otters). Mink did not appear to have declined between the 1990s and the 2000s, and there was no evidence of spatial segregation between the species, or of changes in habitat use or home range size in mink. I did find a change in mink activity patterns, from predominantly nocturnal to predominantly diurnal. This phenomenon has been identified before between predator and prey, but it has seldom been demonstrated between competitors. This study contributes to our broader knowledge of intra-guild relationships but also has practical implications in that it seems unlikely that otter recovery wiII lead to a national decline in mink populations (an idea that has achieved much attention in the media). A further field experiment to test the response of feral mink to the odours of polecats and otters, revealed no evidence of avoidance of otter odour, but a significant attraction to polecat odour. Methodological studies were carried out to assess the utility of a new survey method (tracking raft surveys) and to determine whether or not it was possible to distinguish between mink and polecat footprints. Tracking raft surveys and footprint identification were used throughout this research and both studies wiII have practical applications to field researchers working on these species.