Which relationships exist between the density of mink and their prey?

By Linn Merete Jonstang

Mink have been believed to have more negative than positive effect on their environment in the UK for decades. They are widely distributed and as a wild carnivore, they may damage the populations of other species. Since these species sometimes are of economical and conservational importance, like chicken and salmon, the mink is regarded as a pest by many farmers and game-keepers.

The American mink, Mustela vison:

The mink is 46 – 70 cm long and has a slender body with short legs. The fur is usually black or brown with white patches and has waterproof properties due to its fat content. The fur industry is mainly made up of mink fur. The mink prefer habitat near water and have migrated to almost all parts of Europe and North America. They usually live up to 10 years and feed on most small animals, from fish and frogs to rabbits and mice. Minks have very few natural enemies. They may sometimes be killed by snakes or other carnivores, but their main enemies are humans. (More on this)

The study:

In 1994 E.C. Halliwell and D.W. Macdonald studied the relationship between the population of American mink, Mustela vison, and the population of three prey types along four rivers in the Upper Thames catchment area. [1] The three chosen prey types were fish, moorhen (Gallinula chloropus) and water voles (Arvicola terrestris). Mink were studied along a 20 km section of each of the four rivers in the study: Thames, Thame, Coln and Kennet. The number of minks and the number of prey were counted and compared. The results showed that there was no correlation between fish density and mink density. In other words, the mink population was neither limiting nor limited by the fish population. This was also the case for moorhen density. It was however significant evidence that the mink population was limiting water vole abundance. More mink lead to a smaller water vole population.

Even though there was a negative correlation between the mink density and the water vole density, mink is not necessarily the only or the most important factor limiting water vole abundance. Other factors that might affect the water vole decline are habitat destruction and fragmentation, disturbance by humans, agriculture and pollution. Another study reports that the loss of habitat, combined with minks, have lead to extermination of 88% the water voles’ den sites during the 1990s alone. [2]

The habitat is also believed to play a great role in the density of mink and prey. The rivers containing the most preferable habitats, has the most preferable den sites and the highest population density. There is therefore positive correlation between mean numbers of potential den sites and total numbers of mink, suggesting that mink densities may have been limited by den site availability.

The Thames, Thame, Coln and Kennet rivers are different in their width and depth. The researches were aware of this but they found no correlation between this and mink density.

The study concludes that water voles are the only prey type found to be limited by the mink population. There are however other factors, such as den site availability and agriculture affecting both mink population and the density of their prey.

Sources:

• Original article:

E.C. Halliwell & D.W. Macdonald (1994). American mink Mustela vison in the upper thames catchment: relationship with selected prey species and den availability. Wildlife Conservation Research Unit, Department of Zoology, University of oxford, South Parks Road, Oxford OX1 3PS, UK

• Additional info on the topic:
• http://www.hero.ac.uk/uk/research/archives/2004/return_of_the_natives.cfm

• Mustela vison facts:
• http://en.wikipedia.org/wiki/Mustela_vison
• http://animaldiversity.ummz.umich.edu/site/accounts/information/Mustela_vison.html