Predicting the spread of feral populations of the American mink in Italy: is it too late for eradication?

Distribution of introduced American mink in the Northern Apennine area (Central Italy)

The American mink Neovison vison is a widespread alien carnivore in Europe due to escapes from fur farms through this continent. Impacts by naturalized mink include competition with native species and predation of crayfish and small vertebrates. Therefore, an updated monitoring of mink distribution is required to design management plans. The American mink has been reported with an established population in North-Eastern Italy, in Sardinia, and two small nuclei respectively in the Central and in the Northern Apennine ridge. Available information for the latter dates back to early 1990s. In this note, we described the range expansion of the American mink population in the Northern Apennine ridge and we estimate the current distribution range and the extent of occurrence by using data collected from 2006 to 2021 through the Minimum Convex Polygon (MCP). We compared the current distribution range with that of 1990s. The American mink showed a remarkable range increase since its first escape in the Northern Apennines, thus requiring rapid actions to limit impacts on native biodiversity.

Assessing the cryptic invasion of a domestic conspecific: American mink in their native range

Control of invasions is facilitated by their early detection, but this may be difficult when invasions are cryptic due to similarity between invaders and native species. Domesticated conspecifics offer an interesting example of cryptic invasions because they have the ability to hybridize with their native counterparts, and can thus facilitate the introgression of maladaptive genes. We assessed the cryptic invasion of escaped domestic American mink (Neovison vison) within their native range. Feral mink are a known alien invader in many parts of the world, but invasion of their native range is not well understood. We genetically profiled 233 captive domestic mink from different farms in Ontario, Canada and 299 free-ranging mink from Ontario, and used assignments tests to ascertain genetic ancestries of free-ranging animals. We found that 18% of free-ranging mink were either escaped domestic animals or hybrids, and a tree regression showed that these domestic genotypes were most likely to occur south of a latitude of 43.13°N, within the distribution of mink farms in Ontario. Thus, domestic mink appear not to have established populations in Ontario in locations without fur farms. We suspect that maladaptation of domestic mink and outbreeding depression of hybrid and introgressed mink have limited their spread. Mink farm density and proximity to mink farms were not important predictors of domestic genotypes but rather, certain mink farms appeared to be important sources of escaped domestic animals. Our results show that not all mink farms are equal with respect to biosecurity, and thus that the spread of domestic genotypes can be mitigated by improved biosecurity.