Assessing the potential for impacts by feral mink on wild mink in Canada

Invasive feral American mink (Neovison vison) have had well-documented impacts in Europe and South America. We tested the hypotheses that escape of ranch-raised mink is also common in Canada where the species is endemic, and that declines of Canadian wild mink apparent from harvest data are related to mink ranching. Consistent with these hypotheses, we found positive relationships among Canadian provinces: between mink ranch density and mink harvest density; between ranch density and the density of ranch mink caught by trappers; and between mink harvest density and the density of trapped ranch mink. A multiple regression and variance partitioning demonstrated that the density of trapped ranch mink explained the largest component of unique variation in annual mink harvest by trappers per province. Moreover, the change in mink harvest by trappers per province estimated over a 30-year interval (λharvest) had a close, positive relationship (R2 = 0.92) to the change in ranch density estimated over the same interval (λranch). Our analysis suggests that the conditions exist for feral mink to contribute to wild mink declines through outbreeding depression or the introduction of disease.