Distributional history of the American mink (Mustela vison) in Finland with special reference to the trends in otter (Lutra lutra) populations

The distributional history of the American mink (Mustela vison) in Finland in 1951-93 was studied by means of game inquiries and compared to the trends in otter (Lutra lutra) populations.Minks were brought to fur farms in the late 1920s and the first minks were observed in the wild in 1932.In the early 1950s minks occurred mainly in the western and southwestern coast of Finland, but two decades later minks were found in most parts of the country.Today minks are found almost everywhere in Finland; only few observers report that minks are not found in their area.The relative density of the mink is now highest in eastern Finland, rather high in southern Finland and quite low in Lapland.The data from the archipelago are, however, sparce.Otter density declined in the 1970s, but increased again in some areas in the 1980s, is now highest in the provinces of Kymi, Mikkeli and Central Finland, and almost lacking from SW Finland, especially from the coast.Among the reasons behind the decline in the otter populations may have been environmental pollutants, like dieldrin in inland areas and PCBs in the coast and archipelago.Human disturbance may also have had an effect, especially in the archipelago.The role of the mink is not clear; it seems probable that if there is competition between these species, the otter is the stronger one.