According to the latest monitoring counts in the autumn of 2017, the number of Eurasian beavers in Finland is 3,300–4,500 and that of North American beavers is 10,300–19,100 individuals. The North American beaver is a non-native species and has been classified as an invasive species in Finland’s National Strategy on Invasive Alien Species.
The Eurasian beaver, which was once the native beaver species in Finland, was hunted to extinction in the latter half of the 19th century. To restore the beaver to Finland, both the Eurasian beaver and the North American beaver were introduced in Finland in the 1930s. The North American beaver population increased much faster than that of the Eurasian beaver which survived and increased slowly only in the province of Satakunta.
At present, the area of distribution of the Eurasian beaver comprises most of Satakunta, the western municipalities of the province of Pirkanmaa, southern part of Etelä-Pohjanmaa (especially Kauhajoki) and Kristiinankaupunki in Pohjanmaa. Some Eurasian beavers occur in western Lapland where they probably wandered from Sweden. The first verified observation of the native beaver in Varsinais-Suomi, SW Finland, is from 2016.
The North American beaver population is at its densest in Pohjois-Karjala and the provinces of Etelä-Savo and Pohjois-Savo but it also occurs in other parts of eastern and central Finland and sporadically in Lapland. The first observations from the province of Uusimaa are from 2017. The North American beaver population is spreading westwards and there is a risk that the species will spread further into areas populated by the native Eurasian beaver. At present, the two species are already sympatric in western parts of the province of Pirkanmaa.
It is probable that these two very similar species compete for the best habitats and cannot, therefore, coexist in the same area for any length of time. In the worst case, the North American beaver may displace the native Eurasian beaver if their territories overlap. To safeguard the existence of the Eurasian beaver, immediate steps should be taken to halt the spread of the North American beaver westward.
The size of the beaver population is monitored by carrying out nationwide counts of inhabited winter lodges at three-year intervals. Luke evaluates the size of beaver populations on the basis of these counts. Luke also collected beaver skulls for species determination, particularly in Pirkanmaan and Etelä-Pohjanmaa. DNA samples are also taken in order to establish the precise distribution of both species and to determine the genetic polymorphism of the native one. In addition, Luke participates in other research projects on beavers, by providing guidance to doctoral students, for example.
The monitoring of the abundance of beavers and determining the precise distribution area of both species is highly important to the conservation/management of the populations. Among other things, such data are used by game management authorities when deciding on hunting quota and licences for Eurasian beaver.
Photo on top of the page: Petri Timonen / Luke