Natural and anthropogenic factors of the establishing of invasive fish populations in the aquatic ecosystems of the Vologda Region

The specificity of the territory of Vologda oblast creates favorable conditions for the migration of organisms owing to a dense hydrographical network, great length of rivers, and also its location in the watershed of three seas (White, Baltic, and Caspian), which are connected through the Volga-Baltic and Northern Dvina River transport systems. Currently, different effects of economic activities are the main factors of ichthyofauna change. The analysis of the historical and contemporary reasons for the emergence of new species in the aquatic ecosystems of Vologda Region reveals three categories of nonnative fishes, which include the species (1) expanding their range through natural dispersal, and also (2) deliberately or (3) accidentally introduced forms. The implications of the appearance of new fish species in the aquatic communities of the northern ecosystems are discussed.