Preliminary data to assess the impact of beaver dams on fish migration and the formation of fish resources in the Middle Ob River flood plain (Tomsk Region)

Abstract

Field research enabled the identification of habitat features and the density of beavers’ habitats on a section of the Ob floodplain with an area of about 30 square kilometers. It was established that most beaver families live in lodges and regulate the water level at the sources of floodplain lakes by building dams. The research established that during the under-ice period in these lakes, the oxygen content decreases to below the critical level for the remaining lake-river fish, and dams are an obstacle to their migration to parts of the river system with a favorable oxygen regimen. An experiment was conducted with the descent of water through a dam built by beavers in the source of two floodplain lakes; the number and biomass of migrating fish were counted. On the basis of the obtained data on the species composition, size and weight of the fish, it is proposed that the damage to fish resources caused by the beaver dams in the Ob River floodplain may significantly exceed the commercial value of beavers.