THE DISTRIBUTION OF VIMBA BREAM <i>VIMBA VIMBA VIMBA</i> (ACTINOPTERYGII: CYPRINIDAE) IN THE UNREGULATED SECTION OF THE LOWER VOLGA RIVER
This paper presents recent data on the population of the anadromous Vimba bream ( Vimba vimba vimba ), introduced in the Volga basin. Having resettled from the Volgograd reservoir into the downstream section of the Volga River, to date, Vimba bream can be found throughout the entire unregulated stretch downstream of the Volga hydroelectric power station. Observations show that the population size changes naturally during the year due to its spawning migration. At that, a gradual transformation of the species' seasonal dynamics is observed. As populations settle further downstream, the migratory gatherings of producers downstream of the dam are stretching, and the population density decreases. Also a seasonal redistribution takes place, with reduced migration observed in autumn and increased migration during spring. Meanwhile, the growth rate in the downstream section of the Volga River is comparable to the growth rate of populations in the Volgograd and Tsimlyansk reservoirs. Spawning occurs on in-channel spawning grounds. Yearlings are observed over a distance of 100 kilometers below the dam. In addition to Vimba bream, single individuals of Caspian bream ( V. v. persa ) were also observed.