Habitat associations of upper Volga river fishes: Effects of reservoirs

Abstract

AbstractHabitat associations of upper Volga river fishes are defined within a cycle of spawning, feeding and overwintering migrations. The migration cycles of resident riverine fishes are categorized as obligate rheophils, limno‐rheophils and limnophils. Forty‐four fish species in 14 families occurred in the upper Volga River before regulation. Four mainstem reservoirs were constructed on the upper Volga between 1937 and 1957: Ivankovo, Uglich, Rybinsk and Gorky. They are maintained in a stage of delayed and sustained annual flood pulse. Additional impacts of reservoir construction include the creation of a new pelagic habitat, replacement of floodplains by lacustrine littoral and sublittoral habitats, creation of a complex bathyal habitat from former river channels and replacement of riverine flow patterns by pelagic water mass circulations. Populations of rheophilic species declined, while a new pelagophilic fish guild developed. Forty‐six fish species are now present; seven species were lost and nine introduced after impoundment. Spawning, feeding and wintering habitats are outlined for reservoir guilds. Ichthyomass increased three to four times following reservoir construction and commercial fish harvest from Rybinsk Reservoir between 1945 and 1992 ranged from 2220 to 4304 t/y. Reservoirs of the upper Volga have limited bioproductivity due to a deficiency and uneven distribution of reproductive habitats, decreasing bottom irregularity, seasonal anomalies of flooding and draining of the littoral and sublittoral and underestimating the importance of tributaries. Lack of littoral reproductive habitat can be remedied by increasing the area of protected littoral through the construction of chains of small islands, diking and reclamation of bogged areas. Improved reproduction of migrating local stocks can be achieved by removing sand bars across tributary mouths, construction of artificial spawning grounds and restoration and preservation of preferred habitats in the main channel.