HABITAT ASSOCIATIONS OF UPPER VOLGA RIVER FISHES - EFFECTS OF RESERVOIRS

Habitat 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 rheoph ils, limno-rheophils and limnophils. Forty-four fish species in 14 fam ilies occurred in the upper Volga River before regulation. Four mainst em reservoirs were constructed on the upper Volga between 1937 and 195 7: Ivankovo, Uglich, Rybinsk and Gorky. They are maintained in a stage of delayed and sustained annual flood pulse. Additional impacts of re servoir construction include the creation of a new pelagic habitat, re placement of floodplains by lacustrine littoral and sublittoral habita ts, creation of a complex bathyal habitat from former river channels a nd replacement of riverine flow patterns by pelagic water mass circula tions. Populations of rheophilic species declined, while a new pelagop hilic fish guild developed. Forty-six fish species are now present; se ven species were lost and nine introduced after impoundment. Spawning, feeding and wintering habitats are outlined for reservoir guilds. Ich thyomass increased three to four times following reservoir constructio n 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 anoma lies of flooding and draining of the littoral and sublittoral and unde restimating the importance of tributaries. Lack of littoral reproducti ve habitat can be remedied by increasing the area of protected littora l through the construction of chains of small islands, diking and recl amation of bogged areas. Improved reproduction of migrating local stoc ks can be achieved by removing sand bars across tributary mouths, cons truction of artificial spawning grounds and restoration and preservati on of preferred habitats in the main channel.