Population Dynamics of the Rybinsk Reservoir Fishes throughout the Whole Period of Its Existence: Role of Natural and Anthropogenic Factors

The results of studies of main commercial fish species and their environment undertaken in the Rybinsk reservoir throughout the whole period of its existence are generalized . From the moment of its impoundment and up to early 1990’s fish abundance dynamics and their population indices were determined by combined effect of several factors — fluctuation of reservoir’s overall productivity, recruitment rate and commercial fisheries development . In 1990th it became less obvious that the stocks dynamics of commercially-important fish in the reservoir are determined mainly by natural, environmental factors . By that time the fishing load started to grow disproportionately to the existing stocks . In 1990’s the latter factor became dominant in determining fish stocks state . The fishing in the reservoir became in fact non-regulated and the level of illegal harvesting (poaching) increased sharply . During further four to five years above mentioned increase in the fish harvesting load due to intensive poaching has lead to the undermining of fish stocks . As a result, by the end of 1990th the commercial fish harvests decreased sharply and stabilized at the level lowest for the whole time span since the reservoir impoundment . The decrease in the productivity of other compartments of the Rybinsk Reservoir ecosystem, not related to fish community, was not as sharp . This confirms the suggestion that the poaching particularly was the main reason of the above mentioned decline in the stocks of commercially-important fish . The degree of effect upon populations of certain species is defined by their commercial value . Among all other environmental factors, climate warming has become the main one influencing fish environment quality, their food base and directly and negatively affecting cold-water fish species, limiting their abundance