Long-term changes in the fish population in a lake of the Kuma reservoir system (Karelia, Russia)

The article presents the results of ichthyological research on a large water body of the Kuma reservoir - the Pyaozero Lake. The fish population of the lake includes 16 fish species, representatives of 9 families belonging to 5 faunistic complexes. The salmonids and carp-like fishes (Salmonidae and Leuciscidae) dominate by the number of species (4 species each). The subdominant species are whitefish, and perch. The fish population is formed by the fish species of the boreal plain, arctic freshwater, and boreal foothill complexes. The lake has favorable conditions for the brown trout Salmo trutta, whitefish Coregonus lavaretus, vendace Coregonus albula (Salmonidae), pike Esox lucius (Esocidae), bream Abramis brama, roach Rutilus rutilus (Leuciscidae) and perch Perca fluviatilis (Percidae). The population and ecological analysis has shown a relatively favourable condition for most of the species studied in terms of size and mass. The pike in terms of size-mass indices (length and weight) is now smaller than in the middle of the last century. At the same time, pike has experienced a decrease and roach and increase in maximum life age now compared to the 1950s. There has been a shift in the sex ratio towards females in whitefish, bream, perch, roach, and vendace. This is probably a result of the decline in the populations of these species in the lake. In the Pyaozero Lake, of the biggest commercial values are vendace, perch and whitefish dominating in the research catches. The proportions of roach, bream, and pike were high. The most valuable commercial species, brown trout), is caught in single specimens. To maintain the structure and condition of the fish population in the Pyaozero lake, a set of measures is required, including conservation and improvement of habitat, reproduction, and feeding conditions; tightening of protection measures with declining numbers of fish species e.g., trout, whitefish and bream, regulation of fisheries and increase in artificial reproduction, cultivation, and introduction of native stocks.