Assessment of species composition and population status of fish populations in lakes basin of lake Onega (Karelia) using mathematical statistics methods

The results of the research of biology of mass species of fish such as, a bream (Abramis brama (Linnaeus, 1758)), small fry (Rutilus rutilus (Linnaeus, 1758)), a perch (Perca fluviatilis Linnaeus, 1758), a ruff (Gymnocephalus cernuus (Linnaeus, 1758)) and a pike (Esox lucius Linnaeus, 1758) two lakes - Pryazhinskoye and Shangima. Geographical coordinates of the lake Pryazhinskoye - 61°41′38″N 33°38′31″E, the lake Shangima - 61°41′30″N 33°34′26″E. On the bank of the lake Pryazhinskoye the settlement Pryazha with the population more than 3.5 thousand people is located, anthropogenic influence on a reservoir is small. The lake Shangima which is in 2 km to the west of Pryazha experiences the considerable anthropogenic strain as serves as the tank for dumping of treated waters from the sewer treatment plant where large volumes of soap powder enter, washed etc. The research objective - assessment of species structure and current state of populations of mass species of fish of the lakes Pryazhinskoye and Shangima, which are located in the southern part of the Republic of Karelia. Catching of fishes was carried out to the summer period (June and July) of 2017. In total 400 copies of fishes are investigated: on 200 copies from each lake. It is revealed that the basis in catches was made by a perch (P. fluviatilis) (71 %), the second place was taken by small fry (R. rutilus) (27 %) and in insignificant quantity met a pike (E. lucius) and ruff (G. cernuus). On the lake Shangima the basis of catches was made by small fry (R. rutilus) (52 %), a perch (P. fluviatilis) and a bream (A. brama) made according to 24.5 % and 21.5 %, also in insignificant quantities the pike met (E. lucius). It is established that a ratio of gender of a perch (P. fluviatilis) and small fry (R. rutilus) on both lakes and also at a bream (A. brama) of the lake Shangima, made 3:1 in favor of females. The growth rate of perch (P. fluviatilis) in lake Shangima was larger than in the lake Pryazhinoye, and for roach (R. rutilus) Vice versa. Thus, the features of the species composition and structure of the fish population, the structure of populations of mass species of different trophic lakes in the basin of lake Onega - Pryazhinskoye and Shangima, exposed to different types of anthropogenic influence. Overall, the given results on mass species of fish of lakes Pryazhinskoye and Shangima are consistent with the earlier received results of similar researches of fishes of the lake Konchezero (the basin of Lake Onega).