DIEL AND INTER-SEASONAL DYNAMICS OF SPATIAL DISTRIBUTION OF FISH IN WATER AREA OF WINTERING RIVERBED DEPRESSION

Abstract

To study the dynamics of the spatial distribution of fish under ice cover the research was carried out in the water area of the riverbed depression located in the lower reaches of the Irtysh River (Western Siberia, Tyumen region). The research was conducted by using the hydroacoustic method based on a computerized hydroacoustic software-hardware complex. It was found that, in the diurnal aspect, throughout the entire observation period (December - April), the number of fish in the riverbed increases during the dark period of the day, and during the light period it decreases. The dominant groups of fish change with the change of the period of the day: December - cyprinids prevail in the dark period of the day, in March and April - in the light period of the day, the rest of the time the group of percids predominated. With an increase in water temperature from December to April from 3.7 to 6.5 °C, it was noted that the density of fish decreases from 184 to 8 sp/hect. in the daytime and from 2157 to 91 sp/hect. at night (dark period), respectively. Fish explore the horizons of the water column of the riverbed depression during the day and night from the surface to the bottom with the highest density indicators near the surface, except - the daytime in December. With increasing density of fish at nightfall at the same time, there was an increase used water area of riverbed depression. In the vertical aspect, cyprinids avoid predators (pike, in-connu, burbot) in the diurnal dynamics; the distribution of cyprinids has a significant negative cor-relation with the distribution of the second group of fish. Thus, the features of the vertical and hori-zontal distribution of fish in the diurnal dynamics throughout the entire observation period are the strategy of their survival: for prey - escape from predators, for predators - search for food objects