Density and Distribution of Fish in a River with a Pronounced Heterogeneity of the Environment: Hydroacoustic Survey

A horizontal echosounder has been used to study the spatial distribution of fish in the Savala River lower reaches. Fish densities in different parts of the studied area with varying degree of meandering are compared. It has been shown that river channel morphology influences fish spatial distribution at a high water level in spring. The difference in the density of fish aggregations in areas with varying degrees of river meandering decrease in autumn, with maximum densities being observed in the deepest sections of the river, when an overall decrease in fish density associated with a decrease in water level and downstream migration after spawning has taken place.