Winter Fish Distribution in the Riverbed Depression in the Urtysh River

Abstract

Winter fish distribution is investigated by means of computerized hydroacoustic complexes in the largest riverbed depression in the Irtysh. Fish aggregations whose position, density, abundance, and size composition are much modified during winter are formed under ice in the riverbed depression. In the early winter, the density and abundance of fish aggregations are higher than those before spring. Distribution of fish over the depression changes from month to month, but the attribution of most fish to open water and to near-surface layers remains invariable. In the water area of the depression, the fish are combined into dynamic aggregations. Under ice, the majority of the fish are represented by small-sized cyprinids (Cyprinidae).