Floodplain-channel complex of the lower Irtysh: Dynamics of flood and fish number

Abstract

The dynamics of fish aggregation density in the riverbed was studied using the hydroacoustic method during the intensive phase of the hydrological regime of the Irtysh River – the spring-summer flood. The dynamics of fish density with increasing water levels was recorded taking into account the analysis of average values of the indicator for decades periods of May in 2020 and 2021. During the flood period under study, the size of the share of taxonomic fish groups (cyprinids, percids, coregonids- esociids, unidentified) at the family level varied insignificantly, intensive dynamics were noted for the fish density indicator: Fish density decreased with increasing water level. The decrease in the number of fish in the riverbed is associated with their transition to the flooded floodplain of the river of the studied floodplain-channel complex. With a more powerful flood in 2020, the decrease in fish density in the riverbed occurs more intensively than with a less intensive rise in water level in 2021. The significance differences between decades were noted both for the indicator of the total fish density and for the density of taxonomic groups of fish.