Effect of channelization and regulation on fish recruitment in a flood plain river

Abstract

Abstract The recruitment of 0+ fishes was investigated in the River Morava (a tributary of the Danube), the main channel of which has now been totally isolated by channelization from its flood plain and regulated by weirs between the town of Hodonín and the river's confluence with the River Dyje (Czech Republic). Young of the year fish (YOY), collected by electrofishing, were used as an indicator of the reproduction potential of ichthyocenoses 10 years after the end of channelization and regulation works. Species richness and the structure of 0+ fish assemblages depend mainly on the spawning places and potential nurseries available. In the absence of areas with lentic backwaters or side‐arms with aquatic vegetation in the channelized river, the fish could only use the stabilized banks of stony rip‐rap or rare shallow‐slope gravel shorelines. The dominant species of 0+ juvenile fishes more or less corresponded with the structure of the adult population. Bitterling Rhodeus sericeus (Pallas), gudgeon Gobio gobio (L.), chub Leuciscus cephalus (L.), bleak Alburnus alburnus (L.) and roach Rutilus rutilus (L.) were the most abundant species in all sections of the modified main channel. However, YOY of phytophilous species (pike Esox lucius L., rudd Scardinius erythrophthalmus (L), silver bream Blicca bjoerkna (L), tench Tinea tinca (L), carp Cyprinus carpio (L.) had almost disappeared, and a decline in density was also found for rheophils, such as vimba Vimba vimba (L.), barbel Barbus barbus (L.) and nase Chondrostoma nasus (L.), previously dominant species in the river.