Migration of bream between the main channel and floodplain lakes along the lower River Rhine during the connection phase

Mature bream (>30 cm LF) dominated the fish communities in floodplain lakes along the lower River Rhine in The Netherlands, in terms of biomass, in all lakes at all times. In some lakes bream made up 99 f the total fish biomass. While immature, medium-sized bream (10–30 cm) and white bream and roach were abundant in the main channel of the river, these species were almost absent from the floodplain lakes. Inundation of the floodplains did not lead to spatial homogenization of species and length distributions. Small bream (<10 cm) left the floodplains to become resident in the main channel until maturity. Once mature (c. 30 cm), they returned to the lakes during the next inundation and stayed there. Mature bream that moved into the lakes were significantly smaller and had a lower condition than the resident bream. Turbid clay-pits were probably important sources of bream for the lower Rhine and the recruitment of the 0 year group of bream to the riverine population was influenced by their discharge pattern.