The habitat use of young-of-the-year fishes during and after floods of varying timing and magnitude in a constrained lowland river

Globally, channelisation and artificial levee construction have reduced rivers to single-thread channels isolated from their floodplains. These modifications may be particularly detrimental to fish during floods, because of increased severity of conditions in the main river channel, prevention of fish finding refuge in floodplain habitats, and stranding of fish when floodwaters recede after artificial levees are 'over-topped'. Notwithstanding, few studies have examined the habitat use by young-of-the-year (YoY; age 0+ year) fish in constrained lowland rivers during floods in slackwaters (main channel with little or no discernible current) and after floods on floodplains. This study investigated the community structure and density of 0 + fish species before (main river), during and after floods of varying timing and magnitude in the River Yorkshire Ouse, a constrained lowland river in north-east England. Slackwaters provided refuge for high densities of mainly eurytopic 0+ fishes during floods and high densities of 0+ fishes were found stranded on floodplains after floods. Community composition in slackwaters during floods and on floodplains after floods was significantly different to the main river catches during average daily flows, possibly related to species-specific morphology and behavioural responses to elevated flow. Despite there being floods of greater magnitude during the winter, peak densities of 0+ fish stranded on floodplains occurred in the summer, and probably related to habitat use immediately prior to floods. Fish were also found stranded on floodplains actively managed to store floodwater to protect property and are presumed to permit safe egress for fish. The results are discussed in relation to lowland river rehabilitation, which is particularly important because of potential conflicts between obligations under various European directives to improve the status of fish populations in degraded rivers (Water Framework Directive) whilst at the same time minimise flooding of societal assets (Flood Directive). (C) 2014 Elsevier B.V. All rights reserved.