Mechanically reshaping stream banks alters fish community composition

摘要: Mechanically reshaping stream banks is a common practice to mitigate bank erosion in streams that have been extensively channelised and lowered for land drainage. A perception regarding this activity fish populations will be largely unaffected, at least the short term, because low‐flow wetted channel remains undisturbed. However, response of has rarely quantitatively evaluated. Using Before‐After‐Control‐Impact design, we assessed community responses catchment‐scale event fourth‐order low‐gradient drains an intensive agricultural landscape. Quantitative electric fishing habitat data were collected 2 months before annually 3 years after event. After reshaping, deposited fine sediment levels increased impact reaches, there was significant reduction anguillid eel biomass (by 49%). In contrast, densities obligate benthic gobiid bully species significantly reaches—potentially due reduced predation pressure from eels. Three years structure had returned its preimpact state reshaped areas. Our results suggest that, even highly modified channels, further modification can reduce instream quality displace eels 1 year. Managers should endeavour use control measures conserve bank‐edge cover, especially with eels, these are declining globally.