Fish populations of a small lowland channelized river in England subject to long‐term river maintenance and management works

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Abstract
Fish populations in the River Perry, a small lowland channelized river in England, were affected by long‐term river maintenance and improvement works. Habitat diversity at two ‘old channelized’ sites was low compared with a downstream ‘partially channelized’ site and an unmodified site, where natural river features such as the pool‐riffle pattern were more apparent. The fish community was low in diversity at all sites, with two running‐water cyprinids, dace Leuciscus leuciscus (L.) and chub Leuciscus cephalus (L.), being the dominant fish species. Relative species composition varied between sites, with dace predominating at the ‘old channelized’ sites and chub increasingly dominant at the ‘partially channelized’ and unmodified sites. Population density and biomass estimates of dace were similar at all sites, but chub were up three times more abundant at the ‘partially channelized’ and unmodified sites than at the ‘old channelized’ sites. Populations of dace and chub at the ‘old channelized’ sites contained a higher proportion of small fish than populations at the downstream sites, which exhibited a more balanced population structure. The growth rates of both dace and chub varied between sites. Low recaptures of marked dace suggested a highly mobile movement pattern while higher recapture rates of chub, particularly at the ‘partially channelized’ and unmodified sites, seemed to indicate a more sedentary activity pattern. The conclusion of the study is that long‐term river maintenance and management works may delay the morphological and biological recovery of lowland channelized rivers.