Outcomes of river rehabilitation on instream hydraulics and fish communities

Smith, Michelle Anne

Biological sciences
October 2013

Thesis or dissertation

© 2013 Michelle Anne Smith. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

All fish species have specific habitat requirements, which differ according to life history and life stage. Where requirements are not met, or are inadequate for a particular species, the species will be locally absent or the population in poor condition and abundance. As a result of numerous anthropogenic stressors, river systems, and consequently fish physical habitat, have undergone considerable transformation, frequently resulting in homogenisation of the river channel, often to the detriment of the fish biota present. Following the emergence of the EC Water Framework Directive (WFD) and EC Habitats Directive (HD), there has been an increase in river rehabilitation schemes to ameliorate anthropogenic pressures of rivers and augment ecological status to meet specific obligations. However, despite the extensive implementation of river rehabilitation programmes little follow up monitoring, and dissemination of results takes place leaving a paucity of information on the outcomes of such schemes on in stream hydraulic conditions and fish community composition. Four river rehabilitation schemes on three UK Rivers were monitored to assess the effects of the schemes on instream hydraulic conditions and fish community composition and structure.

Variation of instream hydraulics was assessed before and after the rehabilitation to investigate the environmental outcomes of river rehabilitation schemes. Little significant change in hydraulic conditions was observed following river rehabilitation at all sites surveyed although a significant decrease in depth and a significant increase in flow velocity was observed at the most upstream site following weir removal from the River Dove at Dovedale.

Little change in fish species composition was observed following river rehabilitation at all sites.

Given the importance of physical habitat to fish, surveys were conducted on a meso-scale in heterogeneous rivers to assess differences in hydraulic conditions and fish species composition of different habitat types. Glides were generally deeper than riffles, with fish species composition dominated by >1+ brown trout whereas riffles were generally shallower than glides. The composition of the fish community in riffles generally contained a greater proportion of bullhead and 0+ brown trout than glides.

Due to the importance of fish as an indicator of ecological quality under WFD guidelines, it is imperative to understand the intricate linkages between fish species and hydraulic habitat. Habitat use of all species captured was investigated and despite similarity in the range of values measured, different preferences were shown by different species. The relationship between descriptors of fish community composition and measures of hydraulic habitat were also investigated and revealed that individual hydraulic parameters have little influence over fish community composition.

Department of Biological Sciences, The University of Hull
Cowx, I. G. (Ian G.); Coulthard, Tom J.
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