University of Oulu

Restoration of riverine habitat for fishes - analyses of changes in physical habitat conditions

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Author: Yrjänä, Timo1
Organizations: 1University of Oulu, Faculty of Technology, Department of Process and Environmental Engineering
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.7 MB)
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Language: English
Published: 2003
Publish Date: 2003-10-31
Thesis type: Doctoral Dissertation
Defence Note: Academic Dissertation to be presented with the assent of the Faculty of Technology, University of Oulu, for public discussion in Raahensali (Auditorium L10), Linnanmaa, on October 31th, 2003, at 12 noon.
Reviewer: Docent Timo Muotka
Professor Pertti Vakkilainen


The subject of the study was to search and test restoration measures for the most common physical habitat degradations in Finnish rivers.

Methods for constructing nursery and spawning habitats for salmonid fishes were tested in small rivers dredged for timber floating in the Iijoki watercourse. Physical habitat modelling was used to simulate the effects of restoration measures to the hydro-physical conditions and potential fish habitats. The rehabilitation of the river bed and the placement of boulder structures, especially large boulder dams, made the rapids spatially more complex and increased the availability of potential physical habitat for brown trout (Salmo trutta).

The physical habitat model was applied in the river Siikajoki to estimate the impacts of flow regulation patterns on the physical habitat quality. No single flow event causing a bottle-neck effect on the potential habitat suitable for brown trout was found. In a sensitivity analysis of habitat modelling, modifications of the suitability criteria appeared to have a major influence on habitat suitability for young brown trout.

The applicability of low reefs and narrow side channels for fish habitat improvement was studied, using the large river impoundment of Oulujoki as a test area. Limited validation experiments of the model results were carried out on the basis of fish telemetry experiments and observations by local rod fishermen. The restoration measures appeared to diversify the channel structure and increase sheltered lateral habitats for grayling (Thymallus thymallus).

Habitat structure and fish populations of seven small forest streams and two modified streams were surveyed using visual evaluation and electrofishing studies. None of the studied streams was found to be in pristine condition in all of its reaches. Brown trout was the most abundant species in most of the study streams. In most streams the brown trout distribution correlated positively with substrate size. The accumulation of fine materials on the stream bottom due to forestry operations was estimated to be the most harmful human impact on the studied streams. Some restoration suggestions were made for each of the streams.

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Series: Acta Universitatis Ouluensis. C, Technica
ISSN-E: 1796-2226
ISBN: 951-42-7117-3
ISBN Print: 951-42-7116-5
Issue: 188
Copyright information: © University of Oulu, 2003. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.