Ecological Impacts of In-stream Restoration in Salmonid Rivers

Download or read book Ecological Impacts of In-stream Restoration in Salmonid Rivers written by Saija Koljonen and published by . This book was released on 2011 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Despite the great amount of in-stream restorations conducted in the past decades there is still a disturbing lack of knowledge about the outcome of these measures. The overall goal of this study was to assess the effect of enhanced streambed heterogeneity on the ecology of stream salmonids and stream retention efficiency. Substratum heterogeneity is often considered as one of the most important limiting factors for organisms living in running waters. Winter ecology of rivers has not been broadly studied regardless of the general belief that wintertime conditions strongly influence the survival and population size of stream salmonids. In an experimental study, the paucity of wintertime habitat in simplified channels caused temporary mass loss in age-0 trout. In late spring, channelized stream trout performed catch-up growth with potentially negative effects on long-term fitness. A management implication of this study is that increasing cover availability by in-stream restoration structures may enhance the long term success of juvenile salmonids although the short term effects were minor. Densities of salmon parr in the River Kiiminkijoki showed no response to streambed restoration. Suitable habitat area for salmon parr increased after restoration under summer conditions. However, restoration-induced benefits to winter habitats were marginal, with one study reach indicating even negative values. Most of the areas with good habitat values were located along river margins, indicating that restoration measures had only limited impact on the mid-sections of the river channel. Dredging of small streams may have caused depletion of allochthonous organic matter due to the reduction of retentive structures. In a leaf release experiment, moss cover enhanced retentiveness as well as did various restoration structures (boulders, large wood). Only a very high amount of wood clearly enhanced retention capacity. This underlines the importance of wood as an effective retention structure in headwater streams. This study indicates that habitat complexity as such may be less important than life-stage specific habitat requirements of fish (e.g. cover for overwintering salmonids). Importantly, restoration may only be successful if the measures used target the limiting factor(s) of the ecosystem or the species; for salmonids, habitat complexity does not seem to be this factor.