| Stream restoration is a billion dollar industry in North America. Despite this expenditure there remain questions regarding the effectiveness of current techniques, such as instream structures. The objectives of this research were to assess the impact of instream structures on physical habitat in the Nicolet River (Quebec) and to analyze physical habitat and fish abundance data from a large number of restoration projects using meta-analysis. Results of intensive surveys of the Nicolet River suggest that the installation of weirs and deflectors resulted in a greater frequency of pools. These pools have significantly greater depths, lower velocities and larger sediment size than those without structures. Compilation of data from 211 stream restoration projects showed a significant increase in pool area, average depth, large woody debris and percent cover as well as a decrease in riffle area following the installation of instream structures. The physical changes observed in the Nicolet River resulted in improved trout habitat, as measured by applying habitat preference curves, but uneven stocking practices and fishing pressure confounded attempts to verify differences in trout density among pool types. The meta-analysis, however, showed a significant increase in salmonid density and biomass following the installation of structures, although the relationship with physical habitat variables is not strong. Large differences in density response were observed between species. This compilation highlights the potential of instream structures to create better habitat for and increase the abundance of salmonids, but the scarcity of long-term monitoring of the effectiveness of instream structures is problematic. |
