Short term, small-scale studies of life history response as tools for effectiveness monitoring of instream habitat restoration

Monitoring efforts in the interior Columbia River basin verify whether restoration actions benefit managed fish populations.  In the Entiat River (Washington, USA), instream habitat restoration structures were installed to enhance juvenile rearing habitat, particularly for chinook salmon (Oncorhynchus tschawytscha) and steelhead (O. mykiss).  To complement large-scale, census-based monitoring in several treated and untreated reaches in this basin, I examined density-dependent individual growth and movement for both species in small-scale assays using a single treated and a single untreated reach.  Fish density declined substantially with time in both reaches.  Each responded differently to habitat structures with chinook being substantially more abundant in the treated reach than in the untreated reach, but steelhead showing a more variable pattern. Change in fish density over time made estimates of density-dependent growth problematic, but I did find that movement patterns were both density- and habitat-dependent.  Fish tended to move less frequently in the treated reach relative to the untreated reach, which is suggestive of higher habitat quality despite increased opportunity for competitive interactions.  My results suggest that microhabitat scale, within-reach studies of restoration treatments might be necessary to detect impacts to fish populations, although further analysis and more data are required to establish this conclusively.