|Document Type:||Journal Article|
|Title:||Adult coho salmon and steelhead use of boulder weirs in southwest Oregon streams|
|Author:||P. Roni, D. Van Slyke, B. A. Miller, J. L. Ebersole, G. R. Pess|
|Journal:||North American Journal of Fisheries Management|
The placement of log and boulder structures in streams is a common and often effective technique for improving juvenile salmonid rearing habitat and increasing fish densities. Less frequently examined has been the use of these structures by adult salmonids. In 2004 we compared coho salmon Oncorhynchus kisutch spawner densities and redd counts in 10 paired reaches distributed in seven different streams with artificially placed boulder weir structures (treatment) and without weirs (control). In addition, using annual spawner survey data collected from 2001 to 2005, we examined coho spawner and coho and steelhead O. mykiss redd densities throughout one of our study streams, the West Fork of Smith River Basin (WFS), to examine whether these metrics (redds, abundance) differed among main stem reaches with boulder weirs or main stem reaches or tributary reaches without weirs. Both numbers of coho spawners and peak redd counts (P d 0.05) were significantly higher in treatment than in control reaches in the first study. In contrast, no differences existed in coho spawner counts or steelhead redd counts among reaches within the WFS. Coho redd densities differed significantly among the three categories in the WFS with higher redd densities in tributary reaches than in either mainstream reaches with or without boulder weirs. We detected a positive relationship of both spawner and redd density with percent gravel. Our results from these two related studies suggest that the placement of boulder weirs in bedrock channels leads to localized increases in spawner abundance, though other factors such as amount of spawning area (gravel) appear to influence coho and steelhead spawner abundance and redd construction at a watershed scale. This also suggests that gravel sources are an important factor to consider when placing boulder weirs or other instream structures designed to improve spawning habitat.