Responses of fishes and salamanders to instream restoration efforts in western Oregon and Washington

Abstract

Thirty streams in western Oregon and Washington were sampled during summer and winter to determine the responses of juvenile salmonids, juvenile lamprey (Entosphenus tridentatus and Lampetra spp.), sculpin (Cottus spp.) and giant salamanders (Dicamptodon spp.) to artificial large woody debris (LWD) placement and to examine their habitat preferences. I also monitored the monthly movements of marked juvenile coho salmon (Oncorhynchus kisutch), steelhead ( O. mykiss) and cutthroat trout (O. clarki) between a "restored" reach (with placed wood) and a reference reach (no wood placement) in Shuwah Creek. Juvenile coho salmon densities were 1.8 and 3.2 times higher in treated reaches compared to reference reaches during summer and winter, respectively. Densities of age 1+ cutthroat trout and steelhead did not differ between treatment and reference reaches during summer but were 1.7 times higher in treatment reaches during winter. No significant difference was detected between densities in treatment and reference reaches for trout fry (age 0+ cutthroat and steelhead), giant salamanders, sculpin or lamprey. However, lamprey and coho response to LWD placement was positively correlated with LWD forming pools. Summer densities of coho salmon, cutthroat trout, and lamprey were significantly higher in pools than riffles, whereas densities of age 0 torrent sculpin (C. rhotheus) were higher in riffles than pools. In winter, densities of coho, salmon, cutthroat and steelhead trout, and young of the year trout fry were higher in pools than riffles. These results indicate that the largest fish response to restoration occurs for those species that prefer pools and at those sites with the largest increase in LWD and pool area. Monthly surveys in Shuwah Creek to examine salmonid movement indicated that 0 to 33% (0 to 4 fish) of the marked trout or coho, salmon observed on a given date moved between the restored and reference reach. However, the rapid decline in fish densities in late fall and the increasing proportion of unmarked fish over the course of the study indicated migration to and from the study reaches. These results suggest that it is important to consider fish movements when evaluating habitat restoration and enhancement projects.