Long-Term Coho Salmon Response to Instream Restoration

The Lifecycle Monitoring Project in western Oregon has been estimating salmonid abundance in 8 study basins 1998-present. The West Fork Smith River a 67 km² basin located in Southwestern Oregon is a bedrock dominated system impacted by past land-use practices and has been the focus of extensive stream restoration projects since 1981. In order to evaluate aquatic response to in-stream restoration, this study used long term data sets estimating returning adult and out-migrating juvenile coho salmon Oncorhynchus kisutch in one test basin, seven control basins and coast-wide estimates. Coho smolt production increased dramatically within the test basin over the study period, 1998-present, as well as relative to control basins. Adult returns for the test basin show an upward trend relative to estimates for the Oregon Coast Coho Evolutionarily Significant Unit and two sub-strata population areas. Spawning surveys conducted on a tributary reach, 1958- present, showed a marked decline in peak spawner abundance up to 1980 when in-stream passage and restoration began. Peak spawner abundance increased following treatments and continues to improve. Discussion of potential aquatic responses to the $1.6 million in recent basin-scale in-stream work that was based on over-winter survival studies and habitat modeling previously conducted within the basin.