Greene, C.M. and Beamer, E.M., 2011. Monitoring Population Responses to Estuary Restoration by Skagit River Chinook Salmon. Northwest Fisheries Science Center, Seattle, WA. pp. 22.

While much restoration in Pacific Northwest estuaries has been implemented in order to improve rearing conditions for juvenile Chinook salmon, no studies to date have documented population responses in the focal stock to these restoration efforts. With this intention, we examined the responses of Skagit River Chinook salmon to reconnection and restoration of estuarine by implementing long-term monitoring of juvenile Chinook salmon rearing in tidal delta channels, nearshore, and offshore estuarine habitats. These habitats are strongly associated with rearing stages of juvenile Chinook salmon, especially in fish of wild origin.
This report focuses on results of population monitoring through 2010 and addresses three general questions: 1) Are salmon limited during the early estuarine life stages by capacity and connectivity constraints? 2) Does broad-scale restoration influence local population density? and 3) Has estuary restoration resulted in population- or system-level responses? Our results showed that 1) restoration in the Skagit River tidal delta is needed to address capacity and connectivity limitations, 2) local restoration did improve rearing densities for juvenile Chinook salmon, and 3) system-wide responses can be detected using a before/after control-impact (BACI) design. In addition, it appears capacity limitations still exist in the Skagit River tidal delta, as judged from recruitment patterns into shoreline habitat, and that further tidal delta restoration is warranted. Thus far, we estimate that the amount of restoration work completed in the tidal delta is 12% of goal of the Skagit River Chinook Recovery Plan, and our monitoring work corroborates this estimate.
These findings also shed light on the utility of extensive monitoring in order to document effects of restoration. Responses to restoration would have been impossible to determine without extensive pre-restoration status monitoring and juvenile migrant trapping throughout both pre- and post-restoration phases. Monitoring of transitional estuarine rearing habitats at multiple life stages is helping to pinpoint the contribution of potential rearing areas within the Skagit tidal delta.
Further monitoring as part of the Intensively Monitored Watershed Project (IMW) is needed to refine our ability to detect change at a population level and to examine the sensitivity of other life-stage specific monitoring metrics (nearshore recruits, adult returns) to restoration in the tidal delta. Finally, ongoing monitoring is shedding important light on the status and trends of multiple species of importance in the Skagit River estuary, including Chinook and coho salmon, bull trout, Pacific herring, and surf smelt.