Evaluating Changes in Nearshore Fish Communities Following Removal of the Elwha River Dams

Since 2006, we have been collecting data on intertidal/sub-tidal fish (nearshore) communities from the Elwha River and reference sites in the Strait of Juan de Fuca to assess if fish were responding to significant sediment changes resulting dam removal. Ecologically important forage fish spawn and rear and juvenile salmon migrate through these areas. Beach seine samples included 5 years pre-removal and two years post- removal data.  Trends in species richness/ abundance were consistent throughout with reference areas possessing more species and overall abundance of fish than Elwha River sites.  A multivariate analysis suggested that there was overlap in fish community composition between years but there was some separation in fish assemblage structure between the areas prior to dam removal.  Differences between regions were primarily the result of differences in abundance of several forage fish species.  There were distinct seasonal differences in all regions.  Our plan is to continue to monitor as the system evolves towards a more natural sediment regime. Our ability to detect responses of fish communities to sediment changes will ultimately depend on both biotic and abiotic factors, such as when sediment reaches the coastal environment and how long it takes material to distribute from the river’s mouth.