Monitoring Chinook and Steelhead Escapement on the Elwha River Using Imaging SONAR

On September 17^th, 2011 deconstruction will begin on two dams in the Elwha River, Washington, that will re-open 120 km of pristine salmonid habitat.  A key measure of the success of this restoration action will be the response of salmon populations in the basin.  Due to high sediment loads during dam removal, in addition to the already variable turbidity and flow regimes of the river, SONAR emerges as one of the few techniques that is viable for adult salmon enumeration, particularly during the fall and winter.  Since 2008, we have used both Blueview and DIDSON multi-beam imaging SONAR systems to enumerate upstream passage of adult, ESA listed, summer Chinook and winter steelhead on the Elwha.  We have utilized a variety of deployment systems for the SONAR heads, software programs to facilitate efficient counting of recorded data, and statistical and modeling techniques to derive robust escapement estimates for species that migrate over long time periods.  In addition, we collected data on fish criteria such as relative size, distance from the bank, and time of year in an attempt to partition fish passage into different species.  We produced a range of estimates depending on the inclusion of various fish passage criteria in addition to making adjustments based on observer error. We estimated adult escapement of summer Chinook between 2008 and 2010 to range from approximately 1200 to 2500 fish.  The Elwha SONAR project is currently coupled with a resistance board weir that will enable year round enumeration of adult salmon leading up to, including, and after dam removal to provide robust data with which to measure the success of re-opening salmon habitat.