Evaluation of Juvenile Salmon Production in 2018 from the Cedar River and Bear Creek

This report describes the emigration of five salmonid species from two tributaries in the Lake Washington watershed. The Cedar River tributary flows into the southern end of Lake Washington and Bear Creek flows into the Sammamish River, which in turn flows into the north end of Lake Washington (Figure 1). In each watershed, the abundance of juvenile migrants is the measure of freshwater production upstream from the trapping location. 

In 1992, the Washington Department of Fish and Wildlife (WDFW) initiated an evaluation of sockeye fry migrants in the Cedar River to investigate the sources of low adult sockeye returns. In 1999, the Cedar River juvenile monitoring study was expanded in scope in order to include juvenile migrant Chinook salmon. This new scope extended the trapping season to a six-month period and, as a consequence, also allowed estimation of coho abundance and assessment of steelhead and cutthroat trout movement. 

In 1997, WDFW initiated an evaluation of sockeye fry migrants in the Sammamish watershed. In 1997 and 1998, a juvenile trap operated in the Sammamish River during the downstream sockeye migration. In 1999, the monitoring site was relocated to Bear Creek to evaluate Chinook and sockeye production. Since 1999, the Bear Creek juvenile monitoring study estimates coho production and movement of steelhead and cutthroat trout. 

The primary goal of this study was to estimate the abundance of natural-origin sockeye fry, natural-origin Chinook, and natural-origin coho migrating from the Cedar River and Bear Creek into Lake Washington in 2018. These data allow an estimate of egg to fry survival of the 2017 brood. Daily abundance estimates also characterized the migration timing of each species into Lake Washington.