Cooperative Fish and Wildlife Research Units Program: Washington
Education, Research and Technical Assistance for Managing Our Natural Resources

The Lake Washington fishery for sockeye salmon is an important recreational fishery in a large urban lake alongside Seattle. The fishery has been closed since 2006 due to insufficient spawning escapement by returning adult sockeye. Currently 94% to 99% of juvenile sockeye that enter the lake as do not survive to the presmolt stage in Lake Washington one year later. Previous studies have shown that predation by Cutthroat trout and Northern Pikeminnow could conceivably account for nearly all of the lake-phase mortality of juvenile sockeye, depending on the abundance and size structure of the predator populations in the lake. In addition, the populations of juvenile salmon and alternative prey (Longfin Smelt and Threespine Sticklebacks) potentially influence the variability in seasonal and annual predation mortality imposed on juvenile Sockeye Salmon. In order to properly assess the predatory impacts of coastal cutthroat trout and northern pikeminnow on juvenile Sockeye Salmon the study will accomplish the following two objectives: 1) estimate the abundance of previously identified important predators of juvenile sockeye in the lake (coastal cutthroat trout and northern pikeminnow), and to 2) quantify their predation on juvenile sockeye.