Lake Washington warm water fish diet analysis FY 17

The Muckleshoot Indian Tribe conducted a test fishery to determine the feasibility of conducting commercial fisheries targeting Lake Washington warm water species – this test fishery was approved in the Endangered Species Act (ESA) Section 7(a)(2) Biological Opinion and Magnuson-Stevens fishery Conservation and Management Act Essential Fish Habitat Consultation (F/WCR-2016-4914). This test fishery (which was not funded through the project) provided a unique opportunity to obtain and analyze diet samples of the fish caught. This project supported the analysis of gut contents of potential salmonid predators (primarily smallmouth bass and northern pikeminnow but also largemouth bass and cutthroat trout). Data resulting from this project helped quantify the fraction of analyzed diets that was composed of emigrating Chinook and other salmonids. In the lab, stomach contents were examined under a dissecting microscope and prey items were identified to the lowest practical taxonomic unit. Diets were compared pre and post smolt emigration and among species where sample sizes allowed for statistically valid comparisons. This sampling was restricted to landed catch from the test fishery.

The Lake Washington basin has a plethora of native and exotic piscivores that are known to consume juvenile emigrating Chinook and other salmonids. Recent evidence has indicated
return rates of hatchery Chinook and coho have declined over historic averages and acoustic telemetry data for juvenile coho suggests Lake Sammamish and LakeWashington are where the majority of losses are occurring. This research will identify species that are a concern to emigrating juvenile salmonids in the LakeWashington Basin. Once the data is compiled and
analyzed we can formulate recommendations to mitigate and manage sources of predation