Predation of baby salmon by non-native gamefish is a major concern in the salmon recovery effort.  Co-Managers in Lake Sammamish/Lake Washington are evaluating the direct impact of these predator and studying ways to directly reduce the predator populations.  Trout Unlimited (TU), in an effort to to decrease the impact of these predators are initiating a pilot study, funded by King County, to evaluate the impact on these predator populations when the habitat that supports them (non-native aquatic weeds) are removed.

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Eurasian Milfoil (Myiophyllum spicatum) is native to Europe, Asia, and Africa.  This aquatic weed likely arrived in North America in the 1880’s and has spread across many of the waterbodies in North America.  Milfoil was first recorded in Lake Washington/Sammamish watershed in the mid 1970’s and has spread through much of the watershed.  This nuisance aquatic weed forms a dense canopy and shades out native plant populations of native vegetation within the littoral zone. Milfoil management is typically pursued to address water quality issues, navigation issues, and conflicts with general recreational use; however, the aquatic weed also appears to create preferred habitats for yellow perch, juvenile bass, and other nonnative piscivores.  Milfoil impacts water quality by increasing phosphorous and nitrogen, increasing pH, reducing dissolved oxygen (DO), and increasing temperature (Washington Department of Ecology). This pilot project will evaluate aquatic weed control as a tool for salmon conservation by studying the change in nearshore fish community (abundance) as a result of aquatic weed control efforts.

Study Specifics:

Target Species - Eurasian watermilfoil, Elodea

Methods: Utilization of Diver Assisted Suction Harvesting (DASH)

Treatment Areas:  Idylwood Park, Sammamish Landing, Lake Sammamish State Park (Issaquah Creek), Timberlake Park, Bellevue Park.

Treatment Timeline - June

Diver Survey - June & July

Please direct any questions to David Kyle (TU Project manager) dkyle@tu.org