Managing the Impacts of Walleye on the Resident Fishery of Moses Lake, WA

Moses Lake is third largest natural lake in Washington State.  The native fish composition is unknown and the fishery has been manipulated since the mid-1900s, including stocking non-native fish.  Consequently, the recreational fishery of Moses Lake has been almost exclusively managed for non-native game-fish.  From the 1950s to the late 1970s, Moses Lake was the premier sports fishery in central Washington for panfish, specifically black crappie and bluegill.  Creel surveys demonstrated a shift of catch from black crappie and bluegill in the 1970s and 1980s to primarily yellow perch and walleye by the late 1990s.  The decrease of the economically important black crappie fishery prompted a study conducted by the WDFW and funded by the BPA as off-site resident fish mitigation for the loss of anadromous fish and associated recreation above Chief Joseph and Grand Coulee dams.  The WDFW’s Large Lakes Research Team collected diets, tissue samples for stable isotope analysis, creel data, and quantified fish entrained from Moses Lake via two irrigation outlets.  Results indicated that the combination of predation and entrainment impacted the resident fishery of Moses Lake.  Consumption estimates of >400,000 kg of prey fish a year by walleye and an estimated 500,000 fish entrained from the irrigation outlets were the highest sources of mortality to panfish.  We considered what type of fishery would provide the greatest good to the Moses Lake fishing community and our goal was to manage the walleye population to promote additional fisheries that were not as specialized.  Data from the creel survey and the FAST model were used to develop a regulation that increased the harvest of walleye while maintaining a trophy fishery.  The new fishing regulation permitted anglers a daily harvest of 8 walleye 12” or larger with one fish over 22”.  The previous regulation only allowed a daily harvest of 5 walleye 18” or larger with one fish over 24”.  Although budget constraints have not permitted a follow-up creel survey, our yearly fall walleye index netting surveys indicate walleye have decreased from 36 per net to 19 per net.  Consequently, to effectively manage mixed fisheries it is important to implement measures that act on the assemblage in a top-down approach.