Lake Roosevelt, Columbia River Hydrologic Regime Influence on Age-1 Walleye Recruitment

Hydrologic regime influences on age-1 walleye (Sander vitreus) recruitment in Lake Roosevelt, Columbia River were examined to elucidate recruitment drivers using data from the Lake Roosevelt Fisheries Evaluation Program. Limnological and hydrological data from 1998 to 2002 was related to walleye age-1 catch per unit effort (CPUE) data from 1999 to 2003. Inflow volumes from the Columbia River were significantly related to water retention time in Lake Roosevelt. Regression analysis identified walleye age-1 CPUE being significantly related to inflow volumes, water retention time, and prior year July Daphnia sp. biomass, with Columbia River inflow volumes explaining most of the data variance. July Daphnia sp. biomass was significantly related to both inflow volumes and water retention time. Inflow volumes of the Spokane River, the major spawning tributary, were not significantly related to walleye age-1 CPUE. Consequently, flow data was not influencing walleye spawning success to the point in which it would limit age-1 recruitment.  Walleye age-1 recruitment is increased by lower inflows, creating longer water retention times which lead to increased July Daphnia sp. biomass. Age-1 walleye recruitment appears to be driven by food availability and other environmental factors controlled by inflows.