Walleye and Sauger Movement and Entrainment in Lewis and Clark Lake

Walleye Sander vitreus and Sauger Sander canadensis are both socioeconomically important sportfish species in Lewis and Clark Lake, an interjurisdictionally managed mainstem Missouri River reservoir fishery. Since 2011, adult catch per unit effort (CPUE) of both Walleye and Sauger has remained at approximately 50% of pre-2011 levels. A presumed reason for the suppressed CPUE of adult Walleye and Sauger is substantial entrainment of larval and adult fish resulting from the reservoir’s high turnover rate (7.2 d). Acoustic telemetry was used to quantify adult movement and entrainment and ichthyoplankton trawls were used to assess larval entrainment. Relative importance of factors driving larval entrainment through Gavins Point Dam (GPD), abundance of age-0 fish in the reservoir, and adult movement patterns were assessed using an information theoretic approach. The models with the most support for explaining variation in larval entrainment were week of year and air temperature for Fort Randall Dam (FRD) and water temperature, day of year, and cumulative days of sustained high discharge for GPD. Age-0 Walleye abundance was most supported by mean outflow through GPD, mean annual precipitation, and delta April gage height. Age-0 Sauger abundance was most supported by adult conspecific abundance, April heating degree days, and annual precipitation. Mean weekly adult Walleye movement was most supported by reservoir elevation, season, and mean weekly air temperature. Mean weekly adult Sauger movement was most supported by discharge through FRD and season. We observed that annual larval entrainment (both total including all species and Walleye and Sauger entrainment) through GPD is generally greater than larval entrainment through FRD during 2021–2024. Further, entrainment and exploitation are sources of loss for adult Walleye and Sauger. Our findings suggest flow is a driving factor affecting abundances of larval Walleye and Sauger and flow is affecting abundances and movement patterns of adult Walleye and Sauger in the reservoir.Advisor: Mark A. Pegg