Gizzard Shad and Walleye Relations in Lake Sharpe, South Dakota

Gizzard shad Dorosoma cepediam are important prey species for walleyes in Missouri River and western irrigation reservoirs.  Understanding gizzard shad dynamics at all life stages and how dynamics may be related to climate, reservoir operation, and walleye growth and condition will aid in walleye management in these water bodies.  The objectives of this study were to: i) relate larval shad abundance to climate, reservoir operation, and walleye growth and condition; and ii) examine adult gizzard shad recruitment patterns.  Comparisons relating models of larval gizzard shad abundance to climate and reservoir operation variable indicated no single best model for predicting larval shad abundance for either Missouri River or western reservoirs.  Relationships between larval gizzard shad abundance and walleye growth and condition were highly variable among Missouri River water bodies, and some relationships were unexpectedly negative.  These results suggest that larval dynamics are highly variable and that the larval stage is likely not the appropriate stage for predicting walleye growth and condition.  Adult gizzard shad collected from Lake Sharpe showed markedly consistent recruitment and presence of older fishes.  Recruitment is likely facilitated by winter thermal refugia for juveniles and adults and low biomass of adults.  Overall, this study builds on previous research of both native and introduced gizzard shad populations in South Dakota reservoirs.  However, continuous monitoring and further research is warranted to identify any potential changes in gizzard shad dynamics before costly management actions are necessary.