Gizzard shad reproductive biology and predator-prey relations with walleyes in western South Dakota reservoirs

Gizzard shad Dorosoma cepedianum were introduced into Angostura, Orman, and Shadehill reservoirs to provide increased prey resources for walleye Sander vitreus. The objectives of this study were to assess gizzard shad reproductive biology and determine the extent to which gizzard shad contribute to the walleye prey base. Correlations between gizzard shad year-class strength and my indices of winter severity and winter duration revealed limited evidence that winter harshness solely influenced gizzard shad recruitment to the adult stage. Larval gizzard shad abundance was substantially higher in Orman Reservoir compared to Angostura and Shadehill reservoirs. Mean daily growth rate of juvenile gizzard shad ranged from 0.73 to 1.50 mm/d among the three populations and was significantly lower in Orman Reservoir. Walleye food habits and bioenergetics modeling indicated that mean walleye weight decreased among cohorts until age-0 gizzard shad were consumed and that walleye growth was directly affected by age-0 gizzard shad consumption.