Spring and Summer Water Levels in a Missouri River Reservoir: Effects on Age-0 Fish and Zooplankton

Abstract

The effects of water level on the early life history of fish in Lake Francis Case, South Dakota, were studied by comparing the abundance, growth, diet, and food supply (zooplankton) of selected species in a low-water year (1974) and a high-water year (1975). Young of 21 fish species were collected. Yellow perch (Perca flavescens), white bass (Morone chrysops), buffaloes (two Ictiobus species), and centrarchids were significantly more abundant in net catches in 1975 than 1974. Flooded shoreline vegetation in 1975 apparently enhanced spawning success by providing a more suitable substrate and protective cover for early life stages. First-summer growth of the four most abundant fishes (yellow perch, buffaloes, and white bass) did not change significantly between years. Standing crops of the larger zooplankton (calanoids and daphnids) decreased during the high-water year, perhaps because of predation by age-0 fish. Standing crops of the smaller zooplankton species such as Bosmina longirostris and Chydorus sphaericus increased during the high-water year, as did the overall diversity of the zooplankton community. We conclude that management of water levels in Missouri River main-stem reservoirs to include one high-water year out of every three would greatly enhance the lakeˈs fishery resources.