Cooperative Fish and Wildlife Research Units Program: South Dakota
Education, Research and Technical Assistance for Managing Our Natural Resources

Inter- and intra- reservoir variation in prey fish composition and abundance has an important effect on sport fish populations in the Missouri River. Coldwater habitat in Lake Oahe, for example, provides refuge for rainbow smelt – a forage species that contributes significantly to walleye production. In contrast, prey fish populations in downstream impoundments are dominated by gizzard shad, cyprinids, and young-of-year sport fishes. In the late 1990s, the decline of rainbow smelt in Lake Oahe had significant impacts on walleye production. Although the smelt population has been recovering, low water levels combined with the recent expansion of gizzard shad in Lake Oahe have resulted in a unique food web never before observed in this system. As a result, factors affecting gizzard shad abundance and distribution in Lake Oahe and their contribution to the growth dynamics of walleyes are poorly understood.