Percid populations have generally increased in abundance relative to other groups of fishes in the 15–25 yr four large reservoirs have been operational on the Missouri River in South Dakota. Saugers (Stizostedion canadense) were initially the most abundant percid, but their numbers gradually declined, probably because of the reduction in river spawning habitat and the increase in water clarity. Yellow perch (Perca flavescens) increased to high population levels as the reservoirs filled but later decreased in abundance. Walleye (S. vitreum vitreum) populations were the slowest to develop in the reservoirs, probably because of initial lack of suitable spawning habitat; they later became well established.The yellow perch was one of the most important forage species in the reservoirs, and walleyes and saugers the primary predator and sport fishes. Sportfishing quality 15–25 yr after impoundment was good, but harvest remained low because of the large size of the reservoirs, inadequacy of facilities for anglers, and the relatively sparse human population. Reproductive success was the primary factor regulating the abundance of percids. Year-class strength was primarily determined by climatic rather than biological factors. Above-average precipitation presumably enhanced reproductive success, both directly by increasing the quantity and quality of spawning substrate through higher stream flows and water levels, and indirectly by providing a larger forage supply, thereby apparently reducing predation on young percids, as well as cannibalism. Kew words: Percidae, reservoirs, Missouri River, Stizostedion, Perca, population dynamics, ecology, precipitation, water level
