Effects of walleye predation on the population dynamics of small littoral-zone fishes in a northern Wisconsin lake
We used a bioenergetics model to assess the effects of predation by juvenile walleyes Stizostedion vitreum vitreum on the populations of darters (Percidae) and minnows (Cyprinidae) in Sparkling Lake, Wisconsin. In 1982, when young-of-the-year yellow perch Perca flavescens were scarce, darters and minnows were important in walleye diets throughout the summer. Walleye predation accounted for approximately 100\% of adult darter mortality and 75\% of adult minnow mortality. Walleyes appeared to be important in determining abundance of young-of-the-year darters in October, but had little direct effect on abundance of young-of-the-year minnows. In 1983, when young-of-the-year yellow perch were abundant, darters and minnows were only important in walleye diets in June. Walleye predation accounted for 80\% of adult darter mortality but only 35\% of adult minnow mortality. The decrease in walleye consumption of adult darters and minnows in 1983 compared with 1982 is consistent with the hypothesis that abundant yellow perch year classes buffer littoral-zone fish assemblages from walleye predation. The decrease in walleye predation on darters that occurred with increased abundance of young-of-the-year yellow perch appeared to allow an increase in abundance of young-of-the-year darters. However, for minnows, the decrease in walleye predation did not decrease adult total mortality nor did it lead to an increased young-of-the-year abundance. This implies that walleye predation has a much greater direct impact on the darter population than on the minnow population.