Piscivory by Walleyes and Yellow Perch in Western Lake Erie

We examined stomach contents of 906 age‐0 and older walleyes Stizostedion vitreum vitreum and 1,575 age‐2 and older yellow perch Perca flavescens, collected from western Lake Erie in 1979–1981, to measure preferences for prey type and size and diet overlap among different size groups of these two percids. Seasonal diets closely followed changes in forage‐fish availability. Walleyes ate age‐1 shiners Notropis atherinoides and N. hudsonius in spring, but switched to age‐0 clupeids Dorosoma cepedianum and Alosa pseudoharengus in summer and autumn. Diet selection was governed by abundance of appropriate‐size prey and preferences for forage species. Yellow perch ate invertebrates in spring but clupeids and shiners thereafter; electivity values for prey were low compared with those of walleyes, indicating that yellow perch were the more opportunistic feeders. Diet overlap was greatest among walleye age groups (0, 1, and 2‐and‐older) and least between walleyes and yellow perch. We hypothesize that density‐dependent processes within the percid community probably will occur during years of low shiner and clupeid abundance and that they will be most intense for walleyes. Walleyes were less size‐selective and grew more slowly in 1979–1981 than in 1959–1960, suggesting that forage‐fish availability has declined in the presence of increased walleye stocks. Yellow perch should be less affected by forage‐fish reductions if invertebrates are plentiful. Received August 5, 1983 Accepted August 21, 1984