PREY PREFERENCES OF EURASIAN RUFFE AND YELLOW PERCH - COMPARISON OF LABORATORY RESULTS WITH COMPOSITION OF GREAT-LAKES BENTHOS

The consumption of benthic macroinvertebrates by ruffe (Gymnocephalus cernuus) and yellow perch (Perca flavescens), two potential competitor s in the Great Lakes, was investigated. Laboratory experiments were co nducted to determine the food preferences of ruffe and yellow perch an d to compare their feeding rates on two types of substrate (sand and c obble). For comparison with natural communities, we sampled benthic ma croinvertebrates from western Lake Michigan and compiled published dat a on invertebrate community structure from all of the Great Lakes. Ruf fe and yellow perch both preferentially consumed soft-bodied taxa (e.g ., chironomid midge larvae, mayflies, and non-cased caddisflies) and a voided hard-bodied taxa (e.g., cased caddisflies, snails, and clams) i n laboratory studies. Prey preferences of fish in mixed-fish species t reatments were more diverse than those in single-fish species treatmen ts. Ruffe and yellow perch of similar sizes consumed approximately 5% of their body mass per 24 hours at 20 degrees C on sand, whereas their feeding rates were reduced by over 50% on cobble, where prey were lik ely able to escape predation by hiding. Results from our laboratory ex periments, field survey, and review of published studies indicate that oligochaetes and chironomids, the two most numerous macroinvertebrate taxa in each of the Great Lakes, are vulnerable to ruffe predation. L ess abundant taxa range from vulnerable (amphipods, flatworms, and cad disflies) to invulnerable (sphaeriid clams, gastropods, and zebra muss els). Our study suggests that (I) the composition of benthic macroinve rtebrate fauna in each of the Great Lakes is suitable for ruffe, and ( 2) ruffe and yellow perch will likely prefer similar food resources wh ere they co-occur.