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 competitors in the Great Lakes, was investigated. Laboratory experiments were conducted to determine the food preferences of ruffe and yellow perch and to compare their feeding rates on two types of substrate (sand and cobble). For comparison with natural communities, we sampled benthic macroinvertebrates from western Lake Michigan and compiled published data on invertebrate community structure from all of the Great Lakes. Ruffe and yellow perch both preferentially consumed soft-bodied taxa (e.g., chironomid midge larvae, mayflies, and non-cased caddisflies) and avoided hard-bodied taxa (e.g., cased caddisflies, snails, and clams) in laboratory studies. Prey preferences of fish in mixed-fish species treatments were more diverse than those in single-fish species treatments. 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 likely able to escape predation by hiding. Results from our laboratory experiments, 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. Less abundant taxa range from vulnerable (amphipods, flatworms, and caddisflies) to invulnerable (sphaeriid clams, gastropods, and zebra mussels). Our study suggests that (I) the composition of benthic macroinvertebrate fauna in each of the Great Lakes is suitable for ruffe, and (2) ruffe and yellow perch will likely prefer similar food resources where they co-occur.