The ruffe Gymnocephalus cernuus, an exotic Eurasian percid, recently became established in the St. Louis River estuary, Lake Superior, after accidental introduction. Management actions (catch regulations and stockings) were enacted in 1989 to increase the density of top-level predators in the estuary, and thus to increase predation on ruffe. We conducted a field and laboratory study to determine if, and to what extent, native piscivores consume ruffe. Stomachs of 3,669 predators were examined in 1989–1991. Ruffe occurred in 6.7% of burbot Lota lota, 5.8% of bullheads Ictalurus spp., 4.7% of smallmouth bass Micropterus dolomieu, 2.6% of northern pike Esox lucius, 2.6% of black crappies Pomoxis nigromaculatus, and 1.3% of yellow perch Perca flavescens (4.5% after 1989) captured during the 3-year study. No ruffe were found in 967 stomachs of walleyes Stizostedion vitreum examined. Ruffe were 22.7%, of the diet (by weight) of bullheads (during the only year bullheads were captured) and 0.1–17.9% of the diet of northern pike. Ruffe were 0.9–24.5% of the diet of smallmouth bass that contained fish, 1.5–6.9% of yellow perch that contained fish, and 0.0–10.9% of black crappies that contained fish. Most ruffe eaten were age-0 or small age- 1 fish. In the laboratory, walleyes that were first fed soft-rayed prey or that were also offered soft-rayed prey consumed very few ruffe, whereas walleyes that were first fed spiny-rayed yellow perch or were also offered yellow perch consumed about equal numbers of ruffe and yellow perch. Northern pike and burbot consumed about equal numbers of ruffe and yellow perch in the laboratory. It is unlikely that predation will effectively control the initial expansion of ruffe in other areas of the Great Lakes because native predators initially consume few ruffe, especially if more preferred soft-rayed prey are available.
|Original language||English (US)|
|Number of pages||9|
|Journal||North American Journal of Fisheries Management|
|State||Published - Feb 1996|
Bibliographical noteFunding Information:
We thank Dennis Pratt of the Wisconsin Department of Natural Resources (DNR), John Spurrier and Dennis Anderson of the Minnesota DNR, Reed Glesne of the U.S. Fish and Wildlife Ser-vice's Office of Fisheries Assistance in Ashland, Tom Busiahn and Neil Kmiecek of the Great Lakes Indian Fish and Wildlife Commission, and the crews of the RV Coaster and RV Siscowet for as-sistance in sample collections; D. Zilker and T. Darland for assistance in stomach analysis; and J. E. Miller and G. Yearout for assistance with lab- oratory studies. Comments on earlier versions of this manuscript by J. Spurrier, P. J. Schneeberger, and an anonymous reviewer were helpful and appreciated. Support for this project came from the Minnesota Sea Grant College Program, the U.S. Department of Commerce under grant USDOC-NA86AA-D-SG112, the Minnesota Agricultural Experiment Station under project 72, the National Biological Service's Great Lakes Science Center, the Minnesota DNR, the Wisconsin DNR, the Great Lakes Indian Fish and Wildlife Commission, and the Great Lakes Fishery Commission. This is journal reprint JR324 of the Minnesota Sea Grant College Program, paper 20,740 of the Minnesota Agricultural Experiment Station contribution se- ries, and contribution 916 of the Great Lakes Sci- ence Center.