URBANA--Eurasian ruffe, an invasive fish whose numbers have multiplied dramatically in Lake Superior, have now been spotted in northern parts of Lake Michigan. The good news is that round gobies, which are already abundant in Lake Michigan, may keep ruffe numbers down, according to Gary Lamberti, University of Notre Dame biologist. The bad news is that Eurasian ruffe will nonetheless deplete resources for yellow perch, an important native sport fish.

With funding from Illinois-Indiana Sea Grant, Lamberti and Martin Berg of Loyola University have been studying the relationship among Eurasian ruffe, round gobies and zebra mussels, and how this "exotic triad" can affect yellow perch.

"Exotic species now dominate the food webs of the Great Lakes, including Lake Michigan," said Lamberti. "As more invasive species are introduced to the Great Lakes, they not only compete with native species but also with other invaders."

Each of the three species in the exotic triad poses a unique threat to the ecological and economic health of the region. Zebra mussels, which obstruct water intake pipes and have spread throughout the Great Lakes and the Mississippi River, have cost power plants and other industries hundreds of millions of dollars.

"Round gobies accumulate significant levels of PCBs because their diet includes zebra mussels, which filter water and accumulate high levels of PCBs," said Berg. Although round gobies are not a sport fish, they are a food source for Pacific salmon and smallmouth bass, increasing the risk of elevated levels of contaminants in these game fish.

"Eurasian ruffe are closely related to yellow perch and may compete directly with them for food and habitat in Lake Michigan," said Lamberti. "But unlike yellow perch they have no sport value; they average only six inches in length at maturity and are quite spiny, which also makes them resistant to predators."

The researchers found that although the relationship between these invaders is complex, one fact is simple. The successful species is often the one that gets there first. "In western Lake Superior, Eurasian ruffe have become the dominant fish," said Lamberti. "In Lake Michigan, where round gobies have become numerically dominant, ruffe may be relegated to deeper waters."

Yellow perch in Lake Michigan are pressured early in life by competition from zebra mussels and round gobies. Zebra mussels filter plankton that larval perch need to grow. Gobies not only eat yellow perch eggs, they also compete with young perch for invertebrate food. Even a diminished ruffe presence will further impact the young perch. "Eurasian ruffe and yellow perch will compete for the same resources and it is likely that neither perch nor ruffe will do very well in that scenario," added Lamberti.

As yellow perch grow larger they move to deeper waters, as do Eurasian ruffe. Unlike larger yellow perch, ruffe prefer the bottom habitat, but nonetheless the two species will continue to tap the same food sources.

"The addition of Eurasian ruffe to Lake Michigan waters will likely increase the bottleneck on yellow perch," said Lamberti. "The native fish will experience increased competition during several stages of its life."

Much of this six-year study was done in simulated lake environments and augmented with fish surveys from many parts of the Great Lakes. Two Notre Dame graduate students, Candace Bauer and Aimee Fullerton, were integral to the project.

If you would like more information, visit the Sea Grant Web site on invasive species at www.sgnis.org,  which includes 3-D images of the exotic triad.

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The Illinois-Indiana Sea Grant College Program is one of 30 National Sea Grant College Programs. Created by Congress in 1966, Sea Grant combines university, government, business and industry expertise to address coastal and Great Lakes needs. Funding is provided by the National Oceanic Atmospheric Administration (NOAA), U. S. Department of Commerce, the University of Illinois at Urbana-Champaign and Purdue University at West Lafayette, Indiana.

Irene Miles
Illinois-Indiana Sea Grant
376 NSRC
1101 W. Peabody Dr.
Urbana, Il 61801
Phone:  217-333-8055
Fax:  217-333-8046
miles@illinois.edu