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GLIN==> Eurasian ruffe in Lake Michigan

Posted on behalf of Irene Miles <miles@uiuc.edu>

Eurasian ruffe in Lake Michigan
December 10, 2002

Source: Gary Lamberti  (574)631-8075
Martin Berg (773) 508-8853

Eurasian Ruffe May Increase Pressure on Lake Michigan Yellow Perch

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

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.


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.

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