Lesson 5: Ruffe Musical Chairs

Published: September 2005

Activity: Students use role-play to mimic the behavior of an invasive, non-native fish called Eurasian ruffe (pronounced rough) to experience firsthand how and why the species has multiplied so rapidly in some Great Lakes harbors.

Grade level: 4-8
Subjects: Science, social studies
Setting: Classroom
Duration: 1 hour
Key Terms: Invasive, Nonindigenous, Predator

Objectives
After participating in this activity, students will be able to:

• Explain why fish populations in the Great Lakes change over time.
• List three reasons why non-native ruffe have significant advantages over some native Great Lakes fishes.
• Identify two things that they can do to minimize the spread of ruffe.

Summary
All animals must meet basic needs for food, water, and habitat in order to survive. There are times, however, when some animals can’t meet their needs. One reason may be due to competition for food and habitat caused by an invasive species. By learning about the aggressive ruffe, students begin to see how a single species can cause other fish species to decline, and create a dramatic change in the Great Lakes food web in a relatively short time.

Background
Eurasian ruffe, small members of the perch family, are aggressive fish native to Europe and Asia. They were first discovered in the St. Louis River, the main tributary to western Lake Superior, in 1986. They arrived in the ballast water of an ocean-going vessel. In the absence of natural predators, ruffe populations multiplied rapidly.

Today, ruffe make up an estimated 80 percent of the fish caught in the St. Louis River. Since their arrival, ruffe have spread to other rivers and bays along the south shore of western Lake Superior and northward to Thunder Bay, Ontario. Ruffe also thrive in the waters near Alpena, Michigan on northern Lake Huron. Rapid growth of ruffe populations has reduced food and habitat for native fish with similar diets and feeding habits, including walleye, perch, and a number of small fish.

Several factors allow ruffe to displace native species in newly invaded areas. First, ruffe grow rapidly and produce many offspring. Ruffe can reproduce in their first year, and an average female can produce 13,000 to 200,000 eggs per season. Second, ruffe can tolerate a range of environmental conditions, including murky water. Ruffe are primarily bottom feeders, and they prefer dark environments where they can hide from predators. Finally, even though ruffe are small (usually less than 5 inches), ruffe have few predators due to the spines on their fins.

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