A small, spiral-shaped snail that clones itself and is native to New Zealand has been discovered in Duluth-Superior Harbor and the St. Louis River estuary, raising concerns about the impact of another invasive species.
The snail, called the New Zealand mudsnail, is only about as large as a peppercorn when fully grown. But one snail and its offspring can generate hundreds of thousands of clones each year.
In some Western states, the mudsnail has displaced native insects, snails and other invertebrates that are important food for fish.
The mudsnails were first found in Idaho's Snake River in 1987, and have affected Rocky Mountain trout streams. They were first spotted in the Great Lakes in Lake Ontario in 1991.
More than 100 mudsnails were collected last fall in Duluth by Environmental Protection Agency researchers. The discovery, announced Monday, is the first finding of the tiny snail in Minnesota and Wisconsin waters.
Researchers suspect that they were carried into the Great Lakes via ship ballast water.
"Our lakes, streams and rivers have enough stress on them and they don't need something else like this," said Gary Montz, research scientist for the Minnesota Department of Natural Resources.
Researchers said Lake Superior is too cold for the mudsnail but its harbors and estuaries are warm enough — like in Thunder Bay, Ontario, where it was discovered in 2001.
Doug Jensen, aquatic invasive species program coordinator for Minnesota Sea Grant at the University of Minnesota Duluth, said the mudsnails were discovered in several locations in sediment at the bottom of Duluth harbor.
"We have an established infestation," he said. "Efforts to eradicate them would be virtually impossible."
Jensen said boaters and anglers must learn about the mudsnails so they won't be spread inadvertently to Minnesota and Wisconsin lakes and rivers.
The snails are often attached to aquatic plants or can become embedded in mud, so Jensen urged people to remove vegetation from boats, trailers and fishing gear and to rinse waders, hip boots and boat motors with hot water or let them dry for several days in the sun to kill the snails.
Like other invading species, the full impact of mudsnails may not be known for years.
A parasitic fluke controls mudsnail numbers in its native New Zealand, but the snail has no natural predators here.
Researchers are considering importing the fluke, but it may take years to determine if the flukes might cause their own problems here.