TRAVERSE CITY, Mich. -- DNA tests in three southwestern Michigan rivers have turned up no sign of Asian carp, the huge, voracious fish threatening to invade the Great Lakes, scientists said Friday.
Researchers with the University of Notre Dame and The Nature Conservancy collected water from the Galien, St. Joseph and Paw Paw rivers last fall as part of a project to determine whether bighead or silver carp have reached Lake Michigan or its tributaries. Their DNA was not detected during lab analysis of the samples.
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"This is great news for Michigan, but by no means should we relax our stance on Asian carp and the threat they pose to the Great Lakes basin," said Patricia Birkholz, director of the Office of the Great Lakes.
Fish leave genetic evidence of their presence in their scales and bodily wastes. Scientists with Notre Dame and the conservancy developed methods of using so-called environmental DNA to look for Asian carp in waterways linking the Great Lakes and Mississippi River basins near Chicago.
The carp escaped into the Mississippi from Southern fish farms and sewage lagoons in the early 1970s and have been migrating northward. They have infested parts of the Mississippi and connected rivers, out-competing other fish for plankton. Scientists say if they reach the Great Lakes, the carp -- which can reach 4 feet in length and weigh up to 100 pounds -- could disrupt the food chain and threaten the $7 billion fishing industry.
Michigan, Minnesota, Wisconsin, Ohio and Pennsylvania are pursuing a federal lawsuit seeking to sever the man-made connection between the lakes and the Mississippi.
An electric barrier on the Chicago Sanitary and Ship Canal is designed to block fish migration. But researchers have reported Asian carp DNA in numerous spots above the barrier, although just one actual fish has been found.
The team is trying to determine whether the carp have reached the Great Lakes, which are so big it would be hard to find the invaders until they are well established, said Chris Jerde, a Notre Dame biologist and the project manager.
That's why scientists have been focusing on rivers where the carp might go to spawn. More than 20 rivers connected to the lakes appear to offer suitable carp habitat.
"You could potentially have fish out there (in the lakes) and never see them until they get to these tributaries," Jerde said.
From Sept. 15 to Oct. 5, the Notre Dame and Nature Conservancy team gathered 74 water samples from the Galien River and 122 samples from the St. Joseph and Paw Paw rivers, which are connected. All were negative, Jerde said.
Still to be processed are about 150 samples from the Maumee River in Ohio, which flows into Lake Erie, and the Milwaukee and Menominee rivers in Wisconsin.
The group plans to check other rivers this year, including the Grand, Pere Marquette, Raisin, Belle and Black rivers in Michigan, Jerde said.
"Given the locations we've sampled, I'm assuming the carp are not anywhere in Michigan waters," said Kelley Smith, fisheries chief with the Michigan Department of Natural Resources and Environment, which is supporting the project. "But we have to remain vigilant."