Asian carp are one of the most vexing of invasive species. The fast-growing and aggressive fish from southeast Asia are outcompeting native fish for food and habitat in much of the middle of the United States. And not only are they conquering ecosystems at a voracious rate, they also leap out of the water when spooked by engines, making boating in some of the country’s waterways challenging — so much that people have taken to battling the fish with pitchforks and swords, donning armor and football helmets.

One of the biggest concerns about the species, which was introduced to Southern fish farm ponds in the 1970s, is that they would eventually find their way to the Great Lakes. Once established in an ecosystem, they are virtually impossible to eradicate, and given that they consume up to 20 percent of their body weight per day in plankton and can grow to more than 100 pounds, their presence in the Great Lakes would presumably spell the end to many native species. Also at stake are the food chains that support a $7 billion fishing industry.

And now, concerns are being confirmed as a new scientific report has found positive DNA evidence in and near the Great Lakes.

The paper summarizes findings by Christopher Jerde and other scientists from the University of Notre Dame, The Nature Conservancy and Central Michigan University, gathered during two years of searching the Great Lakes basin for the persistent fish.

However, the positive findings of the paper counter the theory of government scientists who claim that the Asian carp DNA samples could have come from elsewhere, such as droppings from birds that fed on carp farther away and excreted excrement in the Great Lakes area. The source of the DNA is important because it could change the debate over whether to isolate Lake Michigan from the Chicago waterways, a tremendous engineering task that would cost billions of dollars.

"I would say there's at least some evidence for Asian carp being present in southern Lake Michigan," Jerde told The Associated Press in a telephone interview. "The question is how many."

Between September 2009 and October 2011, Jerde and his team gathered more than 2,800 water samples from the Great Lakes area. Lab analysis resulted in 58 positive hits for bighead or silver carp (two of the four types of carp in the family) in the Chicago Area Waterway System and six in western Lake Erie. Some of the Chicago DNA was found in Lake Calumet, where a live bighead carp was caught in 2010.

The Army Corps claims that an electric barrier outside of Chicago is impeding the fish from getting through, even though their DNA has turned up recurrently on the other side.

In the meantime, a lawsuit by five states seeking to have Lake Michigan blocked off was dismissed by a federal judge. Under pressure from Congress, the Army Corps of Engineers has pledged to offer options for preventing species migrations between the Great Lakes and the Mississippi River watershed later this year — but the tenacity of the species may be this plan’s undoing.

Until then, prepare to see more boaters armed with swords and pitchforks.

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