TRAVERSE CITY, Mich. – At least some Asian carp probably have found their way into the Great Lakes, but there’s still time to stop the dreaded invaders from becoming established and unraveling food chains that support a $7 billion fishing industry and sensitive ecosystems, according to a scientific report released Thursday.
Written by experts who pioneered use of genetic data to search for the aggressive fish, the paper disagrees with government scientists who say many of the positive Asian carp DNA samples recorded in or near the lakes in recent years could have come from other sources, such as excrement from birds that fed on carp in distant rivers.
The most plausible explanation is still that there are some carp out there, Christopher Jerde of the University of Notre Dame, the lead author, told The Associated Press.
We can be cautiously optimistic that we’re not at the point where they’ll start reproducing, spreading further and doing serious damage.
Straining for eDNA
The paper summarizes findings by Jerde and other scientists from Notre Dame, The Nature Conservancy and Central Michigan University during two years of searching the Great Lakes basin for Asian carp.
The fish have migrated northward in the Mississippi River and many tributaries since escaping from Deep South ponds in the 1970s. Scientists fear they will out-compete prized sport and commercial species.
Of particular concern are silver and bighead carp, which gorge on plankton – microscopic plants and animals that virtually all fish eat at some point. The carp reproduce prolifically, and the biggest can reach 100 pounds.
Between September 2009 and October 2011, Jerde and his colleagues collected more than 2,800 water samples from parts of the Great Lakes and tributary rivers. The samples were poured through microfiber filters to extract DNA, which fish shed in their excrement, scales and body slime. It’s known as environmental DNA, or eDNA.
Laboratory analysis turned up 58 positive hits for bighead or silver carp in the Chicago Area Waterway System – a network of rivers and canals linked directly to Lake Michigan – 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.
I would say there’s at least some evidence for Asian carp being present in southern Lake Michigan, Jerde said. The question is how many.
More recently, sampling by the U.S. Army Corps of Engineers and other federal agencies also yielded positive results in the Chicago waterways. But while the government team acknowledges the presence of Asian carp genetic fingerprints, it disagrees that they necessarily signal the presence of live fish.
The issue is significant because it could influence the debate over whether to seal off Lake Michigan from the Chicago waterways, a mammoth engineering task that would cost billions of dollars and take years to complete. Five states sought that step in a lawsuit dismissed by a federal judge last December.
The Army Corps of Engineers contends an electric barrier in a canal 37 miles from Chicago is preventing the carp from getting through, even though their DNA has turned up repeatedly on the other side.
In a February report, federal agencies said the genetic material could have been transported by bird feces, fish sampling gear, barges and storm sewers.
But the Jerde team’s paper, published online Thursday by the Canadian Journal of Fisheries and Aquatic Sciences, argues that the likeliest explanation remains the presence of live Asian carp.
You’re requiring all kinds of random events to happen simultaneously, said Lindsay Chadderton of The Nature Conservancy, who contributed to the paper. It’s possible, but highly unlikely.