Asian carp DNA has turned up in Lake Michigan waters off Door County, the Wisconsin Department of Natural Resources reported Tuesday.
The single positive water sample for the jumping silver carp was taken May 31 in Sturgeon Bay near Potawatomi State Park.
The sampling was part of a Lake Michigan-wide survey looking for evidence of Eurasian ruffe, a different type of invasive fish species. The water sample was not screened for the presence of Asian carp DNA until this fall, and the DNR did not get word of the positive result until last week, said Mike Staggs, DNR's fishery director.
The sample was the only positive found among the 282 water samples taken from Wisconsin's Lake Michigan waters this year as part of an invasive fish survey conducted by government crews and researchers from the University of Notre Dame and The Nature Conservancy. Fifty of those of samples were taken in the Sturgeon Bay area.
Nobody is sure at this point what to make of this single piece of microscopic evidence.
There are several potential sources for the genetic scraps, including boat hulls, bird feces, or contaminated bait buckets. It could, of course, also signal the presence of a live fish.
"This is one sample, one time," said Chris Jerde, an assistant professor at the University of Notre Dame who helped pioneer the technique of using DNA to hunt for rare fish populations. "When we start talking about evidence for Asian carp in a system and the use of DNA, we talk about repeated sampling events and repeated detections."
Jerde noted that if Asian carp DNA were commonly spread by means other than live fish, water samples researchers have taken all across the Great Lakes likely would commonly test positive.
"We can talk about alternative pathways (for DNA to get into a water body), but we still have thousands of negative detections throughout the Great Lakes and we have one positive here."
There have been some positive DNA samples taken from Lake Erie, where several live Asian carp were captured more than a decade ago. Despite those disturbing catches, biologists have never been able to find evidence of a breeding population and have therefore speculated the fish were planted or somehow escaped into the lake from fish farming operations.
Department of Natural Resources officials say they are not panicked, but they are planning to go back to the Sturgeon Bay area to do more sampling next week.
"It is what it is," said Bob Wakeman, head of DNR's invasive species division. "We just need to clarify what it means."
Biologists have been using DNA to hunt for Asian carp for four years in and around the Chicago Sanitary and Ship Canal. That manmade river is an artificial connection between the Asian carp-infested Mississippi River basin and Lake Michigan.
The only thing standing between the migrating fish and the big open waters of Lake Michigan is an electric barrier system on the canal that is operated by the U.S. Army Corps of Engineers that for several years was not operated at a voltage strong enough to repel small Asian carp.
While it has become common for survey crews to find Asian carp DNA in water samples taken above that electric barrier, so far only one actual Asian carp has been found in those waters.
Because of the repeated DNA detections in the same area, Jerde and the other biologists who developed the use of "environmental" DNA to fish for carp are confident they indicate at least some live bighead and silver carp have somehow breached the barrier.
They say the next step for Door County is to begin regular sampling.
"If we continue getting positive samples, that would be an indication that the most plausible explanation is live fish," said Jerde.
DNR fisheries chief Staggs said the news is serious, but it's a long way from indicating Asian carp have arrived and are breeding in Wisconsin's Lake Michigan waters. He said even the capture of a handful of fish doesn't necessary mean the fish have successfully invaded.
Biologists note most fish invasions fail to launch reproducing populations because so many things have to go right for the invading fish. First they have to survive to sexual maturity, then they have to find a suitable mate, then they have to find suitable spawning habitat. Then their offspring have to survive long enough to begin the process anew.
"It's a long way from a fish or two to a reproducing population," Staggs said.
The news comes just a couple of months before the Army Corps is expected to release a multi-year study looking at how to permanently separate the waters of the Asian carp infested Mississippi and Great Lakes basin. That likely would mean some type of physical barrier on the Chicago canal.
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