MILWAUKEE -- The pioneers behind using environmental DNA to sniff out traces of Asian carp in the Chicago canal system report in a new study released Thursday that similar genetic surveillance efforts in other areas of the Great Lakes show no new traces of the reviled fish.

"The good news is that we have found no evidence that Asian carp are widespread in the Great Lakes basin, despite extensive surveys in southern Lake Michigan and parts of lakes Erie and St. Clair," said the University of Notre Dame's Christopher Jerde, the lead author of a paper published in the Canadian Journal of Fisheries and Aquatic Sciences.

An electric fish barrier on the Chicago Sanitary and Ship Canal about 35 miles downstream from Chicago's Lake Michigan shoreline is the last line of defense to keep the giant jumping fish from spilling over from the Asian carp-infested Mississippi River basin and invading Lake Michigan. The canal provides an artificial link between the once-separated Mississippi and Great Lakes basins.

Yet water samples taken above the electric barrier over the past three years have routinely tested positive for Asian carp DNA. Even so, there has been only one actual Asian carp caught in the waters above the barrier, despite extensive netting and shocking operations over the past three years.

Three other Asian carp were plucked from the waters of Lake Erie over a decade ago. Those finds came in the only other area that Jerde and his colleagues have detected Asian carp DNA.

Earlier this year, the federal government released its own report that indicated the source of the DNA found in the Chicago canal system may not necessarily be from live fish. The federal researchers determined in lab and field studies that other potential sources include fish-eating birds, contaminated fishing gear, boat hulls, dead fish carried past the barrier on barges and even bits of DNA washed into the canal from storm sewers that might be carrying fish waste. (Some Asian restaurants in Chicago have Asian carp on their menu.)

Jerde and his environmental DNA pioneering colleagues from Notre Dame, the Nature Conservancy and Central Michigan University have long acknowledged these are potential DNA pathways, and they are possible sources for some of the positive samples. But they argue the presence of at least some live fish is the most plausible explanation for the overall pattern of positive detections.

"It's really very telling that the only places DNA has been recovered are where Asian carp have been captured," Jerde said. "If birds or boats were commonly spreading the DNA, then we should be detecting DNA in other places we have surveyed in the Great Lakes."

The source of the DNA is important because if it is coming from live fish, it indicates that the government's electric fish barrier might not be working as well as advertised, and that lends credence to the argument from Illinois' neighboring states that the Chicago canal linking the Mississippi basin and Lake Michigan must somehow be plugged.

The issue was the focus of a 2012 Milwaukee Journal Sentinel series.

• Read more articles by DAN EGAN

Order Reprint