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.
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.
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 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 in a telephone interview.