New technology is helping identify the presence of invasive Asian carp, but some researchers and state natural resources managers are divided over whether positive test results signal a threat strong enough to trigger an aggressive and expensive response.
Scientists are deploying environmental DNA — or eDNA — identification techniques in the Great Lakes and connected rivers, but some state and federal natural resources managers are wary of false positives.
Senate staffers heard from both sides at a pair of briefings in the Capitol last week.
Asian carp are prolific breeders that can quickly overrun and wipe out entire aquatic ecosystems by eating the plankton that native species need to survive. The fish have even been known to injure anglers by jumping several feet out of the water when startled by the noise of boat engines.
Testing for eDNA has proven to be useful, but a positive test result doesn't necessarily mean there are live carp in the water, said Kelly Baerwaldt, eDNA program manager for the Army Corps of Engineers.
Traces can easily be transported between bodies of water on the hulls of fishing boats, in feces of birds that feed on carp, and through sewer systems near fish markets where carp are sold legally, she said.
"There are a lot of birds and there are a lot of boats and there are a lot of fisheries personnel" that could be contaminating carp-free waters with eDNA, said Baerwaldt. "We aren't discounting that it can't be a live fish. We are acknowledging that there are other (sources of eDNA) and we want to be able to say 'How likely is it that it's birds? How likely that it's barges?'"
Researchers such as University of Notre Dame biologist David M. Lodge say a positive result almost always indicates presence of live fish. He said Asian carp are so destructive to aquatic ecosystems and the fishing industry that a positive eDNA test should be a call to action.
"In the vast majority of cases where there's eDNA there are live fish," Lodge said. "Where we've located eDNA, somewhere in the recent past there was a live fish nearby."
While false positives are possible, it's more useful to consider probability, he said.
Asian carp are making their way up the Ohio River, and that has Pennsylvania lawmakers and others concerned. One bipartisan effort would require the Corps of Engineers to work expeditiously to develop an action plan to stop the non-native fish from infiltrating the Great Lakes.
Efforts involving nets, poison and electric barriers already are under way, but those tools are crude, costly and they don't always work, experts told Senate aides.
Conservation managers said they need better tools and testing that's faster and more reliable.
It's important to analyze all available information before deciding whether and how aggressively to respond, said Tammy Newcomb of the Michigan Department of Natural Resources.
"The conundrum for the agencies becomes 'What do you do if you get a positive result?' " Newcomb said.
"We need to be strategic and smart and prudent," she said. "We have to weigh the evidence against our resources available in terms of people and funding, and we need to look at our probability of success. If we're going to go out there, it's going to cost us sometimes hundreds of thousands of dollars."
Southern catfish farmers first imported Asian carp to clean algae from their ponds. The plankton-eating fish also were used in sewage treatment plants. They escaped those closed-water systems during flooding in the 1980s and made their way up the Mississippi River and its tributaries.
An electric barrier between the Illinois River and Lake Michigan is all that blocks their path, but carp are making it past and beginning to invade the Great Lakes, panelists said.