Positive test results for Asian carp eDNA from Lake Erie’s Sandusky and Maumee bays are worrying, but not conclusive.
By Codi Yeager-Kozacek
Circle of Blue
Twenty-three out of a total 500 water samples taken from western Lake Erie this summer have tested positive for Asian carp environmental DNA (eDNA), but researchers have yet to catch a live carp in the lake.
The sampling occurred in the Maumee Bay and River and the Sandusky Bay and River between July 30 and August 4 as part of efforts to follow up on positive eDNA samples collected from the area in 2011. Twenty out of 150 samples taken from the Sandusky Bay area were positive for silver carp, while three out of 350 samples were positive for silver carp in the Maumee Bay area.
Silver carp is one of four invasive Asian carp species — silver, bighead, common and grass — that escaped from aquaculture facilities in the Southern United States in the 1970s and have since infested many waterways in the Mississippi River Basin. The fish are a threat to the Great Lakes region’s $US 7 billion sport-fishing industry, which depends on native species like walleye and yellow perch that could be out-competed by the invasive carp. State and federal efforts — such as the electric barrier in place near Chicago — have, so far, kept the invasion out of the Great Lakes.
But the recent eDNA results raise concerns that at least some carp have gotten into the system, though nobody has seen one.
No Physical Proof
“What we know today, based on extensive sampling, is that (carp) eDNA is present in Sandusky and Maumee Bays in Lake Erie,” Rich Carter, the executive administrator of Fish Management and Research at the Ohio Department of Natural Resources Division of Wildlife, told Circle of Blue. “We know there is a source of eDNA, which could potentially be a live fish or some other unknown source.”
–Rich Carter, executive administrator
Ohio DNR, Fish Management and Research
The eDNA tests can identify genetic material like mucus, feces, and scales in the water and are used to detect species at low abundance levels. But the science cannot yet discern whether this material came from a live or dead fish or from other sources, such as bilge water transported by boats, excrement from fish-eating birds, or melted ice released from fish markets — this means the findings cannot confirm the presence of Asian carp in the Great Lakes without some other, external physical proof.
“This is cause for concern, and we recognize that we need to continue to search for the source of the eDNA,” Carter said. “The evidence suggests that if (the carp) are present, they are present in very low abundance, and we have to recognize that it takes multiple individuals for a chance of reproduction. To date, we have not seen evidence of that.”
Physical proof — in the form of a living, flopping carp — has so far eluded the Michigan and Ohio Departments of Natural Resources (DNR) and the United States Fish and Wildlife Service, despite extensive search efforts.
“We followed up the Sandusky eDNA results in Sandusky Bay and River using a combination of electrofishing and gillnetting, where we used the boats to drive fish into the gill nets, and we did not find any live fish,” Carter said. “It is a technique that has been effective in the Illinois River. If the fish were present, we would expect to catch them.”
What Happens If A Live Carp Is Found
This leaves the agencies with a mystery.
“We are befuddled as to how these sources (of eDNA) are getting into the water,” Charlie Wooley, the deputy regional director of the U.S. Fish and Wildlife Service (Midwest Region), told Circle of Blue. He added that the Fish and Wildlife Service and the Army Corps of Engineers are currently working to test possible pathways the eDNA could take to end up in Lake Erie in the absence of a live carp.
If a live carp is found in the lake, a fish poison, like rotenone, would likely be used to survey the area where the carp was caught, Wooley explained.
“Unfortunately, that would kill everything in the area, but then we could see exactly what is there,” he said. “We have done that in the Chicago Area Waterway System (CAWS), so we have some experience with that and would have the same kind of rapid response, if requested by the DNRs.”
–Charlie Wooley, deputy regional director
U.S. Fish & Wildlife (Midwest Region)
In addition, an advanced genetic analysis would be performed on the captured fish to determine its age and place of origin, Carter said. This process was used on three bighead carp caught in Lake Erie in 1995 and 2000, when the results found that the fish had grown up in southern waters and were likely introduced by humans.
“To know that the carp are established, we would have to see various sizes and age groups,” Wooley said. “If we don’t see any evidence that reproduction is occurring, then we don’t have an established population.”
Wooley said that there is a “concerted effort” to keep the carp out of the Great Lakes, but that the real goal is to find a way to take back territory the carp have already invaded.
“We have rivers like the Upper Mississippi and the Illinois that have just been taken over by these carp,” he said. “The key is to develop a control mechanism, whether it is a chemical or biological control, that we can put into the water and that will only kill silver and bighead carp.”
A similar solution was developed in 1958 to target and control invasive sea lamprey populations in the Great Lakes, when the U.S. Fish and Wildlife Service identified the chemical compound TFM. TFM is applied to streams where the lampreys reproduce. It can cause mortality among species other than lampreys, but the compound is generally considered to do minimal harm to other wildlife when applied in low concentrations. The control efforts have not eradicated the sea lampreys, but they have helped to reduce their numbers.
“Our ultimate goal is to do the same thing for carp, so that we can work to reclaim those great heartland rivers,” Wooley said.