Tracking Aquatic Invasives

Ohio’s canals were important for navigation for less than a century. But even today, what’s left of the state’s canal system creates a conduit between the state’s two large drainage systems – Lake Erie and the Ohio River.
On a warm day early last October, John Stark and Andrew Tucker explored one remaining passage of the old canal system, looking for a fish that they hoped they would not find.

More precisely, they were looking for the genetic fingerprints of bighead carp and silver carp, two species of fish originally from Asia that are spreading rapidly throughout the Mississippi and Ohio river drainages.
Tucker, an aquatic ecologist for the Conservancy’s Great Lakes Project, collected surface water samples from the Muskingum River in eastern Ohio as part of an agreement with the Muskingum River Watershed Conservancy. “As fish move through the water column, they shed cells and blood and tissue,” Tucker explained. “This material is suspended in the water and can be collected as part of a surface water sample.” Researchers with Central Michigan University are working with The Nature Conservancy to screen the extract for the DNA of the troublesome carp.

“Some people have called this a genetic smoke alarm,” Tucker explained, “because it can alert us to the presence of live fish in an area.” The Conservancy and our partners pioneered environmental DNA surveillance and have used it successfully to identify the presence of Asian carp in the Illinois River and the Chicago Area Waterway System. Scientists and policy makers are collaborating to find ways to keep the fish from entering Lake Michigan through this portal.

Environmental DNA testing has indicated that some Asian carp have made their way into Lake Erie’s Sandusky Bay. Scientists don’t believe they have truly established a population there, though. Keeping their numbers low is important, said Stark, a fish biologist for the Conservancy, because these species are density dependent spawners, which means more fish makes it likely that they will start to reproduce.

Although the carp have achieved notoriety by jumping out of the water and hitting anglers in the face, a far greater threat is caused by their diet. Like the zebra and quagga mussels that entered the Great Lakes twenty years ago, the Asian carp are filter feeders that consume plant and animal plankton – the very foundation of the food web.

“They work at the very bottom of the food chain, and because of that they have the capacity to totally alter the ecosystem,” Stark said.

And the canal? Connections between waterways created for the canal system in the 1800s could allow the carp to move from the Muskingum to tributaries of Lake Erie, and on into the lake and the rest of the Great Lakes.
The results of the Muskingum River eDNA testing were expected after the newsletter went to the printer. But regardless of what turns up in this round of sampling, the fish are moving up the Ohio River system. The question is whether we can slow down the invasion before the fish gain a permanent foothold in the Great Lakes.

That’s partly because Stark is busy leading the Conservancy’s freshwater conservation program in Ohio, including the effort to track non-native, invasive species in the Great Lakes and Ohio River basins. He knows that by the time his children have children, the fishing experience in Ohio could be greatly altered. He’s been focused lately on Asian carp, which are moving up the Ohio River and into major tributaries. But they’re just one of several invasive species threatening Ohio waters.

Fish like the round goby and tiny crustaceans like the spiny water flea compete with native species for food and habitat in Lake Erie. The northern snakehead has been found within a few miles of the Ohio River tributaries. And Eurasian ruffe, a fish that would compete head-to-head with many species of small forage fish, is well established in the Great lakes and may soon jump over to the Ohio River watershed.

How does he keep from getting discouraged? “We have much greater awareness today, and that’s a start,” he says. “We’ve had to learn the hard way, but the problem is finally getting the attention that it deserves.”