Sea Grant Outreach
Can Asian Carp Invasion be Averted?
By Kathleen Schmitt Kline
In December 2009, an emergency brigade of 450 Americans and Canadians descended on Romeoville, Ill., armed with nets, boats and thousands of gallons of poison. The 20-agency response was brought on by recent environmental DNA (eDNA) tests indicating that Asian carp were closer to invading Lake Michigan than previously thought.
One of the 450 who dropped everything and headed to Romeoville was Phil Moy, UW Sea Grant fisheries and aquatic invasive species specialist. Fifteen years ago, Moy served as the first manager of a project to erect an electric barrier in the Chicago Sanitary and Ship Canal to repel foreign fish.
Chicago dug this canal more than a hundred years ago to manage wastewater, and its construction joined two major ecosystems that until then had remained distinct. Over the last several decades, Asian carp that escaped from Southern aquaculture and wastewater facilities have been moving up the Mississippi to the Illinois River, and the canal connecting it to Lake Michigan is an ideal pathway for the fish to advance into the Great Lakes.
In December, scheduled maintenance required temporarily shutting down part of the barrier. Because eDNA tests showed Asian carp advancing, a 5.7-mile section of the canal was treated with rotenone, a fish poison, to ensure that no carp would breach the barrier during the maintenance.
Moy said a successful Asian carp invasion is by no means a sure thing even if a fish slips through. “It takes some specific habitat for them to do really well,” he said.
Scientists believe the carp need access to a river with a deep, free-flowing main channel in order to successfully reproduce. If their eggs settle to the river bottom before hatching, the embryos will suffocate and die.
“One hundred kilometers—about 63 miles—is roughly the distance needed to provide enough current to keep the fish’s fertilized eggs suspended in water while they incubate,” Moy said. Out of thousands of tributaries that feed the Great Lakes, only 22 on the U.S. side (four in Wisconsin) meet this criterion. Adding another criterion—the availability of quiet, fertile backwater areas where the newly hatched fish larvae can eat and mature—reduces the list even more.
However, before they can reproduce, the fish would need to find each other within more than 94,000 square miles of the Great Lakes. While a few bighead carp have been captured in Lake Erie, probably due to someone releasing them there, they have yet to multiply into any significant numbers.
Indeed, Moy said it’s all about numbers now.
“We have to keep the numbers as low as humanly possible,” he said. “Even if there are a few Asian carp upstream of the electrical barrier, there is absolutely no assurance that they’ll be able to establish a population.”
Although Moy remains active on the electric barrier project, he acknowledges that it is not a permanent solution. It depends on the fish reacting predictably to a technology that could potentially fail. In addition, it doesn’t do anything to protect the Mississippi River basin from small, floating invasive species coming from the Great Lakes, such as quagga mussel larvae.
Ultimately, he said, the only sure way to keep Asian carp and other invasive species out of the Great Lakes is to permanently sever the link between the Mississippi River and Great Lakes basins.
“I really think that’s the direction we have to go,” Moy said.