By Luke Furman
The grass carp, one of four Asian carp that pose an ecological threat to Lake Erie, is no stranger to North America. In fact, it’s been used here for more than five decades.
Native to the Yangtze River in China, the grass carp possesses natural benefits that led to the species’ importation to Arkansas in 1963 in order to control riverweeds. By the early 1980s, American pond-owners had been using diploid, or fertile, and triploid, or sterile, grass carp for decades to control weed and algae growth in ponds for a more well-balanced ecosystem and natural appearance. Among the grass carp’s favorite subterranean flora include Chara, Naiads, Hydrilla and Elodea, according to the University of Arkansas Division of Agriculture. Not to mention, the bony, cigar-shaped fish is widely consumed for its uncharacteristic non-fishy taste.
But if left to its own instinctual devices and voracious appetite, the diploid grass carp poses a great potential threat to the vegetation of the 11th largest lake in the world.
Grass carp that have either escaped from ponds or traveled up the Mississippi River Basin have been found in rivers surrounding Lake Erie since 1980, but the most recent problem has its origins in 2012. It was that year when four one-year-old diploid grass carp were discovered in the Sandusky River by a commercial fisherman, said Duane Chapman, a researcher for the United States Geological Survey and a leading expert on Asian carp.
Chapman said the discovery of grass carp is an indication that bighead and silver carp could also be spawning in the waterway, and the only way to check for the fertility of the fish is through a blood sample, creating an extra level of difficulty in detection.
Many states have placed restrictions on the introduction of diploid grass carp more than other fish because of its dominating tendencies. It’s been legal to stock triploid grass carp — but not diploid — in ponds in Ohio, Indiana, Pennsylvania and New York, Chapman said, while the states of Iowa, Missouri, Arkansas and Mississippi allow the introduction of diploids. Chapman also said that some “nefarious fish dealings” that skirt laws along with loose regulations might lead to unwanted fish getting into rivers and tributaries.
“Grass carp are inconsistent engineers. They have potential to do a lot of damage and also all they do is eat the areas they like,” Chapman said. “Lake Erie is most at risk because it is the warmest (of the Great Lakes) and its vegetation is already at risk.”
Grass carps do not eat other fish but can still kill them indirectly. The species has a unending appetite for certain vegetation and have the capability to reduce the shorelines of Lake Erie while ignoring problematic plants like the American Lotus, Chapman said. The quantity of vegetation the grass carp consumes also poses risks to the spawning ground of Great Lakes fish. Grass carp can grow as long as 40 inches, weigh as much as 90 pounds and eat 20 to 100 percent of its body weight each day, according to Michigan State University Extension.
The Sandusky River spans 133 miles in Ohio and flows into Lake Erie through the now “high risk” Sandusky Bay. It is the third largest tributary to the western basin of Lake Erie. In addition to the initial 2012 findings, further evidence of fertile grass carp in the Sandusky River was discovered in 2015 when Holly Embke, a graduate student from the University of Toledo, found eight grass carp eggs. The USGS, Great Lakes Fishery Commission, Michigan Department of Natural Resources and Ohio Department of Natural Resources all supported the University of Toledo on the grass carp research effort. The discovery led to more intense research conducted on the Sandusky River and the Maumee River, another tributary of Lake Erie.
The threat of grass carp populations entering the Great Lakes hit a peak in summer of 2017, when more than 7,500 eggs of the fish were found in the Sandusky River, prompting an interagency effort to reduce the risk of introduction of diploid grass carp into Lake Erie. Chapman said that was “a tiny percentage” of the total number of eggs in the river.
In September, the Ohio DNR, the USGS and the Great Lakes Fishery Commission released a joint statement outlining the problem and the steps they are taking to correct it. For the most part, the problem-solving effort remains in the research and preventive stage. Since 2014, the interagency effort had been monitoring the Sandusky
River and only recently increased the state of risk on account of more solid and concerning statistics collected this past summer.
“There’s no way the fish can come from anywhere else but the Sandusky (River),” Chapman said. “It’s a tough thing to control and achieve eradication. We are trying to determine where and where not they can survive. Grass carp have a distinct requirement for their eggs to drift because the young have to find a habitat.”
According to a widely-cited January 2017 study, grass carp have been found in three of the five Great Lakes — Michigan, Ontario and Erie — showing the problem is not isolated to a single lake. The peer-reviewed study, titled “Ecological Risk Assessment for Grass Carp in the Great Lakes Basin,” also lists Lake Erie and Lake Michigan at medium risk and concludes “the invasion process has begun,” but ecological consequences might not appear for 20 to 50 years.
The research and strategy stage involves little direct action to eradicate the fish, but the interagency statement outlines an increased effort in 2018 to target and remove the threat before it becomes more difficult to control.
Great Lakes researchers already have a wide range of problems to control from the algae bloom to sea lampreys. But an outbreak of grass carp is among the most dangerous and pressing problems affecting Lake Erie today and, without intervention, would have major consequences on the future size and ecosystem of the lake.
Photo by Vladimir Wrangel/Shutterstock