Ever since Asian carp were accidentally introduced into U.S. rivers in the 1970s, the invasive fish have been hungrily making their way to the Great Lakes, causing residents of the watershed to dread the arrival of carp in delicate Lake ecosystems, and their potential impacts on the $7 billion fishing industry that represents a major economic driver for the region.
Now, a new study suggests that Asian carp have breached southern Lake Michigan, although they have not yet arrived in numbers great enough to devastate native ecosystems.
Scientists at the University of Notre Dame, Central Michigan University, and The Nature Conservancy spent two years searching for Asian carp by examining genetic material in the Lake and attempting to match DNA samples to two particularly damaging species of Asian carp: silver and bighead carp.
Out of 2,800 water samples, they found 58 positive links to bighead and silver carp in the Chicago Area Waterway System, which flows directly into Lake Michigan, along with six in western Lake Erie.
Questions remain about how many carp are already in the ecosystem—and how long it will take until the fish begin showing up in numbers large enough to cause serious harm.
“The most plausible explanation is still that there are some carp out there,” lead author Christopher Jerde of the University of Notre Dame told the AP. “We can be cautiously optimistic…that we’re not at the point where they’ll start reproducing, spreading further and doing serious damage.”
Still, news of their arrival is likely to dismay residents of Lake Michigan and its environs. Concerns about the aggressiveness of the fish are warranted, given their insatiable appetite for plankton. Asian carp can grow up to four feet long and 100 pounds. The heaviest of carp can eat five to ten percent of their body weight each day in plankton.
This has led to what some biologists call the “marginalization” of native species of fish found in the Great Lakes region, like ciscos, bloaters, and yellow perch, which in turn are eaten by predators species like lake trout and walleye. In areas where Asian carp are already abundant, particularly the Mississippi River Basin, the numbers of native fish have declined and suffered stunted growth as a result of Asian carp out-competing them for food sources.
Back in December, biologist Duane Chapman of the United States Geological Survey (USGS) told TakePart that while native fish were unlikely to go extinct as a result of Asian carp invading the Great Lakes, there were other potentially undesirable effects, like reduced recreational fishing for walleye and yellow perch, which would have major economic consequences.
“Our river fisheries are important but not valued in the billions of dollars,” Chapman told TakePart. “Whereas the Great Lakes fisheries are hugely economically important. If you cause any perturbations in fisheries like Lake Erie’s walleye and yellow perch fisheries, that could be hugely problematic.”
Scientists and fishery managers have tried a number of strategies for carp control, including electric barriers, public awareness programs, and inspections of bait shops, fish processors, and fish markets by the U.S. Fish and Wildlife Service.
No North American fish are large enough to feed on adult Asian carp, according to the Asian Carp Regional Coordinating Committee, making it impossible to control the species through natural means.
“It’s impossible for us to tell the extent of the problem. The Great Lakes are a complex situation. What would happen exactly if Asian carp got into the Great Lakes [in large numbers] is hard to say,” Chapman said. “But we want to avoid it.”