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For Asian Carp, Next Stop Will be Lake Michigan

Aug. 8, 2017
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This summer, a commercial fisherman pulled a live, eight-pound silver carp from the Calumet River near Chicago. The fish, one of four species collectively known as Asian carp (silver carp, grass carp, bighead carp and black carp), was found about nine miles from Lake Michigan, well beyond the electrical barrier on the Chicago Sanitary and Ship Canal designed to keep these fish from advancing towards the lake. The discovery was made during a seasonal “intensive sampling period” that the Asian Carp Regional Coordinating Committee (ACRCC), a collaboration of 40 Great Lakes region governmental agencies, undertakes twice annually. 

A two-week series of emergency ACRCC protocols triggered by the discovery yielded no indication of other carp having breached the electrical barriers. “We treat any capture of Asian carp in a new location as a significant finding,” said Mike Weimer, senior fish biologist with the ACRCC. Weimer said that the agency has an ongoing series of efforts to prevent the fish from reaching the lake. In addition to the maintenance of the electrical barrier, the ACRCC commissions large-scale harvests of carp near the northern end of their population mass on the Illinois River. Weimer estimates that the mass is about 47 miles from the lake, a position that has remained steady for several years. 

This latest finding comes at a perilous time for the Great Lakes. The Trump administration has blocked the release of a U.S. Army Corps of Engineers study of possible additional methods of preventing carp from reaching the Great Lakes; the report was due out in February. While the current systems have, thus far, been mostly successful, many experts doubt the electrical barrier will be 100% effective. Furthermore, Trump’s proposed 2018 budget eliminates the $300 million Great Lakes Restorative Initiative, a program that funds many aspects of the carp-prevention system. “The finding of an adult Asian carp north of the electric barrier is a warning signal,” said Jennifer Caddick of the Alliance for the Great Lakes. “Yet the administration and government agencies continue to put the Great Lakes at risk by continuing with business as usual.”


‘Pulling Off a Spawn’

According to Duane C. Chapman, leader of Asian carp research for the U.S. Geographical Survey, the process of Asian carp reaching and populating the lake is a complicated one. Chapman said that the carp spawning process is a “very complex system” about which researchers still have much to learn. Well-fed carp could possibly spawn every year, Chapman said, but a successful spawn requires a sizable population of adult fish. “You don’t just have one male and female pull off a spawn; it doesn’t work like that,” Chapman said. “It seems unlikely to me that a small population of carp could pull off a spawn.”

Chapman points to the discovery of three bighead carp in Lake Erie between 1995 and 2000. There were almost certainly more carp living in the lake at the time, Chapman said, but researchers found no evidence that the fish had successfully spawned. Should a sizable population of carp reach Lake Michigan, the success of their spawns would depend on how quickly the fish could mature in the colder waters of the lake. Chapman cites the long period between the first appearance of silver carp in the Mississippi River Basin and their more recent population explosion, which, he said, “took 20 years.” A similar invasion of the lake could also take decades to lead to a mass infestation, or a small population could exist and maintain its size indefinitely.

A third, more alarming, outcome would involve a series of successful spawns leading to a population explosion that devastates the lakes and the communities that depend on them. Chapman has little doubt that Asian carp would prosper in the lake. “They will survive,” he said. “They will probably do pretty well. Lake Michigan has everything they need.” He says that the quagga mussel invasion of the lake has shifted the lake’s base of nutrients from its middle to its margins, meaning that a population of invasive carp would almost certainly cluster within this “ring of food” along the lake’s shorelines. From the shorelines, they would also likely infest the many rivers that flow into the lake, including Milwaukee’s inner waterways.

On the fringes of the lake, the carp could devastate Wisconsin’s commercial and sport fishing industries, which generate over $7 billion annually. Asian carp can grow up to seven feet long and weigh more than 100 pounds, eating up to 20% of their body weight in a single day. Silver carp are known for jumping from the water when scared. Hundreds of videos on YouTube offer a terrifying vision of what the Milwaukee River could look like with dozens of Asian silver carp leaping as high as 15 feet from the water as boats pass by. For Milwaukee, where so much of the Downtown revival has been connected to the river’s rebirth as a major recreational attraction, the effect of a carp invasion could be catastrophic.

“Milwaukee’s lake and rivers are its history and future,” Kristen Settle of Visit Milwaukee said. “With more than 120 water-related companies calling Milwaukee home, any compromise to our waterways would likely have a huge economic impact—not only on our tourism industry, but also on our entire economic engine as a city.”

The results of a microbiological study of the carp discovered past the barrier, which could offer clues as to how the fish got to that part of the river, are expected to be released later this summer. 


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