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Invasive Carp Could Spread Across Lake Michigan on Detritus Diet

The fish’s undiscerning palate might make more of the lake habitable to the species than once thought, according to a new study.

Aug 14, 2019
Nicoletta Lanese

ABOVE: Silver carp jumping in the Fox River
RYAN HAGERTY/USFWS

Invasive Asian carp could thrive in the waters of Lake Michigan by chowing down on feces and decomposing organisms, researchers reported August 12 in Freshwater Biology

Two carp species, the bighead (Hypophthalmichthys nobilis) and silver carp (H. molitrix), were brought to the US in the 1960s and dumped into southern sewage lagoons and fish farms to eat away excess algae, according to the Associated Press. The fish found their way to the Mississippi River, traveling through its many tributaries on their way north. The Illinois River now teems with the carp, which make up two-thirds of its fish biomass found there, according to Science News

As the carp make their way towards the Great Lakes, scientists are trying to figure out if and how they could survive there.

“We should be doing everything we can to keep bighead and silver carps out of the Great Lakes,” says Sandra Cooke, a freshwater ecologist at High Point University in North Carolina, in an interview with Science News. Cooke, who was not involved in the work, previously suggested that the invaders could live at only select points around the rim of Lake Michigan, where they would live off their preferred diet of phytoplankton. Zebra and quagga mussels coat the lake bottom and gobble up most of its plankton supply, and some biologists thought this scarcity might stymie the Asian carp’s spread.

But prior studies only analyzed the topmost meter of lakewater, and discounted the fact that the carp species will readily consume detritus when the plankton supply dips. A team led by researchers at the University of Michigan took these factors into account, and modeled whether the lake’s water temperature, depth, and available nutrition could appease the carps’ appetites.  

They found it can. 

“Lake Michigan’s low supply of plankton may not be as strong a barrier as previously thought,” says coauthor Peter Alsip, a freshwater ecologist at the Cooperative Institute for Great Lakes Research based at the University of Michigan, in a press release. “Our study indicates that the carp can survive and grow in much larger areas of the lake than previous studies suggested,” he adds in an interview with the AP

By feeding on a combination of zooplankton, mussel excrement, and other organic matter found floating through the water column, the bighead carp could survive in an area of 11,144 square kilometers in Lake Michigan year-round, and up to 43,308 square kilometers in the summer, according to Science News. Similarly, the silver carp could inhabit 1,436 square kilometers in cooler months, and 2,758 square kilometers in warmer months. 

The carp would likely pass through Lake Michigan on their way to find more suitable food, as if “these fish want to drive on the interstate and they’re looking for a Cracker Barrel,” says Jim Garvey, an aquatic ecologist at Southern Illinois University in Carbondale, in an interview with Science News. Garvey, who was not involved in the study, adds that predicting when and how the carp might usurp Lake Michigan is difficult, but learning where the fish might survive within the ecosystem is a crucial first step.

Lake Michigan’s cold temperatures, depth, and lack of food would pose challenges for the carp, Kevin Irons, the aquatic nuisance species program director with the Illinois Department of Natural Resources, tells the AP. But the Michigan study shows that the fish “can fast for long periods of time and travel long distances quickly.” 

“This reinforces the importance of investing in prevention,” says Irons. A proposed prevention strategy, supported by the advocacy organization Alliance for the Great Lakes, involves equipping the Brandon Road Lock and Dam near Joliet, Illinois, with deterrents such as noise makers and electric barriers, to prevent the carp from passing through, according to the AP.  Eight US governors and two Canadian premiers also endorse the $778 million plan, says the university press release, partially in the interest of protecting the $7 billion fishing industry fueled by the bounty of the Great Lakes.

Nicoletta Lanese is an intern at The Scientist. Email her at nlanese@the-scientist.com.

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