The search is on for Asian carp in Chicago’s waterways. DNA from the voracious fish was found near the Chicago River in November. The hunt for actual fish is expected to last two to three weeks. Environmentalists fear that if the carp have penetrated barriers in Chicago, the fish will be headed toward Lake Michigan, potentially jeopardizing a multi-billion dollar fishing industry. As WUWM’s Marti Mikkelson reports, this is the latest local chapter of invasive water species.
This latest invasive threat has made its way to Chicago via canals leading to the Mississippi River. In the past, most invasives arrived by way of the man-made St. Lawrence Seaway that links the Atlantic Ocean with the Great lakes. That’s the route the sea lamprey took in the 1950s, according to Bill Horns of the Wisconsin Department of Natural Resources. He says the predator is extremely destructive.
“It has a sucker-like mouth. It attaches and rasps a hole into the side of the fish and sucks blood out. Sometimes it detaches and the fish survives. Sometimes the fish will die later but in the end there’s a very high mortality rate of fish that are victims of that,” Horns says.
Horns says the sea lamprey was responsible for decimating large fish of all kinds in the Great Lakes, particularly lake trout. In the 1960s, scientists launched a massive effort to wipe out the sea lamprey, including poisoning their larvae with chemicals. The program has succeeded in controlling the species and allowing lake trout and whitefish to thrive.
Horns says another threat to the Great Lakes has been alewives, a predator that also came in through the St. Lawrence Seaway in the 1960s. Scientists bulked up the populations of other fish to contain the alewives.
“The state started stocking millions of salmon, coho and Chinook salmon. That program accomplished two things, one is it limited alewife abundance and the second thing is it provided a recreational fishery that’s quite valuable now,” Horns says.
Horns says most recently, zebra mussels have been a problem for the ecosystem of the Lakes and scientists have found there’s not much they can do to control the population. He says ironically, if Asian carp enter the Great Lakes, they would eat the mussels, but the devastation would far outweigh that one advantage.
“They eat zooplankton and phytoplankton and that is small, not quite microscopic but very small plants and animals that drift in the water. That’s their food source and so they would be competitors for any fish that also relies on that which most fish do in their early life stages,” Horns says.
Horns describes the Asian carp as a large, healthy fish that typically grows to three feet in length. He says if the carp invade Lake Michigan, they’d have no problem making their way through pollution and cold water up to Milwaukee and Green Bay.
Horns believes it would be futile to try to control the population, because their larvae tend to drift in big rivers and are hard to track. For the next few weeks, scientists in Chicago will continue dropping nets and using electro-prods to determine if the carp have already gone too far.
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