Giant Invaders Threaten Great Lakes Fishery

Giant Invaders Threaten Great Lakes Fishery

A new aquatic invader is eating its way north through Illinois and threatening to enter the Great Lakes via the Chicago River, and the last chance to stop them is just 30 miles from Lake Michigan.

The newest, but certainly not last, biologic threat to the health of the Great Lakes is the Asian carp. The “Asian carp” moniker actually refers to a group of carp species including bighead, silver, grass, and black carps. Aquaculture farmers imported bighead and silver carp into the United States in the early 1970s. The aquaculture industry believed that the carp’s prodigious appetite for small plants and animals (plankton) would make them useful as pond cleaners. While the success of this enterprise is debatable, what is certain is that the fish were somehow released into the wild. A combination of flooding and intentional release likely allowed Asian carp to establish in the Mississippi River ecosystem, where they now dominate the food web in some areas.

The bighead carp can grow to over 50 pounds, while silvers can tip the scales at 100 pounds plus, larger than any native Great Lakes fish. These filter-feeding fish consume huge quantities of plankton using large gill rakers. One estimate suggests that they can consume up to 40 percent of their body weight daily and can fully exchange the contents of their gut 4 times in 24 hours. Silver carp can jump up to 10 feet clear of the water when disturbed, posing a unique hazard to boaters.

The potential impact of this fish is tremendous. The Great Lakes are a plankton-based food web, and most fish in the system rely on plankton as a food source at some point in their life cycles. Smaller fish are wholly dependent on a healthy plankton population. Of course, these small fish provide the forage base for larger predator fish, so the entry of a highly efficient plankton-feeder could be disastrous. The Great Lakes could become a carp pond.

Several factors suggest that the Asian carp could successfully establish in Lake Michigan. They are native to large rivers and lakes of eastern Asia at the same latitudes of the Great Lakes. The fish are highly temperature tolerant, shunning only the coldest temperatures found in the Great Lakes. They reproduce in great numbers and can grow to over 12 inches in less than a year. Free flow of carp from the Chicago River would effectively provide unlimited natural stocking of the fish and encourage an established population.

Biologists have sighted bighead and silver carp less than 60 miles from Lake Michigan in the Illinois River. Between these carp and the lake is an electrical barrier, years in the making, but only turned on in April 2002. The barrier, located approximately 30 miles southwest of the mouth of the Chicago River, was originally designed to prevent other invasive fish, including ruffe and round gobies, from entering the Mississippi River. With gobies already present in Illinois, city, state, and federal agencies are hoping the barrier will prove effective against carp entering the Chicago waterway system. But the use of an electrical barrier that was not designed for this problem can only be a temporary fix.

In the short term, prevention of this invasion requires funding for continued operation of the electrical barrier and immediate construction of a second barrier using different technology. This will require at least $15 million, according to Sea Grant estimates. This funding could be provided through reauthorization of the National Invasive Species Act (NISA). In the longer term, agencies and citizens should prioritize complete separation of the waters of the Mississippi River basin and Lake Michigan. This could be accomplished using a lock system or by actual physical separation, eliminating navigation between the two basins.

This is not a Chicago problem, nor is it a Great Lakes problem. The connection between the Mississippi River basin and the Great Lakes basin affects the ecology of over half of the United States. While the Great Lakes states concern themselves with prevention of an Asian carp invasion, the Mississippi River basin has already suffered the impacts of zebra mussel and round goby invasion from Lake Michigan.

The work necessary to prevent Asian carp invasion of the Great Lakes is work that will prevent ecological destruction of the kind that has become far too common in the last 100 years. Rare is the opportunity to see a new invasion coming, much less one that arguably has the greatest potential negative impact on the Great Lakes fishery since European settlement. This is a golden opportunity to begin elimination of an ecological problem that affects millions of citizens while reinforcing the fact that, just like extinction, invasion is forever.



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Images courtesy of Steven Huyser-Honig,
West Grand Boulevard Collaborative, & Yellow Dog Watershed Preserve.