The Emiquon Nature Preserve in Fulton County is a carefully managed haven for many rare, native wetland species in the Illinois River Valley, but even it is not immune to the proliferation of invasive carp.
Randy Smith is the Nature Conservancy's Illinois River project director. He said silver and bighead carp larva managed to sneak in during a flood while the Emiquon Nature Preserve's water control structure was still under construction.
"(It's) kind of a crazy story. They found their way in through some either buried pipelines or some unconsolidated sediment. They got in as tiny, tiny, little larval fish that had just come into existence in 2015 during that flood, and basically came through sediment or through some tiny, tiny pipelines," Smith said.
Biologists can use a fish bone called an otholith to age them, kind of like rings in a tree trunk. Smith said almost all of the largest carp now living at Emiquon were born in 2015.
"My predecessor used the term bazillions to describe how many of them came in during that process, and now they're all 20 to 25 pounds," Smith said.
Smith said they do track the number of fish caught by the commercial fishers who help manage carp populations at Emiquon. Bluegill munch on carp larva, and there are hopes that largemouth bass and reintroduced native alligator gar will also begin to make an impact.
Smith said carp are problematic for wetland conservation efforts not just because they compete with native species. They also stir up bottom sediments and eat the submersed aquatic vegetation.
"They do a number of very bad things to productive wetlands, and they are a problem here," he said.
The Nature Conservancy is also working with the U.S. Geological Survey and researchers from the University of Minnesota on new carp management techniques.
Once invasive carp are introduced to an ecosystem, it's nearly impossible to extricate them. The Illinois Department of Natural Resources is spearheading a marketing campaign to create more commercial demand for the fish. If successful, that could reduce the number of invasive carp in the Illinois River system, where they've become well-established over the last few decades.
About 1 million pounds on average of the fish are also removed from the northern reaches of the Illinois River each year. Last fall, an additional 750,000 carp were culled from the Starved Rock pool of the Illinois River in what may be a record U.S. freshwater harvest.
Up north, the U.S. Army Corps of Engineers are investing in a $1.2 billion project at the Brandon Road Lock and Dam in Joliet to act as a bulwark against the carp entering the Great Lakes.