Tracking Missouri's Exotics
The Conservation Department is working hard to track zebra mussel infestation. If you think you have spotted a zebra mussel in an area where they are not known to be, call the nearest Conservation Department office.
Another good example of an unfortunate inadvertent introduction is the rusty crayfish, which found its way into a Wisconsin lake in the 1980s, probably introduced by Illinois or Indiana anglers who emptied their bait buckets into fishing lakes.
Studies have shown that the rusty crayfish is more aggressive and is, on average, larger than the native crayfish in the state. They become so large that fish have trouble eating them. In addition, the rusty crayfish reproduces earlier and its young grow faster than other crayfish. All these things allow it to outcompete crayfish native to these waters. In some lakes, the end result of the rusty crayfish was the destruction of the fishery.
Wisconsin is not alone. We have problems with a crayfish introduction right here in Missouri.
The St. Francis River crayfish and the Big Creek crayfish are found in the upper St. Francis River drainage (upstream of Lake Wappapello) in southeastern Missouri and nowhere else in the world. Scientists recently have discovered that an introduced crayfish, the woodland crayfish, has been found in two nearby streams, Stout's Creek near Ironton, and Big Creek near Sam A. Baker State Park.
Woodland crayfish may have been introduced by anglers as bait or by kids told by their parents to release a crayfish they might have brought home. The Black River runs through Johnson's Shut-ins State Park and is only about a 10- to 15-minute drive from Ironton. The woodland crayfish is common in the Black River and, therefore, could have been the source for this introduction.
The introduced woodland crayfish has completely replaced the St. Francis River crayfish in the upper two-thirds of Stout's Creek, and the Big Creek crayfish in much of Big Creek. Both native species are in danger of extinction. Researchers think that this may be because the woodland crayfish is bigger and more aggressive and may interfere with the reproduction of the native species.
We may never know for sure how the woodland crayfish got into these streams. Researchers believe that introductions of exotics may be more common than we think.
Missouri also has its share of land invaders. Purple loosestrife arrived in North America in the 1800s. Native to Europe and Asia, its introduction might have been