The word "exotic" brings to mind something unique, rare and beautiful, but in essence the word primarily refers to something that has come from another place, that is not native. Organisms that have been moved into areas where they did not naturally live are called exotic or introduced species.
Scientists estimate that over the past 100 years close to 4,500 plants and animals have been introduced into North America. Exotic species have been introduced intentionally by natural resource managers to enhance hunting and fishing opportunities or to control other organisms. For example, many of us feel we have benefited from the introduction of pheasants from China and brown trout from Europe.
Introduced species have become a national concern because they can cause problems for native species. Exotic plants or animals can disrupt the harmony of an environment, even completely changing the habitat and displacing the species that originally lived there. Introduced species have been cited as the second leading cause in the extinction of North American freshwater fishes, following habitat destruction and ahead of pollution. In response to the damage caused, President Clinton recently issued an executive order to encourage action to control invasive and introduced species.
Scientists believe introduced species may play a major role in the decline of native fish and other aquatic organisms. The negative effects of introduced species are not always immediately apparent and may be difficult to separate from the problems caused by declining habitat and pollution. Sometimes we don't recognize a problem until an exotic plant or animal has already established itself and driven out other species.
Exotics plants and animals sometimes are introduced intentionally into ponds, lakes or streams in Missouri to increase recreation, to provide food for other fish and to control vegetation.
Sometimes these introductions go awry. Take the common carp, for example. It was intentionally introduced in the U.S. in 1876. At the time, carp were a popular sportfish in Europe. Stocking was stopped by 1895, but the carp had already established itself in Missouri waters. Now they are the most common large fish in the state.
To get an idea of their effect, imagine that each pound of carp takes up the space and resources that might be used by a pound of game fish. Although carp feed a commercial fishing industry in Missouri and elsewhere, the aggressive fish uproot plants, muddy the water and eat the eggs of other fish, adversely impacting native species and their habitats.
Watery creatures are the most difficult of all to control. Exotic species can travel in the ballast tanks of ocean-going vessels or in the water sloshing around in an angler's bait bucket. Juvenile animals might attach to boat hulls or find a pocket of water in a trailer. People may be introducing exotics when they release fish that have grown too large for aquariums into the closest lake or stream.
Such accidental or inadvertent introductions have the most potential for harm. By the time biologists detect damage, the introduced species has been there long enough to become established. Once established, dealing with both the exotic and the resulting damage can be difficult and costly.
The zebra mussel is a good example of the economic damage an invader can cause. Most experts believe that the zebra mussel was introduced into U.S. waters through a ship's ballast water. Because they are new to U.S. waters, they have few or no natural enemies, and their numbers expand and increase quickly. A female can produce 30,000 to 40,000 eggs every year.
Since the arrival of zebra mussels into the Great Lakes in the mid 1980s, the species has spread rapidly. They currently inhabit most of the navigable waters in the Mississippi River Basin and recently were found in the Missouri and Meramec rivers. In many places, they have become so numerous they have clogged industrial, agricultural and municipal water intake pipes and caused some power plants to overheat. Similar problems will likely occur in Missouri.
In addition, zebra mussels could affect the fishing in Missouri. "If the zebra mussel continues to invade Missouri's waters, fishermen in the future will be asking, 'where have all the trophy fish gone?'" said mussel expert and Conservation Department research biologist Sue Bruenderman. "The more zebra mussels we have, the less food available for small fish. Less food means less growth and smaller fish in the long run."
People can help keep zebra mussels from spreading. The Conservation Department suggests washing your boat and trailer with hot water between trips to different bodies of water or, at the least, letting your boat dry out thoroughly for five days, which will kill zebra mussels that might be attached. If you collect your own bait from a lake or stream, make sure you return it to the same lake or stream. This will help prevent exotic species from spreading from one fishing hole to the next.
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 accidental, but it was probably intentional. After all, purple loosestrife is a beautiful flowering plant that has been used medicinally for many years.
The problem is that purple loosestrife spreads quickly and in a short time will completely dominate ponds, lake edges, stream banks and ditches in pastures, fields and roadsides, wiping out native plants in the process. The Conservation Department has been spraying purple loosestrife with herbicide annually since the 1980s. The process has to be repeated every year because seeds are left behind after spraying.
We are all potential vectors for the spread of exotics in Missouri. A child might bring home a frog or crayfish only to have his or her mother insist that the animal be released immediately. If the release point isn't the same as where the animal was captured, the release-especially if the critter is pregnant-might disrupt the habitat.
We can't completely guard against accidental introductions. Gypsy moths can hitch a ride on the web recliner we rested in outside our campsite in Michigan, for example, or a weed seed might stick to the lining of our hunting jacket in North Dakota and fall to the ground in the Bootheel.
The few things we can do, however, may make a huge difference in our quality of life and may prevent the disappearance of some of our treasured native species. Knowing how disruptive even a single introduction of a nonnative species to Missouri can be, we recommend these few simple precautions.
Tell your child that critter they want to keep will be happiest and healthiest where it belongs and may cause big problems elsewhere.
Kids and adults love to learn about nature, but the common and seemingly harmless practice of collecting organisms for study, then releasing them anywhere other than where you collected them can have serious consequences. Think of animals living at a specific address. When you've learned all you can about them and want to release them, make sure you take them home.
Other exotic species in Missouri and their associated problems include:
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