Claws for Alarm

Published on: Aug. 20, 2013

interacting influences. It is difficult to predict the results of every invasion. But we do not want to leave the future condition of our waterways and fisheries to chance.

In fact, it appears that crayfish invasions are being identified at an alarming rate throughout the U.S. Missouri Department of Conservation biologists have documented more than 20 crayfish invasions in Missouri. In every one of these 20-plus invasions, the invading species is native to some part of our state, but has been moved to another.

All of the invasions that have been studied are spreading in size. Department biologists recently reported one invasion that spread about 1.4 stream miles in only one year. And as these invasive crayfish spread throughout streams, native crayfish species are disappearing. To date we have witnessed declines of at least six native species in Missouri. We don’t yet know whether or how other aquatic life forms (insects, fish, amphibians, reptiles, plants, etc.) are being affected, but data from many other states sug;gest that food chains and ecological function are suffering.

No Substitutions

Some wonder why it’s a problem if a native crayfish species is eliminated and replaced by an invasive crayfish species. It’s a good question with multiple answers. First, different species, even closely related ones, have different interactions with other community members. Their substitution will often change the way an ecosystem functions and the way people value that system. This is seen with closely related crayfish species, but it might be easier illustrated using species that are better known to most readers. For example, smallmouth bass and spotted bass are native Missouri sport fish species that don’t always naturally occur together. They look similar, but play different ecological roles. They also hold much different value with the fishing public — the smallmouth bass is generally more highly prized. Spotted bass are not native to Missouri’s Meramec River drainage but invaded there, and are negatively impacting smallmouth bass in much of the drainage (and even impacting largemouth bass in streams). The Department of Conservation received so many complaints about this invasion that regulations were passed to allow liberal harvest of spotted bass in this drainage to manage this invasion.

Another problem with replacement of native crayfish species by invaders is that invasive crayfish populations often rapidly overpopulate waters where they invade, showing much greater abundances than those shown by natives. Overpopulated invasive crayfish overgraze their food

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