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Like an uninvited guest, invasive species find their way into a new party, er, environment that didn’t evolve with them as part of its original suite of species. As such, they may have advantages over the native species that allow them to be hyper-successful. Excessive size, a voracious appetite for defenseless prey, a lack of predators to control their numbers – these qualities can spell disaster for a finely-tuned ecology. Once established, it takes concentrated effort to remove these species, whether they be frogs, rabbits, birds, trees, or weeds. Often, it cannot be done with anything short of carpet bombing, so the best plan is to use less destructive measures relentlessly in hopes of keeping the new population in check. Why bother? Well, if the upset to a local environment is substantial, it can mean the end to whole species or the drastic shrinkage of species of economic concern. From a biology-lover’s perspective, it’s also a crime against nature to let a system be destroyed whose myriad pieces have worked out a balanced survival dance over countless millennia.
One such unwelcome beast is the Asian carp. These fish were brought to the southern U.S. (so actually, they weren’t entirely uninvited) to aid in aquaculture and to keep ponds in wastewater treatment facilities clean. Obviously, these fish will eat anythlng, and a lot of it. Unfortunately, due to flooding accidents they escaped in the 1970s into the Mississippi River and have spread havoc ever since. As filter feeders, they consume astounding volumes of plankton and macroinvertebrates, tiny organisms upon which immature native fish depend for their survival. The carp then grow too large for other fish species to prey upon. Some can grow to over 100 pounds and are as long as seven feet. To make matters worse, they reproduce in huge numbers. These fish have worked their way up several of the main rivers that feed the Mississippi, as well as Big Muddy itself. Their northward drive was stopped, however, at Minneapolis, thanks to St. Anthony’s Falls, the only significant waterfall on the entire length of the Mississippi River.
The falls make a good natural barrier, but in 1963 a series of locks were built, which made it possible for barges to move upstream of Minneapolis. Barge shipping is very efficient – each barge trip is equivalent to 110 semi-truck loads. The passage at St. Anthony’s Falls raises and lowers the barges five stories by the usual means of flooding locks with river water. Asian carp are nearing Minneapolis as they expand their territory. Once there, they could easily swim up alongside a barge in the lowest lock and ride the elevator chain past the falls and continue their destructive march, so to speak, northward. So in order to keep that from happening, Congress decided to close the locks permanently in June of 2015, thereby ending the barge shipping business. It’s the first time a navigable waterway has been shut down in defense of the environment. The shipping business there is fairly small scale, but still important to those involved with it. Overall, however, the preservation of the river ecology was seen as the greater good.