Carpe Carp Diem
Lock up your loved ones. For about two years now, Twin Cities media have touted the coming invasion of two species of Asian carp--the bighead and the silver. Most of the stories have played up the sexiest angle: the silver's bizarre and menacing tendency to leap from the water whenever a motorboat passes.
A leading theory has it that the silvers are mistaking boats for the top predator of their native waters--freshwater porpoises--inspiring the carp to launch themselves into the air to make an escape. Whatever the case, the big fish--they weigh up to 70 pounds--are routinely smashing into boaters. This is a good newspaper story, a great TV story. Less noticed has been the role that lax government regulation played in the invasion and the havoc it may wreak on recent efforts to reintroduce native species to the Big Muddy.
The fact that various state and federal agencies ever countenanced the importation of the alien fish is more than a "story"; it's a scandal, a case study of how industry-friendly resource management screws up public resources. Silver and bighead carp, which now swim as far north as Lake Pepin, were brought to the U.S. by Southern catfish farmers in the 1970s because the fish "naturally"--and cheaply--filtered algae from catfish-rearing ponds.
As aquaculture critics predicted, some of those carp eventually escaped to the Mississippi and commenced reproducing at an appalling rate. With hope fading that their northward spread can be stopped (ruined commercial fishermen on the Mississippi's mid-reaches bleakly speak of "river rabbits"), it now appears yet another Asian visitor has established itself in the Mississippi: the black carp. Like silvers and bigheads, the black carp came at the invitation of catfish farmers, who found the voracious snail-eaters useful in controlling the parasite-ridden mollusks in their ponds.
Since black carp don't jump from the water and bonk people in the forehead, it's difficult to imagine Don Shelby ever chuckling over clips at the end of the ten o'clock broadcast. Still, it's worth noting that this latest gift from the South could spell ruin for what looked like a burgeoning wildlife success story, the restoration of endangered native mussels on the upper Mississippi River.
The mussels got a big boost four years ago, when the U.S. Fish and Wildlife Service determined that the regular dredging of the barge channels threatened to wipe out a plain-looking, four-inch clam called the Higgins eye mussel. In turn, since 2000, the U.S. Army Corps of Engineers has spent about half a million dollars each year on mussel studies and repopulation. The creatures now inhabit reaches of the river where they'd been absent for decades. This year, more than 1,000 adult Higgins eyes have been released into the wild; next year, plans call for the release of about 7,500.
Alas, all these Higgins eyes will make a tasty treat for the black carp, should the fish manage to establish a breeding population in Minnesota. The carp typically scarf three to four pounds of mollusks a day. Biologist Mike Davis, a mussel expert at the Minnesota Department of Natural Resources, is certain that the black carp will devour juvenile mussels. Whether they will eat larger adults, he says, remains an open question.
Still, Davis notes that there's an ironic aspect to the prospect of waterways filled with black carp. The strong-jawed fish will also gorge themselves on zebra mussels, an invasive species that is currently considered one of the greatest threats to the Higgins eye. For mussels, it turns out, the enemy of their enemy is still their enemy.
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