This fall, fishery biologist Duane Chapman was out on the Missouri River with a few of his scientist colleagues fishing for Asian carp, an invasive species originally from China that has recently been added to the federal list of “injurious wildlife.”
Because of their rapacious eating, Asian carp can grow monstrously large: up to four feet long, and weighing in at 100 pounds.
Chapman and his friends didn't have to search for long. Within an hour and a half, they caught 139 silver carp, a particular species of Asian carp, out of the lower Missouri River. Four other carp leapt into their boat independently. (The fish have a habit of jolting out of the water when frightened by the sound of approaching boats. They’ve been known to smack fishermen in the face, breaking jaws and causing other serious injuries).
Asian carp were first introduced into American ponds and fish farms in the 1970s. Because carp eat plankton and zooplankton in great quantities, some pond owners and aquaculture farmers sought the fish out as natural scum cleaners.
Asian carp escaped, likely due to flooding, and have been hungrily making their way through the Mississippi River watershed to the Great Lakes ever since. Scientists and policymakers are concerned that the invasion of Asian carp in the Great Lakes could wreak havoc on the region’s fishing industry, which is worth $7 billion.
Scientists have found only a handful of Asian carp in the Great Lakes in the last few decades, but the fish have already created big problems in America’s rivers, says Chapman, who is a fishery biologist at the Invasive Carp Research Program of the U.S. Geological Survey.
“Asian carp have caused the marginalization of native species of fish, like yellow perch and walleye, as well as native prey fish like gizzard shad,” Chapman said in an interview. “They have declined in numbers, and the ranges that you can find them are smaller. They may not grow as fast because they have to compete with Asian carp for food.”
Because of their rapacious eating, Asian carp can grow monstrously large: up to four feet long, and weighing in at 100 pounds. These larger animals can grow to be 25 years old, and can consume five to 10 percent of their body weight each day in plankton. In some areas of the Mississippi River basin, Asian carp now comprise as much as 97 percent of the fish biomass.
A study released earlier this year by the U.S. Geological Survey found that if carp do enter the Great Lakes, the warm waters of Lake Eerie would provide an ideal habitat for carp populations to grow and thrive.
The race is on to stop them from swimming into the Great Lakes in numbers large enough to establish a breeding population. Scientists have found carp DNA within miles of Lake Michigan.
Five states recently banded together to encourage the federal government to address the problem. Michigan, Wisconsin, Minnesota, Ohio, and Pennsylvania filed suit against the Army Corps of Engineers and Chicago’s Metropolitan Water Reclamation District, claiming that the agencies caused a public nuisance by failing to build barriers between Lake Michigan and rivers where Asian carp are living. The states were joined the Chippewa Indians and Grand Traverse Band of Ottowa.
Earlier this week, U.S. District Judge John Tharp ruled he couldn’t order the agencies to build carp barriers because of a federal law that requires the corps to keep shipping channels open. Tharp said he was “mindful of, and alarmed by, the potentially devastating ecological, environmental, and economic consequences that may result from the establishment of an Asian carp population in the Great Lakes,” according to the Associated Press.
The Supreme Court has refused to order temporary protective measures, including closing Chicago shipping locks and installing nets, on four separate occasions.
Chapman believes that the problem may persist even if protective barriers are constructed. “We could spend a lot of money on revamping the Chicago area waterway and still ultimately be unsuccessful in stopping the invasion,” he said. There are a lot of ways the fish can get around a barrier, no matter how good a barrier you build.”
Even though it’s illegal to do so, some people still stock Asian carp in their ponds in order to eat up messy vegetation. Fish can escape during floods or through drainage pipes.
Fishermen who harvest their own bait occasionally get a small Asian carp in their bucket of bait fish, and without realizing it, transport the carp to a vulnerable waterway. The organization Stop Aquatic Hitchhikers has resources for recreational fishermen who want to avoid the problem.
The Center is calling on enthusiastic fishermen and citizen scientists to take pictures of Asian carp when they catch them, and to immediately call state wildlife biologists if they find a carp in one of the Great Lakes.
Still, fishery biologists are worried about the possibility that someone will get fed up with all the rules. “If you are an invasive species like Asian carp and want to expand your range, all you need is one person who wants to move you, and you have a chance at establishing a new population,” Chapman said.
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