Here are answers to some frequently asked questions about Asian carp, an invasive species of fish that is traveling north on the Mississippi River and threatening to enter the Great Lakes.
What are Asian carp?
There are many species of Asian carp. Bighead and silver carp are considered invasive species and a threat to the Great Lakes.
The fish are known for their immense size and appetite. Asian carp can consume up to 20 percent of their bodyweight each day in plankton.
Bighead carp, native to southern and central China, can weigh up to 110 pounds. Silver carp can weigh up to 60 pounds are native to waters in far eastern Russia and eastern China.
How did they end up in the United States?
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Bighead and silver carp were imported by private fish farmers in Arkansas in the early 1970s. They were used to control plant growth in fish ponds, but by the early 1980s, both species had escaped into open waters. With no natural enemies, the fish have reproduced rapidly and traveled up the Mississippi River.
Have they been spotted in Minnesota?
Yes, but not in large numbers. Two bighead carp have been caught in the St. Croix River -- one in 1996 and one in 2011, according to the state's Department of Natural Resources.
Six other bighead carp were caught in the Mississippi River between Lake Pepin and the Iowa border from 2003 to 2009. Three silver carp have been caught between 2008 and 2011.
The Department of Natural Resources is expected to release studies on Thursday detailing the advance of Asian carp into northern waters.
Why are Asian carp harmful?
Unsuspecting boaters up and down the Mississippi River have been injured when Asian carp, excited by the boat's motor, jump high in the air and sometimes land in the boat.
But the carp are causing even more problems underwater. They consume massive amounts of plankton, the organism at the center of underwater ecosystems.
"These things are robbing everything else that depends on the productivity of the water," said Phil Moy, who studies Asian carp at the University of Wisconsin Sea Grant Institute. "The tiniest fish, the minnows that then feed larger fish that then feed us, all rely on plankton. And here we have a great big fish, and a lot of them, taking the food from everyone else."
Asian carp can eventually dominate some water systems, squeezing out natives and favorite sport fish.
What has been suggested to fight the spread of Asian carp in Minnesota waters?
There are several proposals.
Whitney Clark, executive director of Friends of the Mississippi River, said the state should consider creating a physical barrier to stop carp from moving into our waters.
He said the Ford Dam in St. Paul would be the most logical choice. The lock there allows both recreational and some commercial traffic to pass, but Clark says it might be possible to keep the carp from squeezing through.
"If we could devise an effective barrier within the lock, a sound or electric barrier that would be pretty effective, that might be the way to address that," he said. "If that is determined not to be as effective as we'd like, then obviously closing the lock would be something we would need to study."
But some experts say that efforts to stop the spread of Asian carp will probably fail. They say the focus should shift to how to control Asian carp in areas where it already exists.
Charlie Wooley, with the U.S. Fish and Wildlife Service in St. Paul, said researchers are looking at the use of "bio-bullets" to fight the invasive species.
"These are an encapsulated fish poison that would be ingested by an asian carp, and it would then break down in the gut of the asian carp and kill the asian carp," he said.
The bio-bullet could be made to kill carp and not other fish, or biologists could use hormones to attract the carp so they'd be easier to kill.