Because Asian carp are capable of consuming such a large amount of plankton, they pose a clear threat to other filter feeders, including such native species as the paddlefish (a rare prehistoric oddity that still inhabits big Minnesota rivers) and the buffalo.
What's more, all fish begin life as plankton feeders. That means that juvenile walleye, northern pike, and other prized game fish in the Mississippi may soon find themselves in direct competition for food with big schools of adult Asian carp. To make matters worse, there seems to be nothing in the existing Mississippi ecosystem capable of keeping the Asian carp population in check. They grow so big, so fast, researchers say, that few native predators pose a credible threat.
In the last year, concern over Asian carp has centered on the prospect the fish might spread from the Mississippi watershed to the Great Lakes. Responding to those worries, Congress authorized some $2 million for the construction of an experimental electrical barrier on the Chicago Ship and Sanitary Canal--the waterway that connects a Mississippi tributary to Lake Michigan. Early tests indicate that the barrier is working, but it's too early to say whether it's a success.
Pam Thiel, project leader at the U.S. Fish and Wildlife Service office in LaCrosse, says little can be done to stop the spread of the Asian carp up the Mississippi to Minnesota. There are no plans for an electrical barrier on the Mississippi; and even if there were, such a project would be prohibitively expensive and, owing to the Mississippi's width and size, unlikely to succeed.
According to Thiel there is always hope that Asian carp won't dominate the waters here to the degree they have elsewhere. "One possible saving grace is that the Mississippi River from Dubuque to the Twin Cities is more stable and more diverse, so maybe it will be harder for them to become a dominant fish." But, she allows, "maybe that's just grasping at straws."
In Illinois, meanwhile, officials are wrestling with another option for dealing with the problem: encouraging the development of a commercial fishery and market for Asian carp. Thiel doesn't specifically endorse such a proposal, noting that large-scale fishery operations can have other unintended negative consequences. But on a recent visit to China as part of a Fish and Wildlife Service delegation, she sampled a variety of carp prepared by her hosts. "I had an opportunity to eat bighead, silver, black, and grass carp. They were all very good," she reports. "A good source of protein."