Dear EarthTalk: What exactly are Asian carp and why are they such a big problem lately?
— Lori Roudebush, Portland, OR
Seven species of carp native to Asia have been introduced into United States waters in recent decades, but it’s four in particular—bighead, black, grass and silver—that worry ecologists, biologists, fishers and policymakers alike. Introduced in the southeast to help control weeds and parasites in aquaculture operations, these fish soon spread up the Mississippi River system where they have been crowding out native fish populations not used to competing with such aggressive invaders. The carps’ presence in such numbers is also compromising water quality and killing off sensitive species such as freshwater mussels.
Asian carp are hardy, lay hundreds of thousands of eggs at a time and spread into new habitat quickly and easily. To wit, they can jump over barriers such as low dams. Also, flooding has helped the fish expand into previously unattainable water bodies. And fishers using young carp as live bait have also facilitated the fish’s spread, as have boats going through locks up and down the Mississippi.
The federal government’s Aquatic Nuisance Species Task Force considers the Asian carps to be nuisance species and encourages and supports “active control” by natural resources management agencies. Federal and state governments have spent millions in tax dollars accordingly to prevent the carp from making their way into the Great Lakes, but an elaborate underwater electric fence constructed to keep them out has not worked as well as hoped, and policymakers are reviewing other options now.
Friends and neighbors of the Great Lakes are particularly concerned about the impact Asian carp could have on the region’s $7 billion/year fishing industry. In 2009 the states of Michigan, Minnesota, Ohio, Pennsylvania and Wisconsin filed suit in federal court against the U.S. Army Corps of Engineers and Chicago’s Metropolitan Water Reclamation District seeking measures to prevent Asian carp from moving through the Chicago Area Waterway System into Lake Michigan. While a federal district court dismissed the lawsuit last December, it could resurface in a future appeal.
Regardless of whether the states can keep the Mississippi and Great Lakes systems segregated, Asian carp are expected to keep spreading throughout other parts of the U.S. through river systems that connect up with the Mississippi directly or otherwise. Federal researchers estimate that even if Asian carp are kept out of the Great Lakes, they could affect freshwater fisheries in as many as 31 states representing some 40 percent of the continental U.S.
In the meantime, state and federal agencies are monitoring the Mississippi and its tributaries for Asian carp and testing various barrier technologies to prevent their further spread. For instance, the National Park Service is collaborating with the state of Minnesota’s Department of Natural Resources to construct new dams that are high enough to prevent Asian carp from jumping over. The Asian Carp Regional Coordinating Committee has funded DNA monitoring in potentially affected water bodies whereby researchers can determine whether the troublesome fish are present just by the biological footprints they leave behind. Individuals can do their part by not transporting fish, bait or even water from one water body to another, and by draining and rinsing boats before moving them between different water bodies.