Asian Carp in the Upper Mississippi River System

The introduction of zebra mussels to the Great Lakes and Upper Mississippi River System (UMRS) in the 1980s and 1990s increased public awareness of the problem of invasive species. In response, the United States Congress passed the Non-indigenous Aquatic Nuisance Prevention and Control Act in 1990 and the National Invasive Species Act in 1996. Zebra mussels, however, are not the first, nor will they be the last, non-native species to invade our freshwater ecosystems. Introductions of fishes and other aquatic organisms into inland waters of North America have been increasing dramatically for the past 150 years. The invasion of the UMRS by several Asian carp species provides an excellent illustration of the history and continuing challenge posed by introductions of invasive species.

Presently, four species of Asian carp are established in the UMRS and a fifth species is waiting in the wings. The first Asian carp species to become established in North American was the common carp (Cyprinus carpio), which was introduced in the 1800s by the U.S. Fish Commission to establish recreational and commercial fisheries. Today, common carp are abundant throughout the UMRS. Because this species was established so long ago, data are not readily available to demonstrate the effects of their invasion on native fish communities. Nevertheless, common carp are known to adversely affect aquatic habitats by uprooting vegetation and increasing turbidity.

Three additional species of Asian carp--grass carp (Ctenopharyngodon idella), bighead carp (Hypophthal-michthys nobilis), and silver carp (Hypophthalmichthys molotrix)--have become established in the UMRS during the past two decades. All three species were initially brought to the U.S. in the 1960s and 1970s for use in aquaculture, and became established in the UMRS through accidental and deliberate releases. Data from the Long Term Resource Monitoring Program and catch data from commercial fishers show that the abundance of these species, especially bighead and silver carp, has increased dramatically during the past few years (Fig. 1). Bighead and silver carp are filter feeders, consuming a variety of planktonic organisms, and are capable of significantly reducing zooplankton abundance in ponds and lakes. Because all fishes forage on planktonic organisms during their early life history stages, bighead and silver carp have the potential to adversely affect every species of fish in the UMRS and connecting aquatic systems.

If nothing is done to halt the upstream spread of bighead and silver carp in the Illinois River, they will soon enter the Great Lakes. A potential check on the upstream movement of bighead carp is the electric dispersal barrier being constructed on the Illinois Waterway near Chicago. However, this barrier was originally designed to stop the spread of the round goby (Neogobius melanstomus) from the Great Lakes to the UMRS, and it is unknown whether this barrier will be effective for bighead and silver carp. Researchers at the INHS Great Rivers Field Station and Illinois River Biological Station have initiated projects to assess dietary overlap of bighead carp with filter feeding fishes native to the UMRS, and the effectiveness of various barrier designs for preventing the spread of this invasive species to the Great Lakes.

The black carp (Mylopharyngodon piceus) is waiting in the wings. This species is a molluscivore that was brought to the United States for use in aquaculture ponds. The previous invasions by Asian carp suggest that it is just a matter of time before this species becomes introduced and established into the UMRS, where it will pose a threat to endangered freshwater mussel populations. Once a non-native species successfully invades an ecosystem, it is often difficult or impossible to eradicate. Therefore, it is critical that state and federal management agencies make concerted efforts to stop the establishment and spread of black carp in the UMRS.

John H. Chick, Center for Aquatic Ecology

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