ENVIRONMENTAL AND ECONOMIC IMPACTS OF ASIAN CARPS IN THE ILLINOIS RIVER. Greg G. Sass, Thad R. Cook, Kevin S. Irons, Michael A. McClelland, Nerissa N. Michaels, T. Matthew O’Hara, and Matthew R. Stroub Illinois River Biological Station, Illinois Natural History Survey, 704 North Schrader Avenue, Havana, Illinois 62644 Non-native bighead Hypophthalmichthys nobilis and silver carps H. molitrix have been captured in the La Grange Reach of the Illinois River through routine Long Term Resource Monitoring Program sampling since 1995 and 1998, respectively. Since 2000, bighead and silver carps numbers and biomass have increased greatly. At present, these carps likely dominate the fish community of the Illinois River. Because of the miniscule filtering capabilities of these carps and the great leaping ability of silver carps, the presence of these species is of environmental and economic concern. Environmentally, bighead and silver carps may compete with other native planktivores for food, limit recruitment of sportfishes, and disrupt native food webs. For example, research conducted by the Illinois River Biological Station suggests declines in body condition of native gizzard shad and bigmouth buffalo coincident with increases in abundance of Asian carps. In addition, catches of the Centrarchidae fish complex (bass, sunfishes) continue to decline in the La Grange Reach. Economically, bighead and silver carps can positively and negatively effect river cities and users. Negatively, bighead and silver carps damage commercial fishing gears and may decrease catchability of lucrative species, such as buffalo and catfish. In addition, the risk of injury to recreational users of the Illinois River has increased substantially with the explosion of silver carps and river users may choose not to participate or spend money on river related activities. Because bighead and silver carps feed at the bottom of the food chain and reach large sizes, developing markets and commercial fishing may be the most viable option for controlling these species. Despite uncertainties of the environmental and economic impacts of Asian carps in the Illinois River, precautionary and proactive approaches to develop commercial fishing markets, fund the electric barrier, and prevent the spread of Asian carps to the Great Lakes should be of utmost concern. Keywords: Asian carps, bighead carp, exotic species, Illinois River, silver carp Greg G. Sass Illinois River Biological Station Illinois Natural History Survey 704 North Schrader Avenue Havana, Illinois 62644 309-543-6000 (phone), 309-543-2105 (fax) ggsass@uiuc.edu Platform presentation – no – power point Non-student