Bigheaded Carp Invasion of the La Grange Reach of the Illinois River: Insights from the Long Term Resource Monitoring Program
Kevin S. Irons, Greg G. Sass, Michael A. McClelland, and T. Matt O’Hara
Abstract.—Bigheaded carps, including the nonnative bighead carp Hypophthalmichthys nobilis and the silver carp H. molitrix, have been present in the Illinois River since the mid-1990s. The Long Term Resource Monitoring Program (LTRMP) is part of the U.S. Army Corps of Engineers Environmental Management Program on the Upper Mississippi River System (UMRS) and has monitored fish communities in La Grange Reach, Illinois River since 1990. Standard LTRMP protocols have collected abundance, age and growth, and maturation and recruitment information for these carps as they have invaded the UMRS. Bigheaded carps have been collected in La Grange Reach by the LTRMP since 1995 and 1998, respectively. Since 2000, LTRMP catches of bigheaded carps have increased, and substantial spawning and recruitment has been evident. Length–frequency distribution analyses for both species have provided insight into growth rates, mean sizes at age, and cohort strength. Maturation schedules of bigheaded carps have been variable during the invasion, yet recruitment was positively correlated with Illinois River flow. The LTRMP provides a unique perspective into the invasion of these species and gives initial insights into possible ecological impacts within a large river basin. Biological and life history data collected by the LTRMP may also be useful in understanding and predicting future effects of bigheaded carps within other water bodies.