STATUS OF BIGHEAD CARP AND SILVER CARP ON THE LA GRANGE REACH, ILLINOIS RIVER 
AND POSSIBLE IMPACTS TO THE COMMERCIAL FISHERY. 

Timothy M. O'Hara, Kevin S. Irons, Mike A. McClelland and Mark A. Pegg
Illinois Natural History Survey, Illinois River Biological Station, Havana, IL 
62644.

The La Grange Reach of the Illinois River has historically been a very important 
area for commercial fishing in Illinois. However, over the past one hundred 
years significant changes have occurred in the commercial harvest throughout the 
Illinois River. The intentional introduction of common carp Cyprinus carpio in 
the 1800's drastically changed the commercial fishery by replacing the native 
buffalo as the main catch on the Illinois River. In 1908, commercial fishing 
reached its peak when 11 million kilograms of fish were taken with common carp 
comprising nearly two thirds of the catch. More recently two Asian carp species, 
bighead carp Hypopthalmichthys nobilis and silver carp Hypopthalmichthys 
molitrix, have spread into the Illinois River from the Mississippi River basin. 
This may again prompt a significant change in commercial species composition. 
Reported bighead and silver carp annual commercial harvest has increased 
markedly from 600 kilograms prior to1992 to greater than 50,000 kilograms since 
1997. The Long Term Resource Monitoring Program  (LTRMP) has been monitoring 
fish on the La Grange Reach since 1990, allowing us to detect the presence of 
these exotic species and follow their abundances through time. Catch per unit 
effort for bighead and silver carp has dramatically increased beginning in 2000, 
exhibiting a similar trend to common carp when they were introduced over a 
century ago. The size structure of these exotic fish has also shifted in the 
past two years from smaller individuals that are not preferred commercially to 
larger individuals that are of some value. Over this same time period buffalo 
catch rates and population structure were monitored for potential negative 
trends that may occur. These data and potential ecological and economic impacts 
to the Illinois River commercial fishery will be presented and discussed. 

Keywords: bighead carp, silver carp, Illinois River, commercial fishing, Long 
Term Resource Monitoring Program