The Long-Term Illinois River Fish Population Monitoring Program, 1957-2010

The Long-Term Illinois River Fish Population Monitoring Program has sampled fishes in six navigation reaches of the Illinois River since 1957.  Our long-term data has been collected annually using boat-mounted AC electrofishing at 27 sites.  We tested fish collections over all sampling years for trends in catch rates, species richness, and community composition.  We have collected 205,679 fishes representing 98 fish species (and seven hybrids) from 17 families.  Native fish species richness has increased over time and community analyses revealed changes in fish species composition from a community dominated by common carp (Cyprinus carpio) and goldfish (Carassius auratus) to one of greater species diversity.  Prior to 1976, abundances of native fish species were declining significantly, but since have shown a significant increase. Abundances of non-native species declined from 1957-2000; however, rapid population growth of Asian carps (Hypophthalmichthys spp.) into the Illinois River increased non-native fish species catches.  Many of the trends observed may reflect positive effects of rehabilitation efforts throughout the Illinois River.  Our collections highlight the importance of long-term monitoring programs to detect changes in fish populations over multiple decades and the success of our program has prompted a recent expansion of monitoring effort that includes randomized pulsed-DC boat electrofishing in the Illinois, Mississippi, Ohio, and Wabash rivers.