Fifty years of the long term Illinois River fish population monitoring program

Fishes of the Illinois River have been monitored since 1957 through the Long-Term Illinois River Fish Population Monitoring Program.  Data has been collected in six reaches by AC electrofishing.  We examined fish collections to test for trends in total catches and catch rates, spatial and temporal changes in catch, species collections, spatial and temporal species composition and structure, and selected species.  We have collected 191,042 fishes representing 97 species and seven hybrids resulting in a catch rate of 202 fish per hour of electrofishing.  Community analyses revealed temporal changes in species composition and structure in the upper three reaches of the river from a community dominated by common carp and goldfish to one of greater fish species diversity.  Species diversity increased throughout the river over time, even with the exclusion of introduced species.  Important sportfishes such as bluegill and largemouth bass catches demonstrated increase over time in many areas, while common carp catches decreased.  The trends observed may reflect positive effects of rehabilitation efforts throughout the Illinois River.  Our collections highlight the importance of long-term data sets and the ability to detect trends spanning multiple decades.  Results from our long-term monitoring program may guide future Illinois River rehabilitation efforts.