Fish Community Indices of Biotic Integrity Applied to the Large Rivers of Illinois

An index of biotic integrity (IBI) allows rapid assessment of environmental health at a site by assigning a numerical score that quantifies the quality of the biotic community present.  IBI’s can be more effective than traditional chemical and physical measurements for assessing environmental health because biotic communities may better reflect overall and long-term conditions at a site.  The fish community IBI concept, developed for and used primarily in small streams, has been adapted for large river use.  An IBI for large rivers would be especially useful in Illinois, where large rivers subjected to varying degrees of degradation support a large portion of the fisheries resources.  Our objectives were to evaluate the utility of existing large river IBI’s in the large rivers of Illinois and test for differences in IBI scores among river navigation reaches.  A long-term electrofishing program (LTEF) conducted by the Illinois Natural History Survey samples main channel border fish communities at random sites on the Illinois River and Illinois portions of the Mississippi River.  We applied the Wisconsin Large River IBI to LTEF data from Mississippi River pools 20, 19, and 16, and for the Alton, Peoria, Starved Rock, Marseilles, and Dresden reaches of the Illinois River.  Fish community samples from these navigation reaches were generally within numerical ranges and species compositions used to assign scores with the Wisconsin Large River IBI.  We found significant differences in IBI score among navigation reaches.  These results show that the Wisconsin Large River IBI is useful in evaluating fish communities in the Illinois River and Illinois portions of the Mississippi River and would be a valuable component of a long-term monitoring program.  Ultimately, this information will enhance our ability to detect changes over time while monitoring fish communities in the large rivers of Illinois.