Over 50 years of fish community monitoring in Illinois’ large rivers: The evolution of methods used by the Illinois Natural History Survey’s Long-term Survey and Assessment of Large-River Fishes in Illinois

This document describes the methodological evolution of the Long-Term Illinois Rivers Fish Population Monitoring Program since its inception. The principal changes include a shift from fixed-site sampling to stratified random sampling at the reach scale to benefit statistical robustness and a concurrent shift from AC electrofishing to pulsed-DC electrofishing to increase the breadth of the diversity and size classes of fishes encountered. These changes in methodology were implemented during the 2016 field season and are based on quantitative assessments of program data and other results from recent peer-reviewed publications. These refinements will likely improve the program’s ability to detect and describe patterns and trends in the fish assemblages of the Illinois River and other large rivers of Illinois and the Midwest.