The Long-Term Illinois River fish Population Monitoring Program

Long-term ecological monitoring is essential to gain an understanding of the interaction between spatial and temporal patterns and variability. The goals of our study were to test for trends in (1) overall fish catches; (2) native and nonnative fish species richness and relative abundance; and (3) the fish species assemblages over time using greater than 50 years of fish population data collected from the Illinois River. Fish species richness 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 have since shown a significant increase. Abundances of nonnative species declined from 1957 to 2000; however, rapid population growth of Asian carps (Hypophthalmichthys spp.) in the Illinois River increased nonnative 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 temporal and spatial shifts in fish populations in the context of anthropogenic and natural change in aquatic ecosystems.