Long-term Survey and Assessment of Large-River Fishes in Illinois, 2019

This report presents a summary of those data collected during segment 31 (2019-2020) of the Long-term Survey and Assessment of Large-River Fishes in Illinois (LTEF), an annual survey by members of the Illinois Natural History Survey, with funds administered by the U.S. Fish and Wildlife Service and the Illinois Department of Natural Resources. Sampling for the LTEF program was conducted on six reaches of the Illinois River Waterway and three segments or pools of the lower Mississippi River sampling area. A summary of the Upper Mississippi River data collected for Pools16-18 as part of F-101-R-31 were reported in DeBoer and Lamer (2020) as part of the F-163-R project report to provide continuity and a comprehensive view of the Upper Mississippi River region. In all segments of the LTEF program, all fish species collected were accurately identified, tallied, measured, and weighed. The catch rates of sportfish species were calculated as the number of individuals collected per hour (CPUE ± standard error). Structural indices [Proportional Size Distribution (PSD) and Relative Weight (Wr)] were also calculated for several species of interest to regional managers. Catch rates and species varied among all sampling locations and sampling periods. Emerald Shiner and Gizzard Shad comprised the majority of the individuals caught, and Silver Carp and Common Carp accounted for the greatest proportion of the biomass collected in most sampling areas of the survey. Future analysis of CPUE and PSD trends in sportfish populations sampled by the program may indicate inter-annual recruitment patterns or/and long-term trends in Illinois sportfish populations. Sportfish Catch rates and sizes of popular sportfish species varied greatly among the rivers and reaches sampled during 2018. The most-abundantly collected sportfish species were Bluegill and Smallmouth Bass in the Upper Illinois River and Bluegill and White Bass and in the Lower Illinois River. White Bass were the most-abundantly collected sportfish species on the Mississippi River. Collections of black basses were greatest in the Upper Illinois Waterway. Similar to the last three years, catch rates of Smallmouth Bass in the Upper Illinois River were again the highest ever recorded in SCB habitat, which have been increasing overall since 2000. Our long-term datasets allow us to observe substantial annual variations in the relative abundance and size distribution of many sportfish species, like White Bass. These observations should serve as a catalyst for future research investigating the effects environmental changes and management policies on the health and sustainability of Illinois’ sportfishes. Although the factors controlling the annual variations in the relative abundances of fishes in Midwestern rivers may be difficult to identify, our ability to detect and possibly explain such changes is dependent upon the execution of well-designed fisheries surveys. The operation and maintenance of the LTEF program and the data it generates can contribute to more comprehensive and nuanced understandings that can, in turn, aid in the development of more effective and sustainable management policies for sportfishes in the rivers of Illinois. Invasive Species Although the main focus of F-101-R programs are to conduct monitoring to improve our understanding of population dynamics, life histories, and habitat requirements of sportfish species, the programs sampling strategies may also be useful for documenting trends in the relative abundance of non-native species occupying Illinois large river ecosystems. However, we advise that researchers use caution when interpreting the data we collect on invasive species as our sampling protocols (e.g., restriction to main-channel habitats) may limit our probability of encountering the greatest densities of the species in some instances. Our monitoring and analyses suggest densities of Silver Carp are greatest in the Lower Illinois River, and specifically in the SCB habitat, but that body condition of Silver Carp in the Lower Illinois River has been much lower during the last 6-7 years than during the preceding years, inversely tracking relative abundances. In the Lower Mississippi Sampling Area, Silver Carp abundance was similar to 2018 but body condition continued to decrease. Common Carp continue to contribute the greatest percent biomass while contributing to 2.2% of the total catch.