Upper Mississippi River Restoration Program Long Term Resource Monitoring

Status, trends, and population demographics of selected sportfish species in the La Grange Reach of the Illinois River

Solomon, L. E., R. M. Pendleton, K. A. Maxson, J. N. McQuaid, D. K.Gibson-Reinemer, C. A. Anderson, R. L. Anderson, E. G. Lampo, J. T. Lamer, and A. F. Casper. 2019. Status, trends, and population demographics of selected sportfish species in the La Grange Reach of the Illinois River. Illinois Natural History Survey Bulletin 42:2019002.

Abstract

Sportfish species, specifically, Yellow Bass Morone mississippiensis, White Bass Morone chrysops, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, Black Crappie Pomoxis nigromaculatus, and White Crappie P. annularis, often drive economically valuable fisheries in large river systems, including the Upper Mississippi River System (UMRS). Within the Illinois River, part of the UMRS, these species are routinely sampled by an ongoing, long-term fisheries monitoring program. Through this program, we investigated long-term trends, 1993 through 2017, in catch rates and relative weights and quantified demographic rates from 2012 through 2016. We found all six study species, with the exception of Yellow Bass, to have declining catch rates, with this decline being most stark in larger, older fishes. Population demographics for Yellow Bass, White Bass, Bluegill, and Black Crappie suggest populations are dominated by younger individuals, with only Black Crappie regularly living to age 3 and older, which may be driving population declines. Many environmental stressors are acting on the Illinois River that could be contributing to the lack of older and larger fishes, including but not limited to navigation efforts (impoundment by lock and dams, levee construction), altered hydrology, pollution, sedimentation, lack of overwintering

habitat, and introduction of invasive species. Results of this study demonstrate that additional research to understand mechanisms driving reduced abundance and stunted age structure are needed to identify effective management actions that would benefit populations of recreationally valuable sportfish species.

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