Life-History Expression of Three Popular Sportfish From Three Distinct Habitats in the Illinois River Watershed

Understanding how a fish’s environment affects life-history expression throughout its geographic range is important for effectively managing and conserving important resources. Largemouth bass, black crappie, and bluegill are popular sportfish in the Midwest, making their management and conservation a priority for many natural resource agencies. We collected largemouth bass, black crappie, and bluegill from three distinct habitats in the Illinois River Watershed – the Upper Illinois River/Lower Des Plaines River, LaGrange reach of the Lower Illinois River, and The Nature Conservancy’s Emiquon Preserve, a large restored floodplain wetland – during Spring 2015 to better understand the effect of environmental differences on sportfish life-history expression. These habitats vary in many aspects, including location, contaminant load, bathymetry, water turbidity, and macrophyte abundance. We weighed and measured fishes, categorized visible parasite presence or absence, and extracted otoliths (to estimate fish age), gonads (to determine sex, estimate fecundity, and calculate GSI), and livers (to calculate HSI). Many life-history traits differed among habitats, though the results were often sex- and species-specific; the most-dramatic differences were in ovary weight-somatic weight relationships. Environmental factors appear to affect fish life-history expression, but more research is needed on additional factors involved (e.g., biotic interactions) and the mechanisms of effect. We suggest that management and conservation of these fishes in different habitat types and locations needs to consider life-history expression for these important sportfish.