LAUSR

ABSTRACT Anthropogenic modifications to the environment have had damaging effects on the wildlife that depend on those natural ecosystems. Specific to Upper Mississippi River fishes, channelization, dams, and loss of floodplain connectivity have all been purported as deleterious. In the face of these habitat modifications, understanding habitat requirements of native species is needed to help guide management and restoration efforts. Furthermore, bluegill (Lepomis macrochirus) are an important indicator species that may provide insight to habitat needs of the broader fish community (e.g., “canary in a coal mine”). Prior research suggests bluegill require a mosaic of habitats throughout all life stages (e.g., main channel to backwater connection). As such, the objective of this study was to identify the habitat needs of bluegill in the Upper Mississippi River. We evaluated bluegill habitat use via electrofishing conducted by the U.S. Army Corps of Engineers’ Long-Term Resource Monitoring (LTRM) element. Electrofishing events (n = 4868) were conducted at three field sites throughout the Upper Mississippi River from 1993 to 2017. Our analysis of catch data (n = 83,352) indicates that bluegill prefer backwater macrohabitat over main channel and side channel habitats. Bluegill abundance varied between microhabitat characteristics. Bluegill catch rates were highest in low-flow areas, with velocities ranging from 0 to 0.09 m/sec. In general, catch rates were highest across all pools in moderately shallow depths (0–1.5 m) and in silty substrates. Management efforts that focus on the preservation of backwater habitat and connectivity to the main channel should help to sustain bluegill populations in the Upper Mississippi River. The information garnered in this study can be used to help direct management efforts that not only favor bluegill, but also other members of the Upper Mississippi River fish community.