Backwater Immigration by Fishes through a Water Control Structure: Implications for Connectivity and Restoration

Abstract Recent efforts to reduce sediment loading in large-river backwaters have relied on inexpensive low-maintenance structures that promote river–backwater connectivity. How these structures influence ichthyofauna is not understood. We quantified the distribution of fishes through a stop-log structure installed during the Swan Lake habitat restoration project on the lower Illinois River. Modified hoop nets were systematically fished simultaneously in a two-dimensional 3 vertical × 3 horizontal grid of net locations to capture fish as they immigrated into the lake through the structure. Catches were dominated by gizzard shad Dorosoma cepedianum and freshwater drum Aplodinotus grunniens. Adult freshwater drum, adult common carp Cyprinus carpio, and juvenile silver carp Hypophthalmichthys molitrix exhibited an affinity for the lower two-thirds of the water column. Lengths of freshwater drum increased with depth, particularly during the spring. Common carp catch rates were highest during spring, whereas t...