Fish Assemblages in off-Channel Areas of the Upper Mississippi River System: Implications for Restoration

Over 1.7 million visitors spend 3.5 million visitor-days fishing on the Upper Mississippi River System annually.  Off-channel areas (OCAs) are central to the productivity and diversity of fishes in large floodplain river systems like the Upper Mississippi River System (UMRS).  System changes to accommodate navigation and agriculture have altered the flow regimes and geomorphic features of OCAs and in turn affect fish species composition and structure. To identify important relations between fish assemblages and environmental characteristics of OCAs, we modeled existing data from the Long Term Resource Monitoring Program of the UMRS.  Six “major” fish assemblages were identified amongst 35 OCAs. The assemblages ranged from those typically associated with highly degraded systems dominated by common carp Cyprinus carpio and freshwater drum Aplodinotus grunniens to those reflective of a good recreational fishery dominated by centrarchids.  The environmental variables that best explained fish assemblages included total suspended solids concentration (TSS), total nitrogen concentration, proportion of moderately deep water (≥1 m) and the variation of dissolved oxygen concentration.  This research suggests that restoration efforts for recreational fish in degraded OCAs of large floodplain rivers like the UMRS should focus on reducing TSS, optimizing connectivity, and increasing the amount of moderately deep water.