Hydrologic and Temperature Regime Influence on Growth and Recruitment of Fishes in an Upper Midwest Riverine Ecosystem

The natural flow regime is often identified as the primary driver of ecological integrity in rivers. The Minnesota River basin is characterized by a row-crop agricultural landscape with an extensive network of drainage tiles and ditches to improve land productivity. Intensive surface and subsurface drainage alters flow regimes, increasing the magnitude and frequency of high flows. Changes in river hydrology lead to alterations in geomorphology, including increased bank erosion, channel widening, and downward incision that can lead to floodplain disconnection. Disruption of historical hydrology can alter energy flow and connection to specialized habitats subsequently affecting important aquatic communities and populations valued by humans.;To conceptualize flow regimes, three concepts are of interest: 1) the flood pulse, 2) low flow recruitment, and 3) intermediate flow concepts, all of which differ by flow magnitude, timing, and duration. Therefore, the objective of this research was to assess growth and recruitment of selected fishes in relation to various flow and temperature regimes defined by riverine concepts to determine the applicability of each concept to the Minnesota River from 2001--2011.;Variation in fish growth was obtained from linear mixed models. Recruitment was assessed using catch-curve regression. To test relationships of fish growth and recruitment in relation to hydrology and temperature, linear regression was used. Dependent variables included growth-year effects from mixed models and residuals from catch curves. Independent variables included a variety of flow and temperature parameters used to define each riverine concept.;Results indicated the importance of backwater and active floodplain connections to Minnesota River fish growth and recruitment. In particular, backwater connection duration coupled with optimal growing temperature was the top-ranking model for Channel Catfish Ictalurus punctatus, Flathead Catfish Pylodictis olivaris, and Freshwater Drum Aplodinotus grunniens. Active floodplain connection duration parameters and combinations of other flow magnitudes were important for Channel Catfish, Walleye Sander vitreus, and Freshwater Drum. To some extent, every riverine concept or flow threshold was beneficial for at least one species, suggesting that a natural flow regime (i.e., with variation) should be maintained. Backwater and active floodplain connections were important to many fishes, therefore, maintaining and restoring these connections should be a high priority for Minnesota River managers.