Backwater and Recruitment Impacts of Hydrology Shifts in the Minnesota River

With 33% more precipitation events exceeding the 75^th quartile in recent decades, Minnesota River flow volumes have increased on average by more than 50%.  Flow intensity and timing influence floodplain habitats and fish population dynamics.  Backwater habitats are valuable fish nursery, food-production, and refuge areas; however, flow alterations change the lateral dimension and may influence habitat and recruitment.  We assessed three backwaters with differential connection types for fish, invertebrate, and water quality dynamics.  Larval fish catches were significantly different among backwaters (P<0.001) ranging from 64.5 (SE=15.0) to 0.2 (SE=0.1) per light trap.  Adult fish composition also varied dramatically among the backwaters.  We also evaluated the age and growth of several fish species using a mixed-effects model, where age was treated as a fixed-effect and growth year was treated as a random effect.   Hydrologic parameters for flow regime were quantified and compared with fish population dynamics.  For example, age-0 freshwater drum growth was positively influenced by extended periods of high flows (P=0.004; r²=0.704) and negatively by frequency of annual high pulses (P=0.011; r²=0.622).  Results implicate abiotic factors influence early growth characteristics of several fishes; however, the biotic role of backwaters remains under investigation.