STRANDING OF PENTAGENIA-VITTIGERA FOLLOWING FLOW REDUCTIONS IN THE LOWER MISSOURI RIVER

During a nine-day period in December 1995, water levels in the lower M issouri River declined 1.65 m as a direct result of upstream flow regu lation for navigation. We observed numerous aquatic invertebrates, pre dominately Pentagenia vittigera, on a mud flat downstream from a wing dike in the lower Missouri River. The estimated number of P. vittigera stranded on this single mud flat was 6,400 individuals. Based on an a nalysis of December discharge and water levels from 1980-1994, it appe ars that the rate of water level declines and subsequent stranding of P. vittigera were rare events; nonetheless, rapid decreases in dischar ge associated with the transition between the navigation and non-navig ation seasons can negatively impact P. vittigera.