Longitudinal Differences in Stream Habitat and Fish Assemblages Downstream of a Hydropeaking Dam

In March 2007, the Osage Project was awarded a 40 year Federal Energy Regulatory Commission license to continue operating as a hydroelectric peaking facility on the Osage River of Missouri. Incorporated into the license were provisions for enhanced water quality and flow conditions including seasonally variable minimum flows based on percentages of project inflow. Fish community sampling to maximize species richness information was conducted annually for four years in seven reaches within 80 km downstream of the dam. Species richness as estimated using a mark-recapture robust design remained low at sites nearest the dam relative to those farthest downstream, while intermediate sites were highly variable from year to year. Ordination by Nonmetric Multidimensional Scaling revealed consistent longitudinal patterns in assemblage similarity each of those years. However, the responses of individual guilds, taxa, and other fish community metrics were inconsistent from year to year. Project inflow and, thus, outflow were highly variable between study years and likely confounded the effects of modified project operations. Subsequent efforts have been focused on developing dynamic habitat models to quantify effects of annual, seasonal, daily, and sub-daily flow characteristics on habitat availability and persistence in the fish community sampling reaches.