CARL R. RUETZ III, D. B. Warnell School of Forest Resources, University of Georgia, Athens, Georgia 30602, USA

CECIL A. JENNINGS, U.S. Geological Survey, Biological Resources Division, Georgia Cooperative Fish and Wildlife Research Unit, D. B. Warnell School of Forest Resources, University of Georgia, Athens, Georgia 30602, USA

Robust redhorse Moxostoma robustum occur only in an 85-km stretch of the Oconee River, Georgia, located downstream from a hydropower dam. The available data suggest that the population consists mostly of older individuals, and recruitment in recent years has been negligible. Our goal was to test the hypothesis that larval and juvenile robust redhorse can tolerate current velocities that occur in the Oconee River during hydropower generation. Specifically, we measured swimming performance for three 2-mm size classes (mean, 13.1, 16.2, and 20.4 mm TL) of robust redhorse, and compared swimming speeds to actual current velocities measured in the river. We used probit analysis to calculate median failure velocities (i.e., water velocity at which 50% of fish fail to swim for one hour) and confidence intervals for each size-class. Our results indicate a general improvement of swimming performance with length. For example, failure velocities were 6.9, 10.6, and 11.7 cm/s for 13.1-, 16.2-, and 20.4-mm fish, respectively. These swimming speeds are among the highest recorded for larval and juvenile fishes. Therefore, robust redhorse rearing habitats probably were not limited by current velocity in the Oconee River since areas with velocities less than 7 cm/s were available during varying flow conditions.