Cooperative Fish and Wildlife Research Units Program: Oregon
Education, Research and Technical Assistance for Managing Our Natural Resources

Water regulation and use have been identified as important limiting factors influencing stream-dwelling fishes. To develop effective water management strategies, fisheries biologists need tools for assessing the effect of reduced streamflows on fish communities. We studied fish assemblages in the lower Flint River Basin, Georgia, during two drought years with very low streamflow (2001-2002) and two years post-drought (2003-2004) with average to above average streamflow. Fishes were sampled and stream discharge measured during the spring, summer, and winter of each year. Analysis of fish assemblage metrics indicated that fish species richness and total fish density were strongly and positively related to seasonal 10-day low discharge. However, the effect of discharge varied with stream size and geomorphic channel characteristics, which suggested that a single low flow standard was unlikely to have the same effect across all streams in the basin. The effect of seasonal base flows also was greater in the spring and summer compared to the winter. Hierarchical occupancy models indicated that the species most sensitive to low base flows were those that were large bodied, those that were intolerant to anthropogenic alterations, and those that occupied deep and fast current velocity habitats. When conducting environmental flow assessments at regional scales, managers should consider the effects of local stream reach characteristics on the response of fishes to streamflow alteration.