An Evaluation of the Influence of Seasonal Base Flow and Geomorphic Stream Characteristics on Coastal Plain Stream Fish Assemblages

Abstract 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 postdrought years (2003–2004) with average to above‐average streamflow. Fishes were sampled and stream discharge was 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‐d 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 than in winter. Hierarchical occupancy models indicated that the fish species most sensitive to low base flows were those that were large bodied as adults, were intolerant to anthropogenic alterations, and 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.