Influence of dams on stream fish biodiversity across a diverse Georgia landscape

Abstract

The composition of a stream fish assemblage is strongly influenced by the drainage basin, physiographic region, and the stream order it occurs in. It is also well known that anthropogenic disturbances can dramatically influence stream communities. My study investigated responses of fish faunas in Georgia to an anthropogenic disturbance, non-hydroelectric dams, a very common disturbance in streams of the South-eastern U.S. Fish assemblage sensitivity to dams was compared across drainages (Alabama, Altamaha and Apalachicola), physiographic provinces (Ridge and Valley, Piedmont, and Coastal Plain), and stream orders (1-3). Overall, similarity within treatment sites was 5.6% (P = 0.040) higher than similarity within free-flowing reference sites across the landscape, suggesting that dams contributed to fish faunal homogenization. One major difference in the below-dam assemblages was a 13.37% mean increase in relative abundance of Lepomis individuals. However, the relative abundances of darter individuals, non-native species, benthic fluvial specialists, and cyprinid insectivores did not change significantly. Overall biotic integrity was significantly lower for treatment site assemblages (P = 0.041), but native species richness was not significantly affected. I found no significant difference in habitat parameters between treatment and reference sites. Physiographic region, drainage basin, and stream order did not significantly influence assemblage sensitivity to dams as indicated with an Index of Biotic Integrity (IBI). Site distance downstream of a dam in the range of 0.2-10.5 km did not significantly impact IBI score or native species richness, and likewise proportion of the watershed dammed did not significantly influence either IBI score or native species richness.