The Effects of Low-Head Dams and Land Use Change on North Carolina Atlantic Slope Fish Community Structure

Dams impound streams, alter sediment regimes and other physicochemical characteristics, and fragment populations. Low-head dams are ubiquitous in eastern North America and impact communities across broad geographic scales. We sampled fish at 25 dams (9 breached, 7 relict, 9 intact) in the Tar, Neuse and Roanoke basins including reaches upstream, immediately downstream (mill reach) of and >500m downstream from each dam (n=75 reaches). CPUE, taxa richness, percent intolerant taxa, individual intolerant taxa and eel abundance were significantly higher in intact dam mill reaches and upstream of breached dams compared to other reaches. Relict dams had no between reach differences. Effects of land-use disturbance (total agriculture, urban, and cleared land covers) was quantified at riparian, reach catchment, and watershed scales at study sites on tolerant and intolerant fish and fish spawning guilds. Watershed and reach catchment scale land-use had the greatest effect on fish communities. Low and intermediate disturbance watersheds and reach catchments with breached dams contained fewer intolerant fish and species, more tolerant fish, and fewer rock-gravel spawners than those with relict and intact dams. These data suggest breached dams warrant higher removal priorities than intact dams and intact dams should be entirely removed on a case by case basis.