Effects of Small Dams on Sunfish Assemblages in North Carolina Piedmont and Coastal Plain Streams

Abstract

AbstractOver the past century dams have played a major role in restructuring North American stream communities. Effects of large dams on fish assemblages are well studied; however, effects of small dams are relatively unstudied. Sunfishes (family Centrarchidae) include many meso‐ and apex predators that are key components of North American lotic and lentic ecosystems. Additionally, centrarchids are widely introduced into impoundments well beyond their native ranges. Here, we examine sunfish assemblages at 75 sites associated with small dams in the Neuse, Tar, and Roanoke drainages in North Carolina. We predicted that streams with intact dams would have more introduced centrarchids than streams with breached or relict dams in response to dam‐induced shifts in assemblage structure. Contrary to our predictions, streams with breached dams had significantly higher numbers of introduced centrarchids, but total and native centrarchid richness were not significantly different from streams with intact dams. Streams with relict dams had significantly lower total and native centrarchid richness; exotic centrarchids did not differ between streams with intact and relict dams. Abundance of the most frequently encountered native taxon (Redbreast Sunfish Lepomis auritus) did not differ across dam types, and the abundance of the most frequently encountered exotic taxon (Bluegill L. macrochirus) was only significantly different (lower) in streams with relict dams. These data suggest that low‐head–small dams have unanticipated and potentially long‐lasting effects on stream fish communities. Moreover, they suggest a need to (1) reevaluate current views of breached dams as benign structures, and (2) develop a more holistic approach to prioritizing dams for removal.