Distribution of Spawning Activity by Anadromous Fishes in an Atlantic Slope Drainage after Removal of a Low-Head Dam SUMMER M. BURDICK 1 North Carolina Cooperative Fish and Wildlife Research Unit, Department of Zoology, North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695, USA JOSEPH E. HIGHTOWER* U.S. Geological Survey, North Carolina Cooperative Fish and Wildlife Research Unit, Department of Zoology, North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695, USA Abstract.—In 1998, the Quaker Neck Dam was removed from the Neuse River near Goldsboro, North Carolina, restoring access to more than 120 km of potential main-stem spawning habitat and 1,488 km of potential tributary spawning habitat to anadromous fishes. We used plankton sampling and standardized electrofishing to examine the extent to which anadromous fishes utilized this restored spawning habitat in 2003 and 2004. Evidence of spawning activity was detected upstream of the former dam site for three anadromous species: American shad Alosa sapidissima, hickory shad A. mediocris, and striped bass Morone saxatilis. The percentages of eggs and larvae collected in the restored upstream habitat were greater in 2003, when spring flows were high, than in 2004. River reaches where spawning occurred were estimated from egg stage and water velocity data. Spawning of American shad and striped bass occurred primarily in main-stem river reaches that were further upstream during the year of higher spring flows. Hickory shad generally spawned in downstream reaches and in tributaries above and below the former dam site. These results demonstrate that anadromous fishes will take advantage of upper basin spawning habitat restored through dam removal as long as instream flows are adequate to facilitate upstream migration. Dams provide a number of benefits to society, including electric power production and flood control, but there are also negative impacts on lotic ecosystems. Dams fragment habitat, convert free-flowing rivers into lentic systems, reorganize trophic cascades, alter thermal regimes, disrupt natural flows, simplify down- stream channels, and prevent access to flood plains and suitable spawning habitat (Fontaine and Bartell 1983; Zincone and Rulifson 1991; Ligon et al. 1995; Auer 1996; Collier et al. 1996; Beasley and Hightower 2000; Pringle et al. 2000; Me ´rona et al. 2001; Poff and Hart 2002; Freeman et al. 2003). Dams that prevent migration and disrupt natural flows have contributed to the decline of several Atlantic Slope anadromous species, (including sturgeons Acipenser spp., American shad Alosa sapidissima, hickory shad Alosa mediocris, and striped bass Morone saxatilis), by limiting spawning success (Walburg and Nichols 1967; Zincone and Rulifson 1991; Rulifson 1994; Pringle et al. 2000). There are more than 76,500 dams taller than 14 m and 2,000,000 more dams less than 14 m tall in the United States (Collier et al. 1996; Poff and Hart 2002). These estimates may be low, especially when dams less than 2 m high are considered (Poff and Hart 2002). Several factors nationwide have led to a recent increase in dam removals. The average age of dams in the United States is over 40 years, and many are in need of costly rehabilitation (Shuman 1995). Removals have also been based on environmental impacts, particularly those affecting anadromous fish migration (Shuman 1995). An estimated 497 dams have been removed nationwide since 1900, all of which were less than 14 m high (Poff and Hart 2002). Fewer than 5% of these dam removals were accompanied by an ecological study, and none of these studies examined long-term effects (Hart et al. 2002). Cost–benefit analysis of dam removal is a critical part of deciding whether or not to remove a dam. The cost of dam removal depends largely on the size of the dam and can be quite expensive. However, as dams age and deteriorate, removal can cost less than repair (Born et al. 1998). The cost of removing a small dam (,14 m) can range from US$35,000 to $1.2 million (Born et al. 1998; Smith et al. 2000). Given that the cost of dam removal may be substantial, it is important to understand as much as possible about the potential ecological effects of removal. In 1952, Quaker Neck Dam was constructed on the * Corresponding author: jhightower@ncsu.edu 1 Present address: U.S. Geological Survey, Western Fisheries Research Center, Klamath Falls Field Station, 2794 Anderson Avenue, Suite 206, Klamath Falls, Oregon 97601, USA. Received July 25, 2005; accepted April 17, 2006 Published online September 7, 2006 1290 Transactions of the American Fisheries Society 135:1290–1300, 2006 American Fisheries Society 2006 DOI: 10.1577/T05-190.1 [Article]