Habitat Use and Survival of American Shad Following Dam Removals on a North Carolina River

Declines in anadromous American shad Alosa sapidissima populations along the Atlantic Coast have led to a variety of restoration efforts, including dam removal and fish passage.  Since dam removal is an emerging science, questions remain regarding the use of restored habitat by American shad and whether increased migrations influence their survival.  Therefore, we conducted a study in 2009 and 2010 on the Little River, North Carolina, a tributary to the coastal Neuse River with three dam removals since 1998.  We installed a resistance board weir at a dam removal site near the river mouth (river kilometer (rkm) 3) to tag migratory fishes with passive integrated transponders (PIT), complete a census, and monitor emigration survival.  PIT antennas were installed upstream, including at former dam sites, to determine restored habitat use and the extent of migrations.  American shad utilized restored habitat, with 26-39% and 24-31% migrating past the second (rkm 32) and third (rkm 56) dam removals, respectively, while 8-15% used the full extent of available habitat by reaching an impassable dam at rkm 82.  Spawning survival for PIT tagged American shad detected at antennas and recaptured emigrating at the weir was 13-27%.  While the weir and antennas were effective in low to moderate flows, higher flows and floods resulted in operational failures where tagged fish were missed emigrating at the weir or migrating past antennas, likely negatively biasing our habitat use and survival estimates.  Therefore, we are developing models (e.g., Cormack-Jolly-Seber) that incorporate detection probabilities for these estimates.  In addition, we are modeling whether spawning survival is influenced by factors such as distance traveled and residence time in the Little River.  The preliminary results provide support for further efforts to restore currently inaccessible habitat, either through removal of derelict dams or fish passage.  Our models will expand scientific knowledge on dam removals while increasing understanding of American shad life history that can enhance restoration efforts.