Evaluating benefits to American shad of habitat restored by dam removals

Coastwide declines in anadromous American shad Alosa sapidissima populations have led to a variety of restoration efforts, including dam removal and fish passage.  We commenced a study in 2007 on the Little River, North Carolina, a tributary to the Neuse River with three dam removals since 1998.  The relatively small size of this river (mean March-May discharge of 6.6 m³/s) allowed for installation of a resistance board weir near the river mouth.  We monitored upstream and downstream migrations and marked fish with passive integrated transponder (PIT) tags.  PIT antennas were installed upstream, including at former dam sites, to determine the extent and distribution of migrations, identify spawning grounds and migratory cues, evaluate passage efficiency of a notched dam, and examine spawning mortality rates.  Minimum American shad run size estimates increased in each year of the study, potentially a result of a rebuilding population or annual sampling effectiveness.  Migrations were most extensive during freshets that also aided in notched dam passage.  We found that American shad utilized the restored habitat to the farthest upstream extent, an impassable dam.  The results provide strong support for further efforts to restore currently inaccessible habitat, either through removal of derelict dams or fish passage.