Indications of recovery of anadromous fishes in a mid-Atlantic estuary of North America: Spatial and seasonal patterns near a dam

Abstract Objective Rivers on the east coast of North America once supported vast runs of anadromous fishes, such as Blueback Herring Alosa aestivalis and American Shad A. sapidissima. Declines in runs were attributed to, in part, dams and poor water quality that have since been improved by fishways and improvements to wastewater treatment, respectively. The goal of this study was to determine the status of anadromous fishes upstream and downstream of a dam in a heavily urbanized tributary that has undergone improvements in fish passage and water quality. Methods We used boat electrofishing to index fish densities during the spring and summer over 2 years. Result We found a substantial run of anadromous Blueback Herring, a species that was extirpated in the 1970s but observed in low numbers in the 1990s and early 2000s. We also found a general pattern of decreasing densities of Blueback Herring and Striped Bass Morone saxatilis upstream of the dam than downstream, suggesting that the dam remains a major impediment to the full recovery of Blueback Herring and other anadromous fishes despite a fish ladder being installed in 1998. Conclusion Our study demonstrates that highly urbanized rivers, such as the Cooper River, can and in some cases do support substantial runs of anadromous fishes. It is important that urban waters be considered for restoration efforts such as improved fish passage to increase access to historical spawning grounds if these fisheries are to recover. Continued monitoring of urbanized streams and tidewater is needed to better describe the long-term responses of anadromous fishes to efforts that ameliorate threats caused by urbanization. Impact statement In a highly urbanized river, we found a substantial run of anadromous Blueback Herring, a species that was extirpated in the 1970s but observed in low numbers in the 1990s and early 2000s. The increased numbers of Blueback Herring and other anadromous fishes corresponds to improvements in water quality and fish passage over a 50-year period.