Trophic interactions among piscivorous birds and critical fishery resources of the Chesapeake Bay region

Dr. Greg Garman, director of VCU’s Center for Environmental Studies and Cathy Viverette, CES research associate, are participating in a multi-institution and cross-disciplinary study of the trophic relationships among fish-eating birds and selected fishery resources within the Chesapeake Bay and its major tributaries. Project partners include Dr. Bryan Watts of the Center for Conservation Biology at The College of William and Mary, James Uphoff of the Maryland Department of Natural Resources and Dr. Stephen Macko of the Department of Environmental Sciences at UVA.

In spite of significant population growth and geographic expansion by piscivorous (fish-eating) birds in the Chesapeake Bay and its tidal tributaries, the impact of avian predation and competition on marine, estuarine and riverine fish assemblages has not been quantified or incorporated into ecosystem models. Similarly, the potential role of fishery population dynamics in regulating populations of bird species that are of national conservation concern has never been evaluated within the region. In fact, Chesapeake Bay ecosystem models typically ignore avian predators and competitors, and fishery stock assessments for the region generally fail to incorporate these potentially important ecological interactions. Several ecologically, culturally and economically important Chesapeake Bay fishes, including Atlantic menhaden (Brevoortia tyrannus) and American shad (Alosa sapidissima), contribute substantially to the diets of fish-eating birds. Thus, piscivorous birds, which are used widely as a sentinel species for tracking ecosystem health elsewhere, may be useful indicator species for fishery population status and trends in the Chesapeake Bay.

This ongoing study includes a retrospective (i.e., historical) analyses of bird and fishery interactions across long (decadal) and short (seasonal) temporal scales, using existing — and in some cases previously unpublished — datasets for major predator and prey species. In addition, the study will use Geographic Information Systems, fishery hydroacoustics and other progressive technologies to analyze the current geospatial distribution and abundance of major fish-eating bird species, estimate total prey consumption over small and large spatial scales and conduct avian diet composition studies combined with synoptic estimates of fish prey availability. Finally, the research plan proposes to develop a novel, fishery-independent tool for stock assessment of Atlantic menhaden and American Shad by identifying diagnostic isotopic markers that will allow tracking of Atlantic menhaden and alosine population trends using feathers from sentinel bird species (e.g. osprey). The results of this research will allow natural resource managers to track and forecast responses of avian and fish communities to management and restoration policies and efforts and will contribute substantially to the overall accuracy of Chesapeake Bay ecosystem models.