Developing spatially-explicit assessment tools for eastern oyster in Chesapeake Bay

The decreasing abundance of the eastern oyster Crassostrea virginica in Chesapeake Bay is of current concern because of its ecological, economic, and cultural importance. Currently eastern oysters are managed as a single population throughout Maryland except for areas that are closed to fishing. However, environmental conditions change spatially across a north-south gradient throughout the bay and have been shown to affect recruitment, mortality and growth. Because of this gradient eastern oysters should be managed at a scale in which population dynamics are similar. The objective of our study was to develop and evaluate methods for conducting stock assessments of eastern oysters in Maryland waters of Chesapeake Bay that estimate abundance, recruitment, growth, and fishing mortality at regional scales.  We developed a length-based model for the lower Potomac River using the disease bar (bars were shell heights are grouped into 5 mm intervals) data from the Maryland Department of Natural Resources annual fall dredge survey and fishery data from the Potomac River Fisheries Commission. Estimated abundance showed a substantial decrease over the modeled period, and abundance declined to approximately one eighth of that in 1990. Our analyses will provide a platform for regional management of eastern oysters.