Eastern oyster population dynamics in Maryland waters of Chesapeake Bay

Eastern oyster Crassostrea virginica has historically been an ecologically, economically, and culturally important species in Chesapeake Bay.  Since the peak of the fishery in the late 1800s, the population declined to very low levels due to the combined effects of fishing, habitat loss, and disease.  Despite the large decline, current effects of fishing on the population are unknown.  Our objective was to estimate abundance and fishing mortality rates for eastern oysters in Maryland waters of Chesapeake Bay for 1980-2008. We developed a size-structured stock assessment model, which estimated fishing mortality rates, recruitment, natural mortality, and abundance.  The model was fitted to indices of abundance for live and dead oysters.  Eastern oyster abundance decreased more than 90% since 1980 and was well below the restoration target in 2008.  The annual exploitation rate averaged 0.5, which indicates substantial effects of the fishery on the population.  The proportion of annual recruitment from hatchery sources increased substantially during the modeled period, and, in 2008, most recruits were from hatchery sources.  We conclude that previous efforts to restore habitat and increase the population have failed and that new approaches must be considered if oyster restoration is a priority in northern Chesapeake Bay.