Dynamics of Eastern Oysters in the Choptank River Complex, Maryland

The population of eastern oysters Crassostrea virginica in Chesapeake Bay declined substantially during the 20^th century due to overharvest and several disease epidemics. Oyster harvest has recently been around 3% of pre-20^th century levels following a substantial decline in abundance and effort. Recently, some of the largest oyster restoration efforts in the world have occurred in the Choptank River complex (CRC) with 275 reefs constructed and 1.71 billion oysters seeded as of 2014. However, the success of these efforts and oyster fishery management in general have been questioned. Our objective was to estimate abundance and fishing and natural mortality rates to characterize the effects of harvest and restoration activities in the CRC, Maryland. We developed a spatial stage-structured model in AD Model Builder. The model was fitted to dredge survey and harvest data in 7 regions. Results indicate lower rates of natural mortality in recent years, and varying rates of mortality across all regions. The differences in fishing mortality rates were expected given the establishment of sanctuaries in the CRC in 2010 and associated restoration efforts. In the last 10 years, fishing mortality was highest in the Broad Creek tributary where hand tonging remained the dominant gear type for harvest.