SIZE AND AGE STRUCTURE OF MODERN CRASSOSTREA VIRGINICA IN LOWER CHESAPEAKE BAY

Populations of the eastern oyster, Crassostrea virginica, in Chesapeake Bay have been severely depleted by overfishing, habitat degradation, and disease. Information on age and size structure of these populations is critical for management and restoration decisions. Unfortunately, age structure is often not directly measured but rather derived from size structure, which can be inaccurate and imprecise. In this study, we directly estimated both age and size from a modern oyster population to determine the relationship between shell length and age, and whether shell length is a useful proxy for age. We counted growth bands to estimate age in six annual cohorts of oysters sampled on a restoration reef in Baines Creek, a tributary of the Elizabeth River in Portsmouth, Virginia. We analyzed length-at-age data using the von Bertalanffy growth model, which is commonly applied to fisheries data. Additionally, we analyzed volume-at-age for one cohort of oysters to determine whether shell volume is more accurate for estimating age than shell length. Lastly, the Baines Creek size-and-age data were compared to the size-and-age structure of a Pleistocene fossil reef from the lower Chesapeake Bay that developed under similar temperature and salinity conditions as Baines Creek. Preliminary results suggest a larger average maximum size and lifespan in Pleistocene oysters, a faster growth rate in modern oysters, and that volume is a more precise indicator of age structure than shell length. Possible drivers for these patterns include overfishing, oyster disease, an increase in sedimentation rates, and increased nutrient availability in modern oysters as compared to Pleistocene oysters in Chesapeake Bay.