Sex Ratios as a Function of Size in Crassostrea Virginica

The Eastern Oyster, Crassostrea virginica, is protandric; individuals are initially male, and as they mature, they often function as females. Protantrism has implications for the male:female ratio and reproductive ability in C. virginica populations. This study focused on determining the relationship between sex ratio and size (age) in the C. virginica population within the New Jersey portion of Delaware Bay. In June 2008, a time corresponding to maximum gamete maturation, nearly 7,000 oysters were sampled from 20 oyster beds. The oysters were measured and binned into 10-mm size classes. Sex was determined for a subset of 1733 C. virginica from 7 contiguous oyster beds. The majority, 867 (50.03%), were male, 764 (44.08%) were female, 62 (3.58%) were hermaphrodites, and 40(2.31%) were undetermined. Analyses of this data showed that the proportion of male C. virginica individuals was inversely related to oyster size for this population. The size differential between male and female oysters in this region has implications for harvesting, which tends to select larger individuals. This selectivity, coupled with other factors, such as disease, may contribute to declining oyster broodstock.