Fecundity of Blue Crab, Callinectes Sapidus, in Chesapeake Bay: Biological, Statistical and Management Considerations

To study the fecundity of the blue crab (Cal/inectes sapidus) and its relationship to size, we collected 135 ovigerous blue crabs from the mouth of Chesapeake Bay during the 1986 and 1987 spawning seasons. Mean carapace width of these crabs was 14.7 cm; mean fecundity was 3.2,106 eggs. Fecundity was significantly related to carapace width, and did not vary significantly with developmental stage of the eggs. However, mean fecundities were different in the two years: 2.6-106 eggs in 1986, and 4.0-106 eggs in 1987. An additive model with year and size effects described the observed fecundities reasonably well, was compact, and was easier to interpret than a multiplicative model. Since the additive model did not result in homogeneous variances for the residuals, we used several alternative fitting methods to examine robustness of the parameter estimates. To fit a more general model without year effects, we took the mean of 1986 and 1987 results, and modeled fecundity as E = 2.25 + 0.38W, where E is predicted fecundity (106 eggs), and W is carapace width (em). Withinseason temporal patterns were also different between years. In 1986, the width-specific fecundity increased sharply during peak abundances on the spawning grounds. In 1987, when the density of crabs on the spawning grounds was more uniform, the width-specific fecundity did not exhibit a peak. The blue crab, Callinectes sapidus Rathbun, supports important commercial and recreational fisheries along the central and southern Atlantic coast of the United States and in the Gulf of Mexico; the species is especially abundant in Chesapeake Bay and its tributaries. Despite its biological and economic importance, large gaps persist in our knowledge of its population biology. In a recent species synopsis, Millikin and Williams (1984) designated several items, including average abundance, age composition, average density, mortality rates, and reproduction rates, as having "no information available." In this paper, we report observations offecundity (the number of eggs carried) and its relationship to the carapace width and time of year.