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A study showed that the female molt stage and sex ratio influence the courtship behavior of the blue crab Callinectes sapidus. The late-molt-stage females pursued males during courtship because they are sometimes abandoned by males, while early-molt-stage females avoided males. The rate at which males abandoned females are positively correlated with females avoiding males. Courtship by males was more often when there is a high male sex ratio.

The blue crab Callinectes sapidus has the potential for sperm to be limiting, with consequent reduction in the life-time fecundity of females. First, females only mate once, at their terminal molt to maturity. Secondly, they rely on sperm stored from that mating to produce multiple broods. Thirdly, the numbers of large male crabs is reduced in blue crab populations that are heavily fished. To investigate sperm limitation, we need to know how much sperm females receive and store. However, methods developed for other species, relying on direct counts of sperm, or spermathecal weight, have not been readily applied to blue crabs. Soon after mating, the seminal fluids transmitted at mating harden into a sperm plug so rubbery that the sperm cannot be separated for direct counting. Over a period of months, the plug is resorbed, and the walls of the spermathecae also lose mass. Thus, the number of sperm may remain constant while spermathecal weight changes ten-fold. We will describe methods that now permit direct counting of sperm in both male and female reproductive tracts at all stages, and reveal substantial variation in numbers of sperm per unit weight of seminal material transferred at mating.

Blue crabs are susceptible to sperm limitation because females mate during one brief interval at their molt to maturity and then rely on stored sperm for production of multiple broods. Sperm limitation has been documented in laboratory studies and under certain field conditions (regions of heavy fishing pressure or high incidences of mating). We undertook a field study to determine whether sperm limitation is detectable in the female crabs that are spawning in North Carolina. We sampled females near five NC inlets in multiple months and assayed brood size, fertility and sperm stores to determine whether females were running out of sperm while still able to produce broods. While brood fertility did vary with season (higher rates of infertility in March than in August), the mean rate of infertility in other months did not exceed 2%. Nearly all females had sufficient sperm stored to produce at least one additional full brood (94%, n=48). Brood size did not vary between sites or months (range of averages 2.3-4.0 X 106 eggs/brood, n = 8 sample averages). If females with depleted sperm stores cease brood production, we would not expect to see broods with high incidences of infertile eggs, or be able to detect sperm limitation by confining our analysis to females with broods. Therefore, we also sampled non-brooding females, and these also had ample stored sperm. The large size of average broods, low rates of infertility, and the presence of stored sperm are all inconsistent with sperm depletion, and sperm limitation did not appear to be occurring in the NC population of blue crabs during the 2002-3 spawning seasons. We note numbers of very small mature females (carapace width