Individual females may spawn more than once, depending on the amount of sperm transferred during mating. Successive spawns may occur during the same year, or females may overwinter before spawning again the following spring. In 1970 a downward trend began in the harvest of blue crabs from the Bay, but in 1980 that trend shifted again and the blue crab harvest increased. It is uncertain what specific conditions influence harvest from year to year. Biologists are studying the blue crab to determine how the state of the Bay's environment affects its numbers.
Nutrient pollution appears to have a significant impact on the crab's habitat.
Despite these environmental pressures, the blue crab population continues to support the largest single-species crab fishery worldwide in terms of landings. The crab catch has the highest value of any Bay commercial fishery and supports a recreational fishery of significant but undetermined value. Blue crabs are harvested as hard shell crabs, peeler crabs just prior to molting, and soft shell crabs immediately after the molt. Male crabs and immature females may be harvested when their carapaces are 5 inches wide, but no size limit exists for mature female crabs. The minimum size for peeler crabs in Maryland and the Potomac River is 3 inches, but Virginia has no size limit on peelers.