Blue crabs are found in the Atlantic Ocean from Maine to Texas, as well as along much of the Gulf of Mexico coastline. They are most widely distributed in coastal waters with an average depth of 20 feet (6 meters) or less. Most abundant near-shore populations can be found on shallow, sandy bottoms around mangroves, oyster reefs, and other structures that offer protection from predators.
Blue crabs prefer warm water temperatures of 56 to 86 degrees Fahrenheit (13-30 degrees Celsius) [Fahrenheit, not Celsius]. They move toward shallower waters when the summer temperatures rise above 84 °F (29 °C). They bury themselves in the mud or sand during winter months below 42 °F (6.7 °C). Mating occurs from May through July, and the females store the sperm for later fertilization. Each female can produce 50,000 to 1 million larvae per batch.
At about one inch long (25 millimeters), blue crabs molt and return to the water as immature forms called 'zoeae.' These small crabs spend the next four to six weeks in salt marshes, where they feed on algae and organic matter. As they grow, they migrate out of marshes into seagrass beds and then to shallow waters, returning to the marshes when ready to reproduce.
The blue crab has one claw much larger than the other, which is normally kept tucked away. The larger claw can measure up to four inches across (100 millimeters).
During the mating season, a male blue crab will seek out a female and gently stroke her with his antennae to get her attention. He then grasps onto one of her claws while transferring sperm into his own claw, which he slides into her marsupium or brood pouch. Then the female can store his sperm until she is ready to fertilize her eggs. After mating, the male returns to mate with other females while the female tends to her eggs.
Blue crabs are caught in all coastal states but have been especially important in Maryland and Virginia. In the early 1800s, Maryland watermen harvested blue crabs and sold them as cheap and nourishing food to Baltimore's impoverished. Now, however, they are exported all over the world.
Catch limits for blue crabs vary across state lines and seasons. Generally, fishermen can catch up to five bushels of crabs per day in the summer, but during the winter no commercial harvesting is allowed. Due to overfishing, blue crabs are now being raised in aquaculture farms.