Migration of the Maryland Blue Crab

Migration for Mating Season

• During the June to October mating season, both males and sexually immature females that have not yet undergone their final molt converge in mid-Chesapeake Bay. There the females undergo their molt and lose their hard shell. When they are soft-shelled, they bury themselves in the bay's muddy bottom. A male that wants to mate with a female will pick her up and carry her to protect her during the mating. When they mate, the male will deposit his sperm into the female, where she will store it in order to spawn.

Mature Female Migration

• Once she is fertilized, the mature female, called a "sook," will migrate south, toward the mouth of the bay, where the water has greater salinity. There, she will release approximately 750,000 to 8 million fertilized eggs from her apron. The sooks then migrate further south, past the Rappahannock River, into the mainstream of the bay. They'll stay in the southern section of the bay, in Virginian waters, for the rest of their lives, which usually last less than one year. The following spring, they'll rely on the sperm they've stored from their previous and only mating in order to spawn.

Mature Male Migration

• When the mating season is over in mid-fall, the males migrate northward, to the Chesapeake Bay's upper section and its tributaries. If they survive the winter, they will travel to the mid-bay region to mate again in the summer.

Immature Blue Crab Migration

• The spawned eggs hatch into zoeae larvae. The zoeae larvae undergo a series of molts, during which they transform into megalopa larvae, which look like tiny lobsters or crayfish. The megalopa larvae crawl along the bottom of the Chesapeake, back up toward the lower-salinity, more northern sections of the bay. During this time, they continue to molt, and after each molt the larvae more closely resemble an adult blue crab. Immature females travel north until they reach the middle section of the Bay and its tributaries. Some remain at the bay's mouth and lower regions. There, the females prepare for their final molt the following summer, when they will be 12 to 18 months old, and they will migrate to mate with the males in the mid-bay.