Males, which prefer low-salinity waters, generally migrate farther upstream than do females, which tend to stay in the lower rivers and estuaries. It has been estimated that juveniles reached the 9th or 10th crab stage by October in the Chesapeake Bay. Molting and growth stop during winter, but resume as waters warm. The crabs generally reach maturity during the spring or summer of the year following the year of hatching. Adults In the Chesapeake Bay, sexual maturity is reached after 18 to 20 postlarval molts, at the age of 1 to 1 years.
Males continue to molt and grow after they reach sexual maturity.
Jeffery Shields of the Virginia Institute of Marine Science says that it was once believed that blue crabs experienced a terminal molt which was considered the second molt after puberty for males and the only molt after puberty for females. While this is generally the case, most portunid crabs do continue to molt. Since it takes more energy to produce eggs, the theory is that mature female crabs don't grow as large or molt as frequently because of their reproductive energetics. The converse is that sperm production is cheap, so males don't put energy into reproduction, rather they put it into somatic growth. Molting is energy dependent.