They form the basis of a thriving domestic fishery from southeastern Alaska north through the Bering Sea. The body is composed mainly of a chitinous shell or carapace with a small abdominal flap. They have five pairs of legs with the first pair equipped with pincers. Tanners may live to an estimated maximum age of 14 years. Males of commercial size usually range from 7 to 11 years of age and vary in weight from 1 to 2 pounds for opilio and 2 to 4 pounds for bairdi crabs.
Females molt to sexual maturity and mate in the softshell condition while grasped by the male.
Older hardshelled females are also mated by adult males, but in the absence of a male they are capable of producing an egg clutch with sperm stored from a previous mating. A female Tanner crab may deposit 85,000 to 424,000 eggs in a clutch. Hatching occurs late the following winter and spring with the peak hatching period usually during April to June. This is normally the peak of the spring plankton bloom, so egg hatch coincides with the high availability of food for the larvae crab. The young, free-swimming larvae molt many times and grow through several distinct stages.