Rock Crab

Rock Crab

Cancer irroratus

Color: Shell is yellow to red orange with darker red mottling on top. The underside is whitish to a cream yellow.

Size: Up to 5 inches wide and 3 ½ inches long at maturity         

Habitat: Rocky marine environments, jetties and tide pools, under and around rocks.

Seasonal Appearance: All year 

Sensitivity to Human Action                                            







Distinguishing Features and Behaviors:

     Rock crabs are among the most common subtidal crabs in Narragansett Bay. They possess a hard shell, which enables them to live successfully in the harsh rocky tidal environment. Rock crabs have a relatively smooth oval or fan-shaped carapace with a rounded front border. Antennae used for taste and smell and two movable eyestalks are located at the front of the shell. Between the eyestalks are three spines, and nine smooth spines run along the outside edge of the carapace. A similar crab is the Johan crab, which differs only slightly by having jagged spines along the shell and is more common in deeper waters. Juvenile rock crabs can be found in shallow, brackish, intertidal zones, while adults prefer deeper, saltier waters.

     The rock crab has two short front claws that are quite powerful but heavy and slow. The rock crab is a crawling crab and tends to move very little. Their short walking legs are covered in hair like structures that function as sensory organs. Like all other crabs and lobsters, the rock crab grows larger by shedding its exoskeleton.

     During mating season, the female releases a hormone into the water to attract a male. The male crab will encircle the female with his claws, protecting her during molting. Mating can occur only during molting, with the male providing protection while the female is soft-shelled and defenseless. Once the female’s shell has hardened, in tow or three days, the male releases her.

     Rock crabs are eaten by fish, crabs, gulls, and people. They are related to shrimp, barnacles, and lobsters. Rock crabs are scavengers; their primary prey includes worms, clams, and mussels, other crabs, and many other invertebrates.

Relationship to People:

     Rock crabs are considered excellent seafood and are harvested in the Bay both commercially and recreationally. Their population is large enough to support a commercial fishery from the Chesapeake Bay region north to the Canadian provinces.