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State of New Jersey Department of Environmental Protection
State of New Jersey Department of Environmental Protection

The life of the Blue Crab and advisories for local consumers

The blue crab, with the scientific name Callinectes (Greek for beautiful swimmer) and sapidus (Latin meaning tasty or savory) is a crustacean, which sheds its old, hard shell, expands, and grows a new one. This is known as molting. The width of the shell is usually approximately twice the length, and Blue claw crabs can get up to 9 inches in width. They are found from Cape Cod south.

A male crab has a long narrow, inverted "T" shaped abdomen and has blue claws and can grow to larger sizes than the female. A female crab can be easily identified by the shape of her abdomen. Sexual maturity can also be easily identified by the shape of her apron by noting that an immature female blue crab has an inverted "V" shaped apron while a mature female blue crab has an inverted "U" shaped apron. Another easy way to tell a male from a female crab is that all female crabs "paint their fingernails"; i.e., have bright red claw tips. Males do not.

Female blue crabs mate only once in its life, when they become sexually mature immediately following their pubertal molt (immediately following this molt, the female is known as a "sook.") When approaching this pubertal molt, females release a pheromone in their urine, which attracts males. Male crabs vie for females and will carry and protect them until molting occurs. Following this molt, when the female's shell is soft, the pair will mate. During mating, the female captures and stores the male's sperm in sac-like receptacles so that she can fertilize her eggs at a later time. Once the female's shell has hardened, the male will release her and she will migrate to higher salinity waters to spawn. Mating occurs primarily in relatively low-salinity waters in the upper areas of estuaries and lower portions of rivers. Mating takes place in areas where female crabs normally go to molt—shallow areas with marsh lined banks or beds of submergent vegetation. Extended periods of low temperatures will usually significantly shorten the mating season.

The male may mate during its third or fourth intermolt phase after it matures and he will perform a rather elaborate courtship ritual, or "dance," to get the female's attention. Upon initial contact, the male will stand up high on his walking legs. He will then stretch his claws out wide, extending them fully outwards, and begin slowly waving his swimming legs. Finally, he will snap his body backwards and kick up sand with both his swimming and walking legs. Should the female fail to respond, he will repeat the process again.

After mating, females migrate to high-salinity waters in lower estuaries, sounds, and near-shore spawning areas. They over-winter before spawning by burrowing in the mud. Most females spawn for the first time two to nine months after mating, usually from May through August the following season. The female extrudes fertilized eggs into a cohesive mass, or "sponge," that remain attached to her abdomen until the larvae emerge. The average sponge contains about two million eggs and is formed in about two hours.

After the females mate and migrate to spawning areas, they either remain there for the rest of their lives or move only short distances out to sea. In warmer months, males generally stay in low-salinity waters such as creeks, rivers, and upper estuaries. The maximum age for most blue crabs in the Mid-Atlantic Region is three years, so adults live an average of less than one year after reaching maturity.

Blue crabs are classified as general scavengers, bottom carnivores (eats other animals), detritivores (eats decaying organic matter), and omnivores (eats either other animals or plants). At various stages in the life cycle, blue crabs serve as both prey and as consumers of plankton, benthic macroinvertebrates, fish, plants, mollusks, crustaceans (including other blue crabs), and organic debris. Food is located by a combination of chemoreception (chemical sense) and taction (touch). Blue crabs may play a significant role in the control of benthic populations.

Adult blue crabs prefer mollusks such as oysters and hard clams as their primary food sources. The crab uses the tips of its front-most walking legs to probe the bottom for buried bivalves and to manipulate them after they are located. Some other common food items include dead and live fish, crabs (including other blue crabs), shrimp, benthic macroinvertebrates, organic debris, and aquatic plants and associated fauna such as roots, shoots and leaves of sea lettuce, eelgrass, ditch grass, and salt marsh grass. It will also prey on oyster spat, newly set oysters and clams, or young oysters and quahogs if other food is unavailable.

Predators claim large numbers of young crabs, and crab populations may vary from year to year according to the abundance of predators. Blue crabs are subject to predation throughout their life cycle and are particularly susceptible when they are soft during the molting process.

The blue crab is well known for its cannibalistic habits. Cannibalized blue crabs make up as much as 13% of a crab's diet. Blue crabs in poor health, missing important appendages, heavily fouled with other organisms, and those during or immediately following molt are more likely to be cannibalized.

Eating, selling or taking (harvesting) blue crabs from Newark Bay Complex is prohibited due to contaminant loads in the flesh. Crabs in our estuary are contaminated with PCBs, Dioxin, Mercury, PIHs, which are colorless, odorless, tasteless, persistent carcinogens. The contaminants accumulate in the fatty tissue and can increase your chance of developing cancer, neurological impairments and miscarriage. Women of child-bearing age and children under the age of 5 are at particular risk. The highest levels of chemical contaminants are found in the hepatopancreas, commonly known as the tomalley or green gland. It is the yellowish green gland under the gills.

If you buy blue crabs in the store or acquire them from areas that are taken from water bodies other than the Newark Bay Complex, the following preparation techniques can be followed to reduce exposure to some contaminants that may be in the crabs:

Do not eat the green gland (hepatopancreas).
Remove green gland (hepatopancreas) before cooking.
After cooking, discard the cooking water.
Do not use cooking water or green gland (hepatopancreas) in any juices, sauces or soups.

Again, there is NO safe way to prepare crabs taken from the Newark Bay Complex. It is illegal to take Blue Crabs from anywhere in the Newark Bay Complex, which includes the Passaic and Hackensack Rivers, The Newark Bay, Arthur Kill and Kill Van Kull. This action could result in fines from $100 to $3,000.

For information on this and other New Jersey health advisories contact:
  • NJ Department of Environmental Protection, Office of Science (609) 984-6070
  • Division of Fish & Wildlife (609) 748-2020
  • NJ Department of Health & Senior Services Consumer and Environmental Health Services (609) 588-3123
For background information on the fish consumption advisories, local libraries can refer you to:
NJ Administrative Code 7:25 -14, 18A

For information on Delaware health advisories, contact:

For information on New York health advisories, contact:

For information on Pennsylvania health advisories, contact:

Office of Science
Dr. Gary A. Buchanan, Manager
428 East State Street
P.O. Box 409
Trenton, NJ 08625

Phone: (609) 984-6070
Fax: (609) 777-2852

For Information regarding this site, please contact Terri Tucker.

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Copyright State of New Jersey, 1996-2009
P. O. Box 402
Trenton, NJ 08625-0402

Last Updated: December 2, 2009