The blue crab (Callinectes sapidus, from the Greek calli="beautiful", nectes="swimmer", and Latin sapidus="savory") is a crustacean found in the waters of the western Atlantic Ocean, the Pacific Coast of Central America and the Gulf of Mexico. On the Pacific Coast of Central America it is largely ignored as a food source as picking the meat is considered too difficult. It is the Maryland State Crustacean and the subject of an extensive fishery. They can deliver an extremely painful pinch and are noted for being particularly aggressive and difficult to handle safely by novice recreational crabbers.

Distribution and ecology

The blue crab is native to the western edge of the Atlantic Ocean from Nova Scotia to Argentina. It has been introduced (via ballast water) to Japanese and European waters, and has been observed in the Baltic Sea, North Sea, Mediterranean Sea and Black Sea.

The natural predators of the blue crab include eels, drum, rock fish, spot, trout, some sharks, humans, and cownose sting rays. The blue crab is an omnivore, eating both plants and animals. Blue crabs typically consume thin-shelled bivalves, annelids, small fish, plants and nearly any other item they can find, including carrion, other blue crabs and human waste .

Male and female blue crabs can be distinguished by their "aprons", or their abdomens. Male crabs have a long, narrow apron, while mature female crabs have a wide, rounded one. A common mnemonic is to remember that if the apron looks like the Washington Monument, the crab is male; if like the U.S. Capitol, it is female.

Chesapeake Bay Blue crabs undergo a seasonal migration; after mating, the female crab travels to the southern portion of the Chesapeake, fertilizing her eggs with sperm stored up from the last mating months or almost a year later . In November or December, the female crab releases her eggs. The crabs hatch in a larval form and float in the mouth of the bay for four to five weeks, then the juvenile crabs make their way back up into the bay.

There is evidence that blue crabs in eastern North America, are able to control populations of the invasive green crab, Carcinus maenas; numbers of the two species are negatively correlated, and C. maenas is not found in Chesapeake Bay, where blue crabs are most frequent

Commercial importance in the United States

The Chesapeake Bay, located in Maryland and Virginia, is famous for its blue crabs, and they are one of the most important economic items harvested from it. In 1993, the combined harvest of the blue crabs was valued at around 100 million U.S. dollars. Over the years the harvests of the blue crab dropped; in 2000, the combined harvest was around 45 million dollars. Late in the twentieth century, the Maryland Department of Natural Resources created stricter guidelines for harvesting blue crabs to help increase populations . These include raising the legal size from 5 to 5¼ inches (from 12.7 to 13.3 cm) and limiting the days and times they may be caught.

While blue crabs remain a popular food in the Chesapeake Bay area, the Bay is not capable of meeting local demands. Most whole blue crabs sold in restaurants in Maryland are shipped into the region from North Carolina, Louisiana, Florida, Alabama, Mississippi and Texas and many crabcakes are made of crabmeat imported from overseas especially Mexico and Venezuela. At least one well-known "traditional Maryland" seafood restaurant actually imports a Southeast Asian crab, an industry there that employs about 15,000 people.

In the past U. S. crab meat was picked and processed by a labor force comprised almost exclusively of African-American females. They received transportation to and from work usually on old school buses and were paid by the picked pound with company coins or chits which could be converted to cash at the week's end. That labor force in the U. S. has today been replaced by a Latin American female work force. Some seafood shops being socially sensitive offer crab meat processed both in the U. S. and in Latin America the differences in the quality of the two products being little to none; the Latin American product being about $2.00 a pound less expensive.

The coastal towns of Little River, South Carolina, and Panacea, Florida, host annual Blue Crab Festivals each May.

Harvesting techniques

Blue crabs are commercially harvested by using a trap known as a "crab pot" and referred to as "crab traps" by Southerners (Hear "Song for Johnny" by Georgia artist Vic Waters.) (similar to a lobster pot). The crab pot is made out of wire mesh (older designs of wood and wire also exist, as well as all metal varieties) and is cubical in shape. The crab pot usually contains two "entrances" for the crabs that prohibit exit. These are in the form of a tapered aperture that allows the crab to squeeze through in one direction only. A crab pot is baited with any of several types of meat, including bunker, bluefish, chicken or eel and more recently mesh bags filled with razor clams. The bait is placed in a holding compartment, a separate meshed enclosure in the center of the pot which is accessible through a door on the bottom of the crab pot. This design attracts the crabs through the entrances while preventing them from completely removing the bait. The pots are distributed throughout the crabber's harvesting area in long straight lines and are checked approximately once a day for captures or depleted bait. Crabs that are caught are removed, and the pot is re-baited for the next day.

Crabbers sort the crabs into males ("Jimmies"), immature females ("Sallies"), and mature females ("sooks" or "she-crabs"); females bearing eggs are also known as "gravid." Catch limits for females are more restrictive than for males, and when sold, the buyer will want to know whether he is buying males or females. Those crabs with signs of getting ready to molt or shed are called "busters" or "peelers" and are also separated from the rest, and placed in shedding tanks. These tanks are usually raised and made of concrete blocks, about 3 feet by 5 feet in size. The water is constantly circulated bay or river water, and the crabs are separated into tanks according to the molting stage, determined by a pinkish spot on the swimming fins which gradually turns red, before visible signs of the shell separation are visible. This continual resorting helps prevent the harder shelled crabs from eating the ones that are beginning to actually shed. Once the shed happens, the pressure of the needing-to-be-larger crab helps the shell to crack, and the crab then backs out of the shell. At this point it is extremely vulnerable because the new shell is a gelatinous papery substance which does not protect the crab. Right after shedding, you can observe the crab becoming noticeably larger because the new shell also expands until it hardens, which takes about 48 hours. Crabbers are constantly tending the tank, and after the expansion, the crabs are removed and iced or flash frozen for transportation to market as soft shell crabs. In well tended shedding tanks there is about a 10% mortality rate. If the shedding process is not managed, the mortality can be as high as 50%.

For the recreational crabber, there exist a variety of crab traps. (Recreational crabbers rarely use commercial pots.) The design of a trap can vary widely, but the common varieties are made out of wire mesh. The crab trap is usually cubical or pyramidal in shape although cylindrical designs are also used. The crab trap contains some form of "entrance" for the crabs, such as hinged panels, that are typically closed as the trap is raised from the water. Like the commercial pots, the crab trap is baited with any of several types of meat, chicken usually being the easiest to obtain. The bait is placed in a holding spot in the middle of the trap usually in some form of clip allowing the crab direct access. This design has the potential to more easily allow the crab to escape with the bait but the trap is usually checked frequently enough (every 15 to 30 minutes) to prevent this from happening.Some recreational crabbers add the catch from the traps to a "keeper pot" that holds the live crabs until a substantial harvest is accumulated. When the keeper pot is appreciably full, the contents are prepared for a "crab feast" or for sale.

Crabs can also be caught with a trotline. While this method generally allows one to catch more crabs than other recreational methods, it requires more effort and equipment. This method is used by advanced recreational crabbers and some smaller commercial operations. Other recreational methods involve line crabbing (using a single baited line similar to fishing) or simply wading through the water with a dip net. Crabs can also be taken from a slow-moving motorboat. During the day, crabbers will operate the boat in shallow, grassy waters (flats) and use a long-handled net to scoop them from the bottom, where they can be easily seen moving about. At night, the crabs swim in deeper water. By scanning the water ahead of the boat using a spotlight, the crabs are easily seen and caught. Crabbing after sunset is prohibited in many areas.

Handling caught blue crabs can be quite a challenge. Even when out of the water, they will lunge towards movement they consider a threat. Experienced commercial crabbers deftly and quickly grab with one hand by a back fin close to the body those crabs that escape onto the deck. They rarely, but occasionally also feel the severe pain of a nip. Commercial crabbers usually respond to such pinches by ripping the claw from the crab's body and then prying the pinchers off their hand.

Recent research by scientists at North Carolina State University and the University of Maryland is leading to a new kind of crab harvest that could help the population recover – blue crabs grown and harvested from freshwater ponds, instead of from the sea. The researchers discovered that crabs can tolerate a salinity level of only .3 parts per thousand, which is about the same level found in coastal tap water. They did further work to determine the best set of circumstances for raising crab: population density, food rations, and habitat structure in ponds.

Cooking & Eating

Blue crabs are most often eaten in the hard shell. Steaming them in large pots with water, vinegar and seasoning (Old Bay Seasoning is a popular variety in Maryland) is the norm on the East coast. The crabs are placed on a raised tray (with holes for the steam), in large cooking pots similar to pot used for cooking pasta. There is water under the tray. As the crabs are layered into the pot large amounts of the seasoning is sprinkled between the layers. The lid is then placed on the pot and kept at boiling until the crabs turn red.

However, places like New Orleans, Louisiana, and Savannah, Georgia, tend to boil them in water and heavy cajun seasoning which is similar to boiling crawfish. Stores carry this as "Crab Boil" or "Shrimp Boil" spice, which is added to the water, and the crabs are immersed in the water. Again, they are done when they turn red.

The cooked crabs are cracked by hand but most diners will use a small knife to pry the shell apart and cut the unwanted parts from the crab. However in many Oriental cultures, the eggs (and sometimes the ovaries) of a female crab are eaten along with the meat, sometimes dipped into black vinegar. Thus it is common to purchase live crabs at a time of the year (usually autumn) when they are most fertile, so they will produce the eggs that are considered a delicacy, at the same time turning the ovaries into a more edible and enlarged orange variety. Within these cultures, it is also common advice not to eat crab meat and persimmons together. A small wooden mallet is often used to crack the claws to remove the meat therein.

Male Crabs have an apron on the underside. This is used as a tab, similar to a beverage can. The apron is pried up with the knife, pulled back and cut off. This then reveals an area in the rear of the crab where the knife can be inserted to pry the upper and lower shells apart. The upper shell is usually discarded. The gills known locally in Maryland as "devil" are removed and discarded. There is also the crab's digestive system, considered a high delicacy by some crab eaters but usually removed. Known as 'tomalley' or, in Maryland and Virginia, referred to as 'mustar' or 'mustard', probably referring to the dark yellow color, similar to Dijon mustard.

The meat is pulled out and eaten directly. Crab shells can be very sharp and because the interior of the crab comprises a series of compartments separated by a somewhat pliable but still sharp shell, getting the meat out is also a lot of work for the relatively small amount of edible crab meat.

The picked meat, especially the large chunks from the backfin area, can also be used to make crab cakes, crab soup, crab dip, or other dishes. Larger pieces of meat are preferred by customers, but since they fall apart easily, a cook has to carefully fold in crab meat, rather than stir it. Traditionally crab cakes were fried, but many people today prefer broiled (grilled).

Picked crab meat is also sold commercially, and the canning operations have huge crab picking 'houses' traditionally manned by local women, often the wives of watermen. These women manage to completely remove the meat, sorted into lump, claw, backfin, and the other smaller bits, in less time than the casual crab eater takes just to get into one crab, remove the gills, and pry out the lumps. Today, most picking houses are still usually staffed by women, but they are more often foreign workers with temporary work visas. Inability to get work visas has resulted in shutting down of many picking houses and a loss of markets for watermen in 2009.

Crabs caught just after molting (before the new shell has had time to harden) are prepared as soft shell crabs. Soft shell crabs are prepared by first cutting out the gills, face, and guts. The crab is then battered in flour, egg, and seasoning, then fried in oil until crispy. The result can be served as an entrée, or in a sandwich. When served between bread slices or crackers, the legs stick out on either side, and the entire crab is consumed, legs and all.

Blue crabs average 15% edible meat, and that meat is high in vitamin B₁₂. Just three ounces of crab meat contain a full day's allowance of the vitamin.

Origin of Blue Color

The origin of the blue crab hue stems from a number of pigments in their shell, including Alpha-crustacyanin, which interacts with a red pigment, astaxanthin, to form a greenish-blue coloration. When the crab is cooked, the Alpha-crustacyanin breaks down, leaving only the astaxanthin, which turns the crab red-orange.

References

1. C. E. DeRivera, G. M. Ruiz, A. H. Hines & P. Jivoff (2005). "Biotic resistance to invasion: Native predator limits abundance and distribution of an introduced crab" (PDF). Ecology 86 (12): 3367–3376. doi:10.1890/05-0479.
2. Report: Number of Blue Crabs in Bay Remains Below Long-Term Average, National Oceanic and Atmospheric Administration, July 28, 2008
3. Baltimore Sun, 2007
4. Researchers Turning Freshwater Farm Ponds into Crab Farms Newswise, Retrieved on October 19, 2008.

External links

• Crab Diagram
• Blue Crab Life Cycle
• The Maryland Blue Crab Blue crab fact and information website.
• Boy crabs boogie to bring females out of hiding - the wild dance of male blue crabs propels a jet of pheromones to attract would-be lovers, New Scientist, 7 April 2008
• Chesapeake watermen fear blue crab not coming back - Associated Press, July 16, 2008