By Tom Baird
A scene is played out almost daily along the shores and marshes of the Gulf coast. A blue crab warily approaches a scrap of meat in about five inches of water. After sampling for a moment, she settles down to serious feeding, tearing strips of flesh with her claws and passing them to her mouth. Lulled by this activity, the blue crab, attracted to the bait, realizes her mistake too late and is netted by a weekend crabber.
Of all the edible crabs, the blue crab is the most abundant and popular. Many Americans prefer crab meat to any other kind of seafood, and yet, these leggy crustaceans were once believed to be poisonous.
Crab fishing is one of the largest shell fish operations in the U.S., employing thousands of fishermen and processors. According to the latest figures from the Florida Department of Agriculture and Consumer Services, in 2012, 8,089,890 pounds of hard-shelled blue crab were commercially harvested in Florida waters with a dockside value of $9,934,882. This number pales in comparison to North Carolina with over 30 million pounds of blue crabs harvested commercially, with a dockside value of $21 million. The Chesapeake Bay area has traditionally been the leader in the blue crab harvest industry, contributing significantly to the economies of Maryland and Virginia, yet there have been major declines in the blue crabs harvested from Chesapeake Bay, and Louisiana now ranks number one in blue crab harvest. If Florida harvests about 8 million pounds of blue crab annually, when you consider that it takes 5 to 6 hard crabs to make a pound, that’s a lot of blue crabs. No figures are available for pounds taken by recreational fishermen or school kids.
Although for many years blue crabs were believed to be restricted to the U.S. Atlantic Coast and Gulf of Mexico ranging from Massachusetts to Texas, the blue crab also inhabits the waters of Bermuda and mysteriously appeared in the Mediterranean Sea in 1948. Essentially a shallow water crab, it lives in bays, sounds and mouths of coastal rivers. Normally an inhabitant of salt water, the blue crab is also found in brackish and freshwater. Many Florida rivers have blue crab populations far from the sea.
The scientific name of the blue crab describes it nicely. From Latin, calli, meaning beautiful and nectes, meaning swimmer. In 1896, Mary Rathbun described the blue crab and gave it the species name sapidus, meaning savory. Very apt. Hence, Callinectes sapidus says savory, beautiful swimmer to scientists regardless of their national language.
The blue crab swims beautifully through the water with great speed and ease using a pair of modified appendages that act as paddles. Mature crabs are often brilliant deep blue against a basic creamy white beneath. Bright red may be on the spines of the shell or carapace and on the tips of the claws.
Like all true crabs, the blue crab has 10 legs which may be specialized to walk, swim or pinch. The abdomen is a thin flap tucked below the main body part called the cephalothorax. Inside this hard carapace are the gills and internal organs. The first pair of legs are the large claws, used for catching, cutting and tearing food, and for defense. Behind these are three pairs of walking legs, followed by a pair of swimming legs or paddles.
The sex of the crab may be determined by examining the abdomen or tail folded up under the body. It is usually narrow, triangular, T-shaped and white in the male, but is broad, round and brownish in the female.
Crabs must molt or shed their outer covering or exoskeleton in order to grow. They also have the power to regenerate lost appendages. Ordinarily, the crab increases one-quarter to one-third in size with each molt. During its life cycle a blue crab molts or sheds its shell about twenty-six times. Once the crab sheds its shell, it generally digs into the sand for protection or hides under submerged objects. From this soft state the carapace will pass through stages of hardness until the new shell is quite brittle.
Mating takes place about now, starting in June and through October, and is timed to when the female sheds her covering. The male blue crab carries the female two or more days until she sheds. You may have witnessed this behavior and wondered why one crab was carrying another. As the female mates only once in a molt this insures that the male will be present at the critical moment of shedding and will also be able to protect the soft female until her new shell is hard.
Eggs are carried in a mass containing 700,000 to 2,000,000 eggs in a fold between the abdomen and carapace. The eggs hatch in about 15 days. Of the vast numbers of eggs produced, less than 1 in 1,000,000 will hatch and survive disease, predation and pesticides to become a mature crab. It is illegal to harvest a gravid female with her egg mass. While legal to harvest females, it is also considered good conservation practice to release all female crabs. According to the Florida FWC, “mature females may store sperm in their bodies for several months after mating in order to spawn at a later date. If a mature female is harvested, though she may not exhibit eggs, there is no certainty that she has spawned.”
The molted or soft-shelled crab is quite a delicacy to eat and can be battered, fried and eaten entire. In 2012, 68,898 pounds of soft-shell crabs were harvested in Florida, worth $627,246.
Considering the blue crab’s importance both ecologically and commercially, we need to take care that pollution, habitat destruction, watershed development and over-harvesting don’t damage this Florida resource as has happened in Chesapeake Bay. Crab cakes sound good for dinner tonight.
Tom Baird has been a fisheries biologist, high school and community college teacher (oceanography and microbiology), director of a science and environmental center, teacher of science and principal in Pinellas County as well as an educational consultant. He retired from the Florida Department of Education and he and his wife divide their time between Tallahassee and Cape San Blas.