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). 