Claw Color
Here's an easy way to tell the difference between a male and
female blue crab. Males have blue claws, and, like most humans,
female blue crabs "paint their fingernails" (i.e., the tips of their
claws are "painted" red!)
Abdomen
In addition to the claws, there are other (better) ways to
determine the gender of a blue crab. But first, a little science.
The Atlantic blue crab (Callinectes sapidus) is a member
of the Brachyura - an order of crustaceans having a reduced abdomen,
or "apron," folded against the ventral surface (or belly) of the
animal. An easy way to think about this concept is to make a crab
out of a lobster. You take a lobster, shorten up its tail and fold
it up under its body between the legs, then press the tail up into
its bottom shell until it's flush. Voilą! You now have a crab...
well, sort of! This should help illustrate how a crab evolved to its
current form.
As you will see in the following images, the male and female crab
have entirely different shaped aprons which makes determining gender
very easy. And, the apron is yet again very different for adolescent
and adult females making it easy to determine the female's sexual
maturity (determining the male's maturity is a bit trickier.)
Blue Crab Abdomens
As you can see highlighted in red, the aprons allow you to
quickly determine the gender and maturity of the blue crab.
Sexual Maturity
"Jimmy"
A male blue crab, known as a "Jimmy" to watermen, has a long,
narrow, inverted "T" shaped apron and blue-tipped claws.
Unlike female blue crabs, there is no easy way to distinguish
the sexual maturity of the male. However, upon close inspection,
you will note that the apron of the adolescent male is tightly
sealed to his body whereas the adult male is free to open his
apron (like the mature female, the male opens his apron in order
to mate.) The adult male has locking spines adjacent to the
fifth thoracic segment which hold his apron shut. |
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"Sally"
A immature (adolescent) female blue crab, known as a "Sally"
or "She-Crab" to watermen, is easily identified as having an
inverted "V" or triangular shaped apron and red-tipped claws.
Her apron is tightly sealed to her body and does not open since
she cannot mate or carry eggs. |
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"Sook"
A mature (adult) female blue crab, known as a "Sook" to
watermen, is identified as having an inverted "U" or bell-shaped
apron and red-tipped claws. Her broadly rounded abdomen is free
to open and is not sealed shut as before. She must open her
apron in order to mate and to carry eggs (see "Sponge Crab.") |
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Egg-Bearing Female Blue Crab
"Sponge Crab"
"Pregnant" female blue crabs carry fertilized eggs under their
abdomen. From a distance these eggs resemble a sponge, hence the
term "sponge" crab. It takes about two weeks for the eggs to "ripen"
and be released into the water to hatch. It is illegal in many
states to possess sponge crabs.
Please note that there is a lot of misinformation being
circulated about the female blue crab and whether she has ever
released eggs. Some people wrongly believe that sooks taken from the
brackish waters of the mid to upper Chesapeake Bay have released
eggs (spawned) and are therefore fair game. This is probably not
true. When the female is about to become sexually mature, she molts
and then mates with a male. During this mating, the male's sperm is
transferred to special sacs inside the female for use at a later
time... much later! Here's where we clear up the confusion: Mated,
Yes. Spawned, No. There's a big difference between the two! After
mating, and toward the end of the season, the "impregnated" sooks
will migrate south toward the mouth of the Chesapeake Bay. It is
here, in the high-salinity waters of the extreme lower Chesapeake
Bay and Atlantic ocean, where she actually fertilizes her eggs and
spawns.
What does this mean in plain English? It means that the bulk of
the sooks taken from Maryland and Virginia waters are females that
have probably never released any eggs. Think about this fact the
next time you take a sook from these waters.
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