New Jersey Scuba Diving
Crustaceans - Crabs
These are all so-called "true crabs".
True crabs are crustaceans with extremely reduced tails, which are carried folded under the body. Males are generally larger than females. Presented here are just the most common of many local species. Sizes quoted below are body width. Hermit Crabs are listed elsewhere. They are not closely related.
Crab anatomy - Blue Crab
Cut-away view, from the side:
|AG - antennal gland
DG - digestive gland
E - eye
H - heart
HG - hindgut
M - midgut
|O - oesophagus
S - stomach
SG - supra-esophageal ganglion
TG - thoracic ganglion (nerve)
VNC - ventral nerve cord
A rather disgusting view of the same thing
These crabs have the last pair of legs modified into paddles, with which they are remarkably fast and agile sideways swimmers. Apart from this, they retain the walking and burrowing abilities of other crabs. Swimming crabs are bad-tempered creatures that aggressively defend themselves. Large ones can pinch very painfully, so handle with care !
Blue Crab ( Blue-claw )
Profile by Bill Figley
and Ray Townsend
to 9" across
Cape Cod to Texas
Bays and estuaries, sometimes found in fresh water, spend their winters in the mud.
Blue crabs are relatively stationary and make only local movements. Females prefer saltier waters near inlets for both carrying their young and spending the winter. Males, on the other hand, move to less saline waters at the heads of bays or in tidal creeks. Young hatch in salty waters and move back into bays and estuaries as they grow older.
Blue crabs spawn between June and August, producing 700,000 to 2,000,000 eggs which the female carries on her abdomen. Females may spawn 2 to 3 times before dying. Eggs hatch in 9 to 14 days.
Plant or animal matter, alive or dead.
In order to grow, blue crabs must shed their hard chitinous shells. Shedding is a precarious time, for the crab may get hung up in its old shell and die; if it does emerge successfully, its new shell is very soft, rendering the helpless crab vulnerable to predators. For this reason, crabs usually seek the protection of shallow grass beds during the molt. Young crabs molt every few days, while older crabs molt every 20-30 days. After 15-20 molts, female crabs reach maturity. During the last molt, while the female is still soft, mating takes place. The female mates only once, storing the sperm needed for several spawnings.
He's not bluffing - keep your fingers away !
Recreational & Commercial Importance:
Of all New Jersey's marine fish and Shellfish, more effort is expended in catching the blue crab than any other single species. Surveys conducted by Rutgers University indicate, that three quarters of the state's saltwater fishermen go crabbing and that crabbing comprises roughly 30 percent of all marine fishing activity. Recreational crabbing is particularly important in the Upper Barnegat, Little Egg Harbor and Maurice River estuaries, comprising 65 to 86 percent of the total recreational harvest in these areas. The blue crab is especially popular with rental boaters.
The blue crab supports a valuable commercial fisheries in Delaware Bay. Over 80 percent of the catch is taken during the warmer months in wire traps. The remainder is harvested during the winter with dredges. Since 1940, New Jersey landings have fluctuated widely, with a peak of 2.9 million pounds in 1975. This peak reflects the recent increased abundance of blue crabs.
Sportfishing Facts and Techniques:
Crabs are abundant all along the Jersey coast, from the Hackensack River to Delaware Bay. The best places to catch crabs are in tidal creeks, rivers and shallow bays. One of the most popular methods is to use baited lines or traps from the bank or a boat. Most common baits are bunker and chicken necks, but any fresh fish remains will work well. A very inexpensive bait line can be made by tying a 6 oz. sinker and a large (8/0) hook to 15 or 20 feet of cord connected to a small stick for securing and storing the line. A long handled net is needed to scoop up the crabs which are brought to the surface clinging to the bait. When crabbing from a boat it is a good idea to use both hand lines and traps for sometimes one will produce better than the other. It is also effective to anchor your boat at the bow and stern, to prevent unnecessary movements of the baits. Another technique, especially effective for soft or shedder crabs, is to wade the shallows with a scoop net. This method works only when the water is clear and calm. Remember to release all females bearing an egg mass or sponge.
Acknowledgements & References:
Anthony Hillman (art), Barry Preim (graph), Hamer (1955), Engel (1973), Cargo (1973), Wojcik (1973), Applegate and Sterner (1975), McHugh (1977), Eagleton Poll (1977).
This article first appeared in New Jersey Outdoors - March / April 1980
See Restrictions and Health Advisories for catch limits.
The Lady Crab Ovalipes ocellatus is very similar to Blue Crab, but really too small to eat, growing to a size of 3". It is found in the same environments as the Blue Crab, and has similar habits. In person, it is one of the most attractive creatures in our waters, colored in purple and cream, with some scarlet and blue mixed in. Also known as a Calico Crab.
Lumped together here are what might be considered to be "normal" aquatic crabs. There are many other similar types. The claws of many crabs are good eating - break one off and let the crab go, it will grow a new one. Never take both - you'll kill it.
Rock Crab Cancer irroratus
The Rock Crab is one of the commonest shallow-water crabs. It is usually found sheltering in nooks and crevices. It is a fairly unaggressive species, more likely to hunker down and cover up its face ( as in the top picture ) than pinch if molested. Size: to 5". Range: Labrador to South Carolina.
Green Crab Cancinus maenas
The Green Crab is an introduced species that is originally from Northern Europe, but has invaded many areas throughout the world. It is a direct competitor for native species, especially the Rock Crab, with whom it shares habitat and feeding preferences. Size: to 3". Range: New Jersey to Nova Scotia, and into the Gulf of St. Lawrence.
A Jonah Crab Cancer borealis eats a dead fish
A mating pair of Jonah Crabs. The much larger male holds the vulnerable freshly-molted female in a protective embrace.
The Jonah Crab is similar to the Rock Crab, but it is normally found in deeper water. Occasionally, a Jonah Crab may wander into shallow water and can be found by scuba divers. The Jonah Crab has rough-shaped teeth along the sides of its shell, while the Rock Crab has smooth-shaped teeth. In addition, the Jonah Crab has a more heavily armored appearance than the Rock Crab, and is much more likely to fight back if provoked. Size: to 6". Range: Nova Scotia to Florida.
Black-fingered Mud Crab Panopeus herbstii
Mud Crabs are predators on young oysters and clams; their powerful claws can crush 1/2 " long hard clams; they also attack barnacles and larger clams by chipping their shells. Mud Crabs are often abundant in sponge colonies, among bushy bryzoans and hydroids on pilings, and intertidally under rocks or other debris on protected shores. The Mud Crab's shell has five marginal teeth, compared to as many as nine for the other species here. The claws are distinctly unequal. Size: 1 1/2 ". Range: Massachusetts to Brazil.
Spider Crabs Libinia emarginata are scavengers. Although they are fearsome-looking, they are actually slow moving, and their usual claws-out threat display is mostly bluff. Spider Crabs have relatively small round bodies (to 4"), long legs, and rather weak claws. They are found subtidally to at least 160 ft, on any type of bottom, and are very common in rivers and inlets. They often cover themselves with detritus for camouflage, and can also burrow in soft sediments.
A related species is used for food in Europe. The only thing more unattractive than a Spider Crab is two of them mating.
A large adult Spider Crab
Looks like one of those old Japanese monster movies, doesn't it?
A baby Spider Crab, decorated with algae that it has stuck to itself for camouflage
A small specimen trailing a veil of algea
I'm not sure what these two spider crabs were doing, and I'm sure I don't want to know !
Uca spp (right)
These small crabs are largely terrestrial. Female Fiddler Crabs lack the huge claw of the male, which is very strong, but is used only in dance-like territorial displays. Several species in the area differ mainly by habitat. Fiddlers prefer marshes and stream banks, where huge colonies riddle the peat with tunnels near the waterline. Almost entirely terrestrial, you will findGhost Crabs skittering across the beaches at night. Placed in the water, they may even drown! Both grow to a body size of approximately 1 inch.
Fiddler Crabs tend to live in nasty places. Note the odd left-handed male at upper-right.
I make no claim as to the accuracy, validity, or appropriateness of any information found in this website. I will not be responsible for the consequences of any action that is based upon information found here. Scuba diving is an adventure sport, and as always, you alone are responsible for your own safety and well being.
Copyright © 1996-2016 Rich Galiano
unless otherwise noted