SNOW CRAB
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Description	The Atlantic Snow Crab (Chionoecetes opilio) is the most important commercial crab species in eastern Canada. It ranks sixth in the value order of all commercial species, worth nearly $20 million to Canadian fishermen both in 1979 and 1980. Its value is much higher when the finished product is sold on the market. Furthermore, its complex processing generates an unusually high number (several thousands) of welcomed jobs. Since females never exceed the commercially acceptable and legal minimum size, they are kept by fishermen. Only the males are harvested. When the fishery for snow crabs was developing in eastern Canada, they were know as spider crabs or queen crabs. These names have since been replaced by snow crab, after a ruling by the American Food and Drug Administration stated that if they are to be marketed in the United States, all species of the genus Chinoecetes must bear the earlier established trade name of snow crab. The snow crab is a crustacean (like lobster and shrimp) with a flat and almost circular body, slightly wider in the back. It has five pairs of long spider-like legs that are somewhat flattened, the first one being equipped with claws. The fully grown male is almost twice as large as the female, reaching (although rarely) a maximum shell width of 16.5 cm, a leg span of over 90 cm and a weight of 1.35 kg. The average size crab in the commercial catch measures approximately 11 cm and weighs 0.5 kg. Females grow to a maximum of only 9.5 cm shell width, with a leg span of 38 cm and weight of 0.45 kg. They have no commercial value. Males have proportionally longer legs and larger claws than females. The abdomen, which is relatively small and folded under the body, is quadrilateral in males but circular in females. Shell colour varies. Just after shedding (molting), it is reddish on the upper surface and creamy white beneath. The animal is then called a "white crab". As the shell hardens and ages, it changes to a dull greenish brown above and dull yellow beneath. It eventually will become covered with small marine organisms. Toad crabs (Hyas araneus and H. coarctatus) are other spider-like crabs that are sometimes found in the shallow part of the snow crab habitat. They can be distinguised by their tubular legs, a more elongated body resembling the shape of a violin, and a wider range of colour (from gray to brick red).
Life Cycle	Mating is thought to occur at the end of the winter or in the spring. During the mating period, the male holds the female with his claws until she molts. He may even help her out of her old shell. soon after, sperm is deposited into the openings of the female's sperm sacs located underneath her abdomen. Depending on her size, she then lays 20,000 to 150,000 eggs over a period of a few days. A female can lay and fertilize more than one annual batch of eggs without further mating, since she can store spermatophores for long periods. The eggs are deposited on hairy appendages, located under her abdomen, where they are carried until the following year. During this period, the eggs change colour from bright orange to dark purple or black. In the southern Gulf of St. Lawrence, hatching starts in may and is generally completed by July. Newly hatched crabs (larvae) are about three mm long. They immediately rise to the surface where they are carried by the currents before they settle back on the bottom, most probably at a different place than where they hatched. During this period, they go through three different larval stages before adopting the regular shape of crabs. These young crabs are then only three mm wide across the shell. Since their shell is hard, crabs, like lobsters and other crustaceans, must molt to grow. Molting (ecdysis or shedding) is a process by which an animal gets rid of an old shell in order to grow in size. This process is repeated less and less frequently as an individual gets older and larger.
Anatomy	To the left is cooked Atlantic Snow Crab, broken and identified by its body parts. Soft-shelled crab are very delicate. Immediately upon leaving the ocean, water that is normally in and around the gills drains away and is replaced by air. If the crab are not quickly and gently returned to the ocean, they will float, greatly increasing the risk of death. Soft-shelled crab, even when held under ideal handling and holding conditions, still weaken quickly. They are also extremely sensitive to shock. Avoid any rough handling of the crab on-board and in returning them to the ocean. Soft-shelled crab returned successfully to the sea will regain prime condition - perfect for future harvesting. It is important to cull soft-shelled crab because they are low in meat content consisting of watery, stringy, limp, texture. Soft- shelled crab can be easily by the following characteristics: The underside of the claw is very flexible and on bending will bounce back. The legs are translucent and watery. The top outer shell is bright while the belly side is pale. The soft-shelled crab is free of barnacles. When shaken, the soft-shelled crab makes a rattling noise. To the left, is a female Snow Crab with its roe exposed. The return of unharmed female crab from a catch to the sea ensures a continuing supply of crab for the future. Therefore, regulations prohibit their capture for processing. Female crab are smaller than the male and never reach 3 3/4 inches (9.5 cm) minimum size.
Distribution & Migration	In the pacific, where snow crabs are represented by more than one species, they occur from the Sea of Japan to Alaska, British Columbia, and the States of Washington and Oregon. In the northwest Atlantic, they extend from west Greenland down the Canadian Atlantic coast and into the Gulf of Maine where only a few individuals have been reported. They are totally absent from the northeast Atlantic. Snow crabs are common in the estuary and the Gulf of St. Lawrence, around Cape Breton Island and in the bays of Newfoundland, from Fortune Bay to White Bay. They are also found near Hamilton Bank off Labrador. Snow crabs live most commonly on muddy or sand-mud bottoms at temperatures ranging from -0.5 to 4.5°C. In the Gulf of St. Lawrence, they are usually found at depths of 70 to 140 m, while in Cape Breton the depth varies from 45 to 245 m, and 170 to 380 m off Newfoundland. The distribution of small crabs is not well documented but they are occasionally found with the adults, or on gravelly bottoms at shallower depths. In some areas, there are indications that snow crabs move from gravel bottom to mud bottom, usually in deeper waters, as they reach maturity.
Behavior	Snow crabs feed on a variety of food. Their stomachs may contain remains of different kinds of shellfishes, worms, sea urchins, brittlestars and detritus. They can crush hardshelled animals with their strong claws and mouth-parts. Feeding activity is apparently higher at night. Between molts, the crab builds more organic tissues and prepares a new shell under the old one. When this process is completed and the conditions are suitable, the body shell splits at the back and the crab molts by backing slowly out of the old shell. Large crabs may take up to 10 hours to emerge from the old shell. Immediately after molting, the wrinkled, soft crab takes up water and swells to its new size in a few hours. The soft shell, covering all the body and the legs, gradually hardens and again, more muscles and other tissues grow inside, replacing the water that was absorbed at molting. It may take two months for a commercial-size crab to lose its soft-shell condition and possible more before it is at its best for harvesting. At each molt, mature males grow about 20 percent in width and 60 percent in weight. Since the frequency of molting is not well know, age and growth are very difficult to determine. Very approximately, crabs of the minimum legal size (9.5 cm) are thought to be at least six years old. For protection against enemies, each leg of the crab has a small circular groove at its base, which allows the crab to snap off the leg should it become entangled or held by a predator. A valve at this point prevents major blood loss and a healing scar is quickly formed. A leg bud begins to grow from the scar and the next molt a small new leg is formed. Normally, it takes three molts for the leg to grow back to normal size. At a shell width of 6.5 cm in the Gulf, and 6.0 cm off Newfoundland, most males are mature and can mate successfully. At maturity, the claws of males become proportionally larger than those of females or immature males. In mature females, the abdomen increases proportionally in size and the small appendages under the abdomen become large and branched with many fine hairs upon which the eggs are eventually deposited. Size at maturity for females can be as small as five cm in shell width.
The Fishery	CRAB TRAPS Crab traps differ considerably from those used in the lobster fishery. Crab traps are frames with iron rods and are covered with polyethylene rope webbing, and may be either cone-shaped or rectangular. They are much more expensive than lobster traps because of the material used, and are somewhat larger. Usually only one trap is placed on each line. While the main species caught in the Atlantic area is the Snow Crab, exploratory fishing is being conducted for Rock Crab, Jonah Crab and Red Crab. In the Newfoundland Snow Crab fishery, culling usually takes place on a bench directly under the mini-hatch in the hold of the vessel. Culling is the removal of undersized, soft-shelled, and female crab from the catch and its prompt, but careful, return to the sea. Ideally, the best Snow Crab for processing has a clean, hard shell and with minimum size of 3 3/4 inches (9.5 cm) carapace width. Culling may be minimized by avoiding fishing areas where catch characteristics show crab have recently moulted or where there is a high incidence of small crab.

SOURCE: Communications Directorate
Department of Fisheries and Oceans
Ottawa, Ontario
K1A 0E6
© Minister of Supply and Services, Canada
Cat. No.: Fs 41-33/6-1990E
ISBN: 0-662-17441-0
Reprinted 1993