Types of Crabs

This section will tell you about the armored, pinching and ferocious creatures that you hope would end up as a dish on your dinner plate. You don't need to remember everything in this section to go crabbing. The only thing that you really need is how to tell one specie of crab from the other and how to know if the crab is male or female. You could also read this to increase your knowledge and go impress other crab fisherman.
In the Lower Mainland, you can catch 2 species of crabs that are good for eating. These are the Dungeness Crab and the red rock crab. These crabs are medium to medium-large in size and are both salt water crabs. There are other species of crabs living in the Lower Mainland, but they are not preferred because of their smallish size.

Dungeness Crabs
-Habitat
-Physical Description
-Life Cycle
-Preys and Predators
Red Rock Crabs
-Habitat
-Physical Description
-Life Cycle
-Preys and Predators
Distinguishing Between Males and Females

Dungeness Crabs

A Dungeness crab
A Dungeness Crab

The Dungeness crab (Cancer magister) is the largest crab you can catch in the Lower Mainland. You are still too far south to catch the larger Alaskan King crabs. This is the species of crab that you can buy in most restaurants, supermarkets and seafood stores in the Lower Mainland. Dungeness crabs are considered good for eating because about 25% of its weight is meat and most other crabs only contain 13% of meat. Dungeness crabs support both sport and commercial fishing.

Habitat

The Dungeness crab gets its name from the town of Dungeness, Washington (now called Old Town Dungeness). These crabs live in bays and near shore waters and prefer sandy or muddy bottoms. Although Dungeness crabs are salt water crabs, they can tolerate salt-level changes and can be found in estuaries (where river empties out into the ocean). Dungeness crabs range from Alaska to all the way south in San Francisco. They usually live in waters no deeper than 30 metres but can be found at depth of up to 180 metres.

Physical Description

Basic Diagram of a Crab

Dungeness crabs are crustaceans, a group of animal that also include lobsters, shrimps and prawns. Dungeness crabs have a brownish green carapace with an off-white to yellow coloured under side. The crab possesses a pair of white-tipped claws and 4 pairs of walking legs. The claw are of medium length and have narrow tips. The carapace of a Dungeness crab is roughly fan-shaped and relatively smooth compared to other crabs such as the Alaskan King. Dungeness crabs are not spiny.
Male Dungeness crabs reach legal size at 3 or 4 years of age and weight about 2 to 3 pounds. A large male can exceed 230mm in carapace width (that is one huge crab. You are really, really lucky if you catch one) and 2kg (4.5lbs) in weight. You are lucky if you catch one that is legal-sized and really lucky to catch one over 200mm in carapace width.

Life Cycle

Dungeness crabs mate from spring to fall. The mating takes place between hard-bodied males and soft-bodied females that have just molted (shed their old shell to grow). A male may mate with many females. Females store the sperm until all the eggs are fully developed. A large female can carry 2.5 million eggs.
After hatching, baby crabs are planktonic (planktons) and swim freely. It take 4 months to 1 year and through 6 stages of transformations for a crab to reach juvenile stage.
Crabs grow by molting, which means shedding their old shell. Dungeness crabs molt several times during their first 2 years of life, with males and females growing at the same pace. After 2 years, moltings are reduced to once a year and females grow slower than males, resulting in the size difference between the sexes. During an annual molt, a Dungeness crab grow about 1 inch (2.5cm) in width. Dungeness crabs are soft after molting and can be easily pierced, so they dig into the sand and hide for several days until their shells start to harden. An adult crab requires 2 to 3 months for its shell to completely harden and fill with meat.
Note: It is possible for you to catch a soft-shelled crab. You can test crabs by pinching their large walking legs and see if the shell gives a little. If it gives even a little, you should return the crab to the water because soft-shelled crabs hold a lot of water but little meat, so they won't be good for eating. However, some people insists that the soft-shelled crab meat is the best because the meat is tender, so you are welcome to try it out yourself to see which you prefer.
Dungeness crabs reach sexual maturity at 3 to 4 years of age, the same time when males reach legal size. Dungeness crabs are estimated to have a life span of 8 to 13 years.
Click here to see an illustration of the Dungeness crab life cycle. (this is an outside link)

Preys and Predators

Dungeness crabs usually scavenge for food at the bottom of the sea. These crabs are carnivores and eat almost anything that is meat. Examined stomach contents contain fish, crab, starfish, worm, squid, snail, and eggs from fish and crabs. Dungeness crabs are also cannibalistic. They are in turn eaten by large fishes such as dogfish, hake, halibut, lingcod, sculpins, and wolf eels. They are also a favorite for octopuses. Of course, humans like them too.

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Red Rock Crabs

A red rock crab
A red rock crab

The red rock crab (Cancer productus), also called red crab or rock crab, is a close relative to the Dungeness crab (same genus: Cancer magister and Cancer productus). You will have a hard time trying to find this specie in crabs in stores or restaurants because red rock crabs are deemed too small for commercial fishery. However, you, as a sport fisherman, can catch these crabs and they taste just as delicious as Dungeness crabs.

Habitat

Red rock crabs get their name from their body colour and their preferred habitat. They are commonly found in semi-protected bays and estuaries. They are also found in rocky areas associated with outcrops and rocky headlands (a point of high land jutting out into the sea). Red rock crabs usually reside in places with rocky or gravel bottom and kelp beds because they lack the gill straining apparatus required for living in muddy or sandy bottoms. They can be found from pretidal depth to 79m deep.

Physical Description

Top view of a red rock crab
Top view of a red rock crab

Red rock crabs have a fan shaped carapace with knobby edges. They are dark red to bright red on the top and a yellowish white on the underside. Like the Dungeness crab, red rock crabs also have 4 pairs of walking legs and 1 pair of claws. Their claws are black-tipped, thick and with tooth-like bumps, making them very powerful-looking. Indeed those are very powerful claws. I have seen a red rock crab break another red rock crab's leg off with its claw. Those claws are also pretty big, and some stores actually sell them (but not whole crabs). Red rock crabs also have very strong and thick shells, even thicker than that of the Dungeness crabs. This makes them harder for you to eat, so catch the larger Dungeness crabs if you can. A red rock crab is smaller than a Dungeness crab. Red rock crabs can grow no larger than 158mm across the carapace.

Life Cycle

The life cycle of the red rock crab is very similar to that of the Dungeness crab. Breeding occurs in inshore waters during May to August, between males and females that have just molted. Eggs can be laid from October to early June (of next year), but usually between December and January. Red rocks are born as planktons. They need 3 to 4 months and through 6 stages to reach juvenile stage. Red rocks also grow by molting.
Click here for an illustration of the red rock crab's life cycle. (this is an outside link)

Preys and Predators

Red rock crabs are carnivores and aren't picky eaters. They eat barnacles, bivalves, smaller crabs and dead fish. They are food for large fishes, octopuses, marine mammals and the occasional sport fisherman.

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Distinguishing Between Males and Females

The following information apply to both the Dungeness and red rock crabs.

The underside of a female crab
Undersides of male and female crabs
The underside of a male crab

The best way to distinguish between a male and a female crab (this works other species of crabs as well, such as the blue crab) is to flip the crab over or pick it up (Careful, don't get pinched), and look at the abdominal section near its rear end. A male crab will have a narrow triangular abdomen while a female will have a much wider and more oval abdomen.

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