Overview

Key Features:

Of the 10 marginal carapace teeth, the posterior tooth is the largest and distinguishes Cancer magister from other Cancer species.

Similar Species:

Red rock crab (Cancer productus)
Yellow crab (Metacarcinus anthonyi)

Primary Common Name:

Dungeness crab

General Grouping:

Crabs, barnacles, shrimp, lobster

Geographic Range:

Aleutian Islands, Alaska to Santa Barbara, California

Cancer magister is found from the Aleutian Islands, Alaska to Santa Barbara, California.

Intertidal Height:

-2 to -0.5 feet (-0.6096 to -0.1524 meters)

Notes:

Cancer magister can be found in the very low intertidal. Juveniles can be extremely abundant here.

Subtidal Depth Range:

Minimum Depth: 0 meters or 0 feet
Maximum Depth: 230 meters or 750 feet

Notes:

Cancer magister is found throughout the subtidal.

Habitats:

bay (sandy shore), estuary, exposed rocky shore, exposed sandy beaches, protected rocky shore, protected sandy beaches

Notes:

Cancer magister occupies soft sandy bottoms and eelgrass beds, from very low intertidal to about 360 meters. Juvenile Cancer magister can be extremely abundant in the intertidal zone.

Abundance:

Relative Abundance:

Cancer magister is common to abundant throughout its range.

Species Description:

General:

Cancer magister has a wide, hard and relatively smooth carapace. They have five pairs of legs made up of the same material as their shell, and their foremost pair ends in claws which the crab uses both as defense and to tear apart large food items.

Distinctive Features:

The Carapace of Cancer magister is fan shaped and has 10 small teeth on each side. The posterior tooth is the largest and distinguishes Cancer magister from other Cancer species. The top of its carapace is dark gray-brown tinged with purple and creamy below. Its stout pincers have white tips and are serrated along the upper margin of the palm and finger and it has short walking legs. The color and pattern of Cancer magister varies little between individuals except for slight differences in the amount and intensity of purple on the claws and legs.

Size:

Cancer magister has a carapace length to about 160 mm, and a width to about 230 mm, but usually less than 190 mm. However, there is one report of specimens measuring 330 mm.

Natural History:

General:

Cancer magister is in the family Cancridae. There are 9 species in the genus Cancer, which means hard shell, in California, all of which have black-tipped pincers, except for Cancer magister and the slender crab Cancer gracilis.

Like most crustaceans, Cancer magister must shed its shell in order to grow; this shedding process is called molting. In intervals of about one year, the hard shell of the crab, which will otherwise prevent growth, is cast off. The old shell will slit at the junction of the carapace and the abdomen and the crab will back out of the old shell. During this molting period any missing appendages will be rejuvenated. Once the shell is molted, the crab is considered soft and during this interval of a few days the crab undergoes a period of rapid growth before the new shell becomes calcified and fixes the size of the crab until the next molt. Cancer magister usually molts in shallow water, and these molted skeletons often wash ashore.

Predator(s):

Cancer magister is an important prey item in all life history stages. Adults and juveniles are eaten by a variety of fish including hake, Merluccius productus, halibut, Hippoglossus stenolepis, lingcod, Ophiodon elongates, rockfish, Sebastes, sharks, skates, and wolf eels, Anarrhichthys ocellatus, as well as by harbor seals, Phoca vitulina, and sea lions, Zalophus californianus. Cancer magister's larvae are important food for Pacific herring, Clupea pallasi, Pacific sardines, Sardinops sagax, rockfish and Chinook salmon, Oncorhynchus tshawytscha. And even its eggs are food for marine worms, such as nemerteans.

Cancer magister is an important commercial species harvested along the coast from Alaska to California. They are usually caught in nearshore marine waters under 40 m deep with baited crab pots. Cancer magister is the chief crab species taken commercially on the Pacific Coast and is also an important recreational fishery.

Prey:

Cancer magister feeds on a variety of small invertebrates and fishes including, clams, shrimp, starfish, worms, squid, snails, crabs, and eggs from fish or crabs. This species is also cannibalistic, and will feed on the juvenile crabs during their first year of life.

Feeding Behavior:

Carnivore, Omnivore, Scavenger

Notes:

Cancer magister uses its foremost appendages, which end in claws, to ear apart large food items. The smaller appendages are used to pass the food particles into its mouth. Inside the crab's stomach, food is further digested by a collection of tooth-like structures referred to as a gastric mill.

Seasonal Behavior

January - December

Reproduction:

Male Cancer magister find females with the use of pheromones (chemical scents), and mating occurs only after the female has molted. The male may stay with her for a few days after mating to ensure her protection during this vulnerable time.

Mating most commonly occurs in May and June, however it can happen during other times of the year.

Mating usually takes place outside of estuaries in near-shore coastal locations. The female can store the sperm until the eggs are fertilized, at this point they will be extruded but remain attached to her abdomen for three to five months until they hatch. A large female may carry up to two and a half million eggs. Once the eggs hatch, they become planktonic larvae and do not resemble adult crabs at this time. The free-swimming larvae will go through five larval stages, which include about 10 molts, before reaching maturity at about two years of age.

Juveniles settle in shallow coastal waters, tidal flats, and estuaries, living on eelgrass beds. Cancer magister will then grow through a series of molts until adulthood and continue to occupy estuaries or move into coastal waters offshore.

References

• Alden, P., F. Heath, R. Keen, A. Leventer, and W. Zomlefer. 2002. National Audubon Society Field Guide to California. A.A. Knopf, New York, NY.
• Dungeness Community Web Site. 2006. World Wide Web electronic publication. http://www.dungeness.com/crab/, Accessed [05/16/06].
• Gotshall, D. 2005. Guide to marine invertebrates : Alaska to Baja California. Sea Challengers, Monterey, CA. 117 p.
• Jensen, G.C. 1995. Pacific Coast crabs and shrimps. Sea Challengers, Monterey, CA. 87 p.
• Meinkoth, N.A. 1998. National Audubon Society Field Guide to North American Seashore Creatures. A.A. Knopf, New York, NY. 813 p.
• Pacific States Marine Fisheries Commission. 1996. World Wide Web electronic publication. http://www.psmfc.org/habitat/edu_crab_fact.html, Accessed [05/16/06].
• Phillips, J.B., D. Parker, and B. Tasto. 1986. Dungeness Crab of California and its Close Relatives. World Wide Web electronic publication. http://www.dfg.ca.gov/MRD/dungeness_crab.html, Accessed [05/16/06].

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