Dungeness crab were named after a fishing town on the coast of Washington. Only the males are harvested, the females are thrown back into the water.
A tagging study was conducted by the California Department of Fish and Game. This study showed that crabs reared in the San Francisco Bay grew about twice the rate as ocean-reared crabs. The average carapace was appoximately 100 millimeters after one year. The hypothesis is that warmer bay temperatures and increased food availability is resposible for the rapid growth.
Dungeness crabs are affected by many insecticides. The insecticide carbaryl, also known as Sevin, is particularly toxic to the Dungeness crab. Other toxins include other insecticides and fungicides as well as ammonia. Urban pollutants such as heavy metals, PCB's and hydrocarbons also affect the Dungeness crab. Runoff of pesticides and herbicides affect the Dungeness crab populations as well. Dungeness crabs are not endangered, however, these chemicals can kill or upset the health of Dungeness crab populations.
US Federal List: no special status
CITES: no special status
Dungeness carbs are an important commercial shellfish. Male crabs are harvested along the coast of North America from Alaska to California. The fishery is worth tens of millions of dollars, due to the thousands of crabs caught annually.
Positive Impacts: food
Cancer magister eat a variety of marine invertebrates and fish. As juveniles, the Dungeness crabs feed on fish, shrimp, molluscs and crustaceans. Adults feed on bivalves, crustaceans and fishes. The crabs are able to open shells by chipping away at them with their heavy pinching claws.
Animal Foods: carrion ; mollusks; aquatic crustaceans; zooplankton
Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)
Cancer magister, commonly known as Dungeness crab, is found in the costal waters from Point Concepcion, California, to the Pribilof Islands, Alaska. The Dungeness crabs inhabit the estuaries from Morro Bay, California, to Puget Sound, Washington.
Biogeographic Regions: pacific ocean (Native )
Dungeness crabs are found on the Pacific coast in sandy bottoms below the tidal mark. They can also be found at lowtide in sandy or muddy bays where there is a good growth of eel grass. Dungeness crabs are intolerant of low dissolved oxygen conditions. Also, even low amounts of ammonia are toxic to the crabs. Dungeness crabs also tend to grow better in water that is above six degrees Celsius (Kozloff 1973).
Habitat Regions: temperate ; saltwater or marine
Aquatic Biomes: benthic ; coastal ; brackish water
Other Habitat Features: estuarine
Cancer magister is a decapod. Decopods' thoracic segment is fused with that of the head, to form the cephalothorax, which is covered by a carapace. The Dungeness crab has five pairs of thoracic legs. The first pair of legs is larger then the last four and has pinching claws. Cancer magister is a walking crab and therefore, the last pair of legs is adapted for walking. It has a flat and broad body, oval in shape. The anterior margin of the carapace has nine small teeth on each side, forming an elliptical curve. At the end of the curve, a large, pointed tooth projects directly outward. From this tooth, the carapace slopes backward, forming a narrow posterior end. Males range from 18 to 23 centimeters (about 7 to 9 inches)in width and 10 to 13 centimeters (4 to 5 inches) long. The color of the carapace is reddish-brown, fading towards the back. The legs and ventral side are yellowish.
Range length: 10 to 13 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Seals, sea lions, and a variety of fish eat Dungeness crabs.
Males attract the females by use of pheromones, which are chemical scents. During mating, the male crabs clasp the female so that the undersides of each are close. The male's breeding structures place the sperm into the female's body. This is only possible when the female is soft shelled, right after molting. This lasts less than thirty minutes. Mating occurs in near-shore costal locations, outside of estuaries. The eggs are not fertilized and spawned until the fall, following the summer breeding. After fertilization, about half a million to one million eggs are attatched to the female's abdomen. These eggs are brooded there until spring. The larvae are planktonic and use tidal currents to travel into estuaries. The larvae pass through six stages over a 105 to 125 day period. The last two stages are zoea and megalopa. Zoea have a jointed abdomen and a spined carapace behind the head with large eyes. Megalops have big eyes, an extended abdomen, elongated carapace and swimming legs. After the first molting, the form changes to that similar to the adults. Growth after this point occurs by shedding its shell, molting, at certain periods of time, until it reahces full growth (Headstrom 1979, Mash 1975).
