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May 18 2017

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Dungeness crab (Biology, fishery and conservation) – Video

Review: Abdel Rahman El Gamal (Founder of the video channel)

 

 

This video was filmed in a retail shop located in Monterey, California (USA) where different fish species and crabs are sold. The Dungeness crab is the crab species shown in this video whether sold iced or displayed live.

The Dungeness crab, Metacarcinus magister (formerly: Cancer magister), is also known as market crab, and San Francisco crab and belongs to the family Cancridae. Its common name comes from the port of Dungeness, Washington.  These crabs are one of California’s most popular shellfish and popular seafood prized for its sweet and tender flesh.

Geographical range and habitats: The geographical range of Dungeness crab extends from Alaska’s Aleutian Islands to Point Conception, California. They inhabit eelgrass beds and are usually found on sandy or sand-mud bottoms. Dungeness crabs generally prefer cooler northern and central California waters while they are uncommon south of Point Conception. Typically, these crabs are found at depths of less than 300 feet. Their recent appearance in the Atlantic Ocean, far from their known range has raised concerns about their possible effects on the local wildlife.

Description: Dungeness crabs have a wide, long, hard shell, which they must periodically molt to grow. They have five pairs of legs, which are similarly armored, the foremost pair of which ends in claws the crab uses both as defense and to tear apart large food items. The crab uses its smaller appendages to pass the food particles into its mouth. As been established, the legal measurement for crabs is defined as the shortest distance through the body from the edge of the shell to the edge of the shell directly from front of points (lateral spines). Dungeness crab is one of the largest edible crabs along the Pacific Coast of America. Dungeness crabs are characterized by their light reddish brown on the back.

Typically, the carapace width of mature Dungeness crabs is less than 20 centimeters with females much smaller than males whereas in the adult stage, the average size of female seldom attains a width much greater than 17 centimeters. In females, the abdomen, or tail flap, is much broader than in the male crab. This broad tail flap is allows to accommodate and protect the very large number of eggs until hatched. In both male and female, the tip of the last segment of the tail flap is rounded. As been established, the legal measurement for crabs is defined as the shortest distance through the body from the edge of the shell to the edge of the shell directly from front of points (lateral spines).

Feeding habits: Dungeness feeds on a variety of marine invertebrates and fish. While juveniles feed on fish, shrimp, molluscs and crustaceans, adults feed on bivalves, crustaceans and fishes. They use their pinching claws in opening shells.

Life cycle: Mating between mature crabs occurs immediately after the female has molted and before the new exoskeleton hardens. Upon mating, the female extrudes the eggs from her body several months later; however, they remain attached under her abdomen for three to five months until they hatch into free-swimming crabs which go through five larval stages before reaching maturity after about 10 molts or two years.

Dungeness crab fishery: The most popular methods for catching the crustaceans are with crab pots (or traps), loop traps and hoop nets. Crab pots or traps which are designed to only capture the target crab of legal-sized, Crab pots and traps are generally designed to target a particular species, which means that under-size crabs and accidental capture is usually rare. Moreover, as the pots or traps do not injure the captured animals, it is easy to release any unwanted species or undersized crabs. Because crab pots and traps sit stationary on the seafloor in one location, they do not cause significant habitat destruction.

Whether traps or hoop net are used, periodic checking of the gear is done in order to capture target crabs and in the same time release unwanted catch unharmed.

Conservation: In addition to the periodic inspection of fishing gears (every two hours), the recreational size limit for Dungeness crab has been set to be five and three-quarter inches measured across the shell. Moreover, conservation measures limit the number of crabs kept by recreational crabbers up to ten crabs per day. In addition, no Dungeness crab may be taken from San Francisco or San Pablo bays, which are important crab nursery areas.

 

Permanent link to this article: http://fishconsult.org/?p=14006