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Snow crab

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Snow crab
Tanner crab.jpg
Scientific Classification
Species
  • C. Angulatus
  • C. Bairdi
  • C. Opilio
  • C. Japonicus
  • C. Tanneri
Biomass of Snow Crab
Snow crab chart biomass.gif

Snow crab is the common name for the members of the genus Chionoecetes, which is made up of five different species. Other common names include the Opilio crab or queen crab. Snow crabs live in the Bering Sea and Chukchi Sea. In the Bering Sea, Snow crabs are found at depths of less than 650 feet where it is usually muddy or sandy. Snow crabs tend to migrate from shallower to deeper waters over their lifetime.

Snow crabs have a unique form of protection against enemies. Each one of their legs has a small circular groove at its base. This groove allows the crab to snap off the leg should it become entangled or held by a predator. There is a valve at this point which prevents major blood loss. It also helps by healing the scar quickly. A leg begins to grow from the scar. With the next molt a small new leg is formed. It typically takes three molts for the leg to grow back to normal size. [1]

Contents

Anatomy

The Snow crab lives in the colder waters of both the Pacific and the Atlantic Ocean.[2] Females stop growing after they molt one final time; which occurs after they reach maturity. They rarely exceed 3.15 inches carapace width. Males stop growing after they grow a single large claw. Male snow crab can reach a maximum size of 6 inches in carapace width. Males can live for up to 14 years.[3]

The snow crab is a crustacean with a flat and almost circular body. It is slightly wider in the back. It has five pairs of long spider-like legs that are flattened. The first set is equipped with claws. Shell colour varies. After molting it is reddish on the upper surface and creamy white beneath. The animal is then called a white crab. Once the shell hardens and ages it changes to a dull greenish brown above and yellow beneath.[4]

Reproduction

Eyed snow crab eggs are attached to the female's abdomen by a stalk , or funiculus.

The first stage of reproduction is when the male and female snow crabs mate. After they mate than the female will carry around the eggs for about one year until they hatch into free swimming larvae. The larvae drift with the currents and tides until finally they settle to the ocean bottom. Once there they molt into a miniature version of the adult crab. The crabs continue to molt and grow for several years until they are sexually mature. Females are also able to store extra sperm in small pouches inside their bodies. They can use the extra sperm to fertilize later eggs without mating. Females can produce up to several hundreds of thousands of eggs per year.[5]

Ecology

Snow crabs tend to live in the Bering Sea and Chukchi Sea. In the Bering Sea, snow crabs are found at common depths of less than 650 feet where it is muddy. Snow crabs migrate from shallower to deeper waters over their lifetime. They usually migrate because they have different needs such as prey, and temperature. This all depends on what stage of their lives they are in. Crab eat different things and are consumed by different predators at each stage of their lives. For example larval crab eat plankton and are eaten by fish, such as Pollock, salmon, and herring. Adult Snow crab eat a variety of benthic organisms which include bivalves, brittle star, crustaceans, polychaetes, gastropod, and fish. Their predators include bearded seals, sea otters, octopus, groundfish, Pacific cod, and halibut.[6]

(Chionoecetes opilio) Only male crabs can legally be caught for commercial use. Males of commercial size usually range between 8 and 9 years old and weigh between 1.1 and 2.2 pounds.

Biomass

Biomass refers to the amount of crab in the ocean. Scientist can't find every single crab and weigh them all individually. Instead they use models to estimate. These biomass estimate help determine if a certain area is being fished too heavily or if it may be able to tolerate more fishing. [7] The Alaskan Fishery department uses this information to set the limit on how much crab fishers are allowed to bring in. Over the past couple of decades this time limit has become shorter and shorter. What once used to be a month or two long season is now a week long.

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References

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