Crab fisheries
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Crab fisheries are fisheries which capture or farm crabs. Crabs are found in all of the world's oceans. There are also many freshwater and terrestrial crabs, particularly in tropical regions.
Crabs make up 20% of all marine crustaceans caught and farmed worldwide, with over 1½ million tonnes being consumed annually. The horse crab accounts for one fifth of that total. Other important taxa include flower crabs (Portunus pelagicus), snow crabs (Chionoecetes), blue crabs (Callinectes sapidus), Charybdis spp., edible crabs (Cancer pagurus), Dungeness crabs (Cancer magister) and mud crabs (Scylla serrata), each of which provides more than 20,000 tonnes annually [1].
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[edit] Horse crabs
Horse crabs (Portunus trituberculatus), also known as the gazami crab or Japanese blue crab or horse crab, is the most widely fished species of crab in the world, with over 300,000 tonnes being caught annually, 98% of it off the coast of China [2].
Horse crabs are found from Hokkaidō to South India, throughout the Malay Archipelago and as far south as Australia. In the Malay language, it is known as ketam bunga or "flower crab". It lives on shallow sandy or muddy bottoms, less than 50 m deep, where it feeds on seaweeds and predates upon small fish, worms and bivalves. The carapace may reach 15 cm (6 inches) wide, and 7 cm (2¾ in) from front to back.
[edit] Flower crabs
Flower crabs (Portunus pelagicus), also known as blue crabs, blue swimmer crabs, blue manna crabs or sand crabs, are a large crab found in the intertidal estuaries of the Indian and Pacific Oceans (Asian coasts) and the Middle-Eastern coast of the Mediterranean Sea. The name flower crab is used in east Asian countries while the latter names are used in Australia. The crabs are widely distributed in eastern Africa, Southeast Asia, Japan, Australia and New Zealand.
The carapace can be up to 20 cm in width. They stay buried under sand or mud most of the time, particularly during the daytime and winter, which may explain their high tolerance to NH4+ and NH3 [3].
The species is commercially important throughout the Indo-Pacific where they may be sold as traditional hard shells, or as "soft shelled" crabs, which are considered a delicacy throughout Asia. The species is highly prized as the meat is almost as sweet as the blue crab, although P. pelagicus is physically much larger.
These characteristics, along with their fast growth, ease of larviculture, high fecundity and relatively high tolerance to both nitrate [4] [5] and ammonia [3], (particularly NH3-N, which is typically more toxic than NH4+, as it can more easily diffuse across the gill membranes), makes this species ideal for aquaculture.
[edit] Snow crabs
Snow crabs (Chionoecetes), also known as spider crabs, queen crabs and other names, is a genus of crabs that live in the cold waters of the northern Pacific and Atlantic Oceans [6].
Snow crab are caught as far north as the Arctic Ocean, from Newfoundland to Greenland in the Atlantic Ocean, and across the Pacific Ocean, including the Sea of Japan, the Bering Sea, the Gulf of Alaska, Norton Sound, and even as far south as California for Chionoecetes bairdi. Fishing for opilio (and rarely bairdi) crab has been the focus of the second half of all three seasons of Deadliest Catch on the Discovery Channel.[7]
[edit] Blue crabs
The Chesapeake Bay, located in Maryland and Virginia,is famous for its blue crabs, and they are one of the most important economic items harvested from it. In 1993, the combined harvest of the blue crabs was valued at around 100 million U.S. dollars. Over the years the harvests of the blue crab dropped; in 2000, the combined harvest was around 45 million dollars. Late in the twentieth century, the Maryland Department of Natural Resources created stricter guidelines for harvesting blue crabs to help increase populations[citation needed]. These include raising the legal size from 5 to 5¼ inches (from 12.7 to 13.3 cm) and limiting the days and times they may be caught.
While blue crabs remain a popular food in the Chesapeake Bay area, the Bay is not capable of meeting local demand. Crabs are shipped into the region from North Carolina, Louisiana, Florida and Texas to supplement the local harvest.
[edit] Edible crabs
Edible crabs (Cancer pagurus), also known as Cromer crabs or chancre, is a species of crab found in the North Sea, North Atlantic and the Mediterranean Sea. It is a robust crab of a reddish-brown colour, having an oval carapace with a characteristic "pie crust" edge and black tips to the claws [8]. Mature adults may have a carapace width of up to about 25 cm and weigh up to 3 kg. The edible crab is abundant throughout the northeast Atlantic as far as Norway in the north and northern Africa in the south, on mixed coarse grounds, mud and sand from shallow sublittoral to about 100 m. It is frequently found inhabiting cracks and holes in rocks but occasionally also in open areas. Smaller specimens may be found under rocks in the littoral zone [9].
Edible crabs are heavily exploited commercially throughout their range. It is illegal to catch crabs of too small a size around the coast of Britain, a conservation measure brought in the 1870s. Crabs with a shell diameter of less than 100 mm should not be taken.
[edit] Dungeness crabs
The Dungeness crab inhabits eelgrass beds and water bottoms from the Aleutian Islands in Alaska to Santa Cruz, California [10]. Its binomial name, Cancer magister, simply means "master crab" in Latin.
They measure as much as 25 cm (10 inches) in some areas off the coast of Washington, but typically are under 20 cm (8 inches).[11] They are a popular delicacy, and are the most commercially important crab in the Pacific Northwest, as well as the western states generally [12].
They are named after Dungeness, Washington [10], which is located approximately five miles north of Sequim and 15 miles east of Port Angeles. The annual Dungeness Crab and Seafood Festival [13] is held in Port Angeles each October.
Dungeness crab have recently been found in the Atlantic Ocean, far from their known range, raising concern about their possible effects on the local wildlife [14].
[edit] Mud crabs
Mud crabs (Scylla serrata), also known (ambiguously) as mangrove crabs or black crabs, are an economically important crab species found in the estuaries and mangroves of Africa, Australia and Asia. In their most common form, the shell colour varies from a deep, mottled green to very dark brown. Generally cooked with their shells on, when they moult their shells, they can be served as a seafood delicacy, one of many types of soft shell crab. They are among the tastiest crab species and have a huge demand in South Asian countries where they are often bought alive in the markets. In the northern states of Australia and especially Queensland, mud crabs are relatively common and generally prized above other seafood within the general public.
There has been a huge interest in the aquaculutre of this species due to their high demand/price, high flesh content and rapid growth rates in captivity. In addition they have a high tolerance to both nitrate [15] and ammonia (particularly NH3) tolerance (twice that of the similar sized Portunus pelagicus), which is beneficial because ammonia-N is often the most limiting factor on closed aquaculture systems [16]. Their high ammonia-N tolerance may be attributed to various unique physiological responses which may have arisen due to their habitat preferences [16]. However their aquaculture has been limited due to the often low and unpredictable larvae survival.
[edit] See also
[edit] References
- ^ Global Capture Production 1950-2004. FAO. Retrieved on August 26, 2006.
- ^ FAO fisheries global information system. Retrieved on 2006-08-02.
- ^ a b N. Romano & C. Zeng (2007). Ontogenetic changes in tolerance to acute ammonia exposure and associated histological alterations of the gill structure through the early juvenile development of the blue swimmer crab, Portunus pelagicus. Aquaculture 266: 246–254. doi:10.1016/j.aquaculture.2007.01.035.
- ^ N. Romano & C. Zeng (2007). Acute toxicity of sodium nitrate, potassium nitrate and potassium chloride and their effects on the hemolymph composition and gill structure of early juvenile blue swimmer crabs (Portunus pelagicus Linnaeus 1758) (Decapoda, Brachyura, Portunidae). Environmental Toxicology and Chemistry 26: 1955–1962. doi:.
- ^ N. Romano & C. Zeng (2007). Effects of potassium on nitrate mediated changes to osmoregulation in marine crabs. Aquatic Toxicology 85 202-208
- ^ Jadamec, L. S., W. E. Donaldson & P. Cullenberg (1999). Biological Field Techniques for Chionoecetes crabs. University of Alaska Sea Grant College Program. Part 1 Part 2
- ^ Deadliest Catch Official Site
- ^ Neal, K.J. & E. Wilson (2005). Edible crab, Cancer pagurus. Marine Life Information Network.
- ^ Edible crab (Cancer pagurus). ARKive.org.
- ^ a b The Dungeness Crab. Dungeness community website. Retrieved on August 28, 2006.
- ^ Crabs are measured across the widest part of their back, excluding the legs. See, e.g., 2006-2007 Fishing in Washington Rule Pamphlet (pdf), p. 130.
- ^ Species Fact Sheet. Cancer magister Dana, 1852. FAO (2004-01-22).
- ^ Dungeness Crab and Seafood Festival.
- ^ Andrea Cohen. "Crab nabbed; circumstances fishy", MIT News Office, 2006-08-09.
- ^ N. Romano & C. Zeng (2007). Effects of potassium on nitrate mediated changes to osmoregulation in marine crabs. Aquatic Toxicology 85 202-208
- ^ a b N. Romano & C. Zeng (2007). Acute toxicity of ammonia and its effects on the haemolymph osmolality, ammonia-N, pH and ionic composition of early juvenile mud crabs, Scylla serrata (Forskål). Comparative Biochemistry and Physiology A 148 (2): 278–285. doi:10.1016/j.cbpa.2007.04.018.
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