Blue shark

Blue shark Temporal range: Pliocene to Present
Conservation status
Near Threatened  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Carcharhiniformes
Family:	Carcharhinidae
Genus:	Prionace Cantor, 1849
Species:	P. glauca
Binomial name
Prionace glauca (Linnaeus, 1758)
Range of blue shark

The blue shark, Prionace glauca, is a carcharhinid shark which inhabits deep waters in the world's temperate and tropical oceans. They prefer cooler waters and do not live for example, in the Yellow Sea or in the Red Sea. Blue sharks migrate long distances, for example from New England to South America. Although generally lethargic, they can move very quickly. Blue sharks are viviparous and are noted for large litters of 25 to over 100 pups. They feed primarily on small fish and squid, although they can take larger prey. They often school segregated by sex and size, and this behavior has led to their nickname "wolves of the sea".

Anatomy and appearance

Illustration of Prionace glauca.

Blue sharks are light-bodied with long pectoral fins. The top of the body is deep blue, lighter on the sides, and the underside is white. It grows to Template:M to ft long. The shark's typical weight is 136 to 182 kilograms (300 to 401 lb) and can grow to Template:Kg to lb. The highest reported weight was Template:Kg to lb. They are easy to distinguish from other sharks.

Reproduction

Back of blue shark

They are viviparous, with a yolk-sac placenta, delivering 4 to 135 pups per litter. The gestation period is between 9 and 12 months. Females mature at 5 to 6 years of age and males at 4 to 5. Courtship is believed to involve biting by the male, as mature specimens can be accurately sexed according to the presence or absence of bite scarring. Female blue sharks have adapted to the rigorous mating ritual by developing skin 3 times thicker than male skin.

Ecology

Range and habitat

The blue shark is the most widely distributed animal in the world. It is an oceanic and epipelagic shark found worldwide in deep temperate and tropical waters from the surface to about 350 meters. In temperate seas it may approach shore where it can be observed by divers, while in tropical waters it inhabits greater depths. It lives as far north as Norway and as far south as Chile. Blue sharks are found off the coasts of every continent, except Antarctica. Its greatest Pacific concentrations occur between 20° and 50° North but with strong seasonal fluctuations. In the tropics it spreads evenly between 20° N and 20° S. It prefers waters with a temperature range of 7–16 °C (45–61 °F) but will tolerate temperatures of 21 °C (70 °F) or above. Records from the Atlantic show a regular clockwise migration within the prevailing currents.

Feeding

Squid are important prey for blue sharks, but their diet includes other invertebrates such as cuttlefish and pelagic octopuses, as well as lobster, shrimp, crab, a large number of bony fishes, small sharks, mammalian carrion and occasional sea birds. Whale and porpoise blubber and meat have been retrieved from the stomachs of captured specimens and they are known to take cod from trawl nets. Apparently, blue sharks at most rarely eat tuna.

Predators

Adult blue sharks do not suffer predation on a regular basis, except by humans. Young and smaller individuals may get eaten by any sufficiently large carnivore. However, they are host to several species of parasites. For example, the blue shark is the definite host of the tetraphyllidean tapeworm, Pelichnibothrium speciosum (=Prionacestus bipartitus). They become infected by eating intermediate hosts, probably Opah, (Lampris guttatus), and/or longnose lancetfish, (Alepisaurus ferox).

Relationship to humans

Blue sharks are the most heavily fished sharks mainly as by-catch. It is estimated that 10 to 20 million individuals are killed each year as a result of fishing. The flesh is edible, but not widely sought after; it is consumed fresh, dried, smoked and salted and diverted for fishmeal. The skin is used for leather, the fins for shark-fin soup and the liver for oil. Blue sharks are occasionally sought as game fish.

Blue sharks are not considered dangerous and rarely attack humans. Most interactions take place in deep water and on small boats as they rarely venture close to shore. As of 2008, there had been only 3 encounters with humans and one fatality.

In captivity

Blue sharks, like most pelagic sharks, tend to fare poorly in captivity. Attempts at keeping them using circular tanks with long glide paths, and pools with Template:M to ft central depth gently ascending to zero depth have met with mixed results at best; most specimens last less than 30 days. As with other pelagic sharks, they seem to have trouble avoiding walls or other obstacles. In one case at Sea World San Diego, the blue did fairly well until bull sharks were added to the tank; the bulls ate the blues. The captivity record for blue sharks as of 2008 was held by The New Jersey Aquarium for a specimen that lasted roughly 7 months before expiring of an apparent bacterial infection. Under consideration is studying the sharks in a large naturally secluded environment such as the Great Salt Lake in Utah.

See also

• For a topical guide, see Outline of sharks.
• List of sharks
• List of prehistoric cartilaginous fish

External links

• "Prionace glauca". Integrated Taxonomic Information System. 15 November. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
• Blue shark, Prionace glauca at marinebio.org
• "Blue shark, Prionace glauca" at the Encyclopedia of Life
• Scholz, Tomáš; Euzet, Louis; Moravec, František (1998). "Taxonomic status of Pelichnibothrium speciosum Monticelli, 1889 (Cestoda: Tetraphyllidea), a mysterious parasite of Alepisaurus ferox Lowe (Teleostei: Alepisauridae) and Prionace glauca (L.) (Euselachii: Carcharinidae)". Systematic Parasitology. 41 (1): 1–8. doi:10.1023/A:1006091102174. {{cite journal}}: Invalid |ref=harv (help)</ref>

• ARKive - Images and movies of the blue shark (Prionace glauca)
• Canadian Shark research laboratory