Blue shark
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Blue shark

Common name : blue shark
Scientific name : Prionace glauca
Length : 3.8 m
Weight : approximately 200 kg (400 lb)
Population : unknown
Distribution : in tropical, subtropical and temperate ocean waters
Issue : excessive exploitation
IUCN Red List status : near threatened

Description
The blue shark is an oceanic species that inhabits the tropical and temperate waters of the entire planet. It is found from the surface to a depth of about 350 m, living above continental shelves and seamounts and in open waters. Although the blue shark is one of the most common and widespread shark species, mass fishing is becoming an issue. The blue shark is easily identifiable by its magnificent, sleek and tapered body, deep indigo blue topside and white underside. Its nose is cone-shaped, and its triangular teeth are razor-sharp. It feeds on different types of fish including herring, cod, haddock and mackerel; sea animals such as squid, crab, rays, sea snakes and turtles; as well as crustaceous remains and small sharks. It also occasionally feeds on seabirds and marine debris. The blue shark’s feeding habits are hard to pin down because it feeds at all hours of the day, although it seems to be most active at night. A migratory species, the blue shark can travel up to 9,200 km, according to GPS tracking devices that have been attached to a few individuals. Blue sharks usually travel slowly, following currents, on these transoceanic journeys.

Females reach sexual maturity at 5 or 6 years of age, whereas males mature at around 4 to 5 years. To mate, males attempt to seduce females by adopting a surprisingly aggressive behavior—biting the female! As a result, the sex of a blue shark is usually determined by counting the number of bites on its body. By the same token, millions of years of evolution have led females to develop skin three times as thick as that of males to resist these assaults. After a 9 to 12 month gestation period, females usually give birth to around 25 to 50 pups, but this number can be as high as 135. The lifespan of a blue shark is typically 20 years. Other than human beings, these sharks have no other predators. Younger individuals may be eaten by the larger species of great white shark and tiger shark, but adult blue sharks have no reason to fear these species in vast oceans where, in theory, food abounds.

Threats
Blue sharks are fished in great numbers around the world, with around 20 million individuals caught each year, mainly as bycatch. Bycatch refers to a species caught unintentionally in a fishery while attempting to catch another fish. Although shark meat is eaten, it is not specifically sought after. Shark meat is also used to feed other fish; its skin is used as leather, and its fins are used for shark fin soup, a popular dish in China. At this rate of extraction, the species may be classified as vulnerable in the near or distant future.

Did you know?
The blue shark is viviparous. This term means that the female of the species gives birth to fully formed offspring who matured in the uterus by obtaining nutrients from the placenta.

REFERENCES: Red List of Threatened Species of the International Union for Conservation of Nature (IUCN) and Encyclopedia of Life.

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