The Blue shark, Prionace glauca, is easy to distinguish from other sharks on its blue colouration. It belongs to the family Carcharhinidae, which means that it is a Requiem shark. When you watch a Blue shark from above you will see a deep indigo blue colour, while a Blue shark observed from the side looks bright blue. The belly is white and the tips of the pectoral fins and the anal fin has a dusky coloration. The elongated and slender body of a Blue shark can normally reach a size of 3.8 metres (13 feet), but the longest Blue shark ever found was even larger than that and measured 400 cm. The weight of the heaviest known Blue shark was 205.9 kg. The remarkably long pectoral fins of the Blue shark are always of the same size as the length between the last gill slit and the tip of the shark's snout. The snout is long and has a conical shape. The upper lobe of the Blue shark's caudal fin is considerably bigger than the lower, and the caudal peduncle has a weak keel. There is no interdorsal ridge. All Blue sharks have large eyes covered by nictitating membranes.
The teeth in the upper as well as the lower jaw are equipped with triangular cusps that have smooth or finely serrated edges. The serrated teeth make it easier for the Blue shark to catch slippery animals, such as squids. The teeth are located in rows, and a new tooth will smoothly rotate into place as soon as the old tooth has been worn down, lost or damaged. The Blue shark will only use the first two rows of teeth when it hunts, the other rows are just there to rotate into place when necessary.
The Blue shark is one of the fastest swimming sharks, and can easily keep up the pace with most fish species. The body is long, sleek and perfect for fast swimming since the water resistance becomes very small. The large caudal fin moves side-to-side and provides plenty of power to the Blue shark. It swims in a graceful manner and is strong enough to make leaps out of the water. More research is needed to confirm the maximum speed of the Blue shark. Some scientists estimate the maximum speed to be roughly 35 km/h (22 miles per hour), while others claim that the maximum speed can be as much as 97 km/h (60 miles per hour).
The Blue Shark is found in a large part of the world; between 50º N latitude and 50º S latitude in offshore and inshore waters. It inhabits the Atlantic and Pacific Ocean as well as the Indian Ocean and likes both temperate and tropical waters. It is believed to be the widest ranging chondrichthyian and is highly migratory. One Blue shark that was tagged in the waters off New Zealand was later found 1,200 km off the coast of Chile. The Atlantic Blue sharks follow the warm Gulf Stream and migrate across the Atlantic every year. Their travelling begin in the Caribbean Sea and proceeds along the U.S. coast and then eastward to Europe. They then turn south and follow the West African coastline before they turn west and swim back to the Caribbean Sea.
In the western Atlantic you can see Blue sharks from Newfoundland in Canada and down to Argentina. It is also found in the Central Atlantic and from Norway to South Africa in the Eastern Atlantic. (The Mediterranean included.) In the Indo-West Pacific region it is spread from East Africa to Indonesia and Japan. It is frequently seen around Australia, New Zealand and New Caledonia. In the Eastern Pacific the Blue shark inhabit the vast area between the Gulf of Alaska and Chile.
The Blue shark is chiefly oceanic, but it is also commonly found close to inshore, especially where the continental shelf is narrow. In temperate regions the Blue shark will often stay close to the waters surface in the pelagic areas. In the warm tropical waters it dives much deeper, since it prefers the water temperatures between 7 º and 16 º C that is typically found further down. The known depth range for the Blue shark is 0 - 350 metres, and it is commonly found down to 150 m. Blue sharks will often form huge schools. These schools are always consisting of only males or only females, and all the Blue sharks are of similar size. We still do not know why they do this, but it might be a way of avoiding attacks from larger predators.
A Blue shark feed mainly on squid and bony fish. Pelagic fish typically make up the base of the Blue shark's diet, such as swordfish, tuna, mackerel, cod, herring and sea raven. Seals, flatfish, pelagic red crabs and cetacean carrion are also a part of its normal diet. The Blue sharks will frequently attack fish that is already caught by long-lines or similar fishing gear, which unfortunately means that Blue sharks are often ensnared in the equipment themselves. The Blue shark is also known to sometimes eat sea birds and garbage.
The Blue shark is believed to be one of the most reproductive large shark species, but the minimum population doubling time is still more than 14 years. The reproductive method is viviparous, which means that the eggs are developed into pups inside the female Blue shark and receive nutrition inside her body. After mating the female Blue Shark can store the sperm for several months; sometimes even years. The sperms are protected inside her oviducal gland where they will be provided with nutrition to stay alive. When she finally ovulates, the fertilization takes place and live Blue shark pups are born after a 9 to 12 month long gestation period. One Blue shark litter typically contains 25-50 pups, but litters as large as 135 have been reported. The larger the female Blue shark is, the more pups in each litter. Very small Blue sharks can have litters with no more than 4 pups. A newborn Blue shark pup is between 40 and 51 cm (16 and 20 inches) long. A female Blue shark will not become sexually mature until she has grown to be at least 2.2 - 3.2 meters (7 - 11 feet), while a male Blue shark usually matures when it is between 1.8 and 2.8 meters (6 and 9 feet). The maximum age of a Blue shark exceeds 20 years.
The Blue shark should always be treated with caution since there have been reported attacks on humans. The Blue shark is hunted and sold as food. The meat is sold fresh or preserved, and the fins are popular in soups. The hides of the Blue Shark are used for leather. The Blue shark is classified as low risk/near endangered.
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