The blue shark (Prionace glauca) has a cosmopolitan distribution. It lives in tropical and temperate waters, and is found in large numbers in the Atlantic Ocean, including the Mediterranean. Its wide-ranging habitat also includes South Africa to Indonesia and Japan to New Zealand in the Indian and western Pacific Oceans. Blue sharks swim in the pelagic region, in depths of up to 1,148 ft (350 meters). While they rarely swim near the shore, they may adopt inshore areas of oceanic islands and places where the continental shelf is narrow. They usually move at a leisurely pace, but are perfectly capable of rapid movement. Blue sharks use their caudal fin (tail) to propel themselves forward. They can reach speeds of up to 30 mph, but this aspect has not been extensively studied. They are ectothermic (cold-blooded), which means they have to be wary of expending too much energy in one go. There are records of blue sharks migrating long distances, such as from New England to South America. This is probably a population-specific behavior, and not a generic occurrence. They are sometimes called 'wolves of the sea' due to the structure of their schools, which are sometimes based on sex and size, and their pack hunting strategy. Physical Description ▶► Like all sharks, they have a long, sleek, and streamlined body that is dark blue on the top, light blue on the sides, and almost completely white on the belly. This pattern of colors on their skin is called countershading, and acts as the perfect camouflage in their natural habitat. When viewed from above, their dark back blends into the dark ocean, and when viewed from below, their white bellies are harder to spot against the bright surface. This coloring is also seen in other predatory fish, such as dolphins. ▶► The blue shark has a conical, pointed snout and large eyes. It has two long pectoral fins, one medium-sized dorsal fin and triangular, serrated teeth. ▶► The length of the blue shark usually lies between the range of 6 to 10 feet. They are believed to live for up to 20 years, but their life cycle has not been extensively studied. ▶► Females weigh between 100 and 200 kg (220-440 lb), but the heaviest recorded weight is 391 kg (860 lb). Males weigh much less than females, tipping the scales at 30-60 kg (66-132 lb). Diet ▶► While the blue shark is perfectly capable of taking large prey, the majority of its diet comprises invertebrates such as squids, cuttlefish and pelagic octopi, and small bony fishes. They are opportunistic feeders and if the opportunity presents itself, they will feed on fish caught in nets, or on carcasses. Life Cycle ▶► They are viviparous and give birth to live offspring that have hatched from eggs internally. Depending on the mother's size, it is capable of giving birth to over 100 pups at one time. It goes through a gestation period of between 9 and 12 months. ▶► An interesting fact about the blue shark is that since their mating ritual includes biting, the females' skin has evolved to be three times as thick as the males. ▶► They are naturally preyed upon by larger sharks, such as great white sharks and bull sharks, and killer whales, but otherwise lack a major regular predator. However, blue sharks are usually host to a wide variety of internal and external parasites. Relationship With Humans Blue sharks are not majorly affected by human activities. Likewise, blue shark attacks on humans are less likely than other, larger sharks. ▶► They are considered dangerous to humans and may attack open-water divers. There are accounts of people stranded in the ocean as the outcome of an air disaster or a shipwreck, being attacked by them. The International Shark Attack File lists thirteen documented unprovoked attacks by blue sharks, resulting in 4 fatalities. But the threat that they present to humans is greatly outweighed by the threat we present to them. They are compromised by human fishing nets in which they often get entangled. However, they are not fished for consumption on a commercial level, since their meat ammoniates quickly and isn't popular in any major cuisine. While they are sometimes released, more often than not their fins are cut and sold. The IUCN Red List lists the status of blue sharks as Near Threatened. While they are not over-fished and are not overly at risk from human activities, the species can be helped by finding ways to minimize the loss of blue sharks caught as bycatch.