The Blue Shark (Prionace glauca) is one of the most easily recognized sharks. It has a distinct colouration, a deep indigo blue from above and a vibrant blue on its sides, changing to white underneath. The large pectoral fins are also easy to spot as they are as long as the distance between the tip of the snout to the last gill slit. The blue shark is a long slender shark, reaching 13 feet (3.8 meters) in length. It is likely the most prolific of the large shark species as it is abundant throughout its range. The blue shark has a weak keel on the caudal peduncle and the upper lobe of the caudal fin is larger than the lower. The teeth on both the lower and upper jaw have triangular cusps with smooth or finely serrated edges.
In temperate waters the blue shark is a wide ranging pelagic species occurring near the surface. In tropical waters the blue shark is more commonly found in deeper waters as it prefers temperatures between 46-61 degrees Farenheit (7-16 degrees Celsius).
Blue sharks are found world wide in temperate and tropical waters. They are a pelagic species that rarely comes near shore but have been known to frequent inshore areas around oceanic islands and locations where the continental shelf is narrow. In the Atlantic they can be found from New Foundland, Canada to Argentina and from Norway to South Africa, including the Mediterranean. They range from South Africa to Indonesia and from Japan to New Zealand in the Indian and western Pacific Oceans. In the eastern Pacific, blue sharks range from the Gulf of Alaska to Chile.
The diet of this shark includes many types of fish and squid, and may sometimes eat seals. Although flatfishes make up part of the diet, blue sharks predominantly eat pelagic fishes such as herring, silver hake, white hake, red hake, cod, haddock, pollock, mackerel, butterfish , sea raven, tuna and swordfish. Fish caught on longlines during fishing are often attacked and consumed by blue sharks, who in turn often become ensnared in the fishing gear.
The blue shark is a viviparous species, nourishing the young in the uterus and giving birth to live pups. The new-born pups measure 40 to 51 cm (16 to 20 inches) in length and litters usually consist of between 25 to 50 individuals. Litters of up to 135 pups have been reported. Females reach sexual maturity at a size of 2.2 to 3.2 meters (7 to 11 feet), while for males it is achieved at lengths of 1.8 to 2.8 meters (6 to 9 feet). After copulation the females may retain and nourish the spermatozoa in the oviducal gland for months or even years while she awaits ovulation. Once the eggs have been fertilized there is a gestation period of between 9 and 12 months.