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  • Abigail Chapman

Blue Shark

Blue Shark 

The Blue shark (Prionace glauca), also known as blue dogs, blue pointers and blue whalers, is a part of the Carcharhinidae family. Other members of this family include olive shark, silky shark and Blacktip reef shark. Prionace is derived from Greek, “prion” meaning saw and “akis” meaning point, while the species name glauca is derived from the Latin term “glaucas” meaning bluish grey or green in English, referring to the blue color of the shark.

Blue shark in South Africa

Anatomy and appearance 

Most of the adult blue sharks reach lengths of 1.7 to 2.2 meters long however some may grow even longer at nearly 4 meters and weighing 206kg. The blue shark has a slender body with a large eye and a long conical snout that is longer than the width of its mouth. It has extremely long, pointed pectoral fins, which are typically as long as the distance from its snout to posterior gill slit. The dorsal fin is moderate in size and set back where it is actually closer to the pelvic fin insertion than the pectoral insertion point.


The aerodynamic shape and lightness of the blue shark body allow it to move elegantly across the oceans. It exhibits countershading like many other sharks which helps provide camouflage for the shark as it swims in the open ocean. The upper part is an indigo blue tone while the ventral and the sides are white. This species presents slight sexual dimorphism since the female tends to measure little more than 1 meter in comparison with the male, along with adult females being slightly larger and having thicker skin than males


Habitat

Blue shark habitat
www.iucnredlist.org, CC BY-SA 3.0

The blue shark inhabits a great diversity of areas around the world and is one of the most widely distributed of all shark species.The blue shark’s habitat consists of open ocean areas from the surface to 1,148 ft (350 meters) in depth. They prefer cooler water ranging from 12-20°C. When in the tropics the blue shark seeks deeper waters with cooler temperatures. At night, blue sharks often swim inshore around oceanic islands. The Blue Shark fancies approaching the shores, where divers and boats see it often. It inhabits the epipelagic and mesopelagic zones near the coasts and the continental shelves, but if it dwells in tropical waters, then it tends to go towards deeper waters.


Diet

The Blue shark is a carnivorous predator that feeds on about 24 species of cephalopods and 16 species of fish. Small bony fishes, such as herring and sardines, and invertebrates, such as squid, cuttlefish and pelagic octopi, make up a majority of the blue shark’s diet. They feed actively at night but are known to feed throughout the 24 hours of the day. Blue sharks often aggregate to feed on schools of prey. One of the blue shark’s most common prey items is squid. The blue shark surrounds its prey before attacking it. When needed it joins with other sharks of the same species and cooperates to attack larger prey and facilitate their capture. Its swimming speed and its triangular teeth help this shark tear the skin and flesh of the most complicated animals. Whale carcasses encountered offshore will often have large numbers of blue sharks feeding on them. They are also one of the only non-filter feeding sharks to be recorded feeding on krill.


Population

Blue sharks frequently live to age 15 or 16 in the wild but to about age 8 in captivity. Both sexes reach sexual maturity at age 5 or 6 years old, and reproducing females have litters of 25–50 pups after a 9–12-month gestation period but can have up to 80 pups in a litter. In some cases, litters of as many as 135 pups have been observed. Pups are approximately 35-50 cm in length at birth. Blue sharks are viviparous, giving birth to live young that are nourished by a placental yolk sack internally until they are fully developed. Juveniles typically stay in pupping areas of the subArctic. Since the 1970s, blue shark populations have declined in the Atlantic and Indian Oceans, and they have increased only slightly in the Pacific Ocean. Predators of the blue shark include killer whales (Orcinus orca) and larger sharks including the Shortfin Mako (Isurus oxyrinchus) and the Great White shark (Carcharodon carcharias).


Conservation

The blue shark is the most heavily fished shark in the world with annual global catch estimates of around 20 million individuals each year. These developments prompted the International Union for Conservation of Nature and Natural Resources(IUCN) to list the species as near threatened. Blue sharks are under threat because they are often caught as bycatch by commercial fishing fleets, which often go on to harvest the sharks’ meat and fins. Blue sharks are also sought-after by the sportfishing industry, which releases them after capturing them; however, this can sometimes result in the death of the shark. Some countries have banned shark finning, but still, there are no international treaties linking all aspects of blue shark protection. A group of organizations is committed to regulating fisheries and protecting the species, such as the International Plan of Action for the conservation and management of Sharks, the Sustainable Fisheries Act and the Code of Conduct for Responsible Fisheries from the Food and Agriculture Organization of the United Nations Fisheries and Aquaculture. They do make up 60% of all reported shark catches and singularly dominates both the fin trade and shark meat trade.


Blue Shark
Blue Shark: Steve Woods

Additional special information

It is a slow-swimming animal that increases its speed when feeling stimulated by external factors, such as the presence of animals from which it can feed on. If this happens, it then becomes one of the fastest fish. The blue shark is nomadic and shows a clockwise migration pattern following the Gulf Stream to

the Caribbean, passing along the coast of the United States, Eastern Europe, Southern Africa and back to the Caribbean.

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