The blue shark (''Prionace glauca''), also known as the great blue shark, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

requiem shark Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas (sometimes of brackish or fresh water) and include such species as the tiger shark, bull shark, le ...

, in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Carcharhinidae, which inhabits deep waters in the world's temperate and tropical oceans. Averaging around and preferring cooler waters, the blue shark migrates long distances, such as from

New England New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York to the west and by the Canadian provinces ...

to South America. It is listed as

Near Threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify fo ...

by the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

. Although generally lethargic, they can move very quickly. Blue sharks are

viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

and are noted for large litters of 25 to over 100 pups. They feed primarily on small fish and squid, although they can take larger prey. Maximum lifespan is still unknown, but it is believed that they can live up to 20 years.

Anatomy and appearance

Blue sharks are light-bodied with long

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

s. Like many other sharks, blue sharks are

countershaded Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, an ...

: the top of the body is deep blue, lighter on the sides, and the underside is white. The male blue shark commonly grows to at maturity, whereas the larger females commonly grow to at maturity.FLMNH Ichthyology Department: Blue Shark
. Flmnh.ufl.edu. Retrieved on 2012-12-19. Large specimens can grow to long. Occasionally, an outsized blue shark is reported, with one widely printed claim of a length of , but no shark even approaching this size has been scientifically documented. The blue shark is fairly elongated and slender in build and typically weighs from in males and from in large females. Occasionally, a female in excess of will weigh over . The heaviest reported weight for the species was . The blue shark is also

ectotherm An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life ...

ic and it has a unique sense of smell. Prionace glauca jaw.jpg, Jaws Prionace glauca upper teeth.jpg, Upper teeth Prionace glauca lower teeth.jpg, Lower teeth

Reproduction

They are viviparous, with a yolk-sac

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...

, delivering 4 to 135 pups per litter. The gestation period is between 9 and 12 months. Females mature at five to six years of age and males at four to five. Courtship is believed to involve biting by the male, as mature specimens can be accurately sexed according to the presence or absence of bite scarring. Female blue sharks have adapted to the rigorous mating ritual by developing skin three times as thick as male skin.

Ecology

Range and habitat

The blue shark is an oceanic and epipelagic shark found worldwide in deep temperate and tropical waters from the surface to about . In temperate seas it may approach shore, where it can be observed by divers; while in tropical waters, it inhabits greater depths. It lives as far north as

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of ...

and as far south as

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

. Blue sharks are found off the coasts of every continent, except

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

. Its greatest Pacific concentrations occur between 20° and 50° North, but with strong seasonal fluctuations. In the tropics, it spreads evenly between 20° N and 20° S. It prefers water temperatures between , but can be seen in water ranging from . Records from the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

show a regular clockwise migration within the prevailing currents.

Feeding

Squid are the most important prey for blue sharks, but their diet includes other invertebrates, such as cuttlefish,

blanket octopus ''Tremoctopus'' is a genus of pelagic cephalopods, containing four species that occupy surface to mid-waters in subtropical and tropical oceans. They are commonly known as blanket octopuses, in reference to the long, transparent webs that connec ...

es, and pelagic octopuses, as well as lobster, shrimp, crab, a large number of bony fishes (such as long-snouted lancetfish,

snake mackerel The snake mackerel (''Gempylus serpens'') is the sole species of fish in the monotypic genus ''Gempylus'', belonging to the family Gempylidae (which is also referred to generally as "snake mackerels"). It is found worldwide in tropical and sub ...

and oilfish), small sharks, mammalian carrion and occasional sea birds (such as great shearwaters). Whale and porpoise blubber and meat have been retrieved from the stomachs of captured specimens and they are known to take cod from trawl nets. Sharks have been observed and documented working together as a "pack" to herd prey into a concentrated group from which they can easily feed. Blue sharks may eat

tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: ...

, which have been observed taking advantage of the herding behaviour to opportunistically feed on escaping prey. The observed herding behaviour was undisturbed by different species of shark in the vicinity that normally would pursue the common prey. The blue shark can swim at fast speeds, allowing it to catch up with prey easily. Its triangular teeth allow it to easily catch hold of slippery prey.

Predators

Young and smaller individuals may be eaten by larger sharks, such as the

great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark which can be found in the coastal surface waters of all the major oceans. It is nota ...

and the tiger shark. Orcas have been reported to hunt blue sharks. This shark may host several species of

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson h ...

s. For example, the blue shark is a definitive host of the

tetraphyllidea Tetraphyllidea is a large tapeworm order that contains some 60 genera and about 800 described species. Tetraphyllideans are remarkable for their scolex morphologies, which are the most varied and morphologically complex amongst all tapeworm orde ...

n tapeworm, ''Pelichnibothrium speciosum'' ('' Prionacestus bipartitus''). It becomes infected by eating intermediate hosts, probably

opah Opahs, also commonly known as moonfish, sunfish (not to be confused with Molidae), kingfish, redfin ocean pan are large, colorful, deep-bodied pelagic lampriform fishes comprising the small family Lampridae (also spelled Lamprididae). The f ...

(''Lampris guttatus'') and/or

longnose lancetfish ''Alepisaurus ferox'', the long snouted lancetfish, longnose lancetfish, or cannibal fish, is a species of lancetfish found in the ocean depths down to 1,830 m (6,000 ft). This species grows to in total length and a weight of . It is ...

(''Alepisaurus ferox''). Northern elephant seals (''Mirounga angustirostris'') and

Cape fur seals The brown fur seal (''Arctocephalus pusillus''), also known as the Cape fur seal, South African fur seal and Australian fur seal, is a species of fur seal. Description The brown fur seal is the largest and most robust member of the fur seal ...

(''Arctocephalus pusillus pusillus'') have been observed to feed on blue sharks.

Relationship to humans

Blue shark meat is edible, but not widely sought after; it is consumed fresh, dried, smoked and salted and diverted for

fishmeal Fish meal is a commercial product made from whole wild-caught fish, bycatch and fish by-products to feed farm animals, e.g., pigs, poultry, and farmed fish.R. D. Miles and F. A. Chapman.FA122: The Benefits of Fish Meal in Aquaculture DietsFisheri ...

. There is a report of high concentration of heavy metals ( mercury and

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...

) in the edible flesh. The skin is used for

leather Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hog ...

, the fins for

shark-fin soup Shark fin soup is a traditional soup or stewed dish served in parts of China, Taiwan, and Southeast Asia. The shark fins provide texture, while the taste comes from the other soup ingredients. It is commonly served at special occasions such as ...

and the liver for oil. Blue sharks are occasionally sought as game fish for their beauty and speed. Blue sharks rarely bite humans. From 1580 up until 2013, the blue shark was implicated in only 13 biting incidents, four of which ended fatally.

In captivity

Blue sharks, like most pelagic sharks, tend to fare poorly in captivity. The first attempt of keeping blue sharks in captivity was at

Sea World San Diego SeaWorld San Diego is an animal theme park, oceanarium, outside aquarium and marine mammal park, in San Diego, California, United States, inside Mission Bay Park. It is owned and operated by SeaWorld Parks & Entertainment. SeaWorld San D ...

in 1968, and since then a small number of other public aquariums in North America, Europe and Asia have attempted it.Blue Shark (''Prionace glauca'') in Captivity
elasmollet.org (2007) Most of these were in captivity for about three months or less, and some of them were released back to the wild afterwards. The record time for blue sharks in captivity is 246 and 224 days for two individuals at Tokyo Sea Life Park, 210 days for an individual at New Jersey Aquarium, and 194 days for one at

Lisbon Oceanarium The Lisbon Oceanarium ( pt, Oceanário de Lisboa, ) is an oceanarium in Lisbon, Portugal. It is located in the '' Parque das Nações'', which was the exhibition grounds for the Expo '98. It is one of the largest indoor aquariums in Europe. Arch ...

and 252 and 873 days for two individuals at

Sendai Umino-Mori Aquarium is a public aquarium located in Sendai, Miyagi Prefecture, Japan. It opened in 2015 as a successor to the Marinepia Matsushima Aquarium, which had been open for 88 years. Exhibits Inherited from the Marinepia Matsushima Aquarium are Commerson's ...

. The blue shark that survived the longest in captivity was captured in Shizugawa Bay on July 27, 2018, and taken to the Sendai Umino-Mori Aquarium. The total length at the time of delivery was , the estimated weight was 0.345kg, and the age was about 1 year old. After that, it lived for 873 days, but died due to factors such as disordered swimming due to

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

. At the time of death, the total length was and the weight was 4kg. This growth rate is said to be the same as that of

wild Wild, wild, wilds or wild may refer to: Common meanings * Wild animal * Wilderness, a wild natural environment * Wildness, the quality of being wild or untamed Art, media and entertainment Film and television * ''Wild'' (2014 film), a 2014 A ...

blue sharks. Blue sharks are relatively easy to feed and store in captivity, and the three primary issues appear to be transport, predation by larger sharks and trouble avoiding smooth surfaces in tanks. Small blue sharks, up to long, are relatively easy to transport to aquariums, but it is much more complicated to transport larger individuals. However, this typical small size when introduced to aquariums means that they are highly vulnerable to predation by other sharks that are often kept, such as bull, grey reef,

sandbar In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material and rises from the bed of a body of water to near the surface. ...

and sand tiger sharks. For example, several blue sharks kept at Sea World San Diego initially did fairly well, but were eaten when bull sharks were added to their exhibit. Attempts of keeping blue sharks in tanks of various sizes, shapes and depths have shown that they have trouble avoiding walls, aquarium windows and other smooth surfaces, eventually leading to abrasions to the fins or snout, which may result in serious infections. To keep blue sharks, it is therefore necessary with tanks that allow for relatively long, optimum swimming paths where potential contact with smooth surfaces is kept at a minimum. It has been suggested that prominent rockwork may be easier to avoid for blue sharks than smooth surfaces, as has been shown in captive tiger sharks.

Conservation status

In June 2018 the New Zealand

Department of Conservation An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as Ministry of the Environment ...

classified the blue shark as "Not Threatened" with the qualifier "Secure Overseas" under the New Zealand Threat Classification System. The species is listed as