Blue Shark

The blue shark is also referred to as the great blue shark (Prionace glauca). It is a common shark of the Carcharhinidae family that may be found in all oceans, from warm temperate to tropical regions. The blue shark is also called a blue whaler, which is noted for its attractive, deep-blue coloring contrasting with a pure-white belly. Also, it is a slim shark with saw-edged teeth, a pointed snout, and long, slim pectoral fins. The maximum length of a blue shark is up to 4 metres (12 feet).

Fish form the primary part of its diet, whereas the blue shark is also a scavenger and at times follows ships for extended periods. It is also noted for the speed at which it appears near to slaughtered whales and its avidity in feeding on the carcasses. It is generally thought to be harmful to humans and has been linked to a number of unprovoked attacks.

Physical Appearance and Anatomy

Blue sharks are the light-bodied ones having long pectoral fins. Blue sharks, like numerous other sharks, have a counter-shaded body with a deep blue top, lighter sides, and a white bottom. Commonly, the male blue shark grows to 1.82 - 2.82 m (6.0 - 9.3 ft) at maturity, whereas the larger females grow to 2.2 - 3.3 m (7.2 - 10.8 ft) at maturity. Large specimens may be capable of growing to 3.8 m (12 ft) long.

Occasionally, the outsized blue shark is reported, having one widely printed claim with a length of 6.1 m (20 ft), but no shark even approaching this size has scientifically been documented. The blue shark in males is slender in build, fairly elongated and typically weighs from 27 - 55 kg (60 - 121 lb) and in large females from 93 - 182 kg (205 - 401 lb). A female taller than 3 m (9.8 ft) will weigh more than 204 kg (450 lb). The species' highest recorded weight was 391 kilograms (862 lb). Also, the blue shark is ectothermic and has a unique sense of smell.

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They are viviparous, having a yolk-sac placenta, delivering 4 to 135 pups per one litter. The pregnancy (gestation period) lasts between 9 and 12 months. Females mature at 5 - 6 years of age and males at 4 to 5. Courtship is believed to involve biting by the male, as the mature specimens may be accurately sexed according to either the presence or absence of bite scarring. Female blue sharks have adapted to the rigorous mating ritual by developing the skin 3x times as thick as the male skin.

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Ecology of a Blue Shark

Feeding

Squid are essential prey for blue sharks, but their diet includes the other invertebrates, such as pelagic octopuses and cuttlefish, and lobster, shrimp, crab as well, a large number of bony fishes, mammalian carrion, small sharks and occasional sea birds. Porpoise blubber, whale and meat have been retrieved from the stomachs of the captured specimens and they are well-known to take cod from trawl nets.

Sharks have been observed and photographed operating as a "pack" to herd prey into a small area where they may readily eat. Blue sharks may devour tuna that have been seen, taking advantage of herding behaviour to pounce on the fleeing prey. The observed herding behaviour was unaffected by the presence of numerous shark species in the area, which would typically chase the common prey. Blue sharks can swim at fast speeds, allowing them to catch up with prey easily. Its triangular teeth enable it to easily catch hold of slippery prey.

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Range and Habitat

The blue shark is defined as an oceanic and epipelagic shark that is found worldwide in tropical waters and deep temperate from the surface to up to 350 m (1,150 ft). It may swim close to the beach and be seen by divers in temperate waters, but it prefers deeper waters in tropical areas. It can be found as far south as Chile as north as Norway.

Blue sharks can be found off the coasts of every continent except Antarctica. Its greatest Pacific concentrations take place between 20° and 50° North but have strong seasonal fluctuations. In the tropics, it evenly spreads between 20° N and 20° S. It prefers water temperatures ranging from 12 to 20 °C (54 to 68 °F), but it can be seen in water ranging from 7 - 25 °C (45 - 77 °F). The records from the Atlantic reveal a regular clockwise migration within the prevailing currents.

Predators

Smaller and young individuals may be eaten by larger sharks, such as the tiger shark and the deep blue great white shark. The killer whale type has been reported to hunt blue whale sharks. This shark may host many species of parasites. For example, the blue shark is given as the definitive host of the Pelican Bothrium speciosum (Prionacestus bipartite), tetraphyllidea tapeworm. It spreads the disease by consuming intermediate hosts such as longnose lancetfish (Alepisaurus ferox) and/or opah (Lampris guttatus).

Northern elephant seals (Mirounga angustirostris) have been noticed to feed on blue whale sharks.

Relationship to Humans

Blue shark meat is given as edible but not widely sought after; it is consumed dried, fresh, salted, smoked and diverted for fishmeal. There is a report of a high concentration of heavy metals (lead and mercury) in the edible flesh. The fins are used for shark-fin soup, skin for leather and the liver for oil. Occasionally, the blue sharks are sought as game fish for their speed and beauty.

Blue whale sharks bite humans rarely. From 1580 up until 2013, the blue shark was implicated in only 13 biting incidents, where 4 of which ended fatally.

In Captivity

Blue sharks, like the majority of pelagic sharks, tend to fare poorly in captivity. The first attempt of keeping blue sharks in captivity was in 1968 at SeaWorld San Diego 1968, and since then, a few other public aquariums in Europe, North America and Asia have attempted it. Most of these were in captivity for up to 3 months or less, and afterward, a few of them were released back to the wild. The record time for the blue sharks in captivity is 210 days for an individual at New Jersey Aquarium, 246 and 224 days for two individuals at Tokyo Sea Life Park, and 252 and 873 days for two individuals at Sendai Umino-Mori Aquarium, 194 days for one at Lisbon Oceanarium.

The blue shark, which survived the longest in captivity, was captured in the Shizugawa Bay on 27 Jul 2018 and taken to Umino-Mori Aquarium in Sendai. The total length at the time of delivery was said to be 51 cm (1.67 ft), the estimated weight was about 345g, and the age was around 1 year old. Afterward, it lived for 873 days but died because of factors such as disordered swimming because of dehydration. At the time of death time, the total weight was 4kg and the length was given as 114 cm (3.74 ft). This growth rate is said to be similar to that of wild blue sharks.

Importance of Blue Sharks

In few places, the blue shark is an essential species to marine tourism as photographers, divers and more, enjoy encountering it. In some rare instances, individuals have bitten people, but this occurs only very infrequently. The blue shark has the largest geographic distribution among the sharks and it was historically one of the most (or the most) common pelagic sharks across the world.

Its dense population structure and wide distribution make the blue shark a target of fisheries in a few areas and a common accidentally caught species in longline and gillnet fisheries targeting other species. Moreover, its fins are considered highly valuable, and blue sharks can be the target of illegal 'shark finning' operations, where the fins are cut off and kept while the remaining shark is wasted.

Blue Whale vs Whale Shark

Let us look at the differences between blue whale and shark (blue whale vs whale shark).

• The blue whale (or the megalodon blue whale) is the largest fish worldwide, while the Mammal is the largest animal on the earth.

• Whale sharks Sexually mature at 30 years, while the blue whale sexually matures at 5 to 10 years.

• The whale shark holds a flattened head and two sets of dorsal fins, which are directed towards the back, while the blue whale has a broad and flat head, tapered body shape.

• Whale Shark weighs around 16 to 20 tons with a body length from 18 - 40 feet, while the Blue whale or megalodon blue whale weighs up to 200 tons with a body length of up to 100 feet.

• The whale shark has grey-brown skin color having spots among the pale vertical and horizontal strips, while the blue whale looks as blue underwater while bluish-grey outside water.

Identification

The deep blue shark contains a circular eye, a conical snout and a long pectoral fin. The deep blue shark is recognized with its distinctively colored slender body having a conical snout and long, scythe-like pectoral fins. It has a heterocercal tail, five-gill slits, large circular eyes and a first dorsal fin, which is much larger than the second.

Sometimes, the species is confused with the Shortfin Mako Shark. However, the Blue Shark has longer pectoral fins, smaller gill slits and serrated teeth.

Habitat

Usually, the deep blue shark or the deep blue great white shark is found in the water from 12℃ to 20℃ and it is recorded from the surface to a depth of 350 m.

Did You Know?

Blue sharks usually give birth to live babies! The fertilized eggs remain within the uterus of the mother, where they are nourished by a yolk-sac. The depleted yolk-sac, over time, interlocks with the lining of the uterus of the mother, which then acts a bit like a placenta of a mammal. Blue sharks, in general, give birth to an average of 35 pups.