Basking Shark (Cetorhinus maximus)

Basking-shark-feeding-mouth-detail

  • Name: Basking shark
  • Latin: Cetorhinus maximus
  • Classification: Cartilaginous fish
  • Origin: Worldwide
  • Lifespan: 20-100 years

Taxonomy

Kingdom: Animalia (Animals)
Phylum: Chordata (Vertebrates)
Class: Chondrichthyes (Cartilaginous fishes)
Order: Lamniformes (Mackerel sharks)
Family: Cetorhinidae (Basking Shark)
Genus: Cetorhinus (Basking Shark)
Species: Certorhinus Maximus (Basking Shark)

Apperance

Length: 10m
Weight: 7 tons

Basking sharks are greyish brown in colour with their bellies being slightly paler. They have a large snout which ends in a roundish point. The mouth opens incredibly wide so it stretches right around its head, giving the impression that is it ‘smiling’, lining its enormous mouth are 100 tiny, rounded teeth. A series of long gill slits surround its blunt head. It has a large, triangular dorsal fin with a smaller second dorsal fin and anal fins. The basking shark has a huge liver (making up 25% of its total body weight) which provides it with natural buoyancy.

Relatives

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  • Spiny dogfish (Squalus acanthias) -VULNERABLE-
  • Prickly shark (Echinorhinus cookei) -NEAR THREATENED-
  • Angular roughshark (Oxynotus centrina) -VULNERABLE-
  • Sand devil (Squatina durmeril) -DATA DEFICIENT-

Habitat & Distribution

The basking shark is highly migrational and is known to keep emerging and disappearing in different areas around the globe. They are mostly found of the coast of Northern Ireland and the UK. They seem to prefer temperate oceans and can also be found in the Western Mediterranean sea and the western Atlantic Ocean. They are never found in the tropics. In spring and winter, they have been spotted off the coast of California; however, they are usually found wherever plankton levels are high. In winter, they seem to migrate from shallow to deeper waters; however, their exact pattern of migratory behaviour is yet to be understood clearly.

Map of distribution of the basking shark
Map of distribution of the basking shark

Diet

Basking sharks are found feeding near the surface of the water. Their mouth can open 1.2meters wide and can swim with its mouth open. This allows the water to pass through its gills, prey gets entangled in its gill rakers and is then digested by the shark by closing the movement of its mouth. This feeding behaviour makes them different from the two other filter feeding species. The basking shark eats barnacles, fish eggs, tiny copepods, deep water oceanic shrimp and decapods larvae, however, its diet is made up mostly of plankton.

Behaviour

Basking sharks are slow swimmers who cruise around 2.5-4 mph. They swim by moving their bodies from side to side, not just their tails like other breeds of shark. They also exhibit breeching behaviour, which consists of a sudden explosion of the shark from the water into the air, rolling in mid-air and then crashing back into the sea. The shark will repeat this display 3-4 times in a row. The reason of this behaviour is unknown and also proves to be dangerous to boats, which can cause them to capsize.

Reproduction

There is limited information about the reproduction cycle of the basking shark, but it has been discovered that they are viviparous and the pups demonstrate oophagy (developing pups will feed on unfertilized eggs). Both sexes take up to 18 years to mature. The gestation period was originally estimated to be at around 3.5 year, but this figure has recently been revised to 14 months. The pups are 1.5-2 meters at birth.

Adaptations

  1. The Basking shark has a large mouth which it holds open while swimming. This enables it to filter food from as much as 2,000 tons of water per hour.
  2. The Basking sharks large size means that is has very little natural predators, aside from humans. However, killer whales have been spotted feeding of this animal’s carcass.
  3. Basking sharks have gill rakers along their gills which trap plankton and other invertebrates while it is filtering food.
  4. Basking sharks are named from their behaviour of basking in shallow water. They do this to warm themselves, feed and mate.

Threats

The biggest threat to basking sharks is hunting for its liver oil, meat, cartilage and fins. The oil is rich in vitamin A and is used as a lubricant for machinery, to tan leather and as lamp oil. The livers are sold as an aphrodisiac and is used as an ingredient in health food products and in cosmetics.

Hunting of these sharks are especially at large in Asia, where there fins are used in the infamous shark fin soup. They are captured and killed in Asian shark fisheries where they are either caught in nets or harpooned.

In the wild, they can be struck by boats and jet skis and can be intimidated by tourists hoping to get close to these creatures.

Conservation

IUCN Status: Vulnerable

The Wildlife Trust has currently set up a Basking Shark Project, which aims to shut down UK shark fisheries and educate the public about this species and the dangers they face in our waters. This will hopefully reduce the number of basking sharks killed in boat accidents.

Since this project has come into play, many UK shark fisheries have shut down although many of these animals are illegally hunted, killed and traded to Asia, who pay a lot of money to use their find in their traditional dish, shark fin soup.

Fun Facts

Male: Bull
Female: Cow
Young: Calf
Group: Gam, Grind, School, Herd, Pod, College, Shiver

-Sharks have existed for around 400 million years, long before the dinosaurs.
-A shark may use around 20,000 teeth during its life.

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