Shark of the month: Basking shark

The mysterious basking shark (Cetorhinus maximus) is the second largest fish in the ocean. The whale shark is the largest. The basking shark is also called the sunfish, the bone shark, the elephant shark, the sailfish shark, and the big mouth shark. The basking shark gets its name due to being slow moving and enjoying time basking in the sun. It is uncommon to see such a large shark so close to the surface. Moreover, sometimes the basking shark even jumps out of the water. Researchers believe this is done in an effort to remove as many parasites from the body as possible.sea-79836_960_720

Anatomy and appearance

Basking sharks can weigh up to 7000 kg and the maximum reported size of a Basking Shark is 12 meters. However, most adult basking sharks do not exceed 10 meters. Aside from their large size, basking sharks are characterized by their powerful crescent-shaped tail, extremely large mouth, pointed nose and five huge gill slits which almost encircle the head. Typically the basking shark has a greyish-brownish colour but this can range through to slate grey or black on the dorsal surface. Irregular patches, patterns and streaks mark the sharks flanks and fins while the ventral (underside) of these sharks are predominantly lighter than the dorsal. The basking shark has a particularly large liver that accounts for up to 25% of its body weight. This large liver provides the shark with near-neutral buoyancy.

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Habitat

Basking sharks thrive in waters that ranges from warm to cool in temperature. In addition, they prefer to swim close to the shore and also enjoy swimming near the water’s surface. In fact, they like being near the surface so much, that “sunfish” is their nickname. These sharks often travel through the waters of the Mediterranean Sea, the Pacific Ocean, the Atlantic Ocean, the Sea of Japan, near New Zealand, and Southern Australia. Basking sharks travel alone, in pairs, or in schools (groups) of up to 100 members. One of the best places to swim or dive with basking sharks is Scotland.

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Source: www.iucnredlist.org

Diet

The Basking Shark feeds on zooplankton, small fish and invertebrates. They feed passively by gliding through the water with an open mouth, filtering up to 2000 tons of water per hour. This process is an interesting one that involves another important physical characteristic; gill rakers. The basking shark’s gill rakers are key to its feeding process. The gill rakers are very long, and they are solely responsible for filtering the plankton out of the water. The excess water is then ejected out of the body through the shark’s gill slits. Gill rakers put in so much work that they are replaced annually. They are discarded during the winter months, and new ones sprout in the spring.

Population

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The number of basking sharks is unknown. However, their population is probably decreasing, just like other shark populations, due to overfishing and the hunt for its meat, fins and oil. Basking sharks reach sexual maturity when they are two to four years old. Researchers found out that only the right ovary allows reproduction. The gestation period is about 3.5 years and females generally give birth to 1-2 live young. These young basking sharks are the largest shark pups with a length of approximately 1.7 meters. The lifespan of the basking shark is unknown. However, researchers estimate their lifespan to be about 50 years.

Conservation

The official IUCN Red List conservation status of the basking shark is ‘Vulnerable’ (http://www.iucnredlist.org/details/4292/0). The basking shark is one of the three internationally protected sharks along with the whale shark and the great white shark. Equal to other shark species, basking sharks are vulnerable to overfishing for several reasons. They have a lengthy maturation time, slow growth rate and a long gestation period. These factors combined with an already depleted population in many areas have prompted many countries to establish laws to protect the basking shark from further exploitation. In the past, basking sharks were hunted worldwide for their oil, meat, fins, and vitamin rich livers. Today, most fishing has ceased except in China and Japan. There the fins are sold as the base ingredient for shark fin soup.

Relationship to humans

Basking sharks are not aggressive and are harmless to people.

 

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