Based on size, the basking shark is the second largest fish in the world. They can grow as long as 40 feet. This shark earned its name from its habit of sunning itself on the surface, back awash with its dorsal fin fully exposed. In some areas, such as Scotland and Ireland, they are known as the Sunfish because of their affinity for floating along the surface. Basking sharks are highly migratory species and do not typically stay in one place for more than a few months.
Along with the whale shark and the megamouth shark, the basking shark is one of the three species of large filter-feeding sharks. This shark is often seen swimming with its mouth wide open and drawing a steady flow of water inside its mouth. Because of its size, the basking shark has relatively few known predators, however, great whites have been observed to feed on the remains of basking sharks. Like many sharks, the population of this species is vulnerable due to extensive fishing because of the economic value derived from the basking shark’s meat and liver oil.
The shark has been observed to leap completely out of the water, suggesting that this action is due to an effort to get rid of the parasites attach to its body. Basking Sharks usually have a pungent odor because of layers of mucus and slime produced to drive away parasites and lampreys. The chemicals in this mucus produce rancid odor and the slime has corrosive nature. Basking sharks are relatively social, preferring to swim in groups. Basking sharks are generally considered non dangerous to humans and tolerate divers and boats. However, its huge size and strength should be respected. Also, its skin should be avoided as it can inflict damage on divers and researchers due to its toughness.
Taxonomy
They belong to the order Lamniformes of the family Cetorhinidae. The scientific name of the basking shark is Cetorhinus maximus. The life expectancy of the basking sharks is around 50 years.
Morphology
The basking shark is easily recognized from other sharks by its massiveness, and extended gill slits that almost encircle the head and lunate caudal fin. Its snout is conical in shape and has numerous large gill rakers modified for filter feeding. The liver of the basking shark is very large, which make up about 25% of its body weight. This liver is rich in Squalene, a low density hydrocarbon that gives the shark near neutral buoyancy. The dorsal coloration is typically grayish brown, and at times it can vary from dark gray to nearly black. The color of the ventral side may be similar, or marginally paler or almost white.
Adaptation
Basking shark is known to secrete a rancid smelling mucus that drive away parasitic creatures in the ocean. Also, it is believed that the breaching nature of the shark help it to get rid of its parasites or commensals like remoras and sea lampreys. The thick skin of the shark also makes penetration difficult for parasites and commensals, which acts as an additional defensive mechanism.
Feeding
This shark relies mainly on the passive flow of water through its pharynx by swimming. Through this process, small organisms, krill and plankton are strained from the water by gill rakers located in the gill slits. The Basking shark’s gill rakers have the ability to strain about 2000 tons of water in a single hour.
Habitat
Basking sharks are generally found in temperate waters of both the Pacific and Atlantic Oceans. They are frequently seen by humans at or close to the water surface. They have also been observed along nearly every coastline bordering the Atlantic and Pacific Oceans. This shark is known to venture into bays and estuaries, as well as offshore. They are highly migratory and feed at the surface during summer. In the winter period, basking sharks are absent from November to March insinuating a migration beyond the continental shelf.
Reproduction
Pregnant basking shark is rarely encountered, thus making reproduction process in this shark very difficult to ascertain. However, limited information available revealed that this shark engages in the ovoviviparous mode of reproduction. The gestation period is three years or more. It is proposed that basking shark utilize an oviphagy method as its form of embryonic nutrition whereby an embryo feeds on unfertilized eggs or other embryos within the uterus. Estimation suggests that the female attain maturity between 12-16 years. The young are generally 5 to 5.6 feet. In contrary to the whale sharks, the basking shark gives birth to only a few, quite large babies. Also, it is the assumption of scientists that pregnant female separate from other females during gestation. Basking shark only reproduces at every two to four years.
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References
Bolton, B (2019, may 14). 5 things you didn’t know about the weirdly majestic basking shark. Retrieved from https://www.mnn.com/earth-matters/animals/stories/basking
Fisheries and Oceans Canada (2019). Basking Shark. Cetorhinus maximus. Retrieved from https://www.dfo-mpo.gc.ca/species-especes/profiles-profils/baskingshark-requinpelerin-atl-eng.html
Florida Museum (2017). Basking Sharks. Cetorhinus maximus. Retrieved from https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/cetorhinus-maximus/
OCEANA (2019). Sharks & Rays. Basking Shark. Cetorhinus maximum. Retrieved from https://oceana.org/marine-life/sharks-rays/basking-shark
MARINEBIO (2019). Basking Sharks. Cetorhinus maximus. Retrieved from https://marinebio.org/species/basking-sharks/cetorhinus-maximus/