|The size of basking sharks at various stages of growth and maturity with a human for scale|
|Family:|| Cetorhinidae |
T. N. Gill, 1862
|Genus:|| Cetorhinus |
|Range of the basking shark|
The basking shark (Cetorhinus maximus) is the second-largest living shark, after the whale shark, and one of three plankton-eating shark species, along with the whale shark and megamouth shark. Adults typically reach 7.9 m (26 ft) in length. It is usually greyish-brown, with mottled skin. The caudal fin has a strong lateral keel and a crescent shape.
The basking shark is a cosmopolitan migratory species, found in all the world's temperate oceans. A slow-moving filter feeder, its common name derives from its habit of feeding at the surface, appearing to be basking in the warmer water there. It has anatomical adaptations for filter-feeding, such as a greatly enlarged mouth and highly developed gill rakers. Its snout is conical and the gill slits extend around the top and bottom of its head. The gill rakers, dark and bristle-like, are used to catch plankton as water filters through the mouth and over the gills. The teeth are numerous and very small, and often number 100 per row. The teeth have a single conical cusp, are curved backwards, and are the same on both the upper and lower jaws. This species has the smallest weight-for-weight brain size of any shark, reflecting its relatively passive lifestyle.
Basking sharks have been shown from satellite tracking to overwinter in both continental shelf (less than 200 m or 660 ft) and deeper waters. They may be found in either small shoals or alone. Despite their large size and threatening appearance, basking sharks are not aggressive and are harmless to humans.
The basking shark has long been a commercially important fish, as a source of food, shark fin, animal feed, and shark liver oil. Overexploitation has reduced its populations to the point where some have disappeared and others need protection.
The basking shark is the only extant member of the family Cetorhinidae, part of the mackerel shark order Lamniformes. Johan Ernst Gunnerus first described the species as Cetorhinus maximus, from a specimen found in Norway, naming it. The genus name Cetorhinus comes from the Greek ketos, meaning "marine monster" or "whale", and rhinos, meaning "nose". The species name maximus is from Latin and means "greatest". Following its initial description, more attempts at naming included: Squalus isodus, in 1819 by Italian Zoologist Saverio Macri (1754–1848); Squalus elephas, by Charles Alexandre Lesueur in 1822; Squalus rashleighanus, by Jonathan Couch in 1838; Squalus cetaceus, by Laurens Theodorus Gronovius in 1854; Cetorhinus blainvillei by the Portuguese Biologist Felix Antonio De Brio Capello (1828–1879) in 1869; Selachus pennantii, by Charles John Cornish in 1885; Cetorhinus maximus infanuncula, by the Dutch Zoologists Antonius Boudewijn Deinse (1885–1965) and Marcus Jan Adriani (1929–1995) in 1953; and Cetorhinus maximus normani, by Siccardi in 1961. Other common names include bone shark, elephant shark, sail-fish, and sun-fish. In Orkney, it is commonly known as hoe-mother (sometimes contracted to homer), meaning "the mother of the pickled dog-fish".
The basking shark is a coastal-pelagic shark found worldwide in boreal to warm-temperate waters. It lives around the continental shelf and occasionally enters brackish waters. 910 m (2,990 ft). It prefers temperatures of 8 to 14.5 °C (46.4 to 58.1 °F), but has been confirmed to cross the much-warmer waters at the equator. It is often seen close to land, including in bays with narrow openings. The shark follows plankton concentrations in the water column, so is often visible at the surface. It characteristically migrates with the seasons.It is found from the surface down to at least
The largest accurately measured specimen was trapped in a herring net in the Bay of Fundy, Canada, in 1851. 12.27 m (40.3 ft), and it weighed an estimated 16 t (16 long tons; 18 short tons). Dubious reports from Norway mention three basking sharks over 12 m (39 ft), the largest at 13.7 m (45 ft), during 1884 to 1905, these are dubious because few anywhere near that size have been caught in the area since. On average, the adult basking shark reaches a length of 7.9 m (26 ft) and weighs about 4.65 t (4.58 long tons; 5.13 short tons). Some specimens still surpass 9–10 m (30–33 ft), but after years of large-scale fishing, specimens of this size have become rare.Its total length was
They possess the typical shark lamniform body plan and have been mistaken for great white sharks. 1 m (3 ft 3 in) in width, longer and more obvious gill slits that nearly encircle the head and are accompanied by well-developed gill rakers, smaller eyes, much larger overall size and smaller average girth. Great whites possess large, dagger-like teeth; basking shark teeth are much smaller 5–6 mm (0.20–0.24 in) and hooked; only the first three or four rows of the upper jaw and six or seven rows of the lower jaw function. In behaviour, the great white is an active predator of large animals and not a filter feeder.The two species can be easily distinguished by the basking shark's cavernous jaw, up to
Other distinctive characteristics include a strongly keeled caudal peduncle, highly textured skin covered in placoid scales and a mucus layer, a pointed snout—distinctly hooked in younger specimens—and a lunate caudal fin.In large individuals, the dorsal fin may flop to one side when above the surface. Colouration is highly variable (and likely dependent on observation conditions and the individual's condition): commonly, the colouring is dark brown to black or blue dorsally, fading to a dull white ventrally. The sharks are often noticeably scarred, possibly through encounters with lampreys or cookiecutter sharks. The basking shark's liver, which may account for 25% of its body weight, runs the entire length of the abdominal cavity and is thought to play a role in buoyancy regulation and long-term energy storage.
Basking sharks do not hibernate, and are active year-round. 900 m (3,000 ft) and have been tracked making vertical movements consistent with feeding on overwintering zooplankton.In winter, basking sharks often move to deeper depths, even down to
They are slow-moving sharks (feeding at about 2 knots (3.7 kilometres per hour; 2.3 miles per hour)) and do not evade approaching boats (unlike great white sharks). They are not attracted to chum.
Though the basking shark is large and slow, it can breach, jumping entirely out of the water.This behaviour could be an attempt to dislodge parasites or commensals. Such interpretations are speculative, however, and difficult to verify; breaching in large marine animals such as whales and sharks might equally well be intraspecific threat displays of size and strength.
Argos system satellite tagging of 20 basking sharks in 2003 confirmed basking sharks move thousands of kilometres during the summer and winter, seeking the richest zooplankton patches, often along ocean fronts.They shed and renew their gill rakers in an ongoing process, rather than over one short period.
A 2009 study tagged 25 sharks off the coast of Cape Cod, Massachusetts, and indicated at least some migrate south in the winter. Remaining at depths between 200 and 1,000 metres (660 and 3,280 ft) for many weeks, the tagged sharks crossed the equator to reach Brazil. One individual spent a month near the mouth of the Amazon River. They may undertake this journey to aid reproduction.
On 23 June 2015, a 6.1-metre-long (20 ft), 3,500-kilogram (7,716 lb) basking shark was caught accidentally by a fishing trawler in the Bass strait near Portland, Victoria, in southeast Australia, the first basking shark caught in the region since the 1930s, and only the third reported in the region in 160 years. The whole shark was donated to the Victoria Museum for research, instead of the fins being sold for use in shark fin soup.
While basking sharks are not infrequently seen in the Mediterranean Seaand records exist in the Dardanelles Strait, it is unclear whether they historically reached into deeper basins of Sea of Marmara, Black Sea and Azov Sea.
Basking sharks are usually solitary but during summer months in particular they aggregate in dense patches of zooplankton where they engage in social behaviour. They can form sex-segregated shoals, usually in small numbers (three or four), but reportedly up to 100 individuals.Small schools in the Bay of Fundy and the Hebrides have been seen swimming nose to tail in circles; their social behavior in summer months has been studied and is thought to represent courtship.
Basking sharks have few predators. White sharks have been reported to scavenge on the remains of these sharks. Killer whales have been observed feeding on basking sharks off California and New Zealand. Lampreys are often seen attached to them, although they are unlikely to be able to cut through the shark's thick skin.
The basking shark is a ram feeder, filtering zooplankton, very small fish, and invertebrates from the water with its gill rakers by swimming forwards with their mouths open. A 5-metre-long (16 ft) basking shark has been calculated to filter up to 500 short tons (450 t) of water per hour swimming at an observed speed of 0.85 metres per second (2.8 ft/s). Basking sharks are not indiscriminate feeders on zooplankton. Samples taken in the presence of feeding individuals recorded zooplankton densities 75% higher compared to adjacent non-feeding areas. Basking sharks feed preferentially in zooplankton patches dominated by small planktonic crustaceans called calanoid copepods (on average 1,700 individuals per cubic metre of water). Basking sharks sometimes congregate in groups of up to 1,400 spotted along the northeastern U.S. Samples taken near feeding sharks contained 2.5 times as many Calanus helgolandicus individuals per cubic metre, which were also found to be 50% longer. Unlike the megamouth shark and whale shark, the basking shark relies only on the water it pushes through its gills by swimming; the megamouth shark and whale shark can suck or pump water through their gills.
Basking sharks are ovoviviparous: the developing embryos first rely on a yolk sac, with no placental connection. Their seemingly useless teeth may play a role before birth in helping them feed on the mother's unfertilized ova (a behaviour known as oophagy).In females, only the right ovary appears to function, and it is currently unknown why only one of the organs seems to function.
Gestation is thought to span over a year (perhaps two to three years), with a small, though unknown, number of young born fully developed at 1.5–2 m (4 ft 11 in–6 ft 7 in). Only one pregnant female is known to have been caught; she was carrying six unborn young. Mating is thought to occur in early summer and birthing in late summer, following the female's movement into shallow waters.
The age of maturity is thought to be between the ages of six and 13 and at a length of 4.6–6 m (15–20 ft). Breeding frequency is thought to be two to four years.
The exact lifespan of the basking shark is unknown, but experts estimate to be about 50 years.
Aside from direct catches, by-catches in trawl nets have been one of several threats to basking sharks. In New Zealand, basking sharks had been abundant historically; however, after the mass by-catches recorded in 1990s and 2000s,confirmations of the species became very scarce. Management plans have been declared to promote effective conservations. In June 2018 the Department of Conservation classified the basking shark as "Threatened - Nationally Vulnerable" under the New Zealand Threat Classification System.
The eastern north Pacific Ocean population is a U.S. National Marine Fisheries Service species of concern, one of those species about which the U.S. Government's National Oceanic and Atmospheric Administration has some concerns regarding status and threats, but for which insufficient information is available to indicate a need to list the species under the U.S. Endangered Species Act (ESA).
The IUCN Red List indicates this as an endangered species.
The endangered aspect of this shark was publicised in 2005 with a postage stamp issued by Guernsey Post.
Historically, the basking shark has been a staple of fisheries because of its slow swimming speed, placid nature, and previously abundant numbers. Commercially, it was put to many uses: the flesh for food and fishmeal, the hide for leather, and its large liver (which has a high squalene content) for oil.It is currently fished mainly for its fins (for shark fin soup). Parts (such as cartilage) are also used in traditional Chinese medicine and as an aphrodisiac in Japan, further adding to demand.
As a result of rapidly declining numbers, the basking shark has been protected in some territorial waters and trade in its products is restricted in many countries under CITES. Among others, it is fully protected in the United Kingdom and the Atlantic and Mexican Gulf regions of the United States.Since 2008, it has been illegal to fish for, or retain if accidentally caught, basking sharks in waters of the European Union. It is partially protected in Norway and New Zealand, as targeted commercial fishing is illegal, but accidental bycatch can be used (in Norway any basking shark caught as bycatch and still alive must be released). As of March 2010, it was also listed under Annex I of the CMS Migratory Sharks Memorandum of Understanding.
Once considered a nuisance along the Canadian Pacific coast, basking sharks were the target of a government eradication programme from 1945 to 1970. As of 2008 [update] , efforts were under way to determine whether any sharks still lived in the area and monitor their potential recovery.
It is tolerant of boats and divers approaching it, and may even circle divers, making it an important draw for dive tourism in areas where it is common.
On several occasions, "globster" corpses initially identified by non-scientists as a sea serpents or plesiosaurs have later been identified as likely to be the decomposing carcasses of basking sharks, as in the Stronsay Beast and the Zuiyo-maru cases.
The great white shark, also known as the great white, white shark or "white pointer", is a species of large mackerel shark which can be found in the coastal surface waters of all the major oceans. It is notable for its size, with larger female individuals growing to 6.1 m (20 ft) in length and 1,905–2,268 kg (4,200–5,000 lb) in weight at maturity. However, most are smaller; males measure 3.4 to 4.0 m, and females measure 4.6 to 4.9 m on average. According to a 2014 study, the lifespan of great white sharks is estimated to be as long as 70 years or more, well above previous estimates, making it one of the longest lived cartilaginous fish currently known. According to the same study, male great white sharks take 26 years to reach sexual maturity, while the females take 33 years to be ready to produce offspring. Great white sharks can swim at speeds of over 56 km/h (35 mph), and can swim to depths of 1,200 m (3,900 ft).
Manta rays are large rays belonging to the genus Mobula. The larger species, M. birostris, reaches 7 m (23 ft) in width, while the smaller, M. alfredi, reaches 5.5 m (18 ft). Both have triangular pectoral fins, horn-shaped cephalic fins and large, forward-facing mouths. They are classified among the Myliobatiformes and are placed in the family Myliobatidae.
The tiger shark is a species of requiem shark and the only extant member of the genus Galeocerdo. It is a large macropredator, capable of attaining a length over 5 m. Populations are found in many tropical and temperate waters, especially around central Pacific islands. Its name derives from the dark stripes down its body, which resemble a tiger's pattern, but fade as the shark matures.
The blue shark is a species of requiem shark, in the family Carcharhinidae, that inhabits deep waters in the world's temperate and tropical oceans. Preferring cooler waters, the blue shark migrates long distances, such as from New England to South America. It is listed as Near Threatened by the IUCN.
The whale shark is a slow-moving, filter-feeding carpet shark and the largest known extant fish species. The largest confirmed individual had a length of 18.8 m (62 ft). The whale shark holds many records for size in the animal kingdom, most notably being by far the largest living nonmammalian vertebrate. It is the sole member of the genus Rhincodon and the only extant member of the family Rhincodontidae, which belongs to the subclass Elasmobranchii in the class Chondrichthyes. Before 1984 it was classified as Rhiniodon into Rhinodontidae.
The megamouth shark is a species of deepwater shark. It is rarely seen by humans and is the smallest of the three extant filter-feeding sharks alongside the whale shark and basking shark. Since its discovery in 1976, few megamouth sharks have been seen, with fewer than 100 specimens being observed or caught. Like the other two planktivorous sharks, it swims with its enormous mouth wide open, filtering water for plankton and jellyfish. It is distinctive for its large head with rubbery lips. It is so unlike any other type of shark that it is usually considered to be the sole extant species in the distinct family Megachasmidae, though suggestion has been made that it may belong in the family Cetorhinidae, of which the basking shark is currently the sole extant member. Researchers have predicted the feeding patterns of megamouth sharks in relation to the other two planktivorous sharks; the three plankivourous sharks have ram feeding in common, as it evolved from ram feeding swimming-type ancestors that developed their filtering mechanism to capture small prey like plankton. In addition to the living M. pelagios, however, two extinct megamouth species – the Priabonian M. alisonae and the Oligocene–Miocene M. applegatei – have also recently been proposed on the basis of fossilized tooth remains. An early ancestor of the recent species Megachasma pelagios was reported from the early Miocene (Burdigalian) of Belgium. However, the Cretaceous-aged M. comanchensis has been recently reclassified as an odontaspid shark in the genus Pseudomegachasma, and is in fact unrelated to the megamouth shark despite similar teeth morphology.
Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish. Some birds, such as flamingos and certain species of duck, are also filter feeders. Filter feeders can play an important role in clarifying water, and are therefore considered ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms.
Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, including the sharks and the rays, skates, and sawfish. Members of this subclass are characterised by having four to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.
The lemon shark is a species of shark from the family Carcharhinidae. Lemon sharks can grow to 3.4 metres (11 ft) in length. They are often found in shallow subtropical waters and are known to inhabit and return to specific nursery sites for breeding. Often feeding at night, these sharks use electroreceptors to find their main source of prey: fish. Lemon sharks enjoy the many benefits of group living such as enhanced communication, courtship, predatory behavior, and protection. This species of shark gives birth to live young, and the females are polyandrous and have a biennial reproductive cycle. Lemon sharks are not thought to be a large threat to humans. The lemon shark's life span is unknown, but the average shark is 25 to 30 years.
Lanternfishes are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. They are aptly named after their conspicuous use of bioluminescence. Their sister family, the Neoscopelidae, are much fewer in number but superficially very similar; at least one neoscopelid shares the common name 'lanternfish': the large-scaled lantern fish, Neoscopelus macrolepidotus.
Pelagic fish live in the pelagic zone of ocean or lake waters – being neither close to the bottom nor near the shore – in contrast with demersal fish that do live on or near the bottom, and reef fish that are associated with coral reefs.
The smooth hammerhead is a species of hammerhead shark, and part of the family Sphyrnidae. This species is named "smooth hammerhead" because of the distinctive shape of the head, which is flattened and laterally extended into a hammer shape, without an indentation in the middle of the front margin. Unlike other hammerheads, this species prefers temperate waters and occurs worldwide at medium latitudes. In the summer, these sharks migrate towards the poles following cool water masses, sometimes forming schools numbering in the hundreds to thousands.
The sharpnose sevengill shark, also known as one-finned shark, perlon shark, sevengill cow shark, sharpsnouted sevengill or slender sevengill, is a species of shark in the family Hexanchidae, and the only living species in the genus Heptranchias. Found almost circumglobally in deep water, it is one of the few species of sharks with seven pairs of gill slits as opposed to the usual five. The other shark species with seven gill slits is the broadnose sevengill shark. Though small, this shark is an active, voracious predator of invertebrates and fish. When caught, this species is notably aggressive and will attempt to bite. It is of minor commercial importance.
Forage fish, also called prey fish or bait fish, are small pelagic fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding. They include particularly fishes of the family Clupeidae, but also other small fish, including halfbeaks, silversides, smelt such as capelin and goldband fusiliers.
The seven-arm octopus is one of the two largest known species of octopus; based on scientific records, it has a maximum estimated total length of 3.5 m (11 ft) and mass of 75 kg (165 lb). The only other similarly large extant species is the giant Pacific octopus, Enteroctopus dofleini.
Basking may refer to:
A bait ball, or baitball, occurs when small fish swarm in a tightly packed spherical formation about a common centre. It is a last-ditch defensive measure adopted by small schooling fish when they are threatened by predators. Small schooling fish are eaten by many types of predators, and for this reason they are called bait fish or forage fish.
David William Sims is a British marine biologist known for satellite tracking sharks and the Global Shark Movement Project. He is Senior Research Fellow at the Laboratory of the Marine Biological Association (MBA) in Plymouth, and a Professor of Marine Ecology in the National Oceanography Centre, Southampton at the University of Southampton, U.K.
The giant oceanic manta ray is a species of ray in the family Mobulidae, and the largest type of ray in the world. They are circumglobal and are typically found in tropical and subtropical waters, but can also be found in temperate waters. Until 2017, giant mantas were classified in the genus Manta, along with the smaller reef manta. DNA testing revealed that both species are more closely related to rays of the genus Mobula than previously thought. As a result, giant mantas were renamed Mobula birostris to reflect the new classification.
A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton.
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