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Lifespan, longevity, and ageing

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Maximum longevity: 32 years (wild)
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Distribution

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North and South Atlantic and Pacific Oceans.

Biogeographic Regions: oceanic islands (Native ); atlantic ocean (Native ); pacific ocean (Native )

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Trophic Strategy

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To capture food, this shark swims with its mouth open widely, gillrakers straining plankton from the water. The absence of basking sharks in the winter has led to the belief that they hibernate in deep waters until the following summer and, since they lose their gill rakers in winter, possibly cease to feed during this time.

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Benefits

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This fish was once used for its liver oil and was thus virtually endangered for some time. It is still used in lesser amounts for fish meal and animal feed.

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Benefits

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In some areas, this shark is considered to be a nuisance because it gets tangled in floating nets while basking on the surface. Occasionally, they have been known to ram small boats, presumably by accident.

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Robin Street, University of Michigan-Ann Arbor
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Conservation Status

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No special status.

IUCN Red List of Threatened Species: endangered

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Habitat

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Basking sharks inhabit subpolar and temperate seas moving southward during the winter. They prefer surface waters of the open sea, straying inland only to breed in the summer.

Aquatic Biomes: coastal

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Life Expectancy

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Average lifespan
Status: captivity:
32 years.

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Robin Street, University of Michigan-Ann Arbor
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Morphology

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The basking shark has a conical snout, enormous gills, dark bristle-like gill rakers, and a crescent-shaped tail. Teeth are small and numerous(about one hundred per row) with a single conical cusp usually curved backwards, and similar in both jaws. Color is grayish brown to black above, often with blotches of a lighter color, and pale with blotches on the belly. Average size of this shark ranges from 7-9 m.

Average mass: 3900 kg.

Other Physical Features: bilateral symmetry

Average mass: 2.2e+06 g.

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Reproduction

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Basking sharks are believed to be ovoviviperous. Females mature at 4-5m. Embryos supposedly measure between 1.5-1.8m in length.

Average age at sexual or reproductive maturity (male)
Sex: male:
2920 days.

Average age at sexual or reproductive maturity (female)
Sex: female:
4197 days.

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Street, R. 1999. "Cetorhinus maximus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cetorhinus_maximus.html
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Biology

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Very little information is known about the natural ecology and behaviour of the basking shark. It receives its common name from its feeding behaviour, when individuals appear to be 'basking' on the water's surface, swimming very slowly with their entire dorsal fin out of the water (2). These sharks feed passively (unlike the also plankton-feeding whale shark and megamouth shark (Megachasma pelagios) which can use its head muscles to suck water into the mouth), merely by swimming through the water with their mouths gaping (2). As water passes over the gills, plankton are retained; a fairly large shark can filter roughly 1,500 cubic metres of water an hour (6). These giant fish have occasionally been observed leaping out of the water (2), which is probably related to social behaviour (12). Basking sharks are usually solitary, although pairs and groups of up to 100 individuals have been seen (2). This species mysteriously disappears from coastal waters in the winter months and it was recently suggested that they 'hibernate' in the deep water. It is also thought that during this time of low food availability basking sharks shed and then replace the gill rakers (11). This suggestion has been refuted by scientific satellite tracking of sharks, revealing extensive migrations throughout all seasons (13). The only pregnant female ever caught gave birth to six live young; the prevailing view is that that these sharks are ovoviviparous (8), and it is likely that they only give birth every two to four years (9).
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Conservation

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The basking shark is now protected in the territorial waters of some of the countries, including the UK, in which it occurs (2). In 2002, this species was accepted onto Appendix II of the Convention on International Trade in Endangered Species (CITES), thus reducing international trade in basking sharks (4). A three-year research programme in Britain is currently underway (9). The attraction of these large and appealing creatures for ecotourism may also benefit their conservation.
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Description

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The basking shark is the second largest fish in the seas, after the whale shark (Rhincodon typus); its maximum size is thought to be at least 10 metres long (6). This creature is a gentle giant however, filter-feeding on plankton through the five massive gill slits that almost encircle the head (2). Thousands of fine, bristle-like 'gill rakers' adorn each of the gill arches within the slits (7). The basking shark has an extremely distinctive body shape with its conical, almost pointed snout and large dorsal and pectoral fins that can reach as long as two metres each (8), and a crescent-moon shaped tail (2). The body is a greyish brown colour, either all over or with a paler shade underneath, and is covered with a layer of mucus (9). The large mouth, which may gape one metre across (8), contains many small hooked teeth (2); more than any other shark (9). This species has a particularly large liver that can weigh up to 25 percent of the body weight and provides buoyancy for its oceanic life (2). Juveniles have a distinctive hook-like snout, which changes shape during the first year of life (2).
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Habitat

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These sharks are found at the surface of coastal waters during the summer to feed on seasonally abundant copepods which bloom in frontal areas during spring and summer, but it is thought they migrate further offshore or to deeper waters during winter (11).
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Range

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The basking shark is found throughout the world mainly in cool and temperate waters (7), although some sharks have recently been tagged, and found in tropical waters (10), although it was probably never very abundant (1). There has been some suggestion that the geographically isolated northern and southern hemisphere populations represent distinct species but this remains unclear (6).
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Status

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Classified as Vulnerable (VU) on the IUCN Red List (1), and listed on Appendix II of CITES (4) and Appendices I and II of the Bonn Convention on Migratory Species (CMS) (5).
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Threats

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This species was traditionally hunted for its vast liver, which was sold as an aphrodisiac in Japan, and also used by fishermen for lighting in the UK, whilst the oil was used in the manufacture of cosmetics (2). Due to its long maturation time and slow reproductive rate this species is particularly vulnerable to over-fishing, and targeted populations are very slow to recover from targeted fisheries (1). Today the biggest threat comes from the demand for fins for shark fin soup in the Far East and from accidental by-catch in the fishing industry (14). Although exact population figures are difficult to assess, there has been a reported decline by as much as 80 percent since the 1950s (2).
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Brief Summary

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Basking sharks are the second largest living fish. Only whale sharks are larger. Despite their size, they are not dangerous for humans. Basking sharks don't have any teeth. They catch their food with the help of a filter in their mouth. With this filter, they can sieve the water and remove all kinds of small food particles. The filter is replaced every year.
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Size

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Basking sharks have been credited as reaching a maximum total length of 12.2 to 15.2 m, but even if this is correct most specimens do not exceed about 9.8 m. Males mature at about 4 or 5 m and reach about 9 m, females are mature at 8.1 to 9.8 m. Size at birth unknown; the smallest known free-living individual was 165 cm long. The basking shark is the second largest shark, fish-like vertebrate, and elasmobranch after the whale shark (Rhincodon typus ).
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Distribution

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Coastal and amphitemperate.Western Atlantic: Newfoundland to Florida; southern Brazil to Argentina. Eastern Atlantic: Iceland, Norway and western Barents Sea to Mediterranean and Senegal; western Cape Province, South Africa. Western Indian Ocean: Eastern Cape Province, South Africa. Western Pacific: Japan, the Koreas, China; Australia (New South Wales, Victoria, Tasmania, South and Western Australia), New Zealand. Eastern Pacific: Gulf of Alaska to Gulf of California; Ecuador, Peru and Chile, ?Galapagos Islands.
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Diagnostic Description

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fieldmarks: The great size, enormous gill slits that virtually encircle the head, dermal denticle gill rakers, pointed snout, huge, subterminal mouth with minute hooked teeth, caudal peduncle with strong lateral keels, and lunate caudal fin distinguish this shark from all others. Trunk fusiform and moderately stout. Head moderately long but much shorter than trunk; snout moderately long, pointed and conical, not depressed, flattened and bladelike; eyes small; mouth large and arcuate, ventral on head, gill openings extremely large, extending onto dorsal and ventral surfaces of head, all anterior to pectoral fin bases; gill rakers present on internal gill slits, in the form of hairlike modified dermal denticles with extremely elongated crowns; teeth very small, hooklike, not blade-shaped, and in over 200 rows in either jaws; several rows of small anterior teeth in upper jaw, separated from the laterals by a broad gap. First dorsal fin large, high, erect and angular; second dorsal and anal fins moderately large but less than half size of first dorsal, with broad, non-pivotable bases; pectoral fins long and moderately broad, much shorter than head in adults; pelvic fins smaller than first dorsal fin but larger than second; caudal fin lunate, upper lobe moderately long but less than one-third length of rest of shark, lower lobe nearly as long as upper lobe. Precaudal pits present, caudal peduncle depressed and with strong lateral keels.

References

  • Bigelow & Schroeder, (1948)
  • D. Pauli, (pers. comm.,1983)
  • Davis, (1983)
  • Matthews, (1948)
  • Matthews, (1956)
  • Matthews & Parker, (1950)
  • Parker & Boeseman, (1954)
  • Parker & Stott, (1965)
  • Siccardi, (1961)
  • Springer & Gilbert, (1976)
  • Squire, (1967)
  • Van Deinse & Adriani , (1953)

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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Brief Summary

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A coastal-pelagic shark found in boreal to warm temperate waters of the continental and insular shelves, occurring well offshore and often very close to land, just off the surf zone; enters enclosed bays.This huge, impressive, conspicuous shark is often seen at or near the surface, singly, in pairs, triads or in schools up to a hundred or individuals, basking with dorsal fins out of the water or even with bellies upward, or moving slowly forwards or in short arcs with their mouths open like hoops while feeding. Surface basking in this shark is thought to be correlated with surface concentrations of food plankton and also with courtship and mating. Two, three or more individuals may swim in tandem, in a straight line or in circles, which suggests to some writers that a row of these sharks swimming together may have been mistaken for a single huge 'sea serpent' in the past. [more...] Adult, nonpregnant female basking sharks have immense numbers of small eggs in their ovaries. Presumably this shark is ovoviviparous and has uterine cannibalism like other lamnoids, with embryos feeding on the small eggs and possibly smaller siblings, but this remains to be seen. An unconfirmed record of a fetus about 1.7 m long and the above mentioned free-living individual suggests that size at birth may be about 1.7 m, and hence greater than any other known ovoviviparous or viviparous shark. Age of this shark has been estimated by counting vertebral rings and attempting to correlate them with supposed changes in size of individuals within a population. It has been suggested that birth occurs after a 3 and 1/2 year gestation period, and that two calcified rings per year are laid down until maturity at between 6 to 7 years for males. The biannually calibration of the rings is uncertain and controversial; a yearly rate of ring deposition has been suggested, with possible age at maturity for males doubled to 12 to 16 or more years (D. Pauli, pers. comm.). Whatever the case, the basking shark has proved to be extremely vulnerable to overfishing, perhaps more so than most sharks, and this can be ascribed to its slow growth rate, lengthy maturation time, long gestation period, probably low fecundity, and probable small size of existing populations (belied by the immense size of individuals in their small schools).The basking shark is one of the three types of huge, filter-feeding sharks, the other two being the megamouth and whale sharks. The basking shark may be unique in relying entirely on the passive flow of water through its pharynx generated by swimming for filtration; the other two giant filter-feeders may assist the process of food ingestion by actively pumping or gulping water and food organisms into their pharynxes. The basking shark feeds exclusively on small planktonic organisms trapped on its unique gill rakers, apparently with the help of mucous secreted in its pharynx. Food items include small copepods, barnacle and decapod larvae, and fish eggs. On the average a half ton of material may be present in the stomach of these sharks. While feeding the basking shark cruises with mouth widely open and gills distended, occasionally closing its mouth to ingest its prey. An average adult has been estimated to be capable of filtering over 2000 tons of water per hour assuming a constant cruising speed of about 2 knots. The facts that the basking shark periodically sheds its gill rakers and that plankton densities seasonally fall below levels thought essential to maintain ordinary swimming and metabolic activity in this shark have spawned a controversy over whether or not the species remains active when deprived of gill rakers and high plankton densities. It has been suggested that the basking shark may 'hibernate' on the bottom, perhaps at the edge of continental shelves, until its rakers are replaced and plankton blooms reoccur. Proof of hibernation has never been forthcoming, and an alternate hypothesis has been suggested that the basking shark may turn to benthic feeding when it loses its gill rakers. A possible additional factor is that the massive, oil-filled liver of this species may serve as a metabolic store to supply energy to support a reduced rate of activity (slower swimming in colder, deep water) while gill rakers and plankton supplies regenerate. Estimates have been proposed that, in north European waters, the basking shark drops its gill rakers in early winter and takes about 4 or 5 months to fully replace them.
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Benefits

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The basking shark has been the object of harpoon fisheries from small boats off the Norwegian coast, Ireland and Scotland, Iceland, California, Peru, Ecuador, China, and Japan, often sporadically fished due to periodic depletion of basking shark stocks; during the last century they were also harpooned by whaling vessels . The basking shark has also been taken in nets, including bottom gillnets and even bottom and pelagic trawls, and formerly was a problem to salmon gillnetters in the Pacific northwest of North America by fouling gillnets . Catches of basking shark have been reported to FAO only from Northeast Atlantic (Fishing Area 27) by Norway (Portugal reported one single t in 1987, 1994, 1995 and 1996). Norway' catches had two peaks in 1970 (18,700 t) and in 1975 (18,352 t) then steadily decreased; in 1992 they raised again to 3,658 t but in 1995 and 1996 dropped to 108 and 413 t respectively. The total catch reported for this species to FAO for 1999 was 210 t. The countries with the largest catches were New Zealand (129 t) and Norway (77 t). The basking shark meat is used for human consumption fresh or dried salted; its fins are used for shark-fin soup; its liver, rich in oil and very large, is extracted for its high squalene content but the liver oil was formerly used for tanning leather for lamp oil; the hide is processed for leather and the carcass is rendered for fishmeal. The basking shark has been exploited commercially for centuries in several parts of the world mainly for its liver oil, which was used as lighting fuel for lamps in the past, and during this century as a source of chemical compounds. Several localised basking shark fisheries have shown sharp declines recently and in the past. However, the unpredictable nature of the occurrence of this shark which seems to be driven chiefly by oceanographic processes (Sims and Quayle 1998), its poorly known migratory movements, and the total lack of understanding of the size and structure of the stocks make it difficult to separate natural fluctuations in local abundance from the effects of exploitation on the populations. A fishery around Achill Island, in Ireland, operated from 1947 to 1975 with decreasing catches after an initial peak of 1,800 sharks taken in 1952 (Fowler 1996). Parker and Stott (1965) attributed the decline in this fishery during the early 1960s to overfishing of the local stock. Fowler (1996) notes that few basking sharks occur in the area today. Norway has a basking shark fishery that dates back to the 16th century when the dry flesh was used for human consumption. In the 1960s, a high demand for shark livers spurred a great expansion in this traditional fishery and catches of between 1,266 and 4,266 basking sharks per year were made in the period 1959-80 (Kunzlik 1988, Miklevoll 1989a, Bonfil 1994). Presently, under EU regulations, Norway can only take 400 t of basking shark livers per year (about 2,400 t live weight). However, shrinking markets for basking shark oil and an ageing Norwegian fleet together with the erratic distribution of the sharks have constrained the catches and the quota has never been fully taken (Bonfil 1994). The abundance of basking sharks off the coast of California and the effects of fishing on local stocks are also surrounded by uncertainty. Historical accounts of basking sharks point to both low and high abundances in the region. Clark (1887; cited by Castro et al. in press) reported them as very rare off Monterey while Chute (1930; cited by Castro et al. in press) cited reports of up to 500 sharks at a time. A fishery for basking sharks took place off California during 1924-1950 (Phillips 1948). The yearly average catch was about 25 sharks but up to 200 basking sharks were taken in a single year in Monterey Bay (Roedel and Ripley 1950). The California fishery stopped in 1950 when the price of shark liver oil collapsed and basking shark availability decreased (Squire 1967). Squire (1990) provides some data suggesting that the abundance of basking sharks in California is quite variable. Based on aerial survey reports he found that basking shark apparent abundance north of Point Conception was higher before 1970 than recently, in a period when no significant fishing (directly or as bycatch) has occurred since 1950. However, the drop in apparent abundance is concurrent with decreased survey effort in that area over that period. This author suggests that ENSO and other oceanographic anomalies may be an important factor driving the abundance of basking sharks in California. During the 1950s, the Department of Fisheries and Oceans of Canada conducted a basking shark eradication programme in the West Coast of Vancouver Island following complaints of salmon fishermen who lost their nets and catches to basking sharks. Some 110 basking sharks were killed in 1955-56 and local shark populations have not yet recovered to their original levels (Darling and Keogh 1994). Kunzlik (1988) attributes the decline of basking shark fisheries to the inconsistent nature of their seasonal availability and to collapses in the price paid for their livers, and finds no firm evidence to suggest that the species has been threatened, even locally, by exploitation. Conservation Status : Our poor knowledge of the basic biology of the basking shark precludes the calculation of its intrinsic rebound potential. However, preliminary studies suggest it is a late maturing fish (Pauly 1978) and has few offspring. This points towards a low intrinsic rebound potential which coupled with declines in local abundance suggest a precautionary approach to basking shark exploitation. The IUCN Red List (Camhiet al. 1988) classifies the basking shark as Vulnerableworldwide. Mooney-Seus and Stone (1996) consider this species asData Deficient but stress its potential frailty. The basking shark is protected from fishing in state waters of Florida, all federal waters of the US coasts of the Gulf of México and the Atlantic Ocean, the Isle of Man, and New Zealand. It is proposed for protection in the Mediterranean Sea and British waters (Anon. 1998). Additional information from IUCN database Additional information from CITESdatabase
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Migration

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Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.
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Trophic Strategy

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Selective filter feeder that orients itself towards the most productive zooplankton patches, preferring areas where zooplankton density is above 1 g/m3 (Ref. 88781). Occurrence and movements appear to be correlated to sea surface temperature, in particular to the thermal boundaries at tidal and shelf-break fronts (as these areas may have seasonally productive zooplankton patches which the shark locates and utilizes) (Ref. 50200, 88781, 88826). Often in close association with shoals of other fish such as Clupea harengus and Scomber scombrus in the Northern Atlantic (Ref. 310). During the summer months the basking shark is often seen swimming slowly near the surface with its large mouth held open for approximately 30 to 60 seconds. Water passively enters its mouth, possesses long bristly gill rakers on long gill arches to filter out the zooplankton. It periodically closes its mouth and forcefully constricts its gill arches, probably as a means to expel as much water from the buccal cavitiy (Ref. 33579). On average, about half a tonne of plankton may be found in an individual’s stomach (Ref. 43278). During the winter months found to inhabit the deeper waters of the shelf and shelf edges of the northeast Atlantic (Ref. 50200), the winter diving behaviour may be related to the search for discrete calanoid patches at deeper depths (Ref. 50200).
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Morphology

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Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0
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Life Cycle

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Distinct pairing with embrace (Ref. 205). Courtship behaviour patterns associated with elasmobranch reproduction were documented from an aerial observation which include 'parallel swimming', 'pectoral biting', 'nudging', and 'male on top of female'. Other mating behaviours particular to this species from the same aerial observation include nose-to-tail following; flank approach; close approach involving rostral contact or proximity with the gill, pectoral fin, vent, and dorsum; and echelon swimming (Ref. 37026). Exhibit ovoviparity (aplacental viviparity), with embryos feeding on other ova produced by the mother (oophagy) after the yolk sac is absorbed (Ref. 50449). Estimated gestation period 12-36 months (Ref. 247, 1765, 9030, 88829); TL at birth estimated between 150-200 cm; mating thought to take place during early summer; a female giving birth to young captured in August in Norwegian waters (Ref. 5983). Over a study period of 5 years, courtship-like behaviour was observed off southwest England between May and July, always in surface waters along thermal fronts; because actual mating was not observed, this may occur in deeper water (Ref. 88831). A one-year resting period between pregnancies is thought to occur, resulting in a 2-4 year interval between litters (Ref. 9030, 1765, 88829). Only one pregnant female has been observed giving birth to a litter of 6 pups (Ref. 88830).
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Diseases and Parasites

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Nemesis Infestation. Parasitic infestations (protozoa, worms, etc.)
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Diseases and Parasites

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Dinematura Infestation. Parasitic infestations (protozoa, worms, etc.)
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Diagnostic Description

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Distinguished from all other sharks by the enormous gill slits practically encircling the head; dermal denticle gill rakers; pointed snout; huge, sub terminal mouth with minute hooked teeth; caudal peduncle with strong lateral keels, and lunate caudal fin. Body covered with placoid scales. Blackish to grey-brown, grey, or blue-grey, often with irregular white blotches under the head and abdomen (Ref. 43278). Also Ref. 309, 5983.
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Biology

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The second largest shark, reportedly reaching 1,220-1,520 cm TL (Ref. 247). Thought to live up to 50 years (Ref. 9030, 89083). Semi-oceanic or oceanic species, highly migratory (Ref. 43278). Found on continental and insular shelves, offshore and often close to land, just off the surf zone; enters enclosed bays (Ref. 247). Coastal-pelagic at 1 meter to unknown depths, probably epipelagic (Ref. 58302). Occurs singly, in pairs or groups of 3 or more, or in huge schools (group of up to 100 individuals has been reported) (Ref. 6871, 43278). Prefers water temperature between 8-16 °C (Ref. 88171). Makes extensive horizontal and vertical movements along the continental shelf and shelf edge to utilize productive feeding areas (Ref. 50200). During the summer months, it is found near the surface of boreal to warm-temperate areas (Ref. 43278) feeding on zooplankton by filtering (Ref. 88781). Found in deeper waters during winter (Ref. 6871, 50200, 58302). Undertakes long transoceanic migrations (e.g. from the British Isles to Newfoundland, Canada (Ref. 88824)) and moves between the northern and southern hemisphere in tropical mesopelagic water (Ref. 88825). These migrations have been found to cover distances of over 9,000 km. May form segregations by size or sex (Ref. 88171). Ovoviviparous (Ref. 50449). Regarded as ordinarily harmless and inoffensive but potentially dangerous if attacked (particularly when harpooned) (Ref. 247). In Bay of Fundy, Canada parasitic lampreys have been found attached to the back of basking sharks and sucking their blood (Ref. 83375). Utilized fresh, frozen and dried, or salted (Ref. 9987). Also valued for its liver for oil, fins for soup, hide for leather and carcass for fishmeal (Ref. 247). May be a potential source of anti-carcinoma drugs (Ref. 6034, 6035). Used in Chinese medicine (Ref. 12166). Threatened due to bycatch fisheries (Ref. 83294).
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Importance

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fisheries: commercial
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分布

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分布於世界各溫帶及寒帶海域。臺灣北部及東北部海域有分布。
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臺灣魚類資料庫
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臺灣魚類資料庫

利用

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主要以底拖網、流刺網及鏢旗魚法捕獲,經濟價值高。肉質佳,魚肉紅燒或加工成各種肉製品;鰭可做魚翅;皮厚可加工成皮革;肝可加工製成魚肝油;剩餘物製成魚粉。唯近年來因為過渡捕撈的原因,本物種已被列入國際自然保育聯盟(IUCN)紅皮書中物種受脅評估指標的"瀕危"狀態,亦即野生種群在不久的將來面臨絕滅的機率很高。因此是屬於亟待保育的魚種。
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描述

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體呈紡錘型,軀幹較粗壯。頭大,略側扁。尾基上下方各具一凹窪;尾柄具側突。吻短而圓突。眼略小,圓形,無瞬膜。前鼻瓣短呈圓形;無口鼻溝或觸鬚。口裂寬,廣弧形,下頜短,口閉時不露齒;頜齒小向多,有形,邊緣光滑,齒頭向後,無小齒尖,4-7列在使用,每側每行100餘個。噴水孔微小。鰓孔5個,很寬,由背上側延伸至腹面;鰓耙細長密列。背鰭2個,第一背鰭大而略呈等邊三角形,起點於胸鰭及腹鰭間,後緣凹入,上角略尖圓,下角微尖突;第二背鰭頗小,起點在腹鰭後端之後,後緣凹入,上角尖圓,下角微尖突;胸鰭寬大型,鐮刀狀,後緣微凹入,外角鈍圓,內角鈍圓;尾鰭叉形,尾椎軸稍上揚,上尾叉較長大,近尾端處有一缺刻,下尾叉較短小。體背側灰褐色;腹側白色。
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棲地

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大洋性大型鯊魚,是魚類中體型第二大者。棲息於外海之大陸棚及島棚水域,但時常會出現於岸邊、潮間帶外圍、或內灣。通常1-3尾或多達百尾成群在水表面緩慢的巡游,背鰭會露出水面,或翻身曬腹。濾食性,以浮游無脊椎動物、小魚或魚卵為食。具有季節性洄游習性。可能為卵胎生。
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Basking shark

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The basking shark (Cetorhinus maximus) is the second-largest living shark and fish,[4] 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, with the inside of the mouth being white in color. The caudal fin has a strong lateral keel and a crescent shape. Other common names include bone shark, elephant shark, sail-fish, and sun-fish. In Orkney it is called hoe-mother (contracted homer), meaning "the mother of the picked dog-fish".[5]

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.[6]

Basking sharks have been shown from satellite tracking to overwinter in both continental shelf (less than 200 m or 660 ft) and deeper waters.[7] 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.[8]

Taxonomy

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 Brito 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.[9]

Evolutionary history

The oldest known members of Cetorhinidae are members of the extinct genus Keasius, from middle Eocene of Antarctica, the Eocene of Oregon and possibly the Eocene of Russia. Members of the modern genus Cetorhinus appear during the Miocene, with members of the modern species appearing during the Late Miocene. The association of Pseudocetorhinus from the Late Triassic of Europe with Cetorhinidae is doubtful.[10]

Range and habitat

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.[11] It is found from the surface down to at least 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.[12] 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.[13] It characteristically migrates with the seasons.[14]

Anatomy and appearance

The basking shark regularly reaches 7–8.5 m (23–28 ft) in length with some individuals reaching 9–11 m (30–36 ft).[15][16][17][18][19] The average length of an adult is around 7.9 m (26 ft) weighing about 4.65 t (4.58 long tons; 5.13 short tons).[15] Historical sightings suggest basking sharks around 12 m (39 ft) in length, including three basking sharks estimated at ~40 fod (12.5 metres (41 ft)) and a one ~45 fod (14 metres (46 ft)) were reported between 1884 and 1905, but these visual estimates lack good evidence.[15][20][19][21] A 12.27 m (40.3 ft) specimen trapped in a herring net in the Bay of Fundy, Canada, in 1851 has been credited as the largest recorded.[15][22] Its weight has been estimated at 16 t (16 long tons; 18 short tons).[23][15] A study looking at the growth and longevity of the basking shark suggested that individuals larger than ~10 m (33 ft) are unlikely.[24] This is the second-largest extant fish species, after the whale shark.[4]

Photo of shark in profile, showing split tail, and five dark bands that encircle the body between the head and pectoral bands
Beached basking shark

They possess the typical shark lamniform body plan and have been mistaken for great white sharks.[25] The two species can be easily distinguished by the basking shark's cavernous jaw, up to 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.

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.[26] 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.

Life history

Shot of head in profile with partially opened mouth
Head of a basking shark

Basking sharks do not hibernate, and are active year-round.[7] In winter, basking sharks often move to deeper depths, even down to 900 m (3,000 ft) and have been tracked making vertical movements consistent with feeding on overwintering zooplankton.[27]

Surfacing behaviors

They are slow-moving sharks (feeding at about 2 knots (3.7 kilometres per hour; 2.3 miles per hour))[28] 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.[29] This behaviour could be an attempt to dislodge parasites or commensals.[14] 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.

Migration

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.[7][30] They shed and renew their gill rakers in an ongoing process, rather than over one short period.[31]

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.[12][32]

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.[33][34] The whole shark was donated to the Victoria Museum for research, instead of the fins being sold for use in shark fin soup.[35][36]

While basking sharks are not infrequently seen in the Mediterranean Sea[37] and records exist in the Dardanelles Strait,[38] it is unclear whether they historically reached into deeper basins of Sea of Marmara, Black Sea and Azov Sea.

Social behaviour

A basking shark filter feeding

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.[14] Small schools in the Bay of Fundy and the Hebrides have been seen swimming nose to tail in circles; their social behaviour in summer months has been studied and is thought to represent courtship.[39]

Predators

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 in the US 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.

Diet

Basking shark filter feeding
Basking shark filter feeding at Dursey Sound

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 its mouth 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 (3.1 km/h; 1.9 mph).[31] 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.[40] 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). They will also feed on copepods of the genera Pseudocalanus and Oithona.[41] Basking sharks sometimes congregate in groups of up to 1,400 spotted along the northeastern U.S.[42] 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.[9]

Reproduction

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).[43] In females, only the right ovary appears to function, and it is currently unknown why only one of the organs seems to function.[44]

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.[45] 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.[46][47]

Conservation

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,[48] confirmations of the species became very scarce.[11] Management plans have been declared to promote effective conservation.[49][50] In June 2018 the Department of Conservation classified the basking shark as "Threatened - Nationally Vulnerable" under the New Zealand Threat Classification System.[51]

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).[52]

The IUCN Red List indicates this as an endangered species.[2]

The endangered aspect of this shark was publicised in 2005 with a postage stamp issued by Guernsey Post.

Importance to humans

The "wonderful fish" described in Harper's Weekly on 24 October 1868, was likely the remains of a basking shark.

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.[14] 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.[45] Since 2008, it has been illegal to fish for, or retain if accidentally caught, basking sharks in waters of the European Union.[45] 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).[53][45][54] As of March 2010, it was also listed under Annex I of the CMS Migratory Sharks Memorandum of Understanding.[55]

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, efforts were under way to determine whether any sharks still lived in the area and monitor their potential recovery.[56]

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.[57]

Carcass misidentification

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.[58]

See also

References

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  2. ^ a b Rigby, C.L., Barreto, R., Carlson, J., Fernando, D., Fordham, S., Francis, M.P., Herman, K., Jabado, R.W., Liu, K.M., Marshall, A., Romanov, E. & Kyne, P.M. (2021) [amended version of 2019 assessment]. "Cetorhinus maximus". IUCN Red List of Threatened Species. 2019: e.T4292A194720078.{{cite journal}}: CS1 maint: multiple names: authors list (link)|volume= / |date= mismatch
  3. ^ "Appendices | CITES". cites.org. Retrieved 14 January 2022.
  4. ^ a b "Basking Shark".
  5. ^ Yarrell, William. (1836). A History of British Fishes. Volume II. John Van Voorst, London. p. 397.
  6. ^ Kruska, DC (1988). "Brain of the basking shark (Cetorhinus maximus)". Brain Behav. Evol. 32 (6): 353–63. doi:10.1159/000116562. PMID 3228691.
  7. ^ a b c Sims, DW; Southall, EJ; Richardson, AJ; Reid, PC; Metcalfe, JD (2003). "Seasonal movements and behaviour of basking sharks from archival tagging: no evidence of winter hibernation" (PDF). Marine Ecology Progress Series. 248: 187–196. Bibcode:2003MEPS..248..187S. doi:10.3354/meps248187.
  8. ^ Sims, DW (2008). Sieving a living: A review of the biology, ecology and conservation status of the plankton-feeding basking shark Cetorhinus maximus. Advances in Marine Biology. Vol. 54. pp. 171–220. doi:10.1016/S0065-2881(08)00003-5. ISBN 978-0-12-374351-0. PMID 18929065.
  9. ^ a b C. Knickle; L. Billingsley & K. DiVittorio. "Biological Profiles basking shark". Florida Museum of Natural History. Archived from the original on 21 August 2006. Retrieved 24 August 2006.
  10. ^ Welton, Bruce J. (August 2013). "Cetorhinus cf. C. maximus (Gunnerus) (Lamniformes: Cetorhinidae), A Basking Shark from the Late Miocene Empire Formation, Coos Bay, Oregon". Bulletin, Southern California Academy of Sciences. 112 (2): 74–92. doi:10.3160/0038-3872-112.2.74. ISSN 0038-3872. S2CID 54927140.
  11. ^ a b Basking shark. Department of Conservation. govt.nz
  12. ^ a b Skomal, Gregory B.; Zeeman, Stephen I.; Chisholm, John H.; Summers, Erin L.; Walsh, Harvey J.; McMahon, Kelton W.; Thorrold, Simon R. (2009). "Transequatorial Migrations by Basking Sharks in the Western Atlantic Ocean". Current Biology. 19 (12): 1019–1022. doi:10.1016/j.cub.2009.04.019. PMID 19427211. S2CID 15079141.
  13. ^ Sims, DW; Southall, EJ; Tarling, GA; Metcalfe, JD (2005). "Habitat-specific normal and reverse diel vertical migration in the plankton-feeding basking shark". Journal of Animal Ecology. 74 (4): 755–761. doi:10.1111/j.1365-2656.2005.00971.x.
  14. ^ a b c d Compagno, Leonard J. V. (1984). "CETORHINIDAE – Basking sharks" (PDF). Sharks of the World: An annotated and illustrated catalogue of shark species known to date. Food and Agriculture Organization of the United Nations.
  15. ^ a b c d e Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. p. 256. ISBN 978-0-85112-235-9.
  16. ^ Hernández, Sebastián; Vögler, Rodolfo; Bustamante, Carlos; Lamilla, Julio (2010). "Review of the occurrence and distribution of the basking shark ( Cetorhinus maximus) in Chilean waters". Marine Biodiversity Records. 3: e67. doi:10.1017/S1755267210000540. ISSN 1755-2672.
  17. ^ Schwartz, F. J. (2010). "Basking and whale sharks of North Carolina". Journal of the North Carolina Academy of Science. 126: 84–87.
  18. ^ Matthews, L. Harrison; Parker, H. W. (1950). "Notes on the anatomy and biology of the Basking Shark (Cetorhinus maximus (Gunner))". Proceedings of the Zoological Society of London. 120 (3): 535–576. doi:10.1111/j.1096-3642.1950.tb00663.x. ISSN 1469-7998.
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  20. ^ Collett, Robert (1905). Meddelelser om Norges Fiske i Aarene 1884–1901 (3die Hoved-Supplement til "Norges Fiske", III Slutning). Forhandlinger i Videnskabs–selskabet i Christiania.
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  22. ^ McClain CR, Balk MA, Benfield MC, Branch TA, Chen C, Cosgrove J, Dove ADM, Gaskins LC, Helm RR, Hochberg FG, Lee FB, Marshall A, McMurray SE, Schanche C, Stone SN, Thaler AD. 2015. Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ 3:e715 https://doi.org/10.7717/peerj.715
  23. ^ "Sharks in the Bay of Fundy, New Brunswick". Retrieved 17 October 2014.
  24. ^ Pauly, D. (2002). Growth and Mortality of the Basking Shark Cetorhinus maximus and their Implications for Management of Whale Sharks Rhincodon typus. Vol. Elasmobranch biodiversity, conservation, and management : proceedings of the international seminar and workshop, Sabah, Malaysia, July 1997. Fowler, Sarah L., Reed, Tim M., Dipper, Frances, 1951-, IUCN--The World Conservation Union. Species Survival Commission. Gland, Switzerland: IUCN. ISBN 2-8317-0650-5. OCLC 50526779.
  25. ^ "Basking Shark". San Francisco State University. Retrieved 17 October 2014.
  26. ^ "Basking shark". redorbit.com. 19 March 2007. Retrieved 17 October 2014.
  27. ^ Shepard, ELC; Ahmed, MZ; Southall, EJ; Witt, MJ; Metcalfe, JD; Sims, DW (2006). "Diel and tidal rhythms in diving behaviour of pelagic sharks identified by signal processing of archival tagging data". Marine Ecology Progress Series. 328: 205–213. Bibcode:2006MEPS..328..205S. doi:10.3354/meps328205.
  28. ^ Sims, DW (2000). "Filter-feeding and cruising swimming speeds of basking sharks compared with optimal models: they filter-feed slower than predicted for their size". Journal of Experimental Marine Biology and Ecology. 249 (1): 65–76. doi:10.1016/s0022-0981(00)00183-0. PMID 10817828.
  29. ^ Pelagic Shark Research Foundation. "PSRF Shark Image Library". PSRF. Retrieved 1 June 2006.
  30. ^ Sims, DW; Quayle, VA (1998). "Selective foraging behaviour of basking sharks on zooplankton in a small-scale front". Nature. 393 (6684): 460–464. Bibcode:1998Natur.393..460S. doi:10.1038/30959. S2CID 205000936.
  31. ^ a b Sims, DW (1999). "Threshold foraging behaviour of basking sharks on zooplankton: life on an energetic knife-edge?". Proceedings of the Royal Society B. 266 (1427): 1437–1443. doi:10.1098/rspb.1999.0798. PMC 1690094.
  32. ^ "Giant Shark Mystery Solved: Unexpected Hideout Found". News.nationalgeographic.com. 28 October 2010. Retrieved 15 August 2012.
  33. ^ Howard, Brian Clark (23 June 2015). "Rare, Huge Basking Shark Caught Off Australia". National Geographic.
  34. ^ "Rare, giant basking shark caught off Australian coast". CNN. 23 June 2015.
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Basking shark: Brief Summary

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The basking shark (Cetorhinus maximus) is the second-largest living shark and fish, 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, with the inside of the mouth being white in color. The caudal fin has a strong lateral keel and a crescent shape. Other common names include bone shark, elephant shark, sail-fish, and sun-fish. In Orkney it is called hoe-mother (contracted homer), meaning "the mother of the picked dog-fish".

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.

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Diet

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Minute planktonic organisms; especially copepods, fish eggs and larvae

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North-West Atlantic Ocean species (NWARMS)

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Distribution

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White Bay and Notre Dame Bay Newfoundland, to the Gulf of St. Lawrence, on the Scotian Shelf, along the Nova Scotia coastline, in the Bay of Fundy and south to North Carolina, straying to Florida

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North-West Atlantic Ocean species (NWARMS)

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Habitat

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coastal warm and cool temperature waters

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North-West Atlantic Ocean species (NWARMS)

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Habitat

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nektonic

Reference

North-West Atlantic Ocean species (NWARMS)

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