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The Silky shark (''Carcharhinus falciformis''), also known by numerous names such as Blackspot shark, Grey whaler shark, Olive shark, Ridgeback shark, Sickle shark, Sickle-shaped shark, and Sickle silk shark, is a species of requiem shark, in the family Carcharhinidae, named for the smooth texture of its skin. It is one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge of the continental shelf down to a depth of . The silky shark has a slender, streamlined body and typically grows to a length of . It can be distinguished from other large requiem sharks by its relatively small first dorsal fin with a curving rear margin, its tiny second dorsal fin with a long free rear tip, and its long, sickle-shaped pectoral fins. It is a deep, metallic bronze-gray above and white below. With prey often scarce in its oceanic environment, the silky shark is a swift, inquisitive, and persistent hunter. It feeds mainly on bony fishes and cephalopods, and has been known to drive them into compacted schools before launching open-mouthed, slashing attacks. This species often trails schools of tuna, a favored prey. Its sense of hearing is extremely acute, allowing it to localize the low-frequency noises generated by other feeding animals, and, by extension, sources of food. The silky shark is viviparous, meaning that the developing embryos are sustained by a placental connection to their mother. There is significant geographical variation in its life history details. Reproduction occurs year-round except in the Gulf of Mexico, where it follows a seasonal cycle. Females give birth to litters of up to 16 pups annually or biennially. The newborn sharks spend their first months in relatively sheltered reef nurseries on the outer continental shelf, growing substantially before moving into the open ocean. The large size and cutting teeth of the silky shark make it potentially dangerous, and it has behaved aggressively towards divers. However, attacks are rare as few humans enter its oceanic habitat. Silky sharks are valued for their fins, and to a lesser extent their meat, hide, liver oil, and jaws. Because of their abundance, they form a major component of commercial and artisanal shark fisheries in many countries. Furthermore, their association with tuna results in many sharks being taken as bycatch in tuna fisheries. Although slow-reproducing like most other sharks, the wide distribution and large population size of the silky shark was once thought to buffer the species against these fishing pressures. However, data now suggest that silky shark numbers are declining around the world, which prompted the International Union for Conservation of Nature (IUCN) to reassess its conservation status from Least Concern to Near Threatened in 2007. ==Taxonomy== A scientific description of the silky shark was first published by the German biologists Johannes Müller and Jakob Henle under the name ''Carcharias (Prionodon) falciformis'', in their 1839 ''Systematische Beschreibung der Plagiostomen''. Subsequent authors have assigned this species to the genus ''Carcharhinus''.〔〔 Because Müller and Henle's type specimen was a long female fetus from Cuba, adult silky sharks were historically not recognized as ''C. falciformis'' and were described as a separate species, ''Carcharhinus floridanus'', by Henry Bigelow, William Schroeder, and Stewart Springer in 1943. Jack Garrick, Richard Backus, and Robert Gibbs, Jr. synonymized ''C. floridanus'' with ''C. falciformis'' in 1964.〔 The specific epithet ''falciformis'' is Latin for "sickle-shaped", which refers to the outline of the dorsal and pectoral fins.〔 The silky shark's common name comes from the fine texture of its skin compared to other sharks, a product of its tiny, densely packed dermal denticles.〔 It may also be referred to as blackspot shark (usually used for ''C. sealei''), grey reef shark (usually used for ''C. amblyrhynchos''), grey whaler shark, olive shark, reef shark, ridgeback shark, sickle shark, sickle silk shark, sickle-shaped shark, silk shark, and silky whaler.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Silky shark」の詳細全文を読む スポンサード リンク
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