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The grey reef shark (''Carcharhinus amblyrhynchos'', sometimes misspelled ''amblyrhynchus'' or ''amblyrhinchos'') is a species of requiem shark, in the family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as far east as Easter Island and as far west as South Africa. This species is most often seen in shallow water near the drop-offs of coral reefs. The grey reef shark has the typical "reef shark" shape, with a broad, round snout and large eyes. This species can be distinguished from similar species by the plain or white-tipped first dorsal fin, the dark tips on the other fins, the broad, black rear margin on the tail fin, and the lack of a ridge between the dorsal fins. Most individuals are less than long. Grey reef sharks are fast-swimming, agile predators that feed primarily on free-swimming bony fishes and cephalopods. Their aggressive demeanor enables them to dominate many other shark species on the reef, despite their moderate size. Many grey reef sharks have a home range on a specific area of the reef, to which they continually return. However, they are social rather than territorial. During the day, these sharks often form groups of five to 20 individuals near coral reef drop-offs, splitting up in the evening as the sharks begin to hunt. Adult females also form groups in very shallow water, where the higher water temperature may accelerate their growth or that of their unborn young. Like other members of its family, the grey reef shark is viviparous, meaning the mother nourishes her embryos through a placental connection. Litters of one to six pups are born every other year. Grey reef sharks were the first shark species known to perform a threat display, a stereotypical behavior warning that it is prepared to attack.〔 The display involves a "hunched" posture with characteristically dropped pectoral fins, and an exaggerated, side-to-side swimming motion. Grey reef sharks often do so if they are followed or cornered by divers to indicate they perceive a threat. This species has been responsible for a number of attacks on humans, so should be treated with caution, especially if they begin to display. They are caught in many fisheries and are susceptible to local population depletion due to their low reproduction rate and limited dispersal. As a result, the International Union for Conservation of Nature has assessed this species as Near Threatened. ==Taxonomy and phylogeny== Dutch ichthyologist Pieter Bleeker first described the grey reef shark in 1856 as ''Carcharias (Prionodon) amblyrhynchos'', in the scientific journal ''Natuurkundig Tijdschrift voor Nederlandsch-Indië''. Later authors moved this species to the genus ''Carcharhinus''. The type specimen was a -long female from the Java Sea. Other common names used for this shark around the world include black-vee whaler, bronze whaler, Fowler's whaler shark, graceful shark, graceful whaler shark, grey shark, grey whaler shark, longnose blacktail shark, school shark, and shortnose blacktail shark. Some of these names are also applied to other species.〔 In older literature, the scientific name of this species was often given as ''C. menisorrah''.〔 The blacktail reef shark (''C. wheeleri''), native to the western Indian Ocean, is now regarded as the same species as the grey reef shark by most authors. It was originally distinguished from the grey reef shark by a white tip on the first dorsal fin, a shorter snout, and one fewer upper tooth row on each side. Based on morphological characters, vertebral counts, and tooth shapes, Garrick (1982) concluded the grey reef shark is most closely related to the silvertip shark (''C. albimarginatus'').〔Garrick, J.A.F. (1982). ''Sharks of the genus ''Carcharhinus. NOAA Technical Report, NMFS Circ. 445.〕 This interpretation was supported by a 1992 allozyme phylogenetic analysis by Lavery. 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「Grey reef shark」の詳細全文を読む スポンサード リンク
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