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Spinner shark
The spinner shark (''Carcharhinus brevipinna'') is a species of requiem shark, in the family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species occurs in tropical and warm temperate waters worldwide, except for in the eastern Pacific Ocean. It is found from coastal to offshore habitats to a depth of , though it prefers shallow water. The spinner shark resembles a larger version of the blacktip shark (''C. limbatus''), with a slender body, long snout, and black-marked fins. This species can be distinguished from the blacktip shark by the first dorsal fin, which has a different shape and is placed further back, and by the black tip on the anal fin (in adults only). It attains a maximum length of .
Spinner sharks are swift and gregarious predators that feed on a wide variety of small bony fishes and cephalopods. When feeding on schools of forage fish, they will speed vertically through the school while spinning on their axis, erupting from the water at the end. Like other members of its family, the spinner shark is viviparous, with females bearing litters of three to 20 young every other year. The newborns are born in shallow nursery areas near the coast, and are relatively fast-growing. This species is not usually dangerous to humans, but may become belligerent when excited by food. Spinner sharks are valued by commercial fisheries across their range for their meat, fins, liver oil, and skin. They are also esteemed as strong fighters by recreational fishers. The IUCN has assessed this species as Near Threatened worldwide and Vulnerable off the southeastern United States.
==Taxonomy and phylogeny==
The spinner shark was originally described as ''Carcharias (Aprion) brevipinna'' by Johannes Peter Müller and Friedrich Gustav Jakob Henle in their 1839 ''Systematische Beschreibung der Plagiostomen'', based on the mounted skin of a 79-cm-long specimen collected off Java. This species was subsequently moved to the genera ''Aprion'', ''Squalus'', and ''Aprionodon'' before being placed within the genus ''Carcharhinus''.〔Bester, C. (Biological Profiles: Spinner Shark ). Florida Museum of Natural History Ichthyology Department. Retrieved on May 7, 2009.〕 The tooth shape and coloration of this species varies significantly with age and between geographical regions, which caused much taxonomic confusion.〔 Other common names include blacktipped shark, great blacktip shark, inkytail shark, large blacktip shark, long-nose grey shark, longnose grey whaler, and smoothfang shark.
Based on similarities in morphology, tooth shape, and behavior, the closest relatives of the spinner shark were originally believed to be the blacktip shark and the graceful shark (''C. amblyrhynchoides'').〔Garrick, J.A.F. (1982). "Sharks of the genus ''Carcharhinus''". NOAA Technical Report, NMFS CIRC-445.〕 However, this interpretation was not supported by Gavin Naylor's 1992 allozyme analysis, which suggested that these similarities are the product of convergent evolution and that the closest relative of the spinner shark is the copper shark (''C. brachyurus''). In a 2007 ribosomal DNA study, the spinner shark was found to be the most genetically divergent of all the requiem shark species examined save for the tiger shark (''Galeocerdo cuvier''), being less related to other ''Carcharhinus'' species than the lemon shark (''Negaprion brevirostris'').
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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