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Blacknose shark
The blacknose shark (''Carcharhinus acronotus'') is a species of requiem shark, belonging to the family Carcharhinidae, common in the tropical and subtropical waters of the western Atlantic Ocean. This species generally inhabits coastal seagrass, sand, or rubble habitats, with adults preferring deeper water than juveniles. A small shark typically measuring long, the blacknose has a typical streamlined "requiem shark" shape with a long, rounded snout, large eyes, and a small first dorsal fin. Its common name comes from a characteristic black blotch on the tip of its snout, though this may be indistinct in older individuals.
Blacknose sharks feed primarily on small bony fishes and cephalopods, and in turn fall prey to larger sharks. Like other members of their family, they exhibit a viviparous mode of reproduction in which the developing embryos are sustained by a placental connection. The females give birth to three to six young in late spring or early summer, either annually or biennually, after a gestation period of eight to 11 months. This species is not known to attack humans, though it has been documented performing a threat display towards divers. It is of moderate commercial and recreational importance. The International Union for Conservation of Nature has assessed this species as Near Threatened. In 2009, the U.S. National Oceanic and Atmospheric Administration announced the populations of the blacknose shark off the United States are being overfished, and proposed new conservation measures.
==Taxonomy and phylogeny==
The Cuban naturalist Felipe Poey published the first description of the blacknose shark in 1860 as ''Squalus acronotus'', in his ''Memorias sobre la historia natural de la Isla de Cuba''. Later authors moved this species to the genus ''Carcharhinus''. The type specimen was a 98-cm (3.2-ft)-long male caught off Cuba.
Based on morphological data, Jack Garrick suggested in 1982 that the blacknose shark has a sister relationship to a group containing the whitecheek shark (''C. dussumieri'') and the blackspot shark (''C. sealei''), while Leonard Compagno proposed in 1988 that this shark belongs in a group with five other species, including the silky shark (''C. falciformis'') and the blacktip reef shark (''C. melanopterus''). Molecular analyses have been similarly equivocal regarding the blacknose shark's phylogenetic relationships: Gavin Naylor's 1992 allozyme analysis found this species to be the most basal member of ''Carcharhinus'', while Mine Dosay-Abkulut's 2008 ribosomal DNA analysis indicated affinity between it and the blacktip shark (''C. limbatus'') or the smalltail shark (''C. porosus''). The whitenose shark (''Nasolamia velox''), found along the tropical western coast of the Americas, may be descended from blacknose sharks that experienced the teratogenic effects of incipient cyclopia.〔
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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