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Galapagos shark
The Galapagos shark (''Carcharhinus galapagensis'') is a species of requiem shark, in the family Carcharhinidae, found worldwide. This species favors clear reef environments around oceanic islands, where it is often the most abundant shark species. A large species that often reaches , the Galapagos reef shark has a typical fusiform "reef shark" shape and is very difficult to distinguish from the dusky shark (''C. obscurus'') and the grey reef shark (''C. amblyrhynchos''). An identifying character of this species is its tall first dorsal fin, which has a slightly rounded tip and originates over the rear tips of the pectoral fins.
Galapagos sharks are active predators often encountered in large groups. They feed mainly on bottom-dwelling bony fishes and cephalopods; larger individuals have a much more varied diet, consuming other sharks, marine iguanas, sea lions, and even garbage. As in other requiem sharks, reproduction is viviparous, with females bearing litters of 4–16 pups every 2–3 years. The juveniles tend to remain in shallow water to avoid predation by the adults. Galapagos sharks are bold and have behaved aggressively towards humans, and are thus regarded as dangerous. The International Union for Conservation of Nature (IUCN) has assessed this species as near threatened, as it has a slow reproductive rate and there is heavy fishing pressure across its range.
==Taxonomy and phylogeny==
The Galapagos shark was originally described as ''Carcharias galapagensis'' by Robert Evans Snodgrass and Edmund Heller in 1905; subsequent authors moved this species to the genus ''Carcharhinus''. The holotype was a long fetus from the Galapagos Islands, hence the specific epithet ''galapagensis''.〔Bester, C. (Biological Profiles: Galapagos Shark ). ''Florida Museum of Natural History Ichthyology Department''. Retrieved on April 26, 2009.〕
Garrick (1982) placed the Galapagos shark and the dusky shark at the center of the "obscurus group", one of two major groupings within ''Carcharhinus''. The group consisted of the bignose shark (''C. altimus''), Caribbean reef shark (''C. perezi''), sandbar shark (''C. plumbeus''), dusky shark (''C. obscurus''), and oceanic whitetip shark (''C. longimanus''), all large, triangular-toothed sharks and is defined by the presence of a ridge between the two dorsal fins.〔Garrick, J.A.F. (1982). "Sharks of the genus ''Carcharhinus''". NOAA Technical Report, NMFS CIRC-445.〕 Based on allozyme data, Naylor (1992) reaffirmed the integrity of this group, with the additions of the silky shark (''C. falciformis'') and the blue shark (''Prionace glauca''). The closest relatives of the Galapagos shark were found to be the dusky, oceanic whitetip, and blue sharks.
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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