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Australian blacktip shark
The Australian blacktip shark (''Carcharhinus tilstoni'') is a species of requiem shark, in the family Carcharhinidae, endemic to northern and eastern Australia. Favoring the upper and middle parts of the water column, it can be found from the intertidal zone to a depth of . Appearance-wise this species is virtually identical to the common blacktip shark (''C. limbatus''), from which it can be reliably distinguished only by its lower vertebra number and by genetic markers. Generally reaching in length, it is a fairly stout-bodied, bronze-colored shark with a long snout and black-tipped fins.
Primarily piscivorous, the Australian blacktip shark forms large groups of similar size and sex that tend to remain within a local area. It exhibits vivipary, meaning that the unborn young are provisioned through a placental connection. There is a well-defined annual reproductive cycle with mating occurring in February and March. Females bear one to six pups around January of the following year, after a 10-month gestation period. The Australian blacktip shark is among the sharks most commonly caught by northern Australian commercial fisheries. It is mainly valued for its meat, which is sold as "flake". This species was an important catch of a Taiwanese gillnet fishery that operated from 1974 to 1986, and of the Australian Northern Shark Fishery that continues to the present day. As current fishing levels are not thought to threaten this shark's population, the International Union for Conservation of Nature (IUCN) has assessed it as Least Concern.
==Taxonomy and phylogeny==
The Australian blacktip shark was described by Australian ichthyologist Gilbert Percy Whitley in a 1950 issue of the scientific journal ''Western Australian Naturalist''. He named it ''Galeolamna pleurotaenia tilstoni'' in honor of Richard Tilston, assistant surgeon at Port Essington, Northern Territory. The type specimen is a long female caught from Van Cloon Reef in Joseph Bonaparte Gulf.〔 Later authors have regarded ''Galeolamna'' as a synonym of the genus ''Carcharhinus''. This shark may also be referred to as blacktip whaler, Tilston's whaler shark, and Whitley's blacktip shark.〔
After Whitley's initial description, ''C. tilstoni'' was generally regarded as synonymous with ''C. limbatus'', the common blacktip shark. In the 1980s, additional morphological and life history data again favored the recognition of ''C. tilstoni'' as a separate species, which was eventually confirmed by allozyme studies performed by Shane Lavery and James Shaklee.〔 Several molecular phylogenetic studies based on allozymes, mitochondrial DNA, and nuclear DNA have found that that the Australian and common blacktip sharks form a closely related clade with the graceful shark (''C. amblyrhynchoides'') and the smoothtooth blacktip shark (''C. leiodon'').〔〔〔 The interrelationships between them have not been fully resolved, but available data suggest that ''C. tilstoni'' and ''C. limbatus'' are not the most closely related species within the clade despite their similarity.〔〔
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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