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__NOTOC__ Threatened rays are those vulnerable to endangerment (extinction) in the near future. The International Union for Conservation of Nature (IUCN) is the world’s oldest global environmental organization.〔(International Union for Conservation of Nature (IUCN) ) ''Encyclopædia Britannica''. Retrieved 16 March 2013.〕 It evaluates threatened species, and treats threatened species not as a single category, but as a group of three categories, depending on the degree to which they are threatened: ::File:VU IUCN 3 1.svg Vulnerable species ::File:EN IUCN 3 1.svg Endangered species ::File:CR IUCN 3 1.svg Critically endangered species The term ''threatened'' strictly refers to these three categories (critically endangered, endangered and vulnerable), while ''vulnerable'' is used to refer to the least at risk of these categories.〔 The terms can be used somewhat interchangeably, as all ''vulnerable'' species are threatened, all ''endangered'' species are vulnerable and threatened, and all ''critically endangered'' species are endangered, vulnerable and threatened. Threatened species are also referred to as a red-listed species, as they are listed in the IUCN Red List of Threatened Species. Together rays and sharks make up the class of modern cartilaginous fishes. Modern fish are either cartilaginous or bony. Cartilaginous fishes have skeletons made of cartilage while bony fishes have skeletons made of bone. Because rays and sharks are closely related, they are often studied together. In 2010 a global IUCN study of vertebrates found that of 1,044 cartilaginous (ray and shark) species examined, 345 or 33% were threatened with extinction.〔(Third of Shark and Ray Species Are Threatened, Study Suggests ) ''Science News'', 27 October 2010.〕〔Hoffmann M, C Hilton-Taylor and 173 others (2010) ("The impact of conservation on the status of the world's vertebrates" ) ''Science'', 330: 1503–1509. 〕 There are four orders of rays: stingrays, skates, electric rays and sawfishes. Like sharks, rays are relatively long living and thrive in stable populations. They are K-strategists which grow slowly, mature late sexually and produce few offspring. They cannot recover as rapidly as many faster growing fish can if their populations are depleted.〔(Conservation of Sharks ) CITES AC18 Inf. 1, 2002.〕 As with sharks, rays are increasingly becoming vulnerable because of commercial and recreational fishing pressures, the impact of non-ray fisheries on the seabed and ray prey species, and other habitat alterations such as damage and loss from coastal development and marine pollution. Most particularly, the continuing decline of threatened rays and sharks is the consequence of unregulated fishing.〔(The Future of Sharks: A Review of Action and Inaction ) CITES AC25 Inf. 6, 2011.〕 Manta rays are largest rays in the world, with wingspans reaching 7 metres.〔(Glider of the sea threatened by 'traditional' medicine ) ''New Scientist'', 25 March 2013.〕 They have one of the highest brain-to-body mass ratios of all fish. Manta populations suffer when they are caught as bycatch by fishermen fishing for other species, but fisheries which target manta rays are even more harmful. Manta rays use their gills to filter plankton from the sea. Demand for their dried gill rakers, cartilaginous structures protecting the gills, has been growing in traditional Chinese medicine practices. The market is "bogus" since dried manta gills have never been used historically in Chinese medicine, and there is no evidence that the gills have any medicinal value.〔〔(Manta Rays Endangered by Sudden Demand from Chinese Medicine ) ''ScientificAmerican'', 17 January 2012.〕〔("The global threat to manta and mobula rays" ) WildAid and Shark Savers. 2011 report.〕 The flesh is edible and is consumed in some countries, but is tough and unattractive compared to other fish. To fill the growing demand in Asia for gill rakers, targeted fisheries have developed in other parts of the world, including Sri Lanka, Indonesia, West Africa and Central and South America. Each year, thousands of manta rays, primarily the giant manta ray, are being caught and killed purely for their gill rakers. A fisheries study in Sri Lanka estimated that over a thousand of these were being sold in the country's fish markets each year. In 2011, manta rays became strictly protected in international waters thanks to their recent inclusion in the Convention on Migratory Species of Wild Animals. The CMS is an international treaty organization concerned with conserving migratory species and habitats on a global scale. Although individual nations were already protecting manta rays, the fish often migrate through unregulated waters, putting them at increased risk from overfishing. In 2013, the Convention on International Trade in Endangered Species (CITES) listed both species of manta rays as CITES Appendix II species. This means that the international trade of manta rays will now be monitored and regulated.〔(Proposal 46: Genus ''Manta'' ) ''CITES'', Sixteenth meeting of the Conference of the Parties Bangkok (Thailand), 3–14 March 2013.〕〔(CITES conference takes decisive action to halt decline of tropical timber, sharks, manta rays and a wide range of other plants and animals )〕 Sawfish are a less well known family of rays which have a long rostrum resembling a saw. Some species can reach in length. All species of sawfish are either endangered or critically endangered as a result of habitat destruction and overfishing.〔 Their young stay close to shore, and are particularly affected by coastal developments.〔(Sawfish Is First Sea Fish on U.S. Endangered List ) ''National Geographic News'', 4 June 2003.〕 Because their rostrum is easily entangled, sawfishes can easily become bycatch in fishing nets. They are also exploited for the novelty value of their rostrum, their fins are eaten as a delicacy in China, and their liver oil used as a food supplement. While arguing for a global ban on international commerce in 2007, a representative from the National Museums of Kenya stated, "Only the meat is consumed locally; and artisanal fishermen can retire after catching one sawfish due to the high value of a single rostrum, up to $1,450."〔 In 2013 CITES uplisted the largetooth sawfish to Appendix I. This is CITES highest protection level, and means that all international trade of the species is banned.〔(Proposal 45: ''Pristis microdon'' ) ''CITES'', Sixteenth meeting of the Conference of the Parties Bangkok (Thailand), 3–14 March 2013.〕〔(【引用サイトリンク】title=CITES Appendices I, II and III )〕 ==See also== * List of threatened sharks 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「List of threatened rays」の詳細全文を読む スポンサード リンク
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