|
The pallid sturgeon (''Scaphirhynchus albus'') is an endangered species of ray-finned fish, endemic to the waters of the Missouri and lower Mississippi River basins of the United States. Named for its pale coloration, the pallid sturgeon is closely related to the relatively common shovelnose sturgeon (''Scaphirhyncus platorhynchus''), but is much larger, averaging between in length and in weight at maturity.〔(【引用サイトリンク】 publisher = Montana Fish, Wildlife and Parks )〕 The pallid sturgeon takes 15 years to mature and spawns infrequently, but can live up to a century. A member of the Acipenseridae (sturgeon) family of fish that originated during the Cretaceous period 70 million years ago, the pallid sturgeon has remained essentially unchanged. In 1990, the U.S. Fish and Wildlife Service placed the pallid sturgeon on its endangered species list, because few young individuals had been observed in the preceding decade, and sightings had greatly diminished; the species is now rarely seen in the wild. It was the first fish species in the Missouri River drainage area to be listed as endangered, and a loss of its habitat is thought to be responsible for its decline. The vast majority of the Missouri River drainage system has been channeled and dammed, reducing the gravel deposits and slow-moving side channels that are its favored spawning areas. Until the middle of the 20th century, pallid sturgeon were common and anglers found catching such a large fish in fresh water a rewarding experience. The species is considered to be good-tasting, and its eggs have been used as caviar, although less commonly than those of many other sturgeon. Efforts to prevent the species from becoming extinct have had modest success. Pallid sturgeon are actively being raised in a dozen hatcheries and the offspring are being released back to the wild every year. To better understand pallid sturgeon behavior, researchers have implanted global positioning system transmitters to track their movements and help identify possible spawning areas. Federal and state agencies are working together to improve habitat by restoring spawning areas since restoration of these areas is required if the species is to survive in the wild. == Taxonomy and etymology == Taxonomists S.A. Forbes and R. E. Richardson classified the pallid sturgeon in 1905, grouping it in the ''Parascaphirhynchus'' genus and the Acipenseridae family, which includes all sturgeon worldwide. The pallid sturgeon's closest relatives are the shovelnose sturgeon (''Scaphirhyncus platorhynchus''), which is still relatively common, and the critically endangered Alabama sturgeon (''Scaphirhynchus suttkusi''), which may soon become extinct. These three species belong to the Scaphirhynchinae subfamily, which has only one other genus, ''Pseudoscaphirhynchus'', represented by three species found in west-central Asia. The word pallid means "deficient in color", and compared to other species of sturgeon, the pallid is noticeably paler. The scientific name for the fish is derived from ''Scaphirhynchus'', a Greek word meaning "spade snout" and ''albus'' which is Latin for "white". 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「Pallid sturgeon」の詳細全文を読む スポンサード リンク
|