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Snail darter
The snail darter (''Percina tanasi'') is a species of fish that is found in East Tennessee freshwater in the United States. It is in the perch family (family Percidae) of the order Perciformes. Discovered in 1973, the snail darter was listed as ''endangered'' under the U.S. Endangered Species Act of 1973 by 1975 and was involved in a legal controversy leading to a Supreme Court ruling to approve the completion of Tellico Dam, which posed a risk of extinction for the snail darter by blocking its migratory route — see ''Tennessee Valley Authority v. Hill'', snail darter controversy.
In 1978, the U.S. Fish and Wildlife Service, Tennessee Valley Authority (TVA), and Tennessee Wildlife Resource Agency launched a recovery plan to preserve the snail darter by transferring the species to other river systems.〔Etnier, DA & Starnes, WC. 1993. The fishes of Tennessee. Knoxville, TN: University of Tennessee Press.〕 Its native range was originally in the lower parts of the Little Tennessee River, the Sequatchie River, and in Chickamauga Creek, but was later eliminated from the Little Tennessee River by the completion of Tellico Dam.〔Ashton, MJ & Layzer, JB. 2008. Distribution of the Threatened Snail Darter (Percina Tanasi) in the Upper Tennessee River Drainage. Journal of The Tennessee Academy of Science 83:52-56.〕 The species was then transplanted into the Hiwassee River in southeastern Tennessee. The species inhabits large creeks or deeper portions of rivers and reservoirs with gravel and sand shoals substrate. The snail darter spawns between February to mid-April with the female producing 600 eggs which drift downstream. Juveniles occupy slack water habitats and migrate upstream to the breeding ground. The lifespan of the snail darter ranges between 2 to 4 years. The snail darter adult length ranges between 55 to 90 mm (2.2 to 3.1 inches).〔Page, LM. 1983. Handbook of Darters. Neptune City, NJ: TFH Publications.〕 The species’ diet consists mostly of snails and insects (caddisflies, midges, and blackflies). Snail darters have camouflage dorsal patterns and burrow in the substrate to conserve energy and hide from predators. They are largely preyed upon by banded sculpin (''Cottuss carolinae'').〔Starnes, WC. 1977. The ecology and life history of endangered snail darter, Percina (Imostoma) tanasi (Etnier). Knoxville, Tennessee: PhD dissertation, University of Tennessee. 144 pp.〕 The word ''Tanasi'' derives from capital of the Cherokee Nation located on the Little Tennessee River where the species was discovered.〔Kuehne, RA & Barbour, RW.1983. The American Darters. Lexington, KY: University Press of Kentucky.〕 The species was relisted as threatened in 1984 after being successfully transplanted into other river systems.〔
==Geographic distribution==
The original range of the snail darter was thought to be strictly in the lower portion of the Little Tennessee River with a few individuals dispersing into the headwaters of the Watts Bar Reservoir below Fort Loudon Dam. Prior to the completion of the Tellico Dam in 1979, TVA biologists made several efforts to relocate the remaining individuals of the species into other river systems. In 1975 the species was successfully transplanted to the Hiwassee River, where the population has risen to about 2,500 individuals. Another transplant attempt was made to the Nolichucky River in 1975, but was later stopped by the discovery of another federally protected species, the sharphead darter (''Etheostoma acuticeps''). Other unsuccessful transplant locations included lower parts of the Holston River, French Broad River, and middle Elk River. With the completion of the Tellico Dam, the snail darter was extirpated from the Little Tennessee River. In 1980, additional populations of snail darters were discovered in South Chickamauga Creek in Chattanooga, the lower portion of Big Sewee Creek in Meigs County, the lower Sequatchie River in Marion County, Little River in Blount County, and the lower portion of Paint Rock River in Madison County, Alabama.〔 These discoveries indicated the snail darter’s possible range as being from the lower reaches of major tributaries of the Tennessee River from the northward bend in Alabama upstream; the snail darter was reclassified from endangered to threatened in July 1984.〔
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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