Cumberland Elktoe

Alasmidonta atropurpurea

Description

The Alasmidonta atropurpurea (Cumberland elktoe), described by Rafinesque in 1831, has a thin but not fragile shell, whose surface is smooth, somewhat shiny, and covered with greenish rays. Young specimens have a yellowish-brown shell, and the shells of adults are generally black. The inside of the shell is shiny with colors ranging from white and bluish white to peach or salmon color.

This species is quite similar to Alasmidonta marginata, but tends to differ from the latter by its darker color, less pronounced corrugations on the posterior slope, and the less acutely angular development of the posterior ridge. In older individuals or A. atropurpurea, the posterior ridge may be rather high and the resulting slope may be quite steep, but the posterior ridge retains a rounded character. The two species may occur in adjacent stream systems but do not appear to be sympatric at any locality. The tendency for the shell to be compressed, highly pustulate, and have low to no knobs on the posterior ridge distinguishes this morph from Quadrula cylindrica s.s. [i.e., Q. c. cylindrica ]. It is not easily confused with any other sympatric species.

Behavior

This bradytictic anodontine species was found gravid from October through May, but no fish infested with its glochidia were observed until March. They found Cumberland elktoe glochidia to develop equally well on both fin and gill surfaces. Five fish species collected from the wild were parasitized by Cumberland elktoe glochidia-whitetail shiner (Cyprinella galactura), northern hogsucker (Hypentelium nigricans), rock bass (Ambloplites rupestris), longear sunfish (Lepomis megalotis), and rainbow darter (Etheostoma caeruleum). However, under laboratory' conditions, juvenile specimens transformed only on the northern hogsucker. The period of glochidial encystment (i.e., until transformation into free-living juveniles) took 24 days, at 66.2+°F (19+°C).

Habitat

This species inhabits medium-sized rivers and may extend into headwater streams where it is often the only mussel present. The species appears to be most abundant in fiats, shallow pool areas lacking the bottom contour development of typical pools, with sand and scattered cobble/boulder material, relatively shallow depths, and slow (almost imperceptible) currents. The species has also been observed in swifter currents and in areas with mud, sand, and gravel substratum.

Distribution

The Cumberland elktoe is endemic to very localized portions of the Cumberland River system in Tennessee and Kentucky; the latter state considers it endangered. Historic records exist from the Cumberland River and from its tributaries entering from the south between the Big South Fork Cumberland River upstream to Cumberland Falls. Specimens have also been taken from Marsh Creek above Cumberland Falls. Old records of the related species Alasmidonta marginata exist from other creeks above Cumberland Falls, and there is speculation that these specimens were indeed the Cumberland elktoe. Because the area above the falls has been severely damaged by coal mining, any populations ofA. atropurpurea that might have existed there were likely lost. A record of one fresh dead specimen exists from the Collins River, Grundy County, Tennessee. However, extensive searches of the collection site, other sites in the Collins River, and adjacent rivers have failed to find another specimen. If the species did exist in the Collins River, it has likely been extirpated. Any Cumberland elktoe populations that may have existed in the main stem of the Cumberland River were likely lost when Wolf Creek Dam was completed. Other tributary populations were likely lost due to habitat degradations caused by coal mining, pollution, and spills from oil wells.

Three populations of the Cumberland elktoe have persisted, all of them associated with waters flowing through McCreary County, Kentucky. The species survives in the middle sections of Rock Creek; the upper portions of the Big South Fork Cumberland River basin in McCreary County, as well as in the Tennessee counties of Scott, Fentress, and Morgan; and in Marsh Creek, which likely contains the best surviving elktoe population.

The Cumberland elktoe has apparently been extirpated from the main stem of the Cumberland River, Laurel River, and its tributary Lynn Camp Creek. Based on post-1985 records, populations of the Cumberland lktoe persist in eight tributaries—Laurel Fork and Marsh Creek, both Whitley County, Kentucky; Big South Fork, Scott County, Tennessee, and Mc-Creary County, Kentuclcy; Rock Creek, McCreary County, Kentucky; Clear Fork, Fentress, Morgan, and Scott Counties; Tennessee; North Prong Clear Fork, Fentress County, Tennessee; White Oak Creek, Scott County, Tennessee; and Bone Camp Creek, Morgan County, Tennessee. The latter five streams, which comprise the Big South Fork system, may represent a single metapopulation of the Cumberland elktoe; there may be suitable habitat for the species and/or its fish hosts in intervening stream reaches, potentially allowing for natural genetic interchange to occur.

Considered a "rare species" in 1981, few sites continue to harbor the Cumberland elktoe, although relatively large populations are currently known. Marsh Creek harbors the largest population known in Kentucky, although populations in Rock Creek were also sizable in 1996. In both streams the Cumberland elktoe represented the second most abundant unionid species sampled. Bakaletz. In 1991 the largest population was reported in the Big South Fork system in Tennessee located in the headwaters of Clear Fork, where several hundred specimens were secured from muskrat middens in the late 1980s. Several age classes of the Cumberland elktoe were represented in samples taken from throughout the larger tributaries of the Big South Fork system in Tennessee during a 1986 survey.

Threats

The upper Big South Fork basin population is threatened by coal mining runoff and could also be threatened by impoundments. The Marsh Creek population has been harmed by oil spills, which always remain a serious potential threat. The Rock Creek population could be threatened by logging. All three populations, especially Rock Creek and Marsh Creek, are restricted to such short stream reaches that they could be eliminated by all manner of hazardous events, toxic chemical spills being the chief among them.

Conservation and Recovery

The Cumberland elktoe only survives in three very localized portions of the Cumberland River system, in the middle sections of Rock Creek, the upper portions of the Big South Fork of the Cumberland River basin, and in Marsh Creek. Marsh Creek supports the largest population of the rare mussel. It is crucial that these critical habitats are protected against the development of new dams or impoundments, from acid drainage associated with local coal mining, and from spills of petroleum or other toxic chemicals. The surviving populations of the Cumberland elktoe should be monitored, and research undertaken into its biology and ecological needs, including work on its propagation and rein-troduction techniques.

Contacts

U.S. Fish and Wildlife Service
Asheville Ecological Services Field Office
160 Zillicoa Street
Asheville, North Carolina, 28801-1082
Telephone: (828) 258-3939
Fax: (828) 258-5330

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

Reference

U.S. Fish and Wildlife Service. 10 January 1997. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Cumberland Elktoe, Oyster Mussel, Cumberlandian Combshell, Purple Bean, and Rough Rabbitsfoot." Federal Register 62(7): 1647-1658.