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Alasmidonta raveneliana 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Mollusca Bivalvia Unionoida Unionidae

Scientific Name: Alasmidonta raveneliana Lea, 1834
Common Name(s):
English Appalachian Elktoe, Appalacian Elktoe
Taxonomic Notes: Frierson (1927) mistakenly designated Alasmidonta raveneliana as a junior synonym of Alasmidonta atropurpurea. This was probably due to Frierson's unfamiliarity with either species and because Rafinesque's (1831) original description of atropurpurea did not mention the corrugations on the posterior slope found in atropurpurea but absent in raveneliana. This suggests that Rafinesque has not cleaned the black encrustations from his shells which commonly occur on shells from the region and had obscurred the sculpture of the posterior slope.
A list of synonyms for this species can be found on The MUSSEL project web site (Graf and Cummings 2011).

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A2ac ver 3.1
Year Published: 2012
Date Assessed: 2012-03-12
Assessor(s): Cummings, K. & Cordeiro, J.
Reviewer(s): Bohm, M., Seddon, M. & Collen, B.
Contributor(s): Bogan, A., Dyer, E., Soulsby, A.-M., Whitton, F., Kasthala, G., McGuinness, S., Milligan, HT, De Silva, R., Herdson, R., Thorley, J., McMillan, K., Collins, A., Offord, S., Duncan, C. & Richman, N.
Justification:
Alasmidonta raveneliana is assessed as Critically Endangered. Although there has been documented expansion of one population and discoveries of additional (though likely non-viable) populations of the species since it was listed as Critically Endangered in 2000, the species continues to have a very fragmented relict distribution. Its extent of occurrence is estimated as less than 1,000 km2 and the area of occupancy is likely to be less than 100 km2. There is limited suitable habitat available for this species and what remains is disjointed. All of the surviving populations continue to be threatened by many of the same factors identified at the time of the previous listing. Of the seven surviving populations, five are restricted to scattered pockets of suitable habitat and their genetic viability is of concern. Two of the populations, previously considered the healthiest of the surviving populations, appear to have declined in recent years, and an overall decline in populations of 80% has been documented over the past 20-35 years. With a generation length of between 10-25 years, this decline falls well within three generation lengths (30-75 years) for this species.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This species is restricted to the French Broad and Little Tennessee River drainages, tributaries of the Tennessee River in eastern Tennessee and western North Carolina (Parmalee and Bogan 1998). These two main populations are distinct and represent two separate and distinct conservation units (Bogan et al. 2008). Additional populations of this species have been recently discovered, but all with a very low number of individuals. The extent of occurrence of this species is estimated between 250 and 1,000 km2, with an area of occupancy of no more than 100 km2.
Countries occurrence:
Native:
United States (North Carolina, Tennessee)
Additional data:
Estimated area of occupancy (AOO) - km2:100
Number of Locations:7
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Since its listing as Critically Endangered in 2000, additional populations of this species have been discovered, but all with very low number of individuals: two individuals have been found recently in the North Toe River, Yancey and Mitchell Cos., North Carolina, below the confluence of Crabtree Creek, and 15 live individuals, with no more than two to three at each site and one shell, recorded from the South Toe River, Yancey Co., North Carolina (USFWS 2002).

Overall, the currently known populations of this species are only remnants within this species’ historical range and exist as fragmented and separate entities. All of the surviving populations are separated from one another by major impoundments and/or apparently unsuitable habitat (USFWS 2009). The species survives only in small portions of the Little Tennessee River system, Pigeon River system, and little River in North Carolina and the Nolichucky River system in North Carolina and Tennessee (USFWS 2002).

In 2000, a decline of 80% in populations of this species had been observed over the last 10-25 years (Bogan 2000), which led to an assessment of Critically Endangered. Of the seven known surviving populations of this species, the Nolichucky River system population and the Tuckasegee River population currently appear to be viable. The other five populations of this species currently appear to be comprised of scattered individuals restricted to very short stream reaches, and their viability is presently questionable (USFWS 2009).

Severe floods in 2004 adversely affected population levels, and in some cases the range, of all of the surviving populations. A major decline of this species was documented to be occurring in the Little Tennessee River in 2005 and appears to be continuing (this population appears to have been reduced by at least 70-80%) (USFWS 2009). The Cane River portion of the Nolichucky River system population appears to have been all but eliminated, apparently due primarily to the discharge of pollutants from the Burnsville Wastewater Treatment Plant (Fridell pers. observ. 2008, in USFWS 2009).

Evidence of recent reproduction has been documented in all of the surviving populations, with the exception of the Cheoah River population. Some of the fish hosts for this species have been documented in all areas of currently occupied habitat (USFWS 2009).
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:Yes

Habitat and Ecology [top]

Habitat and Ecology:This species inhabits streams anad rivers where it is found in sand and gravel substrate among cobbles and boulders and under flat rocks, usually in moderate current at depths of less than 1 m (Parmalee and Bogan 1998). Suitable habitat in the majority of streams where the species survives is limited. The majority of the surviving populations are comprised of scattered occurrences of the species, restricted to pockets or short reaches of suitable habitat (USFWS 2009). The generation length of the species is likely to be between 10 and 25 years (M. Seddon pers. comm. 2012).

The fish hosts for this species are the Banded Sculpin (Cottus carolinae) and the Mottled Sculpin (Cottus bairdi) (USFWS 2009).
Systems:Freshwater

Use and Trade [top]

Use and Trade: This species is not utilized.

Threats [top]

Major Threat(s): The USFWS (2009) identifies the following factors as leading to the loss and decline of this species throughout its historic range. These include: habitat loss and alteration associated with impoundments, channelization, mining, and dredging operations; pollutants in wastewater discharges (sewage treatment plants and industrial discharges); runoff of silt, fertilizers, pesticides, and other pollutants from land disturbance activities implemented without adequate measures to control erosion and storm water runoff. Many of these same factors continue to threaten the surviving populations of the species.

The species appears to have been eliminated from most of the Cane River as a result of problems associated with wastewater discharge. A die-off of unknown cause in the Little Tennessee River appears to be continuing and spreading upstream. Ongoing (since summer 2007) exceptional drought conditions are becoming an increasing threat (especially lack of dilution of pollutants in wastewater treatment plant discharges, increasing accumulations of sediment from lack of flushing flows and elevated water temperature) (USFWS 2009).

The Nolichucky River system population, Little Tennessee River population and Tuckasegee River population are sufficiently widely distributed that it is unlikely that a single event would eliminate one or more of them. However, the Cheoah River, Pigeon River, Little River, and Mills River populations are restricted to scattered areas of suitable habitat in much shorter stream reaches making them vulnerable to extirpation from a single catastrophic event, such as a major chemical spill (USFWS 2009).

The genetic viability of the surviving populations remains a concern. All of the remaining populations of this species appear to be effectively isolated from one another by impoundments and several of these populations may be below the level required to maintain long-term genetic viability (USFWS 2009).

Conservation Actions [top]

Conservation Actions: This species has been given a NatureServe Global Heritage Status Rank of G1 - Critically Imperiled (NatureServe 2009), was assigned an American Fisheries Society Status of Endangered (1 Jan 1993), and a previous IUCN Red List Category of Critically Endangered (2000 ver 2.3) (Bogan 2000). This species was assigned a U.S. Fish and Wildlife Service Lead Region of R4 – Southeast. The USFWS listed this species as Endangered in 1994, implemented a recovery plan for the species in 1996, and designated Critical Habitat for the species in 2002. The USFWS Species Recovery Plan Five Year Review (2009) documents that although some of the recovery plan criteria have been met, further improvements need to occur before the species can change from a USFWS listing of Endangered to Threatened.

This species is represented by two separate conservation units corresponding to the French Broad and Little Tennessee River drainages (Bogan et al. 2008).

This species is listed as endangered by both the states of North Carolina and Tennessee. Though this designation prohibits the collection of the species without a valid state collecting permit, it does not provide any protection to the species from other forms of take, or offer any regulatory protection to its habitat (USFWS 2009). The USFWS have pledged to continue working to address threats and improve the status of the species in the streams where it occurs (USFWS 2009). However, the majority of the surviving populations of this species continue to face significant threats associated with development activities, agriculture operations, wastewater discharges, storm water runoff and non-point source pollutants (NatureServe 2009).

Many of the activities that pose a significant threat to the surviving populations of the species and its habitat are not subject to the regulations of section 7 of the Endangered Species Act (i.e., they do not have any federal involvement: no federal permits, authorization, or funding associated with the activity; and therefore no requirement for consultation with the Service if they may adversely affect federally-listed species) (USFWS 2009).

There are plans in place to remove the small hydroelectric Dillsboro Dam on the Tuckasegee River, and detailed monitoring of the habitat conditions will be part of the dam removal plan (USFWS 2009).

Experiments by North Carolina State University in collaboration with North Carolina Wildlife Resources Commission has shown some progress in captive propagation and culture with closely related Alasmidonta varicosa and Alasmidonta viridis (USFWS 2009), and this may play a part in future conservation of this species.

Further monitoring of the existing populations is recommended to determine long term viability and and research into the effects of ongoing threat processes is needed. Effective habitat and site protection is needed to safeguard the species from pollution, siltation and other threats, and policy and law needs to incorporate the habitat needs of the species for effective conservation.

Citation: Cummings, K. & Cordeiro, J. 2012. Alasmidonta raveneliana. The IUCN Red List of Threatened Species 2012: e.T776A3142501. . Downloaded on 18 December 2017.
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