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Lemiox rimosus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA BIVALVIA UNIONOIDA UNIONIDAE

Scientific Name: Lemiox rimosus
Species Authority: (Rafinesque, 1831)
Common Name(s):
English Birdwing Pearlymussel
Synonym(s):
Conradilla caelata (Conrad, 1834)
Taxonomic Notes: 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 B1ab(i,ii,iii,iv) 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): 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:
Lemiox rimosus has been assessed as Critically Endangered as this species has an estimated extent of occurrence of less than 100 km2, with severely fragmented populations as a result of a range reduction to only around 10% of its former range. Continuing threats of alteration and destruction of stream habitat due to impoundment of the Tennessee River and its tributaries for flood control, navigation, hydroelectric power production, and recreation are threatening the remaining subpopulations, although these at present appear stable. Further research is required regarding the taxonomy, population trends, ecology and threats impacting this species to increase knowledge of population status. Conservation measures including site and species protection through policies and legislation would be suggested to allow this species the greatest chance of long-term survival.
History:
1996 Critically Endangered
1994 Endangered (Groombridge 1994)

Geographic Range [top]

Range Description: This species historically had a wide distribution including the Tennessee River and major tributary streams (USFWS 1983). Historical records are known from throughout the Tennessee River drainage, but it is believed to be absent from Cumberland River (Terwilliger 1991, Wilson and Clark 1914) despite an early report there by Rafinesque (USFWS 1983). It is currently known from the Clinch, Powell, Elk (possibly now extirpated), and Duck Rivers in Tennessee and Virginia (USFWS 1983). A disjunct population in the Duck River may be the only viable population; it is likely to be extirpated from Alabama (Mirarchi et al. 2004, Williams et al. 2008).
Countries:
Native:
United States (Alabama - Possibly Extinct, Tennessee, Virginia)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: There are over 125 historical occurrences for this species, but although it was once widespread, especially in Tennesse river (USFWS 1983), it was never common at any location. In Alabama, it is now extirpated but historically occurred in the Tennessee River drainage downstream to Muscle Shoals (Mirarchi 2004).

A 1980 survey in Virginia reported nine occurrences. Similarly, a survey in 1980 in the lower Elk River (120 mile survey) from the Alabama border through Tennessee revealed a single, recently dead shell (tissue attached) in a muskrat midden in Lincoln Co., Tennessee (Ahlstedt 1983),  live specimens were found in the Clinch River (170 mile survey) in 1979, one fresh dead specimen in 1978, nine fresh dead from muskrat middens in 1981, and two live specimens in 1982; and eight live specimens from the Powell River (102 mile survey) in 1979, 18 live specimens in 1981 (USFWS 1983). The last collection of this species in the North Fork Holston River, Virginia, is from the early 1900s, so it is likely to be extirpated there (Jones and Neves 2007).

Populations in the North Fork Holston River, Nolichucky River, Tennessee River, Elk River, and Sequatchie River in Tennessee are probably now extirpated (Parmalee and Bogan 1998), as are all occurrences in Alabama (USFWS 1983).

It currently occupies 10% of its historic range, occurring in only ~170 river km in the Clinch River, ~84 river km in the Powell River in Tennessee and Virginia, and ~60 river km in the Duck River in Tennessee - all of these populations are disjunct and severely fragmented with continuing decline (Jones et al. 2010). However these populations seem to be stable and should remain so as long as their habitat, water quality and ecological conditions are maintained in these rivers (Jones et al. 2010). While therefore still present in three locations, population and range declines have left the remaining subpopulations severely fragmented.

Lillard Mill, Duck River was surveyed in August of 1997 and 59 males, 23 females, and 11 juveniles were found (Watson 1998). This followed a 1,000 individual transplant experiment from this same site to the following sites: Cuck River in Bedford Co.; Buffalo River in Wayne Co.; Nolichucky River in Greene Co.; and North Fork River in Hawkings Co. in 1982 (USFWS 1983) which proved largely unsuccessful.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: This species is almost always found in riffle areas with stable sand and gravel substrates in moderate to fast currents in small to medium sized rivers (Bogan and Parmalee 1983, USFWS 1983). It generally occurs in gravel substrates, usually with some interstitial sand. It is a long-term brooder, with mature glochidia by mid-September, which it broods until the following spring or summer (Ortmann 1916). In laboratory trials, poor infestation rates were obtained using glochidia removed from conglutinates during May and early June. Infestation rates improved during late June and July, after conglutinates disintegrated, suggesting that conglutinates do not serve as a host-attracting mechanism and that glochidia may not be completely mature until summer (TVA 1986). Females have been observed to display a modified mantle margin, presumably as a glochidial host attractant. During the display the female is positioned with its ventral margin oriented upward, slightly elevated above the surrounding substrate. The mantle is protruded beyond the shell margin on the posterior half of the animal. Just posterior of the midpoint, the mantle tissue from the two sides comes together to give the appearance of a small, grayish brown, bulbous knob. Movement is slight, and it is unclear as to whether this is due to muscular movement by the animal or water current (D.W. Hubbs pers. comm. 2010).

Fishes reported to serve as glochidial hosts in laboratory trials include Etheostoma simoterum (Snubnose Darter) and Etheostoma zonale (Banded Darter, Percidae; TVA 1986, Watson and Neves 1998). A possible third host is Etheostoma blennioides (Greenside Darter, Percidae), but results from laboratory trials were not conclusive (TVA 1986, Williams et al. 2008).
Systems: Freshwater

Use and Trade [top]

Use and Trade: This species is not utilized.

Threats [top]

Major Threat(s): The greatest factor contributing to this species' decline is alteration and destruction of stream habitat due to impoundment of the Tennessee River and its tributaries for flood control, navigation, hydroelectric power production, and recreation. Siltation due to strip mining, coal washing, dredging, farming, logging, and road construction is a second factor that has negatively impacted this species. Pollution caused by municipal, agricultural, and industrial waste discharges has also severely impacted this species. Recently, the introduced Asian Clam (southwestern Virginia) has been found in areas (Clinch River) where this species is found. The severity of impacts has not been measured (USFWS 1983).

This species has a very narrow range with declining populations, questionable viability, and limited dispersal capability and is vulnerable to random events. It is a strict riffle dwelling species and is therefore sensitive to changes in water quality and disturbance.

Conservation Actions [top]

Conservation Actions: This species requires protection and expansion of the existing populations and re-establishing populations into habitat that was historically occupied.

This species was listed as federally endangered in the U.S. in 1976 and a recovery plan created (USFWS 1983). Objectives of the recovery plan include: (1) preserve populations and presently used habitat with emphasis on the Clinch and Powell Rivers, (2) determine feasibility of introducing the species back into rivers within its historic range and introduce where feasible, (3) conduct life history studies , (4) determine the number of individuals required to maintain a viable population, (5) investigate the necessity for habitat improvement and if feasible and desirable identify techniques and sites for improvement to include implementation, (6) develop and implement a program to monitor population levels and habitat conditions of presently established populations as well as introduced and expanding populations, (7) assess overall success of recovery program and recommend action (delist, continued protection, implement new measures, other studies, etc.).

The USFWS, in cooperation with the State of Tennessee and Conservation Fisheries, Inc., proposes to reintroduce this species into its historical habitat in the free-flowing reach of the French Broad River below Douglas Dam to its confluence with the Holston River, Knox County Tennessee, and in the free-flowing reach of the Holston River below Cherokee Dam to its confluence with the French Broad River (USFWS 2006). The Pendleton Island occurrence is owned by The Nature Conservancy. Nonessessential Experimental Populations (NEPs) have been established in the Tennessee River below Wilson Dam, Colbert and Lauderdale Cos., Alabama, extending 13.4 km and including the lower 8 km of all tributaries that enter the Wilson Dam tailwaters (USFWS 2001). Nonessessential Experimental Populations (NEPs) have been proposed for reintroduction into the free-flowing reach of the French Broad River below Douglas Dam (Knox and Sevier Cos., Tennessee) to its confluence with the Holston River, Knox Co., Tennessee, and in the free-flowing reach of the Holston River below Cherokee Dam to its confluence with the French Broad River (Knox, Grainger, and Jefferson Cos., Tennessee), where this species currently does not exist (USFWS 2006).

This species has been assigned a NatureServe Global Heritage Status Rank of G1 - Critically Imperilled, and State/Province Status Ranks of S1 - Critically Imperilled for Tennessee and Virginia, and SX - Presumed Extinct for Alabama (NatureServe 2009). Williams et al. (2010) list this species as endangered according to the American Fisheries Society (AFS) assessment. Further research is required regarding the taxonomy, population trends, ecology and threats impacting this species to increase knowledge of population status. Conservation measures including site and species protection through policies and legislation would be suggested to allow this species the greatest chance of long-term survival. Similarly, species management via ex situ conservation and reintroductions is recommended. Additional research is recommended for this species, specifically on its population status, ecology and the effectiveness of conservation actions. This, together with monitoring of the population, is needed to ensure that effective conservation is helping to secure the population of this species for the future.

Citation: Cummings, K. & Cordeiro, J. 2012. Lemiox rimosus. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 01 October 2014.
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