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Arcidens wheeleri

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA BIVALVIA UNIONOIDA UNIONIDAE

Scientific Name: Arcidens wheeleri
Species Authority: (Ortmann & Walker, 1912)
Common Name(s):
English Wheeler's Pearly Mussel, Ouachita Rock Pocketbook
Synonym(s):
Arkansia wheeleri Ortmann & Walker, 1912
Taxonomic Notes: This species was previously known as Arkansia wheeleri, but changed to Arcidens wheeleri in Clarke (1981) and Graf and Cummings (2007).

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: Endangered B1ab(i,ii,iii,iv) ver 3.1
Year Published: 2011
Date Assessed: 2011-07-22
Assessor(s): Cummings, K. & Cordeiro, J.
Reviewer(s): Böhm, M. & Collen, B.
Contributor(s): Dyer, E., Soulsby, A.-M., Whitton, F., McGuinness, S., De Silva, R., Milligan, H.T., Kasthala, G., Herdson, R., Thorley, J., McMillan, K. & Collins, A.
Justification:
Arcidens wheeleri has been assessed as Endangered. This species has an inferred extent of occurrence of between 1,000 and 5,000 km², and exists at five locations with only one remaining viable population. The populations are completely isolated and a low recruitment level has been documented. The number of subpopulations is declining and the ongoing construction of reservoirs, other types of habitat alteration, and low water levels threaten the continued existence of this species.
History:
1996 Critically Endangered (Baillie and Groombridge 1996)
1996 Critically Endangered
1994 Endangered (Groombridge 1994)
1990 Endangered (IUCN 1990)
1988 Endangered (IUCN Conservation Monitoring Centre 1988)
1986 Indeterminate (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description: In the United States, this species occurs in Arkansas, Oklahoma and Texas. NatureServe (2009) have classified it as Critically Imperilled in all of these states. It occurs at five locations and has an estimated extent of occurrence of between 1,000 and 5,000 km².
Countries:
Native:
United States (Arkansas, Oklahoma, Texas)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Only one substantially viable population of this species remains among four or five extant populations that are completely isolated from each other (NatureServe 2009).

This species is currently known to exist in approximately 252 km of the Red River system, Texas/Oklahoma, and 179 km of the Ouachita River system, Arkansas. The only known substantial population—fewer than 1,800 individuals—inhabits a 141 km section of the Kiamichi River, Oklahoma. A smaller, attenuated population—less than 100 individuals—inhabits approximately 111 km of the Little River in Oklahoma and Arkansas, although quality habitat for the species prevails in only a 24 km stretch above the Mountain Fork River. Recent observations of the species in the Ouachita River, Arkansas, are rare and widely separated. The only other recent evidence of the species consists of single shells recovered from Pine and Sanders creeks, Texas, which enter the Red River near the Kiamichi River (USFWS 2004).

The Kiamichi River population is thought to be the only remaining viable population of this species (Vaughn et al. 1996, USFWS 2004). However, extensive declines in the number of sites and abundance in the Kiamichi River have been documented (Galbraith et al. 2008) with most occurrences represented by relict shells or single to few mature adults (NatureServe 2009). Approximately 43 % of historically known populations in the Kiamichi River (below the inflow from Sardis Reservoir) have apparently been extirpated; this is in contrast to above the impoundment where 75 % of historical subpopulations are still extant and five new subpopulations were located in 1994 (Vaughn and Pyron 1995). In 1995, Vaughn and Pyron noted that the youngest mussel they found in their surveys (estimated at 12 years of age) indicated that no recruitment had occurred since the Sardis Reservoir was filled in 1983. Galbraith et al. (2005) found that mean mussel density for the entire river decreased by 65% from 1991 to 2003–2005. In their 2003–2005 surveys, they did not find the species at any of its previously recorded locations, but did find three individuals at a new mussel bed near Moyers, Oklahoma. Galbraith et al. (2005) found live individuals of this species at only a single site in the Little River.

The small, closely situated Red River tributary populations are completely isolated from each other (in terms of larval dispersal between populations), and are regarded here as part of a single area of occurrence, in that they are inhabited by a single metapopulation (USFWS 2004).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: This species inhabits pools, backwaters, and side channels of rivers and large creeks, occupying stable substrates containing gravel, sand, and other materials (USFWS 2004). However, juveniles can be found in shallow waters both on sand bars and muddy bottoms, preferring the oozy mud of the river margins where there is little or no current (Clarke 1981). This species always occurs within large mussel beds containing a diversity of mussel species (USFWS 2004).

The fish host of this species is not known (Clarke 1981, USFWS 2004).
Systems: Freshwater

Threats [top]

Major Threat(s): Impoundment, channelization, and water quality degradation have been identified as principal factors causing the decline of this species (USFWS 2004).  Continued growth and activity of human populations portend that these major factors will continue and expand in influence. Within portions of this species' range, recent proposals to withdraw and transport large quantities of water for human consumption have raised an additional threat (USFWS 2004).

Galbraith et al. (2005) identified that the Kiamichi River has been impacted by logging and construction in the riparian region along with off-road vehicles driving through the river and damaging the mussel bed. They also identified siltation from gravel mining, habitat degradation for tourism purposes, and low water levels as substantial threats to this species.

The Kiamichi River appears to be especially susceptible to low water conditions, particularly during drought years. Galbraith et al. (2005) found several sites devastated during the 2005 drought with mussel beds completely exposed and thousands of mussels found to be dead. These conditions do not appear to be improving as water levels in the Kiamichi River are still very low (USFWS 2004).

The threats posed to the Little River populations include low water conditions and the associated algal blooms, and human disturbance from fishing and swimming. Additionally, several locals apparently witnessed mussel harvesters removing huge numbers of mussels from the Little River between 2003-2004 (Galbraith et al. 2005).

It can be assumed that the threats faced by the Red River and Ouachita River populations are similar to those described above.

Conservation Actions [top]

Conservation Actions: This species has been given a NatureServe Global Heritage Status Rank of G1 - critically imperiled (NatureServe 2009), an American Fisheries Society Status of Endangered (1 Jan 1993), (Williams et al. in press) and a previous IUCN Red List Category of Critically Endangered (1996 ver 2.3). This species was assigned a U.S. Fish and Wildlife Service Lead Region of R2 – Southwest, and is Listed Endangered under the U.S. Endangered Species Act.

The Oklahoma Department of Wildlife Conservation amended its regulations to designate the Kiamichi River a mussel sanctuary (effective 1 January 1993). As such, the river is closed to all commercial mussel harvest. In 1992-1993, the Texas Parks and Wildlife Department designated both Pine and Sanders creeks as mussel sanctuaries, in which no harvest is permitted. In 1997 and 2000, the Arkansas Game and Fish Commission designated the Ouachita River upstream from U.S. Highway 79B at Camden as a mussel sanctuary, in which no harvest is permitted (USFWS 2004).

The United States Fish and Wildlife Service (USFWS) has a Recovery Plan in place for this species. The USFWS Refuges in which this species is known to occur are Little River National Wildlife Refuge and Pond Creek National Wildlife Refuge (USFWS 2004).

It is recommended that measures be taken to protect the health of the mussel beds in both the Kiamichi and the Little Rivers. This includes taking measures to protect riparian habitat around and upstream of mussel beds, along with regulating human activity that could be detrimental to the health of the beds. It is also suggested that measures be taken to maintain water levels over mussel beds during periods of low flow and high temperature. Finally, it is recommended that there is regular monitoring of the known populations of this species.

Citation: Cummings, K. & Cordeiro, J. 2011. Arcidens wheeleri. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 02 October 2014.
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