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Pleurobema hanleyianum

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA BIVALVIA UNIONOIDA UNIONIDAE

Scientific Name: Pleurobema hanleyianum
Species Authority: (Lea, 1852)
Common Name(s):
English Georgia Pigtoe
Synonym(s):
Pleurobema hanleyanum (I. Lea, 1852)
Taxonomic Notes: Spelling of the name follows the original publication (Turgeon et al. 1998). It is difficult to differentiate this species from Pleurobema georgianum and Pleurobema trochelianum in the field due to similar shell characteristics (Parmalee and Bogan 1998), but some morphological features of each are outlined in USFWS (2003). Recent genetic studies were unable to distinguish the painted clubshell from the southern clubshell (listed as endangered), or populations of Georgia pigtoe and Alabama clubshell from southern pigtoe (listed as endangered) (P. Johnson pers. comm. 2002). Although there are some morphological differences that suggest separation, additional studies are required.

Williams et al. (2008) treat this as a valid species.

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: 2012-03-30
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:
Pleurobema hanleyianum has been assessed as Critically Endangered under criteria A2ac, as this species has experienced declines of well over 90% of its historical range. This is estimated to translate into at least 80% reduction in range and population size since the 1950s (or three average generation lengths), to the point where it was officially declared extinct by the IUCN in 1994. However, recent rediscovery means that the Georgia pigtoe is currently only known from a few isolated shoals in the Conasauga River. This species has been extirpated from Alabama (Mirarchi et al. 2004, Mirarchi 2004) where it was endemic to the Mobile basin.
History:
2000 Extinct
1996 Critically Endangered

Geographic Range [top]

Range Description: This species was historically found in the Conasauga River in Tennessee and Georgia, the Coosawatee, Oostanaula, Coosa, and Etowah Rivers in Georgia, and the Coosa River and following tributaries in Alabama: Big Wills, Terrapin, Big Canoe, Yellowleaf, Waxahatchee, Talledega, and Hatchet creeks (USFWS 1999, 2003). In the Coosa River basin in Georgia, it is known historically from the Coosa, Etowah, Oostanaula, Conasauga, and Coosawattee River drainages (Williams and Hughes 1998).

Until recently, the species was presumed extinct, before fresh dead shells were collected in the upper Conasauga River above Dalton, Georgia (USFWS 1999, 2003) and a single large specimen was found alive in the Conasauga River in Georgia (P. Johnson pers. comm. 2005). Williams and Hughes (1998) cite potential records for Pleurobema perovatum in the Conasauga River drainage in Georgia, but it has also been suggested that these Georgia records for Pleurobema perovatum actually represent another Pleurobema species, most likely Pleurobema hanleyianum (J. Cordeiro pers. comm. 2012). As a result, the Georgia Pigtoe is currently only known from a few isolated shoals in the Upper Conasauga River in Murray and Whitfield Counties, Georgia, and in Polk County, Tennessee (Johnson and Evans 2000, Evans 2001, USFWS 2010). Based on this, it is presumed to occur at more than one location, although all current collection sites occur within just over 40 km of river (USFWS 2010). This species has been extirpated from Alabama (Mirarchi et al. 2004, Mirarchi 2004) where it was endemic to the Mobile basin, and is nearly extinct in Tennessee (Johnson et al. 2005). The estimated extent of occurrence for this species is well below 100 km2, with a significantly smaller area of occupancy.
Countries:
Native:
United States (Alabama - Regionally Extinct, Georgia, Tennessee - Regionally Extinct)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Recent collections yielded a few shells from localized portions of one river and a single live individual only. There exist recent collections of a few live and fresh dead shells of this species from localized portions of the upper Conasauga River in Murray and Whitfield counties, Georgia (USFWS 2003). This species has been recently reported as a relict shell from the Conasauga River inside and adjacent to the Cherokee and Chattahoochee National Forests, Polk Co., Tennessee (Johnson et al. 2005). Williams and Hughes (1998) cite potential records for Pleurobema perovatum in the Conasauga River drainage in Georgia, but both P. Johnson and P. Hartfiled believe that Georgia records for Pleurobema perovatum actually represent another Pleurobema (probably Pleurobema hanleyianum), but a consensus has not yet been reached (J. Wisniewski pers. comm. 2007). A specimen from Chewacla Creek (Macon Co., Alabama) in the Tallapoosa River drainage (USFWS 2000, 2004) was initially identified as Pleurobema perovatum, but the specimen has subsequently been identified genetically as Pleurobema hanleyianum (D. Campbell pers. com. 2004).

 In 1990, the U.S. Fish and Wildlife Service initiated a status survey and review of the molluscan fauna of the Mobile River Basin reported 14 species of mussels in the genus Pleurobema, including the Painted Clubshell, Georgia Pigtoe, and Alabama Clubshell, as presumed extinct in the Mobile River Basin, based on their absence from collection records, technical reports, or museum collections for a period of 20 years or more (USFWS 1994). The species was considered extinct by the IUCN (Baillie and Groombridge 1996) in 1994. Recent occurrences are only represented at 1 or 2 localities and only by a handfull of live individuals, dead, or recently dead shell material (USFWS 2003). This species is thought to have been extirpated from well over 90% of its historic range (USFWS 1999, 2003) and is now only known from a few recently dead shells (USFWS 2003) and a single live individual indicating populations are likely no longer viable or extremely small. These declines are likely to have occurred over the past 80 to 100 years (J. Cordeiro pers. comm. 2012). Taking a generation length of at least 13 years (probably more like 20 years) into account, and assuming constant decline, we estimate that there has been a decline in over 80% of this species range since the 1950s-1970s. Since the species is very rare where it occurs, this is likely to translate into a similar percentage decline of the population size.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: This species inhabits stretches of a medium sized river with good current and a sand/gravel substrate A substrate composed of coarse sand and gravel in stretches of rivers with good current provides the most suitable habitat (Parmalee and Bogan 1998).

Pleurobema hanleyianum inhabits shoals of large creeks and small to large rivers. Pleurobema hanleyianum is believed to be a short-term brooder, gravid in spring and summer. Its glochidial hosts are unknown, but some Pleurobema species use members of the Cyprinidae (Haag and Warren 2003, Williams et al. 2008).

Direct life-history data are not available for this species. Freshwater mussels are highly variable in their longevity from species to species (e.g. Haag and Rypel 2011). Studies have shown longevity of Pleurobema species to range from 19 to 45 years (from populations of P. coccineumP. collina and P. decisum: average of 31 years; Haag and Rypel 2011). In a study of fecundity and maturity in a number of freshwater mussels, age at maturity range from less than one year in Lampsilis ornata to up to nine years in Quadrula asperata; unfortunately there was no estimate for representatives of the genus Pleurobema (Haag and Staton 2003). Conservatively assuming a first age of maturity of 2-5 years, generation length (estimated as the average age of a parent in the population) is estimated as around 11-27 years, with three generations spanning approximately 33-81 years.
Systems: Freshwater

Use and Trade [top]

Use and Trade: This species is not utilized.

Threats [top]

Major Threat(s): Habitat loss (dams, channelization, disappearance of suitable shoal habitat, pollution) is the primary cause of this species' decline. There has been extensive impoundment of the Coosa River and its primary tributaries, and the effects of point and non-point source pollution on the surviving isolated populations.

Isolated populations are vulnerable to land surface runoff that affects water quality or the suitability of aquatic habitats within a watershed. Blocked from avenues of emigration to less affected watersheds, they gradually perish if changes in land use activities cause aquatic habitat conditions to deteriorate. While the detrimental effect of any one source or land use activity may be insignificant by itself, the combined effects of land use runoff within a watershed may result in gradual and cumulative adverse impacts to isolated populations and their habitats. Excessive nutrient input from multiple sources (e.g, nitrogen and phosphorus from fertilizer, sewage waste, animal manure, etc.) into an aquatic system can also have negative cumulative effects (USFWS 2003).

Threats are compounded by their restricted range and low numbers. This species is vulnerable to random catastrophic events (e.g., flood scour, drought, toxic spills, etc.). Limited range and low numbers also make the species vulnerable to land use changes within the Conasauga River watershed that would result in increases in non-point source pollution impacts (USFWS 2003).

Conservation Actions [top]

Conservation Actions: This species has been assigned a NatureServe Global Heritage Status Rank of G1 - Critically Imperiled (NatureServe 2009). This species is a U.S. Fish and Wildlife Service candidate species for federal endangered status.

All riparian lands are in corporate or private ownership. This species has been recently reported from the Conasauga River inside and adjacent to the Cherokee and Chattahoochee National Forests, Polk Co., Tennessee (Johnson et al. 2005). The U.S. Fish and Wildlife Service is working to establish a National Wildlife Refuge in the upper Conasauga River. Watershed management outreach has been conducted. The Nature Conservancy has conducted a watershed impact analysis for the Conasauga River watershed. Surveys are ongoing, and genetic studies will be continuing to clarify and confirm taxonomy of this species.

Citation: Cummings, K. & Cordeiro, J. 2012. Pleurobema hanleyianum. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 02 September 2014.
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