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Pleurobema pyriforme

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA BIVALVIA UNIONOIDA UNIONIDAE

Scientific Name: Pleurobema pyriforme
Species Authority: (Lea, 1857)
Common Name(s):
English Oval Pigtoe
Synonym(s):
Pleurobema reclusum (Wright, 1898)
Taxonomic Notes: Williams and Butler (Deyrup and Franz 1994) listed Pleurobema reclusum as a species distinct from Pleurobema pyriforme, but based on recent genetic data (Kandl et al. 1997) and morphological evidence (Clench and Turner 1956) they are viewed as one species (Brim Box and Williams 2000).

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 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): 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 pyriforme has been assessed as Endangered under criteria A2ac. The species has been expirated from 73% of its historic range, and while there are no direct data on the timeframe over which this decline has occurred, it is likely that the majority of this has occurred within the period of three estimated generation lengths of this species (generation length estimated as average age of parent in the population). A decline in range of over 70% is likely to correspond to more than 50% reduction in number. However, further research and record verification is needed to validate the assumptions made on generation length and timeframe of the decline. At present, we use a precautionary approach to list this species as Endangered.
History:
2000 Endangered
1994 Indeterminate (Groombridge 1994)

Geographic Range [top]

Range Description: Historically, this species occurred in the Ecofina, Apalachicola-Chattahoochee-Flint, Ochlockonee, and Suwanee systems in 57 localities (96 records) in Alabama, Georgia, and Florida (Brim Box and Williams 2000). It still exists in all four systems but subpopulations have been lost in the Apalachicola-Chattahoochee-Flint (Chattahoochee River main stem, Randall, Uchee, and Little Uchee Creek; most of Flint River main stem, Patsiliga, Little Patsiliga, Sandy Mount, Gum, Cedar, Chokee, Abrams, Mill, Little Pachitla, and Dry Creeks; Apalachicola River main stem; Spring, Rocky, Marshall, Big, and Cowarts Creeks), and it is nearly extirpated from Alabama (USFWS 2003). In Alabama, it is confined to headwaters of Chipola River and lower Chattahoochee River system with one known extant population in Big Creek, a headwater tributary of Chipola River, Houston Co. (Mirarchi et al. 2004).

The Oval Pigtoe is a wide-ranging species (1,412 km in 11 watersheds) that has lost 73% of its historic extent of occurrence, but still persists in 386 km of several watersheds with an area of occupancy of less than 500 km2. One entire basin of the Oval Pigtoe's distribution, the Suwannee River, is disjunct from the rest, and may represent genetic differences at the species level (USFWS 2003).
Countries:
Native:
United States (Alabama, Florida, Georgia)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: According to the U.S. Fish and Wildlife Service (1998), a status survey and subsequent findings located it at 28 sites: 10 in the Flint River system; 7 in the Chipola River system; 7 in the Ochlockonee River system; 2 in tributaries of the Chattahoochee River; and 3 in the Suwannee River system. Currently, it is known from Econfina Creek in Alabama (Mirarchi et al. 2004), several streams in the ACF basin, including Sawhatchee Creek (only Chattahoochee River system locality); uppermost main stem of Flint River and tributaries Line, Muckalee, Kinchafoonee, Cooleewahee, Chickasawhatchee, and possibly Spring Creeks; upper Chipola River main stem, and Baker and Dry Creeks; upper Ochlockonee River main stem and Barnetts Creek; and New and Santa Fe Rivers in Suwannee River system (USFWS 2003). Presently, it persists in 36 subpopulations overall (USFWS 2003). There is one known extant population in Big Creek, a headwater tributary of Chipola River, Houston Co. (Mirarchi et al. 2004). In 1999 and 2001, this species was found in 5 sites (42 specimens) and 6 sites (87 specimens), respectively, in surveys of 5 sites (each year) in about a dozen tributary streams of the lower Flint River Basin, in southwestern Georgia (Golladay et al. 2002). In the ACF basin, it was recently collected from 17 of 324 sites in Alabama, Florida, and Georgia although no specimens were found in the Chattahoochee River mainstem nor in all tributaries except one in southwestern Georgia (Brim-Box and Williams 2000). In 1999, this species was found to comprise 0.34% (relative abundance) of the 14873 mussels collected in surveys of 46 sites in 12 tributary streams of the lower Flint River Basin, Georgia (Gagnon et al. 2006).

In terms of population numbers at known sites, in 1988, a 0.75 hour search of Dry Creek yielded 17 specimens, and in 1987 a one-hour search on the New River yielded 35 specimens (NatureServe 2009). This species has been historically common at several other sites in the Santa Fe system and at least one Ochlockonee site in Florida, but is now much less common at most sites. Some large series are known from the Alabama portion of the Chipola, but they were collected about 75 years ago. Most known populations are relatively small, but the species appears to be not uncommon in the lower Chipola above Dead Lake. Clench and Turner (1956) considered it to be "relatively rare and perhaps only locally abundant". In 1999, this species was found to comprise 0.34% (relative abundance) of the 14,873 mussels collected in surveys of 46 sites in 12 tributary streams of the lower Flint River Basin, Georgia (Gagnon et al. 2006).  

Discovery of new subpopulations and some range expansion have been documented, but this has only led to small increases in river miles occupied by this species (USFWS 2007).

TRENDS:
Past surveys have documented its extirpation from approximately two-thirds of its historical range (USFWS 1994). The large series reported by Van der Schalie (1940) from the upper Chipola in Alabama are probably unduplicable today. Nearly the entire genus is on the decline, particularly the narrow or regional endemics of the Gulf Coast drainages east of the Mississippi.

The Oval Pigtoe was a wide-ranging species (1,412 km2 in 11 watersheds) that has lost 73% of its historic extent of occurrence, but still persists in 386 km2 of several watersheds. While there are no direct data on the timeframe over which the decline occurred, it is likely that the majority of this has occurred since the early 1970s, as has been seen in other species of freshwater mussel (e.g. Elliptio roakanoensis). One entire basin of the Oval Pigtoe's distribution, the Suwannee River, is disjunct from the rest, and may represent genetic differences at the species level (USFWS 2003).

Latest data suggest that the species is still declining in abundance (USFWS 2007). It is now estimated to have disappeared from over half of its historical range (USFWS 2007).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: This species "occurs in medium-sized creeks to small rivers where it inhabits silty sand to sand and gravel substrates, usually in slow to moderate current. Stream channels with clean substrates possibly offer the best habitat" (Williams and Butler 1994, USFWS 2003). In the ACF basin, it was recently collected at sites with a wide range of substrate types, including sand and detritus (36%), sand and clay or silt (25%), and sand and cobble (24%) and was more common in mid-channel areas with current than along slack-water areas near stream banks (Brim Box and Williams 2000).

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 ranged from less than one year in Lampsilis ornata to up to nine year 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): This species is highly restricted in distribution, occurs in generally small subpopulations, and shows little evidence of recovering from historical habitat losses without significant positive human intervention. Principle causes of decline include impoundments, channelization, pollution, and sedimentation that have altered or eliminated those habitats that are essential to the long-term viability of many riverine mussel populations. Detailed information on these threats can be found in USFWS (2003). Many of the impacts discussed in USFWS (2003) occurred in the past as unintended consequences of human development in the Apalachicolan Region. However, the species and its habitats continue to be impacted by excessive sediment bed loads of smaller sediment particles, changes in turbidity, increased suspended solids (primarily resulting from nonpoint-source loading from poor land-use practices, lack of BMPs, and maintenance of existing BMPs), and pesticides. Other primarily localized impacts include gravel mining, reduced water quality below dams, developmental activities, water withdrawal, impoundments, and alien species. Toxic spills are also a possibility in all extant populations (USFWS 2003). Siltation from poorly conducted agricultural and silvicultural activities; chicken farm litter nutrients; localized industrial, municipal, and residential pollution; watershed development (bridge, highway construction projects, etc.), urban sprawl in upper Flint and Chattahoochee may impact potential populations; competition from Asian Clam is a possibility. Chicken farms and silvicultural activities are on the increase in southeastern Alabama, thus threatening stream habitat there. It is not tolerant of impoundments.

Conservation Actions [top]

Conservation Actions: This species was added to the U.S. federal endangered species list in 1998 (USFWS 1998). A recovery plan was created for this species (USFWS 2003).

The recovery plan (USFWS 2003) outlines the following objectives for recovery: (1) preserve extant subpopulations and currently occupied habitats and ensure subpopulation viability; (2) search for additional subpopulations of the species and suitable habitat; (3) determine through research and propagation technology the feasibility of augmenting extant subpopulations and reintroducing the species into historical habitat; (4) evaluate efforts and monitor subpopulation levels and habitat conditions of existing subpopulations, as well as newly discovered, introduced, or expanding subpopulations; (5) develop and implement cryogenic techniques to preserve genetic material until such time as conditions are suitable for reintroduction; (6) develop and utilize a public outreach and environmental education program; (7) assess the overall success of the recovery program and recommend actions (e.g., changes in recovery objectives, delist, implement new measures, conduct additional studies).

Critical habitat has been designated for 31.4 km of the Econfina Creek in Florida; 190.0 km of the Chipola River, Alabama and Florida; 34.2 km of Uchee Creek, Alabama; 37.8 km of Sawhatchee Creek and Kirkland Creek, Georgia; 380.4 km of the Upper Flint River, Georgia; 302.3 km of the Middle Flint River, Georgia; 396.7 km of the Lower Flint River, Georgia; 177.3 km of the Upper Ochlockonee River, Florida and Georgia; and 83.1 km of the Santa Fe and New Rivers in Florida (USFWS 2006).

The only potentially "protected" occurrences might occur in state parks.

This species has been assigned a NatureServe Global Heritage Status Rank of  G2 - Imperiled, and a State/Province Status Rank of S2 - Imperiled for Georgia, S1S2 - Critically Imperiled to Imperiled for Florida, and S1 - Critically Imperiled for Alabama (NatureServe 2009). Williams et al. (2010) lists this species as endangered according to the AFS assessment.

Continued research is needed into the species' distribution, habitat and threats as part of a targeted monitoring scheme. Species recovery, protection (also for habitat) and legislation are needed.

Citation: Cummings, K. & Cordeiro, J. 2012. Pleurobema pyriforme. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 28 July 2014.
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