Overview

Distribution

endemic to a single state or province

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (<100 square km (less than about 40 square miles)) Pleurobema athearni is known only from the Big Canoe Creek watershed, a western tributary of the Coosa River, northeast Alabama (Gangloff et al., 2006; Williams et al., 2008).

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Range Description

This species is known only from the Big Canoe Creek watershed, a western tributary of the Coosa River, northeast Alabama (Gangloff et al. 2006). Its extent of occurrence lies somewhere between 100 to 600 km2, the latter roughly being the size of the watershed.
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Physical Description

Size

Length: 9.3 cm

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Diagnostic Description

From Gangloff et al. (2006):
Pleurobema athearni is typically more compressed and round in outline than Pleurobema georgianum. It is less elongate and more compressed than Pleurobema decisum and Pleurobema hanleyianum. Larger specimens of P. athearni may exhibit slight corrugations approximately parallel to the posterior ridge along the posterior-dorsal shell slope that are not found in P. georgianum and Fusconaia cerina. Additionally, the umbo cavity in P. athearni is typically intermediate in depth between that of P. georgianum (shallower) and F. cerina (deeper). Pleurobema athearni conglutinates are elongate and red to dark pink and similar in appearance to those of F. cerina. Pleurobema georgianum conglutinates are lighter and appear less elongate. Further, P. georgianum conglutinates appear to consist of a clear central core with glochidia encrusted on the outer surface, whereas those of P. athearni appear to be darker at their core with a lighter outer covering suggesting glochidia retained within the conglutinate. Historically it was misidentified as Fusconaia cerina, but it is the only Pleurobema with a deep umbo cavity (Williams et al., 2008).

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Type Information

Holotype for Pleurobema athearni Gangloff et al., 2006
Catalog Number: USNM 1078388
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Alcohol (Ethanol)
Collector(s): M. Gangloff et al.
Year Collected: 2001
Locality: Big Canoe Creek, 1 KM downstream of St. Clair County Road 36, near mouth of Mukleroy Creek, St. Clair County, Alabama, United States
  • Holotype: Gangloff, M., et al. 2006. A new species of freshwater mussel (Bivalvia: Unionidae), Pleurobema athearni, from the Coosa River Drainage of Alabama, USA. Zootaxa. 1118: 43-56.
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Ecology

Habitat

Habitat Type: Freshwater

Comments: Pleurobema athearni is known only from the Big Canoe Creek watershed, a western tributary of the Coosa River, northeast Alabama (Gangloff et al., 2006). It occurs in shoal habitat in a medium to large Coosa River tributary and its preferred substrate is gravel (Williams et al., 2008).

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Habitat and Ecology

Habitat and Ecology
This species is known only from the Big Canoe Creek watershed, a western tributary of the Coosa River, northeast Alabama (Gangloff et al. 2006). The species occurs in shoal habitat in a medium to large Coosa River tributary. Its preferred substrate is gravel. It is believed to be a short-term brooder, gravid in spring and summer. Its glochidial hosts are unknown, but some Pleurobema species utilise members of the Cyprinidae (Haag and Warren 2003, Williams et al. 2008).

Systems
  • Freshwater
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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 20

Comments: Pleurobema athearni appears to be restricted to one small (<500 km2) watershed in a single creek in northeast Alabama in St. Clair Co. (Williams et al., 2008). Only 19 specimens are known (fewer than a half dozen sites) but only one-third of these were recent collections. Four specimens were found alive between 2000-2004. One gravid individual was found on 26 May 2004, indicating that P. athearni remains reproductively viable (Gangloff et al., 2006).

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Global Abundance

Unknown

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Life History and Behavior

Reproduction

Inner gills approximately 1.5 times larger in surface area than outer gills. No mature or developing glochidia observable in individuals collected in September and October, conglutinates present in late May, suggesting species tachytictic (i.e., short-term brooder). Conglutinates elongate, length 10-15 mm, width ~12 mm, red or dark pink (Gangloff et al., 2006). The glochidial host is not known.

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N1 - Critically Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G1 - Critically Imperiled

Reasons: This recently described species has an extremely limited distribution and range with few recently collected specimens; and habitat degradation is a continuing threat. Although declining, the extent of the decline is not known because the species is known from fewer than two dozen specimens, only one-third of which are recent.

Intrinsic Vulnerability: Unknown

Comments: newly described

Environmental Specificity: Unknown

Comments: newly described

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IUCN Red List Assessment


Red List Category
DD
Data Deficient

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
Cummings, K. & Cordeiro, J.

Reviewer/s
Bohm, M., Collen, B. & Seddon, M.

Contributor/s
Richman, N., 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.

Justification
Pleurobema athearni has been assessed as Data Deficient as it has only recently been described. As a result, we currently have insufficient information on the species to inform an accurate conservation assessment. Current information would suggest it is critically endangered as it is only known to occur in one location, with an area of occupancy of less than 10 km2. Habitat loss is occuring in the area where it is found, which has experienced extreme habitat degradation (evidence from other species). Population trends are unknown for this species, although it has been suggested that the species is in decline; however, the species is known from fewer than two dozen specimens and only one-third of these are recent. Further survey work is needed to ascertain population trends.
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Global Short Term Trend: Decline of 10-30%

Comments: Newly described but only known from 19 specimens, and only one-third of these are recent collections (Gangloff et al., 2006).

Global Long Term Trend: Unknown

Comments: newly described

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Population

Population
This species appears to be restricted to one small population, which remains reproductively viable (Gangloff et al. 2006). This is a newly described species which is only known from 19 specimens, and only one-third of these are recent collections (Gangloff et al. 2006). Overall population trends are therefore unknown for this species, but have been suggested to be in decline. However, there is insufficient data available to verify this.

Population Trend
Unknown
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Threats

Degree of Threat: Very high - high

Comments: From Gangloff et al. (2006), below, it appears habitat loss/modification is the greatest threat:
The Coosa River ecosystem has been reduced to a number of highly fragmented tributary refugia. Only five tributary sub-basins were found to have mollusk speciesrichness levels that approach historic reports (Gangloff 2003). These watersheds, along with tributaries of the Black Warrior, Tombigbee, Cahaba and Conasauga drainages, represent most of what remains of a unique and species-rich aquatic ecosystem (Williams et al. 1992; Lydeard and Mayden 1995; McGregor et al. 2000). Protection of these few remaining fragments is critical to preserving populations of mussels and other aquatic species in the Mobile Basin (USFWS 1989; 2000).

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Major Threats
From Gangloff et al. (2006), it appears that habitat loss/modification is the greatest threat: The Coosa River ecosystem has been reduced to a number of highly fragmented tributary refugia. Only five tributary sub-basins were found to have mollusc species richness levels that approach historic reports (Gangloff 2003). These watersheds, along with tributaries of the Black Warrior, Tombigbee, Cahaba and Conasauga drainages, represent most of what remains of a unique and species-rich aquatic ecosystem (Williams et al. 1992, Lydeard and Mayden 1995, McGregor et al. 2000). Protection of these few remaining fragments is critical to preserving populations of mussels and other aquatic species in the Mobile Basin (USFWS 1989, 2000). It is uncertain what the impact of these threats is on this species.
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Management

Biological Research Needs: Life history virtually unknown; recently described.

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Global Protection: None. No occurrences appropriately protected and managed

Needs: Because of its rarity, this species may qualify for endangered status under the Endangered Species Act.

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Conservation Actions

Conservation Actions
Considering its restricted distribution and rarity, this species should be considered a species of highest conservation concern (Williams et al. 2008).Williams et al. (2010) lists this species as endangered according to the AFS assessment. The species has also been assigned a NatureServe Global Heritage Status Rank of G1 - Critically Imperilled, and a State/Province Status Rank of S1 - Critically Imperilled for Alabama, the state to which it is endemic (NatureServe 2009). There are no species-specific conservation measures currently in place for this species. Further research regarding population trends, life history patterns and threats impacting this species is required. Monitoring of populations and implementation of protection, management and species recovery strategies are required to ensure this species' survival.
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