Overview

Distribution

endemic to a single nation

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Type of Residency: Year-round

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Global Range: (Zero to <100 square km (zero to less than about 40 square miles)) Historically, this species was known from the Tombigbee River near Pickensville, Alabama and the East Fork Tombigbee River downstream of its confluence with Bull Mountain Creek. Mirarchi et al. (2004) cite former distribution in Alabama as the mainstem of the Tombigbee River. A short section of the upper Tombigbee River in Mississippi (Hartfield and Jones, 1989) contained a small persistent population until the mid-1980s but is now extirpated (Mirarchi et al., 2004). A single record from the Big Black River, Mississippi (Hartfield and Rummel, 1985), is believed to be an error (USFWS, 1989). The current range of the species appears to be limited to the East Fork Tombigbee River in Mississippi (USFWS, 1989; 2000; Paul Hartfield, pers. comm. October, 1992) although no live specimens have been found there despite intensive surveys in 1990, 91, 92, 93, 97, 99, 2001 with the last dead shells collected in 1989 and 1990 (Paul Hartfield, pers. comm., September 2003). It is extirpated from Alabama following construction of Tennessee-Tombigbee Waterway (Mirarchi et al., 2004). It is considered historical in Mississippi in the Tombigbee River drainage (Jones et al., 2005) with the unlikely potential that a living population might be found.

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Historic Range:
U.S.A. (AL, MS)

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Physical Description

Diagnostic Description

Specimens of PLEUROBEMA CURTUM and OBOVARIA JACKSONIANA sometimes bear a superficial resemblance. This presents more a problem of identification than of taxonomy. Females of P. CURTUM have a thin, sharp, ventral margin on the gravid gill, while O. JACKSONIANA has a thick, pad-like and round margin on the gravid gill. The shell of female P. CURTUM is tapered to a round point posteriorly. The female O. JACKSONIANA is truncate. Male P. CURTUM have dark greenish- black shells with small tapered umbos. Male O. JACKSONIANA have brownish-black shells with medium to full rounded umbos.(U. S. Fish and Wildlife Service, 1989).

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Ecology

Habitat

Habitat Type: Freshwater

Comments: Found in riffles and shoals on sandy gravel to gravel-cobble substrates and with moderate to fast currents in lotic habitat (USFWS, 2000; Mirarchi et al., 2004). Requires clean water.

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Habitat and Ecology

Habitat and Ecology
This species is found in riffles and shoals on sandy gravel to gravel-cobble substrates and with moderate to fast currents in lotic habitat (USFWS 2000, Mirarchi et al. 2004). This species requires clean freshwater. It is known only from flowing water in medium to large rivers. The preferred substrate of P. curtum is a mixture of sand and gravel or pure sand and may be found in water less than 1 m deep. It is probably a short-term brooder, gravid in spring and summer. Its glochidial hosts are unknown, but it may 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: 0 - 5

Comments: Recent populations are all but extirpated with the last holdout at East Fork of the Tombigbee River (Itawamba/Monroe Co., Mississippi) (USFWS, 2000) showing no live specimens in over a decade (Paul Hartfield, pers. comm., September 2003).

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Global Abundance

Zero to 50 individuals

Comments: This species has not been found alive during recent surveys for over a decade (Hartfield, 1989; USFWS, 1989; Paul Hartfield, pers. comm., September 2003).

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Life History and Behavior

Reproduction

The glochidial host is not known.

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: NH - Possibly Extirpated

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NatureServe Conservation Status

Rounded Global Status Rank: GH - Possibly Extinct

Reasons: This regionally endemic species has declined significantly throughout its range and shows no evidence of recruitment with no recent specimens at the single known extant site in over a decade. It faces major threats. Any impact on the species is significant and the species may already be extinct. Further survey work it needed to determine whether this species is still extant.

Intrinsic Vulnerability: Highly to moderately vulnerable.

Comments: Low population levels cause increased difficulty in completing successful reproduction. When individuals become scattered, the opportunity for the female to become gravid is greatly diminished. With low population levels, any impact is a major threat (USFWS, 1989). Isolated imperiled populations in the Mobile River basin are likely vulnerable to random accidents, such as toxic spills, and to naturally catastrophic events, such as droughts and floods, even if land use and human populations were to remain constant within isolated watersheds (USFWS, 2000).

Environmental Specificity: Narrow. Specialist or community with key requirements common.

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IUCN Red List Assessment


Red List Category
CR
Critically Endangered

Red List Criteria
B1ab(i,ii,iii,iv)

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 curtum has been assessed as Critically Endangered as this regionally endemic species has declined significantly throughout its range and its extent of occurrence is now is believed to be less than 100 km2. There is no evidence of recruitment and no live specimens found within 10 years at the single known extant site and the species continues to be impacted by major threats. Any impact on the species is significant and the species may already be extinct. Further survey work it needed to determine whether this species is still extant.

History
  • 1996
    Critically Endangered
  • 1994
    Endangered
    (Groombridge 1994)
  • 1990
    Endangered
    (IUCN 1990)
  • 1988
    Endangered
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Endangered
    (IUCN Conservation Monitoring Centre 1986)
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Current Listing Status Summary

Status: Endangered
Date Listed: 04/07/1987
Lead Region:   Southeast Region (Region 4) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: E

For most current information and documents related to the conservation status and management of Pleurobema curtum , see its USFWS Species Profile

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Global Short Term Trend: Decline of 70 to >90%

Comments: The decline of the species has been hastened due to the construction of the Tennessee - Tombigbee Waterway. Construction of the waterway has adversely impacted the species by physical destruction during dredging, increasing sedimentation, reducing water flow, and suffocating juveniles with sediment (USFWS, 1989). A small population persisted until the mid-1980s in a short section of the upper Tombigbee River in Mississippi not directly modified by waterway (Hartfield and Jones, 1989) but it is believed extripated as are all Alabama records (Mirarchi et al., 2004).

Global Long Term Trend: Decline of >90%

Comments: The species is nearly extinct and is considered extirpated in Alabama by construction of the Tennessee-Tombigbee Waterway (Mirarchi et al., 2004). It has nto been collected since 1992 (East ForkTombigbee River) (Williams et al., 2008).

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Population

Population
Recent populations are all but extirpated with the last holdout at East Fork of the Tombigbee River (Itawamba/Monroe Co., Mississippi) (USFWS 2000) showing no live specimens in over a decade (Hartfield pers. comm. 2003). Population numbers are extremely low and live specimens have not been reported for over a decade (USFWS 2000, Hartfield and Jones 1989, USFWS 1989, Hartfield pers. comm. 2003).

The decline of the species has been over the last 25-50 years and has been hastened by the construction of the Tennessee-Tombigbee Waterway. Construction of the waterway has adversely impacted the species by physical destruction during dredging, increasing sedimentation, reducing water flow, and suffocating juveniles with sediment (USFWS 1989). A small population persisted until the mid-1980s in a short section of the upper Tombigbee River in Mississippi not directly modified by the waterway (Hartfield and Jones 1989) but it is believed to be extirpated as are all Alabama records (Mirarchi et al. 2004). The species is nearly extinct and is considered extirpated in Alabama by construction of the Tennessee-Tombigbee Waterway (Mirarchi et al. 2004).

Population Trend
Decreasing
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Threats

Degree of Threat: Very high - high

Comments: The continued existence of Pleurobema curtum is dependent upon habitat in the tributaries of the Tombigbee River. The East Fork Tombigbee River is threatened by a clearing and snagging project, sand and gravel mining, the continued diversion of flows, and water removal for municipal use. Runoff of fertilizers and pesticides may adversely affect the species. Such runoff may exceed the streams' ability to assimilate resulting in algal blooms and excesses in other aquatic vegetation. Pesticides which enter the stream are ingested by filter feeders such as P. curtum while being transported downstream (USFWS, 1989). The species is nearly extinct and is considered extirpated in Alabama by construction of the Tennessee-Tombigbee Waterway (Mirarchi et al., 2004).

The principal cause of population decline is habitat modification for navigation. Waterway construction (the Tennessee Tombigvee Waterway by the USACE) adversely affected this species by physical destruction during dredging, increasing sedimentation, reducing water flow, and suffocating juveniles with sediment. Deposition continues in remaining portions of the Tombigbee River that have not already been impacted severely. Water diversion is a continuing threat along with associated accumulation of sediment. Runoff of fertilizers and pesticides adversely affects mussels and leads to eutrophication (USFWS, 1989).

From USFWS (2000):
In the Mobile River basin, the greatest threats are dams (for navigation, water supply, electricity, recreation, and flood control), channelization (causing accelerated erosion, altered depth; and loss of habitat diversity, substrate stability, and riparian canopy), dredging (for navigation or gravel mining), mining (for coal, sand, gravel, or gold) in locally concentrated areas, pollution- point source (industrial waste effluent, sewage treatment plants, carpet and fabric mills, paper mills and refineries in mainstem rivers), pollution- nonpoint source (construction, agriculture, silviculture, urbanization).

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Major Threats
The continued existence of Pleurobema curtum is dependant upon habitat in the tributaries of the Tombigbee River. The East Fork Tombigbee River is threatened by a clearing and snagging project, sand and gravel mining, the continued diversion of flows, and water removal for municipal use. Runoff of fertilisers and pesticides may adversely affect the species. Such runoff may exceed the streams' ability to assimilate, resulting in algal blooms and excesses in other aquatic vegetation. Pesticides which enter the stream are ingested by filter feeders such as P. curtum while being transported downstream (USFWS 1989). The species is nearly extinct and is considered extirpated in Alabama by construction of the Tennessee-Tombigbee Waterway (Mirarchi et al. 2004).

The principal cause of population decline is habitat modification for navigation. Waterway construction adversely affected this species by physical destruction during dredging, increasing sedimentation, reducing water flow, and suffocating juveniles with sediment. Deposition continues in remaining portions of the Tombigbee River that have not already been impacted severely. Water diversion is a continuing threat along with associated accumulation of sediment. Runoff of fertilisers and pesticides adversely affects mussels and leads to eutrophication (USFWS 1989).

In the Mobile River basin, the greatest threats are dams (for navigation, water supply, electricity, recreation, and flood control), channelisation (causing accelerated erosion, altered depth; and loss of habitat diversity, substrate stability, and riparian canopy), dredging (for navigation or gravel mining), mining (for coal, sand, gravel, or gold) in locally concentrated areas, pollution- point source (industrial waste effluent, sewage treatment plants, carpet and fabric mills, paper mills and refineries in mainstem rivers), and pollution- nonpoint source (construction, agriculture, silviculture, urbanization) USFWS 2000).

Low population levels cause increased difficulty in completing successful reproduction. When individuals become scattered, the opportunity for the female to become gravid is greatly diminished. With low population levels, any impact is a major threat (USFWS 1989). Isolated imperiled populations in the Mobile River basin are likely to be vulnerable to random accidents, such as toxic spills, and to naturally catastrophic events, such as droughts and floods, even if land use and human populations were to remain constant within isolated watersheds (USFWS 2000).
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Management

Biological Research Needs: 1. Determine habitat requirements. 2. Conduct life history studies with an emphasis on fish host identification. 3. Determine if culturing in a viable means of conservation. 4. Determine if fish host is in need of similar culturing.

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Global Protection: None. No occurrences appropriately protected and managed

Comments: There are no known protected areas for the species.

Needs: Mobile River Basin recovery plan (USFWS, 2000) calls for: (1) use to fullest extent existing laws, regulations, and policies to portect listed populations and their habitats, and to develop and encourage a stream management strategy that places high priority on conservation; (2) encourage voluntary stewardship through joint initiatives and individual actions as the only practical and economical means of minimizing adverse effects of private land use and activities within watersheds; (3) continue to promote research efforts on life histories, sensitivities, and requirements of imperiled aquatic species, and develop technological capabilities to maintain and propagate them.

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Conservation Actions

Conservation Actions
This species was listed as federally endangered in the U.S. in 1987.

A recovery plan has been created for the species (and four others in the Tombigbee River) (USFWS 1989) which contains the following objectives: (1) protect the habitat where the species occurs, (2) determine habitat requirements and management needs and correct as necessary and feasible, (3) monitor existing populations at not more than 3-year intervals and recommend additional actions as needed, (4) solicit the assistance of the states, other Federal agencies, municipalities and conservation organizations in protecting the remaining habitat.

A specific recovery plan has been created for the Mobile River basin (USFWS 2000) which contains the following objectives: (1) protect habitat integrity and quality of river and stream segments that currently support or could support imperiled aquatic species, (2) consider options for free-flowing river and stream mitigation strategies that give high priority to avoidance and restoration, (3) promote voluntary stewardship as a practical and economical means of reducing nonpoint pollution from private land use, (4) encourage and support community-based watershed stewardship planning and action, (5) develop and implement programs and materials to educate the public on the need and benefits of ecosystem management, and to involve them in watershed stewardship, (6) conduct basic research on endemic aquatic species and apply the results toward management and protection of aquatic communities, (7) develop and implement technology for maintaining and propagating endemic species in captivity, (8) reintroduce aquatic species into restored habitats, as appropriate, (9) monitor listed species' population levels and distribution and periodically review ecosystem management strategy, (10) coordinate ecosystem management actions (more detail in USFWS 2000).

There are no known protected areas for the species. Research is needed into the continued distribution of this species, as well as threats; continued monitoring is needed, but is already implemented under the species recovery plan (see above).

This species has also been assigned a NatureServe Global Heritage Status Rank of GH - Possibly Extinct, and State/Province Status Ranks of SH - Possibly Extinct for Mississippi and SX - Presumed Extinct in Alabama (NatureServe 2009). Williams et al. (2010) lists this species as possibly extinct according to the AFS assessment.
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Relevance to Humans and Ecosystems

Risks

Stewardship Overview: This species was listed as federally endangered in the U.S. in 1987.

A recovery plan has been created for the species (and four others in the Tombigbee River) (USFWS, 1989) which contains the following objectives: (1) protect the habitat where the species occurs, (2) determine habitat requirements and management needs and correct as necessary and feasible, (3) monitor existing populations at not more than 3-year intervals and recommend additional actions as needed, (4) solicit the assistance of the states, other Federal agencies, municipalities and conservation organizations in protecting the remaining habitat.

A specific recovery plan has been created for the Mobile River basin (USFWS, 2000) which contains the following objectives: (1) protect habitat integrity and quality of river and stream segments that currently support or could support imperiled aquatic species, (2) consider options for free-flowing river and stream mitigation strategies that give high priority to avoidance and restoration, (3) promote voluntary stewardship as a practical and economical means of reducing nonpoint pollution from private land use, (4) encourage and support community based watershed stewardship planning and action, (5) develop and implement programs and materials to educate the public on the need and benefits of ecosystem management, and to involve them in watershed stewardship, (6) conduct basic research on endemic aquatic species and apply the results toward management and protection of aquatic communities, (7) develop and implement technology for maintaining and propagating endemic species in captivity, (8) reintroduce aquatic species into restored habitats, as appropriate, (9) monitor listed species population levels and distribution and periodically review ecosystem management strategy, (10) coordinate ecosystem management actions (more detail in USFWS, 2000).

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Wikipedia

Black clubshell

The black clubshell or Curtus's mussel, scientific name Pleurobema curtum) a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels.

This species is endemic to the United States.

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Names and Taxonomy

Taxonomy

Comments: The genus Pleurobema is a confusing lot even among malacologists who are familiar with the genus group. The Mobile Basin Pleurobema are especially confusing given the similarities between nominal species.

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