endemic to a single nation
Regularity: Regularly occurring
Type of Residency: Year-round
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.
U.S.A. (AL, MS)
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 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 Jacksoniana is truncate. Male P. CURTUM have dark greenish- black shells with small tapered umbos. Male Jacksoniana have brownish-black shells with medium to full rounded umbos.(U. S. Fish and Wildlife Service, 1989).
Habitat and Ecology
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.
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.
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).
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).
Life History and Behavior
The glochidial host is not known.
Date Listed: 04/07/1987
Lead Region: Southeast Region (Region 4)
Where Listed: Entire
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
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.
IUCN Red List Assessment
Red List Category
Red List Criteria
- Needs updating
- 1994Endangered(Groombridge 1994)
- 1990Endangered(IUCN 1990)
- 1988Endangered(IUCN Conservation Monitoring Centre 1988)
- 1986Endangered(IUCN Conservation Monitoring Centre 1986)
National NatureServe Conservation Status
Rounded National Status Rank: NH - Possibly Extirpated
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).
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).
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.
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.
Relevance to Humans and Ecosystems
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).
- Bogan, A.E. 1996. Pleurobema curtum. 2006 IUCN Red List of Threatened Species. Downloaded on 7 August 2007.
|This bivalve-related article is a stub. You can help Wikipedia by expanding it.|