|Scientific Name:||Pleurobema decisum|
|Species Authority:||(Lea, 1831)|
Pleurobema chattanoogensis Williams et al 2008
|Taxonomic Notes:||A list of synonyms for this species can be found on The MUSSEL project web site (Graf and Cummings 2011).
Genetic analysis is needed to compare this species with Pleurobema chattanoogaensis and forms of the species (i.e., Pleurobema crebrivittatus and Pleurobema pallidovulvus) that are recognized by the U.S. Fish and Wildlife Service as synonyms.
|Red List Category & Criteria:||Endangered A2c; B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v) ver 3.1|
|Assessor/s:||Bogan, A. & 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.|
Pleurobema decisum has been assessed as Endangered under criteria A2c;B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v) as the species has undergone a steep population reduction, has an inferred extent of occurrence of < 1,000 km2 and area of occupancy of < 500 km2, remaining populations are severely fragmented and isolated and continuing threats from human activities throughout the Mobile River basin are continuing to reduce the area/quality of available habitat, thus resulting in continued declines in EOO, AOO, number of mature individuals and subpopulations. This species is currently known from a few locations within the Mobile River basin, where it was once widespread and faces multiple major threats. The historical decline was approximately 70-80% over the last 25-50 years, but recently has been closer to 60%. Until recently, this species was currently found in only a fraction of its former range with few new occurrences but recent populations have been found in the Conasauga, Luxapallila, and Tombigbee drainages (Cordeiro pers. comm. 2011). The generation length of this species is 18-19, meaning that the species also qualifies as Endangered under criterion A2c due to population declines of over 50% in 3 generation lengths: a 60-80% decline in localities over the past 25-50 years is suspected to equal a population reduction of at least 50% in the past 60 years.
|Range Description:||Formerly widespread throughout the Mobile River basin, Pleurobema decisum was known historically from the Alabama River and Bogue Chitto Creek; Tombigbee River and tributaries (Buttahatchie, East Fork Tombigbee, and Sipsey Rivers and Bull Mountain, Luxapalila, and Lubbub Creeks); Black Warrior River; Cahaba and Little Cahaba Rivers; two Tallapoosa tributaries, Uphapee and Chewacla Creeks; and the Coosa River and tributaries (Oostanaula, Conasauga, Etowah, Chatooga, and Coosawattee Rivers and Kelly, Talladega and Shoal Creeks) in Mississippi, Alabama, Georgia, and Tennessee (USFWS 2004).
The species is endemic to the Mobile River Basin, and is currently found in Alabama, Georgia, Mississippi and Tennessee (Williams et al. 2008). Currently, the species is known from most of the Mobile River Basin and is only absent in the Tallapoosa River drainage above the fall line. The species is present in isolated, diffuse localities in the river drainages Alabama, Coosa, Tallapoosa and Tombigbee where most remaining populations are in tributaries (Williams et al. 2008). The species is known from Bogue Chitto Creek in Alabama River drainage; Buttahatchie, East Fork Tombigbee and Sipsey Rivers in the Tombigbee River drainage; and Chewacla Creek in the Tallapoosa River drainage (USFWS 1993, McGregor et al. 1999). It has recently been found in the Conasauga River, Whitfield and Murray Counties, Georgia in the upper Coosa River drainage (M. Hughes pers. comm. 1997). In the Coosa River basin in Georgia, it is known historically from the Coosa, Etowah, Oostanaula, Conasauga, and Coosawattee River drainages but has not been collected there recently (Williams and Hughes 1998) except in the Conasauga (Johnson and Ahlstedt 2005). Mirarchi et al. (2004) list distribution as endemic to Mobile Basin in Alabama, Georgia, and Mississippi including Alabama, Black Warrior, Cahaba, Coosa, Tallapoosa, and Tombigbee River systems with large populations remaining only in widely scattered localities in Tombigbee River system (may be extirpated from Black Warrior and Cahaba). Jones et al. (2005) list the Tombigbee River drainage in Mississippi. McGregor et al. (2000) failed to find this species in the Cahaba River, Alabama.
It is relatively common in localised reaches of the Buttahatchee and Sipsey Rivers and is rare to uncommon in other occupied streams. The species range is likely to comprise an area of up to 90,000 km2, but taking discontinuities in the species' range into account, the estimated extent of occurrence is probably closer to around 20,000 km2, and its area of occupancy is estimated as between 1,000-2,000 km2.
Native:United States (Alabama, Georgia, Mississippi, Tennessee)
|Range Map:||Click here to open the map viewer and explore range.|
This is a declining regional endemic which faces major threats. It had, until recently, declined significantly to only a fraction of its former range but recently a few new populations were discovered from the Conasauga River inside and adjacent to the Cherokee and Chattahoochee National Forests, Murray/Whitfield Co., Georgia (Johnson et al. 2005) on the Conasauga, Luxapallila, and Tombigbee drainages.
However its former area of occupancy included every major drainage system in the Mobile Basin except the Mobile Delta. Unfortunately it is now limited to approximately six viable populations.
The Sipsey River in the Tombigbee River drainage and Chewacla Creek in the Tallapoosa River drainage support two of the most sizable populations. The known populations are isolated from each other. The species continues to inhabit the East Fork Tombigbee River (Itawamba/Monroe Co., Mississippi), Bull Mountain Creek, Buttahatchee River (Monroe/Lowndes Co., Mississippi), Luxapalila and Yellow Creeks (Lowndes Co., Mississippi), Lubbub Creek, and Sipsey River (Greene/Pickens/Tuscaloosa Co., Alabama) in the Tombigbee River drainage. It also inhabits a short reach of the Alabama River and Boque Chitto Creek (Dallas County, Alabama), Chewacla Creek (Macon Co., Alabama); Coosa River below Weiss dam (Cherokee Co., Alabama) and tributaries Kelly Creek (Shelby Co., Alabama), Big Canoe Creek (St. Clair Co., Alabama), Terrapin Creek (Cherokee Co., Alabama), and Conasauga River (Murray/Whitfield Co., Georgia) (USFWS 20002004).
Johnson and Ahlstedt (2005) located specimens in 2005 in the Luxapallila drainage on the Mississippi/Alabama border. This species was historically collected from the upper Tombigbee River in Sumter and Greene Cos., Alabama, prior to impoundment (Williams et al. 1992).
The species is relatively common in localised reaches of the Buttahatchee and Sipsey Rivers, but is rare to uncommon in other localities (USFWS 2000, 2004). Large populations remain only in widely scattered localities in Tombigbee River system (may be extirpated from Black Warrior and Cahaba) (Mirarchi et al. 2004).
The historical decline was approximately 70-80% over the last 25-50 years but recently has been closer to 60%. Until recently, this species was found in only a fraction of its former range with few new occurrences but recent populations have been found in the Conasauga, Luxapallila, and Tombigbee drainages (J. Cordeiro pers. comm. 2011).
|Habitat and Ecology:||
This species occurs in flowing water in large creeks and rivers. It is usually found in substrates composed of gravel with interstitial sand. Usually found in highly oxygenated streams with sand and gravel substrate in shoals of large rivers to small streams; may be found in sand and gravel in the center of the stream or in sand along the margins of the stream (Shelton pers. obs. 1995, USFWS 2000).
This species has been reported to reach sexual maturity when as small as 26.3 mm (Haag and Staton 2003) but grows to about 70 mm (2.8 in) long with a thick shell (USFWS 2000). It is a short-term brooder, gravid from late May to late July, with glochidia mature by the second week of June (Haag and Warren 2003). Haag and Staton (2003) estimated 94% of females in a population to be gravid during the peak of the brooding period. Glochidia are released in conglutinates that are ovate in outline, thin and orange or white (Haag and Staton 2003, Haag and Warren 2003). In addition to glochidia, P. decisum conglutinates are composed of undeveloped eggs, which are believed to help maintain the conglutinate integrity. Percentage of undeveloped eggs in P. decisum conglutinates has been reported to average 47% (Haag and Staton 2003). Annual fecundity was found to be variable in two Sipsey River, Alabama, populations, averaging 29,433 glochidia per female in one and 40,887 per female in the other (Haag and Staton 2003). One primary glochidial host, Cyprinella venusta (Blacktail Shiner) (Cyprinidae), and one secondary host, Luxilus chrysocephalus (Striped Shiner) (Cyprinidae), were reported based on laboratory trials (Haag and Warren 2003) (Williams et al. 2008). Females first become gravid at 2-3 years, maximum age is 40 years, and the generation length of the species is 18-19 years (A. Bogan pers. comm. 2012).
Habitat modification, sedimentation, and water quality degredation represent the major threats to this species. It may also be threatened by overutilisation for commercial, recreational, scientific or educational purposes (USFWS 1993). Disappearance from significant portions of its range are primarily due to changes in river and stream channels due to dams, dredging, or mining, and historic or episodic pollution events. The species is not known to survive in impounded waters and more than 1700 km of large and small river habitat in the Basin have been impounded by dams for navigation, flood control, water supply, and/or hydroelectric production purposes (USFWS 2004).
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), pollution- nonpoint source (construction, agriculture, silviculture, urbanisation) (USFWS 2000).
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).
This species was listed as endangered in the U.S. under the federal Endangered Species Act in 1993, and is widely considered to be endangered throughout its range (Williams et al. 2008). It has also been assigned a NatureServe Global Heritage Status Rank of G2 - Imperilled (NatureServe 2009).
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 (USFWS 2000).
Critical habitat has been designated in Mississippi in the East Fork Tombigbee Rvier, Bull Mountain Creek, Buttahatchee River, and Luxapalila Creek; in Alabama in the Buttahatchee River, Luxapalila Creek, Coalfire Creek, Lubbub Creek, Sipsey River, Trussels Creek, Sucarnoochee River, Cahaba River, Alabama River, Bogue Chitto Creek, Uphapee complex, Coosa River, Hatchet Creek, Kelly Creek, Big Canoe Creek, and the lower Coosa River; in Georgia in Oostanaula complex; and in Tennessee in Oostanaula complex (637 occuppied, 577 unoccuppied km) (USFWS 2004).
Chewacla Creek, Tallapoosa River Drainage, flows through the Tuskegee National Forest. This species has been recently reported from the Conasauga River inside and adjacent to the Cherokee and Chattahoochee National Forests, Murray/Whitfield Co., Georgia (Johnson et al. 2005). A flood control project on Luxapalila Creek, Mississippi, was modified by the Corps of Engineers to protect listed mussel habitat in that stream (USFWS 2000). Critical habitat has been designated in Mississippi in the East Fork Tombigbee River, Bull Mountain Creek, Buttahatchee River, and Luxapalila Creek; in Alabama in the Buttahatchee River, Luxapalila Creek, Coalfire Creek, Lubbub Creek, Sipsey River, Trussels Creek, Sucarnoochee River, Cahaba River, Alabama River, Bogue Chitto Creek, Uphapee complex, Coosa River, Hatchet Creek, Kelly Creek, Big Canoe Creek, and the lower Coosa River; in Georgia in Oostanaula complex; and in Tennessee in Oostanaula complex (637 occupied, 577 unoccupied km) (USFWS 2004).
Williams et al. (1993) 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 is needed.
|Citation:||Bogan, A. & Cordeiro, J. 2012. Pleurobema decisum. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 16 April 2014.|
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