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Villosa fabalis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA BIVALVIA UNIONOIDA UNIONIDAE

Scientific Name: Villosa fabalis
Species Authority: (Lea, 1831)
Common Name(s):
English Bean Mussel, Rayed Bean
Synonym(s):
Eurynia fabalis Lea 1831
Lemiox fabalis Lea 1831
Margarita fabalis Lea 1831
Margaron fabalis Lea 1831
Micromya fabale Lea 1831
Micromya fabalis Lea 1831
Unio capillus Say 1831
Unio donacopsis De Gregorio 1914
Unio fabalis Lea 1831
Unio lapillus Say 1832
Villosa fabalis Lea 1831
Taxonomic Notes: The entire genus is in need of thorough genetic studies to determine taxonomic validation of the many described and undescribed forms.

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 A2ace ver 3.1
Year Published: 2012
Date Assessed: 2012-04-01
Assessor(s): 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., Collins, A., McMillan, K., Duncan, C., Offord, S. & Richman, N.
Justification:
Villosa fabalis has been assessed as Endangered due to a decline in extent of occurrence of 78 % over approximately 40 years (and more than 70% since 1980, which is estimated to cover three generations) and a range of significant threats continuing to impact populations on a global scale. The Zebra Mussel in particular had a large impact on this species over recent years (since late 1990s/early 2000s). Assuming constant population declines, population occurrences would have declined by a similar amount since 1980. It is likely, however, that declines in occurrences do not directly translate into equal declines in population size, so that we estimate that population declines have exceeded 50% over a period of three generations.

This species was not listed in 1996 (M. Seddon pers. comm. 2012).
History:
1996 Not Evaluated

Geographic Range [top]

Range Description: This species occurs in the United States of America in Alabama, Indiana, Michigan, New York, Ohio and Pennsylvania (NatureServe 2009). It is also found in Ontario, Canada (NatureServe 2009). It is widespread in the Ohio River drainage, from headwaters in western New York and Pennsylvania downstream to near the mouth of the Ohio River (Williams et al. 2008). This species is known in the upper Tennessee River drainage of southwestern Virginia and eastern Tennessee, as well as upper reaches of the Elk River (Williams et al. 2008).

From the total number of streams where this species was historically found, this species is now known in only 22% (extant in 22 streams and a lake currently compared to 106 water bodies historically, = 78% decline) (Butler 2002). This species is no longer found in 'hundreds of miles' of the main sections of the Maumee, Ohio, Wabash, and Tennessee Rivers, as well as the tributaries of these rivers (Butler 2002). This species has been extirpated from several states, including Illinois, Kentucky, Tennessee, Virginia, and West Virginia, which is half of the states that it was previously recorded as extant in (Butler 2002).
Countries:
Native:
Canada (Ontario); United States (Alabama, Illinois - Possibly Extinct, Indiana, Kentucky - Possibly Extinct, Michigan, New York, Ohio, Pennsylvania, Tennessee - Possibly Extinct, Virginia - Possibly Extinct, West Virginia - Possibly Extinct)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Although this species has been reported as 'rare', it may not have been found in abundance due to its small size (Cummings and Berlocher 1990, West et al. 2000). The true status of this species may be further complicated by the fact that not all of its range has been sampled, for example, when surveying the Sydenham River, in Ontario Canada, the species was found at several more sites during 1997-1998 surveys than in the past (1971-1991), which is not thought to be down to expansion in the species range (Cummings and Berlocher, West et al. 2000, Metcalf-Smith et al. 2003). It is suggested that increased sampling effort and also surveying further upstream of the known range of this species may improve the detection of such a small bivalve (Metcalf-Smith et al. 2003). Therefore whether the population is declining, stable or increasing is not known for certain.

This species is now extirpated from 78% of the streams from which it was historically known (over a period of around 40 years; J. Cordeiro pers. comm. 2012). Only a few of the remaining populations are thought to be viable (USFWS 2003). This species is reported to be fragmented in its former range (J. Cordeiro pers. comm. 2010). Population reductions have to be assessed over a period of three generations, which have been estimated as between 27 - 33 years (upper margin estimate for generation length; so since around 1980). Assuming constant population declines, population occurrences would have declined by around 78% since 1980. It is likely, however, that generation length is underestimated due to errors associated with growth ring counting (Anthony et al. 2001). Assuming that declines in occurrences do not directly translate into equal declines in population size, we estimate that declines have exceeded 50% over a period of three generations.

Habitat and Ecology [top]

Habitat and Ecology: This very small species inhabits headwaters and smaller tributaries of river systems (Parmalee and Bogan 1998, West et al. 2000). It has been recorded in and near riffles, most often in water weeds, sometimes 'deeply buried in sand and gravel which is bound together by roots' (Parmalee and Bogan 1998, West et al. 2000). It prefers sandy or a mixture of sand and gravel bottom, along the shallower margins of rivers (Parmalee and Bogan 1998). Additionally it can be found in the 'edges of small islands and in lakes with water up to 4 foot deep' (Parmalee and Bogan 1998).

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 in other species of the genus Villosa have shown ages of between 5 and 12 years being recorded (V. lienosa, V. nebulosa, V. vibex: average of 8-9 years; Haag and Rypel 2011). Assuming a similar longevity for Villosa choctawensis, and conservatively assuming age of maturity to be somewhere between 2 and 9 years (average of 5-6 years; Haag and Staton 2003), we estimate a generation length (estimated as the average age of a parent in the population) of around 4 to 11 years, with three generations spanning around 11 to 33 years. However, this is likely to represent an underestimate of generation length, as it has been suggested that growth ring counts may underestimate age by a factor of between three and ten (Anthony et al. 2001). To err on the side of caution and adjust for the likely underestimate, we use upper margin generation length estimates for the purpose of this assessment. Consequently, population declines have to be assessed since around 1980.
Systems: Freshwater

Use and Trade [top]

Use and Trade: This species is not utilized.

Threats [top]

Major Threat(s): This species is threatened by anthropogenic activities altering the habitat, including 'livestock grazing, river modifications through channelization, tile drains, scour at bridges and downstream of dams, destruction of the riparian zone and instream activities, such as tractor crossings and pipeline construction' (Dextrase 2000). Reservoirs affect the stream hydrology, and row cropping increases the sediment load of rivers in the Sydenham watercourse, both potential threats to this species (Dextrase 2000, The Sydenham River Recovery Team 2001).
Potential threats from invasive species also exist. The Zebra Mussel, Dreissena polymorpha, has devastated some populations of this species in the Great Lakes, whilst limited access to suitable host species during the life cycle may also threaten this species (Butler 2002). Asian Carp and Catfish are introduced species which also pose threats to this species.

Conservation Actions [top]

Conservation Actions: The Sydenham River Recovery Team was established in 1999 to develop a Recovery Plan for the watershed (The Sydenham River Recovery Team 2001). Team members are from the St. Clair Region Conservation Authority, provincial (Ministry of Natural Resources) and federal agencies (Department of Fisheries and Oceans, Environment Canada), the University of Guelph, the Royal Ontario Museum, and three local stewardship councils (The Sydenham River Recovery Team 2001). The plan will have the general objective of 'restoring, to the extent possible, riparian and aquatic habitats within the system, for the benefit and possible recovery of species at risk' (The Sydenham River Recovery Team 2001).

Recently 1000 individuals were translocated from the Aleghany River, PA to the Duck River TN (A. Bogan pers. comm. 2010)

This species has a Nature Serve status of NS G2 (NatureServe 2009). Williams et al. (2010) list this species as Endangered according to the AFS assessment.

Citation: Cordeiro, J. 2012. Villosa fabalis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 31 October 2014.
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