Status of the Rayed Bean, Villosa fabalis (Bivalvia: Unionidae), in Ontario and Canada

Abstract

The Rayed Bean, Villosa fabalis, is a very small freshwater mussel that lives in stable substrates of sand or gravel in shallow riffle areas of rivers and streams. Its host fish in Canada is unknown. Although population trends are difficult to quantify due to a lack of numerical data, the species is generally recognized to have significantly declined throughout its range in recent years. Its global rank was uplisted from G2 to G1G2 by The Nature Conservancy in 1997, and it is currently ranked S 1 in most jurisdictions. In Canada, Villosa fabalis was historically known from the Thames, Sydenham and Detroit Rivers and western Lake Erie in southwestern Ontario. It is now restricted to the middle reach of the Sydenham River. Siltation and agricultural chemicals are likely the most significant threats to the continued existence of this species in Canada. Pollution from urban sources and livestock farming may have caused the extirpation of the species from the Thames River. As the Sydenham River population is one of only a few remaining populations in North America that still show signs of recruitment, preserving this population may be important for the global survival of the species.