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Round Pigtoe Consultation Document

Information on the Round Pigtoe


Freshwater Mollusc

Common name: Round Pigtoe

Scientific name: (Pleurobema sintoxia)

Status : Endangered

Last Examination by COSEWIC : May 2004

Distribution and Biology:

The round pigtoe is a medium to large mussel (up to 130 mm in length). The shell is relatively thick and solid with a roughened surface. Juveniles may be tan in colour but darken with age to a deep reddish brown in mature adults. This species has a wide range of habitat preferences being found in small, medium and large rivers with moderate flows on mixed substrates of gravel, cobble, boulder, mud and sand. In lakes Erie and St. Clair it is often found in sandy nearshore areas at depths of less than 1m whereas river populations are often found at depths greater than 1m.  The round pigtoe was once broadly distributed across southern Ontario in the Lake St. Clair and Lake Erie drainages but is now restricted to the Lake St. Clair delta, Sydenham, upper Thames and lower Grand Rivers with only the Lake St. Clair delta and Sydenham River populations showing signs of reproduction.

COSEWIC Reason for Designation:

Species limited to a small area of occupancy in the Lake St.Clair and three watersheds in southern Ontario with continuing declines in habitat area, extent and quality. Threats include urban, industrial and agricultural development and irreversible impacts from Zebra Mussels in Lake St. Clair, with potential threats from introduction of Zebra Mussels in impoundments in the Sydenham River.

Potential Protective Measures and Impacts:

Legal listing of the round pigtoe will invoke the prohibition provisions of SARA. Over the longer term, potential measures may result in management measures and identification of critical habitat that may impact individuals, businesses, and governments.

Examples of potential protective measures may include:

  • Measures to change land and water use activities – These range from the activities of individuals (i.e. gardening, farming, recreation, etc.) to those of commercial entities (i.e. urban development, farming, ranching, etc.).
  • Measures to improve water quality (i.e. reducing suspended solids and nutrients) and control the timing of water flows into tributaries, aquifers, lakes and rivers.

It should be noted that the recovery planning process will involve further consultation.