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Recovery Strategy For Northern Riffleshell, Snuffbox, Round Pigtoe, Mudpuppy Mussel and Rayed Bean in Canada [Proposed]

9. Habitat: Round Pigtoe

Habitat Identification:The Round Pigtoe typically occurs in medium to large rivers (van der Schalie 1938; Parmalee and Bogan 1998), but also may occur in lakes (Clarke 1981; Strayer and Jirka 1997). In large rivers it may be found in mud, sand and gravel, deeper than 3 m, but also occurs on sand and gravel bars (Gordon and Layzer 1989). In Lake St. Clair, the Round Pigtoe inhabits shallow (<1 m) nearshores with firm, sandy bottoms (Zanatta et al. 2002). In smaller rivers it is often found deeply buried in gravel, cobble and boulders, in or below riffles with moderate flows (Ortmann 1919; Parmalee and Bogan 1998).

Juveniles of the Round Pigtoe are thought to have different habitat requirements than those of the adults, although few studies are available (Gordon and Layzer 1989).

Currently Occupied Habitat: Methods for delineating currently occupied habitat for the Round Pigtoe follow the methods described for the Northern Riffleshell.

Geospatial Description: Currently occupied habitat for the Round Pigtoe can be defined as a 50 km reach of the East Sydenham River, a 20 km portion of Bear Creek through Petrolia, a 30 km stretch of the lower Thames River from Thamesville to Wardsville (Figure 19), three small reaches on the Middle and South Thames rivers near Thamesford and London (Figure 20), a 60 km reach of the lower Grand River from Caledonia to Dunnville (Figure 21) and a large area within the Lake St. Clair delta (Figure 22).

Functional Description: Within the area defined under Currently Occupied Habitat only areas meeting the characteristics described below are deemed to represent habitat in need of conservation:

  • permanently wetted and
  • of a stream order greater than 2 (riverine population only) and
  • mud, sand or gravel
  • steady to moderate flows (riverine populations only)
  • nearshore areas with firm sand or gravel substrate (Great Lakes populations).

Historically Occupied Habitat:  Historically occupied habitat for the Round Pigtoe consists primarily of nearshore habitats in lakes St. Clair and Erie as well as the Detroit and Niagara rivers.


Figure 19: Currently occupied habitat of the Round Pigtoe in the Sydenham and Thames rivers.


Figure 20: Currently occupied habitat of the Round Pigtoe in the Middle Thames and South Thames rivers.


Figure 21: Currently occupied habitat of the Round Pigtoe in the Grand River.


Figure 22: Currently occupied habitat of the Round Pigtoe in the Lake St. Clair delta.