Wood turtle (Glyptemys insculpta) COSEWIC assessment and status report: chapter 4

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Distribution

Global range

The Wood Turtle is endemic to North America and has a discontinuous range from Nova Scotia west through New Brunswick, southern Quebec and Ontario to Minnesota, south to Virginia and Maryland (Ernst et al., 1994; Conant and Collins, 1998).

Canadian range

In Canada, the Wood Turtle occurs in Nova Scotia, New Brunswick, southern and eastern Quebec and south-central Ontario (Ernst et al., 1994; Bider and Matte, 1994; Conant and Collins, 1998; Desroches and Rodrique, 2004) with populations in Ontario ranging north and west to west Algoma in rivers draining into the east end of Lake Superior (Peiman and Brooks, 2003; J. Trottier, 2004; R. Knudsen, 2004, Wesley et al., 2004; Fig. 2). The species’ distribution is discontinuous throughout most of its Canadian range. Approximately 30% of the Wood Turtle’s global distribution is in Canada (Ernst et al., 1994; Conant and Collins, 1998).

Although Wood Turtles have declined in many areas (Kaufmann, 1992a; Litzgus and Brooks, 1996; Harding 1997; Oldham, 1998; Seburn and Seburn, 2000; Cameron et al. 2002; Compton et al., 2002; Saumure, 2004; Seburn and Seburn, 2004; NatureServe, 2004; Daigle and Jutras, 2005), the Extent of Occurrence in Canada has remained basically the same since the mid-20^th century (Fig. 2). There are 60 Element Occurrences (discrete interbreeding populations in a distinct watershed or separated by an effective barrier) in Ontario, but 18 are considered extirpated or historic, 25 are ranked as D (probably not viable) and none have better than a B rating (good predicted viability) (Natural Heritage Information Centre, 2004a and b). There are 122 occurrences of Wood Turtles in Quebec distributed among 37 rivers (Natural Heritage Data Centre, 2005), with 19 rated as historic, species not recorded in last 25 years, 54 rated as extant, with poor locality description, 36 ranked as good, species recorded in fewer than 5 of last 10 years, 12 as poor, species observed once 10-25 years ago, and 1 as excellent, species observed in more than 5 of past 10 years. The Atlantic Canada Conservation Data Centre has 79 Element Occurrence records for New Brunswick and 176 for Nova Scotia (S. Gerreits, pers. comm. 2005). The number of intensively studied areas with known populations is, of course, much lower than the number of occurrence reports.

Extent of Occurrence (EOO) is approximately 500 000 km², based on range maps in Ernst et al. (1994), Conant and Collins (1998) and Fig. 2. The Area of Occupancy (AO) is very difficult to determine, or even estimate, as not all studies used radio telemetry, maps with specific location information are rarely published, and not all studies list the area of the study site or sites. Based on habitat requirements, and estimates of area used (see, for example, Foscarini and Brooks 1997, Wesley 2006), the AO would include the areas of inhabited rivers and a buffer of shoreline. A recent study of Wood Turtles in Ontario’s Algoma District found turtles in 10 of 65 rivers searched and found them only on specific parts of the river that provided critical habitat for nesting, hibernation and foraging/thermoregulation (Wesley, 2006; see also Dubois 2006). Assuming all populations occur (see Abundance) this way, then one can estimate AO as follows. If one takes 438 Element Occurrences as the total in Canada (see previous paragraph), then assumes for each that the occupied stream and riparian areas that contain the critical nesting, foraging and hibernation sites is 100 m wide and 1 km long, then there are 10 ha per Element Occurrence. Therefore, AO = 10 x 438 = 4,380 ha. Alternatively, we could calculate AO by the prescribed grid method (2x2km). In this method, the AO=438x4= 1752km². A third method would be to take the area of a stream occupied by a population as 5000m length by 600 m width =3km² and total AO= 3 x438=1314km². Lastly, if we use the “Quebec“ method (D. Banville pers. comm. 2006) and assume each Element Occurrence= 2.4km², then AO= 2.4x438=1051km².