Gaspé shrew (Sorex gaspensis) COSEWIC assessment and status report: chapter 4

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Distribution

S. gaspensis is currently considered to be the only North American shrew having its entire range within Canada. S. gaspensis are recorded from five regions: one in the Gaspé Peninsula, two in New Brunswick and two in northern Nova Scotia (Figure 2). There are 80 records from the Maritime Provinces and 53 from Quebec, totalling 133 to date (33 locations to 2004). Since the status report of Scott (1988), four additional historical records have been located and 15 new records reported.

Figure 2. Geographic distribution of S. dispar subspecies S. d. dispar, S. d. blitchi and S. gaspensis. The map is modified from Rhymer et al. (2004). Key: 1 = S. gaspensis; 2 = northern U.S. S. d. dispar; 3 = southern U.S. S. d. blitchi; 4 = Overlap of S. gaspensis and S. d. dispar.

Recent surveys indicate less of a geographical gap in range between S. dispar and S. gaspensis (e.g., McAlpine et al. 2004). To date (2004), 20 specimens of S. dispar have been recorded in Canada (11 locations), 12 in southeastern Quebec, 2 from southeastern and one from southcentral New Brunswick, and 6 on mainland Nova Scotia (McAlpine et al. 2004). S. dispar is limited to the mountainous regions of northeastern North America (Figure 3).

Figure 3. Locations within Canadafrom which S. gaspensis and S. dispar have been recorded.

Both species may be more widespread than is currently believed. Many areas of suitable habitat have not been surveyed for shrews. For example, apparently suitable habitat exists for both species in the Cobequid Mountains of Nova Scotia and the Nerepis Hills of New Brunswick (Woolaver et al. 1998; McAlpine et al. 2004). There is extensive granitic talus habitat in the highlands on the east side of Cape Breton Island between Tarbotvale and Cape Smokey (Scott 1988; F. Scott, pers. comm.).

Both species are hard to detect and intensive trapping is required. For example, in Nova Scotia, only one S. disparwas caught in 1,500 nights of trapping (Woolaver et al. 1998; M. Elderkin, pers. comm.) and approximately 1,000 trapping nights for each of four S. dispar trapped in the Smith Brook Valley (Scott and van Zyll de Jong 1989). Similarly, in Forillon National Park on the Gaspé Peninsula a single S. gaspensis was among 27 Sorex specimens trapped on 340 nights of trapping (S. Paradis, pers. comm.).

Extent of occurrence (EO) for S. gaspensis and S. dispar was calculated using the minimum convex polygon technique (C. Lougheed, Environment Canada, pers. comm.).  Parts of polygons that fell in either the Atlantic Ocean (northern Nova Scotia locations) or in the northern United States (southern Quebec locations) were excluded from calculations. For any isolated observations, a 2-km radius buffer was drawn around each location. These calculations gave an extent of occurrence of 13,089 km²for S. gaspensis and 1,369 km² for S. dispar. If the two species are considered subspecies then the total extent of occurrence would be 14,385 km² (combined EO of S. gaspensis and S. dispar).

1 missing AMNH 74510, cited in Scott 1988

Collection abbreviations: AMNH = American Museum of Natural History, New York City; NBM = New Brunswick Museum, Saint John; NMC = National Museum of Natural Sciences, Ottawa; NSM = Nova Scotia Museum, Halifax; RM = Redpath Museum, Montreal; SU = The Vertebrate Museum, Shippensburg University, Shippensburg PA; TWF = private collection of Thomas W. French; USNM = United States National Museum, Washington DC, ACAD = Wildlife Museum, Acadia University.

Author: 1. Roscoe and Majka (1976), 2 Peterson and Symansky (1963), 3.Whitaker and French (1982), 4 French and Kirkland (1983), 5 Rhymer et al. (2004).

We calculated area of occupancy (AO) using two types of grid, one 2 km² and the other 4 km² grid (C. Lougheed, pers. comm.). The 2-km² scale was a conservative estimate of AO while the 4 km² was less conservative. Using a 2-km² grid, the total AO forS. gaspensis was 128 km² and for S. dispar 36 km². The combined AO for both species was 164 km². Using the 4-km² grid, the AO for S. gaspensis was 480 km² and for S. dispar, 128 km². The combined AO for both species was 608 km². Given that the calculated AOs are very small, it is important to note that setting the grid to 4 km² may exclude apparently suitable adjacent habitat that has not been surveyed. We would expect that further surveys in suitable habitat would identify other populations (especially with a systematic sampling design); however, considerable survey effort will be necessary given the low detectability of this species.

No data are available on historical changes in number of populations or extent, but this may be assumed to be relatively stable due to the lack of significant anthropogenic disturbance to their habitat.

Authors: 1. Peterson (1966), 2. McAlpine et al. (2004), 3. Kirkland and Schmidt (1982), 4. Kirkland et al. (1979), 5. Scott (1987), 6. Rhymer et al. (2004), 7. Scott and van Zyll de Jong (1989), 8. Woolaver et al 1998.