Gaspé shrew (Sorex gaspensis) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

Search effort

Both S. dispar and S. gaspensis are best sampled using pitfall traps. A pitfall trap placed below the talus surface in places between rocks is generally most effective (Richmond and Grimm 1950). Often traps can be placed in the litter that accumulates in pockets between talus boulders (F. Scott, pers. comm.).

Sampling with pitfall traps could be biased towards males, at least in S. dispar with 14 of 17 specimens of known sex being male (Table 3). In S. gaspensis 12 females and 19 males of known sex have been captured. Given the assumed biology of this species, the capture of dispersing juveniles and wandering males is expected at a higher rate than the more sedentary females. The association with streams may be a function of streams being used as dispersal routes, rather than breeding habitat. Greater search effort within the crevices of talus slopes is required to identify female breeding habitat.

Recent records for S. dispar on the mainland of Nova Scotia (Woolaver et al. 1998) suggests that the species is more widely distributed and abundant than previously thought. The new site was predicted based on biophysical data from an occupied site and deploying a geographic information system (GIS) algorithm to predict potential areas. Other such potential sites occur throughout the Cobequid Hills in Cumberland and Colchester counties in Nova Scotia. However, no targeted searches have taken place to establish the presence/absence of the shrew in those areas (M. Elderkin, pers. comm.).

Appropriate, intensive sampling is needed to establish the population status of both S. gaspensis and S. dispar over their geographic ranges in Canada. Although talus slopes are not readily identifiable from landsat imagery, steep slopes (40°) may be identified through topographical maps.

Abundance

The population density of both S. gaspensis and S. dispar is unknown. Although on Sagamook Mountain, Mount Carleton Provincial Park (New Brunswick), 67 individuals were captured in 1980, the samples from other locations are small in number.

Fluctuations and trends

No data exist on these population aspects.

Rescue effect

Populations of S. gaspensis are isolated and geographically separated. Given the potentially small home range of the species and limited movement patterns, dispersal between S. gaspensis populations is probably impossible.