Gaspé shrew (Sorex gaspensis) COSEWIC assessment and status report: chapter 2

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COSEWIC Executive Summary

Species information

Part of the Sorex complex comprising 40-50 Holarctic species, the Gaspé Shrew Sorex gaspensis (French, la Musaraigne de Gaspé) and long-tailed or rock shrew S. dispar (French, la Musaraigne longicaude) are closely related, separated to date primarily by size. Both are small, slender and slate-grey in colour with long tails, although S. dispar is slightly larger than S. gaspensis (S. dispar: 3.1-8.3 g, total body length 103-136 mm, tail length 46-67 mm, condylobasal length 16.45-18.70 mm, length of molariform tooth row 3.75-4.30 mm; S. gaspensis: 2.2-4.3 g, total body length 95-127 mm, tail length 45-55 mm, condylobasal length 15.35-16.35 mm, length of molariform tooth row 3.40-3.65 mm). While they are currently recognized as distinct species, the taxonomic status of these species is equivocal. Genetic analyses by Judith Rhymer and colleagues suggest that S. gaspensisshould be recognized as a subspecies of S. dispar, and preliminary results from more detailed ongoing genetic studies currently in progress by Don Stewart and colleagues confirm Rhymeret al.’s findings. Because of current uncertainties regarding the taxonomic status of the species we treat S. dispar and S. gaspensis together in this report.

Distribution

At present, S. gaspensis is the only shrew species unique to Canada, though this may change if it is accorded sub-specific status as S. dispar gaspensis. It has been recorded from five regions, one in the Gaspé Peninsula of Quebec, two in New Brunswick and two in northern Nova Scotia. To date, there are 133 records of the species (33 locations), 80 from the Maritime Provinces and 53 from Quebec. Of these, 16 have been captured since 1988. S. dispar also occurs in Canada, one end of a narrow belt of occurrence that stretches from North Carolina to Maine and the Adirondack Mountains of New York. There are 21 records of S. dispar from Canada (11 locations), from southeastern Quebec (n = 12 specimens), southeastern (2) and southcentral (1) New Brunswick, and mainland Nova Scotia (6). Of these, six have been recorded since 1988.

Habitat

S. gaspensis and S. dispar have similar habitat requirements, being restricted largely to steep slopes in mountainous regions that have differing amounts of rocky outcrops and talus. Both occur mainly on upper, mesic valley slopes that are east, north or west facing with ferns, mosses and other dense vegetation. Overstory trees include species associated with mesic sites, such as yellow birch Betula alleghaniensis and sugar maple Acer saccharum. Recent records of S. gaspensis from Quebec have been in mature mixed forests (four cases), a sugar maple forest with yellow birch, a mature coniferous forest and in one case a regenerating mixedwood. Sampling biased toward habitats that have been presumed to be preferred may make data on habitat preference unreliable.

Biology

Little is known of the biology of either species, reflecting their cryptic, inaccessible habitat and low capture frequencies. They are insectivorous, and are assumed to live for 14-17 months. Like other shrews they probably reach sexual maturity in the second summer after birth. Litter sizes range from 2-6, with the possibility of 1-2 litters per breeding female per year. Adults are believed to have fixed home range, although during the breeding season, males may wander widely in search of females. Young are probably weaned by 25 days of age, when they disperse in search of their own home range. Shrews are expected to be most vulnerable to predation and starvation during weaning and dispersal.

Population sizes and trends

Virtually nothing is known about population sizes and trends of the two species (or subspecies), and apart from some new occurrences our knowledge about their ecology does not appear to have changed since the 1988 COSEWIC status report onS. gaspensis. It is highly likely that both species are more widespread and abundant than presently believed, although the occurrence of presumed preferred habitat is restricted and isolated in the landscape. The lack of systematic inventory and monitoring for these species in known or potential habitat makes it impossible to provide any evaluation of possible population changes.

Limiting factors and threats

Potential threats to these species are limited since their habitat is unsuitable for anthropogenic uses such as forestry, agriculture or mining. Populations are widespread, and although single populations may be lost from an intense fire event, both species appear to be widespread in talus habitats throughout the region.

Special significance of the species

S. gaspensisis significant because presently it is believed to be the only North American Sorex species unique to Canada. Like some other species’ populations in Atlantic Canada, its small, isolated and disjunct population may be a relict of geography and glacial history.

Existing protection

S. gaspensis has been designated as a species of Special Concern in April 1988, by COSEWIC and is on Schedule 3 of the federal Species at Risk Act (SARA 2002). Within the provinces, neither species is protected by provincial endangered species legislation.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5^th2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2006)

Wildlife Species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^Footnotea

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)^Footnoteb

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)^Footnotec

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.