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Sorex pribilofensis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA EULIPOTYPHLA SORICIDAE

Scientific Name: Sorex pribilofensis
Species Authority: Merriam, 1895
Common Name(s):
English Pribilof Island Shrew
Synonym(s):
Sorex hydrodromus Dobson, 1889
Sorex hydrodromus Dobson, 1889.
Taxonomic Notes: Van Zyll de Jong (1982) presented information that calls into question the use of the name hydrodromus for the Pribilof Island shrew, for which the name S. pribilofensis may be correct; the type specimen of hydrodromus does not seem to conform morphologically with samples of shrews from the Pribilofs, and there is uncertainty regarding the type locality ("Unalaska") of hydrodromus. Rausch and Rausch (1997) determined that the correct name for the Pribilof Island Shrew should be S. pribilofensis rather than S. hydrodromus. Jones et al. (1997) and Baker et al. (2003) adopted this change. Hutterer (in Wilson and Reeder 2005) also used the name Sorex pribilofensis.

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(ii)+2ab(ii) ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Woodman, N., Reid, F. & Matson, J.
Reviewer(s): Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)
Justification:
Listed as Endangered because its extent of occurrence is less than 5,000 km², its area of occupancy is less than 500 km², it is known from only one location (Saint Paul) island, and there are continuing threats to the extent and quality of the species' habitat.
History:
1996 Endangered

Geographic Range [top]

Range Description: The known geographic range of this species is confined to Saint Paul Island (90 sqkm), in the Pribilof Islands, Alaska, United States. It is distributed primarily along the periphery of the island. Plant associations supporting shrews in summer occupied nearly 40 sqkm in the late 1980s (Byrd and Norvell 1993). The type locality was reported as "Unalaska Islands, Aleutian Islands." However, attempts to collect shrews from the type locality have not been successful. Presumably the shrews to which the name hydrodromus has been applied were collected on Saint Paul Island of the Pribilof Islands.
Countries:
Native:
United States (Alaska)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: This species is known to occur only on St. Paul Island which is considered to be one location. No shrews have been collected on neighbouring Saint George and Otter islands, despite numerous surveys (Preble and McAtee 1923; Byrd and Norvell 1988, 1993). The species' abundance is unknown, but the total population size is probably more than 10,000 individuals. Jackson (1928) described the Pribilof shrew as "not common" in 1928. Fay (in Fay and Sease 1985) found them to be abundant in 1965. Byrd and Norvell (1988, 1993) reported capture rates of 0.9-4.5 shrews/1000 trap hours over an area of approximately 39 sqkm but gave no estimates of density. Similar trap efforts for Sorex cinereus, a closely related species with similar habitat requirements, resulted in density estimates of two to 30 shrews per acre depending on the period of the cycle when captured (Buckner 1966). Using the lower estimate of two shrews per acre and extrapolating over the 39 sqkm of suitable habitat gives a very rough minimum total population estimate of 19,266 animals on the island.

The population trend is unknown but is suspected to be stable. The shrews have been known to occur on the island for over 200 years (Fay and Sease 1985). The population is believed to have existed on Saint Paul since the area became an island, approximately 16,000 years ago.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: The species' habitat is maritime tundra. On Saint Paul Island, capture rates were highest in dune habitats and grass-umbel habitats, less in forb and mixed habitats, none in Carex or upland habitats; seemingly most abundant in habitats with more tall stems per unit area (Byrd and Norvell 1988).

This species is an invertivore, and the remains of beetles have been observed in some stomachs (Byrd and Norvell 1988).
Systems: Terrestrial

Threats [top]

Major Threat(s): The distribution of S. pribilofensis is naturally restricted to a single island, so this species is vulnerable to localized perturbations. Habitat is largely intact, but human activities and climatic warming are of potential concern (ADFG 2005). Although the effects of climate change on this species' habitat are unknown, these shrews are a relict, cold-adapted species that could be compromised by a warmer climate.

Byrd and Norvell (1993) found the shrews to be distributed widely at relatively high densities, and they identified no immediate threats to the species or to most habitat areas. Little habitat fragmentation has occurred. Of Saint Paul Island's 10,093 hectares, only 2-3% has been developed. This includes the village of Saint Paul, a fish processing plant, the Coast Guard Loran station, an airport, the POSS Helicopter camp (Pribilof Offshore Support Service), and a new seaport. There are approximately 35 miles of roads which section the island into several large parcels. These facilities do not appear to have caused significant fragmentation of the shrew habitat to date (Byrd and Norvell 1988). Potential threats include habitat loss to development and overgrazing by reindeer, and population declines if rats are incidentally introduced to the island.

At present, development activities are primarily directed toward the construction of a major harbour and port facility in Village Cove. Anticipated development includes: expansion of industrial processing facilities both within and near the harbour area; new commercial ventures including a chandlery; expanded support services; increased uses and trespass on traditional subsistence and recreation land; and expansion of air transport facilities and services. Additional future developments may also include expansion of the OCS support services for oil and gas extraction activities. Current land use plans indicate that these developments will occur primarily in the immediate vicinity of the village and harbour and along a development corridor between the village and the airport. Much of this area has been identified as preferred shrew habitat and contains high shrew densities (Byrd and Norvell 1988). Proportionally, this region involves approximately 12% of the total preferred shrew habitat on the island (estimated from Byrd and Norvell 1988, Fig 2).

With recent completion of the new seaport, increased shipping traffic is expected and the potential for Norway rat introductions will increase. The ecological consequences of this possibility are not well known. Rats introduced to different Aleutian Islands have spread across entire islands, invading most habitats. They are believed to function as significant predators of birds and other wildlife on these islands. Byrd and Norvell (1988) predicted that predation on the shrews would increase if rats were introduced to Saint Paul Island. It is also possible that they could introduce disease that is detrimental to the shrews, though this possibility has not been documented.

Reindeer were introduced on the island in 1911 (Fay and Sease 1985). Here they prospered, their numbers reaching a peak abundance of over 2,000 animals in 1938, which was followed shortly by a "crash" to only a few animals. This over-extension of their carrying capacity greatly impacted the vegetation and shrew habitat (Fay and Sease 1985). The herd is now maintained at approximately 500 animals.

Arctic fox and localized house cat predation do not appear to pose serious threats to the long-term viability of the population.

Conservation Actions [top]

Conservation Actions: No specific protection measures are in place for this species. Approximately 10% of the preferred shrew habitat is on USFWS and NMFS land, where the species is potentially protected by use permit restrictions. Other general protection is provided by land use development restrictions identified in the Saint Paul Coastal Management Plan. ADF&G regulations regarding the taking of shrews as "unclassified game" requires a hunting license, but there is not a closed season or bag limit. However, except when it invades human food storage areas, this species is not of interest except to scientific collectors.

The distribution of shrews on Saint Paul is fairly well known and occurrences can be reasonably predicted throughout the range (Byrd and Norvell 1988). Additional surveys are needed on Otter Island where the presence of preferred plant communities suggest the shrew might occur (Byrd and Norvell 1988). Also, surveys should be conducted on Unalaska Island to determine if Sorex hydrodromus actually exists and, if so, to reevaluate its taxonomic relationship to S. pribilofensis.

Present protection needs include: 1. Identifying and protecting sufficient preferred habitat to insure maintenance of a viable population. 2. Minimizing the feral cat population. 3. Managing the reindeer herds to prevent overgrazing of shrew habitat. 4. Preventing introduction of rats onto the island.

Local distributional surveys on Saint Paul Island have been conducted with some statistical sensitivity (Byrd and Norvell 1988, 1993). General information on local distribution and habitat use patterns is available (Byrd and Norvell 1988, 1993). Present research needs include: 1. Total population size and trend estimates. 2. Continued assessment of habitat preferences. 3. Measurement of reproductive capacity. 4. Estimation of feral cat and arctic fox predation levels. 5. Long-term population viability analysis.

Citation: Woodman, N., Reid, F. & Matson, J. 2008. Sorex pribilofensis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 19 September 2014.
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