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BC Conservation Data Centre: Conservation Status Report

Sorex bendirii
Pacific Water Shrew


 
Scientific Name: Sorex bendirii
English Name: Pacific Water Shrew
   
Provincial Status Summary
Status: S2?
Date Status Assigned: April 27, 2015
Date Last Reviewed: February 15, 2015
Reasons: A relatively rare shrew dependent on suitable riparian/aquatic habitat whose range is confined to BC's lower mainland, where there are large-scale ongoing threats due to development and agriculture.
 
Range
Range Extent: D = 1,000-5,000 square km
Range Extent Comments: Range extent is approximately 4000 sq km, estimated using an alpha-hull with alpha=3 (3000sq km using an alpha of 2). The 2009 Recovery Strategy quotes an extent of occurrence of ~5700 sq km (Pacific Water Shrew Recovery Team 2009); this is consistent with the result obtained using a Minimum Convex Polygon. These estimates are based on both historical and recent occurrences. Restricted to southwestern British Columbia in the Fraser Lowland, Northwestern Cascade Ranges, and Southern Pacific Ranges Ecosections. It ranges as far east as the Chilliwack River and Harrison Lake; northern limit of its range is in Squamish, at elevations below 900 m (COSEWIC 2006; Craig and Vennesland 2007; K. Welstead, pers. comm., 2008). Precise eastern limits of the range on the south side of Fraser are not clear. There are unconfirmed sightings from the Skagit River valley; however the Skagit River valley is also within the range of the American Water Shrew (Sorex palustris) and identifications based on captures are needed to confirm the occurrence of S. bendirii there. Precise northern limits of this species range in the Coast Mountains are also unknown.
Area of Occupancy: E = 26-125
Area of Occupancy Comments: [E]
There are 31 2x2km grid cells occupied if historical occurrences are excluded from the analysis. Although TEM ratings were developed for this species by Craig (2007), most of the range has not been mapped; therefore, habitat capability/suitability modelling is not possible for the complete BC range.
 
Occurrences & Population
Number of Occurrences: C = 21 - 80
Comments: About 44 element occurrences (EO) but these include historical museum specimens dating back to 1888 and recent occurrences. Number of extant EOs is unknown. 26 EOs are recent i.e. since 1990.
Number of Occurrences with Good Viability / Ecological Integrity: U = Unknown
Comments: Because the population size at each EO is unknown and indeterminate, viability has to be based on ecological integrity. Habitat assessments need to be done at EOs to assess the quality of occurrences. Historical EOs will be problematic as most have no associated coordinates and their locations can only be estimated to the nearest 1-10 km.
Number of Occurrences Appropriately Protected & Managed: CD = 4 - 40
Comments: A total of 5 provincial and 26 regional parks occur within the species' BC range extent. Actual EOs in protected areas is 7 (2 provincial and 5 regional parks) (COSEWIC 2006).
Population Size: U = Unknown
Comments: No population estimates exist for this species in any part of its range. Various studies (Aubry et al. 1991) in Washington and Oregon suggest it is rare. In BC, Seip and Savard (1990, unpublished data) sampled 22 sites from 1989-1991 in the north shore mountains within the elevational range of this species and captured only 5 S. bendirii at 2 of their 22 sites. Zuleta and Galindo-Leal (1994) surveyed 55 sites at 22 locations throughout the range in 1992 and captured only 3 S. bendirii at 3 sites.
 
Threats (to population, occurrences, or area affected)
Degree of Threat: Substantial, imminent threat
Comments: [A]
Major threats are the loss, fragmentation, and degradation of habitat from human population growth and the associated development of urban- suburban residential areas, malls, golf courses, and roads. Habitat loss includes forested, riparian, and wetland habitats. Water quality is also degraded. Forest harvesting and agriculture have also contributed to habitat loss and degradation (Pacific Water Shrew Recovery Team 2009). Predation by domestic cats was listed in an early COSEWIC report (Galindo-Leal and Runciman 1994) but no data exist on predation rates of cats on S. bendirii. Other threats include mortalities in minnow traps during fish surveys (Pacific Water Shrew Recovery Team 2009).
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: U = Unknown
Comments: No data are available to quantify the short term (10 years) trend in populations size, extent of occurrence, area of occupancy, number of occurrences and/or condition of occurrences. There has been no systematic inventory throughout the BC range in the past 10 years and no systematic assessment of habitat conditions at recent and historical EOs. Nevertheless, based on human population growth rates of ~11% over the past decade for the Greater Vancouver Regional District and Fraser Valley Regional District and the associated loss of habitat (COSEWIC 2006), it is likely that the amount of habitat has declined in the past decade.
Long-Term Trend: DE = Decline of 30-70%
Comments: [DE]
No data are available to quantify the long term trend in populations size, extent of occurrence, area of occupancy, number of occurrences and/or condition of occurrences. No data exist on long term changes in actual known S. bendirii habitat in BC. But various sources (Boyle 1997; Fisheries and Oceans Canada 1998; Moore et al. 2003) demonstrate that there have been major declines in wetlands (87%) and fish-bearing streams (up to 86%) in the lower mainland over the long term beginning in the 1800s and continuing for the past 2-3 decades.
 
Other Factors
Intrinsic Vulnerability: BC=Moderately vulnerable to not intrinsically vulnerable.
Comments: Species matures quickly and reproduces frequently with a generation time of one year but its dispersal abilities may be moderate.
Environmental Specificity: B=Narrow. Specialist or community with key requirements common.
Comments: Most captures are associated with streams and wetlands in coniferous and deciduous forests. A semi-aquatic shrew that can swim and dives underwater to capture aquatic invertebrates, this species is usually captured in close proximity to water (0-50 m). The TEM habitat ratings and Best Management Plan (Craig 2007; Craig and Vennesland 2007) assume that suitable habitat is <100 m from water.
Other Rank Considerations: In 2006, uplisted to Endangered from Threatened by COSEWIC.
 
Information Gaps
Research Needs: See Recovery Strategy (Pacific Water Shrew Recovery Team 2007) for a list of data gaps.The habitat suitability/capability models developed by Craig (2007) from TEM data need to be tested and validated with a standardized species sampling design. Current S. bendirii sampling for environmental assessments are inadequate to test the models because they are required only in Low rated habitats or habitats rated Nil within 100 m of water (Craig and Vennesland 2007). A representative sample of Nil, Low, Moderate, and High rated site series need to be sampled to test the validity of the habitat ratings. Research is also required on dispersal movements of S. bendirii to determine the barriers to movement, the suitability of marginal anthropogenic habitats such as drainage ditches as dispersal corridors, and the validity of a 100 m protective setback. More research is needed to develop and test various sampling methods such as pitfalls traps, minnow traps, and DNA sequencing of faecal pellets.
Inventory Needs: The only comprehensive inventory was the 1992 survey by Zuleta and Galindo-Leal (1994). However, limitations of their study were no surveys in any of the GVRD Parks and no information on the proximity of their trap sites to standing water. A comprehensive standardized inventory applying both species sampling and habitat asessments is required throughout the entire BC range and peripheral areas such as the Skagit River valley and the north shore mountains. The inventory should include historical EOs and any significant protected areas.
 
Stewardship
Protection: Most of this species' range is on private land. Some 16 sites have been proposed by the Recovery Team as areas with critical habitat (see Recovery Strategy for specific details); 14 of these areas are on private land and their degree of protection is unclear. S. bendirii is an identifed wildlife species in the BC Identified Wildlife Management Strategy but only two Wildlife Habitat Areas (WHA) have been proposed.
Management: Management needs mainly involve habitat protection and habitat restoration particularly in areas undergoing urban development. The Best Management Practices Guidelines developed by Craig (2007) provide recommendations on habitat buffers (100 m), watercourse and wetland crossings, connectivity, and restoration. Specific wildlife measures for management in WHA's are outlined in the Identified Wildlife Account for S. bendirii (Lindgren 2004). WHA'a are to extend along the enitire length of a stream and include a 30 m protective zone with no forest harvesting plus a 45 m management zone.
 
Version
Author: Nagorsen, D. and A. Teucher
Date: March 02, 2015
 
References
Boyle, C. A., L. Lavkulich, H. Schreier, and E. Kiss. 1997. Changes in land cover and subsequent effects on lower Fraser Basin ecosytems from 1827 to 1990. Environmental Management 21:185-196.
COSEWIC. 2006l. COSEWIC assessment and update status report on the Pacific water Shrew Sorex bendirii in Canada. COSEWIC Committee on the Status of Endangered Wildlife in Canada Ottawa. 28 pp.
Craig, V. 2007. Species account and preliminary habitat ratings for Pacific water shrew (Sorex bendirii) using TEM data v.2. Draft. Ecologic Research, Surrey. 42 pp.
Craig, V., and R. Vennesland. 2007. Best management practices guidelines for Pacific water shrew in urban and rural areas. Working Draft. British Columbia Ministry of Environment, Surrey. 39 pp.
Fisheries and Oceans Canada. 1998. Wild, endangered and lost streams of the lower Fraser Valley. Summary Report 1997. Lower Fraser Valley stream review, Vol.3. 29 pp.
Galindo-Leal, C. and G. Zuleta. 1997. The distribution, habitat, and conservation status of the Pacific Water Shrew, Sorex bendirii, in British Columbia. Can. Field-Nat. 111(3):422-428.
Galindo-Leal, C., and J.B. Runciman. 1994. Status report on the Pacific Water Shrew, Sorex bendirii, in Canada. Unpubl. rep. submitted to Comm. on the Status of Endangered Wildl. in Can., Ottawa. 27pp.
Lindgren, P. 2004. Pacific Water Shrew (Sorex bendirii) account, Identified Wildlife Management Strategy Accounts and Measures for Managing Identified Wildlife. British Columbia Ministry of Water, Air and Land Protection.
Moore, K. E., P. Ward, and K. Roger. 2003. Urban and agricultural encroachment onto Fraser lowland wetlands-1989 to 1999. Proceedings of the 2003 Georgia Basin/Puget Sound Research Conference. Abstract and Powerpoint presentation.
Nagorsen, D.W. 1996. Opossums, Shrews and Moles of British Columbia. Royal B.C. Mus. Victoria, BC. 169pp.
Pacific Water Shrew Recovery Team. 2007. Recovery strategy for the Pacific Water Shrew (Sorex bendirii) in British Columbia. October Draft. 26pp.
Pacific Water Shrew Recovery Team. 2009. Recovery strategy for the Pacific Water Shrew (Sorex bendirii) in British Columbia. Prepared for the B.C. Ministry of Environment, Victoria, BC. 25pp. + append.
Seip, D. R., and J. Savard. 1990. Maintaining wildlife diversity in old growth forests and managed stands. Annual Progress Report 1989-1990. British Columbia Ministry of Forests, Research Branch, Victoria. 46 pp.
Zuleta, G.A., and C. Galindo-Leal. 1994. Distribution and abundance of four species of small mammals at risk in a fragmented landscape. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. Working Rep. WR-64. Victoria, British Columbia. 80pp.
 

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Suggested Citation:

B.C. Conservation Data Centre. 2017. Conservation Status Report: Sorex bendirii. B.C. Minist. of Environment. Available: http://a100.gov.bc.ca/pub/eswp/ (accessed Dec 10, 2017).