The Pacific Water Shrew

Sorex bendirii

Background Information

The Pacific Water Shrew is a rare species found in the Fraser River Valley, British Columbia. It has a limited range, as seen in the figure below, due to very specific habitat requirements. This limited range extends over a large urban area (Galindo-Leal and Zuleta, 1997).  These small mammals have been recognized as a species in need of protection due to urbanization and development of land for human purposes; they are protected under the federal Species at Risk Act (SARA) and the British Columbia Wildlife Act.  It is listed as "threatened" by the Species at Risk Act (SARA), and "endangered" by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) (SARA, 2006).

The Pacific Water Shrew is found in moist areas, typically near streams, wetlands, and forests with plentiful fine litter on the forest floor. Populations are generally more abundant in mature and old growth stands of forest than in younger ones, although research conducted in different areas is conflicting.  Some research suggests that older and younger forests are equally suitable (Lindgren, 2004). The Pacific Water Shrew has been found at elevations up to 1300 meters A.S.L, but it is generally believed that they will not go above 850 meters. It is usually found within 50 meters of a slow moving source of water (Blood, 1995). Its main food source is freshwater insects in their larval stage, such as mayflies and stoneflies, making them useful in pest control in urban and agricultural areas (Lattik, 2001).

Threats to Habitat

Much of the land that used to be prime habitat for the Pacific Water Shrew has been developed for human purposes. The forest land along streams and wetlands has been developed as land for agriculture, subdivisions, and industrial sites. The population in the Lower Mainland is also growing rapidly. With this growth comes the need for more housing, causing urban grouwth into places that were not previously developed (Galindo-Leal and Zuleta, 1997). Over the past six years, about 25% of the Lower Mainland's natural vegetation has been lost as a result of this development. Many of the Pacific Water Shrew's habitat locations have been lost, and the remaining habitat areas are fragmented and isolated. These forest fragments are believed to be too small to support shrew populations, even though the minimum size of habitat area required to survive is unknown (Blood, 1995).

Another problem regarding the habitat of the Pacific Water Shrew is that runoff from urban and agricultural areas, septic tanks, industrial waste areas urbanization, and logging produce pollution and increase the soil's susceptibility to erosion. These processes negatively affect the water quality of the streams upon which the Pacific Water Shrew depends for food (SARA, 2006).  Agricultural runoff is a big problem regarding habitat suitability because of the ditching and drainage system developed specifically for agricultural practice. Chemicals from pesticides and fungicides can runoff into the ditches and dykes, which make the areas surrounding agricultural areas less suitable for living in (Blood, 1995).

Logging is another cause of the loss of habitat for the Pacific Water Shrew. Narrow strips of forest are typically left to protect fish habitat, but these are not wide enough for the Pacific Water Shrew. The Forest Practices Code assigns 30 to 50 meter wide buffer strips along streams, but some researchers consider that strips as wide as 60 to 100 meters may be necessary (Blood, 1995).  Poor logging practices can also increase soil erosion.

The domestic cat is a minor problem that can affect the population size of the Pacific Water Shrew.  The cat is a main predator of small mammals in suburban areas, and about 80% of its captured prey are shrews (Lindgren, 2004).

This analysis hopes to locate the most suitable habitat areas within the Pacific Water Shrew's current range in British Columbia.

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Jacquelyn Shrimer ~ jshrimer@sfu.ca ~ Geog 355