Pacific pond turtle (Clemmys marmorata) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Pacific pond turtles are most often found in streams, large rivers, slow-moving sloughs and quiet waters (Bury 1986b), although they occur in a wide variety of habitats including ponds, vernal pools, marshes, ephemeral creeks, reservoirs, agricultural ditches, sewage treatment ponds, canals and estuaries (Reese and Welsh 1997; IEP interim report). These turtles can tolerate saltwater for short periods of time, and commonly occur in brackish water (D. Holland pers. comm. to IEP). Habitats are often strewn with rocks or gravel (Bury 1986b), but contain some aquatic vegetation and sites for basking (Ernst et al. 1994).

Pacific pond turtles require deep pools with large woody debris to provide refugia from predators (Reese and Welsh 1998a). They are frequently associated with vegetated banks that may also provide protection from predators while allowing adequate exposure to sunlight for thermoregulation (ibid.). Along the Trinity River in California, Reese and Welsh (1998a) found that in sections of the river with lower water temperatures, turtles are more commonly associated with basking objects (rocks and logs) and baskable bank than sections of the river with warmer water temperatures. This suggests that in British Columbia, where water temperatures are lower than in California, suitable basking areas would be critical for Pacific pond turtles to maintain optimal body temperature.

Use of terrestrial habitat by Pacific pond turtles in northern California has been well documented by Reese and Welsh (1997). Movements on land are most common in summer and winter, with the summer peak corresponding to females seeking nest sites and the winter peak corresponding to both sexes seeking hibernacula. Female turtles spend time on land during every month of the year, whereas males do not use terrestrial habitat during July and August. Preliminary data from Lovich and Meyer (In Press) show frequent small movements of Pacific pond turtles between adjacent ponds and wetlands in the Mojave watershed, California. All of the radiotagged turtles in Reese and Welsh’s 1997 terrestrial habitat study overwintered in mixed, deciduous, and coniferous woodlands.

Trends

No studies have examined the extent of suitable habitat for the Pacific pond turtle in British Columbia. In the United States, damming and other water diversionary methods have created unsuitable habitat for turtles by increasing water velocity, decreasing water temperature, removing bank vegetation and creating barriers to terrestrial habitat (Reese and Welsh 1998a). In the Willamette Valley, seven dams control the waterway where a significant portion of the Oregon pond turtle population remains. Extensive loss of wetland habitat has occurred in California where less than 10% remains unchanged by agricultural development (Lovich and Meyer In Press). Habitat modification and destruction continue to limit the distribution of Pacific pond turtles in the United States (ibid.).

Protection/ownership

The Washington Department of Wildlife purchased 165 acres of land surrounding the turtle ponds in Klickitat County, Washington, for the Western Pond Turtle Project and is continuing to negotiate for ownership of the land surrounding turtle ponds in Skamania County (WPTP website). These are the only two sites in the state of Washington where the Pacific pond turtle remains. There is no formal protection of the Willamette Valley in Oregon; however, the population of Pacific pond turtles is continually monitored by the United States Army Corps of Engineers and the Oregon Department of Fish and Wildlife (USACE website).

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