Pacific pond turtle (Clemmys marmorata) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

The number of Pacific pond turtles along the west coast of North America has dropped dramatically since the late 19th century when this species was “almost constantly for sale in the markets of San Francisco” (True 1884 cited in Carr 1952). The Canadian population of Clemmys marmorata has been extirpated for nearly 50 years and the entire species has become rare or extirpated in the northern- and southernmost parts of its range. After surveys were conducted in Washington state between 1985 and 1990, it was confirmed that the species was no longer present in Puget Sound (where it had been formerly abundant) and that the only two remaining populations were in the Columbia Gorge (Washington Dept. of Wildlife 1991). The number of turtles remaining in these populations totaled 150-200 individuals, which was further reduced when a respiratory disease killed approximately 25% of the turtles in 1990 (WDW 1993). Through captive-breeding, protection of nests in the wild and predator control by the Western Pond Turtle Project, the number of turtles has increased to 450-500 individuals (K. Slavens, unpub. data). 

The current Oregon population is thought to have decreased to less than 10% of its historical size (or approx. 2,000 individuals) (Woodland Park Zoo website). The greatest decline has occurred in the Willamette Valley where damming is extensive. The Willamette Valley Project, conducted by the United States Army Corps of Engineers and the Oregon Department of Fish and Wildlife, is currently monitoring and managing the population. Between 22 and 28 Pacific pond turtle nests have been located by USACE each year since 1992 (USACE unpubl. data).

There are no current population estimates for the Pacific pond turtle in California, Nevada or Baja California; however, this species has decreased and continues to decrease in abundance as 90% of this state’s wetland habitat has been eliminated due to agricultural development (Lovich and Meyer In Press). This turtle remains locally abundant in some parts of northern California, however. In one watershed in the early 1970s, the abundance of Clemmys marmorata was estimated at 215 turtles per hectare of water and in one instance 50 turtles were found in one deep pool of a stream (Bury 1986b). The only population information from Nevada suggests that isolated populations from the Truckee and Carson Rivers may have become extirpated (Buskirk 1991 cited in Ernst et al. 1994). There are also no population estimates available for Baja California.

In the first survey of reptiles and amphibians of British Columbia, Lord (1866), naturalist of the British Boundary Commission, recorded under Actinemys marmorata “I have seen them in nearly every lake and pond east and west of the Cascades. They are also common on Vancouver Island.” (Cook, unpubl.). His description of this turtle, “The general colour is olive, with darker markings, the under-portion being a brilliant yellow”, does not provide enough detail to confidently identify the species as Clemmys marmorata. F. Cook (pers. comm.) states that this description could possibly apply to the western painted turtle (Chrysemys picta bellii), the only other freshwater turtle in the area. However, C. p. bellii has a large dark pattern or blotch on its plastron, bright red in the marginals, bright yellow lines on the head and neck, and no dark markings on the carapace (Ernst et al. 1994; Carr 1952; Cook 1984), none of which fit with Lord’s description. Indeed, Lord’s description of A. marmorata is virtually identical to that given for C. marmorata in modern descriptions (Carr 1952; Ernst et al. 1994). No specimens of C. marmorata (or A. marmorata) from the Boundary Survey were deposited in the British Museum, although Lord did misidentify one juvenile C. p. belli collected from Vancouver Island as A. marmorata, a mistake that was noted by Storer (1937; F. Cook pers. comm.). Juvenile C. marmorata have a dark plastral figure similar to C. p. bellii that is lost as the turtle matures (Carr 1952). It seems that, as C. marmorata and C. p. bellii were the only two species of freshwater turtle in southern British Columbia during the mid-1800s, and as the turtle Lord described as having a brilliant yellow plastron could not have been C. p. bellii, C. marmorata must have been formerly common in southern British Columbia and even Vancouver Island. However, the lack of specimens of C. marmorata in museum collections of Lord’s samples raises serious questions regarding his claims. As these 2 turtle species are quite distinct, then if C. marmorata was not on Vancouver Island, Lord was either extremely careless, or incompetent or dishonest. Unfortunately, there is no clear answer to this conundrum.

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