Category: Status Reports
Published: January 2017
Author(s): Lisa A. Hallock, Anita McMillan and Gary J. Wiles
The Western Pond Turtle (Actinemys marmorata) is a medium-sized, semi-aquatic turtle and is one of two freshwater turtle species native to Washington. Western Pond Turtles were historically distributed through central and southern Puget Sound from Snohomish to Thurston counties, along the Columbia Gorge in Skamania and Klickitat counties, and in Clark County. Currently, the species occurs at six locations in the state, including three sites in Skamania County, and one each in Klickitat, Mason and Pierce counties. The turtles inhabit lakes, ponds and wetlands. They also require the availability of adjoining open upland habitats.
Western Pond Turtles were listed as endangered in Washington in 1993. They were likely locally common in parts of their Washington range historically, but due to factors such as habitat loss, overharvest and introduction of non-native plants, fish and bullfrogs, only about 150 turtles persisted at the two remaining Columbia Gorge sites by 1994. The Puget Sound population was effectively extirpated with the exception of 12 turtles that were opportunistically collected and placed into a captive breeding program at Woodland Park Zoo. Through various recovery actions, including release of captive-bred and wild-bred head-started turtles, the statewide population in 2015 had increased to a total of 800-1,000 turtles at six locations. Two of the sites, Sondino and the Pierce County site, each contain about 250 turtles and together hold half or more of the state's population. These sites are the only ones with population estimates above recovery objectives.
Recovering this species is challenging because of the turtles' slow rate of growth, delayed sexual maturity, limited ability to disperse, complex habitat requirements and the high mortality of eggs and hatchlings. Additionally, Washington populations are at the northern extreme of the species' range. The cool summers typical of maritime climate can slow embryo development and result in high variation in hatchling success especially in South Puget Sound. Such variability may have had less impact on the species' persistence when pond turtles were more common because the long life span of the turtles provided many decades of nesting opportunities. As a result of these intrinsic factors, the recovery process is slow and many decades of effort will be required.
Important known or suspected threats to Western Pond Turtles in Washington include diseases; predation and competition with other species, especially the non-native American Bullfrog (Lithobates catesbeianus); habitat loss and degradation; and small population size and low genetic variation. Recently, shell disease has emerged as a major concern and was found to infect 29-49% of examined turtles in each of the six populations in 2013-2014. At present, it is unclear whether shell disease is causing turtle mortality and negatively affecting reproduction and recruitment, although it is suspected. It appears to occur mostly in head-started turtles, though the relatively few truly wild turtles confound this apparent association.
A variety of recovery actions have directly benefited Western Pond Turtle populations in Washington. All populations continue to be supplemented with head-started juveniles raised at Woodland Park Zoo and Oregon Zoo. From 1991 to 2015, a total of 2,200 captive-bred and wild-bred head-started turtles were released through this program. Investigations are underway to monitor the extent and impacts of shell disease and determine the cause and best treatment of the disease. Other recovery activities include conservation planning; habitat management, restoration and creation of wetlands; population monitoring; research; and predator management focusing primarily on bullfrog removal.
While progress has been made in recovering Western Pond Turtles, the Washington recovery plan goals for downlisting them to threatened have not been met. The statewide population size remains too small and is still heavily reliant on supplementation with head-started individuals. Natural recruitment remains low due to factors such as low hatching success and predation on hatchlings. The recovery sites continue to need annual management to maintain suitable habitat conditions, especially for nesting. Lastly, the consequences of shell disease are not well understood at this time, but likely will setback recovery if the disease impacts reproductive output and/or the lifespan of the turtles. Consequently, it is recommended that the Western Pond Turtle remain a state endangered species in Washington.
Hallock, L. A., A. McMillan, and G. J. Wiles. 2017. Periodic status review for the Western Pond Turtle in Washington. Washington Department of Fish and Wildlife, Olympia, Washington. 19+v pp.