Confronting a New Threat to Western Pond Turtles

Western Pond Turtle (Actinemys marmorata)


About the Species

Western pond turtles range from Washington’s Puget Sound to the northern reaches of the Baja California peninsula on America's West Coast. Turtle hatchlings leave the nest when they are about 20-25mm long, leaving them prone to predation by invasive bullfrogs. The population has dramatically declined due to this predation and habitat fragmentation. For more than 20 years, local zoos have implemented a head-start program in which wild turtle eggs are brought into controlled conditions and the hatchlings are reared over winter. They are returned to the wild when they are large enough to escape hungry bullfrogs.

More recently, a new danger has emerged in both wild and zoo environments: a potentially fatal disease that damages the shell of adult turtles. This is a concern to conservationists because western pond turtles are long lived (40+ years) and reproduce slowly; thus losing an adult means a loss of as many as 30 years of hatchling production.

CBSG's Role
At the invitation of the Recovery Team coordinating conservation activities in Washington, CBSG facilitated a Population and Habitat Viability Assessment (PHVA) workshop for the state’s western pond turtle population. Key objectives for the workshop included an evaluation of the current status of both the species and the conservation program, as well as a clarification of the state Recovery Team’s future research and management agenda.

Workshop participants created a detailed “threat map” of the diverse biological and institutional challenges to species conservation. CBSG created detailed demographic simulation models using the population viability analysis (PVA) toolVortex. These models revealed the critical importance of adult survivorship to long-term species viability.

The Results

A number of key management actions were identified and prioritized through the PHVA process. The results of the modeling reinforced the importance of mitigating the threat of hatchling predation by invasive bullfrogs. Moreover, the PVA results stimulated the group to begin urgently coordinating a research program to evaluate the behavior and impacts of the emerging ulcerative shell disease. The workshop discussion highlighted the need for improved information sharing among stakeholders, resulting in the formation of a set of thematic subgroups to address research questions and management recommendations.

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