Apple Valley, MN, December 13, 2012—Computer simulation models for a turtle species native to the west coast have revealed that when it comes to saving the species from extinction, keeping adult turtles alive longer is equally as important as rescuing the babies from hungry predators.

The Conservation Breeding Specialist Group (CBSG), part of the International Union for Conservation of Nature’s (IUCN) Species Survival Commission (SSC), recently conducted a workshop to help guide conservation planning for the western pond turtle(Actinemys marmorata), which is endangered in Washington state.  

Habitat loss and high levels of predation on western pond turtle hatchlings by invasive bullfrogs and other local species have caused their numbers to decline in Washington.

This led to intensive conservation efforts by Seattle's Woodland Park Zoo, Oregon Zoo, and the Washington Department of Fish and Wildlife to ensure hatchling survival beyond the bite-sized phase of their youth.

Woodland Park Zoo invited CBSG to facilitate a PHVA workshop, where those involved in these efforts could evaluate the program and assess threats to the species with the best available scientific information and tools.

Population and Habitat Viability Assessment (PHVA) workshops like this one provide scientific analysis for the creation of detailed conservation recommendations for endangered species. One component of PHVA is the implementation of computer simulation models, which are used to predict species population size outcomes under different scenarios.

CBSG Program Officer Dr. Phil Miller and CBSG member Sara Zeigler created a population model to predict how Washington’s pond turtle population would grow or shrink if this trend of high hatchling mortality persisted. They created another model to evaluate a prediction that the population would still grow to abundance even if adult turtles didn’t live very long. The results were surprising.

“While the model identified high hatchling predation-based mortality as a major cause for current population declines,” said Miller, “Our analysis also identified adult survivorship as a primary driver of future population growth.”

Western pond turtles are long-living (40+ years) and reproduce slowly. Losing an adult means a loss of as many as 30 years of hatchling production. The model showed that though hatchling deaths negatively affected the population, maintaining high survival rates for adult turtles will be critical if the species is to be saved from extinction.

This news caused great concern for the workshop participants, since a disease commonly referred to as “shell-rot” has recently been found in some reintroduced adult turtles. As its name suggests, this disease causes ulcerative lesions in a turtle’s shell that may lead to the animal’s death. The causes, detailed effects, and possible scope of this condition remain a mystery.

In reaction to the model results, participants immediately began formulating plans for investigating shell disease. If the condition is found to be fatal to adult turtles, a greater effort will be placed on mitigation of the threat, knowing that adult longevity is vital to the long-term survival of the species.

For the past 20 years, Woodland Park Zoo, Oregon Zoo, and the Washington Department of Fish and Wildlife have safeguarded western pond turtle hatchlings. This is called “head-starting.” Eggs are gathered from wild turtle nests, and the hatchlings are raised in captivity until they become too big for bullfrogs to eat. Turtles are then released back into the wild.

Thanks to head-starting, the population has increased over the past twenty years in Washington from only 150 turtles to 1,500.

At the workshop, zoos currently participating in the head-starting efforts, including San Francisco and San Diego Zoos who work with western pond turtle conservation in California, have pledged to work together more closely to share information, expertise, and experience in order to manage their turtle populations more effectively.

The workshop was hosted by Woodland Park Zoo and funded by the zoo and other project partners including Washington Department of Fish and Wildlife, Oregon Zoo, and the NW Zoo & Aquarium Alliance. Members of the Western Pond Turtle Recovery Team, along with associated species experts and stakeholders, participated in the workshop and contributed their expertise and experience.

CBSG is a Specialist Group of the International Union for Conservation of Nature (IUCN) Species Survival Commission (SSC). CBSG provides species conservation planning expertise to governments, Specialist Groups, zoos and aquariums, and other wildlife organizations by using professional facilitation and the application of science-based planning tools.