Once thriving in the millions from Mexico to Canada, they are now extinct in British Columbia, critically endangered in Washington state and considered a "species of special concern" by the California Department of Fish and Game, researchers say.
So the sight of six wee baby pond turtles paddling around Thursday in three shallow, water-filled plastic tubs in a back workroom at the Oakland Zoo is a beacon of hope to scientists. It's the early result of a new captive-breeding program - the first of its kind for the species - developed by a professor at Sonoma State University in conjunction with Oakland and San Francisco zoos to give the little guys a head start in life and rebuild their population.
"We decided we needed to do something before it was too late," said Margaret Rousser, lead keeper of Oakland's children's zoo, where the six turtles are being raised. More will arrive in the next week or so as they continue to hatch in a lab at Sonoma State's Rohnert Park campus.
The pond turtles, which grow to about 12-inches in length and can live up to 60 years, have suffered because of man's encroachment on their habitat in marshy, boggy areas and the introduction of several non-native species to their environment.
"For instance, people get Eastern Bull Frogs as pets, and then when the frogs get too big to manage, they let them go in the wild," Rousser said. "But those frogs are native to the Midwest and they're voracious predators of the pond turtle, eating the young ones up in one bite. Or they get to the eggs before they even hatch, so the turtles never get a chance.
"Also, the Red-eared Slider turtles are a problem," she said. "They are also non-native, and a very common turtle pet. Again, when they get big, people let them loose in a local stream where they compete for resources with the pond turtle.
"And the Sliders have been winning," she said.
Championing the cause of the pond turtle, Nick Geist, a biology professor at Sonoma State - with help from his graduate students and Oakland Zoo staffers - spent the summer monitoring a Lake County site for mother turtles, following them to their nests and collecting eggs. Geist then placed 57 viable eggs in five incubators in his lab, and the first six hatched about a week ago. They were delivered to Oakland, and the next group will go to San Francisco. They'll be cared for at the zoos for about a year, until large enough to be released back where the eggs were originally found.
"After raising them under optimal conditions for nine or 10 months, they can get to the size they would grow in the wild in maybe three or four years," Geist said. "At that point, their shell has hardened and they are virtually immune to predators. But as babies, they're tender morsels. The bull frogs chow down on them like they're popcorn."
Until recently, the plight of the pond turtle has been somewhat overlooked, Geist said. "Part of the problem is, (turtle) numbers can be kind of deceptive," he said. "Because they live so long, you can look at a population and it looks fine. But if you analyze it, you realize you're seeing only old turtles basically waiting to die. Not any younger babies."
The head start program is modeled after a similar effort in Seattle. Geist first got involved while researching the temperature at which the pond turtle's sex is determined.
"Here's the only aquatic turtle we have in California, and we really know very little about its biology," Geist said. "Instead of having a sex chromosome like we do, the sex of the baby turtle is determined by the temperature in the nest during the incubation period. We know that warmer temperatures determine females, and cooler gives you males. But nobody knows what that critical temperature is."
In terms of conservation, that can be a problem, he said. "If you end up with 100 percent males, that's not going to do the turtle population any good," he said.
This research may also provide scientists with more information on the potential effects of global warming. "If the variation of just a few degrees makes a difference in the sex ratio, it might help us find out what warming of the entire planet might do to a delicate species like this," Rousser said.
Reach Angela Hill at email@example.com.