STATESMAN JOURNAL (Salem, Oregon) 13 January 08 Raising turtles in captivity may help restore numbers - Zoo officials say it lets turtles grow too big to fit in bullfrogs' mouths (Henry Miller)
Bullfrogs love baby western pond turtles to death ... as an appetizer, main course, side dish and dessert.
So much so that the native turtles are listed as a species of concern in Oregon and are on Washington state's Endangered Species List.
So officials with both the Oregon Zoo in Portland and the Woodland Park Zoo in Seattle came up with a plan.
They collect native turtle hatchlings in the wild, raise them for a year until they're about 4 inches, which by gape-and-gullet standards is too big to fit in a bullfrog's mouth. Then they release them into the wild.
"They went from less than 100 to more than 1,500," said Dr. David Shepherdson about pond turtles at the three release sites in the Columbia Gorge.
Shepherdson is the conservation program scientist at the Oregon Zoo, which raises 50 to 60 pond turtles each year in a program called "head-starting."
"In terms of cost, the program costs us about $15,000 a year," Shepherdson said. "So it works out to roughly $200 to $250 a turtle.
"Which isn't too bad, but we can't keep doing that forever. Really, head-starting is just to get us back over this hump to where the turtle numbers are at the level at which they can produce a lot of offspring in the wild."
Because the turtles don't hibernate, but grow year-round at the zoo, they achieve the size of 2-year-olds during the nine to 11 months that they are raised from hatchlings. A bonus is that having the turtles at the zoo provides a great teaching moment, he added.
"People love to look at them," Shepherdson said. "And it's great for us because it's a great way to tell people the story about invasive species."
But just turning turtles loose once they've outgrown being on a bullfrog's menu isn't enough.
Because the chance of those turtles' hatchlings making it to adulthood in the presence of bullfrogs are slim to none, he said.
So the second half of the effort is to keep frog numbers in check.
"There has to be some form of bullfrog control," Shepherdson said. "Once turtle numbers are up to their historic levels -- then a bit of good bullfrog control will allow them to become self-sustaining populations."
There's several ways to crimp the non-native invasive bullfrogs.
"You can gig for the adults," he said about spearing them. "Although that's pretty time-consuming."
A more effective alternative is to remove the eggs, which are laid on the surface of ponds in the late spring.
"And then there's probably the most effective strategy in the long-term, to manage the water levels in the wetlands to the disadvantage of bullfrogs," Shepherdson said.
Bullfrogs normally take two years to change from tadpoles to frogs, which makes them vulnerable to water fluctuations when they're in the middle of their development, unlike native frogs that take a year to make the transition.
And ironically, manipulating water levels mimics what historically happened naturally before man changed the environment, Shepherdson said.
"You know we have that time in September or October when it doesn't rain at all, so our wetlands get pretty dry at that time," he said. "And if you drain a pond for a time in the late summer, you'll kill a lot of the bullfrog tadpoles before they have a chance to metamorphose."
In re-establishing western pond turtle populations using head-started offspring, both bullfrog controls -- collecting and destroying eggs and dropping water levels -- are being used.
"It's a very effective technique for increasing the number of turtles," he said about head-starting. "But you do have to keep up with the habitat restoration, which in this case is the removal of the bullfrogs, or a reduction in their numbers at any rate."
Late last summer, the latest batch of 50 turtles raised for 10 months at the Oregon Zoo were released at a site at Pierce National Wildlife Refuge near Ridgefield, Wash.
It was the final release at the third site in Washington. Next year, they'll start releasing the turtles at a new site, the last scheduled in the series for the head-starting program.
"Once you set up four breeding populations of turtles, that's the goal," Shepherdson said. "We have three, and we need to establish one more.
"So I'm thinking, I'm hoping, that we'll be done with the captive-rearing program in four or five years."
Raising turtles in captivity may help restore numbers