WHITE SALMON, Klickitat County — In ponds close by the Columbia River Gorge, Washington state biologists have gone to extraordinary lengths to revive endangered populations of western pond turtles.

They have hired contractors to kill bullfrogs — an invasive species introduced from other parts of the country, that feast on the young turtles. They have attached radio transponders to turtles’ shells to track their movements. And each summer, they trap some of the turtles afflicted with a shell disease, and send them for a lengthy stay at the Oregon Zoo in Portland for specialized medical care.

The western pond turtles, which dine on insects, crayfish and other small creatures, are a broader indicator of the health of wetlands, which are important to a wide range of species. They are one more intriguing example of the diversity of wildlife native to our region.

“They are very charismatic,” said Stefanie Bergh, a state Department of Fish and Wildlife district biologist, as she held a restless turtle recently recovered from a trap baited with a hole-punched can of sardines. “They are just a really cool species that not everybody gets to experience.”

These turtles, which can live for more than a half century, were once found throughout much of Western Washington, including in ponds all over the Puget Sound region and Southwest Washington. Development and dams destroyed much of their habitat, some were grabbed by humans to be sold as pets or for their meat, and ravenous bullfrogs found their way to the turtles’ remaining refuges.

In 1993, they were listed as endangered in Washington state, all but gone from the Puget Sound region, and down to about 150 turtles found at two Columbia Gorge sites. During that decade, the Woodland Park Zoo in Seattle, and then the Oregon Zoo, stepped in to start breeding turtles in captivity, and to take in freshly hatched wild turtles, and raise them over the winter to give them a head start free from predators.

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Through the years, the work to save the turtles has been financed from numerous sources including the Bonneville Power Administration, federal and state grants, and funds from fees charged for personalized license plates (but not from the sale of fishing and hunting licenses). Partners helping the turtles include the two zoos as well as the University of Illinois.

All of these efforts appear to be having some success, as an estimated 800 to 1,000 western pond turtles now dwell in Washington. They are found in six locations, with the biggest population living in ponds in Klickitat County owned by the state, which does not publicly disclose the location to keep away poachers.

Last week, Bergh, assisted by two Oregon State University students, went to the Klickitat County ponds to check up on the turtles. They are tucked away in a scenic spot, a pond ringed by cottonwood trees and covered with lily pads blooming with yellow flowers.

This has been a prime spot for bullfrogs, which can lay thousands of eggs  in a single cluster. But contractors now arrive several times a week during the summer months to remove egg masses, net tadpoles and use night spotlights to find and spear adults.

With the aid of transponders, the biologists can track female turtles to their nests, then place mesh over the openings so that hungry mammals don’t devour the eggs.

“It’s an  ongoing battle … 100 percent,” Bergh said.

As turtle populations have rebounded, there has been another big concern – a disease that creates lesions and soft spots on shells and can cause the turtle to give off a foul odor. It may be caused by a fungal infection, and biologists say it may have initially resulted from the stresses put on some of the captive turtles held in the zoos.

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The disease has been spotted in photo archives that date to 2003, and by 2014 it was found in up to 49 percent of the turtles in the six Washington sites, and even more in recent years.

On last week’s visit to the Klickitat site, some of the diseased turtles were trapped. They are being sent to the Oregon Zoo where they will undergo surgery to debride their lesions, and be treated with an antifungal medication.

“We have seen some turtles where the disease has stopped progressing,” Bergh said. ” But really right now we don’t know the long-term efficacy of the treatment. We are just trying to do our best to help the turtles out.”