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Turtles returned to their historic home at Mountain Lake

Turtles returned to their historic home at Mountain Lake

Twenty-eight young western pond turtles, whose ancestors once provided meat for Ohlone Indians and soup for Spanish explorers, swam freely for the first time this weekend into the clear waters of Mountain Lake in San Francisco’s Presidio.

The event marked a new step in the transformation of a once blighted, polluted, swampy and pest-filled urban sore into the unique experimental jewel that biologists are trying to create in the middle of the city.

For Dana Terry, a biology graduate student at Sonoma State University, and Jessie Bushell

, director of conservation at the San Francisco Zoo, the event was crucial to that recovery effort and a chance to help stem a population crisis that threatens the turtle species in California.

“They used to live happily around every lake and pond in the Bay Area, but no more,” Terry said as he prepared to move the young turtles from a set of plastic tubs he and a group of interns brought from the zoo to the water’s edge.

Every turtle had already been injected with a tiny dose of a hormone called corticosterone that is natural to them, Terry said, and each carries a tiny radio transmitter on its back so he can check on the group’s health and their responses to stress induced by a new environment.

“I hope they’ll be really happy in the lake because they’ll eat like fiends,” said Bushell, who had nurtured the turtles since they were hatched at the zoo as infants barely the size of a quarter, with soft shells no bigger than fingernails. Now 3 years old, their shells are hard and 5 to 6 inches across, she noted.

“We’ve tried to feed them as naturally as possible with natural foods — the same stuff they’ll be eating in the lake — like bugs and flies and crayfish larvae and bits of water plants,” she said.

Terry, clad in brown hip waders for the arduous job of freeing the turtles, explained his own task. Three weeks ago, he said, a first group of 14 turtles were “soft released” into the lake — not fully free but safe inside a pen moored to the shore beneath a thick tangle of alders and wax myrtles.

On Saturday, Terry and his helpers waded to the pen while Presidio assistants brought him the second group of 14 turtles by rowboat.

These would be “hard released” into the water at the same time as the penned turtles, Terry said, and all 28 would be free to fend for themselves, feasting on the lake’s abundant bugs, larvae and plants and basking on logs already installed nearby for their comfort.

“Eventually, perhaps, they may nest and reproduce — in another five years or so,” Bushell said hopefully.

Mountain Lake already has been cleared of almost all its urban pests, such as abandoned goldfish, unwanted carp and the nasty red-eared sliders — the turtles bought in pet stores that people later dumped. The lake has been successfully dredged, and its water is being aerated by pumps in a dozen spots.

Records show that Terry’s turtle species, Actinemys marmorata, was once abundant in Mountain Lake and in many other natural lakes and ponds in San Francisco. They provided food for the local Ohlone people and the early Spanish explorers and settlers, and during the Gold Rush were a restaurant feature. No one knows when they disappeared here.

But now that Mountain Lake is being restored, its sensitive wildlife is returning, and scientists are helping.

The natural fish known as three-spined sticklebacks — about 3,000 of them — have been reintroduced, and 1,000 Pacific chorus frogs are in the lake, too. The turtles are the next step, and there’s more to come.

As weekend visitors filled the lake’s southern shoreline and tennis players crowded the courts of nearby Mountain Lake Park,Jason Lisenby, a Presidio biology technician, was still worried.

“Please don’t start releasing your own pet goldfish and your own pet turtles or any other critters into the lake again,” he urged the visitors. “They won’t survive, and they’ll interfere with the natural life we’re returning to make the lake alive again.”