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Scientists to perform first-of-its-kind study on turtles released into SF lake

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Western Pond turtles, like the one pictured, will be released into Mountain Lake in the Presidio on Saturday. (Natasha Dangond/Special to S.F. Examiner)

Wildlife specialists are hoping the revered adage that slow and steady wins the race will ring true this weekend for the western pond turtle.

The only freshwater turtle native to California, the species flourished in The City’s lakes decades ago. But years of destructive elements — including unwanted pets dumped in parks, the introduction of various diseases to wildlife and more recently the state’s historic drought — have virtually eliminating it from San Francisco.

That could change come Saturday when the first batch of turtles is introduced into Mountain Lake in the Presidio, one of three remaining natural lakes in The City that is nearing the end of a years-long cleanup and restoration effort.

“There are no longer native, established populations of turtles left in San Francisco,” said Jessie Bushell, director of conservation for the San Francisco Zoo who has spent the past three years helping to raise the nearly 60 turtles that will be released beginning Saturday.

“We’re hoping that by introducing the turtles to Mountain Lake, we can re-educate people about this shy and elusive but really interesting animal,” she said.

The turtles’ release will also mark the start of a first-of-its-kind scientific study of the creature.

Each turtle has been fitted with a dime-size transmitter that will allow scientists to track their movement and, hopefully, locate the turtles after they have lived in the lake for some time to check their stress levels, said Jonathan Young, a wildlife ecologist for the Presidio Trust.

Of the 30 or so turtles that will be moved to the lake Saturday, half have been living in a mesh cage at the lake for the past two weeks. They will be set free in what’s called a “soft release” to determine whether spending time acclimating to their new environment in the protection of a cage will give them a better chance of survival.

The other 15 turtles that will be released Saturday are still at the zoo and will be given a “hard release,” or simply placed in the lake without time to adjust.

In a month, scientists will collect as many turtles as possible and check their blood to determine their stress levels. Scientists will in turn use that information to design the release of the remaining 30 turtles, likely in September.

“If we find that putting them in an acclimation cage before being released is beneficial, then we can maximize their survival,” Young explained.

The turtles are the third native species to be introduced to Mountain Lake following the removal of invasive plants and animals, along with cleaning up a half-dozen feet of residue at the bottom of the lake caused primarily by sediment from state Highway 1, which cuts through the Presidio to the Golden Gate Bridge.

More than 150 three-spined stickleback fish, which provide insect control and food for native birds and reptiles, and the Pacific chorus frog were introduced in April. California floater mussels and rough-skinned newts are set for introduction later this year or next year.

Wildlife experts are urging residents not to release unwanted pets or other nonnative animals into Mountain Lake or other bodies of water in The City. Animals may be dropped off at a local rescue shelter or the SPCA.

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