Posted on Sun, Feb. 05, 2006
Scientist: Frog's decline threatens Sierra ecology
By Juliana Barbassa
YOSEMITE NATIONAL PARK - The mountain yellow-legged frog has survived for thousands of years in lakes and streams carved by glaciers, living up to nine months under snow and ice and then emerging to issue its raspy chorus across the Sierra Nevada.
But the frog's call is rapidly going silent as a mysterious fungus pushes it toward extinction in its remaining refuge in national parks.
``It's very dramatic,'' said Lara Rachowicz, a Yosemite biologist who is leading an effort to save the tiny creature. ``One year, you visit a lake and the population will seem fine. The next year you go back, you see a lot of dead frogs scattered along the bottom of the pond. In a couple years the population is gone.''
There are about 650 populations left in Yosemite, Sequoia and Kings Canyon national parks, but most lakes have only one to five frogs -- not enough to guarantee their survival -- and 85 percent of them are already infected with the lethal fungus.
At one time, the frogs were so thick that tadpoles frothed shallow waters, and it was hard not to step on a frog on shore.
Their decline started when trout were stocked in Sierra lakes -- first carried in buckets by mule and then dropped by plane -- to supply fishermen. The voracious fish, which are still being introduced into the high Sierra outside park boundaries, are leaving only isolated groups of the frogs scattered over widespread lakes as high as 13,000 feet.
Despite living within the protective borders of some of the nation's most beloved parks, the remaining frogs can't resist the onslaught of the fungus and can't travel far enough in trout-infested streams to repopulate areas devastated by the fungus.
For the past five years, they've been disappearing at a rate of 10 percent a year, Rachowicz said at a gathering last month of 24 experts trying to save the frog.
The chytrid fungus, which has been linked to the extinction of amphibians in places as far away as Australia and Costa Rica, kills the frogs by growing on their skin, making it hard for them to use their pores and regulate water intake. The frogs die of thirst in the water, Rachowicz said, pointing to a photograph of an emaciated frog floating belly up in a shallow pool.
In a handful of years the frogs may be gone, leaving the high-elevation lakes in silence, and snapping the local food chain.
``There would be an unraveling of that web of life, because this species plays such an important role,'' said Roland Knapp, a research biologist with the Sierra Nevada Aquatic Research Laboratory.
The frog's disappearance would affect about 300 species in the rugged high country, from the insects they prey on to the garter snakes and coyotes that eat them, said Knapp, who led a survey counting the frogs in more than 6,500 bodies of water in the parks in 2000-02 and 2005.
What's frightening about the fungus's attack on amphibians is that it kills them quickly even in untouched habitats, scientists said.
``It's a mass extinction in the making,'' said J. Alan Pounds, main author of an article in the January issue of Nature that linked global warming to the fungus first named by scientists in the late 1990s.
Amphibians are facing an ecological disaster on a global scale. The Global Amphibian Assessment, a worldwide collaborative survey by hundreds of scientists completed in 2004, found that one-third of the world's 5,743 amphibian species are threatened and 168 are possibly extinct.
``I suspect that climate change is involved in general in these enigmatic declines,'' Pounds said. ``Ultimately, we have to have a transition to cleaner energy technologies, to cleaner sources of energy. But by then, it might be too late for the mountain yellow-legged frogs.''
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