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Yellow-legged frog under threat
07/02/2006 10:45 - (SA)
California - 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 range.
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.
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% of them are already infected with the lethal fungus.
At one time, the frogs were so thick that tadpoles frothed the water in 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 scattered over widespread lakes as high as 3 900m.
Deadly fungus
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% 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.
While the species deserves to be designated as endangered, the United States Fish and Wildlife Service lacks the funds to complete the process and the frog lingers on a waiting list.
Federal officials also questioned whether listing it as endangered would help, since the immediate threat to its survival isn't coming from agriculture or development that threatens other species and can be curbed.
Food chain could be broken
In a handful of years the frogs may be gone, leaving the high elevation lakes in silence, and snapping the local food chain.
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 to 2002 and 2005.
What's frightening about the fungus' 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.
His research in the misty jungle of Costa Rica's mountains offers the first solid clue to what's been an international scientific mystery - the disappearance of as many as 112 amphibian species since 1980.
Trout to be removed
Pounds concluded that global warming has created conditions that favour the fungus, and helps explain why 65 species of vibrantly colored harlequin frogs in Costa Rican forests have succumbed to it in the last two decades - five of them after 1987, an unusually warm year.
No research has been done to prove a link between climate change in the high Sierra and the fungus' lethal spread here, but scientists who gathered in the park in January said they can't wait for those studies.
Park biologists will examine the possibility of breeding the critters in captivity, which no one's done successfully. They may also re-establish frogs in areas where they've disappeared, and continue to remove nonnative trout from some high Sierra lakes. Trout removal has had promising results in Sequoia and Kings Canyon, but might prove unpopular with anglers.
Amphibians are facing an ecological disaster on a global scale - and the majority of endangered species don't enjoy such dedicated attention.
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.
- AP
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