NORTH COUNTY - A North County researcher whose work with amphibians has led him to research a fragile species of endangered frogs says that the disappearance of amphibian species across the globe should be cause for concern.

San Diego Zoo biologist Jeff Lemm is raising dozens of "froglets" in his lab at the San Diego Zoo's Wild Animal Park.

Dozens more are still tadpoles, but eventually, he hopes that all 70-some specimens will become adult members of the shrinking mountain yellow-legged frog population.

The small frogs used to live on Palomar Mountain and at Pauma Creek in San Diego County, but are now only found in the San Gabriel, San Bernardino and San Jacinto mountains, Lemm said.

"They've been extinct here for 30 years," he said during a talk at the Agua Hedionda Lagoon Discovery Center in Carlsbad. "They're doing terrible."

So are many other species of amphibians, which are threatened by development and other factors - specifically, water pollution, a lack of genetic diversity and an influx of non-native species, Lemm said.

For example, the African clawed frog was originally imported in the 1930s because it emitted a chemical used in human pregnancy tests. But now, the clawed frog is wiping out native populations of frogs by eating them and moving in on their territory.

Perhaps the largest threat to frogs, said Lemm, is a disease called chytridiomycosis that is caused by a fungus and is wiping out whole populations.

Lemm wrote a book last year about amphibians in San Diego County, and during his presentation in Carlsbad, he said biologists widely consider amphibians to be the proverbial "canaries in the coal mine," with die-offs indicating larger environmental ills to come.

"Amphibians and other water-dwelling creatures are usually the first to show signs of environmental problems," he said.

As far as amphibians are concerned, the news is grim: Of the world's 6,000 known species, a third are extinct or near extinct, Lemm said.

"People kind of get bored with it, but it's a big deal. More than a quarter of the world's species went extinct in the last 10 years," he said.

In order to help species such as the mountain yellow-legged frog bounce back, researchers and zoos are trying to institute a sweeping captivity breeding program, Lemm said.

"We're trying to get at least 500 species into captivity and establish a managed breeding program," he said. "But with 6,000 species out there, which 500 do you choose? And how do you pay for it?"

Those questions have been answered to a certain extent by his work with the mountain yellow-legged frog, a species that likes high elevations and cold, pure water.

Regulating the temperature, quality and nutrient balance of the water has been one of the most challenging aspects of raising the frogs from tadpoles, Lemm said.

"There's a lot to being a frog-keeper," he said, adding that other factors, such as diet and exposure to ultraviolet light, must also be regulated.

The plan is to breed the frogs Lemm raises, eventually releasing some back into their original habitats, but he must wait until he has a group of mature adult frogs until they can begin breeding.

"We haven't even gotten that far yet," he said. "We're getting close, though. Nobody's ever kept these frogs in captivity."

It's been about eight months since the oldest of Lemm's mountain yellow-legged frogs grew from tadpoles, and those are beginning to show signs of adult behavior patterns, he said.

Ultimately, it may be research and rehabilitation efforts such as Lemm's that help amphibian populations recover from the effects of biological and man-made hazards, but he said that something must also be done to prevent the further loss of habitat.

"You can only take so many bricks out of the wall before it collapses on you, and we're taking a lot of bricks out of the wall," he said.

- Contact staff writer Tom Pfingsten at (760) 731-5799 or tpfingsten@nctimes.com.

A sample of North County amphibians:

- Arboreal salamanders, which live in trees.

- Garden slender salamanders, which have about 10 species in the county and are adapting well to development.

- Western or California toad, the most common native toad.

- Arroyo toad, an endangered toad with a call that sounds like a high-pitched trill.

- Red-spotted toad, a desert-dweller.

- California chorus frog, which often lives in rocky areas.

- Pacific chorus frog, which is extremely common and found in a variety of colors.

- Western spadefoot, a troubled species averse to development. These are found mostly found in undisturbed areas.

- American Bullfrog, a non-native species that comes from East Coast of the U.S.

- African clawed frog, a non-native species imported in the 1930s; releases toxic chemicals when distressed, eats native frogs.

- California red-legged Frog, which is endangered and threatened by development. This is the species of Mark Twain's jumping frog of Calaveras County.