Frog Population Drop Linked to Pollution : Mark Jennings, who grew up in Santa Paula, has been researching amphibians for a U.S. Forest Service project.

Mark Jennings, a biologist with the California Academy of Sciences in San Francisco, can remember the exact day when, as a boy growing up in Ventura County, he found his first yellow-legged frog in Santa Paula Creek near his home. That was in May, 1970, and when he returns these days to visit his parents in Santa Paula, he still goes looking for those frogs.

Only there aren’t any more.

“When you walked the creek then, you saw foothill yellow-legged frogs sunning themselves. Now, all over Southern California the frog is gone,” he laments.

But for Jennings, this isn’t mere nostalgia for boyhood days. He’s become one of the nation’s leading experts in amphibian population measurement and a key contributor to a major new pollution-effects study completed last month by the U.S. Forest Service. He’s also a leading character in a recent nonfiction book--which reads like a suspense novel--by Ventura author Kathryn Phillips.

It’s not just his former hometown hoppers that Jennings can’t find anymore. He and his professional colleagues all over America and in Brazil, Europe and Asia are coming up empty-handed in their quest for many major breeds of these once-abundant animals.

This spring, a Scientific American magazine lead story framed the issue: “The Puzzle of Declining Amphibian Population.”

In the research Jennings did for the Forest Service and the University of California’s dauntingly named Crocker Nuclear Laboratory Air Quality Group, he encountered various theories.

“Possibly, the frogs are the [dying] canary in the coal mine for the rest of us--because of increases in ultraviolet radiation, atmospheric pollution and other stresses that have accumulated,” he speculates.

His own data indicate that human settlement patterns, in particular, have disturbed these creatures profoundly.

As with bird and fish populations in other parts of the world, the frogs are not reproducing. “The adults just don’t come out of hibernation due to the assaults on their immune system,” he says, and then adds, “but while the other animals are declining, major species of frogs have disappeared.”

In a burst of dark humor, his colleagues who assembled the Forest Service report about California entitled it, “Is the Sierra Frog Population Croaking?”

In this connection, Jennings offered an invitation to the public: “Times readers can be the eyes and ears of science in Ventura County. If you see a frog, not a tree frog or a toad but a ‘true’ frog with a little bit of size , take a picture for me.”

He recommended reading Kathryn Phillips’ book for a description of “true” frogs, but the pictures in that book or any serious frog book will also give you an idea what to look for.

Any sightings you capture on film should be sent to him, care of the California Academy of Sciences, Department of Herpetology, Golden Gate Park, San Francisco 94118.

Jennings and Phillips recommended that Earthwatch provide computer-equipped readers with the address of an Internet site called FROGLOG. It’s the cyberspace journal of the Declining Amphibians Population Task Force, which has headquarters in London.

The World Wide Web address is https://aes info.open.ac.uk/info/other/FROGLOG.html.

Author Phillips stresses the importance of continuing research on this issue. While there are many bio-indicators affecting various frog populations worldwide, she says, “there is no single canary in the mine [but] as an amphibian that experiences so many environmental inputs, they suffer from declining quality of air, aquatic quality and soil quality.”

In other words, they respond rather like us, only, scientists fear, earlier.

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* FYI: For a true-life mystery about this county’s--and the world’s--disappearing amphibian population, read Kathryn Phillips’ “Tracking the Vanishing Frogs,” a Penguin Book, $15.