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An endangered amphibian is making a comeback, one lake at a time.
In California’s Sierras, the mountain yellow-legged frog carries clout disproportionate to its size, which is four inches long, because biologists consider it a keystone species. In addition to keeping lakes healthy by feasting on algae during its tadpole phase, this freckled amphibian passes nutrients up the food chain when predators gobble it up.
Unfortunately, the frog’s realm began to unravel decades ago when nonnative trout were sown into High Sierra lakes. So ravenous were the angler-pleasing salmonids that over time the fisheries flourished and the frogs vanished. Today it’s estimated that the frog is down to six percent of its historic range.
“We’ve seen that as the frogs disappear, it’s not just the frogs that disappear,” explains Roland Knapp, a biologist at the Sierra Nevada Aquatic Research Laboratory. “It’s the snakes that feed on the frogs that disappear; it’s the birds that feed on the frogs that disappear. So even though they’re not a wolf in the sense of being this charismatic species, they are an incredibly important piece of this food web.”
As crews in Sequoia and Kings Canyon national parks are ridding lakes and, in some cases, entire high-country basins of trout, frog populations that had been hanging on in the ecosystems are making a quantum leap.
Once a lake is cleared of fish, any amphibians remaining in the area hop to it. In one lake, which in 2001 had 166 frogs and tadpoles, the population exploded to 14,000 tadpoles and 3,600 frogs by 2004, when 95 percent of the trout had been evicted.
“They just reclaimed the entire habitat,” says Danny Boiano, who with Harold Werner oversees the restoration project for the parks. “At a lake just downstream of that lake, we had counted, I think, two tadpoles and two frogs, and now we are consistently getting from 1,200 to 1,600 frogs.”
With success in 11 lakes, wildlife biologists are now proposing to purge fish from an additional 75 high-altitude lakes and about 50 miles of stream. If the regional director approves the project after public review, park biologists will have a restoration roadmap for the next quarter-century. The goal is creating a more natural ecosystem, says Werner. “We want to try and put all the pieces back like they belong.”
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