Endangered Mountain Yellow-legged Tadpoles Turning into Frogs at San Diego Zoo

November 20, 2006

The number of mountain yellow-legged frog tadpoles is changing at the center for Conservation and Research for Endangered Species (CRES), and that is great news for this endangered frog species. As the tadpoles continue to metamorphose into froglets they get one step closer to helping repopulate this amphibian species in the San Bernardino, San Jacinto, and San Gabriel mountains. The Southern California population of the mountain yellow-legged frog is considered among the most critically endangered species in North America, according to the U.S. Fish and Wildlife Service.

In a multiagency conservation partnership with the U.S. Geological Survey, the U.S. Fish and Wildlife Service, the U.S. Forest Service, and California Department of Fish and Game, CRES scientists and staff are trying to keep a healthy captive population of these frogs, with an eye to the future repopulation in the wild. In mid-August, the Geological Survey, Forest Service, and Fish and Game, as well as other agencies, conducted an emergency rescue of the tadpoles, in peril in rapidly drying intermittent pools along a stream in the San Jacinto Mountains.

"Our district biologist noticed a rapid decline in water levels over the course of just a couple of weeks. When it appeared that the pools with the tadpoles in them would dry up, we notified the U.S. Fish and Wildlife Service. The very next day we had a multiagency response team at the site," said Gar Abbas, aquatic ecosystems program manager, Forest Service. The agencies attempted to find habitat that would support the tadpoles, but were unsuccessful.

 "When we searched and found no suitable habitat remaining in the creek to relocate the tadpoles, a rescue of tadpoles from five pools was determined necessary," said Adam Backlin, supervisory ecologist, U.S. Geological Survey. CRES received 82 tadpoles soon after their rescue. Although five of them died shortly after arriving at CRES, the remainder are doing well. Seven of them have already fully metamorphosed into froglets, and most of the others are sprouting legs, indicating they will become froglets soon.

"The tadpoles and froglets are doing really well and we should see more tadpoles changing over fall and winter," said Jeff Lemm, research animal coordinator for CRES. The mountain yellow-legged frog had almost completely disappeared from the San Bernardino Mountains before the 2003 wildfires that devastated Southern California. After those fires, biologists found no trace of the frogs in the area, and they were thought to have disappeared in that mountain range, leaving only a handful of small populations in the San Jacinto and San Gabriel Mountains. Fortunately, a small population has been rediscovered in the San Bernardino Mountains since that time, but the species' population is still very small.

 "I believe rescue efforts such as these are important for the recovery of some endangered species, especially in populations that may otherwise decline well beyond recovery levels without agency assistance," said Tim E. Hovey, associate fisheries biologist, Fish and Game, underscoring the importance of governmental and non-governmental agency cooperation.

 "The initial goal with these tadpoles is twofold," said Ron Swaisgood, Ph.D, division head for the Applied Animal Ecology Division of CRES. "Some of these will remain to establish a captive breeding program once they reach reproductive age. We plan to headstart the other tadpoles until they have metamorphosed into frogs and are less vulnerable to predators before releasing them back to the wild."

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