Endangered Frog is Making a Comeback in Yosemite Park

October 4, 2016 | Erica Tennenhouse

yellow-legged frog
Photo credit: Wikimedia Commons

Study suggests declines of amphibian species may be reversible, with appropriate management.

The Sierra Nevada yellow-legged frog, once on the brink of extinction, has recently experienced a marked population increase in Yosemite National Park, according to a study published in the Proceeding of the National Academy of Sciences, suggesting that drastic declines in other amphibian species may be reversible.

The study authors write that the Sierra Nevada yellow-legged frog is “emblematic of the global decline of amphibians,” as it went from being one of the most abundant amphibians in California’s Sierra Nevada mountains a century ago to recently being listed as “endangered” under the US Endangered Species Act.

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This dramatic change in status was triggered by the introduction of non-native predatory fish into the frog’s habitat in the early 1900s. Then, in the 1970s, a deadly fungus known as the chytrid fungus began spreading through the Sierra Nevada, decimating hundreds of yellow-legged frog populations.

But according to the results of more than 7,000 surveys of frog populations in Yosemite National Park conducted over the past two decades, Sierra Nevada yellow-legged frog abundance has taken an unexpected turn and is now increasing at an average rate of 11 percent per year.

“The question is: why are they recovering now?” says study lead author Roland Knapp, from the University of California’s Sierra Nevada Aquatic Research Laboratory, in an interview with New Scientist. “The fish and fungus are still there.” 

The comeback may be partially due to the National Park Service’s decision to stop stocking non-native fish in some Yosemite lakes.

Results from a lab experiment also suggest that many frogs have evolved resistance the chytrid fungus. Specifically, frogs from populations with a long history of exposure to the fungus have become less susceptible than those from populations that have never been exposed.

Another key factor driving the recent population boom has been the ongoing efforts aimed at protecting the species’ natural range.

“This shows there is hope that at least some species can recover, given the time and the habitat in which to do it,” says Knapp, though he cautions that the fungus still poses a major threat to many amphibian species, particularly those with small populations.

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