Bringing Back the Frogs of Yosemite

This article originally appeared on My Yosemite Park

Just like in John Muir’s day, frogs and toads can still be found jumping about the rivers and alpine lakes of the Sierra Nevada. However, some of the amphibians in Yosemite National Park are currently threatened, endangered or otherwise listed as species of special concern, including the California red-legged frog, the Sierra Nevada yellow-legged frog, and the Yosemite toad. The park’s scientific conservation efforts these days are mostly directed toward saving the red-legged frog and the yellow-legged frog, which naturally evolved in the Sierra Nevada’s lakes.

Red-Legged Frogs Reintroduced

After 50 years, the California red-legged frog made famous in Mark Twain's short story The Celebrated Jumping Frog of Calaveras County returned to Yosemite in 2017.

The federally threatened red-legged frog disappeared from the park after non-native, predatory American bullfrogs were placed in a reflection pond outside the Ahwahnee Hotel in the 1950s. Bullfrogs are voracious eaters, dining on everything from “native frogs, toads, salamanders, small mammals, snakes, turtles and even birds and bats,” say Yosemite officials. They are primarily responsible for the massive decline in the red-legged frog in the park.

In the 1970s the park's open-garbage sites led to an increase in the raccoon population, which also contributed to the frog's demise. The park service, with five other organizations, aims to reintroduce 4,000 red-legged tadpoles during the next three years. Measuring 2-5 inches long, it's the largest native frog in the western United States.

"Small animals like frogs and turtles are the indicators of environmental health and an important part of the food chain. We have to save them in order to conserve all wildlife," said San Francisco Zoo & Gardens President Tanya M. Peterson in a statement. "We are grateful to Yosemite National Park and Yosemite Conservancy for asking us to partner on this significant collaboration, which will have an immediate impact right in our own backyard."

Starting in 2017, more than 4,000 California red-legged frogs, which were bred in captivity at the San Francisco Zoo, have been released in Yosemite. Seventy-five of these frogs were fitted with radio transmitters to help scientists learn more about their behavior to influence future reintroductions. Years ahead of what many predicted, eggs were found in a pond in Yosemite Valley in 2019, signaling a new population of red-legged frogs and seeming like a good sign for the population’s reintroduction.

Decline of Yellow-Legged Frogs

Originally, Yosemite’s high-elevation lakes contained no fish, which allowed frogs to become abundant. These lakes used to be home to thousands of Sierra Nevada yellow-legged frogs. In fact, they were so abundant in Yosemite that park officials say people had a hard time avoiding stepping on them. But, after game species of fish such as trout were introduced, yellow-bellied frog populations declined as tadpoles were predated upon by non-native fish.

In the late 1800s, visitors to the park’s lakes increased – visitors that wanted to fish recreationally. Yosemite started stocking lakes with different types of trout to create the wanted recreation. Not all fish in Yosemite are non-native species. A few native species of fish, such as rainbow trout, occur naturally at lower elevations of the park’s Tuolumne and Merced Rivers, including in the Yosemite Valley.

By the 1970s the introduced non-native fish and amphibian chytrid fungus had affected the frog population to the point of near extinction in the park. With the disappearance of the frogs, also went the garter snakes that depend on the frogs for food. Today, the Sierra Nevada yellow-legged frog is one of the world's most critically endangered amphibians, having lost at least 93% of their populations, according to the National Park Service. They are federal and state candidates for listing as endangered.

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