Oakland Zoo, San Francisco Zoo, and Sequoia and Kings Canyon National Parks Release Critically Endangered Frogs to Bolster Wild Populations

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Date: August 30, 2017
Contact: Mike Theune, NPS Information Officer, 559-565-3703

Tadpoles were emergency-airlifted from remote park locations and transported to Oakland Zoo and San Francisco Zoo to be cleared of disease, raised into frogs, immunized, and released back into their natal lakes in hopes of restoring their dwindling populations in the wild.

SEQUOIA AND KINGS CANYON NATIONAL PARKS, Calif. August 30, 2017 – Oakland Zoo, San Francisco Zoo, Sequoia and Kings Canyon National Parks, and U.S. Fish and Wildlife Service partnered for a third year in efforts to recover endangered mountain yellow-legged frog populations in the wild.
Mountain yellow-legged frogs are threatened by non-native predators and disease (chytridiomycosis), which is caused by amphibian chytrid fungus and is responsible for the decline or extinction of more than 200 amphibian species worldwide. The mountain yellow-legged frog has been listed as Endangered by the U.S. Fish and Wildlife Service since 2014.
The frogs that were released were raised from tadpoles in quarantine at both the Oakland Zoo and San Francisco Zoo, as part of a “head-start” program to increase their chance of survival in the wild. The program involves collecting diseased tadpoles from wild populations, clearing them of disease upon arrival at zoos, growing them into healthy juvenile frogs, and inoculating the frogs to boost their immune response to the fungus before reintroducing them to their population sites.
Amphibian chytrid fungus has been present in Asia, South America, and Africa for approximately a century, but has spread to almost every continent in recent decades, likely due to the worldwide exportation of amphibians.
Of the 215 healthy young frogs that were transported by helicopter and released into lakes in Sequoia and Kings Canyon National Parks over the past two weeks, Oakland Zoo raised 99 of them and San Francisco Zoo raised 116 of them.
“Our collaboration with biologists and several government agencies has given us the opportunity to inoculate these frogs against the deadly disease that has already wiped out 90% of this species in the wild,” says Margaret Rousser, Zoological Manager at Oakland Zoo. “We are honored to be able to make a real difference in the conservation of this species.”
The release indicates the success of the program, now in its third year and ongoing. The program looks to continue and succeed as other groups of tadpoles are salvaged and brought to zoos for more head-starting.
“This partnership has been critical to the recovery of the mountain yellow-legged frog,” says Sacramento Fish and Wildlife Office Field Supervisor Jennifer Norris, Ph.D. “We’ve been able to maximize the expertise of each partner to successfully recover and relocate over 400 frogs over the past couple years alone.”
“These frog reintroductions are the result of close collaboration and effort by many partners,” says Danny Boiano, Aquatic Ecologist at Sequoia and Kings Canyon National Parks. “However, the expertise provided by the zoos has been instrumental to the success of being able to return so many frogs to the wild.”
“Immunizing frogs is a new tool in our toolbox to save at risk populations,” says Jessie Bushell, Director of Conservation at the San Francisco Zoo. “Just like vaccinating people, we are jump starting their disease fighting immune systems. When released, these frogs will be better able to fight future chytrid infections. It might seem like a lot to go through, but letting populations completely die out is not a good option.”
The conservation collaboration between the Sequoia and Kings Canyon National Parks, the U.S. Fish and Wildlife Service and zoos is trying to helping to save a native California species and give it the opportunity to thrive and repopulate in the wild. Seeing flourishing frogs in healthy habitats is the ultimate goal of the rescue for recovery, so future generations are able to experience and learn about these animals first-hand.


The mountain yellow-legged frog complex in the Sierra Nevada is comprised of two species (Rana muscosa and Rana sierrae) that inhabit high elevation aquatic habitats. Although historically abundant, these frogs have been extirpated from more than 92 percent of their geographic ranges, with many of the remaining populations depleted. Declines were first recognized during the 1970s and have accelerated markedly since the 1990s. The realization that these patterns would rapidly place these species at risk of extinction led to Endangered listings for both species under the U.S. Endangered Species Act. Mountain yellow-legged frogs in the Sierra Nevada occur between the headwaters of the Feather River and the headwaters of the Kern River. Rana sierra occupies the northern and central Sierra Nevada south to the vicinity of Mather Pass (Fresno County), whereas Rana muscosa occupies the Sierra Nevada south of this area.
These two parks, which lie side by side in the southern Sierra Nevada in Central California, preserve prime examples of nature’s size, beauty, and diversity. Over 1.8 million visitors from across the U.S. and the world visit these parks to see the world’s largest trees (by volume), grand mountains, rugged foothills, deep canyons, vast caverns, the highest point in the lower 48 states, and more.
The Bay Area's award-winning Oakland Zoo is home to more than 700 native and exotic animals. Oakland Zoo is dedicated to the humane treatment of animals and wildlife conservation onsite and worldwide; with 50¢ from each ticket donated to support conservation partners and programs around the world. California Trail, a transformational expansion, opens in 2018 and will further our commitment to animal care, education, and conservation with a focus on this state’s remarkable native wildlife. Nestled in the Oakland Hills, in 500-acre Knowland Park, the Zoo is located at 9777 Golf Links Road, off Highway 580. The East Bay Zoological Society (Oakland Zoo) is a nonprofit 501(c)3 organization supported in part by members, contributions, the City of Oakland and the East Bay Regional Parks.
Established in 1929, the San Francisco Zoo & Gardens connect people to wildlife, inspire care for nature and advance conservation action. An urban oasis, the Zoo & Gardens are home to over 1,000 exotic, endangered and rescued animals representing more than 250 species as well as seven distinct gardens full of native and unusual plants. Located at the edge of the Pacific Ocean where the Great Highway meets Sloat Boulevard, the Zoo is open 365 days a year from 10 am to 5 pm and is accessible by San Francisco Muni “L” Taraval line.
The mission of the U.S. Fish and Wildlife Service is working with others to conserve, protect, and enhance fish, wildlife, plants, and their habitats for the continuing benefit of the American people. We are both a leader and trusted partner in fish and wildlife conservation, known for our scientific excellence, stewardship of lands and natural resources, dedicated professionals, and commitment to public service.

Last updated: August 29, 2017

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