Thanks to dedicated and persistent efforts by researchers and conservationists, mountain yellow-legged frogs are making a comeback in Yosemite National Park after being reintroduced to various lakes.
Nestled along a remote lakeshore in Yosemite National Park, life flourishes with coyotes, snakes, birds, tadpoles, and frogs. These frogs, once missing from this vibrant picture, are pivotal to the ecosystem. Just a decade ago, the scene was starkly different; it was eerily quiet as the frogs, key players in this environment, had vanished due to a lethal fungal infection known as amphibian chytrid fungus.
Today, the concerted actions of scientists and conservation specialists to rescue and then reintroduce mountain yellow-legged frogs back into this and several other lakes in Yosemite have led to their populations thriving once again.
A comprehensive study led by biologist Roland Knapp from UC Santa Barbara (UCSB), along with a team from UCSB, the University of Colorado, Boulder, the University of Tennessee, and Yosemite National Park, chronicles a long-term effort involving 24 reintroductions across 12 sites in Yosemite over the span of 17 years. Remarkably, during this period, the frogs have developed partial resistance to the chytrid fungus, Batrachochytrium dendrobatidis (Bd), which enables them to survive alongside it. The findings have been published in the journal Nature Communications.
“Returning to these lakes where the frogs are recovering and just observing is a powerful reminder of what we’ve achieved,” remarked Knapp, who is based at UCSB’s Sierra Nevada Aquatic Research Laboratory. “You can sit by the water with tadpoles swimming around you and adult frogs lounging nearby on the shore. There are birds swooping down to feed on them and snakes preying on them, bringing the lake back to life.”
The amphibian chytrid fungus Bd has severely impacted native frog populations throughout Yosemite. Once the predominant amphibian in the high elevations of California’s Sierra Nevada mountains, the Sierra Nevada yellow-legged frog (Rana sierrae) has sadly disappeared from over 90% of its historical territory in the last century. It now holds an “endangered” status under the Endangered Species Act. Nevertheless, through their extended research study, Knapp and colleagues successfully reinstated breeding populations by relocating Bd-resistant frogs to areas where the species had been wiped out. Their success represents a hopeful step for amphibian conservation efforts.
“Our modeling indicates that many reintroduced populations have a strong chance of persisting for over 50 years,” stated Knapp. “These findings serve as an exceptional example of how introducing resistant individuals can lead to the recovery of species affected by disease across a landscape, which holds significant implications for many threatened amphibian species and other organisms facing threats from new pathogens.”
Amphibians represent the most at-risk class of vertebrates, with over 40% of species facing extinction. Within a short time, the rise of the amphibian chytrid fungus (Bd), primarily driven by human activities, has led to a dramatic decline in global amphibian diversity, jeopardizing countless populations while many species face extinction in their natural habitats. Even those in the safest reserves have succumbed to what Knapp refers to as an “invisible killer.”
Such success is especially remarkable, according to Knapp. “It’s astonishing, considering where we stood 10 or 15 years ago, uncertain if this frog would still inhabit our landscapes, watching how everything has reversed is truly remarkable.”
A significant amount of meticulous work has been required to achieve this progress.
The reintroduction processes necessitate thorough planning; researchers must assess various factors such as elevation, severity of winter, and potential predation risks when selecting ideal locations for the frogs. Close supervision of the relocated frogs is an extensive, ongoing task, often requiring researchers to hike in and capture each frog at a given site multiple times a year.
Over several years of monitoring the relocated populations, the team noted the emergence of new adult frogs, signaling a successful revival. Conducted within the safeguarded environment of a national park, their work highlights the importance of preserving and revitalizing the natural processes of these ecosystems, as emphasized by Knapp.
What about the possibility of expanding this approach throughout the entire Sierra Nevada region, serving as a proof of concept and potentially setting a standard for similar conservation initiatives worldwide?
“Having that broader view is crucial,” Knapp explained. “We have developed a validated strategy that is effective for Sierra Nevada yellow-legged frogs, enabling us to restore them within the extensive area of Yosemite National Park. This frog, which has been nearly pushed to extinction by the pathogen, is now exemplifying how we may rejuvenate amphibians across the globe.”
Knapp’s co-authors on the study include Mark Wilber from the University of Tennessee Institute of Agriculture; Maxwell Joseph of CU Boulder and Planet; Thomas Smith, also affiliated with UC Santa Barbara; and Robert Grasso at Yosemite. Funding for the project came from the Yosemite Conservancy, the National Park Service, and the National Science Foundation.
