The rare Sierra Nevada yellow-legged frog was once the most abundant amphibian in the mountain lakes of the high Sierra Nevada. Hundreds of frogs would be visible along lakeshores, acting as a fascinating animal encounter for hikers. But the population has since declined dramatically, including in Yosemite National Park, and they’re now considered a Federal Endangered species and California Threatened species.
Their population has declined around 95% in the area, with surveys conducted between 2005-2007 showing that the Sierra Nevada yellow-legged frog was very much headed towards extinction. Their abundance once placed them as a keystone predator and prey in the high mountains, but the introduction of fish into naturally fishless bodies of water, in addition to other factors, have demolished their population.
Bodies of water in Yosemite National Park above 4,000 feet were originally free of fish, as steep waterfalls in Yosemite Valley and Hetch Hetchy Valley kept the fish from reaching upstream habitats. But between 1897 and 1990, fish were stocked in lakes, ponds, streams and rivers throughout the park, reaching places they’d never lived before. The park began phasing out fish stocking when they realized the damage it was doing to native populations in 1972, and by 1990 the practice was ended entirely, but the damage was already done.
Around 250 bodies of water and 800 miles of rivers and streams inside Yosemite are estimated to contain populations of nonnative fish. Their impact on native populations is well documented, feeding on aquatic insects and amphibians while competing for food with many other native animals.
Work is being done to help these frogs recover, though. Yosemite National Park began removing fish from some lakes experimentally back in 2007 after researchers in Sequoia and Kings Canyon found that doing so helped the area’s mountain yellow-legged frog populations to recolonize and thrive in lakes. At the same time, a fungal disease called chytridiomycosis or “Chytrid” has been devastating frog populations in the Sierra Nevada, but the Sierra Nevada yellow-legged frog seems to be adapting to the fatal effects.
Through the reintroduction of these fungus resistant frogs and through the removal of fish in several high-altitude lakes, Yosemite is now cautiously optimistic that the Sierra Nevada yellow-legged frog could both survive and thrive.