Yellow-legged frogs were once the most common frog in mountain lakes throughout the Sierra Nevada, but in recent decades were nearly wiped out by non-native species and by disease. By 2005, biologists could only find 11 widely scattered populations, with perhaps a couple of thousand frogs total.
Biologists hope that removing non-native predatory trout will give the species enough breathing room to survive other threats, including pollution and habitat degradation from livestock grazing. One study suggests that pollution from airborne agrochemicals have played a significant role in the decline of Sierra Nevada frogs.
Initially, park scientists will identify and restore suitable lakes usually where frogs are absent, where they can then reintroduce about 20 adult frogs per site. The adults are collected from well-established populations elsewhere in the park. They are given a micro-chip similar to those used for pets before being released into their new home lakes.
Seven lakes are ready to support frog populations. Frogs have already been successfully reintroduced at two of those sites. Park scientists plan to reintroduce frogs at two more of these seven sites in the coming years and expect the frogs to recolonize the remaining three to lakes on their own from nearby sources.