Courtesy/Vance Vredenburg

Mountain yellow-legged frogs killed by a fungus disease at Sixty Lake Basin in 2006

The mountain yellow-legged frog, once a ubiquitous presence in the Sierra Mountains, was added to California’s list of threatened and endangered species.

The California Fish and Game Commission voted unanimously Thursday to list the Sierra population of the species as threatened. A closely related southern California species was listed as endangered.

The frogs were once so abundant that Sierra hikers once needed to take care to avoid stepping on them. But, under assault from invasive trout, fungus disease, farming pollution wafting up from the Central Valley and other threats, the population has declined more than 90 percent and the amphibians have become difficult to find.

Thursdsay’s ruling triggers a range of protections. Killing one of the frogs or removing one from a stream will now be illegal, for example.

“The state protection is very important,” said Jeff Miller, a conservation advocate at the Center for Biological Diversity, which petitioned for state protection of the frogs in 2010. “Next is trying to get the feds to federally list the Sierra population.”

Miller said he expects the federal government to list the species as endangered or threatened under the more stringent Endangered Species Act next year.