Mountain yellow-legged frog populations have improved in areas where nonnative trout have been removed/NPS

To give endangered frogs and other native species a leg up, human-introduced trout will be eradicated – sometimes with a chemical – from dozens of high-elevation ponds, streams, and lakes in Sequoia and Kings Canyon national parks in California.

The newly approved plan, signed August 23 by National Park Service Pacific West Regional Director Laura Joss, allows the use of piscicide, a chemical substance that is toxic to fish, in 33 bodies of water and 16 miles of streams, most of which are above 10,000 feet elevation. Physical treatments such as gill-netting, electrofishing, trapping, and disruption of egg nests will be utilized in 52 bodies of water and 15 miles of streams.

“While physical treatment methods such as gill-netting and electrofishing are our preferred methods to remove nonnative fish, the Selected Action allows for the use of piscicides in specific areas where physical methods cannot accomplish project objectives,” Superintendent Woody Smeck said on the park planning website, where the plan, record of decision and background information are available.

In response to public comments, agency feedback, and new technical information, the National Park Service reduced the number of areas selected for piscicide treatment. CFT Legumine, the only piscicide registered for use in California, will start to be used in summer 2017 at the earliest. Physical methods will be used in the meantime.

Although the plan is expected to aid multiple native species, the biggest beneficiaries will be two types of yellow-legged frogs, Rana muscosa and Rana sierrae, which are listed as endangered under the federal Endangered Species Act due to effects from nonnative trout and disease (amphibian chytrid fungus). Initial studies showed encouraging population growth.

Sequoia and Kings Canyon began eradicating nonnative trout from selected lakes in 2001. By 2013, fish were eradicated from 10 lakes. Yellow-legged frogs in nine of these lakes remained disease-free three years after fish removal. Average yellow-legged tadpole density in these nine lakes increased by 13-fold, while average yellow-legged frog density increased by 14-fold. Two of the restored yellow-legged frog populations are now the largest in the Sierra Nevada.

From 1870 to 1988, nonnative trout – including golden, rainbow, golden/rainbow hybrid, brook, and brown trout – were introduced into many until-then fishless waterbodies throughout the parks. Studies conducted in the Sierra Nevada have documented that the widespread introduction and continued presence of nonnative trout have caused substantial impacts to native species. After all treatments are completed, self-sustaining nonnative trout populations will continue to exist in 465 bodies of water (221 lakes, 186 ponds, 58 marshes) and hundreds of miles of streams.