To Save Frogs, Park Service Plans to Use Pesticide in Sierra Nevada

Mountain yellow-legged frog | Photo: USFWS Pacific Southwest Region/Flickr/Creative Commons License

Now that the federal government shutdown is over and the National Park Service is getting back to work, the staff at Sequoia and Kings Canyon National Parks have extended public comment on a plan to eradicate invasive fish from high-elevation lakes in the Sierra Nevada.

The plan would use nets, electrical shocks, and biodegradable fish poison to remove non-native trout from 87 bodies of water in the parks' upper elevations that had no fish in them before the state began stocking them for the benefit of anglers. About 41 miles of stream would be treated as well. The intent is to restore the high-country wetlands to their original fish-free condition so that native wildlife, including the parks' endangered yellow-legged frogs, can recover in those areas.

The majority of the parks' 549 high-elevation lakes, ponds, and marshes wouldn't be affected by the plan, and the Park Service has specifically omitted lakes that are popular with sport anglers.

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Fish stocking in the high Sierra has been devastating for the range's yellow-legged frogs. In the high country of Sequoia and Kings Canyon National Parks, the ranges of two yellow-legged frog species adjoin: Rana sierrae, the Sierra Nevada yellow-legged frog, and Rana muscosa, the southern mountain yellow-legged frog.

Both species are candidates for protection under the Endangered Species Act, and both have been severely affected by predation by non-native fish in high elevation wetlands. In addition, the two species have been devastated by a fungal disease, Chytridiomycosis, which has been implicated in frog die-offs around the world. Frogs are more susceptible to the fungus when predation pressure pushes them out of cold deep waters into warmer shallows.

An aspect of the Parks' plan that may draw some opposition is their proposed use of a pesticide, Legumine®, to kill fish in some lakes where netting and electric shock prove less effective. Legumine is a formulation of the old-school organic gardening pesticide rotenone combined with an emulsifier. Rotenone is extremely toxic to fish in concentrations essentially harmless to birds and mammals, and organic gardeners using it as an insecticide have long been cautioned not to use it near lakes and streams.

The Park Service says treatment would involve the lowest effective dose of the pesticide, projects that lakes treated with Legumine will be clean within three years, with most of them being pesticide-free within a year.

But pesticide applications on public lands rarely take place without objection from the public, so this aspect of the plan may be controversial. Comments obtained in the scoping phase of the plan's environmental review pointed out that Legumine would also kill non-target animals in the treated lakes and ponds, including the very frogs the plan seeks to restore.

Invertebrates are also highly susceptible to rotenone -- hence its use in gardening -- and previous studies have indicated that populations of aquatic insects can take a very long time to recover when their homes are treated with fish poisons.

Now that the shutdown's over, the public can again read the plan's Draft EIS online. The comment period is open until December 17 of this year. More information on submitting comments is available at the Parks' website.

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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