This fall, the California Department of Fish & Game will begin poisoning a section of Alpine County’s Silver King Creek, home to the native Paiute cutthroat trout, the rarest trout in America. The idea is to eliminate the nonnative trout that pose dangers to the Paiute of hybridization and competition for food.
After being listed as an endangered species, the Paiute’s status was reclassified to “threatened” in 1975 to allow regulated angling. This January, the United States Fish and Wildlife Service (USFWS) proposed the $500,000 Silver King project to restore a pure population of the Paiute, with the goal of eventually delisting it. But using rotenone, an organic, plant-derived insecticide, to kill the nonnative trout has raised criticism from residents and from environmental organizations such as the Center for Biological Diversity. “We are very concerned about the effects of the use of this poison,” says Nancy Erman, professor emeritus of aquatic ecology at UC Davis.
Rotenone, which has been used for fishery management for over 50 years with varied results, would be applied for up to three years. Rotenone has some toxicity to all animals but is particularly effective in killing fish because it inhibits gill-breathing animals’ use of oxygen.
Critics of the plan point out that the California Department of Fish & Game continues to stock nonnative fish in area creeks for angling. “It’s a very difficult and complex situation,” says the Center for Biological Diversity’s Peter Galvin. “The larger issue is one of land management: when nonnative species are gaining advancement, the root causes need to be addressed in a holistic fashion.”
Galvin points out that the planted nonnative fish can migrate from one stream to another, where they can mate with the Paiute. “Fish and Game is biting its own hand in the recovery process by continuing to stock nonnative species,” he says. The section of creek to be poisoned is a nine-mile stretch of the upper portion of Silver King Creek, which flows into the Carson River, south of Lake Tahoe. Potassium permanganate, a neutralizing agent, will be used to prevent the poison from spreading into other sections of the creek.
Rotenone has a spotty history when used as a fish management tool. Some critics say it kills amphibians while failing to rid areas of the target fish. USFWS biologist Chad Mellison insists those accusations are false. “We’ve tried to get the story straight and want to dispel any accusations that rotenone treatments have failed in the past.” Rotenone has been used in the Silver King Creek basin on several different occasions with success; there are four other locations in the area where the Paiute has been restored.
In 1997, the California Department of Fish and Game dumped 16,000 gallons of rotenone into Plumas County’s Lake Davis to rid it of the growing pike population that was threatening the lake’s native trout. The poisoning resulted in contaminated groundwater and a lawsuit that cost the state $9.7 million. Less than two years after the poisoning, pike began to reappear in the lake. “There are far more errors in rotenone projects than successes. Even after the species is restored, hybridization almost always recurs,” charges Erman.
At Silver King, the poison will be applied once a year, about 10 to 12 gallons at a time, with the treatment’s effectiveness assessed after each application. Once the nonnative species are killed off, the area will be stocked with genetically pure source populations of Paiute.
Erman believes rotenone carries potentially significant environmental consequences. “There are at least two studies showing major changes in the composition of invertebrates in the Silver King area, meaning there are very severe effects to non-target species,” she says. Erman says there is also an indirect impact on the food chain, which could lead to extinction of some of the non-target species, such as the mountain yellow-legged frog, a species proposed for listing under the Endangered Species Act. “Rotenone kills all gill-breathing animals, not just fish, and studies have shown that some invertebrate taxa are permanently eliminated,” she says. She believes that there are viable alternatives, such as net fishing, to using rotenone.
Galvin says viable options have not been explored. “We want a more analytical study of the effects on the environment, as well as the nonchemical alternatives. The Forest Service and Fish and Game have been less than willing to fully debate possible alternatives.”
Once all criteria in the recovery plan are met, management passes to the state, which may open that section of the creek to angling. “We have an opportunity to restore a rare species and create a very unique trout fishery,” says Bob Williams, supervisor for Nevada Fish & Wildlife.
“The real purpose of this project is to set up a fishery in the future,” says Erman, pointing out that the four creeks in which the Paiute have been restored are too remote for angling. “The nonnative fish that now exist in that section of Silver King Creek were planted by Fish and Game, and they are planning to use rotenone to correct this.”
Galvin believes the project only addresses the symptoms. “If you don’t take systematic action in treating the problem, you have to keep treating the same problem again and again.”