Preparing For Restoration

Cutthroat trout spawning in a creek
Cutthroat trout spawning

NPS/Neal Herbert


Part of the fish restoration process is the removal of non-native fish from the recovery area. Piscicides are toxins which remove fish from habitats where nets, electrofishing, angling, traps, or other mechanical methods are impractical or ineffective. With the exception of sea lamprey control in the Great Lakes, all fish removal projects in the United States use piscicide containing the natural compounds rotenone or antimycin. Biologists in Yellowstone National Park have used rotenone in formulations approved by the Environmental Protection Agency in High Lake and East Fork Specimen Creek (2006-2009), Goose Lake (2011), Elk Creek (2012-2014), Grayling Creek (2013-2014), and Soda Butte Creek (2015- 2016) to remove non-native fish species.

Rotenone occurs in the roots, stems, and leaves of tropical plants in the pea family (Fabaceae). Ingestion has a relatively minor effect on land animals because the enzymes and acids of the digestive system break it down. Rotenone must be absorbed into the bloodstream, usually across the gill membrane. It kills by inhibiting the biochemical reaction mitochondrial cells use turn nutrients into energy. Essentially, rotenone starves the cells, causing death.

To treat a section of stream, rotenone is dripped in at a rate determined by the volume, speed, and temperature of the water. Further downstream, potassium permanganate is added to the water to neutralize the rotenone. Rotenone is quickly broken down in the environment by sunlight and readily binds to sediments or organic matter in the water. The rapid degradation and dissipation mean that managers have a short window of effectiveness to successfully remove nonnative fish.

Unfortunately, piscicides impact all gill-breathing aquatic organisms, like non-target fish species (i.e., native fishes), larval amphibians, and macroinvertebrates. To reduce potential impacts on non-target organisms specialists use a minimum dosage of rotenone, for short periods of time. Biologists limit treatment areas and leave recovery intervals between treatments. All treatments in Yellowstone National Park have been, and will continue to be, conducted during late summer or fall to avoid impacts on amphibians in early developmental stages. Research conducted during these treatments provides strong evidence that they have not significantly impacted benthic macroinvertebrates or amphibians in Yellowstone in the long-term.

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1 minute, 32 seconds

To maintain the natural biodiversity of the Yellowstone ecosystem, sometimes you have to start small. Fish biologist Todd Koel discusses efforts to restore native fish in Grayling Creek, a cup of eggs at a time.

Last updated: March 24, 2017

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