Preparing For Restoration

Cutthroat trout spawning in a creek
Cutthroat trout spawning

NPS/Neal Herbert


Liberalization of creel limits, mandatory kill regulations for anglers, and electrofishing by biologists are effective tools for the selective removal of nonnative species. However, in some instances these tools cannot completely eliminate the invaders. In those cases, barriers and chemical treatments are considered. Some natural barriers already exist; sometimes modifications to natural structures can complete barriers to upstream migration. In a few places, barriers must be completely fabricated. Once native trout are protected from invasion, selective removal continues or, if necessary, chemical treatment is used to eliminate nonnative species. Following reduction or removal of unwanted species, stocking boosts or restores native fish.

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 piscicide fish removal projects in the United States use mixtures 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), Soda Butte Creek (2015-2016), and upper Gibbon River, and Wolf, Grebe, and Ice lakes to remove nonnative 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, to be harmful. It kills by inhibiting the biochemical reaction some cells use to turn nutrients into energy. Essentially, rotenone starves the cells, causing death.

To treat a section of stream, rotenone is applied at a lethal rate determined by the volume, speed, and temperature of the water. Farther 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 result in a short window of time to successfully remove nonnative fish.

Unfortunately, piscicides impact all gill-breathing aquatic organisms, including 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 to amphibians in early developmental stages. Research conducted during these treatments provides strong evidence benthic macroinvertebrates and amphibians in Yellowstone have not been significantly impacted 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: May 8, 2023

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