Yellowstone National Park fisheries biologists will soon discharge the fish poison rotenone into much of the Upper Gibbon River drainage, which will be off-limits for part of September.
The project, which runs Monday until Sept. 13, is designed to scrub nonnative rainbow trout and brook trout out of the watershed, a step that would enable the reintroduction of westslope cutthroat trout and Arctic grayling.
Those two species are native to the Yellowstone River watershed but are not thought to be native to the Upper Gibbon system. The mottled sculpin, a minnow, is the only fish species known to naturally occur in the Gibbon above Gibbon Falls, park documents say.
Among eight stream watersheds from which Yellowstone has removed or plans to remove exotic species, the Gibbon project is by far the most ambitious. An estimated 111 miles of stream and seeps will be poisoned, according to the park’s native fish conservation plan.
The Upper Gibbon drainage includes Grebe, Wolf and Ice lakes and the streams that flow out from those waters. To make sure the nonnative rainbow and brook trout are wiped out, the treatments may be repeated in 2020. Reintroduction of fish is to begin in 2020 or 2021.
Westslope cutthroat and Arctic grayling were nearly eliminated from Yellowstone due to being out-competed and hybridizing with exotic trout. In recent years, the park has tried to restore both species to the East Fork of Specimen Creek, Goose Lake and Grayling Creek.
Starting Monday, Virginia Cascades Drive, Wolf Lake Trail and Wolf Lake Cutoff trail up to Ice Lake will be off-limits. Backcountry areas north and south of the road between Canyon and Norris junctions are also closed. The closures will lift if the poisoning operations wrap up early.