The Arctic Grayling Adaptive Management Project is focused on identifying the limiting factor, or factors, for Arctic grayling in the upper Centennial Valley of southwestern Montana - one of the last populations of endemic adfluvial grayling remaining in the Upper Missouri River drainage. Arctic grayling (Thymallus arcticus) are a freshwater holarctic salmonid that were once widespread throughout the Upper Missouri River drainage as a glacial relict population. Red Rock Lakes National Wildlife Refuge encompasses nearly all of the currently occupied grayling spawning habitat within the Centennial Valley.
The estimated number of Arctic grayling in the 2018 Red Rock Creek spawning population was 387, which is not significantly different from the previous year. Peak predicted grayling spawning was 14 May. The estimated number of Yellowstone cutthroat trout in the Red Rock Creek spawning population was 916, an approximate reduction of 72% from the highest estimated population in 2014 and an increase of 237% from 2017. No angler harvest of Yellowstone cutthroat trout occurred.