Sunny Slope grayling
Arctic grayling are a unique fish because remnant populations were native to only two of the lower 48 states-Michigan and Montana. Grayling were apparently isolated in both of these areas by the last period of glaciers, which ended 10,000 to 12,000 years ago. Michigan's grayling were extinct by 1936, but Montana populations continue to persist in a fraction of their historic range. In fact, the only remaining native stream dwelling grayling population in the lower 48 states is found in the Big Hole River in southwest Montana. Declines in Montana's native grayling populations are attributable to:
- degradation of habitat, especially dewatering caused by irrigation;
- interactions with non-native salmonids (trout family); and
- overharvest by anglers.