Fraser dating 30039
Significant local declines and a few extirpations have occurred in Washington (WA NHP, pers. In Montana, many populations are declining with previously reported mussel beds from the Blackfoot, Big Hole, Bitterroot, Clark Fork, and Middle Snake Rivers are extirpated (Stagliano et al., 2007); with 25 of ~40 originally reported sites not viable or extirpated and only 5 new viable sites found (Stagliano, 2010). Sites in the upper Columbia River in Washington still maintain viable populations (WA NHP, pers. Taylor (1952) cites occurrences in the Snake Headwaters, Upper Snake (into Idaho), Upper Yellowstone, and Missouri headwaters (into Montana). In Wyoming, Beetle (1989) lists occurrences in streams in Lincoln, Sublette, Teton, and Uinta Cos.; while Cvancara (2005) lists occurrences in the Snake and Missouri River drainages in Yellowstone National Park, the Snake River drainage in Teton, Lincoln, and Sublette Cos., and Bear River drainage in Lincoln and Uinta Co. Murphy (1942) cited over 20,000 individuals in a 3/4 mile channel of the Truckee River in California, but it is not known if this population still exists.
This species has likely recently been extirpated from the Umatilla River in Oregon (Brim Box et al., 2003).
In environments where host fish are abundant and human threats minimal, they can attain very high densities (The taxon is declining, in terms of area occupied and number of sites and individuals (Frest and Johannes, 1995; Hovingh, 2004) but the degree of the decline is unclear (possibly 10-30%).
It is sparingly documented in southeast Alaska and questionably the Chukotski Peninsula in Russia (Baxter, 1987); including Revillagigedo Island and north to Naha Bay at 55 degrees latitude at Naha Bay, Alaska (Gustafson et al., 1997) and Prince of Wales Island (Metcalfe-Smith and Cudmore-Vokey, 2004).
Recently in California: Mc Cloud River, Hat Creek, Pit and S Fork Pit River, Spanish Creek, Truckee River, Scott River, S Fork Eel River, Shasta River, San Antonio Creek, N Fork Stanislaus River, N, M, and S Fork Tuolumne River, S Fork American River, and M Fork Feather River (Howard, 2010).
Howard (2008) found reduction in both number of sites and number of individuals at remaining sites for historically known populations in the Plumas, Tahoe, and Eldorado National Forests and the Lake Tahoe Management Basin in California.
comm., 2009) although it is still widespread in the state.