Distribution, Status, and Likely Future Trends of Bull Trout within the Columbia River and Klamath River Basins

Abstract

Abstract We summarized existing knowledge regarding the distribution and status of bull trout Salvelinus confluentus across 4,462 subwatersheds of the interior Columbia River basin in Oregon, Washington, Idaho, Montana, and Nevada and of the Klamath River basin in Oregon, a region that represents about 20% of the species' global range. We used classification trees and the patterns of association between known distributions and landscape characteristics to predict the likely distribution of bull trout in unsampled subwatersheds. Bull trout are more likely to occur and the populations are more likely to be strong in colder, higher-elevation, low- to mid-order watersheds with lower road densities. Our results show that bull trout remain widely distributed and occur in most of the subbasins representing the potential range. Some strong and relatively secure populations exist. In general, bull trout are better represented in the region as a whole than many other native species. Important declines in distributi...