Rangewide climate vulnerability assessment for threatened Bull Trout

Abstract

The bull trout, listed as threatened under the Endangered Species Act, is well adapted to the cold waters of the Northwest. Recent changes in climate have caused winter flooding and warmer summer water temperatures in the region, reducing the cold-water habitats that bull trout depend on. The southernmost bull trout populations, found in Oregon, Washington, Idaho, Montana, and Nevada, are currently restricted to small reserves where the coldest waters still exist. These shrinking habitats have created a severed environment being further split by dams, poor water quality, and invasive species. The goal of this project was to determine how these factors threaten the species regionally by using predictions of stream temperature to map habitat areas that support juvenile bull trout. Results show that maintaining larger areas of cold water habitat had the greatest, positive impact on bull trout habitat conservation. Other conditions that support bull trout include very cold summer water temperatures, fewer winter floods, and fewer human disturbances (such as the building of dams). Based on these results, specific climate adaptation actions that local managers might consider include prioritizing land and water use to foster colder summer water temperatures, controlling invasive species, increasing connectivity between Bull Trout habitats, and continuing monitoring efforts. To ensure that these results and habitat maps could be incorporated into management actions, researchers met with stakeholders including the U.S. Fish and Wildlife Service (USFWS), the U.S. Forest Service, and the Burns Paiute Tribe. As a result, the maps were used in forest planning for the Lolo National Forest in Montana, the Wenatchee River basin, and in the lower Pend Oreille River during the relicensing process for local dam operations. In addition, the recovery plan proposed by the USFWS incorporated these models into detailed analyses of bull trout habitat loss, which managers can use to prioritize actions in their Recovery Unit Implementation Plans.