AWR Special Report #9
A Special Report on the Bull Trout
(Salvelinus Confluentus)

Threats to Bull Trout Viability

According to the U.S. Fish and Wildlife Service and the U.S. Forest Service the leading causes in the demise of the bull trout are habitat destruction and degradation brought about by logging and road-building. Other threats include dams, grazing and associated water diversions, mining, poaching, competition with introduced fish species, legal harvest, drought, global warming, and homesite subdivision.

Logging and roadbuilding cause stream sedimentation, which fills in spawning areas and smothers eggs. Logging can remove overhanging vegetation and woody debris necessary for keeping stream temperatures low and creating pool habitat. Dams fragment and isolate bull trout into genetically non-viable remnant populations by preventing migration. Mining poisons prime waters with toxic mine tailings and cyanide. Improper cattle grazing reduces streamside vegetation, leads to higher stream temperatures and increased sedimentation, and can trample and collapse banks and streambeds. Water diversions for agriculture dry up crucial streams. Poachers inflict a heavy toll on bull trout using nets, blasting caps, shotguns, and other methods to decimate spawning bulls. Exotic species introduced by management agencies compete with bull trout and sometimes interbreed, creating sterile offspring. Lake trout are thought to have a negative impact on bull trout populations in Montana's Flathead Lake and Idaho's Priest Lake.

Population Status and Extinction Risk
The U.S. Fish and Wildlife Service status review found that highly migratory populations of bull trout have been eliminated from the largest, most productive river systems. Extinction risks increase sharply when population sizes drop below 1,000 to 2,000 individuals or 500 spawning pairs, due to small population size and genetic isolation. Fish and Wildlife found few populations in the U.S. exceeding this size. Compounding these risks are the effects of habitat destruction. According to the U.S. Forest Service, 82% of all bull trout populations and stream segments rangewide are threatened by degraded habitat conditions. According to the Montana Department of Fish, Wildlife & Parks, 90% of Montana's bull trout populations are at risk of extinction. In Oregon, 81% are at moderate to high risk of extinction. In Idaho, 69% of bull trout populations are declining and at risk of extinction. In Washington, a majority of populations are declining. Nevada's only bull trout population, in the Jarbidge River, is isolated and at risk of extinction. The U.S. Fish and Wildlife Service summarized their scientific status review by stating "Virtually every bull trout population within the conterminous United States is threatened by a wide variety of land and water management practices."