© Dave Bickford
At a Glance
Bull trout are members of the salmonidae family, but they are not true trout. Instead, they are char – a group which includes brook trout, lake trout and dolly varden. Bull trout exhibit two distinct life histories, or patterns of behavior. Migratory bull trout are larger fish that spend part of the year feeding in lakes and big rivers and then reproduce in smaller streams. Resident bull trout are smaller fish that spend their entire lives in the same stream or river where they were born.
Range: Northern Rockies, Northwest and Western Canada.
Habitat Type: Cold, clear water in mountains and larger coastal rivers.
Primary Diet: Mainly piscivorous (fish eating).
Estimated Population: Less than 500,000 remaining, mostly in isolated groups of less than 1,000 individuals.
States with Current Habitat
Bull trout require the coldest water of all species native to the Rocky Mountains (summer temps less than 58 degrees F and spawning temps less than 48 degrees) and are therefore a leading indicator species for aquatic ecosystem health within the Rocky Mountain region. They spawn in the fall and often migrate long distances to lay their eggs in loose, silt-free gravels. Both juveniles and adults are often found in or near deep pools and overhead cover such as logjams, boulders or undercut banks, where they find protection from predators in cool water temperatures.
Because of their dependency on cold, clean water and pristine habitat, bull trout have been largely extirpated from much of their historic range. The best bull trout habitat occurs within large watersheds that have cold, clean water. Especially important are unrestricted well-vegetated floodplains, meaning that stream channels have room to move and create new pools, side channels and other habitat features. Therefore, current bull trout strongholds are often within or downstream from protected wilderness and roadless areas, where dams, road building, grazing, logging and other landscape impacts are limited or nonexistent.
Threats related to Global Warming
As late summer flows are affected by global warming, fewer rivers will be able to provide ample cold water for bull trout. Bull trout distribution is also related to air temperature, so the heightened ambient air temperatures of the bull trout’s habitat caused by global warming are reducing their survivable habitat. The warming climate also affects precipitation and timing in the Rockies, which is predominately driven by snowfall and snowmelt. The timing and duration of spring runoff could dramatically affect stream temperatures, habitat creation, and therefore the spawning activities of the bull trout.
Trout Unlimited is working to conserve, protect and restore bull trout habitat throughout their historic range. TU partners with state and federal agencies and private landowners on projects that include installing large trees and rootwads for overhead cover, fencing riparian corridors in agricultural areas to reduce sedimentation, removing fish passage barriers such as undersized or perched culverts, mine reclamation and improving irrigation practices to increase streamflows.