Physical Characteristics: Can be up to 41 inches long and weigh 32 pounds, though the average is usually much less, with variation across range. Fins have white leading edges, with a head and mouth larger than most salmonids, giving it its name. Their coloring is pale yellow to crimson spots on a darker background; spawning adults develop varying amounts of red on the belly. Unlike other members of the salmonid family, they lack teeth on the roof of their mouths.
Diet: Young bull trout feed on plankton and other aquatic invertebrates. As they grow older, they rely on eating other fish, including eggs and fry, and species like whitefish and other trout.
Habitat: Bull trout require very specific habitat components to spawn and survive. Water must generally be below 55 degrees F, have clean gravel beds, deep pools, complex cover such as snags, and expansive systems of interconnected waterways to facilitate spawning migrations. They favor deep pools of cold lakes and large rivers, as well as high mountain headwaters. It is for these reasons that the presence or absence of bull trout is an excellent indicator of water quality.
Range: Found in cold, clear waters of the high mountains and coastal rivers—in which they may be anadromous—of northwestern North America. The Clearwater Basin provides many crucial and ideal waters for bull trout, including the headwaters of the primary river drainages. Virtually all of the Clearwater River and its tributaries are bull trout habitat, as are the adjacent St. Joe and Salmon River systems. The strongholds are the upper North Fork Clearwater and the upper St. Joe Rivers, which are located in the Upper North Fork Roadless Area (which is proposed for wilderness by conservation groups).
Reproduction: After their fourth year, they are ready to spawn in the fall. Bull trout will return to their birth river only if the temperature there is ideal–in the mid 40′s–with clear water and a silt-free bottom. Any changes in the habitat will definitively prevent them from spawning. Unlike salmon, bull trout do not die after spawning and will return many times to spawn during their lifetime. The eggs require 4-5 months to incubate, hatching in late winter or early spring. Fry remain in the natal streambed up to 3 weeks before emerging.
Threats: Officially listed as a threatened species, certain menaces to bull trout recovery are habitat degradation and fragmentation, blockage of migratory corridors, poor water quality, the effects of climate change and past fisheries management practices, including the introduction of non-native species such as brown, lake and brook trout. Mating with the latter species produces sterile offspring. Logging roads are perhaps the major habitat threat to bull trout in the Clearwater region, though other habitat alterations from mining and off-road vehicle use may be significant in certain areas.
Miscellaneous: Bull trout may either be migratory or resident. Resident bull trout spend their entire lives in the same stream or creek, and are generally smaller, growing up to 10 inches long. Migratory bull trout move to large water to over-winter and then migrate back to smaller waters to reproduce. These migratory forms grow larger, reaching 35 inches long and up to 32 pounds.
Learn more about efforts to recover bull trout populations.