The bull trout (Salvelinus confluentus) is actually a member of the char genus, a relative of the true trout and salmon. Char can be differentiated from trout and salmon by their light spots on a dark background. Trout and salmon have dark spots on a light background. In Montana, bull trout are native to rivers, streams and lakes in the Columbia (Kootenai, Clark Fork, Bitterroot, Blackfoot, Flathead, and Swan drainages) and Saskatchewan River (St. Mary and Belly drainages) basins.
The bull trout is a long-lived species, generally reaching sexual maturity at five years of age. They spawn in small streams between late August and early November, building nests, or " redds", in which they lay their eggs. The hatched fry do not emerge from the redds until the following spring. Bull trout may eventually grow greater than 3 feet in length and weigh more than 20 pounds.
Montana bull trout display various life history strategies. Some bull trout are residents, spending their entire lives in a single stream. Other bull trout have migratory life histories, either living in major rivers as sub-adults and adults and then migrating into smaller tributaries to spawn (fluvial) or living in lakes and reservoirs as sub-adult and adults and migrating into tributaries to spawn (adfluvial). Migratory bull trout can move great distances (>150 miles) in response to environmental changes and spawning cues.
Bull trout have very specific habitat needs for many of its stages, making it more vulnerable to environmental degradation than most other salmonids. Adult bull trout require cold water temperatures, clean cobble/boulder substrates, and overhead cover. Spawning redds are only constructed in stream reaches where upwelling ground water is available to aerate the buried eggs. Bull trout eggs are easily smothered by low levels of silt. Emerging fry and juveniles require clean rock stream substrates with sufficient open spaces for them to hide in as they develop into sub-adults.
The bull trout is a Montana Species of Concern and was listed as "threatened" by the U.S. Fish and Wildlife Service in 1998. Declines in bull trout abundance and distribution have been caused by habitat loss and degradation from land and water management practices; population isolation and fragmentation from dams and other barriers; competition, predation and hybridization with introduced non-native fish species (lake trout, northern pike, brook trout and others); historical overharvest; and poaching. Although their numbers and distribution have declined from historical levels, bull trout populations exhibiting resident and migratory life histories can be found throughout their historic range in Montana.