Bull Trout Facts and Science

Bull trout are a type of char, which is a part of the salmon family. While this particular trout strongly resembles another char, the Dolly Varden, work published in 1978 proved bull trout to be a distinct, separate species. As a member of the arctic fish’s subgroup, albeit the southernmost descendant, bull trout have very specific requirements for their habitats – particularly water that is sufficiently cold.

Bull Trout Facts

Bull trout range in color from brown above, through olive green, to a belly that pales to white. Against this darker background, small spots of pale yellow to crimson are scattered. Adults develop differing amounts of red on their bellies in spawning. While they are similar in appearance to brook trout, a few characteristics distinguish the two: unlike the brook trout, bull trout never have spots on the dorsal fin, and the range of colors of the spots against the olive green and bronze-brown back includes salmon, orange, and pale yellow. They differ from lake trout in that the bull trout has a tail fork which is not as deep.


While the bull trout is a subspecies of char, it has no recognized subspecies itself. There are two forms which bull trout exhibit: migratory and resident. The latter dwell in the same creek or stream for their entire lives. The former move to overwinter in larger water bodies, migrating back to their smaller home waters to reproduce. One bull trout form, anadromous, is in the population in the Coastal-Puget Sound and uses the ocean to rear its young but spawns in streams and rivers.


When bull trout dwell in waters, it is a definitive sign that those waters are healthy. Bull trout are extremely sensitive to water quality and have exacting requirements in their habitats. They must have a water temperature that is colder than most salmonids. Their habitats must be complex, with deep pools and riffling streams, large logs in abundance and undercut banks. For spawning as well as rearing, bull trout rely on the cleanest of stream substrates. They also require lake, river, and ocean habitats with a connection to headwaters streams for feeding and spawning migrations.

Because of these specific requirements and reliance on healthy water, and the increase of pollution, the bull trout’s range today is much reduced from its former expanse. Today they are native to western Canada, Nevada, Montana, Idaho, Oregon, and Washington. They can be found most readily in clear, cold mountain waters and in coastal rivers.


The diet of bull trout shifts as they grow and are capable of tackling larger prey. Bull trout tend to be predators of fish primarily, especially when they are large. Smaller members of the species subsist primarily on insects, both aquatic and terrestrial.


Between their fourth and seventh years of age, bull trout reach their sexual maturity. When the fall temperatures have fallen below 48 degrees Fahrenheit, or 8 degrees Celsius, the bull trout spawn in cold streams with clean gravel, unpolluted water, gentle stream slopes, and cobble substrates.They like areas that allow water to flow over the eggs. A common element of spawning areas is that they have groundwater-influenced stream flow or have cold water springs associated with them.

Life Cycle

Bull trout have been observed living for as much as 12 years. Their eggs need a lengthy incubation period, particularly in comparison to other trout or salmon: generally four to five months. After hatching in early spring or late winter, the fry remain up to three weeks in the shelter of the stream bed before emerging. The juveniles continue to prefer the stream bottom until they have enough growth to take on the fish that will be their primary food source.

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