Subadults and Adults

As you know by now, bull trout have three life-history forms: adfluvial, fluvial, and stream-resident. The adfluvial life-history form migrates between lakes or reservoirs and spawns in rivers or streams. The fluvial life-history form lives in large rivers and migrates to smaller rivers or streams to spawn. The stream-resident form is non-migratory and spends its entire life in small streams.

Because there are three life-history forms, it is hard to generalize about adult bull trout habitat requirements. One thing, however, is clear: the bull trout is a cold-water species. They are uncommon wherever water temperatures rise above 59°F for extended periods. Another generalization that we can make is that most migratory bull trout remain in tributaries for one year or more before moving into large rivers downstream. After they reach large river habitats, they can remain there for brief periods or for several years before either moving into lakes or returning to tributary streams to spawn. Click on the buttons below to learn more about subadult and adult bull trout.


Growth and Maturity


Many stream-resident populations of bull trout reach maturity at about 8 inches, and their growth rate plateaus after that. But fluvial and adfluvial populations continue to grow and often show diet-related growth spurts at ages in excess of five years. It is clear that the rate of migratory bull trout growth varies with habitat.

In habitats where bull trout achieve sizes in excess of 16 inches, sexual maturity usually is reached in their fifth summer (4+). Not all mature bull trout spawn every year. One study in Alberta found that only 27% of the adult bull trout tagged in the Clear-water River returned to spawn the next year. Another study in Flathead Lake suggests that in any year about 40% of the adult bull trout remain in Flathead Lake during the spawning season.

Maximum size varies greatly, but the largest recorded bull trout was taken in Lake Pend Oreille, Idaho. It was almost a yard long and weighed about 33 pounds. Under the appropriate conditions, bull trout regularly live to be ten years old, and under exceptional conditions, they can reach ages in excess of 20 years. The oldest bull trout recorded (24 years old) was from the upper North Thompson River, in the Fraser system in British Columbia, Canada.

Subadults and Adults

As you know by now, bull trout have three life-history forms: adfluvial, fluvial, and stream-resident. The adfluvial life-history form migrates between lakes or reservoirs and spawns in rivers or streams. The fluvial life-history form lives in large rivers and migrates to smaller rivers or streams to spawn. The stream-resident form is non-migratory and spends its entire life in small streams.

Because there are three life-history forms, it is hard to generalize about adult bull trout habitat requirements. One thing, however, is clear: the bull trout is a cold-water species. They are uncommon wherever water temperatures rise above 59°F for extended periods. Another generalization that we can make is that most migratory bull trout remain in tributaries for one year or more before moving into large rivers downstream. After they reach large river habitats, they can remain there for brief periods or for several years before either moving into lakes or returning to tributary streams to spawn. Click on the buttons below to learn more about subadult and adult bull trout.


Growth and Maturity


Many stream-resident populations of bull trout reach maturity at about 8 inches, and their growth rate plateaus after that. But fluvial and adfluvial populations continue to grow and often show diet-related growth spurts at ages in excess of five years. It is clear that the rate of migratory bull trout growth varies with habitat.

In habitats where bull trout achieve sizes in excess of 16 inches, sexual maturity usually is reached in their fifth summer (4+). Not all mature bull trout spawn every year. One study in Alberta found that only 27% of the adult bull trout tagged in the Clear-water River returned to spawn the next year. Another study in Flathead Lake suggests that in any year about 40% of the adult bull trout remain in Flathead Lake during the spawning season.

Maximum size varies greatly, but the largest recorded bull trout was taken in Lake Pend Oreille, Idaho. It was almost a yard long and weighed about 33 pounds. Under the appropriate conditions, bull trout regularly live to be ten years old, and under exceptional conditions, they can reach ages in excess of 20 years. The oldest bull trout recorded (24 years old) was from the upper North Thompson River, in the Fraser system in British Columbia, Canada.

Subadults and Adults

As you know by now, bull trout have three life-history forms: adfluvial, fluvial, and stream-resident. The adfluvial life-history form migrates between lakes or reservoirs and spawns in rivers or streams. The fluvial life-history form lives in large rivers and migrates to smaller rivers or streams to spawn. The stream-resident form is non-migratory and spends its entire life in small streams.

Because there are three life-history forms, it is hard to generalize about adult bull trout habitat requirements. One thing, however, is clear: the bull trout is a cold-water species. They are uncommon wherever water temperatures rise above 59°F for extended periods. Another generalization that we can make is that most migratory bull trout remain in tributaries for one year or more before moving into large rivers downstream. After they reach large river habitats, they can remain there for brief periods or for several years before either moving into lakes or returning to tributary streams to spawn. Click on the buttons below to learn more about subadult and adult bull trout.


Growth and Maturity


Many stream-resident populations of bull trout reach maturity at about 8 inches, and their growth rate plateaus after that. But fluvial and adfluvial populations continue to grow and often show diet-related growth spurts at ages in excess of five years. It is clear that the rate of migratory bull trout growth varies with habitat.

In habitats where bull trout achieve sizes in excess of 16 inches, sexual maturity usually is reached in their fifth summer (4+). Not all mature bull trout spawn every year. One study in Alberta found that only 27% of the adult bull trout tagged in the Clear-water River returned to spawn the next year. Another study in Flathead Lake suggests that in any year about 40% of the adult bull trout remain in Flathead Lake during the spawning season.

Maximum size varies greatly, but the largest recorded bull trout was taken in Lake Pend Oreille, Idaho. It was almost a yard long and weighed about 33 pounds. Under the appropriate conditions, bull trout regularly live to be ten years old, and under exceptional conditions, they can reach ages in excess of 20 years. The oldest bull trout recorded (24 years old) was from the upper North Thompson River, in the Fraser system in British Columbia, Canada.