Movement & Migration | CSKT | Division of Fish, Wildlife, Recreation, & Conservation

Movement and Migration

Three life history forms of bull tout live in Montana: resident, fluvial, and adfluvial. Residents remain in their natal streams (the small streams where they were born). But two of the forms—fluvial and adfluvial—migrate. And they do it more than twice (unlike Pacific salmon, bull trout are repeat spawners). Their first trip comes when they are just juveniles when they emigrate from the spawning areas where they were born to larger rivers or lakes where they will spend their adult life—the fluvial form migrating into large rivers, the advluvial form into lakes.

Then, once these fish become sexually mature, they leave their river and lake homes and migrate back to their spawning areas in the headwater reaches of their drainages, the places where they themselves were born. There, they spawn. When they are finished, they turn around and return to their adult habitats (either a river or lake). For some of these fish and before there were dams on the Clark Fork River, this was a 300-mile round trip. Because they are repeat spawners, they do this every year or every other year.

Bull trout make other movements, too. When its hot in the summer, they may migrate into cooler tributary streams. And in the winter, they may migrate to areas of upwelling ground water or deep pools. So bull trout—at least the migratory forms—are travelers, moving long distances from one end of the drainage to the other multiple times throughout their lives.

Juvenile Migration

Both resident and migratory bull trout live in the Jocko. The difference is resident bull trout stay in headwater reaches their entire life, while migratory bull trout leave the small streams where they were born when they are juveniles, most when they are between one and three years old. They migrate downstream to the lower Flathead and Clark Fork Rivers where they mature into adults. These have what's called a fluvial life history form. Historically, before there were dams, some juvenile bull trout migrated all the way to Lake Pend Oreille, spending their adult lives in the lake. These are called adfluvial bull trout. When it comes time for fluvial and adfluvial bull trout to spawn, they migrate all the way back to the headwaters of the Jocko, a trip of over 165 miles.

Spawning Migration

Bull trout can travel a long way when they migrate. Their migrations are among the longest of all for species of trout that migrate in rivers and streams. Historically in the Jocko, every year spawning bull trout migrated over 165 miles to their spawning grounds, and after spawning, they turned around and covered the same distance on their return migration.

Two of the life-history forms of bull trout—fluvial and adfluvial—make migrations as a normal part of their life cycle.

Fluvial

Fluvial fish hatch in streams, migrate to a larger river to mature, and return to their natal stream to spawn. Every year, fluvial bull trout migrate from the Lower Flathead and Clark Fork Rivers to the headwaters of the Jocko to spawn. Starting in the summer, when water temperatures are warmest and the flow lowest, they leave the large rivers where they spend most of their adult lives and travel up the Jocko to its headwater tributaries—the North, Middle, and South Forks of the Jocko—where they spawn. After spawning, they return to the Clark Fork and Flathead Rivers.

Adfluvial

Adfluvial fish hatch in streams, migrate to a lake or reservoir to mature, and return to their natal stream to spawn. Historically, every year, adfluvial bull trout migrated from Lake Pend Oreille in Idaho and swam to headwater streams to spawn. Starting in the summer, when water temperatures were warmest and flows lowest, some of those fish migrated out of the lake and into the Clark Fork River. From there they entered the Flathead River and finally the Jocko River. They traveled up the Jocko to its headwater tributaries— the North, Middle, and South Forks where they spawned. After spawning, they returned to Lake Pend Oreille, traveling 165 miles each way.

Migrating Bull Trout

Seasonal Migrations

Bull trout commonly make long-distance annual or seasonal movements among various riverine habitats, apparently in search of feeding opportunities and refuge from warm, low-water conditions in mid-summer and ice in winter. Little is known about these movements, but it is likely that river residency and migratory behavior in each bull trout population reflects local adaptations to the specific habitats historically available in the basin.

For example, bull trout often move seasonally to find safe places to overwinter. For stream-resident populations, these overwintering areas can be critical to the survival of a population. That's because during many winters, smaller streams are often covered with ice and develop ice on the streambed. By moving to deep pools, larger streams, or main-stem rivers bull trout can avoid these icing conditions.

Side-channel habitats with upwelling groundwater and low flow velocities (like sloughs) are also important as long as there is suitable cover in the form of living and dead large woody debris (logs in the stream). These areas have relatively warmer water in winter and cooler water in summer because of the upwelling groundwater. Although the use of overwintering habitat and cold-water refuges in summer may be seasonal, they are critical habitat components.

Movement and Migration

Three life history forms of bull tout live in Montana: resident, fluvial, and adfluvial. Residents remain in their natal streams (the small streams where they were born). But two of the forms—fluvial and adfluvial—migrate. And they do it more than twice (unlike Pacific salmon, bull trout are repeat spawners). Their first trip comes when they are just juveniles when they emigrate from the spawning areas where they were born to larger rivers or lakes where they will spend their adult life—the fluvial form migrating into large rivers, the advluvial form into lakes.

Then, once these fish become sexually mature, they leave their river and lake homes and migrate back to their spawning areas in the headwater reaches of their drainages, the places where they themselves were born. There, they spawn. When they are finished, they turn around and return to their adult habitats (either a river or lake). For some of these fish and before there were dams on the Clark Fork River, this was a 300-mile round trip. Because they are repeat spawners, they do this every year or every other year.

Bull trout make other movements, too. When its hot in the summer, they may migrate into cooler tributary streams. And in the winter, they may migrate to areas of upwelling ground water or deep pools. So bull trout—at least the migratory forms—are travelers, moving long distances from one end of the drainage to the other multiple times throughout their lives.

Juvenile Migration

Both resident and migratory bull trout live in the Jocko. The difference is resident bull trout stay in headwater reaches their entire life, while migratory bull trout leave the small streams where they were born when they are juveniles, most when they are between one and three years old. They migrate downstream to the lower Flathead and Clark Fork Rivers where they mature into adults. These have what's called a fluvial life history form. Historically, before there were dams, some juvenile bull trout migrated all the way to Lake Pend Oreille, spending their adult lives in the lake. These are called adfluvial bull trout. When it comes time for fluvial and adfluvial bull trout to spawn, they migrate all the way back to the headwaters of the Jocko, a trip of over 165 miles.

Spawning Migration

Bull trout can travel a long way when they migrate. Their migrations are among the longest of all for species of trout that migrate in rivers and streams. Historically in the Jocko, every year spawning bull trout migrated over 165 miles to their spawning grounds, and after spawning, they turned around and covered the same distance on their return migration.

Two of the life-history forms of bull trout—fluvial and adfluvial—make migrations as a normal part of their life cycle.

Fluvial

Fluvial fish hatch in streams, migrate to a larger river to mature, and return to their natal stream to spawn. Every year, fluvial bull trout migrate from the Lower Flathead and Clark Fork Rivers to the headwaters of the Jocko to spawn. Starting in the summer, when water temperatures are warmest and the flow lowest, they leave the large rivers where they spend most of their adult lives and travel up the Jocko to its headwater tributaries—the North, Middle, and South Forks of the Jocko—where they spawn. After spawning, they return to the Clark Fork and Flathead Rivers.

Adfluvial

Adfluvial fish hatch in streams, migrate to a lake or reservoir to mature, and return to their natal stream to spawn. Historically, every year, adfluvial bull trout migrated from Lake Pend Oreille in Idaho and swam to headwater streams to spawn. Starting in the summer, when water temperatures were warmest and flows lowest, some of those fish migrated out of the lake and into the Clark Fork River. From there they entered the Flathead River and finally the Jocko River. They traveled up the Jocko to its headwater tributaries— the North, Middle, and South Forks where they spawned. After spawning, they returned to Lake Pend Oreille, traveling 165 miles each way.

Seasonal Migrations

Bull trout commonly make long-distance annual or seasonal movements among various riverine habitats, apparently in search of feeding opportunities and refuge from warm, low-water conditions in mid-summer and ice in winter. Little is known about these movements, but it is likely that river residency and migratory behavior in each bull trout population reflects local adaptations to the specific habitats historically available in the basin.

For example, bull trout often move seasonally to find safe places to overwinter. For stream-resident populations, these overwintering areas can be critical to the survival of a population. That's because during many winters, smaller streams are often covered with ice and develop ice on the streambed. By moving to deep pools, larger streams, or main-stem rivers bull trout can avoid these icing conditions.

Side-channel habitats with upwelling groundwater and low flow velocities (like sloughs) are also important as long as there is suitable cover in the form of living and dead large woody debris (logs in the stream). These areas have relatively warmer water in winter and cooler water in summer because of the upwelling groundwater. Although the use of overwintering habitat and cold-water refuges in summer may be seasonal, they are critical habitat components.

Movement and Migration

Three life history forms of bull tout live in Montana: resident, fluvial, and adfluvial. Residents remain in their natal streams (the small streams where they were born). But two of the forms—fluvial and adfluvial—migrate. And they do it more than twice (unlike Pacific salmon, bull trout are repeat spawners). Their first trip comes when they are just juveniles when they emigrate from the spawning areas where they were born to larger rivers or lakes where they will spend their adult life—the fluvial form migrating into large rivers, the advluvial form into lakes.

Then, once these fish become sexually mature, they leave their river and lake homes and migrate back to their spawning areas in the headwater reaches of their drainages, the places where they themselves were born. There, they spawn. When they are finished, they turn around and return to their adult habitats (either a river or lake). For some of these fish and before there were dams on the Clark Fork River, this was a 300-mile round trip. Because they are repeat spawners, they do this every year or every other year.

Bull trout make other movements, too. When its hot in the summer, they may migrate into cooler tributary streams. And in the winter, they may migrate to areas of upwelling ground water or deep pools. So bull trout—at least the migratory forms—are travelers, moving long distances from one end of the drainage to the other multiple times throughout their lives.

Juvenile Migration

Both resident and migratory bull trout live in the Jocko. The difference is resident bull trout stay in headwater reaches their entire life, while migratory bull trout leave the small streams where they were born when they are juveniles, most when they are between one and three years old. They migrate downstream to the lower Flathead and Clark Fork Rivers where they mature into adults. These have what's called a fluvial life history form. Historically, before there were dams, some juvenile bull trout migrated all the way to Lake Pend Oreille, spending their adult lives in the lake. These are called adfluvial bull trout. When it comes time for fluvial and adfluvial bull trout to spawn, they migrate all the way back to the headwaters of the Jocko, a trip of over 165 miles.

Spawning Migration

Bull trout can travel a long way when they migrate. Their migrations are among the longest of all for species of trout that migrate in rivers and streams. Historically in the Jocko, every year spawning bull trout migrated over 165 miles to their spawning grounds, and after spawning, they turned around and covered the same distance on their return migration.

Two of the life-history forms of bull trout—fluvial and adfluvial—make migrations as a normal part of their life cycle.

Fluvial

Fluvial fish hatch in streams, migrate to a larger river to mature, and return to their natal stream to spawn. Every year, fluvial bull trout migrate from the Lower Flathead and Clark Fork Rivers to the headwaters of the Jocko to spawn. Starting in the summer, when water temperatures are warmest and the flow lowest, they leave the large rivers where they spend most of their adult lives and travel up the Jocko to its headwater tributaries—the North, Middle, and South Forks of the Jocko—where they spawn. After spawning, they return to the Clark Fork and Flathead Rivers.

Adfluvial

Adfluvial fish hatch in streams, migrate to a lake or reservoir to mature, and return to their natal stream to spawn. Historically, every year, adfluvial bull trout migrated from Lake Pend Oreille in Idaho and swam to headwater streams to spawn. Starting in the summer, when water temperatures were warmest and flows lowest, some of those fish migrated out of the lake and into the Clark Fork River. From there they entered the Flathead River and finally the Jocko River. They traveled up the Jocko to its headwater tributaries— the North, Middle, and South Forks where they spawned. After spawning, they returned to Lake Pend Oreille, traveling 165 miles each way.

Seasonal Migrations

Bull trout commonly make long-distance annual or seasonal movements among various riverine habitats, apparently in search of feeding opportunities and refuge from warm, low-water conditions in mid-summer and ice in winter. Little is known about these movements, but it is likely that river residency and migratory behavior in each bull trout population reflects local adaptations to the specific habitats historically available in the basin.

For example, bull trout often move seasonally to find safe places to overwinter. For stream-resident populations, these overwintering areas can be critical to the survival of a population. That's because during many winters, smaller streams are often covered with ice and develop ice on the streambed. By moving to deep pools, larger streams, or main-stem rivers bull trout can avoid these icing conditions.

Side-channel habitats with upwelling groundwater and low flow velocities (like sloughs) are also important as long as there is suitable cover in the form of living and dead large woody debris (logs in the stream). These areas have relatively warmer water in winter and cooler water in summer because of the upwelling groundwater. Although the use of overwintering habitat and cold-water refuges in summer may be seasonal, they are critical habitat components.