Fry may remain in the stream bed for up to three weeks before emerging. Juvenile fish retain their fondness for the stream bottom and are often found at or near it. Bull trout may live near areas where they were spawned or migrate from small streams to larger streams and rivers or from streams to lakes, reservoirs or salt water. Smaller resident fish remain near the areas where they were spawned while larger, migratory, fish will move considerable distances to spawn when habitat conditions allow. For instance, bull trout in Montana's Flathead Lake have been known to migrate up to 250 km to spawn.
Migration is important to maintaining healthy bull trout populations.
Bull trout are vulnerable to many of the same threats that have reduced salmon populations in the Snake River Basin. Due to their range of preferred cold water habitat conditions and life history requirements, bull trout are also more sensitive to increased water temperatures, poor water quality and degraded stream habitat than many other salmonids. In many areas, continued bull trout survival is threatened by a combination of factors rather than one major problem. For example, past and continuing land management activities have degraded stream habitat, especially along larger river systems and stream areas located in valley bottoms. Degraded conditions have severely reduced or eliminated migratory bull trout as water temperature, stream flow and other water quality parameters fall below the range of conditions which these fish can tolerate.