Bull Trout
Pacific Region  
 

BIOLOGY

 

Bull trout

Illustration by J. Tomelleri

DESCRIPTION OF THE SPECIES

Bull trout (Salvelinus confluentus) were listed in 1999 as threatened throughout their range in the coterminous United States, which includes Washington, Oregon, Idaho, Montana and Nevada. Bull trout are a cold-water fish of relatively pristine streams and lakes in the Pacific Northwest of the United States. They are grouped with the char, within the salmonid family of fishes.

They have the most specific habitat requirements of any of the Pacific Northwest salmonids, including the "Four C's": Cold, Clean, Complex, and Connected habitat. Bull trout require the coldest water temperatures; they require among the cleanest stream substrates for spawning and rearing; they require complex habitats, including streams with riffles and deep pools, undercut banks and lots of large logs; and they need connection from river, lake and ocean habitats to headwater streams for annual spawning and feeding migrations.


They are excellent indicators of water quality. Protecting their habitat improves the water quality of rivers and lakes throughout the Pacific Northwest.

The bull trout is primarily threatened by habitat degradation and fragmentation, blockage of migratory corridors, poor water quality, past fisheries management and the introduction of non-native species such as brown, lake and brook trout.  

Bull trout. Photo by Justin Cook, U.S. Fish and Wildlife Service.

Bull trout photo by Justin Cook, U.S. Fish and Wildlife Service.

LIFE HISTORY

Some bull trout populations are migratory, spending portions of their life cycle in larger rivers or lakes before returning to smaller streams to spawn, while others complete their entire life cycle in the same stream. Some bull trout in the Coastal-Puget Sound population migrate between fresh water and the marine environment.

Bull trout can grow to more than 20 pounds in lake environments and live up to 12 years. Under exceptional circumstances, they can live more than 20 years.

RANGE

In the Columbia River Basin, bull trout historically were found in about 60 percent of the basin. They now occur in less than half of their historic range. Populations remain in portions of Oregon, Washington, Idaho, Montana and Nevada. In the Klamath River Basin, bull trout occur in 21 percent of their historic range.

THREATS TO BULL TROUT

Bull trout have declined due to habitat degradation and fragmentation, blockage of migratory corridors, poor water quality, past fisheries management, and the introduction of non-native species such as brown, lake and brook trout. While bull trout occur over a large area, their distribution and abundance has declined and several local extinctions have been documented. Many of the remaining populations are small and isolated from each other, making them more susceptible to local extinctions.


Expected global climate change threatens bull trout throughout their range in the coterminous United States. With a warming climate, cool-enough spawning and rearing areas are expected to shrink during warm seasons, in some cases very dramatically, causing them to become even more isolated from one another. Climate change will likely interact with other stressors, such as habitat loss and fragmentation, invasions of non-native fish, disease and other threats, to render some current spawning, rearing and migratory habitats marginal or wholly unsuitable.


For more information including biology, status, and other related documents please go to ECOS.fws.gov.

Last updated: October 12, 2010