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Bull Trout

Photo of bull trout under water. Photo by Joel Sartore/National Geographic Stock with Wade Fredenberg/USFWS.

Scientific Name: Salvelinus confluentus

Status: Threatened

Critical Habitat: Designated

Listing Activity: Bull trout in the coterminous United States were listed as threatened in 1999. Critical habitat was initially designated in 2005 and revised in 2010. A Bull Trout Recovery Plan, including designation of six recovery units and implementation plans for each, was finalized in 2015.

Potential Oregon Range Map

  • Background

    Bull trout are a species of char, a group in the salmonid family distinct from other trout and salmon. Other North American char species include Dolly Varden, lake trout, brook trout, and arctic char.  Bull trout are the only char species native to Oregon. Char are distinguished from trout and salmon by a lack of black spots on the body, small scales, and being highly adapted to life in very cold water. 

    Historical Status and Current Trends

    Bull trout are native throughout the Pacific Northwest. In Oregon, bull trout were historically found in the Willamette River and its major tributaries on the west side of the Oregon Cascades; the Columbia and Snake Rivers and their major tributaries; and in streams in the Klamath basin. Currently, most bull trout populations are confined to headwater areas of tributaries to the Columbia, Snake, and Klamath rivers.

    Bull trout are vulnerable to many of the same threats that have reduced salmon populations. Due to their need for very cold water and their long incubation period for their eggs, bull trout are more sensitive to increased water temperatures, poor water quality and degraded stream habitat than other salmonids. Further threats to bull trout include hybridization and competition with non-native brook trout, predation by and competition with non-native brown trout and lake trout, poaching, and human-made structures that block migration and divert water from stream channels.

    In many basins, continued survival of the species is threatened by a combination of factors rather than a single major threat. Past and continuing land management activities have degraded stream habitat, especially along larger rivers and streams located in valley bottoms. As a result water temperature, stream flow and other water quality parameters fall below the range of conditions which bull trout can tolerate. Dams and other in-stream structures impact bull trout by blocking migration routes, altering water temperatures, and killing or trapping fish. Degraded conditions, along with barriers to migration, have severely reduced or eliminated the migratory life history. In many watersheds, remaining populations of bull trout are small, resident fish isolated in headwater streams. Nonnative brook trout, also in the char family of fishes, were introduced throughout much of the range of bull trout, are common to these headwater streams and where they are abundant, compete for food and space and hybridize with bull trout.

    Habitat

    Bull trout occur in the coldest waters of the state, typically where temperatures rarely exceed 60°F. Besides very cold water, bull trout require stable stream channels, clean spawning gravel, complex and diverse cover, and unblocked migration routes.

    Life History

    Bull trout express a resident or migratory life history. Resident fish live their entire life in the streams where they are spawned. Migratory fish hatch in small headwater streams, and migrate to larger rivers, lakes, and reservoirs where food resources are more abundant to grow to maturity before returning to their natal streams to spawn. Larger migratory fish will migrate considerable distances between spawning and rearing habitat. Bull trout in Montana's Flathead Lake have been known to migrate up to 250 kilometers (150 miles).  Unlike Pacific salmon species that spawn once and die, bull trout spawn multiple times in their lifetime.  For migratory bull trout this may mean migrating multiple times between headwater spawning streams and large river rearing habitats. 

    Small bull trout eat terrestrial and aquatic insects and shift to preying on fish as they grow larger. Large bull trout are primarily fish predators. Bull trout co-evolved with native whitefish, sculpin, other trout and salmon.  These species are all important food sources for bull trout. Adult resident bull trout are typically small, but given an abundant prey base migratory bull trout can grow to 36 inches in length and weigh up to 32 pounds. Bull trout reach sexual maturity between age four and seven years and are known to live as long as 12 years. They spawn in the fall after temperatures drop below 48 º F, in streams with ample cold, unpolluted water, clean gravel and cobble substrate, and gentle stream slopes. Many spawning areas are associated with cold water springs or areas where stream flow is influenced by groundwater. Bull trout eggs require a long incubation period compared to other salmon and trout, hatching in late winter or early spring. Fry may remain in the stream gravels for up to three weeks before emerging into the water column.

    Conservation Measures

    Many of the same management actions that are implemented to protect other declining salmonids will also benefit bull trout. Stream habitat protection and restoration activities to improve habitat, water quality and flows, as well as projects to ensure safe passage of migratory fish at dams, diversions and other barriers are all priorities for Oregon’s native fish. To address the threat of non-native brook trout, management agencies are researching new methods of eradication and planning for small scale suppression and control projects.  In basins where bull trout were historically present the feasibility of their re-introduction is under consideration.  In addition, the State of Oregon implements fishing regulations appropriate to the conservation of all bull trout populations throughout the state.

    References and Links

    U.S. Fish and Wildlife Service. 1998. Determination of threatened status for the Klamath River and Columbia River Distinct Population Segments of bull trout. Federal Register (63):31647-31674.

    U.S. Fish and Wildlife Service. 1999. Determination of threatened status for bull trout in the coterminous United States. Federal Register (64):58910-58933.

    U.S. Fish and Wildlife Service. 2005. Designation of Critical Habitat for the Bull Trout. Federal Register (70): 56211-56311.

    U.S. Fish and Wildlife Service. 2010. Revised Designation of Critical Habitat for Bull Trout in the Coterminous United States.  Federal Register (75): 63897-64070.

    U.S. Fish and Wildlife Service. 2015. Recovery Plan for the conterminous United States populations of bull trout (Salvelinus confluentus). Federal Register (80): 58767-58768.

     

     

    Last updated:  February 25, 2020

     

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