(Map may reflect historical as well as recent sightings)
Bull trout were listed as threatened in June 1998. Critical
habitat was designated in 2005. A recovery plan was drafted in
2005 and has not been finalized. In January 2010, the USFWS proposed a revision of critical habitat.
Bull trout are members of the salmon family known
as char. Bull trout, Dolly Varden and lake trout are all species
of char native to the northwest. Char are distributed farther
north than any other group of freshwater fish except Alaskan
blackfish and are well adapted for 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
major tributaries on the west side of the Oregon Cascades; the
Columbia and Snake Rivers and major tributaries east of the Cascades;
and in streams of 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 waters
and a long incubation time, bull trout are more sensitive to increased
water temperatures, poor water quality and degraded stream habitat
than many other salmonids. Further threats to bull trout include
hybridization and competition with non-native brook trout, brown
trout and lake trout, overfishing, poaching, and man-made structures
that block migration.
In many areas, continued survival of the species 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 streams
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. In many watersheds,
remaining bull trout are smaller, resident fish isolated in headwater
streams. Brook trout, introduced throughout much of the range
of bull trout, easily hybridize with them, producing sterile offspring.
Brook trout reproduce earlier and at a higher rate than bull
trout so bull trout populations are often supplanted by these
non-natives. Dams and other in-stream structures also
affect bull trout by blocking migration routes, altering water temperatures
and killing fish as they pass through and over dams or are trapped
in irrigation and other diversion structures.
Bull trout are seldom found in waters where temperatures are
warmer than 59º to 64º F. Besides very cold water, bull trout
require stable stream channels, clean spawning gravel, complex and
diverse cover, and unblocked migration routes.
Small bull trout eat terrestrial and aquatic insects but shift
to preying on other fish as they grow larger. Large bull trout
are primarily fish predators. Bull trout evolved with whitefish,
sculpins and other trout and use all of them as food sources.
In the Willamette Basin, chinook salmon are an important food
source for bull trout. Adult bull trout are usually small, but
can grow to 36 inches in length and weigh up to 32 pounds. Bull
trout reach sexual maturity at between four and seven years of age
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 abundant 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
Bull trout may be either resident or migratory. Resident fish
live for their entire life near areas where they were spawned. Migratory
fish are usually spawned in small headwater streams, and then
migrate to larger streams, rivers, lakes, reservoirs or salt water
where they grow to maturity. 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 kilometers (150 miles) to spawn.
Many of the same management actions that are being done to protect
other declining salmonids may also help bull trout. Stream and
habitat protection and restoration, reduction of siltation from
roads and other erosion sites and modification of land use practices
to improve water quality and temperature are all important. Several
state agencies have also enacted regulations reducing or prohibiting
bull trout harvest. States have also adopted conservation plans
to help bull trout populations recover.
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