The bull trout (Salvelinus confluentus) was first listed on June 10, 1998. It is currently
designated as threatened (64 FR 58909 58933) in the U.S.A., conterminous, (lower 48
states). Within the area covered by this listing, this species is known to occur in: Idaho,
Montana, Nevada, Oregon, Washington. The species is fairly widespread in Oregon,
occurring in 16 counties.
Bull trout are members of the char subgroup of the Salmonid family. Bull trout, Dolly
Varden and lake trout are species of char native to the northwest. Char species such as
bull trout live farther north than any other group of freshwater fish except Alaskan
blackfish and are well adapted for life in very cold water. Bull trout living in streams
grow to about four pounds while those in lake environments can weigh more than 20
Bull trout exist in five distinct population segments: Coastal-Puget Sound, St. Mary-Belly
River, Klamath River, Columbia River, and Jarbridge River. The Klamath River and
Columbia River population segments occur within Oregon.
Rieman et al. (1997) summarized existing knowledge of bull trout distribution within the
interior Columbia River Basin in Oregon, Washington, Idaho, Montana, and Nevada, and
within the Klamath River Basin in Oregon, and concluded that the bull trout is most
likely to occur in colder, higher-elevation, low- to mid-order watersheds with low road
density. Elevation is associated with temperature, stream order, and other variables and
has been used to define habitat patches for the bull trout (Rieman and McIntyre 1995).
Specific location information for the two DPSs existing in Oregon are provided below.
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 River Basin. Currently, most bull trout
populations are confined to headwater areas of tributaries to the Columbia, Snake, and
Klamath Rivers. Rieman et al. (1997) suggest that, even historically, bull trout
distribution is likely to have been patchy because of natural passage barriers, thermal
barriers, stringent habitat requirements, and by some life history factors discussed below.
The bull trout exhibits both resident and migratory life-history strategies (Rieman and
McIntyre 1993). Resident bull trout complete their entire life cycle in the tributary (or
nearby) streams in which they spawn and rear. Migratory bull trout spawn in tributary
streams where juvenile fish rear one to four years before migrating to either a lake
(adfluvial form), river (fluvial form) (Fraley and Shepard 1989, Goetz 1989), or in certain
coastal areas, to saltwater (anadromous) (Cavender 1978, McPhail and Baxter 1996,
WDFW et al. 1997). Resident and migratory forms may be found together, and either
form may give rise to offspring exhibiting either resident or migratory behavior (Rieman
and McIntyre 1993).
Four life-history forms of char are recognized, each exhibiting a specific behavioral or
life history pattern (Brown 1994). Resident fish live their whole lives near areas where
they were spawned. Migratory fish are usually spawned in small headwater streams and
then migrate to larger streams or rivers (fluvial), lakes or reservoirs (adfluvial), or salt
water (anadromous) where they grow to maturity. Smaller resident fish remain near the
areas where they were spawned in smaller, high elevation streams and seldom reach size
of over 30 cm (Brown 1994; USFWS 2002a). Larger, migratory fish will move
considerable distances to spawn when habitat migrate up to 250 km to spawn (USFWS
Because bull trout life history patterns include migratory and resident forms, both adults
and juveniles are present in the streams throughout the year. Bull trout adults may begin
to migrate from feeding to spawning grounds in the spring and migrate slowly throughout
the summer (Buchanan et al. 1997). In Oregon, most bull trout spawn in September and
October, though populations in the Metolius River Basin can begin spawning as early as
July (Bellerud et al. 1997, Buchanan et al. 1997) and mid to late August in the Klamath
River Basin (Klamath Basin Bull Trout Working Group, unpublished data). Bull trout
eggs incubate from 100 to 145 days, usually in winter, after which the alevins require 65
to 90 days to absorb their yolk sacs (Buchanan et al. 1997). They remain within the
interstices of the streambed as fry for up to 3 weeks before filling their air bladders,
reaching lengths of 25-28 mm, and emerging from the streambed in late April (Brown
1994, Buchanan et al. 1997).
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
River 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 up to 32 pounds. Bull trout
reach sexual maturity at between 4 and 7 years of age and are known to live as long as 12
years. They spawn in the fall after temperatures drop below 9EC, 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 ground water. Bull trout eggs require a long
incubation period compared with other salmon and trout, hatching in late winter or early
spring. Fry may remain in the stream gravels for up to 3 weeks before emerging (USFWS
The size and age of the bull trout at maturity depends upon the life-history strategy.
Resident fish tend to be smaller than migratory fish at maturity and produce fewer eggs
(Fraley and Shepard 1989, Goetz 1989). The bull trout normally reaches sexual maturity
in 4 to 7 years and may live longer than 12 years. Repeat- and alternate-year spawning
has been reported, although repeat-spawning frequency and post-spawning mortality are
not well documented (Leathe and Graham 1982, Fraley and Shepard 1989, Pratt 1992,
Rieman and McIntyre 1996).
The bull trout is an opportunistic feeder, with food habits primarily a function of size and
life-history strategy. Resident and juvenile migratory bull trout prey on terrestrial and
aquatic insects, macro-zooplankton, and small fish (Boag 1987, Goetz 1989, Donald and
Alger 1993). Adult migratory bull trout feed on various fish species (Leathe and Graham
1982, Fraley and Shepard 1989, Brown 1992, Donald and Alger 1993). In coastal areas
of western Washington, the bull trout feeds on Pacific herring (Clupea pallasi), Pacific
sand lance (Ammodytes hexapterus), and surf smelt (Hypomesus pretiosus) in the ocean
(WDFW et al. 1997).
In the Columbia River and Klamath River Basins, the bull trout occurs with native
cutthroat trout (Oncorhynchus clarki subspecies), resident (redband) and migratory
(steelhead) rainbow trout (O. mykiss), chinook salmon (O. tshawytscha), sockeye salmon
(O. nerka), mountain whitefish (Prosopium williamsoni), and various sculpin (Cottidae),
sucker (Catostomidae), and minnow (Cyprinidae) species (Mauser et al. 1988, WDF et al.
1993, WDFW 1998).
Bull trout are seldom found in waters where temperatures are warmer than 15 C to 18 ºC.
Besides very cold water, bull trout require stable stream channels, clean spawning gravel,
complex and diverse cover, and unblocked migration routes (USFWS 2002a).
The bull trout has more specific habitat requirements than most other salmonids (Rieman
and McIntyre 1993). Habitat components that influence its distribution and abundance
include water temperature, cover, channel form and stability, valley form, spawning and
rearing substrate, and migratory corridors (Fraley and Shepard 1989; Goetz 1989;
Hoelscher and Bjornn 1989; Sedell and Everest 1991; Howell and Buchanan 1992; Pratt
1992; Rieman and McIntyre 1993, 1995; Rich 1996; Watson and Hillman 1997). Watson
and Hillman (1997) concluded that watersheds must have specific physical characteristics
to provide the habitat requirements necessary for the bull trout to successfully spawn and
rear and that these specific characteristics are not necessarily present throughout these
watersheds. Because the bull trout exhibits a patchy distribution, even in pristine habitats
(Rieman and McIntyre 1993), individuals of this species should not be expected to
simultaneously occupy all available habitats (Rieman et al.1997b).
Migratory corridors link seasonal habitats for all bull trout life histories. For example, in
Montana, migratory bull trout make extensive migrations in the Flathead River system
(Fraley and Shepard 1989), and resident bull trout in tributaries of the Bitterroot River
move downstream to overwinter in tributary pools (Jakober 1995). The ability to migrate
is important to the persistence of bull trout (Rieman and McIntyre 1993, M. Gilpin, in litt.
1997, Rieman et al. 1997). Migrations facilitate gene flow among local populations when
individuals from different local populations interbreed, or stray, to non-natal streams.
Local bull trout populations that are extirpated by catastrophic events may also become
reestablished by migrants.
Migrant forms of the bull trout move downstream to a river or lake where they feed on
other fish and grow to maturity. After entering the river or lake, juvenile bull trout grow
rapidly, often reaching sizes over 300 cm (20 inches) and approximately 1 kg (over 2
pounds) by the time they are 5 to 6 years old. Migratory bull trout live several years in
larger rivers or lakes, where they grow to a much larger size than resident forms before
returning to tributaries to spawn. Growth differs little between life forms during their
first years of life in headwater streams, but diverges as migratory fish move into larger
and more productive waters (Rieman and McIntyre 1993). Resident and migratory forms
may live together, but it is unknown if they represent a single population or separate
populations (Rieman and McIntyre 1993).
The bull trout is found primarily in cold streams, although individual fish are found in
larger, warmer river systems throughout the Columbia River Basin (Fraley and Shepard
1989; Rieman and McIntyre 1993, 1995; Buchanan and Gregory 1997; Rieman et al.
1997). Water temperature above 15 ° C (59 °F) is believed to limit bull trout distribution,
a limitation that may partially explain the patchy distribution within a watershed (Fraley
and Shepard 1989, Rieman and McIntyre 1995).
Spawning areas are often associated with cold-water springs, groundwater infiltration,
and the coldest streams in a given watershed (Pratt 1992, Rieman and McIntyre 1993,
Rieman et al. 1997, Baxter et al. 1999). The requirement for cold water during egg
incubation has limited the spawning distribution of the bull trout to high elevations in
areas where the summer climate is warm. Rieman and McIntyre (1995) found in the
Boise River Basin that no juvenile bull trout were present in streams below 1,613 m
(5,000 feet). Similarly, in the Sprague River Basin of south-central Oregon, Ziller (1992)
found in four streams with bull trout that “numbers of bull trout increased and numbers of
other trout species decreased as elevation increased. In those streams, bull trout were
only found at elevations above 1,774 m” (5,500 feet).
Goetz (1989) suggested optimum water temperatures for rearing bull trout of about 7 to 8
°C (44 to 46 °F) and for egg incubation of 2 to 4 °C (35 to 39 °F). For Granite Creek,
Idaho, Bonneau and Scarnecchia (1996) observed that juvenile bull trout selected the
coldest water (8 to 9 °C [46 to 48 °F], within a temperature gradient of 8 to 15 °C [46 to
60 °F]) available in a plunge pool. In Nevada, adult bull trout have been collected at sites
with a water temperature of 17.2 °C (63 °F) in the West Fork of the Jarbidge River (S.
Werdon, pers. comm., 1998) and have been observed in Dave Creek where maximum
daily water temperatures were 17.1 to 17.5 °C (62.8 to 63.6 °F) (Werdon, in litt. 2001).
In the Little Lost River, Idaho, the bull trout has been collected in water having
temperatures up to 20 °C (68 °F); however, these fish made up less than 50 percent of all
salmonids when maximum summer water temperature exceeded 15 °C (59 °F) and less
than 10 percent of all salmonids when temperature exceeded 17 °C (63 °F) (Gamett
All life-history stages of the bull trout are associated with complex forms of cover,
including large woody debris, undercut banks, boulders, and pools (Fraley and Shepard
1989, Goetz 1989, Hoelscher and Bjornn 1989, Sedell and Everest 1991, Pratt 1992,
Thomas 1992, Rich 1996, Sexauer and James 1997, Watson and Hillman 1997). Jakober
(1995) observed the bull trout overwintering in deep beaver ponds or pools containing
large woody debris in the Bitterroot River drainage, Montana, and suggested that suitable
winter habitat may be more restricted than summer habitat. Maintaining bull trout habitat
requires stability of stream channels and of flow (Rieman and McIntyre 1993). Juvenile
and adult bull trout frequently inhabit side channels, stream margins, and pools with
suitable cover (Sexauer and James 1997). These areas are sensitive to activities that
directly or indirectly affect stream channel stability and alter natural flow patterns. For
example, altered stream flow in the fall may disrupt the bull trout during the spawning
period, and channel instability may decrease survival of eggs and young juveniles in the
gravel from winter through spring (Fraley and Shepard 1989, Pratt 1992, Pratt and
The bull trout may spawn each year or in alternate years (Batt 1996), and survival among
spawners is high between repeat spawning events. Mark-recapture studies of bull trout
spawners from Rimrock Lake (Washington) have shown that spawners each year include
fish on their fifth spawning run (Paul James, Central Washington University, Ellensburg,
Washington, pers. comm., 2003). The bull trout varies in the timing of out-migration,
and in the timing and frequency of spawning. The multiple life-history strategies found
in bull trout populations represent important diversity (both spatial and genetic) that help
protect these populations from stochastic events.
Preferred bull trout spawning habitat consists of low-gradient stream reaches with loose,
clean gravel (Fraley and Shepard 1989) and water temperatures of 5 to 9 °C (41 to 48 °F)
in late summer to early fall (Goetz 1989). In the Swan River, Montana, abundance of
bull trout redds (spawning areas) was positively correlated with the extent of bounded
alluvial valley reaches, which are likely areas of groundwater to surface water exchange
(Baxter et al. 1999). Survival of bull trout embryos planted in stream areas of
groundwater upwelling used by bull trout for spawning were significantly higher than
embryos planted in areas of surface-water recharge not used by bull trout for spawning
(Baxter and McPhail 1999). Pratt (1992) indicated that increases in fine sediment reduce
egg survival and emergence.
The bull trout typically spawns from August to November during periods of decreasing
water temperatures. Water temperatures during spawning generally range from 4 to 10
°C (39 to 51 °F). Redds are often constructed in stream reaches fed by springs or near
other sources of cold groundwater (Goetz 1989, Pratt 1992, Rieman and McIntyre 1996).
Migratory bull trout frequently begin spawning migrations as early as April and have
been known to move upstream as far as 250 km (155 miles) to spawning grounds in
Montana (Fraley and Shepard 1989, Swanberg 1997). In Idaho, bull trout moved 109 km
(67.5 miles) from Arrowrock Reservoir to spawning areas in the headwaters of the Boise
River (Flatter 1998). In the Blackfoot River, Montana, the bull trout began spring
migrations to spawning areas in response to increasing temperatures (Swanberg 1997).
Depending on water temperature, egg incubation is normally 100 to 145 days (Pratt
1992), and after hatching, juveniles remain in the substrate. Time from egg deposition to
emergence of fry may surpass 200 days. Fry normally emerge from early April through
May, depending on water temperatures and increasing stream flows (Pratt 1992, Ratliff
and Howell 1992).
Population Trends and Risks
Bull trout are vulnerable to many of the same threats that have reduced salmon
populations. Because of their need for very cold waters and 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 nonnative brook trout, brown trout, and lake trout;
overfishing; poaching; and man-made structures that block migration (USFWS 2002a).
In many areas, continued survival of the species is threatened by a combination of factors
rather than one major factor. 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 that 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 also reproduce earlier and at a higher rate
than bull trout, so bull trout populations are often supplanted by these nonnatives. Dams
and other instream 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 (USFWS 2002a).
Non-native salmonids (members of the trout and salmon family) have been widely
introduced and have become established in numerous areas throughout the range of the
bull trout. These species include the brook trout (Salmo fontinalis), lake trout, brown
trout (S. trutta), Arctic grayling (Thymallus arcticus), and lake whitefish (Coregonus
clupeaformis). Kokanee (a freshwater form of O. nerka), nonnative strains of rainbow
trout, and nonnative subspecies of cutthroat trout have also been introduced into areas
where the bull trout did not occur naturally.
The goal of bull trout recovery is to ensure the long-term persistence of self-sustaining,
complex interacting groups of bull trout distributed across the species native range.
Recovery of bull trout will require reducing threats to the long-term persistence of
populations, maintaining multiple interconnected populations of bull trout across the
diverse habitats of their native range, and preserving the diversity of bull trout life-history
strategies (e.g., resident or migratory forms, emigration age, spawning frequency, local
habitat adaptations). To accomplish this goal, the following four objectives have been
identified: maintain current distribution of bull trout within core areas as described in
recovery unit chapters and restore distribution where recommended in recovery unit
chapters; maintain stable or increasing trends in abundance of bull trout (abundance
levels defined in recovery units); restore and maintain suitable habitat conditions for all
bull trout life history stages and strategies; and conserve genetic diversity and provide
opportunity for genetic exchange (USFWS 2002b).
Critical habitat was designated for bull trout in the Columbia and Klamath River Basins
on October 6, 2004 and revised on September 26, 2005. The critical habitat encompasses
a total of 939 miles of streams in Oregon, designated as critical bull trout habitat, along
with 27,322 acres of lakes and reservoirs in that state.
The primary constituent elements (as listed in 70 FR 56212) for bull trout are as follows:
(i) Water temperatures that support bull trout use. Bull trout have been documented in
streams with temperatures from 32 to 72 °F (0 to 22 °C) but are found more frequently in
temperatures ranging from 36 to 59 °F (2 to 15 °C). These temperature ranges may vary
depending on bull trout life history stage and form, geography, elevation, diurnal and
seasonal variation, shade, such as that provided by riparian habitat, and local groundwater
(ii) Complex stream channels with features such as woody debris, side channels, pools,
undercut banks to provide a variety of depths, velocities, and instream structures;
(iii) Substrates of sufficient amount, size, and composition to ensure success of egg and
embryo overwinter survival, fry emergence, and young-of-the-year and juvenile survival.
This should include a minimal amount of fine substrate less than 0.25 inch (0.63
centimeter) in diameter;
(iv) A natural hydrograph, including peak, high, low, and base flows within historic
if regulated, currently operate under a biological opinion that addresses bull trout, or a
hydrograph that demonstrates the ability to support bull trout populations by minimizing
daily and day-to-day fluctuations and minimizing departures from the natural cycle of
flow levels corresponding with seasonal variation;
(v) Springs, seeps, groundwater sources, and subsurface water to contribute to water
and quantity as a cold water source;
(vi) Migratory corridors with minimal physical, biological, or water quality impediments
between spawning, rearing, overwintering, and foraging habitats, including intermittent
seasonal barriers induced by high water temperatures or low flows;
(vii) An abundant food base including terrestrial organisms of riparian origin, aquatic
macroinvertebrates, and forage fish; and
(viii) Permanent water of sufficient quantity and quality such that normal reproduction,
and survival are not inhibited.