Threatened and Endangered Species Bull Trout Fact
Threatened and Endangered Species:
Bull Trout Salvelinus confluentus Fact Sheet
OFFICIAL STATUS: Threatened- Threatened species are species that are likely to
become endangered species within the foreseeable future throughout all or a
significant portion of their range.
LISTED: 63 Federal Register; No. III; June 10, 1998
HISTORICAL STATUS: Bull trout were once common throughout the Pacific Northwest,
ranging from northern California to the Bering Sea. They have travelled one of
the longest migration routes of any trout in North America for thousands of
PRESENT STATUS: Bull trout are extinct in California and inhabit only one river
system in Nevada. Oregon and Washington populations are at a high risk of
extinction, as well as some Idaho populations. Montana bull trout are considered
secure in only 2 percent of the stream segments they inhabit. Fish biologists
consider bull trout at moderate risk of extinction in 65 percent of their
Montana range and at high risk of extinction in 33 percent of their range.
HABITAT: Bull trout live in clean, cold rivers west of the Continental Divide in
Montana. Unlike the introduced rainbow and brown trout, bull trout inhabit the
entire river system from the mainstem to the highest elevation tributaries.
Clean gravel with upwelling ground water is critical for spawning. Cover, in the
form of undercut banks, overhanging vegetation and instream woody material is
needed to protect bull trout from predators. Complex habitat, characterized by a
variety of pools, riffles and water depths and velocities, is important to meet
the seasonal needs of all age classes of bull trout. Long spawning migrations
make habitat connectivity important. Fish passage barriers, such as irrigation
developments, may interrupt bull trout movements.
LIFE HISTORY: Non-migratory forms of the bull trout spend their entire lives in
relatively small tributary streams. Some migratory forms live in lakes as adults
and move up to small tributaries to spawn. Young trout stay in the tributaries
from one to four years before moving downstream to lakes. Other migratory forms
live in rivers as adults and move into tributaries to spawn. Bull trout reach
sexual maturity at age five. Spawning occurs in fall, although they begin the
upstream spawning migration during spring high water. This may be an adaptation
to the presence of beaver dams, which would impede fish movements at low water.
Adult bull trout move back downstream soon after spawning.
AID to IDENTIFICATION: Bull trout have pale yellow spots along the back and red
or orange spots along the sides. The general appearance is that of light spots
on a darker background, as is the case with all of the chars (true trout have
dark spots on a lighter background). The leading edge of the fins is white and
the dorsal fin is translucent.
REASONS for DECLINE: Competition with exotic fish species and hybridization with
brook trout are partly to blame. Habitat degradation is also a significant part
of the problem. Uncontrolled livestock grazing and poorly designed logging road
construction elevate water temperatures and cause sedimentation of spawning
gravels as well as loss of stream habitat structure and overhead vegetative
cover. Dewatering of streams during the irrigation season prevents bull trout
movements to and from spawning habitat. Irrigation diversion structures often
act as fish passage barriers and cause bull trout to enter irrigation ditches
where they are lost to the population. Improper placement of road culverts also
impedes bull trout movements.
RECOMMENDATIONS: Immediately release any bull trout incidentally caught while
fishing (it is illegal to deliberately fish for bull trout). Assure that any
activities initiated in bull trout habitat will not adversely affect this
species or its habitat.
COMMENTS: Bull trout, because of their dependence on high quality habitat, are
an indicator of stream health. Introduced species, such as rainbow and brown
trout, are able to survive in a broader range of habitat conditions.
REFERENCES: The Relationship Between Land Management Activities and Habitat
Requirements of Bull Trout, by the Montana Bull Trout Scientific Group, 1998,
available from MT Dept. of Fish, Wildlife and Parks.
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