Fishing

Everything you wanted to know: bull trout

Bull trout (Salvelinus confluentus)

Species summary and status: The bull trout was once found throughout the Columbia River Basin, east to western Montana, south to northern Nevada, west to California and possibly as far north as southeastern Alaska. The main populations remaining in the lower 48 states are in Montana, Idaho, Oregon, and Washington, with a small population in northern Nevada. 

The bull trout has small, pale yellow-to-crimson spots on a darker background, fading to white on the belly. Bull trout and Dolly Varden look very similar, and were once considered the same species. Both have small, pale yellow to crimson spots on a darker background, which ranges from olive green to brown above, fading to white on the belly. Spawning adults develop varying amounts of red on the belly. Both species also exhibit differences in size, body characteristics, coloration, and life history behavior across their range.Taxonomic work, published in 1978 and accepted by the American Fisheries Society in 1980, identified bull trout as distinct from the Dolly Varden. Compared to Dolly Varden, bull trout are larger on average, with a relatively longer and broader head. Bull trout are mainly an inland species, while Dolly Varden are more common in coastal areas. In Washington, both species are present in the Puget Sound area.

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.

Bull trout reach sexual maturity 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° Fahrenheit (8°C), in streams with 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 (4-5 months), hatching in late winter or early spring. Juvenile fish retain their fondness for the stream bottom and are often found at or near it.

Some bull trout may live near areas where they were hatched. Others migrate from streams to lakes, reservoirs (or, in the case of coastal populations, salt water) a few weeks after emerging from the gravel. Migratory bull trout attain a greater size than resident stream fish. However, lakes and reservoirs are not good spawning habitat, so migratory bull trout may swim considerable distances to spawn when habitat conditions allow. For instance, bull trout in Montana’s Flathead Lake have been known to migrate up to 155 miles (250 km) to spawn. Migration is important to maintaining healthy bull trout populations.

The U.S. Fish and Wildlife Service (Service) announced Sept. 4, 2014, the availability of a Revised Draft Recovery Plan for the Coterminous U.S. Population of Bull Trout. Bull trout are listed as threatened under the Endangered Species Act in the lower 48 United States. It occurs in Montana, Idaho, Washington, Oregon, and Nevada. The Service recently published a Final Recovery Plan for the Coterminous U.S. Population of Bull Trout on Sept. 30, 2015.

Looking forward: Although
 bull
 trout 
are 
widely
 distributed 
over
 a 
large
 geographic 
area,
the
 effects 
of 
human
 activities 
over
 the 
past
 century
 have 
reduced
 their
 overall
 distribution 
and
 particularly 
their
 abundance. 
Increased
 habitat
 fragmentation
 from 
dams,
 diversions,
 land 
and
 water
 management
 practices,
and
 human
 development 
has 
reduced 
the
 amount
 of
 available
 connected
 habitat.

Increased
 isolation 
of 
local
 populations 
and

 decreased
 connectivity
 between 
bull
 trout 
Core 
Areas 
is
 resulting 
in 
 a 
loss 
o f
the
 migratory 
life
 forms
 of
 bull
 trout
 and 
is 
 a 
major 
concern 
for 
population viability.

 Bull
 trout 
tend 
to
 be 
more 
migratory
 than 
other 
western
 native 
trout.

 Fish 
passage 
along 
migration 
routes
 that
 connect
 foraging,
 migrating,
 and 
over‐ wintering 
habitat
 with 
spawning 
tributaries
 are
 crucial 
to 
bull
 trout 
life 
history 
and
 maintaining 
sufficient
 genetic
 variability.

 Fragmentation,
 isolation,
 and 
the
 resulting
 inability
 for 
local 
populations 
and
 Core
 Areas
 to
 exchange 
individuals 
and 
genetics
 remains
 a 
potential 
obstacle 
to 
population
 viability.



Loss 
of 
habitat 
quality 
has 
been 
recognized 
as
 one 
of 
the 
two 
major
 human 
influences 
in 
the
 loss 
of
 bull 
trout 
populations 
across 
the 
west.


It 
is 
well 
documented 
that 
introduced
 populations 
of 
brook 
trout 
and 
lake 
trout
 often
 become
established 
and 
threaten 
bull
 trout, 
likely 
through 
the 
primary 
mechanisms
 of
 competition 
and 
predation. 

In 
the 
case 
of
 brook 
trout ,
hybridization 
is 
also 
an
 added
 factor.

 Hybridization 
between 
brook 
trout
 and 
bull 
trout 
results 
in 
offspring
 that 
are
 frequently 
sterile

At 
present, 
there 
are 
multiple 
State, 
Federal,
 Tribal, 
private,
 and 
Canadian conservation 
efforts 
to 
improve
 the 
status 
of
 bull 
trout 
in 
the 
northwestern 
United
 States
 and 
Canada.
 Project 
implementation 
has
 generally 
followed
 a
 site‐specific 
and
 opportunity‐based 
approach, 
rather 
than 
a
 watershed‐based 
approach,
 with 
varied
 results
 and 
accomplishments.
 
With
 two
 nations,
 five
 states,
 multiple 
federal 
agencies, 
and
 numerous
Tribal
 nations 
involved,
 it
 has 
been
 difficult 
to 
discern 
a 
coordinated 
or 
prioritized
 basis 
for 
bull 
trout 
restoration 
and 
habitat
 status.

All data compiled from:

Western Native Trout Initiative

Idaho Fish and Game

U.S. Fish and Wildlife

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