Montana Ecological Services Field
585 Shepard Way, Suite 1 • Helena, Montana 59601 • 406-449-5225 • (FAX)
Applied Research and Technical Assistance
Helena Field Office
Demographic and genetic response of cutthroat trout to
Habitat fragmentation has led to isolation of populations of native fishes
like westslope cutthroat trout (Oncorhynchus clarkii lewisi) and
bull trout (Salvelinus fontinalis). Migration barriers may disrupt
population structure at larger spatial scales or even restrict movement
among complementary habitats within a patch, both of which may be
important to buffer effects of disturbance. Based on this, a major focus
of native trout conservation has been to re-establish historical
connectivity among habitat patches within stream networks by removing
human-made migration barriers. A significant challenge in some cases is
to balance the competing threats of isolation versus invasion by nonnative
trout. Nonetheless, migration barriers on many small streams are being
removed throughout the western US, sometimes at great expense, and
systematic monitoring of the response of fish populations to these actions
may not be occurring.
Perched stream culvert
at road crossing in the Clearwater National Forest, Idaho
Removal of migration barriers is expected to benefit native trout by
restoring or increasing genetic diversity, resilience to disturbance, and
resistance to ecological and genetic effects of nonnative trout
invasions Evaluation of fish community response and demographic and
genetic benefits to key species that result from barrier removal projects
is needed to guide future efforts. The objective of this project
is to critically evaluate whether, and how quickly, the expected
demographic and genetic benefits of connectivity accrue in formerly
isolated westslope cutthroat trout populations after removal of human-made
trout (~130 mm TL) from unnamed tributary to East Fork Lolo Creek, Lolo
cutthroat trout (~350 mm TL) from unnamed tributary to East Fork Lolo
Creek, Lolo National Forest.
initial geographic focus is in the upper Lolo Creek watershed in western
Montana where the US Forest Service is removing or replacing a number of
fish passage barriers (culverts) on small tributary streams occupied by
westslope cutthroat trout. The study design is a
before-after-control-intervention (BACI), where the individual,
population, and community responses to reconnection will be measured
through time (before and after restoration of fish passage.
removed from tributary to East Fork Lolo Creek, Lolo National Forest
during summer 2008.
replacing undersized culvert in tributary to East Fork Lolo Creek, Lolo
National Forest during summer 2008.
being installed in tributary to East Fork Lolo Creek, Lolo National Forest
during summer 2008.
photograph of replacement culvert that provides passage for aquatic
organisms. Photo taken fall 2008.
The project is
expected to provide a targeted evaluation of whether barrier removal promotes
the demographic and genetic diversity expected to facilitate persistence of
native inland fishes in a variable landscape. More generally, the results
might help biologists prioritize future reconnection projects by understanding
where such actions may be most successful.
USFWS National Fish Passage Program
Dr. Doug Peterson (PI-US Fish and Wildlife Service), Dr. Helen Neville (Trout
Unlimited); Shane Hendrickson (US Forest Service, Lolo National Forest)
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