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State Wildlife Grants Project Details

Native Trout Threats and Spawning Investigations (T-030)

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Project Location

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The goal of this project is to determine the distributions and abundances of existing native cutthroat trout and fluvial bull trout populations through radio telemetry and analysis of existing habitat condition assessment data. Investigators studied whether 75 mm and longer westslope cutthroat trout occupied a niche similar niche to 75 mm and longer brook trout by comparing biomasses, population densities, and individual fish condition factors prior to and following total removal of brook trout in reaches (2.3 to 3.0 km) of three headwater streams in Montana. Data indicated that densities of juvenile brook trout negatively affected body condition of juvenile westslope cutthroat trout using two separate analyses. Results indicated that interspecific competition between brook trout and westslope cutthroat trout was nearly as strong as intraspecific competition within westslope cutthroat trout, especially among juveniles, providing insight into one mechanism by which brook trout displace westslope cutthroat trout. Further results can be found in the associated reference reports.

Time Span

05/30/2005–06/30/2007 "Completed"

Primary Investigator

  • Brad Shepard
  • Co-Principal Investigator

    • Chris Clancy


  • Mountain Streams


  • Shepard, B.B. 2009. SWG T30 Final Report: Factors that influence invasion of nonnative brook trout and their displacement of native cutthroat trout in the Northern Rocky Mountains. Montana Fish, Wildlife & Parks. 85 pp.

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  • Clancy, C. and B. Shepard. 2008. Final project report for T30: Native trout threats and spawning investigations. Montana Fish, Wildlife & Parks. 3 pp.

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