Year of Award

2011

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Fish and Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Chair

Lisa Eby

Commitee Members

Chris Clancy, Mike Mitchell, Robb Leary, Tom McMahon

Keywords

Bitterroot River, bull trout, genetic assignment, genetic population structure, metapopulation structure, migratory life history, monitoring, Salvelinus confluentus

Abstract

Bull trout Salvelinus confluentus are a species of conservation interest and are currently listed as threatened by the U.S. Fish and Wildlife Service. Understanding and conserving the genetic and life history diversity of bull trout populations across their range is critical as conservation, management, and recovery plans are developed. Numerous studies in different regions have shown that local bull trout populations in close geographic proximity are typically very genetically different and evidence for dispersal among neighboring tributary populations is weak. In addition to genetic diversity, maintenance of life history diversity may increase resilience of bull trout populations. The larger migratory forms have been linked to high reproductive potential and increased population persistence in unstable environments as the distribution of adults across multiple habitats may buffer them against stochastic events. Ensuring the persistence of both genetic and life history diversity are important conservation priorities. I evaluated the genetic population structure of bull trout in the East Fork Bitterroot River, Montana and identified which tributaries produced the majority of fluvial fish using genetic assignment. My data showed that populations in tributaries are genetically distinct from each other and fish in the main stem East Fork; however, dispersal of individuals among populations was apparent suggesting a metapopulation structure. My results indicate that the scale of management for bull trout in the East Fork is the basin and that migratory fish may be important for maintaining gene flow among small populations and genetic variation within them. Given the importance of migratory fish, I examined how well we are tracking migratory bull trout populations and threats to their existence. The evaluation of the current monitoring protocol revealed that redd count surveys are not useful. Even though mark-recapture surveys are common, there are few locations where population estimates are obtained. Improving the protocols and combining approaches may improve our inference, specifically, conducting redd counts and electrofishing population estimates in areas identified as supporting migratory fish. In general, threats such as roads, grazing allotments, and wildfire have been well tracked, although future threats to river habitat conditions (e.g., temperature and degradation) and invasions of brown trout are yet to be fully evaluated.

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© Copyright 2011 Leslie Grace Nyce