Date of Award:

5-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Phaedra Budy

Committee

Phaedra Budy

Committee

Bethany Neilson

Committee

Charles Hawkins

Committee

Joseph Wheaton

Committee

Brett Roper

Abstract

Recent declines in many species of aquatic organisms have raised concerns about loss of biodiversity in river systems and the need to protect populations in peril. To conserve endangered species, scientists need to know information about the habitats organisms use throughout their life cycle and how environmental stressors cause populations to grow or decline. The goal of this research was to improve our understanding of the life-cycle requirements for bull trout (Salvelinus confluentus), a threatened freshwater fish species. I assessed environmental factors that affect bull trout egg incubation success and quantified juvenile bull trout movement patterns and survival rates. I then integrated this information into a life-cycle model that I used to evaluate how populations might respond to changes in survival, growth, reproduction, or migration rates, as a result of management actions, environmental variability, or climate change.

Bull trout egg survival was much lower in stream incubation environments with high amounts of fine sediment compared with environments with less fine sediment. High rates of downwelling, a process that drives surface water into the gravel, appeared to improve egg survival rates. Juvenile bull trout demonstrated diverse movement patterns, and I was able to better estimate survival rates for this size class by accounting for movement out of the study area. Changes in juvenile survival rates and the time it took for individuals to mature had the largest influence on overall population trend. Bull trout populations that were composed of individuals that spawned earlier in their life cycle and grew more slowly were more vulnerable to changes in reproductive success (e.g., egg survival). In contrast, populations composed of late-maturing individuals that grew to larger sizes were more vulnerable to changes in adult survival rates (e.g., via harvest or predation). The potential for individuals to disperse, or move from one population into another to reproduce, was important to sustain declining populations when neighboring populations were stable. Collectively, this research demonstrates that bull trout require access to habitats throughout entire watersheds to maintain all components of their complex life cycles. Diversity in life-history traits, such as variation in age at maturation and migratory behavior, is important to help populations recover from environmental catastrophes and to persist in a changing environment.

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