Date of Award:

5-2012

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Phaedra Budy

Committee

Phaedra Budy

Committee

Brett Roper

Committee

Mevin Hooten

Committee

John C. Schmidt

Committee

Chris Luecke

Abstract

Brown trout (Salmo trutta), one of the world’s most successful introduced species in river and lake systems, negatively impacts native species through predation, competition, and systemwide effects. Thus, there is a need to understand factors controlling the distribution of brown trout, in order to prioritize and develop conservation and management strategies. Within the context of invasion success, I investigated how the physical characteristics of the Logan River influence the distribution of brown trout, as well as the potential for brown trout predation on a native fish, the mottled sculpin (Cottus bairdi).

In chapter 1, I evaluated whether changes in the river from downstream to upstream contribute to potentially higher mortality of larval brown trout during flood events, due to the movement of substrates where these early life-stages develop. Potential mortality was not greater at high elevations, because brown trout locally chose low-movement areas to deposit their eggs. In chapter 2, I investigated the importance of spawning gravel availability, versus other habitat factors, in influencing the density of eggs deposited by brown trout. Winter ice conditions, distance from a reservoir, and to a lesser-extent the availability of small substrates, best explained the density of brown trout egg locations. Finally, in chapter 3, I evaluated the potential predatory effects of exotic brown trout on native mottled sculpin (Cottus bairdi). The diets of brown trout consisted of a high percentage of sculpin, which contrasted to a low percentage in diets previously documented for native Bonneville cutthroat (Oncorhynchus clarkii) on the Logan River.

My research suggests that winter ice conditions and distance from reservoirs are important drivers of the brown trout distribution, which could extend to other systems. These drivers, including how they may be influenced by future climate change and habitat alteration, should be considered in management efforts to control brown trout expansion and to limit the predatory impacts of brown trout.

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Comments

This work made publicly available electronically on September 20, 2012.

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