Date of Award:

8-2023

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Phaedra Budy

Committee

Phaedra Budy

Committee

Michelle Baker

Committee

Soren Brothers

Committee

Janice Brahney

Committee

Rob Van Kirk

Abstract

Reservoirs and their associated rivers provide water for agricultural and municipal uses, ecological benefits for fish and wildlife, and associated recreational activity. However, in the Greater Yellowstone Ecosystem climate change and population growth are putting pressure on water quality and supply, potentially damaging the unique and economically important coldwater trout habitat that these systems support. In this study, the author investigates the impact of changing water quality and supply on trout habitat quality, quantity, and selection to assist conservation goals in the Henry’s Fork Watershed in eastern Idaho. The study found that higher availability of cold-water refuge habitat in Island Park Reservoir during the hot summer months increased trout and salmon populations. The amount of cold-water refuge habitat was positively related to Island Park Reservoir water levels. The study also found that submerged aquatic vegetation were a critical part of fish habitat in the Henry’s Fork River, creating habitats that could provision both food and predator avoidance simultaneously. This study also found that increasing submerged aquatic vegetation in the Henrys Fork River has the potential to affect fish movement to improve angling. More research is needed to determine the net effect of submerged aquatic vegetation on trout populations in river ecosystems. This study highlights the importance of refuge habitat and reservoir conditions to fish populations in connected river-reservoir systems, as well as the importance of submerged aquatic vegetation for trout habitat quantity, quality, and preferences. The findings of this study have important implications for adaptive management actions that seek to improve fish habitat refuges while maintaining important water supply benefits for all stakeholders.

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