Date of Award:

5-2022

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Phaedra Budy

Committee

Phaedra Budy

Committee

Mary M. Conner

Committee

Mark C. McKinstry

Committee

John C. Schmidt

Committee

Charles B. Yackulic

Abstract

Many fishes are critically imperiled, particularly in their native rivers, due to human water use and dam construction, which can dramatically alter habitats and block fish migratory routes. The introduction of invasive sport-fishes that prey on native fish further threatens native species that maybe restricted to only a single river basin (i.e., “endemic”). To preserve native fishes in river systems with degraded habitats, managers need to understand the effects of conservation actions to ensure limited resources are applied effectively. Two commonly applied native fish conservation actions include removal of invasive fishes, and translocations of native fish from one place into another with suitable habitat to establish new populations. My primary research goals were 1) to assess the population-level native fish responses to invasive fish removal, 2) understand what factors lead to successful establishment of new endangered humpback chub populations through translocations of juveniles, and 3) to investigate alternative strategies for reducing invasive brown trout using angling, disturbance of eggs, and electrofishing, in multiple connected populations (i.e., trout move between them)experiencing different levels of warming and climate change. My research was conducted using data collected over 10 years in the Colorado River and its tributaries in Grand Canyon National Park.

I found native fish populations increased by about 480% when invasive trout populations were reduced by 60% or more. Increases in native fish were also greatest in warmer areas in years when spring flooding occurred. Translocated humpback chub populations were limited when numbers of introduced rainbow trout were higher and when floods washed ash from a fire into one stream in 2014. However, I found flooding was generally beneficial to humpback chub, which was probably because additional food was washed into their habitats. Finally, while future declines in Colorado River reservoir storage and warming of streamflow may reduce brown trout, successful Grand Canyon-wide reductions would require increasing trout removals throughout the river system particularly in tributary climate change refuges. In summary, translocations can contribute toward native fish conservation, but continued invasive fish removal and protection of natural river flow are also critical to meeting conservation goals.

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