Date of Award:

5-2010

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Advisor/Chair:

Todd Crowl

Abstract

This study addressed a fundamental question in applied ecology and conservation; what is the predatory impact of introduced piscivorous sport fish on imperiled native fish populations? More specifically, which of many introduced species and size-classes represent the greatest threats and should be targeted for control? In order to explore this important question, an integrated analysis of stable isotopes, quantified observed diet analysis, and stable isotope mass-balance models were used to quantify trophic interactions. These tools were used to construct food web models that were then compared to draw inferences regarding the relative contribution of prey fish, including rare native fish, to the diet of introduced sport fish. The stable isotope-derived food web illustrated a slight decoupling in energy flow between a pelagic and a benthic-littoral sub-web. The quantified diet analysis suggested piscivory was low overall, and that the introduced sport fish assemblage relied heavily on zooplankton and aquatic insect prey. The integrated stable isotope and quantified diet analysis demonstrated that the consumption of prey fish, particularly pelagic prey fish, was typically underestimated using stomach content analyses. From the evaluation, comparison, and integration of food web models, I suggest that substantial predation was occurring on the early life stages of Utah Lake fishes, including native fishes, and it was not being observed using stomach content analysis. My comparative modeling demonstrated that introduced sport fish are an impediment to native fish conservation and identified the small size-class of white bass as the most immediate threat.

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