Date of Award
Master of Science (MS) in Biology
"The principal purpose of this research was to analyze the effects of resident fish communities and lake habitat on energy source use and trophic position of stocked rainbow trout. Stable isotope analysis was used to accomplish this goal, with stable carbon isotope ratios indicating the source of carbon, pelagic or littoral, in each species' diet and stable nitrogen isotope ratios determining species' relative trophic positions. The research was conducted in 15 eastem Washington State lakes, all stocked with rainbow trout for sport fishing purposes. I found wide confidence intervals around the % estimated littoral carbon in most of the lakes. However, the estimate of percent littoral carbon used by stocked rainbow trout could be predicted by several factors including the complexity of the resident fish community, amount of littoral vegetation present, and the presence of other resident trout and brown bullhead. In addition, significant negative correlations were detected between rainbow trout [gamma]15N and resident fish community complexity and the presence of other resident trout. As a consequence, alteration of rainbow trout stocking densities is recommended in aquatic systems containing complex resident fish communities and/or resident trout and/or brown bullhead, as the presence of those specific constituents negatively correlated to stocked rainbow trout littoral carbon use and/or trophic position. Despite these findings, stable isotope analysis does have limitations and difficulties, as seen in this research. Based on poor confidence intervals for estimated percent littoral carbon use, the diet of sampled organisms was difficult to assess. In addition, a more specific analysis of each sampled species' relative trophic position could not be done because I did not have clear baseline [gamma]15N for littoral primary consumers in several of the lakes. As a result, conclusions should be considered preliminary and tentative. An extensive sampling regimen is recommended for similar future studies to avoid these issues"--Document.
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Mahoney, Kevin, "Resident fish community impacts on stocked rainbow trout ecology in 15 eastern Washington lakes" (2012). EWU Masters Thesis Collection. 24.