Using stable isotope analysis to assess the effects of hypolimnetic oxygenation on diet in a mixed cold- and warmwater fish community
Line-diffuser hypolimnetic oxygenation was initiated in North Twin Lake, Washington, in 2009 to mitigate reductions in Rainbow Trout (Oncorhynchus mykiss) and Brook Trout (Salvelinus fontinalis) habitat due to temperature-dissolved oxygen “habitat squeeze”. Previous studies demonstrated that trout populations rapidly expanded into increased hypolimnetic habitat within the first few years of oxygenation and previous short-term diet analyses indicated an effect on fish diet; however, the long-term effects on fish ecology have yet to be established. In this study, stable isotope analysis of fish liver tissue suggests relatively few differences in feeding ecology of principal coldwater fish species in North Twin Lake compared to unoxygenated South Twin Lake. When compared between lakes, Rainbow Trout and Brook Trout diets contained similar proportions of Daphnia, Chironomidae, and Chaoboridae. Littoral and epilimnetic-focused Golden Shiner (Notemigonus crysoleucas) diets were also similar between lakes. Observed similarities between Golden Shiner and trout diets suggest the effects of interspecific competition between salmonids and non-salmonids may be limiting trout growth and survival. Fisheries managers should therefore consider both habitat limitations and interspecific competition when managing for coldwater fish species in mesotrophic, dimictic lakes.
KeywordsStable isotope analysis Hypolimnetic oxygenation Fish diet Trout Interspecific competition
The Colville Confederated Tribes Fish and Wildlife Department partially funded this work and provided gill nets, an electroshocking boat, and all fish liver samples. The authors thank the Washington State University Isotope Core Laboratory for sample analysis. The authors also thank Raymond Lee, Gary Thorgaard, and Steve Katz for their stable isotope analysis, fish physiology and biology, and statistical analysis guidance, respectively. The study also received support from the Washington State Lake Protection Association Nancy Weller Student Scholarship and the Idaho Chapter of the American Fisheries Society Graduate Student Scholarship. Finally, this research was approved by the Washington State University Institutional Animal Care and Use Committee.
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