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<br />Bioenergetics provides a framework to quantify the biomass of prey consumed by fishes <br />based on their thermal experience, growth rate, body condition and the availability of <br />their prey. Using data on seasonal diet composition, it becomes possible to estimate <br />predation by the type of prey consumed, e.g., invertebrate vs. fish. By calculating the <br />amount of food consumed by a fish in each size class (trophic stanza), and scaling these <br />per capita estimates of prey consumption up to the entire population with abundance data, <br />it becomes possible to estimate of overall demand for fish prey by piscivores. Population <br />level estimates of piscivore consumption of various prey clarifies which species or size <br />class of piscivores may be exerting the greatest predation demand in a fish community. <br />Because the predation impact on native fishes by nonnative piscivores is of increasing <br />concern within Critical Habitat for endangered fishes in the Upper Colorado River Basin, <br />bioenergetics analysis has the potential to identify which species or size-class of <br />nonnative piscivores exert the greatest predation threat to native fishes. The level of <br />refinement attainable by applying the bioenergetics framework is reliant upon the quality <br />of the data available. Examination of piscivore diet by season is necessary to detect <br />predation on native vs. nonnative species. Projection of predation demand by piscivores <br />at the population or river reach level is reliant on sound estimates of piscivore abundance. <br />Further, these estimates of abundance should be unbiased in their representation of size <br />classes in the population. By meeting these sampling standards accurate estimates of the <br />amount of fish prey consumed by piscivores are possible. This information would allow <br />managers to identify the most problematic species and target the most predaceous size <br />classes to optimize the ecological and economic efficiency of efforts to remove or control <br />nonnative piscivores. Further, these estimates can be used to determine how many <br />nonnative piscivores need to be removed to protect and restore native fishes and facilitate <br />recovery of endangered ones. An example is presented for nonnative channel catfish, <br />northern pike and smallmouth bass in the Yampa River using available data and <br />identifying data needs and model limitations that must be addressed by additional <br />research to optimize the utility of this technique. <br />Elemental and stable isotope markers of non-native fish provenance in the Upper <br />Colorado River basin <br />Whitledge, Gregory W.1, Brett M. Johnson, Patrick J. Martinez 2, and Anita M. Martinez2 <br />I Dept. of Fishery & Wildlife Biology, Colorado State University, Ft. Collins, CO; <br />2Colorado Division of Wildlife, Grand Junction, CO. <br />Non-native centrarchids are present throughout much of the Upper Colorado River basin <br />and can adversely affect recovery of threatened and endangered native fishes through <br />predation or competition within critical habitats. Identification of sources of centrarchids <br />to critical riverine habitats is crucial if centrarchid control efforts are to proceed in an <br />efficient and effective manner. We are employing stable isotope and elemental analyses <br />of fish otoliths to determine origins and reconstruct movements of centrarchids in and <br />upstream of the Grand Valley reach of the Colorado River. Otoliths are metabolically <br />inert structures whose elemental and stable isotopic compositions reflect those of the <br />10 <br />r-" <br />L <br /> <br /> <br />1 <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />