Tuesday, June 5, 2007 - 9:00 AM
83

Using Ecosystem Production Budgets to Assess Resource Limitation of Native and Non-Native Fishes in Colorado River, Grand Canyon

Wyatt F. Cross1, Colden V. Baxter2, Robert O. Hall Jr.1, Theodore A. Kennedy3, Scott Rogers4, Emma J. Rosi-Marshall5, and Michael D. Yard2. (1) Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, (2) Stream Ecology Center, Department of Biological Sciences, Idaho State University, Box 8007, Pocatello, ID 83209, (3) USGS Grand Canyon Monitoring and Research Center, Flagstaff, AZ 86001, (4) Arizona Game and Fish Department, Region II, Flagstaff, AZ 86001, (5) Biology, Loyola University Chicago, Chicago, IL 60626

The Colorado River below Glen Canyon Dam has been drastically altered with regard to temperature and flow regimes, sediment supply, and community composition. As a consequence, abundance and distribution of native and non-native fishes have changed, including steady declines in abundance of some native fishes (e.g., humpback chub) and increased abundance of many non-natives (e.g., rainbow trout, carp). We hypothesize that these changes are, in part, due to altered food availability associated with dam operations. To test this hypothesis we constructed ecosystem production budgets for 2 contrasting reaches of the Colorado River (near Glen Canyon Dam and 362 kilometers downstream). Using these budgets, we compared food availability (i.e., invertebrate and algal production, detrital pools) to annual energetic demand of native and non-native fishes. Our initial results demonstrate that directly below Glen Canyon Dam, invertebrate production is sufficient to support the energetic demands of dominant invertivorous non-native fishes (i.e., rainbow trout). Further downstream, food limitation is likely for native invertivorous fishes (e.g., humpback chub), but not for native (e.g., suckers and dace) and non-native (e.g., carp, catfish) omnivores. Our estimates will help guide research priorities and management decisions aimed at conservation of native fishes and ecosystem services in the Colorado River.