Sarah E. Zahn1, Emma J. Rosi-Marshall1, Colden V. Baxter2, Michael D. Yard2, Theodore A. Kennedy3, Wyatt F. Cross4, and Robert O. Hall5. (1) Department of Biology, Loyola University Chicago, 1050 W. Sheridan Rd, Quinlan 419-Dept of Biology, Chicago, IL 60626, (2) Stream Ecology Center, Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, (3) Grand Canyon Monitoring and Research Center, USGS, Flagstaff, AZ 86001, (4) Department of Ecology, Montana State University, Bozeman, MT 59717, (5) Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071
Glen Canyon Dam (GCD) has dramatically changed the Colorado River, causing native fishes to decline; non-native fishes are now abundant. The decline of natives may be linked to physical habitat changes and interactions with non-natives. We collected native juvenile flannelmouth suckers (Catostomus latipinnis) and all size classes of the non-native fathead minnow (Pimephales promelas), from 5 sites along the Colorado River (ranging from 48-362 km, below GCD) in September 2006 and April 2007 for stable isotope analysis and gut content analysis. In April, fathead minnow guts contained predominately diatoms (90-96%) at all but one site (17%). In the upstream reaches, juvenile flannelmouth suckers relied on diatoms (36%) and amorphous detritus (21%); further downstream they consumed aquatic invertebrates, mainly chironomids and simuliids (19-98%), terrestrial invertebrates (51-57%) and terrestrial vegetation (2-29%). Stable isotope data demonstrated overlap in resource utilization across sites and seasons. Diet analysis suggests that diets overlap in the upstream reaches but may diverge further downstream, while stable isotope analysis suggests resource competition. These data may indicate that juvenile native suckers compete for resources with the non-native fathead minnows.
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fish, diets, food webs