Fitting In: Coupling Food Webs and Translocation In Native Fish Restoration

Efforts to restore native fish communities may depend on translocation into suitable habitats.  However, success of translocations has been mixed.  The federally endangered humpback chub Gila cypha (HBC) is endemic to the Colorado River Basin and populations continue to decline, so conservation of HBC may depend on translocation.  However, incomplete removal of non-native rainbow trout Onchoryhnchus mykiss (RBT) at translocation sites could foster competition for food resources and predation limiting the establishment of HBC.  We used stable isotope analysis to determine trophic position and diet source of the resident native fish community and introduced RBT and HBC in Shinumo Creek, Grand Canyon in June and September 2010 and 2011.  Mean trophic position was similar for HBC 3.05 (range = 2.38 to 3.75) and RBT 3.15 (range = 2.13 to 3.67) among sampling periods and were consistently higher than native resident fishes.  Between HBC and RBT, δ ¹³C differed during all sampling periods (P < 0.001), and HBC were consistently aligned over native resident fishes in bi-plot space suggesting HBC predate on resident native fishes.  In Shinumo Creek RBT may preclude HBC from consuming the full breadth of available food resources with implications for establishing HBC sympatric with RBT.