Food Web Dynamics in Bright Angel Creek, Grand Canyon: Implications for Native Fish Conservation

Non-native trout removal is being conducted by the National Park Service and other stakeholders to restore and enhance native fish communities in Bright Angel Creek (BAC), Grand Canyon. To assess resource availability and evaluate the effects non-native brown (BNT) and rainbow (RBT) trout have on the food web in BAC, we sampled fish, benthic invertebrates, and drifting invertebrates seasonally from November 2010 to September 2011. Food habits of BNT and RBT were evaluated from stomach samples collected during invertebrate sampling periods, and potential diet overlap between native and non-native fishes was examined using ¹³C and ¹⁵N stable isotopes. Invertebrate drift rates varied seasonally ranging from 95.3 g dry mass (DM) day^-1 to 169.5 g DM day^-1. Native fish (speckled dace and bluehead sucker) and Corydalus sp. were the dominant food types found in BNT stomachs, whereas Baetis mayflies and filamentous algae dominated RBT stomachs. Piscivory was 18% and 5% for BNT and RBT, respectively. Stable isotope analysis indicated native and non-native fishes occupied similar trophic positions and consumed similar resources during the study period. Our results indicate BNT and RBT can affect native fishes through resource consumption and BNT are more likely to have an impact through predation.