Predation by introduced fishes on endangered humpback chub and other native species in the Little Colorado River, Arizona

Fishes in the Little Colorado River in the Grand Canyon, Arizona, were sampled monthly from July 1991 to June 1995 as part of a study of the ecology of endangered humpback chub Gila cypha. Diets of five introduced predatory fish species were examined. Stomach contents varied among species and were low in diversity and dominated by algae (primarily Cladophora), aquatic insects, and fishes. Humpback chub plus other native species were a significant component of the diet (13.7% frequency of occurrence among 219 of 408 stomachs that contained food). Predation mortality from introduced fishes may significantly affect the native species by depleting numbers and reducing recruitment.