Longitudinal and temporal patterns of food availability for endangered humpback chub, Gila cypha, in the Little Colorado River, Arizona

Authors: Jeffrey* Muehlbauer, Theodore Kennedy, Eric Kortenhoeven, Joshua Smith

Year: 2015 (xlvii)

Abstract

The Little Colorado River (LCR) in northern Arizona provides spawning and rearing habitat for the largest population of endangered humpback chub, Gila cypha, in the Colorado River Basin. However, relatively little is known about the aquatic food web in this river, particularly the aquatic insect community that is presumed to compose the bulk of the drift-feeding chubÁ¢â‚¬â„¢s diet. Here, we present results from two years of spatially and temporally-intensive study on aquatic insects in the LCR. We found pronounced seasonal patterns of aquatic insect activity, peaking in mid-April and otherwise remaining fairly low throughout the remainder of the year. Additionally, light availability, as related to the contrasting influences of canyon orientation and bicarbonate buffering, appears to act as a strong spatial control on aquatic insect densities throughout the LCR. We close by describing the implications of this spatial and temporal variation in the aquatic foodbase for humpback chub population dynamics.