E. Humpback Chub Early Life History in and around the Little Colorado River
Variation in availability of insect larvae and other food resources may play an important role in determining patterns of juvenile humpback chub growth and survival in the Little Colorado River (LCR). To understand whether differences in the quantity or quality of food resources are an important driver underlying differences in humpback chub growth or movement among habitats, it is necessary to place estimates of juvenile humpback chub growth and survival in the context of the LCR and mainstem food webs as a whole. A food web context is critical because humpback chub are one of several species of fish (i.e., flannelmouth sucker and bluehead sucker) that rely heavily on the LCR for spawning and rearing. Several investigators have documented low invertebrate abundance and biomass in the LCR that provides spawning and nursery habitat for humpback chub and other fish. Food quality could also affect humpback chub growth in the LCR. Quality could be related to the nutritional quality of the organic matter and invertebrates eaten by chub and/or to concentrations of metals and other toxins in their food. Our goal is to develop “metal webs” for the LCR and parts of the mainstem Colorado River in Grand Canyon. We are developing quantitative food webs to measure metal flux (mercury, selenium, and other trace metals) in the Colorado and Little Colorado rivers in Grand Canyon. These studies will identify key pathways of metal exposure to important fish species, such as the endangered humpback chub, and quantify fluxes of contaminants to riparian food webs via the mechanism of aquatic insect emergence.