Resource Use by Larval and Early Juvenile Native Fishes in the Little Colorado River, Grand Canyon, Arizona

Abstract

We investigated resource use by early life stage (≤30 mm, total length) humpback chub Gila cypha, speckled dace Rhinichthys osculus, bluehead suckers Catostomus discobolus, and flannelmouth suckers C. latipinnis in the Little Colorado River, a tributary to the Colorado River in Grand Canyon, Arizona. Significant logistic regression models for habitat use were developed for all species pairwise combinations except flannelmouth sucker–humpback chub and flannelmouth sucker–speckled dace; correct classification probabilities ranged from 54% to 81%. Parameters used in discriminating among habitat use included depth, distance from shore, cover, and substrate. Logistic models were also developed to compare habitat use among larval stages within species, and most combinations produced significant models. Classification probabilities ranged from 60% to 95% in these models with the variables of depth, distance from shore, current velocity, cover, and substrate contributing to the various models. Behavioral observations revealed significant differences in vertical use of the water column and feeding locations among bluehead suckers and the two cyprinids. Diet analysis supported differences observed in feeding location and also identified some differences in diel feeding patterns. These differences in habitat use, behavioral time budgets, and diet indicate that some resource partitioning occurs among larval fishes in the Little Colorado River. Further laboratory study is needed to verify the mechanisms that sustain differential resource use in this system.