Fish Associations and Environmental Variables in Age-0 Colorado Squawfish Habitats, Green River, Utah

Age-0 Colorado squawfish Ptychocheilus lucius were sympatric with seven native and 15 introduced fishes in the Green River, Utah, 1979–88. Larval Colorado squawfish was the most abundant fish captured in summer drift (38%), which included suckers Catostomus spp. (33%), speckled dace Rhinichthys osculus (14%), and channel catfish Ictalurus punctatus (3%). However, ephemeral shoreline embayments (backwaters) used by Colorado squawfish as nursery habitats were dominated by introduced fishes, including red shiner Notropis lutrensis (87%) in summer, and red shiner (65%) and fathead minnow Pimephales promelas (16%) in autumn. Abundance of most fishes was highest in years of lower, more historic summer flows. Most fishes in backwaters inhabited a wide range of environmental conditions, but were most abundant in habitats deeper than 15 cm. We detected no segregation in habitat use between young Colorado squawfish and non-native fishes. Hydrologic conditions in the regulated Green River presumably favor the establishment and proliferation of fish invaders from more mesic environments.