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<br />ABSTRACT <br />Habitat use and associations of native and nonnative fish species <br /> <br />in secondary channels of the San Juan River, New Mexico and Utah <br /> <br /> <br />were investigated. Most species and age-classes of each (larvae, <br /> <br /> <br />juveniles, and sub-adults/adults) utilized shallow, low velocity <br /> <br /> <br />habitats with silt substrate. Discriminate analysis revealed <br /> <br /> <br />broad overlap in habitat use among species, with a general trend <br /> <br /> <br />of older age-classes occurring in deeper habitats with faster <br /> <br />current velocities. Overall, discriminate function analysis was <br /> <br /> <br />able to correctly classify the species and age-classes 17.2% of <br /> <br /> <br />the time. Native juvenile fish exhibited the greatest <br /> <br /> <br />interspecific association with nonnatives while native <br /> <br /> <br />adults/sub-adults showed the least. These results suggest that <br /> <br /> <br />the greatest potential for negative interactions among native and <br /> <br /> <br />nonnative fishes appears to be during the juvenile stage. The <br /> <br /> <br />probability of interaction, however, depends on the availability <br /> <br /> <br />of resources and density of individuals. <br /> <br />1 <br />