Habitat use and association of native and nonnative fishes in the San JuanRiver, New Mexico and Utah

Habitat use and associations of native and nonnative fish species in second ary channels of the San Juan River, New Mexico and Utah were investigated. Most species and age classes within species (larvae,juveniles, subadults, a nd adults) used low velocity habitats with silt substrata. Discriminant fun ction analysis revealed broad overlap in habitat use among species, with a trend of older age classes occurring in deeper habitats with faster current velocities. Overall, discriminant function analysis was able to correctly classify species and age classes, based on habitat use, 23.4% of the time. Native juvenile fishes exhibited the greatest interspecific association wit h nonnative fishes, whereas adult and subadult native fishes showed the lea st. Depending on the availability of resources, overlap in habitat use may result in negative interactions among native and nonnative fishes.