FACTORS ASSOCIATED WITH THE DISTRIBUTION AND ABUNDANCE OF NON-NATIVE FISHES IN STREAMS OF THE AMERICAN WEST by

Non-native fish species have been implicated in native fish extinction and endangerment in the United States. Access to standardized data from across the American West allowed the opportunity to study the distribution and abundance of native and non-native fish species at a scale that has rarely been approached previously. Nonnative fishes comprise 1 of every 4 individual fish in the West and are distributed across 50% of the total length of western streams. The greatest abundance and distribution of non-native fishes is in the southwestern states (AZ, CA, CO, NV, UT). The non-native species with the greatest abundance and distribution were those introduced as sport fishes. We found non-native fishes present in all streams influenced by all types of landuse and all levels of human disturbance, and not positively correlated with human disturbance. Because the type of non-native fishes found varied by land-use and level of human disturbance, it is important that the effects of non-native species be studied at an individual species level. However, there were some general conclusions we could make from the study of non-native fishes as a whole. Non-native species were more commonly