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<br />salmonids were not included in this review. Available data were adequate for <br />identifying <br /> <br />areas where species' range or abundance had increased but not for identifying <br />decreases in range. <br /> <br />Various studies, that were completed since 1982, provide information on <br />extensions of nonnative fish distribution and changes in relative abundance. <br />Reports and publications from these studies were reviewed and changes in range <br />extensions or relative abundance were superimposed on the maps of Tyus et al. <br />(1982) to provide a summary of current knowledge. Not all of the available <br />annual reports, final reports, published literature, and data sets were used <br />in this issue paper. . Rather, selected information that provided information <br />on range extensions and changes in relative abundance of nonnative fishes were <br />used. In some instances, personal communication with Upper Basin researchers <br />are used since reports of completed studies are not available. Although there <br />are other reports and completed studies with information on distribution and <br />relative abundance of nonnative fishes, we believe that changes in these two <br />factors were considered in updating the figures of Tyus et al. (1982). <br /> <br />Relative abundance of nonnative fish species used in this issue paper are <br />considered "abundant" if they were captured in the hundreds to thousands <br />(100+); "common" if they were captured in the tens (10 to 99); and <br />rare/incidental if they were captured in the ones (1 to 9). The data were <br />collected using a variety of gear types, primarily electrofishing and seining. <br />Some of the limitations in the data include differential vulnerability of the <br />various species, life stages, and sizes of fishes to the various gear types <br />and sampling strategies that were used; habitat types may not have been <br />sampled in proportion to availability; variability in different times of day, <br />times of year, flow conditions, and habitat availability when sampling <br />occurred; discrepancies caused by variable effort, sampling locations, and <br />efficiency of technicians; etc. Also, not all species captured were counted <br />or listed in summary tables by the principal investigators. <br /> <br />The life histories of the 42 fish species that have been introduced, either <br />intentionally or accidentally, into the Upper Colorado River Basin were <br />reviewed from the published literature. Nonnative, warmwater fish species <br />that may be IIproblematicll to the recovery effort by preying on, or competing <br />with, the razorback sucker were identified based upon their distribution and <br />relative abundance in the Upper Basin and pertinent life history information. <br /> <br />Finally, various options to prevent or reduce adverse impacts of nonnative <br />fishes on the razorback sucker and other endangered fishes in floodplain <br />habitats were identified. <br /> <br />RESULTS AND DISCUSSION <br /> <br />The forty-two (42) species of nonnative fishes, that have been introduced into <br />the Upper Basin, are summarized in Table 1. <br /> <br />2 <br />