Why were nonnative fish species introduced into the Colorado River system?
Sixty-seven nonnative fish species have been introduced into the Colorado River Basin since the 1880s. At least 36 fish species, mostly game fishes from the eastern United States, were introduced between 1930 and 1950. Some species were intentionally introduced by state and federal agencies to address public demand for sportfisheries during that time. Unfortunately, unauthorized introduction of other nonnative fishes also occurred. Unintentional introductions occurred when some species, which had been intentionally stocked in ponds and reservoirs for sportfishing, subsequently escaped into the river system. Some of these escapees successfully established self-sustaining populations in areas occupied by native fishes. Why are some of the same agencies that introduced nonnative fishes to the river system now working to remove them? Up until the mid-twentieth century the public’s values and priorities did not emphasize preservation of native species and the environment. Over time, society
