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. . 2. Why are these fish endangered? The fish are endangered because of human impact on their habitat over the past 100 years. The two types of habitat alterations that probably have had the greateSt impact have been water development and introductions of non-native fish. or . Water development Human population growth since the turn of the cenrury created a significaru demand for water and hydroelectric power in westem stales. To meet that demand. hWldreds of Water projects, including dams, canals and inigation projects, have been constructed on the Colorado River and its tributaries. Most of these projects were constructed prior to the Endangered Species Act of 1973. This law requires each federal agency to review its activities and proposed projects to determine the impact on endangered species. Water projects have restricted the fish to about 25 percent of their former range and have blocked some of the spawning mignuion routes of the Colorado squawfish and ;lther species. The remaining habitat has been changed considerably. For example, many of the rivers' "backwaters" have :Iisappeared. To survive and grow. YOWlg native fish need the protection of backwaters. which have wanner water and are separated from the river's main channel. Also, tailwaters six to 20 miles downstream from dams can be as much as 15 degrees colder than the rare fishes' preferred habitat. And in the lower Colorado River Basin, below Lake Powell, water development has transformed the once free-flowing, silty and warm waters of the Colorado River into a series of lakes connected by cold, clear waters downstream of dams. The native fish have been unable to adapt to :!lese habitat changes. Non-natlve fish introductions of non-native fish into rivers, lakes and reselVoirs also have taken a ton on the native fish. Construction Jf dams led to increased public demand for fishing in lakes and reselVoirs. To increase fishing opporttmities. private :itizens and state and federal wildlife agencies began stocking non-native fish in the Colorado River in the late 1800s. These non-natives compete with native fish for food and space, probably with more success. gjstorically, there were only 14 fish species in the upper Colorado River Basin. But now the four endangered fish :Jave to compete with an additional 41 non-native species. Also, some of the non-natives are efficient predators that ,rey on the eggs and YOWlg of endangered fish. :>ther factors )ome native fish have been killed intentionally. Some local residents may prefer to catch nonhero pike, channel =atfish and othernon-native spon fish they may consider more desirable. When they hook a native fish, they may ;imply toss it on the rivelbank to die. \nd in the mid-196Os, the chemical rotenone was used to reduce native fish populations and make way for non-native :pon fish in portions of the upper Green and San Juan rivetS before the dosure of dams at Flaming Gorge and Navajo =lVoirs. Follow-up studies found the total nnmher of fish had dropped, but the ratios of various species remained Ibout the same. Researchers concluded there was no lasting effect on the native fish species. Since then, the public IllS come to appreciate wildlife for more than consumption. and public policy now reflects that attitude shift. )tiler factors that may have contributed to the fishes' decline include ponution and parasites. Among the chubs, lybridization may also be a factor. i. Which ash species are native to the upper Colorado River Basin? )nly 14 species of fish are native to the upper Colorado: the Colorado squawfish, humpback. chub. bonytail chub. azotback sucker. Colorado River cutthroat trout, Rocky Mowuain whitefish. roundtail chub, speckled dace, Kendall Vann Springs dace, f1anneImouth sucker, mowuain sucker, bluehead sucker, mottled sculpin and the paiute sculpin. 2