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<br />Water development
<br />Human population growth since the turn of the century created a significant demand for water and
<br />hydroelectric power In western states. To meet that demand, hundreds of water projects,
<br />Including dams, canals and Irrigation projects, have been constructed on the Colorado River and
<br />Its tributaries. Most of these projects were constructed prior to the Endangered Species Act of
<br />1973. This law requires each federal agency to review Its activities and proposed projects to
<br />determine the Impact on endangered species. Water projects have restricted the fish to about 25
<br />percent of their former range and have blocked some of the spawning migration routes of the
<br />Colorado squawfish and other species.
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<br />The remaInIng habitat has been changed consIderably. For example, many of the rivers'
<br />"backwaters" have disappeared. TO.survlve and grow, young native fish need the protection of
<br />backwaters, which have warmer water and are separated from the river's main channel. Also,
<br />tailwatars 6 to 20 miles downstream from dams can be as much as 15 degrees colder than the rare
<br />fishes' preferred habitat. And In the lower Colorado River Basin, below Lake Powell, water
<br />development has transformed the once frea-flowlng, silty and warm waters of the Colorado River
<br />Into a serIes of lakes connected by cold, clear waters downstream of dams. The native fish have
<br />been unable to adapt to these habltat'chsnge.s;_'~ ...
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<br />Non-native fish
<br />Introductions of non-native fish Into rivers, lakes and reservoirs also have taken s toll on the native
<br />fish. Construction of dams led to Increased public demand for fishing In lakes and reservoirs.
<br />To Increase fishIng opportunities, private citizens and state and federal wildlife sgencles began
<br />stocking non-native fish In the Colorado In the late 1800s. These non-natives compete with native
<br />fish for food and space, probably with more success.
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<br />Historically, there were approximately 33 fish species In the Colorado River Basin. But now the
<br />four endangered fish have to compete with more than 41 non-native species. Also, some of the
<br />non-natives are efficient predators that prey on the eggs and young of endangered fish.
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<br />Other factors
<br />Some native fish have been killed Intentionally. Some local residents may prefer to catch northern
<br />pike, channel catfish and other non-natlve aport fish they may consider more deslrsble. When they
<br />hook a native fish, they may simply toss It on the riverbank to die.
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<br />And in the mid-1960s, the chemical rotenone was used to reduce native fish populations and make
<br />way for non-native sport fish In portions of the upper Green and San Juan rivers before the
<br />closure of dams at Flaming Gorge and Navajo reservoirs. FOllOW-Up studies found the total
<br />number of fish had dropped, but the ratlos of various species remained about the same.
<br />Researchers concluded there was no lasting effect on the native fish species. Since then, the
<br />public has come to appreciate wildlife for more than consumption, and public policy now reflects
<br />that attitude shift.
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<br />In the lower basin habitat alteration and fragmentation and non-native fish Introduction are
<br />believed to be the principle causes of decline.
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<br />Other factors that may have contributed to the fishes' decline include pollution and parasites.
<br />Among the chubs, hybridization may also be a factor.
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<br />3. Which fish species are native to the upper Colorado River Basin?
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<br />Only 14 species of fish are native to the upper Colorado: The Colorado squawfish, humpback
<br />chub, bonytall chub, razorback sucker, Colorado River cutthroat trout, Rocky Mountain whitefish,
<br />roundtail chub, apeckled dace, Kendall Warm Springs Dace, flannel mouth sucker, mountain
<br />sucker, bluehead sucker, mottled sculpin and the paiute sculpin.
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<br />4. Which fish spe':!es are native to the lower Colorado River Basin?
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<br />Twenty-seven species are native to the lower Colorado: gila trout, Apache trout, longfin dace,
<br />bonytail chub, humpback chub, roundtail chub, Virgin River chub, gila chub, Little Colorado
<br />spinedace, Virgin River spinedace, moapa dace, spikedace, woundfin, Colorado squawflsh, Las
<br />Vegas Valley dace, speckled dace, loach minnow, sonora sucker, flannelmouth sucker, desert
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