8221

• UCREFRP Catalog Number: 8221
• Author: Van Steeter, M. M.
• Title: Historic and Current Processes Affecting Channel Change and Endangered fish Habitats of the Colorado River Near Grand Junction, Colorado.
• USFW Year: 1996.
• USFW - Doc Type: Doctor of Philosophy.
• Copyright Material: NO

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complex channel areas significantly (p>O.OOl) more often than would be
predicted if selection was random.

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FACTORS LEADING TO THEIR DECLINE
Physical and Thermal Barriers
It is not clearly understood why many native fishes are nearing
extinction, but several factors are thought to be important. One obvious
factor is their reduced range. Dams and diversions span the Colorado
River and its tributaries from its headwaters to the Gulf of California.
This has fragmented their habitat and the loss of riverine reaches is
thought to be a major factor in the extirpation of native fishes from the
lower Colorado River basin (Stanford and Ward, 1986). There are fewer
main-stem dams in the upper basin, but they have caused similar
fragmentation and inhospitable conditions. For example, water
temperatures below Flaming Gorge Dam on the Green River are too cold
for Colorado squawfish spawning for approximately 108 kilometers (68 mi)
downstream until its waters are diluted by the Yampa River. Berry (1988)
suggests that these cold temperatures could be detrimental to endangered
fish larvae which are flushed out of the Yampa River system into the
Green, and subsequently experience "cold shock." There is also evidence
that temperatures in the upper reaches have always been sub-optimal for
reproduction relative to the lower basin (Kaeding and Osmundson, 1988).
Therefore, blocked access to the warmer waters of the lower basin, and the
cooling effect of dams in the upper basin, are potentially detrimental to the
reproduction and survival of native fishes.

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