8023

• UCREFRP Catalog Number: 8023
• Author: Wydoski, R. S. and J. Hamill.
• Title: Evolution of Recovery Programs for Upper Colorado River Fishes.
• USFW Year: n.d.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

that the Utah Cooperative Fishery Research Unit in Logan conduct investigations
on changes in habitat and fish populations in Dinosaur National Monument,
Colorado-Utah due to the closure of Flaming Gorge Dam. The conclusion of the
1963-66 studies was that the large native fishes disappeared from the 105 km
reach below Flaming Gorge Dam because of cold water releases {Vanicek 1967;
Vanicek, Kramer and Franklin 1970}. However, all fish species present before
impoundment were still found in the Green River below its confluence with the
Yampa River because of the ameliorating effect of the Yampa on water
temperatures in the Green River.

The work conducted by the Utah Cooperative Fishery Research Unit during
1963-1966 focused on the basic life history of the Colorado squawfish and
bony tail chub (Vanicek 1969; Vanicek and Kramer 1969; Vanicek, Kramer and
Franklin 1970) and macroinvertebrates (Pearson 1967; Pearson et ale 1968).
These studies suggested that the Colorado squawfish formed strong year classes
in 1959, 1961, 1963, 1964 and possibly 1966 (Vanicek 1967) while in 1962 and
1965, the year classes were weak. Vanicek (1967) collected 275 young-of-the-
year in 1964, 42 in 1965, and 560 in 1966. The formation of strong year
classes during years when streamflows and water temperatures are more suitable
for survival of recruits is probably an evolutionary life history strategy of
the Colorado squawfish (Tyus 1984). Another interesting outcome of Vanicek's
work was the difficulty in separating the various Gila, especially during the
early years of life. This led to the study of Gila taxonomy by Holden (1968).

Holden (1973) studied the abundance and distribution of native fishes in
the Upper Colorado River Basin and documented problems with recruitment of

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