7356

• UCREFRP Catalog Number: 7356
• Author: Wydoski, R. S. and J. F. Hamill.
• Title: Chapter 8 - Evolution of a Cooperative Recovery Program for Endangered Fishes in the Upper Colorado River Basin
• USFW Year: 1989.
• USFW - Doc Type: Draft.
• Copyright Material: NO

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consequence of the Yampa's ameliorating effect on water temperature.
Work by the Utah Cooperative Fishery Research Unit during 1963-1966
focused on basic life history of the Colorado squawfisn and bony tail {Vanicek
1967; Vanicek and Kramer 1969; Vanicek et ll.--1970Yand on macroinvertebrate
abundance and distribution {Pearson 1967; Pearson et ll. 1968}. These
studies suggested that year classes of Colorado squawfish were strong in
1959~ 1961, 1963, 1964, and possibly 1966 (Vanicek 1967), but weak in 1962
and 1965. Formation of strong year classes during years when streamflow and
water temperatures are more suitable for survival of_ recruits could be an
evolutionary life history strategy of this species (Tyus 1986, Chapter 19).
Vanicek (1967) also reported difficulty in separating the various species of
Gila, especi ally duri ng early 1 ife stages. Thi sled to a study of Gil a
taxonomy by Holden (1968; Holden and Stalnaker 1970), but taxonomic ~uestions
were not fully answered. It was not until 1989 that the USFWS contracted
wit~ the Smithsonian Institution to comprehensively review the problem with
the goal of resolving the taxonomic confusion surrounding the Gila species.
Holden (1973) studied relative abundance and distribution of native
fishes in the upper basin and documented problems with recruitment of
squawfish in Echo Park (DNM) where juveniles were abundant in 1968, scarce in
1969, and non-existent in 1970. However, he reported young-of-year from the
Green River in Desolation Canyon in 1971 and in Canyonlands National Park in
1970 and 1971. During 1974-76, studies focused on obtaining further life-
history information on the endangered fishes (McAda 1977; Seethaler 1978).
McAda (1977; McAda and Wydoski 1980) provided new biological information and
synthesized all known life-history data on razorback sucker in the upper
basin. Seethaler (1978) provided a comprehensive summary of the life history
of the Colorado squawfish, including the first data on reproduction,