7047

• UCREFRP Catalog Number: 7047
• Author: Tyus, H. M. and C. A. Karp.
• Title: Habitat Use and Streamflow Needs of Rare and Endangered Fishes in the Green River, Utah
• USFW Year: 1991.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

the native fishes indicates that habitat conditions are suitable for certain
life stages of Colorado squawfish, humpback chub, and razorback sucker,
despite the proliferation of many non-native species. Population augmentation
and study of razorback sucker and bonytail chub in the upper Green River
should aid in their recovery.
Flow needs of the rare fishes in the mainstream Green River are
influenced by many factors including time of year, life history stage, and
associated species. As indicated in Figure 9, reproductive activities of the
Colorado squawfish, razorback sucker, and humpback chub are associated with
spring and early summer hydrologic events. Additional alteration of these
hydrologic events may affect migration of Colorado squawfish and razorback
sucker, and spawning of Colorado squawfish, razorback sucker, humpback chub
and other native fishes.
Gradually declining summer flows and maintenance of low, stable flows in
late summer and autumn are presumably necessary for growth and survival of
young Colorado squawfish and young of the other rare native fishes. Abrupt
fluctuations in surface water elevation in late summer to spring could strand
Colorado squawfish (young and adults) and presumably other backwater
inhabitants. Unnatural, high Flaming Gorge releases during the summer and
early autumn are correlated with recruitment failure of Colorado squawfish.
Stable winter flows through ice breakup provide suitable shoreline habitats
and reduce shoreline scouring during some years, especially in the upper Green
River near Jensen, Utah. Such flows may be important to overwinter survival of
young and adults of native species in some locations. Very high winter flows
flood off-channel, shoreline habitats and may provide an undesirable winter
refugium for some introduced fishes including channel catfish. Alteration of
historic flow regimens may have directly impacted razorback sucker recruitment
in the Green River basin, and its survival is imperiled. Humpback chub is rare
in Whirlpool Canyon of the upper Green River, and its status and habitat needs
in Desolation and Gray Canyons are not well understood.
Changes in Green River flows due to the operation of Flaming Gorge Dam
have resulted in alteration of river morphology. A reduction in the magnitude
and duration of flooding, and sediment removal by the dam, are presumably
responsible for stream channel changes that may continue for some time in the
future (Andrews 1986). Although future changes in instream habitats of the
Green River are difficult to predict, there is an indication that the
continuing invasion of riparian and upland vegetation into riverine flood
zones can stabilize banks and also produce a narrowed, deeper channel (Graf
1978; Fisher et al. 1983). In addition, dense growths of saltcedar become
established when dependable moisture is provided to river banks via daily
flooding as occurs in regulated systems (Turner and Karpiscak 1980). All of
the above changes may impact the endangered fishes by reducing or eliminating
ephemeral backwater and eddy habitats.
Studies of factors limiting the distribution and abundance of rare fishes
in the Green River are complicated by the variability of the environment
(e.g., seasonal fluctuations in discharge, temperature, food base, and species
abundance) and logistical problems associated with studying fishes in large,
turbid rivers. The determination of limiting factors for rare fishes is
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