7752

• UCREFRP Catalog Number: 7752
• Author: Stanford, J. A.
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin
• USFW Year: 1993.
• USFW - Doc Type: Review and Synthesis of Ecological Information, Issues, Methods and Rationale.
• Copyright Material: NO

The reader is encouraged to consult the review anicles for detailed descriptions of the many years

of study devoted to these interesting fishes.
As noted above, the historical range of the four species included the potamon and
transitional reaches of the Green and Colorado River systems, including most of the larger

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tributaries, in particular the Yampa, White, Dolores and Gunnison Rivers. Today, ranges of these
fish are fragmented by dams and diversions, and populations have declined dramatically in relation
to distributions at the turn of the century (Quartarone 1993). Bony tail chub are close to extirpation;
but they were successfully cultured along with humpback chub, squawfish and razorback sucker at
the Dexter National Fish Hatchery, Dexter, New Mexico (Johnson and Jensen 1991) and brood
stocks currently are being held in several locations. Because of their comparative rarity in the wild,
ecological information on the historical range of bonytail chub is more fragmentary than for the
other species of concern. A few specimens of bony tail chub were collected in the 1970s in the
Green and Yampa Rivers (Kaeding et al. 1986), but their phenology (life history) and exact cause of
disappearance in the Upper Colorado River Basin system are unknown.
Humpback chub are found only in whitewater canyon segments (Figure 1). Migrations are
limited, and it may be that humpback chub were always restricted to specific canyon segments, at
least as adults. Spawning in the Upper Colorado River Basin occurs on the declining limb of the
spring runoff event in association with the 200C isotherm (Kaeding and Zimmerman 1983).

Humpback chub interact behaviorally and probably hybridize with congeneric, endemic roundtail
chub (Gila robusta), which are more abundant throughout the Upper Colorado River Basin
(Kaeding et a!. 1990, Karp and Tyus 1990). Much of what is known about the life cycle of
humpback chub is based on unpublished studies in the Grand Canyon where they migrate from the
regulated Colorado River into the unregulated Little Colorado River to spawn. Similar migratory
behavior has not been documented in the Upper Colorado River Basin and exact locations of
spawning sites are unknown (Richard Valdez, BioWest Inc, Logan, UT, personal communication;

Larry Crist, U.S. Bureau of Reclamation, SaIt Lake City , UT, personal communication).

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