7309

• UCREFRP Catalog Number: 7309
• Author: Tyus, H. M., R. A. Valdez and R. D. Williams.
• Title: Status of Endangered Fishes in the Upper Colorado River, 1985.
• USFW Year: 1985.
• USFW - Doc Type: Salt Lake City, Utah.
• Copyright Material: YES

r...:.":'"
.,

I
.if,

Upper Mainstem: USFWS '~tensified studies of humpback in Black
Rocks in 1983 and 1984 to determine spatial and tempu,-~l relationships
between the spawning of humpback chub and roundtail chub (Archer et al.
1985). These investigations confirmed the high affinity exhibited by
the species for the limited Black Rocks habitat, as reported earlier
by Valdez and Nilson (1982). In contrast, roundtail chub, radiotagged
simultaneously in Black Rocks, exhibited widespread and nomadic move-
ments to and from the area. Studies initiated by the Utah Division of
Wildlife Resources (UDWR) in Westwater Canyon in 1985 confirmed the pre-
sence of a substantial population of humpback chub, although a high in-
cidence of intermediate forms (specimens with characters of both hump-
back and roundtail chub) was reported. ~

~

San Juan-Colorado: Also in 1985, investigations in Cataract and
upper Lake Powell, UT (Valdez et al. 1985) yielded 9 humpback chub~
including 2 adults, 1 juvenile and 6 yay (the yay are classified as
suspected because of the lack of definitive identification criteria).
An additional 10 suspected yay were captured in upper Lake Powell near
Imperial Canyon. These findings indicate that a population of hump-
back chub might occur in the region of Cataract Canyon.

Remarks: The humpback chub remains restricted in its distribu-
tion to a few canyon areas and the short Black Rocks ~ection. Its
life history needs remain unknown, and the taxonomic difficulties of
identifying young and juvenile life stages remain. This fish is rare
and its status endangered. The possibility of genetic introgression
between the humpback and other Gila species may become a critical
issue. ----

Bonyta i 1

Green: Bony tail were reported numerous in the Green River within
Dinosaur National Monument from 1964-1966 (Vanicek and Kramer 1969),
but less common in the Yampa River, and in Desolation Canyon from 1968-
1971 (Holden and Stalnaker 1975). Declining populations in the upper
basin and in the lower basin as early as the 1960's (Miller 1961)
prompted the USFWS to list the bony tail as "Endangered." No confirmed
specimen has been captured in the Green River Sub-basin in recent years;
however, many bony tail-like specimens have been collected.

-25-

I