1108

• UCREFRP Catalog Number: 1108
• Author: Valdez, R. A.
• Title: Fisheries Biology And Rafting Annual Summary Report - 1987
• USFW Year: 1988.
• USFW - Doc Type: ‎(Contract no. 6-CS-40-03980)‎.
• Copyright Material: NO

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for striped bass. Continued efforts by BOR in 1981 near Gypsum Canyon and
initial efforts by FWS in 1979-81 in Cataract Canyon yielded humpback chub and
Colorado squawfish, but not in the numbers seen in 1980. From 1982 to 1984,
BOR equipped adult Colorado squawfish in upper Lake Powell with radio transmit-
ters in an attempt to locate fish concentrations, monitor movements and locate
possible spawning areas. Small numbers of adults were found in the Imperial/
Gypsum Canyon areas in July and August of these years, but no spawning areas
were identified. Seining in these areas yielded numerous larval and young-of-
the-year (YOY) Colorado squawfish, indicating that reproduction may occur in
upper Lake powell or in the river immediately upstream, wi thin Cataract
Canyon.

In 1985, BOR continued studies with radiotelemetry in the Imperial/Gypsum
Canyon areas, and initiated intensive investigations within Cataract Canyon
(Valdez 1985). The studies in Cataract Canyon yielded significant numbers of
YOY as well as juvenile and adult Colorado squawfish and humpback chub. Two
fish, tentatively identified as bonytail (one adult and one YOY), were also
reported from Cataract Canyon. These findings indicated the need for
addi tional studies to locate possible spawning areas in the canyon and to
assess the importance of habitats in upper Lake Powell to these species.

Field efforts for the current investigation were initiated in Cataract Canyon
on July 11, 1986 (Valdez 1987). Six trips were conducted through the canyon
between that date and October 6, 1986, with the objectives as previously
stated. Regarding the objective of locating specific spawning si tes for
Colorado squawfish; none have been identified in the Cataract Canyon Region,
but the variation in sizes and ages of larvae indicate that many of these young
fish are being transported by river currents from more than one spawning site
upstream as well as from sites in the immediate vicinity. Most of these larvae
appear to be originating from the Green River system. Regarding the objective
of determining whether a humpback chub population exits in Cataract Canyon; the
presence of larvae, YOY, juveniles, and adults is strong evidence that a
reproducing population inhabits the canyon. However, morphological variation
in the species has made positive identification in the field very difficult.
Further examination of the morphological variant of Gila sp. that inhabits
Cataract Canyon is needed in order to confirm the existence of a population of
G.~. Finally, regarding the objective of assessing the influence of BOR's
operation of Lake Powell on nursery habitat of Colorado squawfish; capture of
YOY squawfish and chubs in the backwaters of extreme upper Lake Powell suggests
that these young endangered fishes are reaching the lake in unknown numbers and
are using the habitat formed at certain lake levels.

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