7400

• UCREFRP Catalog Number: 7400
• Author: Valdez, R. A.
• Title: The Endangered Fish of Cataract Canyon
• USFW Year: 1990.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

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SUMMARY OF FINDINGS
(Continued)

Although specific spawning sites were not located and adults with expressible gametes were not
found, the presence of numerous larval and yay Colorado squawfish and humpback chub indicated
that spawning by these species occurred within the st.udy area Spawning by Colorado squawfish in
this region of the upper basin may have occurred consist.ently over unidentified cobble bars which
presented the appropriate set of spawning conditions in a given year. Nine such cobble bars were
located in the lower 50 miles of the Green River and four in the lower 50 miles of the Colorado River.
The large complex of cobble bars in the middle of Cataract Canyon was also considered a possible
spawning site for Colorado squawfish. Spawning by humpback chub was suspected in at least. one
location within Cataract Canyon, between river miles 201.5 and 212.4. Larvae, YOY, juveniles, and
adults were captured in this reach, including two adults in spawning condition.

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This investigation showed that the lower 50 miles each of the Green and Colorado Rivers above their
confluence, as well as the Colorado River from the confluence to Lake Powell were important nursery
areas for YOY Colorado squawfish. Average catch per effort of YOY Colorado squawfish in the lower
50 miles of the Green River was among the highest in the upper basin with 72 fish!100 m2. Maximum
average catch rate in Cataract Canyon was 32 fish/100 m2.

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Time of hatching and thus size of age-O Colorado squawfish may affect their overwinter survival.
Spawning times, based on back-calculations from known length to age relationships, varied by as much
as one month during this 4-year st.udy. Of the 4 years studied, warming of water temperature and
hatching times were delayed most. in 1986 when spawning did not peak until early August and average
length in early October was 30.6 mm TL. compared to average length of 34.0 to 38.7 for the othergcohorts at the same time. This difference in size may determine lipid content and thus
overwinter
condition and survival.

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