7403

• UCREFRP Catalog Number: 7403
• Author: Valdez, R. A. and W. J. Masslich.
• Title: Interim Report No. 2 - 1990 Humpback Chub Monitoring in Cataract Canyon.
• USFW Year: 1990.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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RESULTS

SamDle Effort and Fish Captured

The following tables summarize the results of Trip No.2 Table 1 is a summary of sampling
effort by gear type; Table 2 presents the catch composition by species; Table 3 is a summary of
endangered fish; and Table 4 is a list of endangered fish captured. Table 5 presents the meristic
measurements taken on any Gila captured.

Endan2ered Fish Captured

A total of 99 Colorado squawfish and 2 humpback chub were captured during Trip No. 2
(Table 3). The Colorado squawfish included 13 juveniles ranging in size from 61 - 336 mm TL, and
86 yay (1990 year class) ranging in size from 27 - 59 mm TL.

The majority of the yay Colorado squawfish (74 of 86) were found downstream of Ten Cent
Rapid (RM 200) in the former lake basin. This section of lake was riverine in character due to the
low pool elevation of Lake Powell. Discovery of this large number of yay Colorado squawfish in
this region is significant because it indicates that there is movement of yay into Lake Powell With
lakes levels higher in previous years (1985-1989) and with few backwater nurseries available, assessing
these numbers has been difficult. Now, we are able to say that, at least in 1990, significant numbers
of yay Colorado squawfish were transported into or moved into the Lake Powell basin. If this has
happened in other years when lake levels were higher, the absence of nursery backwaters and the
presence of large numbers of predators has prevented us from assessing the numbers of fish involved.
The numbers of Colorado sQuawfish, particularly yay, moving into T Jl1c-p P91.veY <1ftmJally CgYlEi Qe
~ 1!ecause of a lack of nursery habitHt and lar~e numbers of predators in the lake, their
chances of survival are probably minimal. ^

Currently, riverine conditions exist to below Sheep Canyon (RM 176), including a well defined
channel and significant velocities. However, due to the unique channel morphology in this area
associated with the low lake level, habitat for yay and early juvenile Colorado squawfish may be
limited. Only 4 backwaters were counted in this area (RM 191-RM 177) where 10 were noted during
Trip No. 1. Lack of backwaters in this area is probably due to the river channel actively cutting into
large deposits of sediment laid down in the inflow area since 1983. In most areas the shorelines of
the river are characterized by high (10-20 foot), steep, actively eroding silt cutbanks. A few areas of
shear cliff, where the river has completely eroded the sediments from the canyon wall also exist in
this reach, particularly on the outside of bends in the river. Consequently, any yay or juvenile
Colorado squawfish that have moved or been transported into the inflow region during winter or
spring runoff would be forced to face rigors associated with the main channel in the inflow region,
including predation by the lake dwelling species. Electrofishing and netting below Ten Cent Rapid
(RM 200) produced large numbers of channel catfish, stripped bass, and walleye, indicating that the
inflow area continues to support large numbers of these predatory species despite the increasingly
riverine nature of the area.

The potential exists for more backwater habitat to be created in this area as thunderstorm
runoff flushes sediments from tnbutary canyons. This backwater habitat may become more prevalent
when lake levels rise to reflood the newly created channels.

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