7614

• UCREFRP Catalog Number: 7614
• Author: Valdez, R. A.
• Title: Cataract Canyon Trip Report No. 2 -- Assess Reproductive Activity of Humpback Chub -- ‎(April 11-16, 1988)‎.
• USFW Year: 1988.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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What Happened Last Winter?

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As we reached the last rapids of Cataract Canyon (powell's, Repeat, Ten
Cent, Imperial) and entered Lake Powell on April 15, 1988, we noted a band of
heavy silt and rocks deposited along both shorelines extending approximately 3
to 5 vertical meters above the present water level and up to 15 meters from the
shore. It was evident that this was the result of large masses of ice that
were transported from upstream, carrying entrapped sediment and stones. As
these small ice bergs melted, their silt cargo was deposited along the
shoreline. This was evidence that the Colorado River in lower Cataract Canyon
and upper Lake Powell was heavily frozen during the winter of 1987-88.

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This is supported by aerial observations made by UDWR personnel (personal
communication with Miles Moretti, April 20, 1988) during eagle and raptor
surveys in the area. The aerial survey on January 27, 1988, revealed that
although much of the Colorado River from Potash through Cataract Canyon was
only partly frozen, solid ice cover extended from the base of Big Drop 3
downstream into Lake Powell (the survey ended at Dark Canyon, where there was
still solid ice cover). Mr. Miles reports that the last four major rapids
(Powell's, Repeat, Ten Cent and Imperial) were completely covered with a solid
ice canopy; the texture of the ice surface was not noted. Mr. Miles also
reported that this was the most severe icing condition on the Colorado and
Green Rivers in about 5 years of aerial surveys.

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wi thin the shoreline band of ice-deposited silt observed on April IS,
1988, we discovered large numbers of fish carcasses; primarily adult carp.
Many had been partially consumed by birds (many ravens were seen in the area),
but most were easily identified. Two informal transects were conducted to
assess the relative numbers of carcasses. Two biologists walked along the
shoreline and counted and identified the carcasses.

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Transect 1 was located at RM 200.7 on river left (facing downstream). The
transect was 185 m long, measured parallel to the shoreline, and included the
entire width of the silt band, 10-15 m. The number of carcasses found along
this transect was 329 adult carp and 8 channel catfish. No other species were
found. The river bank was heavily scoured, such that tamarisk plants up to 8
feet tall had been uprooted. The ground and rocks were covered with 2 to 5 cm
of silt within this band. Fish remains were scattered along the entire
transect, but several concentrations of 50+, within 10 to 20 m sections,
accounted for well over half. These large concentrations of carcasses were
found on relatively flat ernbayrnents that were natural collecting areas for
debris, suggesting that the already-dead fish had been washed into the area.

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Transect 2 was also located at RM 200.7, directly across the river from
Transect 1. This transect was 90 m long (parallel to shoreline) and similar in
width to Transect 1. A total of 123 adult carp and 1 channel catfish were
found. The situation here was similar to Transect 1 in that major
concentrations of fish accounted for 80% of the total number of fish carcasses.
As wi th Transect 1, the concentrations of fish were in areas that were
relatively flat--the most likely depositional area for floating items. The
fish did not appear to be physically damaged, as might be the case if ice were
crushing or pinning them to the rocks or other chunks of ice.

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