WSP12345

• File Number: 8240.200.10.B
• Description: UCRBRIP Annual Reports
• Basin: Colorado Mainstem
• Date: 1/12/1995
• Author: UCRBRIP
• Title: 1994 Annual Reports Package Part 2
• Water Supply Pro - Doc Type: Publication

Numerous samples have been sent to the larval Fish laboratory, CSU for
counting and identification. Therefore, the information presented here
is preliminary.

Five species of native fish were captured. They were: ~ sp.
(n=579), Colorado squawfish (n=345), bluehead sucker (n=134), speckled
dace (n=46) and flannelmouth sucker (n=35). Most native fish were
captured in August (n=529). JUly (n=2B4) and September (n=241)
captures were similar, while the fewest number of natives was found in
June (n=94).

Gila sp. were the most numerous natives encountered in every month but
September. They were most numerous in August (n=352), then July
(n=113), September (n=67) and June (n=47), respectively. Most Gila sp.
were captured above Three Fords rapid (RM 156.4). Gila sp. appeared to
have left backwater habitats for main channel habitats between the
August and September surveys. The apparent substantial growth of fish
during the summer may have accounted for this early shift. Mean length
of all Gila sp. captured in June was 67.5 rnm, indicating that these
were Age 1+ fish. By July, only 3 Age 1+ fish were encountered. Age 0
fish had a mean length of 30.4 mm in July. By September, these same
fish exhibited a mean length of 60.B rnm.

Growth patterns for Colorado squawfish mimicked those of Gila sp., but
captures differed. More squawfish were captured in September (n=144)
than other months. Captures followed, in descending order, the
following pattern: July (n=97), August (n=71), June (n=33).. Note
should be taken, however, that 69 of the September squawfish captured
were caught in 1 seine haul in a backwater at RM 143.6. Most squawfish
were encountered below the known spawning site at Three Fords rapid (RM
156.4) As with Gila sp., mean length of fish caught in June (67.4 mm)
indicated Age 1+ fish were sampled. In July, only 3 Age 1+ fish were
encountered and Age 0 fish had attained a mean length of 24.9 mID. Mean
length of Age 0 fish had increased to 57.7 mm by September.

Captures of bluehead suckers most closely followed those of Gila sp.
Mean lengths increased from 30.0 mm in July to 57.1 mm in September,
when the number captured dropped >50%. Flannelmouth suckers were
encountered in low and relative stable numbers through the summer.
Mean lengths by month indicated Age 1+ fish utilizing backwaters in
June, but Age 0 fish in backwaters thereafter. Mean lengths increased
from 3B.9 mID in July to 66.2 mID in September. Speckled dace were most
numerous in August samples, which accounted for B7% of all captures.
Mean length in August was 27.4 mID. This had increased to 38.0 mID by
September, but this figure is based on a very low sample size (n=4).

Although analysis of habitat use, habitat features, non-native fish
communities, etc. remain, preliminary data indicate there was spawn in
both Gila sp. and Colorado squawfish in 1994. In addition, conditions
for growth appear to have been excellent with a resultant phenomenal
growth rate in native fishes. Some tables illustrating the information
discussed here follow.

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