7080

• UCREFRP Catalog Number: 7080
• Author: Carter, J. G., V. A. Lamarra and R. J. Ryel
• Title: Drift of Larval Fishes in the Upper Colorado River
• USFW Year: 1986
• USFW - Doc Type: Journal of Freshwater Ecology
• Copyright Material: YES

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FIGURE 6. Length-frequency distribution of the non-native fathead minnow in
surface drift and shoreline seine hauls from the Parachute Site
on the upper Colorado River.

RESULTS OF PALISADE STUDY

Species eo.position And Relative Abundance

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Of the 14 fish species encountered only eight were found in drift
samples (Figure 2). In addition to these eight, largemouth bass (Micro terus
~~m~~1~s), carp (Clprinus ~~~~io), red shiner (N~!ropis !~trensis , channel
catfIsh (Ictalurus meats), brown trout (Sa1mo trutta) and rainbow trout
(Sa1mo garr~'~,:'i.if'we-;:e-captured with other-gear ~ but not as drifting
larvae. fhese six species are non-native to the upper Colorado River Basin.
The five native species (b1uehead sucker, f1anne1mouth sucker, speckled
dace, roundtai1 chub and mottled sculpin) made up 90 percent of the catch in
shore1 ine drift nets. Of the three non-native species in drift (white
sucker, fathead minnow and green sunfish), only the white sucker made up a
significant proportion of the drift (8.6 percent).

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Weekly Drift Patterns

Drift of larval fishes was monitored for 10 weeks, from July 6 to
September 13. Variations in mean weekly drift densities appear to be
related to river discharge and water temperature (Figure 7). Few fish were
found drifting before and at the initiation of drift net sampl ing. Drift
fish were first detected the second week of July when water temperatures
first reached 16.0oC.

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