8022

• UCREFRP Catalog Number: 8022
• Author: Muth, R. T., et al.
• Title: Reproduction and Early Life History of Razorback Sucker in the Green River, Utah and Colorado, 1992-1996.
• USFW Year: 1998.
• USFW - Doc Type: 34,
• Copyright Material: NO

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EXECUTIVE SUMMARY

This report integrates results of studies conducted in 1992-1996 on larvae of razorback
sucker Xyrauchen texanus in reaches of the middle Green River, Utah and Colorado, or lower
Green River, Utah, Studies included two Colorado River Recovery Implementation Program
projects (numbers 34 and 38) conducted as part of the Flaming Gorge Research Program and
research sponsored by the National Park Service. Objectives were to (1) develop effective
methods for collecting larval razorback suckers in rivers, (2) document reproduction by
razorback suckers, (3) assess the distribution and relative abundance of larval razorback suckers,
(4) associate razorback sucker spawning dates with main stem discharges and temperatures, and
(5) estimate growth rates and describe the diet of larval razorback suckers in nursery habitats.
Sampling occurred during spring and early summer in reaches near known razorback sucker
spawning areas or reported capture locations of individual tuberculate or ripe fish and with
quiet-water habitats accessible to fish larvae under varied river discharges. Drift nets were used
to collect drifting larvae, and light traps, seines, or dip nets were used to sample larvae in flooded
and backwater habitats.
Larval razorback suckers were collected in each year of sampling from the middle
(1992-1996) and lower (1993-1996) Green River. These captures represent the first confirmed
reproduction by the species in the middle Green River since 1984 and the first ever records of
razorback sucker larvae in the lower Green River. A total of 1,735 larvae was caught in the
middle Green River and 440 in the lower Green River. Of all individuals collected from the
middle Green River, 1,651 were captured by light traps, 69 by seines, 12 by drift nets, and 3 by
dip nets. In the lower Green River, 415 specimens were caught by light traps and 25 by seines.
Catches of larval razorback suckers were highly variable among years and reaches.
Numbers captured per year ranged from 20 in 1992 to 1,217 in 1994 for the middle Green River
and from 5 in 1995 to 222 in 1996 for the lower Green River. In the middle Green River, the
Escalante (711 larvae), Jensen (700), and Ouray (318) reaches combined produced over 99% of
the total catch. Only six individuals were caught in the Echo Park reach, and none was captured
from the Island-Rainbow Park reach. In the lower Green River, 363 larvae were collected from

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