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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180C (mean, 150C). Observations by Tyus (1987) on ripe fish in 1984 were supported by seine
collections of sucker larvae (N = 33; 10,6-13,6 mmTL) tentatively identified (later confirmed) as
razorback sucker from quiet shorelines downstream of suspected spawning areas. Tyus and Karp
(1990) located concentrations of ripe razorback suckers (N= 191) at two sites during 1987-1989:
(1) the mouthofthe Yampa River just before it enters the Green River (7% of the total number
collected); and (2)the Green River upstream of Jensen, Utah, adjacent to the Escalante Ranch at
river kilometers (RK) 486.4-504.0 (93% of the total number collected); note - river kilometers
measured upstream of the Green River confluence with the Colorado River. Ripe fish captured
at those sites were from runs associated with bars of cobble, gravel, and sand substrates in water
averaging 0.63 m deep with a mean velocity of 0.74 m/s. Tyus and Karp (1990) concluded that
spawning activities were associated with increasing and highest spring flows (typically May
through June) and mean water temperatures of 14,1 oC (range, 9-170C), Although the Escalante
site appears to be the primary spawning area for razorback suckers in the middle Green River,
Modde and Wick (1997) concluded that spawning probably occurs at secondary sites. Individual
razorback suckers in tuberculate or ripe condition have been collected within recent years
elsewhere in the Green River drainage, including reaches of the lower Green River in
Labyrinth-Stillwater Canyon, often near the mouth of the San Rafael River (e.g., Tyus 1987;
Miller and Hubert 1990; Muth 1995; Chart et al. 1997).
Prior to our investigation, direct evidence of reproduction by razorback suckers in the
upper Colorado River basin within recent decades or information on the species' natural early life
history in riverine environments were limited to those larvae collected by Tyus (1987) and
captures of a few early juveniles from backwaters (e.g., Smith 1959; Taba et al. 1965; Gutermuth
et al. 1994; Utah Division of Wildlife Resources, unpublished data), However, diagnostic
characters for distinguishing larval razorback suckers from larvae of sympatric suckers were only
recently developed (Snyder and Muth 1990) and previous sampling for riverine razorback
suckers did not target early life stages. This report integrates results of studies conducted during
1992-1996 on razorback sucker larvae in reaches of the middle or lower Green River (Figure 1)
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

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