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

in late afternoon or early evening ranged from 17 to 260C (mean, 21 OC) in the middle Green
River and from 15 to 330C (mean, 220C) in the lower Green River.
Mean daily discharge and instantaneous daily water temperature data in each year of the
investigation for the mainstem middle and lower Green River, respectively, were from U.S.
Geological Survey gages near Jensen (gage number 09261000) and Green River (09315000),
Utah. Mean daily discharges of the middle Green River for the April-July period each year
during 1992-1996 averaged 108,240, 139,281, and 275 m3/s, respectively. Annual maximum
(peak) mean daily discharges of the middle Green River were 270 m3 Is on 13 May 1992, 566
m3/s on 28 May 1993,331 m3/s on 20 May 1994,526 m3/son 8 June 1995, and 623 m3/s on 20
May 1996. During 1993-1996, average April-July mean daily discharges of the lower Green
River each year were 288, 143,373, and 320 m3/s, respectively. Peak mean daily discharges of
the lower Green River were 710 m3/s on 31 May 1993,331 m3/s on 22 May 1994,829 m3/s on 19
June 1995, and 679 m3/s on 22 May 1996,

Fish Collections

Sampling was intended to target razorback sucker larvae, and captures of other fishes
were secondary to the objectives ofthe 5-year investigation. However, those secondary captures
provided a general description of the assemblages of small fish in habitats and during periods
sampled for larval razorback suckers, and roughly illustrated the vulnerability of different species
or life stages to the collecting gear and techniques employed. Further, sampling procedures and
overall scope ofthe investigation evolved over time, and rigorous comparisons of fish
distribution and abundance among species, years, river reaches, or gear types were not warranted
because of unequal effort and variability in environmental conditions.
Middle Green River.-Sampling began in early to mid-May each year, about when
main-channel water temperatures first consistently reached or exceeded 140C, and continued until
captures of suspected razorback sucker larvae had declined to only a few fish per collection or
ceased (mid- or late June in 1992, 1994, and 1996; early July in 1993; early August in 1995).
Collections were made about once per week in 1992 (an exploratory year) and about twice per
week in subsequent years. Quiet-water habitats were sampled with seines (1992-1993), light

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