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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This trend was most pronounced in 1996 when 83% of the total number oflarval razorback
suckers caught in the lower Green River (184 out of 222) were collected 3 to 28 d before the date
of first capture in the middle Green River; estimated dates of first reproduction in 1996 were 2
April in the lower Green River and 9 May in the middle Green River.

Spawning Periods

Estimated annual spawning periods for razorback suckers varied temporally among years
in both the middle and lower Green River but generally spanned 4-6 weeks each year and were
associated with increasing and highest spring flows (Figures 4 and 5). Dates of reproduction in
the lower Green River were probably underestimated in 1993 because of restricted sampling and
in 1995 because of low captures of larvae, and therefore, those results were excluded from the
following comparisons. Over all years, spawning in the middle Green River extended from
mid-April (1994) through late June (1995) but generally ranged from early or mid-May through
late Mayor early June. Spawning in 1993, 1995, and 1996 appeared to be concentrated during
mid- to late May. In contrast, most spawning in the low-flow ye~ of 1994 was estimated to
occur during late April to mid-May. Within the reproductive period across all years, mean daily
discharges of the mainstem middle Green River ranged from 78 to 623 m3/s (mean, 370 m3/s) and
instantaneous daily water temperatures ranged from 8.0 to 19.50C (mean, 140C). Spawning in the
lower Green River in 1994 occurred from late April through late May at mainstem discharges of
134-331 m3/s (mean, 233 m3/s) and water temperatures of 12.5-20.50C (mean, 17.50C).
Discharges and water temperatures ofthe lower Green River in 1996 during early April through
early June spawning ranged from 145 to 679 m3/s (mean, 376 m3/s) and from 10.0 to 21.0oC
(mean, 14.50C), respectively. Most spawning was estimated to occur during early through
mid-May in 1994 and mid- through late April in 1996.
Of the selected mainstem water temperature and discharge parameters associated with
earliest dates of spawning, excluding 1993 and 1995 for the lower Green River, none appeared to
be adequate for predicting when first reproduction would occur (Table 5). Each parameter varied
considerably among years within each river section, and trends were inconsistent. Dates of first
reproduction in most years generally coincided with a relatively steep and consistent increase in

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