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

A total of 363 larval razorback suckers was recorded from collections in the middle
Stillwater Canyon reach (340 were captured by light traps and 23 by seines), 76 from seine or
light-trap collections in the San Rafael River confluence reach (all but two were captured by light
traps), and 1 was collected by light traps from the Green River Valley reach (Table 4), Within
the middle Stillwater Canyon reach, 80% of the total number of razorback suckers captured were
from Millard Canyon and 19% were from the Anderson Bottom-Bonita Bend area. All razorback
sucker larvae collected from the San Rafael River confluence reach were caught in nursery
habitats at or immediately downstream of the mouth of the San Rafael River.
Mean catch rates (CPUE) oflarval razorback suckers for both river sections were often
low (rarely exceeding 0.50 fish/unit of effort) and were highly variable among years, reaches, and
gear types (Tables 3 and 4). Ofthe sampling methods employed, we decided that comparisons of
CPUE among most years and among the primary reaches sampled were most valid, although
problematic, for light-trap collections. Mean CPUE (reaches combined) for the middle Green
River among years ranged from 0.02 fishfh of light trapping in 1995 to 1.00 fish/h in 1994 (Table
3); mean CPUE was similar between 1993 (0.12 fish/h) and 1996 (0.16 fishfh). In each year,
mean catch per hour of light trapping among the three primary reaches was highest for the
Escalante reach, followed in descending order by the Jensen and Ouray reaches. Mean catch
rates among years for the lower Green River, reaches combined, ranged from 0.01 fish/h oflight
trapping in 1995 to 1.36 fishfh in 1993 (Table 4). However, if 1993 results are excluded because
of the abbreviated sampling period (17-19 June), the highest annual mean CPUE occurred in
1994 (0.22 fishfh). Mean catch rates were highest for the middle Stillwater Canyon reach, and
the highest overall mean CPUE was for that reach in 1996 (1.52 fish/h of light trapping).
Temporal distribution of razorback sucker captures in both river sections varied among
years, and dates of capture over all years ranged from 16 May (1994) to 21 July (1995) in the
middle Green River and from 7 May to 9 July (1996) in the lower Green River (Figures 2 and 3),
In most years, larvae were first caught 20-30 d after the earliest estimated date of spawning
(Figures 4 and 5), and numbers collected had usually peaked by early or mid-June. The earliest
collection of razorback sucker larvae from the lower Green River each year during 1994-1996
occurred on (1994) or before (1995 and 1996) the earliest capture date in the middle Green River.

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