WSP01924

• File Number: 8240.200.46.D.3
• Description: Ruedi Reservoir
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/15/1987
• Title: Ruedi Round II and Green Mountain Water Sales Biological Opinion
• Water Supply Pro - Doc Type: Biological Opinion

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investigation, 46 larval squawfish were collected with fine-mesh hand nets
from two IS-mile reaches of the Colorado River immediately upstream and
downstream of its confluence with the Gunnison River (Table 6). Although the
sampling effort was similar in the two river reaches, 96 percent of the larval
captures occurred immediately below the Gunnison River confluence (RM 162-
164). Only 2 (4 percent) of the larvae were collected from the upstream
reach. These observations may indicate that most fish were spawned in the
downstream reach or that the larvae were spawned in the upstream reach and
drifted downstream to the area where most of the captures were recorded.

Table 6. Larval Colorado squawfish captures from the Colorado River
reaches upstream and downstream of the Gunnison River confluence.

Upstream Reach (RM 186-171)

Downstream Reach (RM 170.9-156)

Date
(mo./day)

No. caught Size range
(Tl, mm)

Date No. caught
(mo./day)

Size range
(TL, mm)

1982 -

8/12
8/24

1
1

o

o
o

o
o

o
o

13.8
10.5

o
o

23

1
5

1
6

4
4

44

1983
1984

9/21

12.2-19.2

8/06
8/21
1985
7/22
8/29

10.9
10.3-11.5

12.1
11.4-17.4

1986

8/21
8/28

9.2-13.8
11.5-14.8

Total ----z-

RM = river mile, the location on the river measured as the distance from the
confluence of the Colorado and Green rivers (RM 0).

Postlarval Young-of-Year Occurrence

No postlarval young-of-year Colorado squawfish greater than 25 mm total length
were collected from above the Gunnison River confluence in a total of
57 samples collected in the fall of 1982-1986. However, a total of
62 Colorado squawfish were collected in the IS-mile reach below the confluence
of the Gunnison River (54 samples). The 1982-1984 catch rate of young-of-year
squawfish in the 10-mile reach immediately downstream of the confluence of the
Gunnison River (RM 160-170) warranted classification of this reach as a "Major
Young-of-Year Nursery Area" by the Upper Colorado River Basin Biology
Subcommittee (1984).