9692 ‎(2)‎

• UCREFRP Catalog Number: 9692
• Author: Tyus, H. and Haines
• Title: Biology of Young Colorado Squawfish
• USFW Year: n.d.
• USFW - Doc Type: 81-89
• Copyright Material: YES

86 TYUS AND HAINES
48
48 Y . 46.247 - 0.576X
r . -0565 44
E 44 0 0
-5
I 40
>- 40
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~ 36 36
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0 32 32
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28 28

40 60 80 100 120 140 160 180 200 220

5

Y = 4.730 - 0.024X
r = -0.859

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E
o 3
o
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-1

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STREAMFLOW em 'Is eo)

Y = 50296 - 0140X
r . -0.810

20 40 60 80 100 120 140 160

o
o 0

Y = 4.281 - 0.039X
r = -0.797

-1

-2

-3

20 40 60 80 100 120 140 160
STREAMFLOW em3/seo)

FIGURE 3.-Regressions of Colorado squawfish mean total length (Y) on mean August-September streamflow,
and log,.(fish/IOO m2) (Y) and streamflow in the lower (left) and the upper (right) Green River, 1979-1985 and
1987-1988. Flows for the lower Green River were measured at the town of Green River, Utah; flows for the upper
Green River were measured at Jensen, Utah.

River within 3 to 15 d after hatching, and who
presumed that they were present in a 6-km river
reach for only about 1-2 d. We are aware of no
age-O or age-l juveniles captured in autumn above
the mouth of the Yampa River in the last 10 years.
Some age-O fish present in our upper Green Riv-
er samples could be the result of spawning below
the Yampa River. However, we believe that the
vast majority, ifnot all, ofage-O Colorado squaw-
fish found in the upper Green River are the result
of downstream drift from the Yampa River. Ra-
diotracking of adults on spawning migrations has
not confirmed other spawning locations in the up-
per Green River (Wick et al. 1983; Tyus 1985, in
press). Drift oflarvae into the Green River is well
documented (Haynes et al. 1984; Nesler et al.
1988), and summer and autumn concentrations
of age-O Colorado squawfish downstream from the
Yampa River spawning area suggested down-
stream movements. Finally, substrates in most of
the upper Green River (from Jensen to Desolation
Canyon) are fine silts and sand rather than cobbles
and boulders that exist in the known spawning
areas. We presumed that spawning would not oc-
cur on such substrates.

Although our data are not as extensive for the
lower Green River, we presume that a similar pat-
tern of larval drift occurs there. Years of radio-
tracking migrating adults and collecting ripe fish
there have indicated that RK 225-257 is a major
spawning area, and no other such area has been
confirmed downstream. Larvae were caught in drift
nets 8 km downstream (at RK 217) of the spawn-
ing area, and seining results show summer and
autumn concentrations of postlarval Colorado
squawfish downstream of the spawning area. Thus,
data collected at the Green River site support our
conclusions drawn from the Yampa River regard-
ing larval movement, and it is possible that larvae
drifting out of the Yampa River reach nursery
habitats in the lower Green River.
We were concerned about the validity of using
hatchery-derived growth equations for estimating
Colorado squawfish spawning dates from total
length of fish, particularly for the larger postlar-
vae, a concern also expressed by Nesler et al.
(1988). Average temperatures in the Green River
at mean larval hatching dates ranged from 20 to
250C, but the July-August backwater tempera-
tures at fish capture averaged 25-280C. Thus,