9341

• UCREFRP Catalog Number: 9341
• Author: Modde, T., R. T. Muth and B. G. Haines
• Title: Floodplain Wetland Suitability, Access, and Potential Use by Juvenile Razorback Suckers in the Middle Green River, Utah
• USFW Year: 2001
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

1 100 MODDE ET AL.
70 670
60 discharge 1995 sss
50 453
40 340
30
-
20 -
E 10
?i00plankton 113 ??
E
Z
p 0
10 20 30 10 20 30 10 20 30 90 20 30
10 20 30 10 20 0
pt
Y

70
670 t11
V
y
0 60 discharge
1996
s6s
0
0
N
50
453
40 $40
30 ~
227
20
10 zooplankton 113
0 -
1o 20 30 10 20 30 10 20 30 10 20 30
10 20 30 10 20 0
May Jun Jul Aug Sep Oct
FIGURE 3.-Green River discharge (solid line; right scale) and zooplankton density (broken li ne; left scale) in
Old Charley Wash d uring 1995 and 1996.
during the high-flow period. Pucherelli et al.
(1988) reported that most channel backwaters do
not exist in the middle Green River until flows
recede to approximately 109 m3/s, well after ra-
zorback sucker larvae were collected in the Green
River (Muth et al. 1998). Solar radiation increases
temperature in the relatively shallow, no-velocity
floodplain, providing a more favorable environ-
ment for age-0 fishes. The temperature preferen-
dum for 6-year-old hatchery reared razorback
suckers (150-300 mm) is between 22.9°C and
24.8°C (Bulkley and Pimental 1983). Tempera-
tures were either at or just above this preferendum
during most of the summer in Old Charley Wash,
exceeding 25°C in August 1995 and July 1996.
Because the temperature tolerance and preference
of younger fish are higher than those of adults
(Boehlert 1981), the temperatures observed in Old
Charley Wash were probably nearly optimal for
the growth of razorback sucker juveniles.
Throughout spring and summer, water tempera-
tures in the wetland were warmer than those in the
main channel. Dissolved oxygen concentrations
and water depth were sufficient to support fish
through the warmwater months. Dissolved oxygen
concentrations were rarely below 5.0 mg/L, the
concentration suggested by Boyd (1979) as opti-
mal for warmwater pond fishes.
This favorable physical environment was com-
plemented by high prey densities. High zooplank-
ton densities in Old Charley Wash coincided with
access by larval razorback suckers to floodplains
in the Green River. Mabey (1993) reported zoo-
plankton densities of 7.1/L and 1-5/L (using a 63-
µm mesh) in riverine backwaters near Ouray in
July and August, respectively, compared with
311.4/1- and 690.2/L during the same time in Old
Charley Wash. In high-velocity main-channel hab-
TABLE L-Time periods when larval razorback suckers were collected in the Green River, Utah, and the number of
days larvae had access to floodplains in the Ouray National Wildlife Refuge wetland complex (i.e., flows above 575
m3/s) in the presence (regulated) and absence (unregulated) of the Flaming Gorge Dam.
Days larvae had
access to floodplain
Duration wetlands
Number (d) of
Dates larvae of larvae larval Un-
Year present collected collections Regulated regulated
1993 19 May-8 Jul 292 52 0 17
1994 15 May-15 Jun 1,277 32 0 0
1995 13 Jun-21 Jul 32 39 0 10
1996 3 Jun-27 Jun 174 25 0 5