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

84

TYUS AND HAINES

TABLE 3.-Catch of age-O Colorado squawfish in different habitats, September-October 1979-1981; C = fish
seined/lOO m2, E = number of seine hauls.

Backwater Shoreline Eddy Main channel Side channel
Year C E C E C E C E C E
1979 22.6 106 0.0 2 0.0 8 0.6 11 0.0 9
1980 22.6 187 4.7 49 0.0 11 0.0 I 3.0 11
1981 11.2 72 0.1 80 0.2 48
Mean 18.8 122 1.6 44 0.1 22 0.3 6 1.5 10

gradient reaches, induding stratum C, D, and G,
yielded lower average catches (mean, 4.1/100 m2;
Table I).

the lower Green River (strata A and B) and in
59% in the upper river (strata E and F).
In autumn, Colorado squawfish occupied back-
waters that were warm, deep (I-tests, P < 0.05),
and turbid (G-tests, P < 0.01, Table 4). Back-
waters with Colorado squawfish averaged about
170C, about 20 warmer than the average of those
without the species (Table 4).
Colorado squawfish were usually captured in
deeper backwaters (mean depth, 38 cm), but the
fish was more abundant in larger backwaters only
in the upper Green River (t-test, P = 0.05), where
average sizes were 269 m2 and 1,158 m2 for back-

Habitat Use

Catch of postlarval Colorado squawfish in low-
er-gradient reaches during 1979-1981 was great-
est in backwaters (84%) but postlarval fish were
also captured in shorelines, side channels, runs,
and eddies (Table 3). In all years combined (1979-
1985, 1987, 1988), the catch of age-O Colorado
squawfish averaged 13.31100 m2 in backwaters.
The young were absent in 37% of backwaters in

TABLE 4. - Relationships between some variables in backwaters and presence of Colorado squawfish in the Green
River, September and October 1979-1985 and 1987-1988. N = number of backwaters. The study area in lower
Green River ranged from river kilometer (RK) 35 to RK 211; the study area in upper Green River ranged from
RK 340 to RK 515. The symbols ( and G denote the (-test and G-test of differences between means for species-
absent and species-present; asterisks denote significance at P s 0.05* or P s 0.01**; NS = not significant.
Species absent Species present
Variable Mean SD N Mean SD N Test
Lower Green River
Temperature ("C) 17.7 5.7 82 19.4 4.4 118 1*
Maximum depth (em) 22.4 22.2 87 33.9 26.5 147 1*.
Size (m2) 309.9 644.8 32 493.7 622.6 49 toNS
Turbidity (%) G**
Clear 12.5 2 7.0 4
Moderate 68.8 11 26.3 15
Turbid 18.7 3 66.7 38
Substrate % GoNS
Silt 89.7 78 84.6 126
Sand 10.3 9 14.1 21
Gravel 0.0 0 0.7 I
Cobble 0.0 0 0.7 1
Upper Green River
Temperature ("C) 12.2 4.5 166 14.6 4.6 100 1**
Maximum depth (em) 33.1 24.3 190 41.8 25.3 128 1**
Size (m2) 269.0 354.5 55 1,158.0 1,638.4 30 1**
Turbidity (%) G*.
Clear 39.6 19 0.0 0
Moderate 27.1 13 33.3 7
Turbid 33.3 16 66.7 14
Substrate % GoNS
Silt 68.9 128 66.7 86
Sand 30.1 56 33.3 43
Gravel 0.0 0 0.0 0
Cobble 1.0 2 0.0 0

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