8162

• UCREFRP Catalog Number: 8162
• Author: Osmundson, D. B., R. J. Ryel, M. E. Tucker, B. D. Burdick, W. R. Elmblad and T. E. Chart.
• Title: Dispersal Patterns of Subadult and Adult Colorado Squawfish in the Upper Colorado River.
• USFW Year: 1998.
• USFW - Doc Type: \
• Copyright Material: YES

950
OSMUNDSON ET AL.
TABLE 3.-Length-weight regression coefficients (SEs
in parentheses) used in calculation of relative condition of
Colorado squawfish captured from the Colorado River
during 1990-1994. Relative condition (Kn) was expressed
as Kn = 100 x M?/Me, where M, is the observed mass
(g) and MQ is the expected mass (g) as calculated from
log10Me = log10(length)-m + b. Length is measured in
millimeters.
Month N Slope (m) y-Intercept (b) R2
Apr 81 3.17326 (0.061) -5.54824 (0.167) 0.972
May 257 3.25981 (0.030) -5.77281 (0.083) 0.978
Jun 128 3.20661 (0.038) -5.60323 (0.010) 0.983
120
90
related to fish size. Mean displacement between
consecutive captures was 43.8 km (SE = 15.5; N
= 17) for Colorado squawfish less than 500 mm
(at time of second capture), 13.3 km (SE = 3.5;
N = 68) for fish 500-599 mm (between first and
second captures), and 3.1 km (SE = 0.8; N = 34)
for fish 600 mm and longer (at first capture). Mean
displacement was not significantly different be-
tween fish 500-599 mm and those 600 mm and
longer, but displacements for both groups were
significantly less than for fish smaller than 500 mm
(ANOVA, Tukey-Kramer multiple comparison, P
< 0.05). Also, mean displacement of fish 550 mm
and longer (7.5 km; SE = 2.5; N = 70) was sig-
nificantly less (t-test, P = 0.008) than that of fish
smaller than 550 mm (33.6 km; SE = 10.2; N =
30). The proportion of total displacements con-
sisting of long-distance displacements (>10 km)
was significantly different between all size-groups
(test of proportions, all P < 0.003) and was in-
versely related to length: for fish smaller than 500
mm, 59% of displacements were farther than 10
km; for fish 500-599 mm long, 28%; and for fish
600 mm and longer, 6% were long distance.
Body Condition
Mean relative body condition (K„) of Colorado
squawfish varied with river reach and fish length-
class (month-specific constants are shown in Table
3). In the lower reach, fish condition declined with
increasing length (Figure 6): mean condition fac-
tors of fish 500-599 and 600-699 mm were sig-
nificantly lower (ANOVA, Tukey-Kramer multi-
ple comparison, P < 0.05) than those of fish 200-
299, 300-399, or 400-499 mm. Also, mean K. of
fish 400-499 mm was significantly lower than that
of fish 300-399 mm (P < 0.05). In contrast, body
condition of upper-reach fish increased with fish
length, and mean K. was highest in fish 700-799
mm. Mean K. of fish 600-699 mm was signifi-
cantly higher than those of fish 400-499 or 500-
115
C 110
O
a
C 105
O
U
> 100
95
Upper reach
85 11 1
200-299 400-499 600-699 800-899
300-399 500-599 700-799
Length-class (mm TL)
FIGURE 6.-Mean relative condition (K) of Colorado
squawfish by length-class and Colorado River reach. Error
bars represent 95% confidence intervals.
599 mm, and mean Kn of fish 700-799 mm was
significantly higher than that of fish 600-699 mm
(P < 0.05).
Mean Kn began to differ between reaches once
fish attained 500-599 mm. However, reach com-
parisons could not be made for all length-classes
because no fish 200-299 mm and only two 300-
399-mm fish were captured in the upper reach, and
in the lower reach, no fish 700 mm or larger was
captured. Significant differences were detected be-
tween reaches within length-classes of 500-599
and 600-699 mm (t-test, P < 0.0004 for both),
but not for fish 400-499 mm long (P = 0.14).
Relative Abundance of Forage Fish
Small fish (<100 mm) densities in backwaters
were generally higher in the lower reach than in
the upper reach: mean annual CPUE (fish per area
seined) during fall surveys (1991-1995) was 5.7/
m2 (SE = 0.4) in the lower reach and 3.3/mz (SE
= 0.4) in the upper reach. Results from ANOVA
and multiple comparison (obtained by using log-
transformed data) indicated that the difference for
the 5-year period was significant (ANOVA, P <
0.0000001); however, within years, the only sig-
nificant difference was in 1994 (Tukey-Kramer
multiple comparison, P < 0.05). Three introduced
species, red shiner Cyprinella lutrensis, fathead
minnow Pimephales promelas, and sand shiner No-
tropis stramineus, together made up 84-99% of all
fish within annual reach samples. Though fish den-
sities within backwaters were lower in the upper