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

DISPERSAL PATTERNS OF COLORADO SQUAWFISH
700
650
E 600-
E
550 1993-1994
rn
C
500
f>3
0 450
1991-1992
400
350
1 2 3 4 5 6 7
Stratum
FIGURE 2.-Mean length of Colorado squawfish by stra-
tum. Lengths of fish captured in 1991 and 1992 (heavy
line) and those captured in 1993 and 1994 (light line) were
pooled. Error bars represent 95% confidence intervals.
Results
Distribution
Mean length of Colorado squawfish captured in
this study progressively increased upstream (Fig-
ure 2). Because samples from strata 2, 3, and 5
were small, lengths of fish captured were pooled
into 1991-1992 and 1993-1994 periods for statis-
tical tests. Analysis of variance (ANOVA) re-
vealed that for 1991-1992 data, mean lengths in
strata 3, 5, 6, and 7 differed significantly from the
mean in stratum 1; those in strata 5-7 differed from
the mean in stratum 2; mean lengths in strata 7
and 3 also differed ((ANOVA, Tukey-Kramer
multiple comparison; P < 0.05). Regression in-
dicated significant relationships (Figure 3) be-
tween total length and rkm in 1991 (r2 = 0.59, P
< 0.0001) and 1992 (r2 = 0.60, P < 0.0001);
slopes between 1991 and 1992 were not signifi-
cantly different (P = 0.28).
For 1993-1994, differences in mean lengths
among strata were not as pronounced as in 1991-
1992. Significant differences were found only be-
tween stratum 1 and strata 3, 5, 6, and 7 (ANOVA,
Tukey-Kramer multiple comparison, P < 0.05).
Mean lengths in the two most downstream strata
were significantly greater during 1993-1994 than
during 1991-1992 (t-test, P < 0.0001). In the up-
per reach, mean lengths declined from 1991-1992
to 1993-1994 (significantly only in stratum 7;
t-test, P = 0.012). Regression indicated significant
relationships between total length and rkm loca-

i uuv
800
600
400
200
0
1000
800
E 6o0
E 400
200
1)
C o
(1) 1000
(ti 800
0
600
400
200-
0
1000-
800-
600-
400-
200-
947
1991 $
$+++
N=89 +
+
+

r-squared = 0.59 P < 0.0001

1992
N=91

+
+
+
+ r-squared = 0.60 P < 0.0001

1993 ++ +
N= 160
+
+
+
+
r-squared = 0.22 P < 0.0001
1994
+
N = 127
+

r-squared = 0.32 P < 0.0001
0 30 60 90 120 150 180 210 240 270 300
River kilometer
FIGURE 3.-Relationship between Colorado squawfish
length and kilometers upstream from the lower end of the
study area (river kilometer 0 at the Green River conflu-
ence) during 1991-1994.
tion in 1993 (r2 = 0.22, P < 0.0001) and 1994 (r2
= 0.32, P < 0.0001). Slopes were not significantly
different between 1993 and 1994 (P = 0.13), but
both differed from slopes of relationships for 1991
and 1992 (all P < 0.003).
Netting catch rates indicated that adult distri-
bution changed during 1991-1994. During 1991-
1992, very few adult Colorado squawfish were
caught in the lower reach. In 1991, Colorado
squawfish 500 mm and longer were captured only
in stratum 3 (one fish) and none in strata 1 or 2,
resulting in an overall mean CPUE in the lower
reach of 0.02 fish (?500 mm) per net (SE = 0.02;
N = 47 net sets). In contrast, 42 fish 500 mm or
longer were captured with nets in the upper reach,
for a mean CPUE of 0.30 (SE = 0.07; N = 139).
A similar pattern was evident in 1992: Colorado
squawfish 500 mm or longer were captured only
in stratum 3 (six fish) and none in strata 1 or 2.