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
reach, greater backwater area per unit length of
river existed there, averaging 0.18 ha/km, than in
the lower reach, where backwater area averaged
0.06 ha/km (C. McAda, USFWS, unpublished
data). Hence, overall abundance of small forage
fish in the two reaches may have been more similar
than indicated by CPUE data alone.
Catch rates of larger fusiform, soft-rayed fish
were generally higher in the upper reach than in
the lower reach, with highest catch rates occurring
in the uppermost stratum. Those fish 100 mm and
longer included native roundtail chub Gila robusta,
bluehead suckers Catostomus discobolus, flannel-
mouth suckers C. latipinnis, nonnative white suck-
ers Catostomus commersoni, and various sucker
hybrids. Common nonnative species susceptible to
the two gear types but considered largely invul-
nerable to predation were the deep-bodied com-
mon carp Cyprinus carpio and the spined channel
catfish Ictalurus punctatus and black bullhead
Ameiurus melas.
Electrofishing catch rate of fusiform-shaped fish
100 mm and longer was higher in stratum 3 than
in stratum 1 (P < 0.05), but CPUE in stratum 3
was not significantly higher than in stratum 2.
Catch rates in upper-reach strata were each higher
(ANOVA, Tukey-Kramer multiple comparison, P
< 0.05) than in all lower-reach strata (Figure 7).
Among upper-reach strata, the catch rate in stratum
7 was higher than in strata 5 and 6 (P < 0.05),
and no significant difference was detected between
strata 5 and 6. For all fish 100-300 mm (excluding
ictalurids), mean electrofishing CPUE was signif-
icantly higher in each upper-reach stratum than in
any lower-reach stratum (P < 0.05), though no
differences in CPUE were found among strata
within either reach.
Trammel-netting CPUE of fusiform-shaped fish
displayed a trend similar to electrofishing with
rates generally higher in upstream strata. Catch
rates were not significantly different among years
within any lower-reach stratum nor among lower-
reach strata within years (ANOVA, Tukey-Kramer
multiple comparison, P > 0.05). The CPUE in
stratum 5 was significantly higher (P < 0.05) than
that in stratum 1 during 1992 and 1994 and higher
than stratum 3 CPUE in 1994. In stratum 6, CPUE
was significantly higher than in stratum 1 in all
years, higher than in stratum 3 in 1993 and 1994,
and higher than in stratum 5 in 1993. In stratum
7, CPUE was significantly higher than in all other
strata except stratum 6 in 1993. When all three
years were considered, CPUE in stratum 7 was
951
80
60
Electrofishing
> 100 mm (fusiform)
G
E
40
t
LL 20 ?
0 y'
20
15
N
G
N 10
LL
Trammel netting
> 100 mm (fusiform)
41
Electrofishing
100-300 mm (all)
0
12
10
_G
8
O
r 6
t
rn 4
2
0
2 3 4 5
Stratum
FIGURE 7.-Electrofishing and trammel-netting catch
per unit effort (CPUE) by stratum for potential forage fish-
es of large Colorado squawfish. Electrofishing (top) and
trammel netting (middle) catches of fusiform fish more
than 100 mm in total length include roundtail chub, flan-
nelmouth sucker, bluehead sucker, white sucker, and suck-
er hybrids. Electrofishing CPUE of fish 100-300 mm (bot-
tom) includes all species except channel catfish and black
bullhead. For trammel netting, separate bars within each
stratum represent CPUE from (left to right) 1992, 1993,
and 1994 (no 1994 data in stratum 2); electrofishing was
conducted in 1993 only. Vertical lines are ±SE of the geo-
metric mean.