8163

• UCREFRP Catalog Number: 8163
• Author: Osmundson, D. B. and K. P. Burnham.
• Title: Status and Trends of the Endangered Colorado Squawfish in the Upper Colorado River.
• USFW Year: 1998.
• USFW - Doc Type: \
• Copyright Material: YES

964

OSMUNDSON AND BURNHAM

30 Upper and Middle
Subreaches

.1982 N = 46
01991-1992 N=89

20

10

o

300-349 400-449 500-549 600-649 700-749 800-849 900-949

;R 30
e......

Middle
Subreach

.1974-1976 N = 66
01991-1995 N = 175

>-
g 20
Q)
::::J
0-
Q) 10
...
U.

o~
300-349 400-449 500-549 600-649 700-749 800-849 900-949

30

Lower
Subreach

.1979 N=33
01991-1994 N = 58

20

10

o
250-299 350-399 450-499 550-599 650-699 750-799 850-899
300-349 400-449 500-549 600-649 700-749 800-849 900-949

Length-class (mm)

FIGURE 3.-Length distributions of Colorado squawfish
captured (N) during recent and earlier surveys. Reaches
and years were pooled as shown (see Table 1) to meet
sample size objectives (>30 fish per distribution) and to
keep sampling gear types consistent among time periods.

subreaches of the upper reach: this was between
the distributions of the combined 1974-1976 pe-
riod and the combined 1991-1995 period (Figure
3, middle panel) in the middle subreach (P =
0.00001, K-S test). The proportion of captured fish
less than 550 mm was significantly greater (P =
0.00001, test of proportions) for 1974-1976 than
for recent years, and many of the fish (35%) were
less than 450 mm during 1974-1976. The highest
proportion of fish less than 450 mm in recent years
was 10% in the lower subreach during 1991-l992
(data not shown). Comparisons between distribu-
tions in other years (Figure 3, top and bottom pan-
els) failed to indicate significant differences (P >
0.05, K-S test) between early and recent periods.
Comparisons among recent years.-In the upper
subreach of the upper reach, fish 600-649 mm

30 Upper
20 Subreach
.......
~ 10
~
>-
u 0
c:
Q)
:J
0- 30
Q)
.....
LL
20
10

I~

1993-1994

N=38

o
250-299 350-399 450-499 550-599 650-699 750-799 850-899
300-349 400-449 500-549 600-649 700-749 800-849 900-949

Length-class (mm)

FIGURE 4.-Length distributions of Colorado squawfish
captured (N) in the upper subreach of the upper reach
during 1991-1992 and 1993'-1994.

were the most abundant group during 1991-1992,
but a significant change (P = 0.03, K-S test) in
size distribution to smaller fish in 1993-1994 oc-
curred, and the 550-599-mm size-class became
dominant (Figure 4). In addition, the proportion of
fish less than 550 mm significantly increased (P
= 0.01, test of proportions) between 1991-1992
and 1993-1994, which would be consistent with
an influx of young fish from the lower reach.
In the middle subreach, differences in size dis-
tribution were significant only between 1993-1994
and 1995 (P = 0.02, K-S test): in 1995 there was
a smaller proportion of fish less than 500 mm (P
= 0.04, test of proportions). Comparisons between
individual years also indicated a difference be-
tween size distributions in 1994 and 1995 (P =
0.04, K-S test): the proportion of fish less than
550 mm declined between 1994 and 1995 (P =
0.02, test of proportions).
In the lower subreach, size distributions did not
significantly change (P = 0.80, K-S test) between
1991-1992 and 1993-1994. An apparent increase
in the proportion of fish captured in the 450-499-
mm length-class from 17% (1991-1992) to 28%
(1993-1994) was not significant (P = 0.34, test of
proportions).

Reproductive Success

Results from seining surveys indicated that
1986 and perhaps 1987 were comparatively good
years for Colorado squawfish reproduction in the
upper reach. No larval or age-O fish were collected
from the upper subreach during the 1986-1994

c,