9565

• UCREFRP Catalog Number: 9565
• Author: Bestgen, K. R. and e. al.
• Title: Population Status of Colorado Pikeminnow in the Green River Basin, Utah and Colorado
• USFW Year: 2007
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: NO

STATUS OF GREEN RIVER COLORADO PIKEMINNOW

1363

TABLE 2,-Abundance estimates, 95% confidence intervals (CIs), and coefficients of variation (CVs) for adult C:450 mm TL)
and recruit-size (400--449-mm) Colorado pikeminnow in various river reaches in the Green River basin, Utah and Colorado,
2000-2003. I

Reach

95% CI

Adults

Recruits
CV Abundance 95% CI CV
33 0
15 0
31 0
34 0
20 43 24-87 35
13 45 26-84 31
15 5 2-24 90
17 0
9 107 76-158 19
10 133 93-199 20
18 22 7-78 70
16 43 22-91 38
16 163 114-247 20
22 72 3&-154 39
21 152 90-269 29
16 71 48-116 23
20 31 16-{j9 41
22 89 53-162 30

Year

Abundance

2000
2001
2002
2003
2000
200]
2002
2003
2000
2001
2002
2003
200]
2002
2003
2001
2002
2003

317
320
277
224
1,100
746
643
407
1,613
],184
834
663
699
757
62]
355
261
227

Desolation--Gray c~yon

Lower Green River I
I
I

unique animals captured lin 2002 and 2003 (33 and 31,
respectively) was only o~e-third or one-fourth of those
captured in 2000 and 20t1 (82 and 120, respectively)
despite approximately equivalent sampling effort
among years. Probabiliti s of capture were also very
low in 2002 and 2003[ (Table 3). No estimate of
Colorado pikeminnow re ruit abundance was available
for the Yampa River in t\ y year because only a single
recruit-size fish was cap red (in 2000).
The abundance of adul Colorado pikeminnow in the
White River was higher' han that in the Yampa River
from 2000 to 2003 but d4clined more dramatically over
the study period. The es1timated number of adult fish
declined steadily from 1,100 (SE = 220) in 2000 to 407
I
(SE = 68) in 2003, a reduction of about 63%. The
confidence intervals fori the abundance estimates in
2000 and 2001 did not oyerlap with that for 2003, and
the same was true for 2?01 and 2003. Regression of
abundance as a function of time (n = 4) showed a
negative relationship (l~g [abundance] = 633.26 -
0.3131. year; r2 = 0.97, ~;: 0.016). Consistent with the
abundance estimates, th~ number of unique animals
captured declined steadily over the study period, from
265 in 2000 to 106 ~n 2003. The White River
abundance estimates had moderately good precision,
CVs ranging from 13% tF 20%.
The only abundance eftimate not within reasonable
expectations was that f01 the White River in 2000. In
that year, one unusually rrge fish (1,240 mm TL) was
captured, and because 0 the extremely low predicted
probability of capturin this fish (0.000062) this
individual inflated the Huggins model abundance

Yampa River

White River

Middle Green River

] 84-623
245-437
157-512
123-434
767-1,653
586-973
49]-864
300-573
1,359-1,948
986-1,441
593-1,192
491-9]8
527-963
504-1,166
423-942
270-496
184-388
154-352

estimate by over 16,000 individuals. This individual
was removed from the data set and the analysis rerun to
arrive at the more realistic abundance estimate
reported.
Colorado pikeminnow recruits in the White River
were rare during the study period and ranged from 45
(SE = 14) in 2001 to 0 in 2003, reflecting a decline in
the number of recruits in the White River during this
study. The confidence intervals for the abundance
estimates of the few recruits present in the White River
in 2000 and 2001 did not include, and were higher
than, the estimates in 2002 and 2003. As was the case
for all estimates of Colorado pikeminnow recruit
abundance, the White River recruit estimates were less
precise than those for adults, CV s ranging from 31 % to
90%.
The abundance of adult Colorado pikeminnow in the
middle Green River was the highest of any of the
reaches studied in the Green River basin but exhibited
a pattem of decline similar to that observed in the
White River. Abundance was estimated at 1,613 fish
(SE = 149) in 2000 but declined steadily to 663 fish
(SE = 107) in 2003, a reduction of 59%. The
confidence interval for the abundance estimates in
2000 did not overlap with those in 2002 and 2003, nor
did those for 2001 and 2003, suggesting a significant
decline in Colorado pikeminnow abundance over the
study period. Regression of abundance as a function of
time (n = 4) also showed a negative relationship
(loge[abundance] = 610.90 - 0.3018. year; r2 = 0.99,
P = 0.003). The number of unique animals captured
declined from 563 in 2000 to 97 in 2002 but increased