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<br />STATUS OF GREEN RIVER COLORADO PIKEMINNOW
<br />
<br />1365
<br />
<br />TABLE 3.-Maximum probabilities of capture of Colorado pikeminnow from the Green River basin, 2000--2003, for each
<br />reach, sampling pass, and year. Values are Ihe maxima from quadratic relationships treating probability of capture as a function
<br />of TL and TL 2 for each river reach and year, with asymptotes at about 540 mm. Estimates of p* (probability of capture over all
<br />sampling occasions) were from the Cormack-Jolly-Seber component of the model used to estimate annual survival rates
<br />(recaptures between years; see text), p's per pass were scaled by capture rates. Because p* was estimated in this manner, we
<br />could calculate abundance estimates for the Yampa River in 2002 and 2003, when no animals were recaptured between passes
<br />within a single year,
<br />
<br />Reach
<br />
<br />Sampling
<br />pass
<br />
<br />2000
<br />
<br /> Year
<br />2001 2002 2003 Mean
<br />0,165 0,045 0,014 0,068
<br />0,117 0,045 0,017 0,064
<br />0,171 0.045 0,076 0,116
<br />0,15] 0,045 0.036 0,083
<br />0,104 0,110 0,103 0,104
<br />0.120 0,084 0,052 0,085
<br />0,082 0,122 0.064 0.094
<br />0,102 0,105 0,073 0.D95
<br />0,050 0,045 0,037 0,054
<br />0,067 0,052 0,060 0.073
<br />0,179 0.D35 0.078 0,122
<br />0,099 0,044 0,058 0,083
<br />0,125 0,056 0.G35 0,072
<br />0,125 0,049 0.025 0,066
<br />0,095 0,056 0,067 0,073
<br />0,1 ]5 0,053 0,042 0,070
<br />0,087 0.089 0,048 0.075
<br />0,109 0,125 0,056 0,096
<br />0,274 0,088 0,087 0,150
<br />0,156 0,101 0,064 0.107
<br />0,117 0,065 0,056 0,087
<br />
<br />Yampa River
<br />
<br />1
<br />2
<br />3
<br />Mean
<br />1
<br />2
<br />3
<br />Mean
<br />1
<br />2
<br />3
<br />Mean
<br />1
<br />2
<br />3
<br />Mean
<br />1
<br />2
<br />3
<br />Mean
<br />Overall mean
<br />
<br />White River
<br />
<br />Middle Green River
<br />
<br />Desolation-Gray Canyon
<br />
<br />Lower Green River
<br />
<br />0,047
<br />0,077
<br />0,173
<br />0,099
<br />0,101
<br />0,085
<br />0,110
<br />0,099
<br />0,086
<br />0,113
<br />0,197
<br />0,132
<br />
<br />0,110
<br />
<br />River reaches and similar to that in the Yampa River.
<br />Point estimates of abundance declined from 355 fish in
<br />2001 to 227 in 2003, a 36% reduction. Overlapping
<br />confidence intervals among pairs of point estimates
<br />indicated that the differences were not statistically
<br />significant. Regression of abundance as a function of
<br />time (n = 3) suggested a negative relationship
<br />(loge[abundance] = 453.24 - 0.2236" year; r2 =
<br />0.955, P = 0.136). The number of unique animals
<br />captured declined from 143 in 2001 to 65 and 54 in
<br />2002 and 2003, respectively. Lower Green River
<br />abundance estimates had moderately good precision
<br />(CV = 16-22%).
<br />Colorado pikeminnow recruits in the lower Green
<br />River reach were moderately common compared with
<br />other reaches during the study period, ranging from 31
<br />in 2002 to 89 in 2003. The corresponding CVs ranged
<br />from 23% to 41 %.
<br />
<br />Basinwide Abundance Estimates
<br />
<br />The abundance of adult Colorado pikeminnow in the
<br />Green River basin declined over the 2000,-2003 period
<br />(Table 4; Figure 3). In 2000, when sampling was
<br />restricted to the middle Green River basin (middle
<br />Green River, Yampa River, and White River), the
<br />abundance of adult Colorado pikeminnow was esti-
<br />mated as 3,030 (SE = 287) individuals. No sampling
<br />
<br />effort was allocated to the Desolation-Gray Canyon
<br />and lower Green River reaches that year, so no
<br />abundance estimates are possible. In 2001, when
<br />sampling was basinwide and included the Desola-
<br />tion-Gray Canyon and lower Green River reaches, the
<br />abundance of adult Colorado pikeminnow was 3,304
<br />(SE = 206); it declined to 2,142 (SE = 233) by 2003, a
<br />35% reduction. The confidence intervals for the 2001
<br />and 2003 basinwide estimates did not overlap.
<br />We also estimated the basinwide abundance of
<br />Colorado pikeminnow in 2000, when no estimates for
<br />the Desolation-Gray Canyon and lower Green River
<br />reaches were available. To accomplish this, we made
<br />the conservative assumption that the abundance of
<br />Colorado pikeminnow in those unsampled reaches in
<br />2000 was the same as that in 2001 (1,054). Summing
<br />that estimate with the middle Green River estimate
<br />(3,030) yielded a basinwide estimate of 4,084 fish for
<br />2000, which suggests that the abundance of adult
<br />Colorado pikeminnow in the Green River basin
<br />declined by as much as 48% from 2000 to 2003. The
<br />average CV for the riverwide abundance estimates for
<br />2000-2003 was relatively low at 9% (range, 6-11 %).
<br />The abundance of Colorado pikeminnow recruits
<br />over the period 2000-2003 varied from 130 to 412 fish
<br />per year and, on average, the number of recruits
<br />represented only 8.9% (range, 4.7-13.3%; Table 4) of
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