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STATUS OF GREEN RIVER COLORADO PIKEMINNOW 1369 varied by almost an order of magnitude over the duration of ISMP sampling. The CPUE indices were highest for the White River and middle Green River reaches and lower for the Yampa River and the lower Green River reach. If the CPUE indices reflected population size, the abundance of Colorado pikeminnow in the Green River basin increased rather dramatically from 1991 to 2000, particularly in the middle Green and White rivers. The CPUE data suggest that the abundance of Colorado pikeminnow in the Yampa and lower Green River reaches increased at a slower rate until 2000. Like the abundance estimates and those for A, the CPUE indices declined in all river reaches after 2000. Correlation of annual abundance estimates and ISMP CPUE indices for all river reaches combined (n = 15 [none for the Desolation-Gray Canyon reach]) from 2000 to 2003 suggested a positive and moderately strong relationship (r = 0.70, P = 0.005). Correlation coefficients for annual abundance estimates and ISMP indices for individual river reaches were relatively strong for the middle (0.95; n = 4) and lower (0.99; n = 3) Green River reaches and moderately strong for the White (0.85; n = 4) and Yampa rivers (0.67; N = 4). Length-Weight and Length Frequency Analyses The mean TL of adult Colorado pikeminnow remained essentially the same in each period, 548 mm in 1991-1999 (SD = 71.2) and 544 mm (SD = 67.9) in 2000-2003. The mean length of recruits was also similar in each period, 428 mm in 1991-1999 (SD = 14.5) and 430 mm (SD = 15.9) in 2000-2003. Analysis of covariance showed that the length-weight relationships for fish captured in ISMP reaches in the two periods differed, but not significantly. The estimated relationships for Colorado pikeminnow 127-859 mm in length for 1991-1999 and 2000- 2003 are as follows: loge(weight) = -12.365 + 3.10501oge(TL) (SE: intercept = 0.099, slope = 0.016) and loge(weight) = -12.20 + 3,0680 loge (TL) (SE: intercept = 0.222, slope = 0.036). According to these equations, the predicted weight for a 600-mm Colorado pikeminnow in 2000-2003 would be 1,679 g, or about 6.9% less than that of a fish of the same length in 1991-1999 (1,803 g). Colorado pikeminnow captured from 2000 to 2003 ranged from 30 to 1,240 mm TL. The mean TL of all captured and recaptured Colorado pikeminnow includ- ed in capture-recapture analyses was 499.4 mm (SD = 103.3). The largest Colorado pikeminnow captured was -0- Middle Green R -{:r- Lower Green R ""*'" Y ampa River ___ White River 4 ~ 3 ~ ::l 0.,2 '" u 1993 2003 1995 1999 2001 1997 Year FIGURE 8,-Interagency Standardized Monitoring Program captures of subadult and adult Colorado pikeminnow per hour of electrofishing effort in the Green River basin, 1991-2003. from the White River, and it, along with two other individuals 900 and 980 mm long, were the only fish captured that exceeded 900 mm. Length frequency distributions for the Colorado pikeminnow captured in 2000-2003 in the upstream Yampa, White, and middle Green river reaches show that most were relatively large, as only 7.0% of all fish were less than 450 mm (Figure 9). In contrast, the proportion of relatively small Colorado pikeminnow increased progressively downstream in the Green River. For example, from 2001 to 2003, 24.7% of the Colorado pikeminnow sampled in the Desolation-Gray Canyon reach were less than 450 mm. In the lower Green River reach, the abundance of fish less than 450 mm (including many < 100 mm) was even higher, at 68% of all Colorado pikeminnow captured. The population structure of recruit and adult-size Colorado pikeminnow in ISMP reaches changed between the periods 1991-1999 and 2000-2003 (Figure 10). The number of recruits (186) averaged 24.7% (7.9-58.5%) of the number of adults in samples (826) in the period 1991-1999. During that period, there were 4 years (3 from 1992 to 1994) when the proportion of recruits was relatively high (>20%), 3 years when it was moderate (> 10-20%), and 2 years when it was relatively low (0-10%). In contrast, from 2000 to 2003, the mean number of Colorado pike- minnow recruits (14) captured in the ISMP reaches was only 3.4% of the number of adults captured (418). The proportion of recruit-size Colorado pikeminnow was low in 2000 (6.6%) and zero from 2001 to 2003. Discussion The abundance of adult Colorado pikeminnow in the Green River basin declined during the study period from over 3,300 fish in 2001 to about 2,142 in 2003, a reduction of 35%. Nonoverlapping confidence intervals for the years 2001 and 2003 for basinwide Green River