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1 1 1 1 i F11 1 1 at the downstream reaches of Maybell and Lily Park (Table 4). The Lily Park northern pike sample demonstrated the lowest index of the four reaches (3.068). Similar to the yearly indices, the effect of the changing coefficients was most pronounced in the larger, heavier fish (Figure 7). Examining the 95 % confidence intervals for the X coefficients of the regression lines indicates the slope of the Craig and Lily Park regression lines were significantly different from that shown for the Juniper reach (Figure 8). There were no significant differences between the slope coefficients for the Craig, Maybell, and Lily Park regression lines. Slope coefficients reported in Carlander (1969) for northern pike ranged from 2.902 to 3.271, and encompass six of the eight coefficients estimated for Yampa River northern pike. The slope coefficients for Yampa River northern pike in 1989 and the Juniper reach exceeded the highest estimate reported in Carlander. Using the standard length-weight regression calculated for northern pike for the estimation of relative weight indices (Willis 1989), it can be seen that the slope coefficients estimated in 1989-1990, and four all four river reaches exceeded that of the standard regression (3.059). Average lengths, condition factors. and relative weight indices Average length of northern pike samples was calculated by river reach and year (Appendix A, Table A-3). A consistent pattern was evident between the Craig, Maybell, and Lily Park reaches (Figure 9). The average length of northern pike declined from 1986-88 to 1989, increased again in 1990, and declined again to the smallest average length observed over the study period for all three of these reaches. Also consistent was the increase in average northern pike size from Craig downstream to Maybell to Lily Park in all four time periods. Northern pike size in the Juniper reach was quite different in both pattern and magnitudes. Based on the relatively large coefficients of variation (Std error/mean) associated with these average lengths, the patterns indicated by the mean estimates are not statistically significant. This is evident in the broad overlap of the 95% confidence intervals for each average length estimated. This variability may be attributed to some combination of small sample sizes, sampling variability, and population variability. Indices of body condition in northern pike were calculated by river reach and year (Appendix A, Table A-4). Condition factors showed that, over all four reaches, northern pike condition declined from 1986-88 to 1989 and 1990, then increased to the highest levels observed during the study period in 1991 (Figure 9). Northern pike sampled in the Craig reach had the highest condition factors among the four reaches, and the lowest in the Juniper reach in all four years. For all four reaches, large coefficients of variation and overlapping 95 % confidence intervals for northern pike condition factors indicated a lack of statistical significance in any patterns demonstrated. Mean condition factors for northern pike using total length ranged from 0.47-0.69 in Carlander (1969). Mean condition factors estimated for Yampa River northern pike were relatively higher in comparison, with the estimates for northern pike in the Yampa River exceeding the range reported in Carlander for three of four years in the Craig reach, one of four DRAFT March 12, 1996 r 29