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Platania. Dudley, and Maruca. 2000. Drift of Fishes in the San Juan River 199[-1997. FINAL r-:: '-.') .... .....1 00 --J relatively constant at Mexican Hat during this study. Daily maximum channel catfish CPUE levels were higher in 1995 and 1996 than previons years but peaked in 1997 at almost three-times the previous maximum level. Relationship of Annual Drifi CPUE and Flow Regime Seven hydrograph variables were determilled from gauge information taken from Four Comers, New Mexico, and Bluff, Utah (near Mexican Hat) statiolls (Table 4). In general. 1991 and 1996 were low-flow years, 1992 and 1994 were periods of moderate flow on the San Juan River, and 1993,1995, and 1997 were high-flow years (Figure 12). Flow exceeded 10,000 cfs only in 1993. 1995, and 1997. The peak flows in 1993 were only about 85% of those recorded in 1995 or 1997. but 1993 had more days with mean daily discharge above 2,500 (and especially 5,000 cfs) than any other year. In contrast, the number of high flow days in 1996 was exceptionally small not only during the spring runoff but also during the summer spawning period. Peak discharge in 1996 did not exceed 4,000 cfs at either Four Comers or Bluff, and there were about twice as many days below 500 cfs as was recorded during the next driest year. Althongh peak flows in 1994 were 10,000 cfs at Four Comers, there were a moderate number of days when flow was <500 cfs. While trends in high and low-flow years were mirrored at both sites, peak flows at Bluff did not exhibit the magnitude or duration of those observed at Four Comers. While there was a high level of intercorrelation among the hydrograph variables examined (Table 5) there were a number of variable pairs (at both locations) that were not significantly correlated. At Four Comers, number of days with average discharge greater than 5,000 cfs was not significantly correlated with days greater than 8,000 cfs, days greater than 10.000 cfs, or days less than 1.000 cfs. The number of days greater than 10,000 cfs was significantly correlated with only days greater than 8,000 and days less than 1,000 cfs. Number of days with discharge less than 500 cfs was not correlated with days greater than 8,000 and 10,000 cfs. Generally. nnmber of days less than 500 (or 1,000) cfs and greater than 8.000 (or 10,000) cfs are measures of different phenomena, the former being more influenced by precipitation during the winter and spring while the latter is more affected by precipitation during summer. Correlatioll among variables for Bluff exhibited the samc general pattern as observed at Four Comers. Number of days with average discharge less than 500 cfs was not significantly correlated with days greater than 5,000 cfs or days less than 1,000 cfs. The absence in variation in Colorado pikeminnow larval density over the seven years precluded its illclusion in this analysis. Drift density of red shiner, channel catfish, and speckled dace were examined with hydrograph variables to determine if there were significant correlations. Correlation coefficients for two sites and two measures of catch rate (mean annual and maximum daily CPUE) were contrasted with each of the seven hydrograph variables and resulted in 84 correlation coefficients and correspollding hypothesis tests. None of the correlation coefficients for red shiner CPUE and hydrograph variables were significantly different from zero. Several of the correlation coefficients for channel catfish and speckled dace were significantly different from zero. For channel catfish at Four Comers, mean annnal CPUE was negatively correlated with number of days discharge was greater than 2,500 cfs and 5,000 cfs, and positively correlated with number of days discharge was less than 500 cfs (Figure 13). Maximum daily channel catfish CPUE was negatively correlated with maximum discharge and munber of days discharge was greater than 2,500 cfs, and also positively correlated with number of days discharge was less than 500 cfs (Figure 14). For channel catlish at Mexican Hat, only the correlation coefficient for mean annual CPUE and number of days discharge was greater than 10,000 cfs was significant (Figure 15). For speckled dace at Four Comers, mean annual CPUE was positively correlated with number of days discharge was greater than 10,000 cfs (Figure 16). Maximum daily CPUE was positively correlated with maximum discharge, number of days above 8,000 cfs, and nnmber of days 27