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r:-) (",J 1-6 -...1 -.: (,C Platania, Dudley, and Maruca. 2000. Drift of Fishes in the San Juan River 1991-1997. FrNAL flannelmouth sucker ranked fust in abundance in 1992, and channel catfish was the most abundant in 1994,1996, and 1997. While rank order and abnndance of species varied between years, red shiner, speckled dace, and/or channel catfish typically dominated the catch. Red shiner and channel catfish comprised a large portion of the total catch in both 1991 and 1996; other species were represented by notably fewer individuals. The species-specific relative abundance of fish collected in 1993 was generally equal except for speckled dace. In 1992, 1994, and 1997 speckled dacc, tlannelmouth sucker, bluehead sucker, and channel catfish numerically dominated the catch. Speckled dace was less abundant relative to channel catfish nunlbers for all three years. However, flanne1mouth sucker was notably more abundant in 1992 than in 1997 while the reverse was true for blue head sucker. The abundance of all species, especially red shiner and speckled dace, was relatively high in 1995. A portion of the annual differences in species abundance was the result of variation in the numbers of each species collected at each site (Figures 4 and 5). The Four Comers site was generally dominated by native fishes (e.g., speckled dace, flannelmouth sucker, and blnehead sucker). An exception to this observation was in 199 I when a large number of red shiner was collected at that site. The trend at Mexican Hat was the exact opposite with channel catfish and. to a lesser degree, red shiner numerically dominating the annual catch. In 1993 and 1994, moderate numbers of drifting speckled dace and tlannelmouth sucker were collected at Mexican Hat. Mean Annual and Maximum Daily Catch-Per-Unit-Ejfort (CPUE) Mean annual CPUE of the six most abundant species varied considerably but annual differences in maximum daily CPUE were much greater (often an order of magnitude). While mean annual CPUE and maximum daily CPUE appeared moderately related, there were exceptions to this general trend. The two catch rates were different measures of larval density or reproduction. Maximum daily CPUE was a gauge of reproductive intensity on a short time scale, while mean annual CPUE was a measure of reproduction for the summer sampling period (i.e., July alld August) and so the latter value potentially included non-reproductive periods. However. all species analyzed had a relatively protracted spawning period that, over the tenure of the study, included most of the summer. Both mean annual and daily maximum CPUE for all species analyzed were variable between sites and years (Figure 6). Mean annual CPUE for red shiner peaked at the Four Comers site in 1991 but was also elevated in 1995 and 1996. Maximum daily CPUE of red shiner varied considerably between years at Four Comers and included a relatively higb value in \993. At Mexican Hat, annual red shiner catch rates were relatively low except in 1995 and 1996. Fathead minnow mean annual CPUE was stable across ycars and sites with the exception ofa large catch at Four Comers in 1991 (Figure 7). Maximum daily CPUE offathead minnow reached its highest levels during 1995 and 1996 at both sites but was still low compared to other species. Speckled dace mean annual CPUE exhibited considerable annual variation at both sites but was lowest ill 1992 and 1996 when few individuals were collected at either site (Figure 8). The maximum daily CPUE of speckled dace achieved its highest level at both sites during 1997. Flannelmouth sucker mean annual catch rates were highest during 1991, 1992, and 1995 at Four Comers and during 1993, 1994, and 1995 at Mexican Hat (Figure 9). Catch rates of flannelmouth sncker at Mexican Hat were considerably lower than those recorded at Four Comers. Maximum daily CPUE of flannelmouth sucker was highest in 1992 and 1995 at Four Comers and 1995 in Mexican Hat. Dritiing bluehead sucker was most abundant during the summers of 1995 and 1997 at both sites (Figure 10). Both mean annnal and daily maximum CPUE of bluehead sucker was higher at Four Comers than at Mexican Hat. There was a large variation in the mean annual catch rate of channel catfish at Four Comers with 1991, 1994, and 1996 being the years whell highest values wcre recorded (Figure II). Maximum daily CPUE for channel catfish at Four Comcrs varied linle except for 1996 when it achieved its greatest level. Channel catfish mean annual CPUE was ]8