San Juan River Recovery Implementation Program Summary Report 1991-97

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above near RM 75. Capture of a larval Colorado squawfish at RM 128 during August 1996 was the first larvae collected below the suspected spawning site in the Mixer. Young -of -the -year Colorado squawfish have primarily been found in the lower 15 miles of the San Juan River and the Lake Powell inflow area as far as 6.3 miles below Piute Farms (Figure 2). Lashmett (1993, 1994) collected a total of 12 YOY Colorado squawfish in this area including 1 in 1992 and 11 in 1993 and reported that backwaters were fairly common in the reach between RM 4.0 and RM -11.0. Three more YOY Colorado squawfish were caught in this area in 1994 by Archer et al. (1995). This is an area that is influenced by the level of Lake Powell and has reduced gradient and predominately a sand substrate. Archer et al. (1995) captured seven YOY Colorado squawfish in 1994 including six between RM 8.0 and RM 25.2 and one at RM 122.6 during nursery habitat studies. Five more larval Colorado squawfish, originally identified as roundtail chub by Archer et al. 1996, were captured between RM 12 and RM 24 in August 1995. All of these fish were captured in backwaters. The Colorado squawfish captured at RM 122.6 represented the most upstream record of a YOY since 1987. In 1987 and 1988,19 YOY Colorado squawfish were found, 2 between RM 146 and RM 121, 6 between RM 86 and RM 81, and 11 between RM 16 and RM 6. These capture locations for larvae and YOY are also shown on Figure 2. The 1996 and 1997 studies by Archer (1997) on stocked YOY Colorado squawfish have found that the fish did not all move dramatically downstream, and that nearly 1 year after the initial 1996 stocking some fish still remained above the Mixer, less than 20 miles below the stocking location ( Shiprock). Also, the stocked fish were distributed down the river from just below Shiprock to Lake Powell, suggesting that habitat throughout this portion of the river was generally favorable for this size (large YOY) of Colorado squawfish. Some grouping of young Colorado squawfish was found in specific habitats (up to 20 or more young Colorado squawfish were found in some individual seine samples), and as the data are reviewed more fully some preferences for river sections may emerge. The stocking size of these fish was about 60 mm, larger than the 10 -15 mm size of wild larval Colorado squawfish that have been found drifting in the river. This size difference may explain why the stocked fish used habitats further up the river than those in which wild YOY have generally been found. Young -of -the -year Colorado squawfish stocked in August 1997 were also found distributed below stocking sites. In addition, in October 1997 the YOY were also found nearly 10 miles above the Shiprock stocking location. The 1997 stocked fish averaged about 45 mm TL and apparently could move about the river quite easily to find acceptable habitats. Young -of- the -year Colorado squawfish were also stocked in August 1997 and were also found distributed below stocking sites (Archer 1997). In addition, in October 1997 relatively large numbers of YOY were also found nearly 10 miles above the Shiprock stocking location. The 1997 stocked fish averaged about 45 mm TL and apparently could move about the river quite easily to find acceptable habitats. Based on this information, San Juan River subreaches that provide important habitats for Colorado ' squawfish include the lower 16 miles of river for young Colorado squawfish, RM 119 to RM 148 for adults (including spawning areas), and perhaps another area below the Mixer near RM 75 for spawning adults. Larger young Colorado squawfish that do not emerge in the river and drift downstream appear to find suitable habitat throughout the river below Hogback Diversion. ' San Juan River Recovery Implementation Program December 1997 Summary Report 24 PR -602 -1