San Juan River Recovery Implementation Program Summary Report 1991-97

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Razorback Sucker: Since only one wild razorback sucker has been collected since 1987 in the San Juan River, experimentally stocked razorbacks have been used to address habitat use. Studies of stocked razorback sucker from 1994 to 1997 (Ryden and Pfeifer 1995b, 1996b) showed that stocked fish were generally moving downstream from stocking sites but used most portions of the river below Hogback Diversion, the most upstream stocking site. Some of the stocked fish were beginning to show signs of sexual maturity in 1996 and four of them (plus another three that were seen while electrofishing but not captured) were found in close proximity in the spring of 1997 near the mouth of McElmo Creek (see Figure 1) in what may have been a spawning aggregation (Ryden 1997b). The razorback suckers captured at that location were all ripe males and were found with congregations of ripe, and apparently spawning, flannelmouth suckers; a species that also is found in other razorback sucker spawning areas in the Upper Basin System. At this time no specific areas of the river below Hogback Diversion have been determined to be more important for razorback sucker than other areas, but additional monitoring of the stocked razorback sucker may provide this information in the next few years. Other Native Species: Bluehead sucker, flannelmouth sucker, and speckled dace are widely distributed in the San Juan River. In general, native flannelmouth sucker, bluehead sucker, and speckled dace were found to be most abundant in upstream reaches (RM 158 to 100) and declined downstream (Buntjer et al. 1994, Ryden and Pfeifer 1995a). The trend for flannelmouth sucker changed somewhat in 1995 and 1996, with the most fish being caught below RM 100. Distribution of bluehead sucker and speckled dace did not change in 1995 compared to results from previous years. The cause of the change in flannelmouth sucker distribution during 1995 and 1996 is not known. In the canyon reach below Mexican Hat (RM 52), numbers of native species were reduced during all years of sampling. Roundtail chub adults were primarily found between RM 119 and RM 140, within and a few miles below the Mixer (Ryden and Pfeifer 1993, 1994, 1995a). Young roundtail chub were found from RM 107 to RM 130 in most years studied and also below RM 100 in 1993 (Buntjer et al. 1993, 1994; Archer et al. 1995). A few roundtail chub have also been found in a few other parts of the river system, but the prevailing evidence suggests they are primarily found in the tributaries and do not maintain much of a mainstem population. Habitat Studies Bliesner and Lamarra (1994, 1995) mapped habitats of the San Juan River for six different periods from December 1992 to August 1994. This information is discussed in detail in Section 5.2.3.1. Figure 3 shows the spatial distribution of habitats in mid -June 1994 mapped at a flow of from about 6,000 to 8,000 cfs at the Four Corners gage, and Figure 4 shows the spatial distribution of habitats in mid- to late - August 1994 when flows at Four Corners ranged from about 550 cfs to 1,000 cfs. The June information represents habitat during the spring high flow period, and the August information represents habitat during the summer low flow period. Habitats used by adult Colorado squawfish and razorback sucker during runoff conditions include eddies, slackwater, and other low velocity habitats. Figure 3 indicates that these types of habitats were rare during June 1994 and in fact represented less than 2 percent of the total available habitat in the river. No subsections of the river contained relatively more of these habitats than other areas. San Juan River Recovery Implementation Program December 1997 Summary Report 26 PR -602 -1