San Juan River Recovery Implementation Program Summary Report 1991-97

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l are typically found in backwaters or flooded riparian areas where water temperatures are higher than in the main river (Wick et al. 1983). As high flows recede, adults move toward spawning areas, often migrating over 100 miles. Spawning areas are typically riffle -run areas with cobble substrates. Following spawning (typically in July), the adults often move back to the areas they migrated from. In the Green River, some adults spend most of their time in tributaries, such as the White River or upper Yampa River. They move down the tributaries to spawning sites and then back up the tributaries following spawning. Other adults live in the main rivers, such as the Green and Colorado, year- round, migrating up or down the river to their spawning sites. Adults are typically found in runs along shorelines during the summer and fall, probably using low velocity pockets alongside the main current. During winter, adults move relatively little and prefer slow velocity habitats (Valdez and Masslich 1989) such as slow runs, slackwaters, eddies, and backwaters. Studies in the San Juan River have generally shown that habitat use by adult Colorado squawfish is generally similar to that seen in other Upper Basin rivers, but some differences do occur. Based on 83 ground contacts of radio - tagged adult Colorado squawfish over a 5 -year period, 52 percent of the contacts were from run habitats, 18 percent were from eddy habitats, and 12 percent were from shoreline habitats (Ryden and Pfeifer 1993, 1994, 1995a, 1996a). This differed from the habitats ' used in the Green and Yampa rivers where shorelines were used more than 50 percent of the time and may be related to the prevalence of run habitat in the San Juan System. During the summer, patterns of habitat use appeared to be related to spawning activities (i.e., staging, egg deposition, and resting) and, in general, conformed to patterns observed in other populations during the same period. Miller (1994a, 1995) intensively followed Colorado squawfish radio - tagged ' by Ryden and Pfeifer (1994, 1995a) during the spring and summer of 1993 and 1994. During June and early July the fish staged in eddies, slackwaters, and secondary channels that were often warmer than the main river, including the mouth of the Mancos River. The Mancos River (RM 122.6) is the only tributary that is currently used by Colorado squawfish in the San Juan System, and then only at its mouth during runoff periods. The mouth of the Mancos River is dammed by the flow of the San Juan River at this time and provides a warmer, backwater habitat. By mid -July all the fish moved out of staging areas to spawning sites at RM 131 and RM 132 within an area called the "Mixer" (an extensively braided section of the river from RM 129.8 to RM 133.4). During 1994, spawning activities were observed over cobble bar habitats in close proximity to, but in different locations from, the spawning activity noted in 1993. During the time spent in the spawning area, the fish used run habitats about 60 percent of the time and eddy and slackwater areas about 35 percent of the time. These habitats were adjacent to the fast, chute -type habitats where actual spawning likely occurred and were probably used for resting and feeding during the spawning period. Spawning chutes were characterized by fast water velocity and clean loose cobble with a median ' diameter of 60 -80 mm. One site (RM 131.1) had overhanging vegetation providing shade and cover (Miller 1995). Following spawning, the fish dispersed upstream and downstream from the spawning area. Run habitat was used the most in the late summer and fall periods, although eddies and ' slackwater habitats were still an important part of the habitats used. A limited amount of information on winter habitat use was collected on three adult Colorado squawfish during February 1994 (Miller 1995). Runs were used about 90 percent of the time, and eddies were used the remaining 10 percent of the time. The fish were active, especially during midday, suggesting active feeding. These observations differ from those made by Valdez and Masslich (1989) in the Green River in that Colorado squawfish in the San Juan River were much ' San Juan River Recovery Implementation Program December 1997 Summary Report 18 PR -602 -1