San Juan River Recovery Implementation Program Summary Report 1991-97

Home Browse Search

within the valley bottom. This reach also includes the largest number of oil wells adjacent to the river channel. Two perennial tributaries, Chinle and McElmo creeks, and six major ephemeral channels flow into the San Juan River in this reach. Related Biological Information: Low numbers of both ad ult and YOY Colorado squawfish have been captured from this reach, primarily in the vicinity of Bluff, Utah, between RM 75 and 85. Three adult and six YOY Colorado squawfish were captured in Reach 3 during the period from 1987 to 1989. More recently one adult was captured and radio - tagged in Reach 3 in 1993. This individual exhibited migratory movements to a suspected spawning area upstream during the spring of 1994, then returned to Reach 3 where it was recaptured on two occasions. Fidelity of this fish to a location in Reach 3 indicates that this reach provides habitat suitable for resident fish during late summer, fall, winter, and early spring. Sporadic capture of both adult and juvenile roundtail chub in Reach 3 between 1987 and 1996 also suggests some degree of suitability of the reach for this species. The presence of roundtail chub in this reach is probably also associated with its position downstream of the confluence of the Mancos River. The Mancos River is a likely source of many of the roundtail chubs found in the San Juan River in both Reach 3 and 4. Miller (1994b) found the species to be common to abundant in the Mancos River, particularly in the upper reaches. Reach 4 (RM 106 -130) Just above Aneth, Utah, to below the "Mixer." The valley width decreases slightly from Reach 3 to Reach 4. Total water surface of Reach 4 is less than the adjacent reaches over a range of flows, indicating a slightly narrower and deeper main channel. Some characteristics of this reach are intermediate between Reach 3 and Reach 5, including both channel gradient (0.00164 ft/ft) and sinuosity, both of which are increasing in an upstream direction from Reach 3. Reach 4 has a large amount of island area, second only to Reach 5, and a corresponding high number of secondary channels. Many of the islands located in this reach are not extensively vegetated and are fairly unstable, especially when compared to islands in Reach 5, but are more stable than islands in Reach 3. Low velocity habitats such as slackwaters, pools, eddies, and backwaters are more prevalent in this reach than in those reaches downstream. Several large, permanent backwaters are located near the confluence of the Mancos River. No municipalities occur near the river in this reach, reducing effects of human activity relative to the adjacent reaches. One perennial tributary, the Mancos River, and three major intermittent tributaries join the San Juan River within this reach. Related Biological Information: This reach, particularly the upper portion from the confluence of the Mancos River (near RM 122) to RM 130, appears to provide important habitat for Colorado squawfish. A substantial portion of adult Colorado squawfish captured in the San Juan River have been taken from the upper portion of Reach 4. Extensive use of this same area by radio - tagged adults, including suspected prespawning staging activities, provides additional evidence of the importance of this reach to the species. Sporadic capture of YOY Colorado squawfish in this reach between 1987 and 1996 suggests that this reach may also provide some nursery habitat. Relatively large numbers of roundtail chub have also been captured in Reach 4, mostly in the vicinity of the confluence of the Mancos River. San Juan River Recovery Implementation Program December 1997 Summary Report 8 PR -602 -1