San Juan River Recovery Implementation Program Summary Report 1991-97

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more active. However, this could have been due to warmer temperatures and lack of an ice cover, since the winter of 1993 -94 was a relatively warm winter on the San Juan River. As part of data integration for the 7 -year research effort, habitat utilization curves were developed by Miller (1997) for Colorado squawfish during the months of February, June, July, August, and October. Curves were developed by comparing habitats used by radio - tagged fish to habitats available in the immediate vicinity of the fish. The data indicated that radio - tagged adult Colorado squawfish exhibited a preference for eddies, pools, and slackwaters during June of 1993 and 1994. During July, the fish appeared to exhibit a preference for runs, but still used eddies and slackwaters relatively frequently. Chutes were the most commonly used habitat type during August 1993, pools during October 1994, and eddies in February 1994. A thorough analysis of habitat preference data and detailed descriptions of habitats will be presented in the adult Colorado squawfish habitat use report to be completed late in 1997. These data should be useful in developing flow recommendations for this species, particularly for June and July during prespawning and spawning activities. Based on studies in other Upper Basin rivers, backwaters are the primary habitat for young Colorado squawfish until they reach 120 -200 mm TL, usually in their second or third year of life (USFWS 1990). Sampling efforts aimed at younger life stages of Colorado squawfish in the San Juan River have resulted in the capture of over 40 YOY since 1987. Although a variety of slow water habitats were sampled in these studies, including backwaters, embayments, secondary channels, and eddies, all of the young Colorado squawfish were caught in backwaters. ' Due to the relatively low number of young Colorado squawfish in the San Juan River, Lentsch et al. (1996) initiated a study in 1996 to investigate the habitat use of stocked YOY Colorado squawfish. In November 1996 and August 1997, 50,000 YOY Colorado squawfish were stocked at Shiprock, ' New Mexico, and 50,000 were stocked at Mexican Hat, Utah. Preliminary data from this study tend to support the conclusion that backwaters are a preferred habitat of young Colorado squawfish in the San Juan River (Archer 1997), particularly during the late spring -early summer period. However, selection of other habitats by young stocked Colorado squawfish indicate that other habitat types in the San Juan River may be important to early life stages, particularly during winter and early spring. ' During the December 1996 and March 1997 sampling periods, the majority of Colorado squawfish were captured in small secondary channels, but were also captured in flow - through backwaters, shoreline habitats, and backwaters. During June, the majority of young Colorado squawfish were captured in backwaters and flow - through backwater habitats, although some were also captured in shoreline and secondary channel habitats. During October 1997, YOY Colorado squawfish stocked in August were found in a variety of low velocity habitats, many of which were in secondary ' channels. All of these are "low velocity habitats" with similar characteristics to backwaters such as low or no velocity. Yearling fish from the November 1996 stocking were found in a variety of shoreline habitats, including shoals and eddies, in October 1997. These areas typically had a higher velocity than the areas where the YOY were captured, but still would be classified as low velocity habitats by Bliesner and Lamarra (1994, 1995). These data suggest a possible shift in habitat preference from the winter /early spring to summer periods. Previous studies in the Upper Basin have suggested that temperature differences among backwaters and flow - through backwater habitats may influence the distribution of young Colorado squawfish in these habitats (Tyus and Haines 1991). During the winter and early spring, backwater San Juan River Recovery Implementation Program December 1997 Summary Report 19 PR -602 -1