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<br />. <br /> <br />. <br /> <br />. <br /> <br />Lt. Colonel Dorothy F. Klasse <br /> <br />10 <br /> <br />removed from around the cobbles. Rearrangement of the cobbles <br />will result in more stability of the armor layer. On the falling <br />limb. the armor layer becomes a trap for sands until finally. the <br />sand reservoir is again filled. Without cobble movement. sand <br />will be scoured only to a depth of one-half to one median cobble <br />diameter below the cobble bed surface." <br /> <br />In the flume experiments. the sand level was observed approximately 0.50 to 1 <br />cobble diameter below the surface of the cobble bed. which compared to field <br />observations of sand depth at approximately 0.50 to 1 median cobble diameter. <br />O'Brien reported a cobble size range of 50~100 mm with a median size of 75 mm <br />at the spawning site. Milhous (19B2) proposes discharges of approximately <br />one-half that required to initiate cobble movement will be capable of <br />extracting sands and fines from the cobble substrate. Thus. after the supply <br />of sand diminishes. flows of sufficient magnitude and duration are required to <br />scour the cobble bed in preparation for spawning and incubation. <br /> <br />Colorado Souawfish Activitv' San Juan River <br /> <br />As a result of the biological opinion for the Animas-La Plata Project. <br />Reclamation agreed to fund approximatelY 7 years of research on the San Juan <br />River and its tributaries. While these studies are not yet complete. annual <br />reports indicate that a small reproducing population of Colorado squawfish <br />exists on the San Juan River. Based on radio telemetry studies and visual <br />observations. two potential spawning areas have been located at river mile <br />132.0 and 131.15 (Miller 1994. Ryden and Pfeifer 1995a). Both of these sites <br />are located in an area of the river known as the "Mixer" (river mile 133.4 to <br />river mile 129.8). The highest concentration of adult Colorado squawfish in <br />the San Juan River occur between the Cudei Diversion (river mile 142.0) and <br />Four Corners (river mile 119.2). Ryden and Pfeifer (1995a) report that a <br />Colorado squawfish captured at river mile 74.8 (between Bluff and Mexican Hat) <br />made a 50-60 mile migration to the Mixer during the suspected spawning season <br />in lSS4. The fish then returned to within 0.4 river miles of its original <br />capture location. <br /> <br />Successful reproduction was documented in the San Juan River in 1987. 1988. <br />1992. 1993. and 1994. by the collection of young-of-year Colorado squawfish. <br />Majority of the young-of-year squawfish were collected in the San Juan River <br />inflow to Lake Powell fBuntjer et al. 1994. Lashmett 1994. Platania 1990). <br />Some young-of-year squawfish have been collected from the ViCinity of the <br />Mancos River confluence in New Mexico and in the viCinity of the Montezuma <br />Creek confluence near Bluff. Utah. and at a drift station near Mexican Hat. <br />Utah (Buntjer et al. 1994. Platania 1990). In 1994. a young-of-year squawfish <br /> <br />,-'\ <br />