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<br />C) <br />c) <br />.... <br />co <br />00 <br />i\) <br /> <br />Adults <br />During the 7-year research period, no adult wild razorback sucker were collected in the San Juan River <br />(Ryden 2000a), and only one was caught during studies conducted in the late 1980s (Platania 1990). <br />Because of this, experimental stocking of hatchery-reared subadult (large juvenile) razorback sucker was <br />initiated in 1994. Between March 1994 and October 1996, 939 fish were stocked at four sites (RM 79.6, <br />RM 117.5, RM 136.6, and RM 158.6) below Hogback Diversion (Ryden2000b). Radiotelemetry and <br />electrofishing captures of some stocked fish provided information on subadult and adult fish habitat use. <br /> <br />In addition to habitat use, Ryden (2000b) mapped habitat in the general areas where radio- tagged fish <br />were fmUld, using methods similar to those used by Miller and Ptacek (2000). This resulted in habitat <br />selection determinations based on the availability of the various habitats used and on habitat richness. <br />Figure 3.4a shows radio-tagged razorback sucker habitat selection and Figure 3.4b shows mean habitat <br />richness values from 1994 through 1997 averaged by month. Run habitats were selected during low-flow <br />periods from late sununer (August) through late autumn (December), and slow-water habitats (edge pools, <br />pools, and eddies) were selected during the rest of the year. The fish also utilized inundated vegetation <br />during peak spring flows. These data show the fish selected lower-velocity habitats year-round, utilizing <br />run habitats only during low-flow times of year when velocities were reduced. The fish selected pools and <br />eddies most of the remainder of the year. <br /> <br />Habitat richness values remained fairly high (6 to 7), except during late sununer and autumn (Figure 3.4b). <br />Although not as high as habitat richness values for Colorado pikeminnow, the values indicated that <br />razorback sucker utilized fairly habitat-rich portions of the river, except during late sununer and autumn. <br /> <br />No suspected spawning locations were found by monitoring radio-tagged razorback sucker. However, <br />three adult ripe males were collected and three more adults were observed at RM 100.2 during May 1997 <br />electrofishing surveys (Ryden 2000b). This probable spawning aggregation was collected over shoreline <br />cobble nm/riffle habitat, along with spawning flannelmouth sucker. During this same sampling trip, five other <br />ripe male razorback sucker were individually collected from groups of spawning flannelmouth sucker in <br />similar habitats. During 1999 sampling, both ripe male and female razorback sucker were collected in the <br />same habitat at RM 100.2, although none of the fish collected in 1999 had been caught in 1997 (D. Ryden, <br />USFWS, Personal Communication). This habitat was similar to Green River spawning habitat (Tyus <br />1987). It is not known if the stocked razorback sucker in the San Juan River will show fidelity to this area. <br /> <br />September 2000 <br /> <br />3-10 <br /> <br />Program Evaluation Report <br />