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<br />00.1616 <br /> <br />Adults <br />During the 7 -year research period, no adult wild razorback sucker were collected in the San Juan <br />River (Ryden 2000a), and only one was caught during studies conducted in the late 1980s (Platania <br />1990). Because of this, experimental stocking of hatchery-reared subadult (large juvenile) <br />razorback sucker was initiated in 1994. Between March 1994 and October 1996, 939 fish were <br />stocked at four sites (RM 79.6, RM 117.5, RM 136.6, and RM 158.6) below Hogback Diversion <br />(Ryden 2000b). Radiotelemetry and electrofishing captures of some stocked fish provided <br />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 <br />fish were found, using methods similar to those used by Miller and Ptacek (2000). This resulted <br />in habitat selection determinations based on the availability of the various habitats used and on <br />habitat richness. Figure 3.4a shows radio-tagged razorback sucker habitat selection and Figure <br />3.4b shows mean habitat richness values from 1994 through J 997 averaged by month. Run habitats <br />were selected during low-flow periods from late summer (August) through late autumn <br />(December), and slow-water habitats (edge pools, pools, and eddies) were selected during the rest <br />of the year. The fish also utilized inundated vegetation during peak spring flows. These data show <br />the fish selected lower-velocity habitats year-round, utilizing run habitats only during low-flow <br />times of year when velocities were reduced. The fish selected pools and eddies most of the <br />remainder of the year. <br /> <br />Habitat richness values remained fairly high (6 to 7), except during late summer and autumn <br />(Figure 3.4b). Although not as high as habitat richness values for Colorado pikeminnow, the values <br />indicated that razorback sucker utilized fairly habitat-rich portions of the river, except during late <br />summer and autumn. <br /> <br />No suspected spawning locations were found by monitoring radio-tagged razorback sucker. <br />However, three adult ripe males were collected and three more adults were observed at RM 100.2 <br />during May 1997 electrofishing surveys (Ryden 2000b). ~is probable spawning agl!fegati~as <br />collected over shoreline cobble run/riffle habitat, along with spawniQg flannel mouth sucker. <br />-- .......~._- <br />During this same sampling trip, hve other ripe male razorllaCK sucker were individually collected <br />from groups of spawning flannelmouth sucker in similar habitats. During 1999 sampling, both ripe <br />male and female razorback sucker were collected in the same habitat at RM 100.2, although none <br />of the fish collected in 1999 had been caught in 1997 (D. Ryden, USFWS, Personal <br />Communication). This habitat was similar to Green River spawning habitat (Tyus 1987). It is not <br />known if the stocked razorback sucker in the San Juan River will show fidelity to this area. <br /> <br />~ <br />['J <br /> <br />September 2000 <br /> <br />3-10 <br /> <br />Program Evaluation Report <br />