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<br />o <br />(";') <br />.... <br />...., <br /> <br />Colonel John N Reese <br /> <br />DRAFT <br /> <br />10 <br /> <br />,!;;,. <br /> <br />locations in the lower Colorado River, they are considered rare or incidental <br />and may be continuing to decline. <br /> <br />In the Upper Basin,. above Glen Canyon Dam, razorback suckers are found in <br />limited numbers in both lentic and lotic environments. The largest population <br />of razorback suckers in the Upper Basin is found in the upper Green River and <br />lower Yampa River (Tyus 1987). Lanigan and Tyus (1989) estimated that from <br />758 to 1,138 razorback suckers inhabit the upper Green River. In the Colorado <br />River most razorback suckers occur in the Grand Valley area near Grand <br />Junction, Colorado; however, they are increasingly rare. Osmundson and <br />Kaeding (1991) report that the number of razorback sucker captures in the <br />Grand Junction area have declined dramatically since 1974. <br /> <br />In the San Juan River subbasin, small concentrations of razorback suckers have <br />been reported at the inflow area in the San Juan arm of Lake Powell, Utah <br />(Meyer and Horetti 1988), and at least one specimen was captured in the San <br />Juan River near Bluff, Utah, in 1988 (Platania 1990; Platania et al. 1991). <br />In Bestgen (1990) additional captures of small numbers of razorback suckers <br />also were reported from the Dirty Devil and Colorado River arms of Lake <br />Powell . <br /> <br />Beginning in May 1987 and continuing through October 1989, complementary <br />investigations of fishes in the San Juan River were conducted in Colorado, <br />New Mexico, and Utah (Platania 1990; Platania et al. 1991). In 1987, a <br />total of 18 adult razorback suckers (6 recaptures) were collected on the south <br />shore of the San Juan arm of Lake Powell (Platania 1990; Platania et al. <br />1991). These fish were captured near a concrete boat ramp at Piute Farms <br />Marina and were believed to be either a spawning aggregation or possibly a <br />staging area used in preparation for migration to some other spawning site. <br />Of the 12 individual razorback suckers handled in 1987, 8 were running ripe <br />males while the other 4 specimens were females that appeared gravid. <br /> <br />In 1988, a total of 10 razorback suckers were handled at the same general <br />location, 5 of which were in reproductive condition (Platania et al. 1991). <br />Six of the ten individual specimens in the 1988 samples were recaptures from <br />1987. Also, in 1988, a single adult tuberculate male razorback sucker was <br />captured at approximately river mile 80 on the San Juan River near Bluff, <br />Utah. Particularly noteworthy is that this is the first confirmed record of <br />this species from the main stem San Juan River. The presence of this <br />reproductively mature specimen suggests that the razorback may be attempting <br />to spawn in some unknown location within the riverine portion of the San Juan <br />drainage. No razorback suckers were captured in 1989. No larval specimens, <br />nor any other size classes of razorback suckers (other than adults), have ever <br />been documented in the San Juan River drainage. <br /> <br />All recent captures of wild razorback suckers in the upper basin have been <br />mature adults. In 1994 an experimental augmentation program was initiate don <br />the San Juan River; 30 radio-tagged razorback suckers and 656.razorback <br />suckers marked with passive integrated transponder (PIT) tags were released in <br />the San Juan River. There is no evidence anywhere in the Colorado River <br />system that indicates significant recruitment to any population of razorb.ack <br />