WSP07323 - Laserfiche WebLink

Home Browse Search

b c":) C:J razorback sucker as the fish they had caught. However, prior to the 1976 capture by VTN Consolidated, Inc., there were no scientifically verified reports of razorback sucker captures in the San Juan River drainage. i.I"' .;::. The current distribution and abundance of razorback sucker has been significantly reduced ~ throughout the Colorado River system (Holden and Stalnaker 1975; McAda and Wydoski 1980; Minckley 1983; McAda 1987; Tyus 1987; Marsh and Minckley 1989). The only substantial population of razorback suckers remaining, made up entirely of old adults {McCarthy and Minckley 1987}, is found in Lake Mohave; however, they do not appear to be successfully recruiting, While limited numbers of razorback suckers persist in other locations in the lower Colorado River, they are considered rare or incidental and may be continuing to decline. In the Upper Basin, above Glen Canyon Dam, razorback suckers are found in limited numbers in both lentic and lotic environments. The largest population of razorback suckers in the Upper Basin is found in the upper Green River and lower Yampa River (Tyus 1987). Lanigan and Tyus (1989) estimated that from 758 to 1,138 razorback suckers inhabit the upper Green River. In the Colorado River most razorback suckers occur in the Grand Valley area near Grand Junction, Colorado; however, they are becoming increasingly rare. Osmundson and Kaeding (1991) report that the number of razorback sucker captures in the Grand Junction area has declined dramatically since 1974. In the San Juan River subbasin, small concentrations of razorback suckers have been reported at the inflow area in the San Juan arm of Lake Powell, Utah (Meyer and Moretti 1988), ami one specimen, an adult, tuberculate. male. was captured in the San Juan River near Bluff. Utah. in 1988 (Platania 1990; Platania et al. 1991). In Bestgen (19901 additional captures of small numbers of razorback suckers also were reported from the Dirty Devil and Colorado River arms of Lake Powell. Beginning in May 1987 and continuing through October 1989. complementary investigations of fishes in the San Juan River were conducted in Colorado. New Mexico, and Utah IPlatania 1990; Platanis et al. 19911. In 1987, a total of 18 adult razorbacks (6 recaptures) were collected on the south shore of the San Juan arm of Lake Powell {Platania 1990; Platania et al. 19911. These fish were captured near a concrete boat ramp at Pi ute Farms lVIarina and were believed to be either a spawning aggregation or possibly a staging area used in preparation for migration W some other spawning site. Of the 12 individual razorbacks handled in 1987, 8 were running ripe males while the other 4 specimens were females that appeared gravid. In 1988, a total of ro razorback suckers were handled at the same general location, 5 of which were in reproductive condition (Platania et al. 1991). Six of the ten individual specimens in the 1988 samples were recaptures from 1987. Also, in 1988. a single adult tuberculate male razorback sucker was captured at approximately river mile 80 on the San Juan River near Bluff, Utah. Particularly noteworthy is that this is the first confirmed record of this species from the main stem San Juan River. No razorback suckers were captured in 1989. No larval specimens. nor any other size classes of razorbacks (other than adults). have ever been documented in the San Juan River drainage, All recent captures of wild razorback suckers in the upper basin have been of mature adults. In 1994. an experimental augmentation program was initiated on the San Jtlan 9