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Lanigan and Tyus (1989) estimated that only 978 :t 232 adult razorback sucker remained in the Green River above Desolation Canyon during 1981-86, which very likely is only a small fraction of the historic population. Some researchers believe that dramatic declines have occurred since 1970. However, accurate annual population estimates, based on recovery of fish tagged in the earlier study, are biased by differential tag retention, although the population clearly has remained "much less than 1000" (Kenneth P. Burnham, Colorado State University, 1 June 1993 letter to Tim Modde, U.S. Fish and Wildlife Service, Vernal, UT). A few young razorback sucker have been collected in the Green River in recent years (e.g., three fish < 415 mm in 1993, Tim Modde, U.S. Fish and Wildlife Service, Vernal, UT, personal communication), and the age structure of the few razorback sucker collected annually on the Colorado River has declined in recent years (Chuck McAda, U.S. Fish and Wildlife Service, Grand Junction, CO, personal communication). Thus, some recruitment of adult cohorts may be occurring in both the Green and Colorado Rivers, perhaps related to higher flows. Whether stable or declining, the population of razorback sucker in the Green - Yampa system likely has not exceeded more than 1,000 fish in the last two decades. Since most of the very few razorback sucker captured in the Upper Colorado River Basin are older fish, I conclude, as does Tyus (1991a), that very little recruitment of adult razorback sucker has occurred since the 1960s. Razorback sucker have been obseIVed spawning, or in spawning condition (ripe) during the rising limb of the spring runoff at temperatures 5-lOoC below (McAda and Wydoski 1980, Tyus 1987) the experimentally observed optimum range (20-220C) for reproduction (Inslee 1982, Hamman 1985, Marsh 1985). Razorback sucker were commonly (50 or more per year) collected in the IS-mile reach of the Colorado River in the early 1970s, mostly in a gravel pit connected to the river near Grand Junction, CO (McAda and Wydoski 1980, Valdez and Wick 1983). That gravel pit washed out in the 1984 spring flood of record, and only incidental captures were made subsequently (Osmundson and Kaeding 1991). However, in the spring of 1993, sixty-seven razorback sucker were taken from another gravel pit (Etter Pond). One ca. 20 year old fish was collected, but the rest were nine years old, corresponding to spawn during the 1984 flood when the 9