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i specimen was captured on 1 July in 1999 (Fig. 9). Back-calculation of spawning dates based on captures of larvae suggested that spawning occurred from late March to early June, which is substantially earlier and over longer period than in the middle Green River. Most spawning occurred when flow levels were relatively low or increasing and when water temperatures were relatively low but rising. Flow levels during spawning were variable within and among years and water temperatures in the Green River were also variable and ranged from 7 to 21 °C in 1998. Those environmental conditions were similar to those during other sampling years since 1993 (Table 8), except that water temperatures were generally cooler and days prior to peak discharge were higher. Differences could be an artifact of the manner in which spawning times were calculated or may represent real differences in conditions in those years. In general, razorback suckers spawned in the lower Green River from eazly-April to early-May when water temperatures were 10 to 16°C and when accumulated degree days ranged from about 350 to 1100. Spawning generally began 28 to 78 days prior to the highest flow day during spring runoff and nearly always before water temperature reached 14°C. In contrast to the middle Green River, larvae in the lower Green River were captured prior to or during high flow periods. DISCUSSION Previous investigators classified the population of razorback suckers in the middle Green River as precariously small but stable between 1985 to 1992 and estimated population abundance at about 300 to 600 animals (Modde et al. 1996). Modde et al. (1996) also estimated annual survival rate, ~, at about 0.71 (SE = 0.0246) and concluded that some recruitment must be occurring to sustain the population at that level. Our more recent analysis suggested that 20