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ture of razorback :r, Utah, between d Year-class 1994 1991 1993 1993 1993 1993 > 1993 1 1993 1 1991 ed on May 17 and a -f May when the .2°C to 13.4 Co. anged from 205 y). No fish were twning bar after and flows ex- at the Jensen, tune) at 479 m3/ with peak dis- ie spawning bar divided between gure 3). During r individual fish area. During the leys, transmitter located near the , the only female first located near Slanted 10 d pre- fish 33 was not tween 2330 (18 ). During 18-19 RAZORBACK SUCKER SPAWNING IN THE GREEN RIVER 2500 4) 2000 0 v i 1500 rn 0 t 1000 0 M 500 E Z . Nocturnal Diurnal 33 35 36 39 40 41 Individual Fish FIGURE 3.-Diurnal (0700-1859 hours) and nocturnal (1900-0659 hours) periods in which individual razor- back suckers were recorded in the vicinity of the studied spawning bar (middle Green River, Utah, at river kilo- meter 504) between 1 May and 6 June 2000. May, fish 33 was detected in the vicinity but up- stream of the spawning bar. Fishes 33 and 36 mon- itored 23-25 May appeared to be moving down- stream from the spawning area (Figure 4). On the last diel monitoring day, the last fish remaining in the spawning area (code 33) left the spawning area before the completion of the 24-h monitoring pe- riod. Discussion 941 Both wild and hatchery-reared male and female razorback suckers in the middle Green River were found simultaneously in the spawning area at rkm 504 during the ascending limb of the hydrograph. Fish were already on the spawning area on our first collection date, 1 May, and the last radio- tagged fish left the area on 25 May. Modde and Irving (1998) and Tyus and Karp (1990) detected, via electrofishing, wild razorback suckers at the same spawning area as early as 20 April and as late as mid June. This more extensive period may be related to the broader population sampled via electrofishing rather than telemetry (which was limited to just 18 individuals). Although sampling in our study occurred during the period that wild fish have spawned in previous years (Tyus and Karp 1990; Modde and Irving 2000), we did not determine whether additional hatchery-reared fish occurred on the spawning bar earlier or later. Both hatchery-reared and wild razorback suckers mon- itored during the study left the spawning area be- fore peak flow. Nearly half the fish collected on the spawning bar were hatchery-reared fish, and most were stocked the previous year. Although the spawning area at 504 rkm is the primary spawning area for razorback sucker in the middle Green Riv- er, the capture percentages of total population were relatively low: 0.6% of hatchery fish stocked in 1998 and 1999 (Modde et al. 2004) and a minimum FIGURE 4.-Locations of radio-tagged razorback suckers near the studied spawning bar (middle Green River, Utah, at river kilometer 504) during hourly monitoring on (A) 16-17 May, (B) 18-19 May, and (C) 23-24 May.