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of nonnative cyprinids declined by 41% in 1995. Their numbers increased in the latter portion of the sampling periods as well. Larval sampling effort in and neaz the mouth of the San Rafael River was very compazable both years of study: 1994 (333.2 light trap hrs) and 1995 (350.8 hrs). An additional 107.9 hours was accumulated in the lower Green River in 1995, which yielded two razorback sucker larvae. Nursery habitat availability, not assessed as part of this study, is likely a necessary component in interpreting the catch data and in ultimately determining relative annual reproductive success. Green River mean flow for the months of May and June varied considerably from 1994 (May mean - 244.1 cros, 8620 cfs; June mean-169.8 cros, 5996 cfs) to 1995 (May mean- 298.8 cros, 10,550 cfs; June mean- 665.5 cros, 23,500 cfs). Due to higher water levels, there appeared to be more flooded habitat available in 1995 than 1994 during the sampling period. Whether or not increased available habitat influenced larval captures or if reproductive output was decreased could not be determined from the information collected in the present study. In the future it will be necessary to understand the efficiency of sampling gear and the distribution of the target organisms in available habitats to better interpret results. A concern within the Recovery Program and the focus of this study was the origin of the razorback sucker larvae collected in the lower Green River. Sampling for razorback sucker in both the middle and lower Green River begins when main channel water temperature reaches 14°C (Muth et al. 1998). However spring time water temperatures typically warm quicker in the lower Green River than the middle Green River reach. In 1994, water temperature at Green River, Utah (L1SGS gage # 09315000), reached a consistent 14°C on 12 April, a month eazlier than this temperature was reached at Jensen, Utah (CTSGS gage # 09261000). In 1995, cold, wet weather continued until late May for most of the state of Utah. The thermal regime at Jensen reflected this weather pattern and 14°C was not reached unti126 June. Water temperature at Green River, Utah, was only delayed slightly from the previous yeaz with 14°C reached and maintained on 23 April, however summer daily maxima were lower than in 1994 (Figure 2). Such temperature data suggests that razorback sucker would spawn eazlier in the lower Green River. Thermograph data collected by UDWR in 1997 indicates that average daily temperatures in the San Rafael mimic those of the lower Green River and daily maxima were slightly higher than the Green River through the months of April and May. A total of 481arva1 razorback suckers were collected during this study. Twenty-eight of those (58.3%) were collected in the mouth of the San Rafael River, 181arvae (37.5%) were collected in habitats immediately downstream (RK 156.2-152.8), and two (4.2%) were collected more than 100 km downstream of the confluence. No razorback sucker larvae were collected in habitats upstream of the San Rafael /Green River confluence. Muth et al. (1998) reported only one capture of razorback sucker larvae in the Green River Valley during 5 years of sampling (1993-1997). During this period of time in excess of 1,700 razorback sucker larvae have been captured as result ofmulti-agency efforts (iJSFW5, NPS, and Colorado State University Larval Fish Lab). This lone collection suggests that transport of lazval razorback sucker from the upstream spawning azea is limited. Mean age for razorback sucker larvae captured in the lower Green River in 1994 and 1995 was 17 d (Muth et al. 1998). Although we cannot discount the possibility that a larvae hatched in the Jensen area could be captured 17 days later in the mouth of the San Rafael River, we believe that it is unlikely that such a concentration would locally aggregate after such a disparate distance (344.5 RK; 214.0 RM). More intensive larval light trapping neaz the Jensen spawning baz in 1994 (as well as years subsequent) revealed larvae of a 7