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144 HAMILTON ET AL. locations where they were collected by light trapping. On the other hand, larvae used in the Ouray study (Hamilton et aI., 1996) were spawned from hatchery-held adults that were induced to spawn by injection of hormones. Larvae in the Ouray study came from two spawns, whereas the wild larvae probably came from several adults that had spawned under natural conditions. Studies with Pacific salmon (On- corhynchus sp.) found that wild fish had higher survival rates than hatchery-reared fish (Felton et al., 1990). Similarly, the hatchery-spawned larval razorback sucker may have been less fit to deal with stresses than wild-spawned larvae. Con- sequently, larvae used in the Ouray study might have been more sensitive to stressors than wild larvae. Nevertheless, based on the available literature summarized in Table 4, whole-body residues measured in wild razorback sucker larvae were comparable to residues in other species where adverse effects on survival and growth were observed. Other Inorganic Elements in Larvae A few inorganic elements seemed elevated in the ICP-MS scan of the composite sample of larvae from Stewart Lake Drain. The concentration of cadmium in larvae was 4.9 !J.g/g, which was greater than the maximum concentra- tion of 0.8 !J.g/g reported in the NCBP (Schmitt and Brum- baugh, 1990). Values in the NCBP were given as wet weight tissue concentrations. For comparison purposes, those values were converted to dry weight concentrations by assuming 73.8% moisture in whole-body fish tissue, which was the average for the percentage moisture in 315 fish samples collected as part of the NCBP (Schmitt and Brum- baugh, 1990). The concentration of copper in larvae was 40 /lg/g, which was greater than the 85th percentile value of 3.82 /lg/g, but less than the maximum concentration of 88.2 /lg!g in the NCBP. The concentration of lead in larvae was 3.8 /lg/g, which was greater than the 85th percentile value of 0.84 /lg/g, but less than the maximum value of 18.6/lg!g in the NCBP. The concentrations of selenium in larvae were 5.8 and 8.0/lg/g, which were greater than the 85th percentile value of 2.8 !J.g/g and close to the maximum value of 8.8 /lg!g in the NCBP. The concentration of zinc in larvae was 299/lg/g, which was greater than the 85th per- centile value of 1311-lgjg, but less than the maximum value of 452 /lg!g in the NCBP. The concentration of arsenic in larvae was not elevated compared to the NCBP data. Mer- cury and strontium were not measured in the larvae, but have been reported as inorganic elements of concern in water, sediment, or biota in the Green River (Stephens et ai., 1988, 1992; Peltz and Waddell, 1991; Finger et aI., 1994; Hamilton et aI., 1996). Mount et aI. (1994) investigated cadmium, copper, lead, and zinc individually in the diet with 33-day-old rainbow trout (Oncorhynchus mykiss) for 60 days. He reported no effects on survival or growth at residue concentrations in fish of 6.8 /lg/g for cadmium, 36 /lgig for copper. 10 /lg g for lead, and 303 /lg!g for zinc. Each of these concentrations were close to or greater than the concentrations in larvae for the present study. Consequently, cadmium, copper, lead. and zinc residues in the razorback sucker larvae in the present study may not be elevated to concentrations of concern. Vanadium concentrations in razorback sucker larvae (1.7 /lg!g) were close to a residue value of 2.05 \.lg!g present in rainbow trout that had reduced growth and reduced feeding response (Hilton and Bettger, 1988). Consequently. vanadium seems to be the only element, other than sel- enium, elevated sufficiently in larvae to be of concern. CONCLl'S[O~ The range of selenium in wild razorback sucker larvae in the present study was as low as 3/lg/g as a whole-body residue, which suggests that if larvae from adults with low selenium residues drift to a relatively low selenium area, they probably will survive to the juvenile life stage. In fact, this scenario apparently happened at Old Charlie Wash, as evidenced by the collection of 28 young of year razorback sucker in 1995 (Modde, 1996) and 45 in 1996 (Modde, 1997). However, if larvae start out with low selenium residues. as occurred at Cliff Creek and Stewart Lake Drain, then accu- mulate selenium through waterborne and dietary exposures to concentrations greater than the toxic threshold of 4 /lg/g, there seems little likelihood of their survival to the juvenile stage. Conversely, larvae with elevated selenium concentra- tions, such as those at Sportsman's Drain, can reduce their selenium burden by depuration if larvae can reach a rela- tively clean nursery area. Nevertheless, the widespread pres- ence of elevated selenium residues, i.e., >4/lg/g, in larval razorback sucker from Cliff Creek to Old Charlie Wash inlet suggests that widespread selenium contamination of the Green River is occurring and may be adversely affecting the reproductive success of the endangered razorback sucker. Other recent articles have also concluded that selenium concentrations in the upper Colorado River basin, which includes the Green River, are elevated sufficiently in water. food organisms, and fish tissue to suggest that selenium is causing adverse effects in razorback sucker and possibly other fish (Hamilton and Waddell, 1994; Waddell and May, 1995; Hamilton, 1998; Hamilton et ai., 1996, 2000; Stephens and Waddell, 1998). ACKNOWLEDGMENTS The authors thank B. Haines (USFWS. Colorado River Fishery Project. Vernal. UT) for light trapping the larval razorback suckers: Dave lrving lUSFWS, CRFP. Vernal, UT) for information on Little Stewart Lake: and John Besser, Jim Fairchild. Kurt Maier. Barb Osmundson. and Doyle Stephens for reviewing the manuscript.