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SElENIUM IN RAZORBACK SUCKERS IN GREEN RIVER. CTAH I' , -'J were collected near Browns Park (river kilometer [rkJ ... 632-635; distance from the confluence of the Green and Colorado rivers, rk 0.0), Echo Park (rk - 553-555), Stewart Lake Drain/Ashley Creek area (rk... 482), and Ouray NWR (rk - 407-413) for trace element analysis (Waddell and Wiens, 1994b). In 1991, 15 composite fish samples (four species collected, and composited by species) were collected from Jensen, Stewart Lake Drain/Ashley Creek area, Leota Bottom, Sheppard Bottom, and Ouray (Waddell and Wiens, 1994b). In these 40 samples, concen- trations of selenium ranged from 1.9 to 49l!g/g, and selenium residues were determined to be strongly correlated with fish location. Selenium concentrations were highest in fish from the Stewart Lake Drain/Ashley Creek area and Jensen areas where 82% of the samples exceeded the pro- posed toxicity threshold of 4 l!g/g derived from several laboratory and field studies with a variety of fish species (Lemly, 1993). These two river reaches receive surface water known to contain high selenium concentrations, and sub- surface water sources are also likely contaminated. Waddell and Wiens (1994b) concluded that their data demonstrated some temporal variation. Selenium concentrations were higher in 1991 samples than in the 5 previous collection years (1978, 1980, 1984, 1986, 1987). The Green River provides critical habitat for endangered Colorado squawfish (Ptychocheilus lucius), razorback sucker (X yrauchen texanus), bony tail (Gila elegans), and humpback chub (Gila cypha). The largest extant riverine population of razorback suckers in the upper Colorado River basin occurs in the Green River, but recent collections of razorback sucker larvae in the lower 210 km ofthe Green River strongly suggest localized reproduction (Muth et aI., 1997). The Green River is currently the focus of a major habitat restoration program within the Recovery Imple- mentation Program for the Endangered Fishes of the Upper Colorado River Basin. Attempts to rear wild-caught razorback sucker larvae in captivity have produced mixed results. In 1994, approxim- ately 50 larval razorback suckers were collected using light traps from Millard Canyon (rk 53.9) or the Anderson Bot- tom-Bonita Bend area (rk 49.9-50.7) in the lower Green River and taken to the Larval Fish Laboratory (Ft. Collins, CO) for rearing. All but 2 of these larval fish died within 2 weeks (Muth and Wick, 1997), even though proven culture techniques were used. One potential cause or contributing factor for this mortality may have been handling stress due to the long transportation period from the lower Green River to the Larval Fish Laboratory. Because of concerns raised by NIWQP studies about contaminant problems in the Green River (Stephens et al., 1988, 1992; Peltz and Waddell, 1991), the observed mortality may have been due to contaminants; however, contaminant residues were not measured. [n contrast, wild razorback sucker larvae col- lected in 1996 from the Green River and reared in a pond near Vernal, Utah, with few other fish species present had what was considered to be relatively good survival (29Joo. B. Haines, USFWS, personal communication. 1996). The purpose of this study was to determine the concentra- tions of selenium in larval razorback suckers previously collected from the Green River. The analysis was conducted on larvae previously collected by light trapping by the Larval Fish Laboratory (Ft. Collins, CO) or the Colorado River Fishery Project (USFWS, Vernal, UT) related to other projects. Most larval razorback suckers collected in light traps were probably S; 1 month post hatching (10-15 mm total length). Even though spawning habitats for razorback sucker have been speculated to be limited and the critical life stages are those from fertilized egg through the first year (Miller et al., 1982), 1735 larvae were collected in the middle Green River and 440 larvae collected in the lower Green River in 1992-1996 (Muth et al.. 1997). How- ever, no juveniles over 1 year old have been found in the upper Colorado River basin, which includes the Green River. In contrast, Modde et al. (1996) suggested that some recruitment must be occurring because population esti- mates for adult razorback sucker (450-580 mm total length) in the Green River could detect no significant decrease in population between 1982 and 1992. They characterized the population as precariously small but dynamic. The present study sought to determine the potential for selenium to reduce larval survival in these critical habitat areas. METHODS AND MATERIALS Study Sites Larval razorback suckers were collected between May 6 and June 13, 1994, by light traps (Muth, 1995) from five nursery habitat sites on the Green River: Cliff Creek. Stewart Lake Drain, Sportsman's Drain, Greasewood Cor- ral at Ouray NWR, and inlet of Old Charlie Wash (Fig. 1). Cliff Creek is a tributary on the east side of the river, Stewart Lake Drain and Sportsman's Drain are outlet canals on the west side of the river, and Greasewood Corral is a side channel (perhaps an old ox bow) and the inlet to Old Charlie Wash is a canal, both on the east side of the river. Collections for razorback sucker larvae were made by the Larval Fish Laboratory or the Colorado River Fishery Project and were part of a study to assess reproduction. distribution, and movements of mainstem razorback suckers in the Green River conducted under the Five-Year Flaming Gorge Research Program. All nursery habitat sites where razorback sucker have been collected were low or zero-velocity habitats connected to the main channel during times of high flow in spring or early summer. As flows increase and habitats flood, eddies are formed near the mouths of these habitats, which serve to transport larvae from the main channel into these habitats. After collection, larvae were measured for total length.