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480 Io0• B. C. Osmundson et al. / EXPLANATION /•' I GENER RRFUGAIM A? OF 70.16' \ ? • / ?C,? 1 Loma C9Q / / 70 Sow / Launch Cameo UTAH Gp?? .km 245.5 J Palisade COLORADO ' k" p 9B q? 70 0 6 MILES h9 s \ Grand ?s q 6o Q Junction\ Grand .? e ,yo \\\\\\\ Valley WeWater 5 KI Mae ion rkm 297.8 .._.._ ._.. Gyp s rkm 205•3 ...... RM_ . 215, DENVER I*Pky, gee CG SLGy 70• pD? so J •R1 ti C O L O R A D O •••/ y? Fig. 1. Colorado River in the Grand Valley, with designated river kilometers (rkm), including Walter Walker State Wildlife Area (rkm 263.1) (rkm), where the confluence of the Green and Colorado Rivers is considered rkm 0.0 (converted from river miles as mapped by Belknap and Belknap 1974). In the center of the Grand Valley lies the city of Grand Junction, where the confluence of the Gunnison and Colorado Rivers occurs (rkm 275.1). Collection of Muscle Plugs and Selenium Determination In 1994, muscle plugs were collected from 39 Colorado pikeminnow inhabiting the Colorado River in the Grand Valley. Because many Colorado pikeminnow in the Grand Valley have been implanted with passive integrated transponder (PIT) tags, individual fish can often be identified. Thirteen Colorado pikeminnow were captured and biopsied in the "15-mile reach" (a specific reach identified for recovery efforts) of the Colorado River between Palisade and the Gunnison River confluence (rkm 297.7 to 275.1) (Figure 1). Twenty-four Colorado pikeminnow were captured and biopsied in the "18-mile reach" (another recovery area) of the Colorado River between the Gunnison River confluence and Loma (rkm 275.1 to 245.5). Of these 24, 16 were captured at Walter Walker State Wildlife Area (WWSWA), a prespawn- ing staging area at rkm 263. 1, currently used by Colorado pikeminnow and razorback suckers. Also, two Colorado pikeminnow were captured and biopsied in Horsethief and Ruby Canyons between Loma (rkm 245.5) and Westwater (rkm 205.3). During 1995, a total of 45 Colorado pikeminnow were captured at WWSWA. Of these, 11 were fish previously biopsied in 1994. Six of the 45 fish were captured multiple times during summer 1995 and had muscle plugs taken each time. In 1996, muscle plugs were taken from a total of 35 Colorado pikeminnow captured at WWSWA. Of these 35 fish, three had been previously biopsied in both 1994 and 1995. Four of the 35 fish were captured and had plugs taken several times during the 1996 summer. Muscle plugs were taken following procedures specified by William- son (1992) in which a different 5-mm sterile biopsy punch was used on each fish and discarded after use. Disposable forceps (also used only once) were used to remove the muscle plug from the biopsy punch. Muscle plugs were taken from the dorsal area approximately 1-2 cm anterior to the origin of the dorsal fin and 1-2 cm to either side of the spine. Samples were placed in chemically cleaned vials, chilled with wet ice in the field, frozen the same day, and kept frozen until preparation for analysis. Muscle plugs were collected by U.S. Fish and Wildlife Service biologists while conducting concurrent Colorado pikem- innow distribution and abundance surveys (see Osmundson and Burn- ham 1998, Mourning 1995 for capture methods). For fish repeatedly sampled over time, the second or third muscle plug was taken immediately adjacent to the location of previous biopsies (1-2 cm from dorsal fin). Determination of Selenium in Fish Muscle Plugs All sample preparation prior to neutron activation analysis was conducted by the Environmental and Contaminants Research Center (ECRC) and has been described by Waddell and May (1995). Samples were transported to the University of Missouri Research Reactor (MURR) staff where the determination of the radionuclide Seem was made using procedures of McKown and Morris (1978). Sample transfer, irradiation, and detection parameters for the determination of the radionuclide Se77- in fish muscle plugs by neutron activation have been described by Waddell and May (1995). Statistical Treatment A Wilcoxon signed-rank test was used to determine how selenium concentrations in muscle plugs changed in 11 recaptured Colorado pikeminnow between 1994 and 1995 (Snedecor and Cochran 1972). To calculate sample means of selenium concentrations in Colorado pikeminnow from WWSWA for each year, multiple plugs from the same fish (taken at time spans ranging from 1 day to >2 months) were averaged together to calculate a mean concentration per fish per year. A linear regression was performed to determine how change in body weight affected selenium concentrations in the muscle plugs (Dowdy and Wearden 1983). Percent changes in body weight were transformed by aresin (X)-1/2 to improve normality (Zar 1974). A linear regression r