Selenium concentrations in the Colorado pikeminnow (Ptychocheilus lucius):Relationship with flows in the upper Colorado River

A Department of the Interior (DOI) irrigation drain-water study of the Unco mpahgre Project area and the Grand Valley in western Colorado revealed high selenium concentrations in water, sediment, and biota samples. The lower G unnison River and the Colorado River in the study area are designated criti cal habitat for the endangered Colorado pikeminnow (Ptychocheilus lucius) a nd razorback sucker (Xyrauchen texanus). Because of the endangered status o f these fish, sacrificing individuals for tissue residue analysis has been avoided; consequently, little information existed regarding selenium tissue residues. In 1994, muscle plugs were collected from a total of 39 Colorado pikeminnoe captured at various Colorado River sites in the Grand Valley fo r selenium residue analysis, The muscle plugs collected from 16 Colorado pi keminnow captured at Waiter Walker State Wildlife Area (WWSWA) contained a mean selenium concentration of 17 mu g/g dry weight, which was over twice t he recommended toxic threshold guideline concentration of 8 mu g/g dry weig ht in muscle tissue for freshwater fish. Because of elevated selenium conce ntrations in muscle plugs in 1994, a total of 52 muscle plugs were taken du ring 1995 from Colorado pikeminnow staging at WWSWA. Eleven of these plugs were from fish previously sampled in 1994. Selenium concentrations in 9 of the 11 recaptured fish were significantly lower in 1995 than in 1994. Reduc ed selenium in fish may in part be attributed to higher instream flows in 1 995 and lower water selenium concentrations in the Colorado River in the Gr and Valley. In 1996, muscle plugs were taken from 35 Colorado squawfish cap tured at WWSWA, and no difference in mean selenium concentrations were dete cted from those sampled in 1995. Colorado River flows during 1996 were inte rmediate to those measured in 1994 and 1995.