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<br />Hamilton
<br />
<br />The reason for the decline of these species is thought to be due to a
<br />combination of factors including stream alteration (dams, irrigation, dewater-
<br />ing, channelization), loss of habitat (spawning sites and backwater nursery
<br />areas), changes in flow regime, blockage of migration routes, water tempera-
<br />ture changes, competition with and predation from introdticed species, para-
<br />sitism, and changes in food base (USFWS, 1987). A combined approach for
<br />recovery of the four endangered fish in the upper Colorado River basin, with
<br />emphasis on Colorado pikeminnow and razorback sucker, has been under-
<br />taken by the Recovery Implementation Program for Endangered Fish Species
<br />in the Upper Colorado River Basin, which was initiated in 1987 (USFWS,
<br />1987). The Recovery Program is a joint effort of the U.S. Fish and Wildlife
<br />Service, U.S. Bureau of Reclamation, Western Area Power Administration,
<br />states of Colorado, Utah, and Wyoming, Upper Basin water users, environmen-
<br />tal organizations, and the Colorado River Energy Distributors Association. The
<br />goal of the IS-year program is to reestablish self-sustaining populations of the
<br />four species while allowing continued development of water. The remaining
<br />population of razorback sucker in the Green River has been estimated at about
<br />1,000 individuals by Lanigan and Tyus (1989) and at 300 to 600 by Modde,
<br />Burnham, and Wick (1996). Razorback sucker are very rare in the upper
<br />Colorado River where only 10 fish have been found in the river between 1989
<br />to 1995 (C. McAda, personal communication, 1998). The last one was cap-
<br />tured on May 4,1995, in a backwater of the Walter Walker State Wildlife Area
<br />(WWSWA), near GrandJunction, CO. Similarly. the population of Colorado
<br />pikeminnow is considered low relative to historical levels and has been esti-
<br />mated to be 600 to 650 individuals in the upper Colorado River (Osmundson
<br />and Burnham, 1996).
<br />The recovery program did not seriously consider contaminant concerns
<br />until 1994, even though irrigation and pollution were suggested in 1976 as
<br />possible conuibuting factors to the decline of the currently endangered fish
<br />(Seethaler, McAda, and Wydoski, 1979), with contaminants possibly affecting
<br />Colorado pikeminnow (Osmundson and Kaeding, 1989). Because little aquatic
<br />contaminant research was being conducted in the Colorado River basin prior
<br />to the late 1980s, contaminants were not considered to be associated with the
<br />decline of endangered fishes.
<br />
<br />RECENT INVESTIGATIONS OF SELENIUM CONTAMINATION IN
<br />THE COLORADO RIVER BASIN
<br />
<br />The National Contaminant Biomonitoring Program has documented tem-
<br />poral and geographic trends in concentrations of persistent environmental
<br />contaminants, including selenium. that may threaten fish and wildlife. Sele-
<br />nium concentrations in whole-body fish in the Colorado River basin have been
<br />among the highest in the nation, and exceeded the 85th percentile, which is
<br />an arbitrary point distinguishing "high" concentrations (Walsh, Berger, and
<br />Bean, 1977; Lowe, May, and Brumbaugh. 1985; Schmitt and Brumbaugh,
<br />
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<br />Hum. Eeo\. Risk Assess. Vol. 5, No.6, 1999
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