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Hamilton in 1889. The Jordan party seined razorback sucker in the Uncompahgre and Gunnison rivers near Delta, CO. However, Ellis (1914) captured no razorback sucker in 1912 in either the Uncompahgre or the lower Gunnison rivers near Grand junction, CO, but did collect three from the Colorado River near Grand junction, which contrasted with his ready collection of other sucker species in the Uncompahgre and Gunnison rivers, Later, Chamberlain (1946) noted that razorback sucker were found only in the lower portion of the Gunnison River near its confluence with the Colorado River, which may have been the source of the fish. Similarly, Hubbs and Miller (1953) collected about 700 suckers in the Colorado River at the mouth of the Gunnison River in 1946, but only seven were razorback sucker. Based on the above information, Wiltzius (1978) concluded "Since the humpback [razorback] sucker in the upper Colorado River apparently was noticeably declining as early as 1912 and quite rare by 1946, it would be illogical to attribute upper-basin dam construction, which did not get underway until 1937, as the primary cause for this species' decline." Bestgen (1990) in his review of the status of razorback sucker a,lso stated that severe declines of razorback sucker occurred prior to, and after, construction of mainstream Colorado River basin dams, whose construction was long thought to be a major factor in the decline of fish that inhabit big nvers. Based on information in Minckley et ai. (1991), who reviewed a substantial amount of gray literature concerning the historical collection of razorback sucker in the upper and lower basins, it seems the razorback sucker was abundant before 1900, but records after that date suggested a reduced occur- rence. Minckley et ai. (1991) also noted that essentially all records were of adults, and stated that "The historic absence of young (small) fish from collections is striking." Historical accounts showed that Colorado pikeminnow, bonytail, and razor- back sucker were present in the Dolores River in the 1920s and were caught and used for food (Quartarone, 1993). However, in 1971 Holden and Stalnaker (1975) found none of these fish in the Dolores River, which they attributed to the river being "far from its natural state due to irrigation uses and its record of rather severe pollution." Four Colorado pikeminnow were found in the lower 2 km of the river in 1992, but not in a 1982 survey effort (Valdez, Masslich, and Wasowicz, 1992). The decline of razorback sucker in the upper Colorado River basin in the 1900 to 1920s may be similar to the declines observed in lakes Mead and Mohave in the lower basin. In the early 1950s, Lake Mead was about 15 to 20 years old (Hoover [Boulder] Dam was virtually completed in 1935) and razorback sucker were considered abundant due to the entrapment of resi- dent adult fish from the dam closure. The population declined in the 196Os, which Sjoberg (1995) concluded correlated with the predicted longevity of the species and probable loss of the original cohort of adults to old age. In Lake Mohave (Davis Dam was completed in 1951), similar declines have been observed with captures of razorback sucker in recent years consisting of fish 1166 Hum. Ecol. Risk Assess. Vol. 5. No.6, 1999