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stages has further complicated efforts to monitor and manage rare <br />t <br />U11~?; a taxonomic key for the early life stages has only <br />recently been developed (Muth et r1[. i:~t`sb). <br />Changes in Abundance and Distribution <br />The original range of humpback chub probably included swift, <br />deepwater areas throughout the main channels of the Colorado and <br />Green rivers (USFWS 1974, Holden and Stalnaker 1975b). Uncertainty <br />about distribution exists because populations may have been <br />eliminated by human activities before the species was discovered. <br />(USFWS 1979). Former humpback chub habitats in the lower basin may <br />have been lost when Colorado River dams were cor,struczad (nr`ijar <br />of a1. 1985) prior to 1946, the year humpback chubs were first <br />described (hliller 1946). This speculation is based on a resemblance <br />between those areas prior to inundation and present day humpbacks <br />chub habitats. <br />Humpback chubs may have formerly inhabited the Colorado River <br />area that was later inundated by Lake Mead (Miller 1955). However, <br />they would have been eliminated by creation of the Iake in the 1930s <br />(USFWS 1979}. Humpback chubs were not discovered in G1en~Canyon on <br />the Colorado River in Utzh during preimpoundment investigations <br />(Smith 1959, McDonald anal Dotson 1960). They were collected from <br />Lake Fowe11 rind the Colorado River downstream from Glen Canyon Dam <br />after its closure ire 1`J f,4 (E{oldr_n and Stalnaker 1970, Holden 1973, <br />Suttkus and Clemmer 1977). The clam altered flow and temperatures <br />downstream; this in turn probably de~~astated Gi1n populations in <br />4 <br />