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flow of about 15 m3 Is in late summer (Tyus and Karp 1989). The study area monitored included river kilometers 76 to 17, the range ofthe Yampa River adult humpback chub population. Humpback chub identification. Yampa River humpback chub and roundtail chub (Gila robusta) are not always easily identified, especially in the field working with live specimens that one intends to release. Many large adult (> 250 mm) humpback chub are easy to identify by obvious presence of a nuchal hump and subterminal mouth with overhung fleshy snout, but many fish have intermediate characters. Juvenile fish (< 150 mm) are even more difficult to identify (Karp and Tyus 1990). We adapted criteria of Douglas et al. (1989) and Muth (1990) for identifying the fish in the field (Table 1). Adult samDling. During the three year study, two passes in 1998 and three passes with electrofishing gear and angling in 1999 and 2000 were made to collect adult humpback chub. The raft electro fishing system consisted of Smith-Root 5.0 GPP or Coffelt VVP-15, pulsed direct current fished at 200-300 V and 5-7 A.~ Generally, both sides of the the river between river km 72 and 17 (traveling downstream) were electrofished. The crew for each raft consisted of an oarsman and a netter. On most occasions, two rafts worked opposite shorelines. At least one support raft worked with each electro fishing raft. Netters attempted to capture all fish in 1999 and only endangered fishes in 1999 and 2000. Every 15 minutes, or when a live well was filled with fish, or when an endangered fish was captured, collection efforts ceased and data collected and recorded and fish released. Data collected included weight (nearest gram) and length (total length [TL] to the nearest millimeter) for all roundtail chub, humpback chub, and Colorado 3