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Executive Summary The humpback chub (Gila cypha) is endemic to the Colorado River basin, and it occurs only in isolated populations in narrow canyon bound reaches of the mainstem Colorado River and its major tributaries. The Yampa Canyon population is one of five aggregations in the upper Colorado River basin, each consisting of only a few hundred to a few thousand fish. Little is known about humpback chub in Yampa Canyon because of inaccessibility of the canyon, confusing Gila taxonomy, and its low numbers. Almost nothing is known about this population's size, survival, r~cruitment rates, and population trend. The objectives of this study were to: 1) develop procedures for monitoring humpback chub population trends to serve as a response measure for management activities, e.g., non-native fish reduction; 2) if feasible, estimate population size; and 3) develop procedures for determining reproductive success. In 1998 we began a three year study that consisted of multiple sampling passes each year in the Yampa River in Dinosaur National Monument from Deerlodge to Echo Park (75 kIn) to assess the humpback chub population. Sampling consisted primarily of electro fishing and angling. Captured humpback chub were scanned for presence of a PIT tag; if a pit tag was implanted in the fish it was recorded, if none was found, one was inserted and the fish released. Each pass through Yampa Canyon took 4-5 days Subsequent passes were made 7-10 days later. Electrofishing and angling captured 86 humpback chub in Yampa Canyon. The catch distribution extended from Laddie Park (river km 17) upstream to Disappointment Draw (river kIn 72). This range was similar to that of historic data. The distribution was very uneven; most fish preferred deep pools and eddies associated with large boulders. Most adult sampling was VI