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13 analyses, mark-recapture age and growth analyses, and age composition analyses were conducted according to accepted, standard procedures. Analytical methods were influenced by sample sizes available (e.g. per river, year, sex, and season stratifications, etc.). All fish lengths were recorded as total length to the nearest millimeter and weights recorded to the nearest gram. Capture locations were recorded to the nearest 0.1 km. All data was computerized using a PC and stored on back- up floppy discs. Age estimates, annular measurements, and associated capture data will be entered into DISBCAL computer programs to determine body-scale relationship, back calculated growth, age composition, average length/weight at age, annual mortality, and mortality between age groups if sample sizes are adequate. RESULTS Job 1. Title: Gamefish species life history data. Objective: To determine 3-year trends in abundance, distribution, reproductive success, and size structure of non-native, non- sa1monid gamefish populations in Upper Basin rivers in Colorado. Northern Pike - Yampa River Northern pike were again sampled in all four study reaches in 1990 (Table 1). The relative abundance of 143 fish captured among the four reaches was similar to the previous years. Slightly less effort was expended in the fall in the Hayden-Craig reach in favor of sampling the other three reaches. This accounts for the differences observed between the 1989 and 1990 sample numbers for Hayden-Craig and Lily Park. Also, instead of continuing sampling in known habitats concentrating northern pike above Craig, one trip was directed at the river reach between Craig and Juniper Springs. This 64 km reach represents a transition from abundant pike habitat containing numerous fish to habitat occupied by adult Colorado squawfish, and characterized by much less low- velocity habitat, especially after spring runoff. The Hayden-Craig reach is the only one of the four in which Colorado squawfish have not been collected. Sampling for pike in flooded tributaries and other backwater habitats was possible through the third week of June in 1990. Forty additional pike were tagged and ten pike were recaptured in 1990. Eighteen tagged pike have been removed from the population, bringing the marked pike population to 210 fish (not adjusted for tag loss). Overall, 38 pike have been recaptured, 6 of these have been second time recaptures (16%). No pike have been recaptured a third time. Forty-two pike were removed from the Yampa River between Craig and Hayden, tagged if necessary with a yellow F10y tag, transported to Elkhead Reservoir, and released. Pike captured in 1990 ranged in