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Observations on the Little Colorado River population of the humpback chubs, during May 1987, 1988. .C.O. Minckley . Biology Department, Northern Arizona University Flagstaff, Arizona 86011 During May of 1987 and 1988 research was conducted on the population of humpback chubs occurring in the Little Colorado River from it's confluence upsteam 10 km. Native fishes dominated the catch, with the humpback chub being the most common fish taken. Reproduction was confirmed in this species by the presence of fish exhibiting secondary sexual characteristics, expression of gametes, breeding colors and larval fish. Reproduction was not observed. In 1987, 82.5% of the humpback chubs captured were tagged and 11.9% were recaptured. Movement of recaptured 1988 fish was within the lower.1,200 m of the Little Colorado. Six fish previously tagged by Arizona Game and Fish were also recaptured. These later fish had grown from 2-46 mm in total length. In 1988, 60.5% of the chubs taken were tagged. Of that number, 21.3% were recaptured. Maximum upstream movement in 1988 was 9.2 km, maximum downstream movement was 2.9 km. The mean number of days at large during 1987 was 3.4; in 1988 it was 4.4 days. In 1988, 20 fish tagged in 1987 were recaptured.. Also, 31 fish tagged by other agencies were recaptured. Fish tagged in 1987 had grown from 0-42 mm. The other older recaptures had grown from 1-69 mm and one fish had been at large almost eight years. Based on preliminary examination of otoliths, it appears likely this species lives at least 34 years (W.L. Minckley pers. comm.). The population estimate for 1987 was 5,783'F679 humpb ck chubs. In 1988 it was estimated that 7,060:t574 humpback hubs were present. Both of these estimates are for the lower 1 00 m of the Little Colorado. This study was funded by the Arizona Game and Fish Department, nongame branch. Additional logistic support was provided by the Glen Canyon Ecological Survey and numerous river companies. 67