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16 The 4.5 mile reach between intensive survey sites was sampled in a more general manner primarily by electroshocker to provide a broad cross-section of the fish population. Physical data were collected only at sites of rare fish captures. Biological Measurements Each habitat present in the intensive reaches were sampled with every effective gear type. Rare fish captures were located to the highest level of precision possible and water depth, velocity measuremen~ and the predominant substrate type recorded. All fish collections were identified to the nearest 0.1 mile and accompanied with detailed information regarding date, time of day, measure of effort, habitat type, substrate type, and a series of depth and velocity measurements to describe the range of conditions present in the sample area. All fish samples were processed and the information entered on standard data forms (Appendix A-I). Fish larger than 100 mm were weighed and measured individually. Smaller fish were sorted into 10 rom groups and counted. Endangered or rare fishes encountered were handled with utmost care and the needed information collected with the least possible stress on the fish. Stomachs were removed from the rare fish that did succumb and the rest of the carcass frozen for later examinations. All rare fishes greater than 175 mm in total length were tagged with a Carlin dangler tag attached below the dorsal fin (Figure 4). Field identification of Gila was difficult. During the past season. dorsal and anal ray c~s (Holden et al. 1974) were relied on to distinguish between~. robusta. ~. cypha and~. elegans. In the future, classification of the Gila group will utilize the technique of Smith, Miller and Sable (1979) to further differentiate the species in this group. Special Investigations To expand upon these rare fishes' life histories requires some very intensive study of specific fish populations and/or ~dividual fishes. Only a small beginning was made during the past year to be expanded upon next year. During 1979. a broad survey of young-of-the-year (YOY) squawfish distribution was carried out to determine extent of recruitment and general distribution. Also. a limited amount of work was done to examine YOY utilization of backwater areas. Next year, data will be collected on food habits of young-of-the- year squawfish and all sympatric species from one area in both the Colorado and Green Rivers. Further work will be conducted on patterns of use of the backwater areas and the hydraulics and biological factors that influence the utilization of this particular habitat by squawfish.