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53 <br />Refuge. No adults were ever trapped; therefore, their abundance <br />in September, 1977, is unknown. Standing crop in September 1977, <br />0.81 kg) is made up from the first year young. Standing crop <br />in September 1978, (9.84 kg) is composed of two age groups. The <br />survivors of the 1977 season contributed less than 0.5 kg to the <br />standing crop. Age Group II contributed the larger biomass to <br />the population and was also the most widely distributed age group. <br />In order to evaluate the environmental performance of BLM <br />habitat on the pupfish population, production values were <br />calculated. At the end of the first season (September 1977) <br />production was determined for first generation pupfish (3'.1 kg). <br />For September, 1978,,1 divided production into the two age,groups. <br />Total production for 1978 is 13.7 kg or 39 gm of fish per square <br />meter. Production was most influenced by the numbers of pupfish <br />young (Group II). Age Group II accounts for nearly 85 percent <br />of the annual production.. <br />Estimation of pupfish production in this study required <br />several assumptions and this data should be interpreted <br />accordingly. Major assumptions were: <br />1. Egg mortality, mortality and,growth of <br />young were assumed to be linear. <br />2. Immigration of pupfish into the sanctuary <br />was insignificant. <br />Some support for the second assumption came from drift net <br />data collected from the upstream dam. During the sample period <br />no pupfish young or eggs were ever collected, however, mosquito <br />fish fry were. <br />In summary, the repopulation of pupfish in BLM Sanctuary <br />appears successful. Evidence has been presented that suggests <br />population stability, and segregated distribution downstream of <br />age groups. Young pupfish made the greater contribution to the <br />production estimates.