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1979 THE ENDANGERED SPECIES: A SYMPOSIUM and Deacon (1979) provide a detailed de- scription of fluctuations in population size and probable causes for these fluctuations through December 1976. Data on fluctua- tions in population size presented here ex- tend through December 1978 (Fig. 13, Table 4). Figure 13 illustrates the direct and marked influence of relatively small changes in water level in Devils Hole on minimum population size of Cyprinodon diabolis. The water levels indicated in Figure 13 refer to a reference point established by USGS above the maximum water level. Therefore, depth of water in the habitat increases as the dis- tance below the reference point (in feet) de- creases. In addition, the water level shown is actually the minimum level permitted by the 55 courts during the time indicated. The first level indicated (3.9) represents the lowest wa- ter level reached prior to intervention of the courts. Water levels normally fluctuated somewhat above the level indicated, but al- most never below that level. Generally, wa- ter levels were highest in winter and very near the permissible minimum during the summer irrigation season. This, of course, re- flects the fact that the water level in Devils Hole is directly and rapidly influenced by pumping of groundwater nearby. The somewhat erratic population fluctua- tions in 1972 and 1973 reflect responses to temporary management attempts as well as to scouring floods which occurred during this period (Deacon and Deacon 1979). Once 550 500 450 400 350 300 250 200 150 ~ 3.3 100 3.9 1972 73 74 75 76 3.0 77 78 2,7 Fig. 13. Devils Hole pupfish population size compared to minimum water levels 1972-1978.