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<br />MODELING CUI-UI RECOVERY
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<br />1 0 20 30 40 50 60 70 80 90 1 00 11 0 1 20
<br />Supplementary water (x1 ,000 acre-feet)
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<br />FIGURE I.-Probability of cui-ui population persistence (over 200 years) as a function of supplemental water.
<br />Vertical lines show supplementary water values at which the various curves (reflecting larval survival estimates)
<br />intersect the 85% and 95% probability of persistence levels. Cui-ui could be "delisted" as endangered at 0.95
<br />probability of persistence or reclassified as threatened at 0.85 probability of persistence.
<br />
<br />vised. For the moment, we concentrate on the
<br />intermediate best estimate results. The conclu-
<br />sion, in this case, is that cui-ui recovery requires
<br />about 70,000 acre-feet of supplemental water each
<br />year.
<br />If this water had been made available imme-
<br />diately in the spring of 1991, and if the model
<br />were known to be accurate, cui-ui could have been
<br />considered capable of recovery after only I year.
<br />Because the model and its input parameter (de-
<br />mographic) values cannot yet be considered exact,
<br />the term recovered, as used above, must be used
<br />tentatively. Assurance of recovery will require
<br />many years of monitoring and data refinement.
<br />Threatened conveys a less critical status than
<br />endangered, although it does not assure a species'
<br />survival. Accordingly, iflikelihood of persistence
<br />falls above some arbitrarily determined level of
<br />concern but below 95%, reclassification to threat-
<br />ened status may be warranted. If an 85% certainty
<br />level of persistence is chosen to define this level,
<br />reclassifica~ion could occur concomitantly with a
<br />yearly addition of 17,000 to 107,000 acre-feet
<br />(corresponding to larvae survival of 0.003 and
<br />
<br />0.001, respectively). The best guess estimate re-
<br />quires about 40,000 acre-feet.
<br />We must caution that the model considers den-
<br />sity feedback on run size only aild does not in-
<br />corporate random, year-to-year fluctuations in
<br />mortality and fecundity. Therefore, predicted pop-
<br />ulations are overestimated (see Appendix). The
<br />40,000 and 70,000 acre-feet figures thus probably
<br />err on the low side. These levels were selected as
<br />the thresholds for reclassification and deli sting, re-
<br />spectively.
<br />The relations shown in Figure I presume an
<br />immediate addition of the supplemental water.
<br />Results of the runs accounting for procrastination
<br />(Figure 2) show that when water is acquired in
<br />1994 and in 10,000-acre-foot yearly increments,
<br />the eventual, sustained amount of supplemental
<br />water needed is 83,000 acre-feet; cui-ui recovery
<br />will take 2 + (83,000/10,000) = II years (the year
<br />2002). With 3,000 acre-feet increments, recovery
<br />will require well over 120,000 acre-feet yearly of
<br />supplemental water. Inasmuch as this amount of
<br />water is not realistically obtainable, recovery will
<br />not likely occur. In this scenario, other conser-
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