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Squawfish Population Viability Analysis --July 1993 Page 18 Regardless of the combination of j and m values,th~ steady state distribution of adult ages is constant, and follows a geometric distribution; prob(Adult of age x+7) = d(1-d)(x-l) where d is the death rate (= l-adulCsurvival = 0.19). The mean of such a geometric distribution is theinverse of its parameter, the death rate, d. The mean adult age is thus 7 plus (lId), or 12 years, which is thus the generation time for population genetic considerations. If there were no human harvest of Colorado squawfish, d would be lower and the generation time longer. For example with d = 0.10, the generation time would be 17 years. 1.15 Discussion of Demography The foregoing analysis, based on animal age as a key independent variable, worked through the largest available (i.e., computer readable) block of data to arrive at a self-consistent picture of the demography and life history of the Colorado squawfish. From the foundation of this demography, further modeling forays can be taken into the aspects of ecology and river geometry that threaten the future existence of the Colorado squawfish. It would be instructive to perform an analysis based on size rather than age to see if the same patterns emerge. 2.1 Introduction to Genetics Genetics plays three different roles in a population viability analysis. First, genetic differences (consistent across the genome) can help to delineate separate population subregions, each of which is considered to have unique value and each of which must have independent viability to be considered recovered. Second, genetic analysis can sometimes be used to infer important dynamical parameters, such as dispersal rates of individuals between local populations. Third, an erosion of genetic variability in local populations, or in the regional population, can increase extinction probabilities and can even lead populations into what Qilpin and Soule (1986) have termed "extinction vortices," such as a case wherein environmental stochasticity exacerbates inbreedIng and inbreeding depression makes the population more susceptible to environmental stochasticity. 2.2 Current Knowledge of Squawfish Genetics