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<br />Squawfish Population Viability Analysis --July 1993 <br /> <br />Page 38 <br /> <br />Fundamentally, this could lead to the kind of extinction vortex that Gilpin <br />and Soule (1986) delineate in their paper on population viability analysis. <br />It must be emphasized that this argument is speculative and is not quantified <br />as to its degree of threat. Nonetheless, it is consistent with the data <br />available to us. <br /> <br /> <br />Size Distribution of <br />Adult Squawfish <br /> <br />Individual Growth Rate <br /> <br /> <br />Harvest <br /> <br />Allee Effects <br /> <br />Flow Modification <br /> <br />Resource. Depletion <br /> <br />Figure 3.7. A causal loop structure to show the effect of a shift of size <br />distribution on the abundance of adult Colorado squawfish. <br /> <br />3.6 Trend Analysis <br /> <br />If one had good census data on closed populations of Colorado squawfish, <br />one could perform a trend analysis, basically a regression of populations <br />size on time. Such data are have been used for grizzly bears, desert <br />tortoises and for Morro Bay Kangaroo Rats. They are not available for the <br />Colorado squawfish, mainly due to the long life of the fish, its movement <br />and due to the errors and bias associated with sampling. Nonetheless, there <br />is nothing in any of the data to suggest that one would expect to find a <br />downward trend in the Green River portion of the Colorado squawfish' s <br />range. If the actual A were 0.98 (2% negative growth), the population <br />would be today almost half the size it was in 1967. This seems not to be <br />the case. Indeed, everything suggests a reduced but stable population size. <br />