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Squawfish Population Viability Analysis --July 1993 Page 43 squawfish dynamics. Based on considerable experience with spatial phenomenon, I guess that source/sink dynamics are possible, which means that the entire Upper Basin is one interactive dynamic system, incapable of single-unit or subdivided recovery. 5. The Final PV A Model. I constructed a grand computer simulation model to answer the question of time to extinction. This model ignored age-structure and only counted adults. The model ignored genetics and possible inbreeding depression. The model ignored demographic stochasticity. The model ignored juvenile movement and thus the Minimum Viable Length issue just discussed. The model assumed positive local (based on 20 mile river segments) carrying capacities, local A'S greater than 1.0 and diffusional movement of adults between local populations. Diffusion movement has the character that population density differences are evened out with time. Moderate to very high environmental stochasticity could be applied to local populations. The environmental stochasticity could be partially correleted along rivers. Over a substantial range of parameter values, this model never predicted extinction. Mean time to extinction was arbitrarily long. This conclusion was not sensitive to the actual parameters, so long as they satisfied the requirements listed above. The model leads to the conclusion that the Colorado squawfish is viable. The real question is of the structural stability of the model. What if A'S are less than l.oo? What if the environment is perfectly correlated? What happens if parts of the system are isolated from other parts? What happens if the fundamental ecology of the Colorado squawfish is deteriorating because of the increasing densities of exotics? Well, with all of these eventualities, the Colorado squawfish could be driven extinct. Acknowledgements I thank Chuck McAda, Pat Nelson, Doug Osmundson, Tom Dowling, Harold Tyus, John Hawkins and Ed Wick for discussiqn and insights. However, the interpretations from the data and their suggestions are my own. I thank Chuck McAda for providing data in computer-readable form.