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<br />Squawfish Population Viability Analysis --July 1993 <br /> <br />Page 15 <br /> <br /> <br /> <br />10 <br />9 <br />8 <br /> <br />o 7 <br />.<6 <br />5 <br />4 <br />3 <br />2 <br />1 <br /> <br />survival <br /> <br />Year T <br /> <br />YearT+l <br /> <br />Figure 1.6 <br /> <br />1.13 Estimation of Per Year Adult Death Rate <br /> <br />Assume that the Colorado squawfish population size in the Green and <br />Yampa is roughly constant (A = 1.00). (It is not necessarily to assume that <br />the population size is at carrying capacity, K). Assume also that the age <br />structure is at equilibrium (is stationary). This seems reasonable given the <br />general stability in the length distribution from 1981 to 1989. If these <br />assumptions are true (or are close to being true) then the observed size <br />distribution is. governed by the death rate (or the survivorship curve) of the <br />adults. In fact, if weight is converted to age based on 15 rom of growth <br />per year for adults, the distribution in the Figure 1.7, below, is the <br />survivorship curve for adults. The constant slope (explaining a <br />surprisingly large 93% of the variance) is -.201, whose antilog is 0.81. <br />Thus, the per year survival rate of adults is 81 %. This rate includes human <br />induced mortality, but it is not confounded by tag loss or any other such <br />consideration. Rich Valdez estimates that researchers can cause 2% adult <br />mortality per year and in some locales of heavy sport fishing the Colorado <br />squawfish mortality could be as high as 10% per year. <br />