Using Pontryagin's maximum principle, the optimal death strategy that maximizes the total reproduction of a population, which has the density dependent growth rate and the weight dependent reproduction, is investigated. As the result, it is shown that the optimal survival curve has a critical age, before which the mortality takes the highest admissible value and after which the lowest. In a population with this optimal death strategy, the change of resource level affects the length of the stage of high mortality. The switching age is explicitly calculated in a special case with a simple growth rate function and a simple weight dependence of reproduction. The average value of mortality or growth coefficient through the prereproductive stages are calculated and compared with the Le Cren's data, where trout was reared in varying resource levels.
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