A Fur Seal Population Model Based on Age Structure Data

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Abstract
About 16 000 female fur seals from the Pribilof Islands population were aged in pelagic collections from 1958 through 1974. A simple simulation model of the female population was used to vary population parameters until a minimum chi-square value was achieved for the fit of simulated annual age structures to those observed in the pelagic collection. Population trajectories resulting from either a diminishing reproductive rate or diminishing adult female survival rate approximated estimated pup population sizes, which were not used in developing the model, except that a subset of five observations was used to constrain model trajectories to the general neighborhood of the observed pup populations. The main finding of the study was that adult female survival rates varied sharply during the 1964 through 1974 period, after the major period of harvests of female fur seals. Further study of the age structure data may thus be useful in evaluating the poorly understood long-term reduction in abundance of Pribilof fur seals.

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