Modeling Long-Term Fluctuations in Fish Stocks

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Abstract
Many pelagic fish stocks change rapidly in abundance, with intervening periods of about 50 years. The physical environment does not display such abrupt changes but has a variance that increases with time. A simple population model with multiple equilibrium states exhibited the observed behavior when subjected to this type of stochastic variability. The periodicity exhibited by the model is of the same order as the observations. Thus the assumption by fisheries management of a natural persistence in stocks is questionable.