Abstract
A modification of Schaefer's surplus yield model that takes into account variations in year-class strength is introduced. Expressions for long-term equilibrium yield under assumptions of both linear and density-dependent recruitment are derived and compared. Strategies for exploitation under nonequilibrium conditions are discussed and equations derived. The model is fitted to a stock of mackerel and projections for the stock biomass in 1980 under various levels of fishing mortality are made. Key words: mathematical model, fisheries management, stock biomass projections

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