An Exponential Surplus-Yield Model for Optimizing Exploited Fish Populations

A surplus-yield model of fishery dynamics which assumes the Gompertz growth function is developed, resulting in an implied exponential relationship between catch per unit effort and fishing effort, and in an asymmetrical yield curve. A maximum sustainable yield, predicted by the exponential model, is obtained from a population size which is about 37% of the environmentally limited maximum size. Three methods for estimating the parameters of the exponential model, adapted from those used for the linear model of Schaefer (1954, 1957), are presented. The exponential model is compared with the linear model using examples of the fisheries for the California sardine, Sardinops caerulea (Girard), and yellowfin tuna, Thunnus albacares (Bonnaterre) of the eastern tropical Pacific and western Atlantic Oceans. Management implications are discussed.