IS f0.1 an appropriate harvesting strategy for the cape hakes?

Abstract

Time-series of catch per unit effort (CPUE) for the Cape hake stocks demarcated by ICSEAF in the Benguela region show steady declines until the late 1970s, followed by slowly increasing trends once catch levels were reduced. Analysis of these data by means of a dynamic form of the production model is discussed briefly, and it is shown that sustainable-yield-determining parameters could not be estimated with any reasonable degree of precision prior to the data contrast provided by the change in CPUE trends in the late 1970s. In general, an f0.1 harvesting strategy has been applied to allow recovery of these resources from their depleted levels of the late 1970s. Analysis indicates that, except for ICSEAF Division 1.6, these stocks have now reached their equilibrium biomass levels under such a strategy. The question thus arises whether f0.1 is the appropriate long-term strategy, i.e. to what extent current catches (or catch level increments) should be “traded” for future CPUE improvements. This is examined by means of Clark’s bioeconomic model, which indicates that strategies corresponding to a lower fishing effort than that for f0.1 are economically more advantageous. The precision with which the shape of the surplus production function can be estimated is poor; the implications of this for the choice of an appropriate harvesting strategy are discussed briefly. It is suggested that, as an initial amended strategy for most of these stocks, catch levels should be pegged at their f0.1 equilibrium levels once the corresponding biomass level is exceeded. However, for Division 1.6, a change from an f0.1 to an f0.2 strategy is proposed. The economic advantages of this strategy are illustrated. © 1987 Taylor & Francis Group, LLC.