Negative shocks in an age-structured bioeconomic model and how to deal with them

Abstract

We consider an age-structured bioeconomic model of a fishery where periodic negative shocks affect recruitment and somatic growth. The model is relevant for fish stocks that are subject to environmentally driven events such as diseases, match-mismatch relationships between plankton blooms and spawning, or recruitment failure. The nature of the optimal fishing strategy is pulse fishing. We vary the period and severity of the shocks to investigate how the optimal management scheme adapts and what factors trigger fishing pulses. Two principles largely govern fishing. The first is to harvest when the number of small cohorts in the stock is minimal. Small cohorts emerge from negative shocks to recruitment. The second principle is to fish when shocks to growth have the least impact on the weight distribution in the stock. Furthermore, we consider how net present value and total catches depend on the period of shocks and the average impact (impact times frequency). In the case of average impacts, we observe close to linear relationships that make reasonable generalizations of our results, for example to different impact levels, viable. The structure of predictable negative shocks in the model is a significant simplification but allows us to crystallize drivers of adaptations in the fishing strategy.