Optimal Harvesting of Age-structured Fish Populations

Abstract

A generic age-structured model for optimal harvesting is formulated and analyzed. The aim is to maximize utility from the harvest, net of effort cost. Yield depends on effort, catchability, and population age structure. The recruitment function is nonlinear. The age-structured model can be viewed as a generalization of the biomass approach. Comparison with the biomass model shows that the age-structured information influences the optimal steady-state population and harvest and the qualitative features of optimal transition. Pulse fishing or interior limit cycles are possible, but the optimal solution may represent a smooth, sustainable harvest even when the model is linear in effort. Linearity assumptions do not guarantee the optimality of constant escapement. If the age distribution is dominated by young age classes, the optimal yield may be lower with higher biomass. With knife-edge selectivity, the optimal steady state may become independent of the interest rate.Fisheries, bioeconomics, optimal harvesting, age-structured models, pulse fishing, Beverton-Holt population model, endogenous recruitment., Environmental Economics and Policy, Production Economics, Public Economics, Research Methods/ Statistical Methods, Q22, Q57, C61,