Optimal fishing policy for two species in a three-species predator-prey model: The case of capelin, cod and juvenile herring in the Barents Sea

Abstract

This paper presents a management model for the Barents Sea capelin and cod fisheries including juvenile herring in the biological model as the young herring influences the cod-capelin system. The objective of the study is to balance model-complexity of biology and economics when investigating possible optimal catch strategies given that one aims to maximize economic rent in the fishery. The three species constitute a highly dynamic system, also because prey-predation relations are functions of ages within each stock. A top-down approach is employed and the biological growth equations relate to stock biomass estimates. Economic relations are based on empirical data and previous studies. Optimal fishing strategies are identified by employing a numerical feedback rule for optimal fishing through dynamic programming. The feedback rule suggests that previous TAC (total allowable catch) levels on average have been too large for both capelin and cod over the past 30 years, according to the management objectives assumed in the study. Moreover, presence of some herring in the system is important for the economic yield although the herring fishery is closed. This indicates that a focus only on the capelin-predator role of herring is too narrow, as herring is also an important prey for cod.