An Optimal Control Framework for Multi‐Species Harvesting in the Southern Black Sea

ABSTRACT

The management of marine fisheries requires balancing ecological sustainability with economic profitability, particularly in ecosystems vulnerable to overexploitation. This study develops a multi‐species optimal control modeling framework for the southern Black Sea, focusing on three key species: horse mackerel ( Trachurus mediterraneus ) as prey, and Atlantic bonito ( Sarda sarda ) and bluefish ( Pomatomus saltatrix ) as non‐competing predators. The model is formulated as a system of ordinary differential equations with seasonal harvesting restrictions, where the objective functional maximizes discounted net profit. Numerical simulations based on 2008–2022 landing data reveal that the optimal control strategy yields approximately 46% higher discounted net profit than the constant‐harvest baseline while preserving positive and stable population trajectories across all species. An approximate, seasonally averaged control strategy performs comparably, suggesting a more practical alternative for data‐limited fisheries. Cross‐implementation analyses further demonstrate that optimal policies derived from reduced two‐species model structures can substantially underperform when applied to the full three‐species system, highlighting the importance of accounting for key predator interactions in harvest optimization. Sensitivity analyses indicate that the principal management insights are robust to moderate changes in key biological and economic parameters. These findings suggest that coordinated, time‐varying harvesting of interacting stocks, informed by key trophic interactions, can improve economic performance while maintaining viable population dynamics within the model framework.