The approach to optimal management targets under climate change and challenges faced by fisheries

Long-term fishery management targets are typically defined in terms of optimal equilibrium productions (harvests). However, reaching the optimal target is complicated by the fact that most fisheries must pass through a stock-drawdown phase (non-equilibrium harvests), often under shifting socioeconomic and changing climatic conditions. During stock-drawdown phase when initial biomass is higher than the optimal biomass that produces optimal yield, the difference between these two biomass levels (defined as “ endowment” ) is progressively depleted. In this phase, both catch and fishing effort often exceed levels consistent with long-term optimal harvests, leading to substantial and persistent excess capacity. Existing dynamic bioeconomic models largely focus on optimal equilibrium and open access outcomes, providing limited guidance on the length of time it takes to reach optimal targets and how excess capacity emerges during the transition. This study develops a discrete-time dynamic bioeconomic model that explicitly incorporates both drawdown harvests and equilibrium harvests. For a given fishery, the model quantifies important fisheries dynamics, including: (1) the length of time it takes to reach optimal management targets (MSY or MEY); (2) the externality such as the magnitude (“stickiness”) and persistence of excess capacity; and (3) the potential time to stock collapse in the absence of management. Through scenario analysis, the model estimates the impacts on fishery dynamics (including economic performance) arising from climate-induced productivity declines and challenges faced by fisheries, such as nonlinear catchability driven by technological improvements, market-driven fluctuations in fish prices and harvesting costs, and local stewardship in effort controls. This model presents an operational and tractable framework for proactive fishery management.