Optimal Management of the Baltic Sea Fishery Under Climate Change: An Ecological-Economic Age-Structured Multi-Species Model Analysis

Abstract only.To achieve sustainable fisheries, ecosystem-based fisheries management\ud yields increasing attention. However, so far mainly single-species models\ud are used to develop management advice, not accounting for species\ud interaction. In particular many traditional fisheries economic models have\ud been criticized by biologists, especially if results were gained by rather\ud simple biomass models. Therefore, age-structured ecological-economic\ud models have the potential to foster communication between economists and\ud stock assessment scientists. Biological assessment models, on the other\ud hand, rarely explicitly take into account economic considerations. To\ud overcome these shortcomings, we develop an age-structured, multi-species\ud fishery model that incorporates dominant biological interactions like\ud predation via multi-species models. Given the ultimate goal of providing\ud most appropriate management advice for the operating fishery we adopt an\ud economic objective function (present value of resource rents) and\ud determine optimal management. In the Baltic Sea, the stock dynamics of\ud the 3 most important fish species cod, herring and sprat are strongly\ud interlinked by predation as well as competition. Accordingly, we develop a\ud biological multi-species model that can be used to predict coupled stock\ud dynamics under different management scenarios. We include\ud environmentally-sensitive stock-recruitment functions in the model and\ud simulate stock trajectories for a period of 30 years under an assumed\ud climate change scenario. By further adding an age-structured ecologicaleconomic\ud model, we derive the optimal multi-species management strategy\ud in terms of net present value of resource rents. We evaluate the cost (as\ud deviation from the optimum) of alternative management scenarios, e.g.\ud when introducing side-conditions on minimum stock sizes or maximum\ud year-to-year changes in the fishery. Specifically, we evaluate the economic\ud and ecological sensibility of the present long-term management plan for\ud Baltic cod in a multi-species framework