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• 1. [Article] Generalization of Age-Structured Models in Theory and Practice

  A generalization of the harvesting functions and the stock updating functions in age-structured bioeconomic models is outlined. Using this generalization everything from completely uniformly distributed ...

  Citation × Citation Citation Abstract Copy Title: Generalization of Age-Structured Models in Theory and Practice Author: Steinshamn, Stein Ivar A generalization of the harvesting functions and the stock updating functions in age-structured bioeconomic models is outlined. Using this generalization everything from completely uniformly distributed fish to extreme schooling is taken care of. The classical Beverton-Holt model comes out as a special case of the generalized model. Both the theoretical outline as well as practical numerical examples are provided, and the generalization can be applied both for simulation as well as optimization purposes given appropriate software. Here we apply advanced non-linear programming to maximize the net present value in a bioeconomic setting where the new updating and harvesting functions are used as constraints. This is possible thanks to new software, such as KNITRO, for solving highly nonlinear problems. Applications of this generalized model produce interesting new results. One such practical result is that pulse fishing seems to become less and less economically profitable as we move from uniformly distributed fish to schooling species. The main reason why pulse fishing cease to be optimal in schooling fisheries, is that the economies of scale present in search fisheries gradually disappear when we move from search fisheries to schooling fisheries. This may have important implications for how fish stocks ought to be managed in the future, especially with respect to total allowable catches based on bioeconomic criteria. Title: Generalization of Age-Structured Models in Theory and Practice Author: Steinshamn, Stein Ivar A generalization of the harvesting functions and the stock updating functions in age-structured bioeconomic models is outlined. Using this generalization everything from completely uniformly distributed fish to extreme schooling is taken care of. The classical Beverton-Holt model comes out as a special case of the generalized model. Both the theoretical outline as well as practical numerical examples are provided, and the generalization can be applied both for simulation as well as optimization purposes given appropriate software. Here we apply advanced non-linear programming to maximize the net present value in a bioeconomic setting where the new updating and harvesting functions are used as constraints. This is possible thanks to new software, such as KNITRO, for solving highly nonlinear problems. Applications of this generalized model produce interesting new results. One such practical result is that pulse fishing seems to become less and less economically profitable as we move from uniformly distributed fish to schooling species. The main reason why pulse fishing cease to be optimal in schooling fisheries, is that the economies of scale present in search fisheries gradually disappear when we move from search fisheries to schooling fisheries. This may have important implications for how fish stocks ought to be managed in the future, especially with respect to total allowable catches based on bioeconomic criteria. Close

• 2. [Article] Viability of Transboundary Fisheries and International Quota Sharing

  This paper examines the viability of the management of a transboundary resource, the Bay of Biscay anchovy (Engraulis encrasicolus L.). A deterministic model is used to simulate the anchovy dynamics, with ...

  Citation × Citation Citation Abstract Copy Title: Viability of Transboundary Fisheries and International Quota Sharing Author: Curtin, Richard, Martinet, Vincent This paper examines the viability of the management of a transboundary resource, the Bay of Biscay anchovy (Engraulis encrasicolus L.). A deterministic model is used to simulate the anchovy dynamics, with the fish stock consisting of two age groups, “young" and “old", while recruitment follows a Beverton Holt pattern. Two countries, France and Spain, harvest the resource, with two different types of gear, the purse seiner for Spain and the pelagic trawler for France. These technologies impact the different age-groups of anchovy at differing rates. A regulatory agency defines an annual fishing quota and its allocation between the two countries, with the aim of sustainability in the overall allocation design. A set of constraints is defined to describe the sustainability of the system which encompasses the economic, ecological and social aspects of the fishery. The optimal harvest share between the two countries is found and a number of scenarios are then tested in relation to their ability to remain within the set of constraints, or viability kernel. Other scenarios, including the historical trajectory, the optimal harvest share trajectory and the minimum time of crisis trajectory, are examined. Title: Viability of Transboundary Fisheries and International Quota Sharing Author: Curtin, Richard, Martinet, Vincent This paper examines the viability of the management of a transboundary resource, the Bay of Biscay anchovy (Engraulis encrasicolus L.). A deterministic model is used to simulate the anchovy dynamics, with the fish stock consisting of two age groups, “young" and “old", while recruitment follows a Beverton Holt pattern. Two countries, France and Spain, harvest the resource, with two different types of gear, the purse seiner for Spain and the pelagic trawler for France. These technologies impact the different age-groups of anchovy at differing rates. A regulatory agency defines an annual fishing quota and its allocation between the two countries, with the aim of sustainability in the overall allocation design. A set of constraints is defined to describe the sustainability of the system which encompasses the economic, ecological and social aspects of the fishery. The optimal harvest share between the two countries is found and a number of scenarios are then tested in relation to their ability to remain within the set of constraints, or viability kernel. Other scenarios, including the historical trajectory, the optimal harvest share trajectory and the minimum time of crisis trajectory, are examined. Close