Search

Search Results

• 1. [Article] Growth Overfishing

  Growth overfishing squanders large parts of the potential rents in fisheries. Many of today’s fisheries are characterized by a severely truncated age-distribution, which in addition may have irreversible ...

  Citation × Citation Citation Abstract Copy Title: Growth Overfishing Author: Diekert, Florian K. Growth overfishing squanders large parts of the potential rents in fisheries. Many of today’s fisheries are characterized by a severely truncated age-distribution, which in addition may have irreversible ecological consequences. Nevertheless, the implications of age-differentiated harvesting for management have received surprisingly little attention in the literature. In the present paper, optimal and non-cooperative exploitation paths for a generic age-distributed resource are derived. We show that, in the case of perfect selectivity, competition between two agents is sufficient to dissipate all rents. Akin to the classical Bertrand competition in prices, each agent has an incentive to target fish at a younger age. That is, the “race to fish” extends to the dimension of age. This observation is crucial also with respect to management: Individual quotas are not able to restore efficiency unless accompanied by gear regulation. Moreover, it turns out that quotas specified in terms of numbers are far superior to those specified in terms of volume or value. Title: Growth Overfishing Author: Diekert, Florian K. Growth overfishing squanders large parts of the potential rents in fisheries. Many of today’s fisheries are characterized by a severely truncated age-distribution, which in addition may have irreversible ecological consequences. Nevertheless, the implications of age-differentiated harvesting for management have received surprisingly little attention in the literature. In the present paper, optimal and non-cooperative exploitation paths for a generic age-distributed resource are derived. We show that, in the case of perfect selectivity, competition between two agents is sufficient to dissipate all rents. Akin to the classical Bertrand competition in prices, each agent has an incentive to target fish at a younger age. That is, the “race to fish” extends to the dimension of age. This observation is crucial also with respect to management: Individual quotas are not able to restore efficiency unless accompanied by gear regulation. Moreover, it turns out that quotas specified in terms of numbers are far superior to those specified in terms of volume or value. Close

• 2. [Article] Age Structure Metrics for Precautionary Management: Can Simpler Assessment Techniques Save Fish, Time, and Money?

  Stock assessment techniques currently used in the United States are extremely costly to implement, involve significant data requirements, and are inaccessible to all but a few stock assessment scientists. ...

  Citation × Citation Citation Abstract Copy Title: Age Structure Metrics for Precautionary Management: Can Simpler Assessment Techniques Save Fish, Time, and Money? Author: Harte, Michael, Heppell, Selina, Sylvia, Gil, Cusack, Christopher, Larkin, Sherry Stock assessment techniques currently used in the United States are extremely costly to implement, involve significant data requirements, and are inaccessible to all but a few stock assessment scientists. A systematic decrease in fishery yields and the designation of several species as overfished on the west coast of the United States have resulted in stricter protocols regarding sustainable fisheries management and the rebuilding of overfished stocks, including the need to set annual harvest limits for all exploited species. An alternative and simpler approach to stock assessment which could address this need is described and an evaluation framework set up. Although no results have been obtained to date, possible costs and benefits of incorporating this approach into fisheries management are discussed. Title: Age Structure Metrics for Precautionary Management: Can Simpler Assessment Techniques Save Fish, Time, and Money? Author: Harte, Michael, Heppell, Selina, Sylvia, Gil, Cusack, Christopher, Larkin, Sherry Stock assessment techniques currently used in the United States are extremely costly to implement, involve significant data requirements, and are inaccessible to all but a few stock assessment scientists. A systematic decrease in fishery yields and the designation of several species as overfished on the west coast of the United States have resulted in stricter protocols regarding sustainable fisheries management and the rebuilding of overfished stocks, including the need to set annual harvest limits for all exploited species. An alternative and simpler approach to stock assessment which could address this need is described and an evaluation framework set up. Although no results have been obtained to date, possible costs and benefits of incorporating this approach into fisheries management are discussed. Close

• 3. [Article] Simulation Model Evaluation of Some Fisheries Balance Indicators

  Chronic overcapacity has been identified as a major cause of the overfishing of Europe’s fish stocks and the poor economic performance of the European fishing fleets. Mechanisms are needed to ensure that ...

  Citation × Citation Citation Abstract Copy Title: Simulation Model Evaluation of Some Fisheries Balance Indicators Author: Scott, Robert, Sampson, David Chronic overcapacity has been identified as a major cause of the overfishing of Europe’s fish stocks and the poor economic performance of the European fishing fleets. Mechanisms are needed to ensure that the capacity of European fishing fleets remain proportionate to available fish stocks. To that end, the European Commission developed “Guidelines for an improved analysis of the balance between fishing capacity and fishing opportunities”, which specify a minimum set of fleet-based technical, biological, economic, and social indicators that purportedly measure the balance between fishing fleets and fish resources. A bioeconomic simulation model was developed to assist in the evaluation of some of these balance indicators. The model is age-structured, like standard single-species stock assessment models, but accommodates multiple independent fish stocks that are harvested by multiple independent fishing fleets. The fish stocks occupy multiple spatial regions with diffusion of fish between regions. The fishing fleets choose where and how to fish based on anticipated profits. Randomness is included in the simulated system in the annual fish recruitments and their spatial distribution. The model was used to generate a series of balance indicators that were then compared against the true conditions in the simulated fisheries to evaluate whether the indicators provide accurate signals of system status. The simulations showed that randomness in recruitment propagates directly into randomness in the balance indicators implying that it will be difficult to detect meaningful signals from any short time series of balance indicator values. Title: Simulation Model Evaluation of Some Fisheries Balance Indicators Author: Scott, Robert, Sampson, David Chronic overcapacity has been identified as a major cause of the overfishing of Europe’s fish stocks and the poor economic performance of the European fishing fleets. Mechanisms are needed to ensure that the capacity of European fishing fleets remain proportionate to available fish stocks. To that end, the European Commission developed “Guidelines for an improved analysis of the balance between fishing capacity and fishing opportunities”, which specify a minimum set of fleet-based technical, biological, economic, and social indicators that purportedly measure the balance between fishing fleets and fish resources. A bioeconomic simulation model was developed to assist in the evaluation of some of these balance indicators. The model is age-structured, like standard single-species stock assessment models, but accommodates multiple independent fish stocks that are harvested by multiple independent fishing fleets. The fish stocks occupy multiple spatial regions with diffusion of fish between regions. The fishing fleets choose where and how to fish based on anticipated profits. Randomness is included in the simulated system in the annual fish recruitments and their spatial distribution. The model was used to generate a series of balance indicators that were then compared against the true conditions in the simulated fisheries to evaluate whether the indicators provide accurate signals of system status. The simulations showed that randomness in recruitment propagates directly into randomness in the balance indicators implying that it will be difficult to detect meaningful signals from any short time series of balance indicator values. Close