Estimates of large-scale purse- seine, baitboat and longline fishing capacity in the Atlantic Ocean: an analysis based on a stock assessment of bigeye tuna

摘要

The Data Envelopment Analysis (DEA) approach for estimating fishing capacity cannot be applied effectively to tuna fisheries in the Atlantic Ocean because the available information is highly aggregated, and therefore inadequate for that purpose. Thispaper presents an alternative approach based on the traditional definition of fishing capacity, for which capacity is a hypothetical maximum yield that can be produced at a point in time, given the capital stock, regulations, current technology and resource abundance. The estimates of capacity obtained are based on inputs and outputs from a stock assessment of Atlantic bigeye tuna (Thunnus obesus) that incorporates information about age-specific selectivity and time trends in fishing efficiency. An algorithm is used to infer the potential magnitude of catches for a fishery in a given time period, assuming that the fishing mortality could be as high as the values estimated for neighbouring time periods. These are then used to infer, on the basis of theassessment results, the output capacity (in tonnes) for each fishery and for all fisheries combined. The results obtained suggest that the output capacity has exceeded the stock's potential long-term productivity since about 1992. These results are preliminary, however, as the robustness of the method should be tested, especially with regard to the level of aggregation used in the stock assessment (i.e. the number of fleets examined, the time steps used, etc.).