Stock assessment and risk analysis for the South Atlantic population of albacore Thunnus alalunga using an age-structured production model

The South Atlantic population of albacore is assessed by means of an (observation-error) age-structured production model. Relative abundance (cpue) series up to 1993 from the Republic of China, Japan and South Africa are used in the model-fitting process. Coefficients of variation and confidence intervals for the estimates are obtained using the (conditioned) parametric bootstrap and the percentile methods respectively. The sensitivity of the results to violation of some of the assumptions made by the model, changes to the values of its input parameters, and changes to the abundance series used in the model-fitting process are examined. The results of the age-structured production model are contrasted with those of an age-aggregated observation-error estimator and those of a Bayesian estimator which allows also for fluctuations in recruitment. The resource was estimated to be markedly depleted — to probably slightly above 20% of its pre-exploitation level expressed in terms of exploitable biomass — and to...