Evaluación de la polaca (Micromesistius australis) del Atlántico sudoccidental, período 1987-1999.
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Taking into account the commercial catches by the Argentine fleet and other fleets that operated around Malvinas Islands (SW Atlantic) in the 1987-1999 period, the current state of southern blue whiting (Micromesistius australis) is assessed. A sequential analysis (Cohort Analysis) tuned, in an ADAPT conceptual framework with six independent indices of abundance, was performed for the southern blue whiting stock of the SW Atlantic. Commercial catch data of the Argentinian fleet and other fleets that operate around Malvinas Islands were used.The indices included catch per unit of effort of different fleets and data from Argentine-British research surveys. The analysis showed that the decreasing trend in biomass observed in previous studies went on during the last years. At the beginning of 1999, the spawning biomass was estimated at 518,000 tons or 34. of the unexploited spawning stock. Recruitment also showed a decreasing trend, followed by stabilization. The current instantaneous fishing mortality rate (F99) was estimated at 0.15 and the exploitation rate at 0.5, which is a rather high value. The future abundance of the stock was modeled to meet three different management targets in the long term:(1) to maintain the spawning biomass above 30. of the virgin spawning biomass with an associated risk not higher than 10. ,(2) to maintain the spawning biomass above 20. of the virgin spawning biomass with a risk not higher than 10. , and 3 to maintain biomass at the current level.F for the three targets were 0.085, 0.15 and 0.10, respectively. The corresponding biologically acceptable catches for the year 2000 would be 47,000 t, 76,000 t and 54,000 t. Only in the first case a slight long-term recovery was predicted: 8. in total biomass and 12. in spawning biomass. For the second modeled target, that is coincident with the current F (0.15), a long term reduction of 21. and 26. in total and spawning biomass were projected. In case (3), provided that recruitment is kept at the level observed in the last decade, no significant changes in abundance were predicted.