Long-term population structure, mortality and modeling of a tropical multi-fleet fishery:: the red grouper Epinephelus morio of the Campeche Bank, Gulf of Mexico

This paper develops a precautionary bioeconomic approach for the red grouper (Epinephelus morio) multi-fleet fishery in the Campeche Bank, Gulf of Mexico, based on a long-term analysis covering the years 1980-2000. Population structure was estimated through commercial sampling of the three fishing fleets participating in the fishery: two Mexican (one artisanal and the other industrial) and one Cuban (industrial). Length frequency distributions (LFDs) did not show significant differences between the Mexican industrial and the Cuban fleets, but differed from those of the artisanal fishery, which targets smaller individuals. The lack of differences in the LFDs between years suggests that the population structure was stable during the last two decades. However, the instantaneous coefficient of total mortality Z, estimated through length-converted catch curves, significantly increased during the 21-year period of analysis, being in average 1.22 times higher in 2000 than in 1980. Annual estimates of yield and Z, together with unit costs of effort and ex-vessel prices, were used as inputs to build a bioeconomic yield-mortality model. A sensitivity analysis was performed under three scenarios of natural mortality M (0.16, 0.25 and 0.35 per year). The yield at maximum economic yield (Y-MEY) and the associated mortality levels Z(MEY) and F-MEY were always the most conservative bioeconomic reference points (BRPs). The yield at maximum biological production (Y-MBP), Y-MEY and mortality-related BRPs were substantially lower than those based on maximum sustainable yield (MSY), thus constituting useful target BRPs for precautionary management. The bootstrap method used for determining the uncertainty associated at BRPs, shows that the best targets BRPs were Y-MEY and Y-MBP, whereas MSY is confirmed as a risky and limit BRP. A simple approach to the formulation of risk-averse management strategies was explored using the percentiles of cumulative distributions of MSY, Y-MBP and Y-MEY estimates generated from bootstrap against Z. We conclude that the red grouper fishery at Campeche Bank is overexploited and that immediate management actions are needed to prevent stock collapse. (C) 2003 Elsevier B.V. All rights reserved.