Abstract

In the tropics, spawning aggregations represent ideal opportunities to target cornmercially important fishes, to the level that intense and effective fishing can eliminate much of the population. The commercially important Nassau grouper forms large seasonal spawning aggregations at specific locations along the coral reefs of the westem Atlantic and Caribbean. In the Mexican Caribbean, the effects of the gillnet fishery on the Nassau grouper, taken during its annual aggregations, were analyzed from 1991 to 1997. Fishing effects on grouper mean size and sex ratios were not clear. Mean size for both sexes decreased and later increased apparently inresponse to both fishing and variable recruitment. The size-selectivity of gillnets against both small and large individuals may have masked the impact of fishing on population size structure. The sex ratio was female-biasedfor the overall penod and remained close to unity for each individual reproductive season, but sex ratio may not be a good indicator of exploitationin this primarily gonochoristic species. However, landings substantially declined and the aggregation disappeared from its traditional site; both of these are suggestive of serious problems. Although several factors could be involved, fishing is strongly implicated as probable cause for these changes. Fishery managers seriously need to consider the establishment of marine reserves as an altemative to protect all the known Nassau grouper aggregations along the southem coast of QUintana Roo, Mexico.

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