Disappearance of a Nassau grouper spawning aggregation off the southern Mexican Caribbean coast

Abstract

A Nassau grouper spawning aggregation formed in large numbers (e.g. 1000 to 15000 ind.) for more than 50 yr at the traditional aggregation site off Mahahual, Quintana Roo, Mexico (eastern Yucatan Peninsula). However, in the early 1990s the aggregation ceased forming at the site, and only small aggregations were found south of the site (1 to 2 km) moving northward along the fore reef. The spawning aggregation progressively disappeared, and in 1996 no aggregation formed even in areas adjacent to the site. Changes in grouper mean total length, size-frequency dis- tribution and sex ratios analyzed from the commercial catch (taken from the migrating aggregation), showed that mean body size fluctuated and that the sex ratio was female-biased. The grouper aggre- gation showed evidence of overexploitation in terms of disappearance, reduction in number and fluctuations in size; however, the latter may be a recruitment effect. Fishery management and con- servation alternatives, through the implementation of a network of no-take marine reserves and a total fishing ban, are necessary for protecting the Nassau grouper and other aggregating reef fishes, not only in the Mexican Caribbean Sea but also along the Mesoamerican Barrier Reef System.