Density patterns and age structure of the queen conch ( Aliger gigas ) in a coral reef lagoon in the Mexican Caribbean

The queen conch ( Aliger gigas ) is one of the most important fishery resources in the Caribbean; however, its populations have declined markedly as a result of overexploitation. This study evaluated the population density and size structure of the species within the Banco Chinchorro Biosphere Reserve, Mexico, during 2015, 2016, and 2018, encompassing the final phase of a 5-year total fishing closure and the period immediately following its termination. A total of 35 sampling stations were distributed across six zones of the reef lagoon. At each station, five circular surveys with an 8 m radius were conducted during each sampling campaign. The highest densities were observed in the Central and Southern Leeward zones, whereas the lowest occurred in the Southern Windward zone. Population density increased during the fishing closure and reached its maximum in 2016, suggesting a partial recovery associated with reduced fishing pressure. Despite this increase, the population was dominated by juveniles and subadults, while sexually mature individuals represented only a small proportion of the stock. Spatial variation in size distribution revealed distinct areas functioning as recruitment, growth, and potentially reproductive habitats within the reserve. Conversely, the scarcity of large individuals suggests the long-term effects of selective harvesting on the adult component of the population. Comparison between siphonal length and lip thickness indicated that only 6.2% of individuals simultaneously met the legal minimum harvest size and a morphological criterion associated with sexual maturity, whereas 10.03% attained the minimum legal size without having reached reproductive maturity. These findings indicate that siphonal length alone may not adequately protect the reproductive stock of A. gigas . Accordingly, size-based management regulations should be complemented by biological indicators of maturity, such as lip thickness, to enhance conservation measures and promote the sustainable management of queen conch populations in Banco Chinchorro. Collectively, these findings provide a robust scientific baseline for future conservation and management actions aimed at safeguarding reproductive stocks and ensuring the long-term sustainability of A. gigas fisheries.