Abstract

Fishing pressure has effects on life-history characteristics and population parameters of target species. Some of these effects may be evident on size distributions of the populations. The oyster Crassostrea virginica is an important fishing resource along the Gulf of Mexico coast. The objective of this study was to document historic variations in size of this species at the coastal lagoon of the La Mancha Natural Reserve. A reconstruction of the size structure was made from shells found in modern and ancient middens built as the result of the fishery. Main length of shells from an ancient shell midden on the recent wave-cut foredune at Playa Paraíso beach, a contemporary shell midden on the lagoon shore, and from living oysters from the same lagoon were measured, and their size distributions compared by means Chi-square test. Comparison between the contemporary and the ancient midden yielded a significant difference (p < 0.05), showing a displacement of the shell length towards lower values in the modern shell midden. Also, size distribution of living oysters differed significantly (p < 0.05) from those from modern and pre-Hispanic middens, showing a greater frequency of lower size values and the disappearance of the high size classes. These results may indicate changes in resource availability as a consequence of depletion of the most valuable size classes because of a more intensive exploitation by contemporary fishermen. However, more exhaustive and extensive studies must be done to obtain conclusive information.

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