Abstract

Fishing pressure has effects on life-history characteristics and population’s parameters of target species. Some of these effects can be seen on size distributions of the populations. The oyster Crassostrea virginica is an important fishing resource at the Gulf of Mexico coast. The objective of this study was to document historic variations on size of this species at the coastal lagoon of the Natural Reserve of La Mancha. T o reach that goal, a reconstruction of the size structure was made from shells found on modern and ancient middens, which have been built as the result of fishery. Main length of shells was measured and compared between an ancient shell midden on the recent wave-cut platform of the beach Playa Paraíso, a contemporary shell midden on the lagoon shore and living oysters from the same lagoon. A Chi-square test was conducted in order to compare size distributions. Comparison between contemporary and 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 differ 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. It could be an evidence of fishing impacts, reflecting changes on the resource availability as a consequence of depletion of the most valuable size classes because of the more intensive exploitation by contemporary fishermen. However, more exhaustive and extensive studies most be done to obtain conclusive information.

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