EFFECTS OF THE OVER HARVESTING ON AN EDIBLE COCKLE (Cerastoderma edule Linaeus, 1758) POPULATION ON A SOUTHERN EUROPEAN ESTUARY

摘要

Estuaries are among the most productive habitats in the world, providing important functions and goods. Among these supplies, shellfish is an important economic resource. In Portugal (southern Europe), the edible cockle (Cerastoderma edule) is a popular food item for humans, and their populations are submitted to hard harvesting pressures both by traditional methods and for recreational purposes. The population of C. edule was studied for 18 months (2005-2006) in an intertidal sand flat of the Mondego estuary (central Portugal). In the beginning of 2005, C. edule population showed high abundance and biomass. During the summer of that year, human harvesting increased considerably, resulting in significant changes in the population structure, dynamics and secondary production. An estimate on the harvest for the studied area resulted in amounts of 4 to 7 ton shell free dry weight for 3.82 ha area. As a result, adults practically disappeared, the population structure was disrupted and the production decreased to negative values due to over-harvesting.