Effects of human activities on long-term trends in sandy beach populations:the wedge clam Donax hanleyanus in Uruguay

Abstract

A long-term analysis of the structure of a bivalve population consisting of the wedge clam Donax hanleyanus is described for an exposed temperate sandy beach of Uruguay. The potential effects of human harvesting on the sympatric bivalve Mesodesma mactroides (yellow clam) and of salinity were analyzed through time and space (longshore variation). Inter-and intra-annual fluctuations of the different population components (recruits, juveniles and adults) were detected. D. hanleyanus showed uneven periods of abundance, with the occurrence of peaks of different magnitude that appeared related to fluctuations in the fishing effort targeting on the yellow clam. D. hanlepanus showed a marked longshore variability in population structure and abundance along the 22 km of sandy beach sampled Spatial variations in salinity and also in the amount of fishing effort exerted on Ad. mactroides seem to be key factors in explaining t h ~s variation. This study suggests that further research on sandy beach populations should include human activities as important factors affecting long-term trends.