Comparison between disturbed and undisturbed areas of the Patagonian scallop (Zygochlamys patagonica) fishing ground “Reclutas” in the Argentine Sea

In this study we compare the composition, structure and biomass of the species assemblage in the Patagonian scallop management unit “Reclutas” (39°00′–39°30′S and 55°45′–56°05′W), in areas subjected to fishing effort (FG) and in the exclusion area (REX), between 1998 and 2002. Data obtained during 1995 and previous to the beginning of the scallop fishery are also considered as baseline condition. No differences in species richness or species composition were detected between areas in the study period. Patagonian scallop biomass was always higher at REX, but by-catch biomass was similar in both areas. The kind of analysis made during this study only allowed us to detect differences in the Patagonian scallop biomass between areas during the study period, while by-catch biomass, as a whole, apparently presented no differences between disturbed and undisturbed areas. Nonetheless, ABC curves in FG in 1998 matched with an undisturbed area, but from 2001 they showed a pattern coincident with a moderately disturbed area. In REX, the pattern observed in 1998 was not quite clear, but in 2002, this unfished area matched with and undisturbed area, as expected for an exclusion area. In addition, multidimensional analysis suggested a differentiation between FG and REX after 1998. Based on analysis of species (dis)similarities we could attribute this differentiation to an increase in predators biomass (Volutidae) and the detritivore ofiuroid Ophiactis asperula, a decrease in the fragile species (Sterechinus agassizii) and the target species of the fishery, Zygochlamys patagonica, and the founding of Chaetopterus variopedatus and Idanthyrsus armatus tubes in the fishing ground.