Natural stocks of the scallop Argopecten circularis, and relationships with the galateid crab Pleuroncodes planipes in the pacific coast of Baja California Sur, Mexico

New data have been obtained concerning the transportation and probable dispersion of the mollusc Argopecten circularis, by the pelagic red "crab" Pleuroncodes planipes. The relation of this Anomuran crab with natural beds of A. circularis implanted in Magdalena Bay and over the continental shelf of Baja California Sur, and its seasonal abundance, were studied on the basis of material collected with fishing nets of different lengths. The most significative variation in the abundance of P. planipes was observed in the range of 0-50 m depth, which corresponds to the migration cycle of the species during the reproductive period. 82 % of P. planipes were observed with juveniles of A. circularis over the chelipeds. The average size of P. planipes and A. circularis were 52.1 mm and 3.5 mm (largest diameter), respectively, with the size of the mollusc ranging from 8.5 mm to 1.0 mm. Biomass of A. circularis oscillated from 10.6 kg.ha^-1 (15 m deep) and 0.9 kg. ha^-1 (29 m deep). Both populations were collected over muddy-sand bottoms mixed with crushed shell, at temperatures between 14.0 to 15.8° C and salinity around 35 ‰. The establishment of exploitable banks of A. circularis in Magdalena Bay is linked undoubtedly to the recruitment period of this species which coincides with the migratory cyle of P. planipes, induced by the presence of cold waters from the California current.