POPULATION-STRUCTURE AND EXPLOITATION OF BOLINUS-BRANDARIS (MOLLUSCA,GASTROPODA) OFF THE CATALAN COAST (NORTHWESTERN MEDITERRANEAN)

The purple dye murex, Bolinus brandaris, a prosobranch mollusc which i s very common in the Mediterranean, is a resource of local importance. It is fished all the year round using a special type of dragged gear that is highly efficient for catching this species, which represents 7 3% of the commercial catch of this gear. The bathymetric size distribu tion of the mollusc is significantly correlated with depth. The purple dye murex grows relatively less in total length and shell width than in aperture. The species shows a slight positive allometry with regard to the increase in weight. During the year two groups of monthly leng th frequency can be distinguished: one from April to October and other from November to February. In 1993 the annual catch of the purple dye murex off the Catalan coast was 360 tonnes. The species is fished mai nly in the southern half of the littoral (98% of the annual catch). Th e catches during the year are markedly seasonal, being lowest in summe r and highest in late autumn and winter. The hourly yields are signifi cantly correlated with depth, but not with the duration of the haul.