The purple dye murex Bolinus brandaris (Gastropoda: Muricidae) fishery in the northwestern Mediterranean: from overfishing to depletion over a two-decade period

Abstract

The purple dye murex (Bolinus brandaris), a gastropod mollusc, is a resource of local importance within the Mediterranean Sea (Spain, France, Italy, Tunisia, Greece and Turkey). It is fished all along the Catalan coast (NW Mediterranean), although fishing is concentrated in the area of the Ebro River Delta, where it is caught with bottom trawl, boat dredge and trammel nets. In the last two decades, from 2002 to 2023, a steady decreasing trend along the Catalan coast has been observed in landings (92% reduction, from 240.5 to 19.8 t), daily catch per vessel (78% reduction, from 14.1 to 3.1 kg/day/vessel), and fishing effort (fishing days with the sale of purple dye murex at the auction; 63% reduction, from 17068 to 6400 days). The three types of fishing gear involved in the purple dye murex fishery operate on different fishing grounds at different depths, which implies that the purple dye murex is fished throughout its bathymetric distribution and size range. The boat dredge and bottom trawl hourly yields markedly declined by 69% and 40%, respectively, over the past six years. Immature and below minimum landing size individuals represent an important proportion of the catch. Considering the presence of immature individuals in the catch, boat dredging is the most detrimental for the species. At present, the economic dependence of fleets on purple dye murex is very low (1.3% revenue from first sale at the auction). The results of the assessment indicate that the purple dye murex population in the Ebro Delta is depleted.