Geostatistical analysis of densities of Liocarcinus depurator (Brachyura: Portunidae) on the western Mediterranean from 1994 to 2003

Abstract

Bottom trawl estimates of densities of the portunid crab Liocarcinus depurator along the Mediterranean coast of Spain from 1994 to 2003, covering a depth range of 50–800 m, were analysed using non-linear geostatistical techniques. The variation of the spatial distribution was modelled through variogram analysis using depth as a covariate. Patch size ranged from 20 to 75 km. Crab density showed a general decrease from 1994 to 2003. L. depurator high-density areas were characterised as either occasional or permanent (always present every year). High-density patches appeared to be associated with either upwelling or strong river influence, i.e. the Western Alboran Sea and the Ebro Delta. The application of non-linear geostatistical techniques proved useful in identifying permanent high-density population patches, thereby highlighting regions of special interest for the ecology of the species.