The rock sea urchin P. lividus constitutes a very valuable marine resource which must be carefully managed. The objective of this work is to identify the most appropriate locations for the sustainable harvesting of P. lividus in the coast of Cantabria (Bay of Biscay) in order to establish adequate management measures. The study was carried out in five coastal areas distributed along 110 km of coastline. 41 transects and two depth ranges (<5m and 5-10m) were considered for the study. Sea urchin abundance was recorded in situ and replicates of 10 individuals per depth range were collected at 21 transects. Total body size, fresh weight, gonadal fresh weigh and gonadal index were measured at the laboratory. Differences between coastal areas and depth ranges were analyzed using ANOVA and Kruskal-Wallis tests. Significant differences were subsequently analysed by Bonferroni and Mann-Whitney post-hoc tests. Correlations between abundance and biometrical variables were studied by linear regression models. Percentage frequency distributions of the biometric variables were built and used to estimate the available stock of commercial individuals (size>55mm). The results showed significant differences between areas but not between depth ranges. All the biometric variables, except the gonadal index, showed significant negative correlations against abundance data. Three areas showed low densities with big individuals and two areas showed high densities with smaller individuals. Despite the average smaller size of the individuals, the latter two areas accumulated the 71% of the commercial stock, being the most suitable zones for the sustainable harvesting of P. lividus.