Variación espacio-temporal de la densidad poblacional de erizo rojo Strongylocentrotus franciscanus (Echinodermata: Echinoidea: Strongylocentrotidae) en Baja California

density estimations of red sea urchin strongylocentrotus franciscanus were recorded in ten sites with commercial fisheries on the west coast of baja california, mexico. the estimations for the years 2003, 2005, 2006 and 2008 were compared. the variations observed in the study sites indicate important spatial and temporal differences in density and size structure, influenced by fishing intensity and sporadic recruitment in each site. we found two sites (san jeronimo island and sacramento reef) with a high density and wide size structure; with a predominance of individuals of sizes from 50 to 80 mm with lest impact possible in fishing mortality for all sites.