Human predation has affected population size structures (in the sense of distribution of body size within particular populations), which has been used to track losses of larger and more fertile individuals from populations. In this sense, human exploitation can also decrease the reproductive output of invertebrate populations such as the endangered limpet Patella ferruginea. A total of 7077 individuals of this protected limpet were analysed among “Under custody” and “Without custody” sites, the strongest indication of human exploitation being the absence of a great number of larger limpets at “Without custody” sites. Likewise, recruitment was lower in “Without custody” than in “Under custody” sites, although the mean density was not affected. The presence of 4084 individuals inside the harbour area of Ceuta indicates the requirement of the involvement of harbour authorities and environmental agencies in a global conservation plan, establishing small fenced reserve areas in artificial breakwaters and natural substrates where dense populations are settled. These reserves could be useful as a focus for larval export via their previous rebalance of sex ratio.