Growth lines within the beak microstructure of the octopus Octopus vulgaris Cuvier, 1797

Octopus vulgaris Cuvier, 1797 is commercially the most important species in the central-eastern Atlantic cephalopod fishery. The estimation of growth parameters in wild octopus populations is essential to management of the fishery. As there are problems with methods based on length-frequency modal analyses for describing growth from field data and there is a lack of age determination techniques for octopod species, estimation of the growth rates of natural populations is currently difficult. The present work describes the use of beaks to determine the age of O. vulgaris, using a new method based on a sample of beaks from 25 animals caught in the area in 1993. After sectioning different planes of the beaks embedded in resin blocks, they were analysed to select the best with which to observe growth increments. The sagittal plane (from outer to inner) revealed a pattern of increments of similar width in the internal rostral area of all the beaks analysed that are possibly related to the age of the animal. The number of these increments does not exclude daily deposition.