MEPS 441:141-149 (2011)  -  DOI: https://doi.org/10.3354/meps09399

ABSTRACT: Several internal structures have been used to estimate age in the cephalopod Octopus vulgaris, but with limited accuracy. We estimated age by investigating growth increments (rings) in the upper beaks of octopus collected between 2003 and 2010 in the Bay of Naples, Italy (Mediterranean Sea). To validate the daily periodicity of ring deposition, ‘thermal shock marking’ was for the first time applied to live octopuses fished between 2009 and 2010; this method produced a mark on the beak corresponding to the day of thermal shock, enabling us to elucidate the relationship between ring number and time elapsed (i.e. ~30 d). In addition, rings were counted in >700 preserved specimens of O. vulgaris collected between 2003 and 2009, also in the Bay of Naples. The estimated age of of these octopuses ranged from about 70 to 370 d. Specimens with similar body weights had different numbers of rings, confirming the view that body size is a not a good index of age. Additionally, the relationship between body weight and number of rings was affected by sex and season, with the distance between rings clearly correlated to seasonal temperature oscillations. Our data suggest that different cohorts of octopus exist in the Bay of Naples and that temperature has a strong influence on growth. Overall the results demonstrate that growth increments in the upper beak of O. vulgaris provide a reliable method of aging that can be applied to assessing differences in the growth patterns in wild populations, and one that provides a record of environmental influences upon an individual.

KEY WORDS: Octopus · Age · Thermal marking · Upper beak · Seasonal variability