Beak increment counts as a tool for growth studies of the common octopus Octopus vulgaris in southern Brazil

Abstract

The common-octopus Octopus vulgaris Cuvier, 1797 has high commercial value, and it is the most important octopus species on landings all over the world. Age estimation is vital for the comprehension of species life cycle and population dynamics, and further elaboration of an adequate management planning of its exploitation. In this study, 120 beaks of O. vulgaris had its growth increments counted and, assuming a daily basis periodicity, growth curves were adjusted taking into account the relation between estimated age (a) and dorsal mantle length (DML), total weight (Wt) and upper beak crest length (CrL). The octopuses analyzed ranged from 50 to 163 mm of DML (162 and 290 marks, respectively) and 55 to 1,498 g of Wt (164 and 356 marks, respectively, considering a one year life expectancy). The best fit for all the analyzed situations was found using potential equations: DML = 0.876a^0.871, WT = 0.001a^2.424, CrL = 0.210a^0.790, considering individuals with number of marks from 118 to 356. Counting increments on the upper beak of octopus appears to be a relatively simple and useful way of estimating its age.