Study of the growth of <i>Octopus vulgaris</i> in the Moroccan Mediterranean Sea by direct age estimation through the analysis of upper beaks

Abstract

Abstract Beaks are one of the most important sclerochronological structures used to study the age and growth of cephalopods, in particular Octopus vulgaris Cuvier, 1797. The present study provides results of ageing of 128 O. vulgaris (56–239 mm dorsal mantle length, DML; 121–5974 g total weight, TW) collected in the southern Moroccan Mediterranean coasts between Fnideq and Jebha. The number of increments corresponding to the age (days since hatching) varied from 137–368 in females and from 129–382 in males. There was a significant correlation between beak and somatic growth. The correlation coefficients of the growth curves DML-Age and TW-Age were similar for both power and exponential models: DML = 0.185Age 1.188 ( R 2 = 0.547), DML = 35.933e 0.005Age ( R 2 = 0.546), TW = 0.00002Age 3.260 ( R 2 = 0.532), TW = 29.56e 0.014Age ( R 2 = 0.541). The average width of the increments was similar between females and males. It varied significantly with season and stage of sexual maturity. Comparison of the growth curve with those estimated by other authors showed that Moroccan Mediterranean O. vulgaris grew faster than that of Sardinia (Italy) and slower than that of the Mauritanian coast.