Determining the age and growth of wild octopus using stylet increment analysis

Abstract

Stylet increment analysis is a method of octopus age estimation that quantifies growth rings within stylets (reduced internal shells found in the mantle). This method was applied to wild Octopus pallidus to determine gender and seasonal influences on age and growth. A total of 503 individuals (94 males and 409 females) were aged, revealing that O. pallidus can reach a maximum age of approximately 1.6 yr and that spawning occurs throughout the year. Male octopuses on average were significantly larger (550 and 482 g for males and females, respectively) and older (259 and 243 d for males and females, respectively) than female, and overall growth rates were positively correlated with temperature at hatching. However, these differences were secondary to individual growth heterogeneity. Growth of males ranged from 1.32 to 5.33% body weight (bw) d–1 and females from 1.55 to 6.9% bw d–1, with no relationship between age and size evident regardless of sex. Stylet increment analysis is a promising technique that could play a role similar role to statoliths in squid as an ageing tool.