Geographic, intraspecific and sexual variation in beak morphology of purpleback flying squid (Sthenoteuthis oualaniensis) throughout its distribution range

In this study we investigated 745 specimens of purpleback flying squid Sthenoteuthis oualaniensis across a large distribution range to investigate geographic, intraspecific and sexual variations in beak morphology. Beak morphometric variables showed significant spatial and intraspecific differences (P<0.05), with samples from the north-western Indian Pacific Ocean and the South China Sea having the largest and smallest beaks respectively. Multivariate statistical analysis indicated that the morphological characteristics of squid beaks would be useful for the identification of population structures and sex determination. Environmental conditions may be the major reason for variations in beak morphology between geographic populations throughout large distribution areas. In contrast, genetic differences may contribute to most of the intraspecific variation in beak morphology in the South China Sea. To address this clearly, further research needs to be done on morphology combined with genetic evaluation to compare methods of geographic and intraspecific population identification.