Purpleback Flying Squid Sthenoteuthis oualaniensis in the South China Sea: Growth, Resources and Association with the Environment

The purpleback flying squid (Ommastrephidae: Sthenoteuthis oualaniensis) is an important species at higher trophic levels of the regional marine ecosystem in the South China Sea (SCS), where it is considered to show the potential for fishery development. Accordingly, under increasing climatic and environmental changes, understanding the nature and importance of various factors that determine the spatial and temporal distribution and abundance of S. oualaniensis in the SCS is of great scientific and socio-economic interest. Using generalized additive model (GAM) methods, we analyzed the relationship between available environmental factors and catch per unit effort (CPUE) data of S. oualaniensis. The body size of S. oualaniensis in the SCS was relatively small (<19.4 cm), with a shorter lifespan than individuals in other seas. The biological characteristics indicate that S. oualaniensis in the SCS showed a positive allometric growth, and could be suitably described by the logistic growth equation. In our study, the sea areas with higher CPUE were mainly distributed at 10°–11° N, with a 27–28 °C sea surface temperature (SST) range, a sea surface height anomaly (SSHA) of −0.05–0.05 m, and chlorophyll-a concentration (Chl-a) higher than 0.18 μg/L. The SST was the most important factor in the GAM analysis and the best fitting GAM model explained 67.9% of the variance. Understanding the biological characteristics and habitat status of S. oualaniensis in the SCS will benefit the management of this resource.

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&lt;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.