Morphological, molecular, and ecological evidence in population determination and fishery management of purpleback flying squid Sthenoteuthis oualaniensis in the South China Sea

Morphological, molecular, and ecological evidence in population determination and fishery management of purpleback flying squid Sthenoteuthis oualaniensis in the South China Sea

Purpleback flying squid Sthenoteuthis oualaniensis has great potential to be an important fishery in the South China Sea, while its complex population structure causes difficulties for fishery management. In this study, specimens were sampled monthly throughout 2018 and identified at the population scale from the aspects of morphological, molecular, and ecological traits. Corresponding to the appearance of the photophore, the purpleback flying squid could be divided into two populations as the medium population and the dwarf population, also indicated by significant differences in mantle length. In the phylogenetic tree, all individuals fell into two lineages, and in each lineage, there was no sub-lineage corresponding to geological isolation or seasonal change. Fishes were the main food for purpleback flying squid, occupying approximately half of the total, followed by squid and crustaceans. Stable isotope analysis suggested that neither body size nor gender affected trophic niches. Spring and autumn were the main feeding periods of both the medium and the dwarf populations, followed by the spawning peak in winter and the second peak in summer. Despite the morphological differences at the population or even species scale, two populations of purpleback flying squid mixed in terms of habitat space, food selectivity, and developmental process, with no need for differentiated management.