AGE, GROWTH AND POPULATION STRUCTURE OF PURPLE BACK FLYING SQUID, STHENOTEUTHIS OUALANIENSIS IN THE SOUTH CHINA SEA IN SPRING BASED ON STATOLITH MICROSTRUCTURE

The current study investigated the purple back flying squid (Sthenoteuthis oualaniensis) collected by light attracting falling-net fishing vessels in the spring of 2015 in the South China Sea. The mantle lengths of S. oualaniensis were ranged from 10.22 to 199.01 mm while the body mass were ranged from 1.3 to 328.8 g. The Age, growth and popu-lation structures of S. oualaniensis were studied based on the microstructure of statolith. The result showed that there were two groups of S. oualaniensis in the South China Sea: the medium-sized (with photophore on the dorsal mantle) and dwarf groups (without photophore on the dorsal mantle) accounting for 59.38% and 40.62%, respectively, and that there was no large group whose mantle lengths were more than 500 mm. The ages of the sample were ranged from 38 to 126d among which the dominant age was from 51 to 80d, accounting for 81.33%. According to the AIC values of these five growth models in different waters and groups, the exponential growth model appropriately reflect the growth of S. oualaniensis in northern South China Sea and Nansha adjacent waters; the exponential growth model suitably explain the middle-size group and the power function growth model was best for dwarf groups. Moreover, the individual growth rate of squid in the northern South China Sea was slightly slower than that in Nansha adjacent waters. The growth rate of the dwarf groups first increased rapidly and then gradually decreased while the medium-sized groups were totally on the contrary.