Statolith Microstructure Estimates of the Age, Growth, and Population Structure of Purpleback Flying Squid (Sthenoteuthis oualaniensis) in the Waters of the Xisha Islands of the South China Sea

Abstract

In this study, we aimed to estimate the age, growth, and population structure to explore the life history of purpleback flying squid (Sthenoteuthis oualaniensis) by statolith microstructure in the waters of the Xisha Islands of the South China Sea. The purpleback squid, S. oualaniensis, has been the most important economic cephalopod resource of the South China Sea; however, little is known about its life history, especially its age and population structure. The age and growth pattern have been explored via the statolith microstructure of this species of squid, specimens of which were caught randomly between January and March and between May and August of 2018, 2019, and 2020 in the waters surrounding the Xisha Islands of the South China Sea. The results indicated that the range of the mantle length (ML) was 63–229 mm for females and 59–184 for males, and the body weight (BW) ranged from 13 to 435 g for females and from 7 to 152 g for males; the ages were estimated as being between 81 and 298 days for females and between 67 and 286 days for males, respectively. The hatching date extended from January to December, with a peak between November and March of the following year, suggesting the presence of one spawning group (winter–spring group). Significant differences existed between the ML growth and the BW growth. The relationships between ML and age were best described by the linear function for females and the power function for males; the relationship between BW and age were best described by the exponential function for females and the power function for males, based on our AIC models, respectively. S. oualaniensis is a fast-growing squid; the growth rate is the fastest during the young life stage, and it decreases after the subadult stage (120–150 days). After the first spawning behavior, the inflection point of the growth was recognized at the age of 180–210 days (6–7 months). This study provided basic, favorable information for the fishery biology, ecology, and resource management of purpleback flying squid (S. oualaniensis) of the South China Sea.

Beak Microstructure Estimates of the Age, Growth, and Population Structure of Purpleback Flying Squid (Sthenoteuthis oualaniensis) in the Xisha Islands Waters of the South China Sea

“…In this species, males reach maturity more quickly than females of the same age [58], a phenomenon also common in other Ommastrephidae species [59,60]. Previous studies have estimated the life span of S. oualaniensis in other areas of the South China Sea with statolith increments; these life spans have mostly been 1-4 months, except for squid collected in the western waters of the Philippines (life span: 95-275 days, 3-9 months) [23,24,26,27,61]. For example, the life span of squid in the Bashi Channel, the eastern tropical Pacific Ocean, the northern Pacific Ocean, and the Bay of Bengal is approximately 2-6 months (53-155 days, 84-168 days, 52-186 days, and 40-120 days, respectively) [22,25,62,63] (Table 2).…”

“…Studies of the fishery biology and ecology of cephalopods found that the beak can help to determine taxonomy, age and growth patterns, and pigmentation, as well as to estimate biomass [18][19][20][21]. Previous growth studies have summarized the morphological characteristics and growth patterns of S. oualaniensis statoliths [22][23][24][25][26][27], but fewer studies have explored the growth pattern and pigmentation of S. oualaniensis beaks [28][29][30][31][32].…”

Insights into the divergent evolution of the oceanic squid Sthenoteuthis oualaniensis (Cephalopoda: Ommastrephidae) from the Indian Ocean

“…2002), and their high economic development value in the Northwest Indian Ocean has been pointed out (Lu et al. 2022). India has launched an aspiring project to explore these resources from the southeastern Arabian Sea (Mohamed et al.…”

“…PBFS forms a target in commercial fishery in China (Lu et al. 2022) and is yet to be a part of the major cephalopod fishery in India. This may be attributed to the unconventional nature of this resource (Chembian 2013) and the oceanic lifestyle of oegopsid squids, which generally frustrates their sampling (Fernndez‐Alvarez et al.…”

Morphological Differences and Contour Visualization of Statoliths in Different Geographic Populations of Purpleback Flying Squid (Sthenoteuthis oualaniensis)

“…Previous studies of statoliths in the purpleback flying squid mainly focused on their microstructure [38][39][40], microchemistry [41], growth characteristics [18], morphological analysis [42][43][44], and the effects of life and growth patterns [24]. Studies regarding the discrimination of different geographical populations of purpleback flying squid based on statolith morphology mostly used traditional morphometry [42], whereas few employed Fourier transform and landmark methods [32].…”