Life-history traits, maturation, and energy allocation of a small mesopelagic squid Abralia multihamata

Abstract

Enoploteuthid squids are abundant and are typically bycatch in commercial fisheries, playing a significant role in the trophic structure of the mesopelagic boundary community. The life-history traits and maturation of Abralia multihamata in the waters off the southeastern Taiwan Strait were studied through statolith microstructure analysis. Additionally, energy allocation between somatic and reproductive growth was evaluated in relation to maturity stage and hatching season. The results indicated that the estimated age of 299 post-recruit individuals ranged from 43 to 150 days and that hatching occurs year-round, with a peak in autumn. Significant sexual dimorphism was observed in maturation, growth patterns, and energy strategies. Males began maturing at a smaller size (25.8-28.2 mm) but at an older age (68.4-78.8 days) than females (36.0-37.6 mm at 50.3-70.3 days). Non-asymptotic and asymptotic growth models were best described by the exponential and von Bertalanffy growth function for females and males, respectively, though pre-recruit individuals are still needed to establish complete growth patterns. Significant differences in somatic condition, lifetime growth, and reproductive investment were observed in males across hatching seasons, whereas these measures in females varied with reproductive development. This suggests that A. multihamata females and males, with differing relative energetic demands, likely employ sex-specific energy utilization strategies. There were no energy trade-offs between somatic condition and reproductive investment but negative correlations between lifetime growth and reproductive investment, supporting the hypothesis that cephalopods prioritize energy from ingested food to maintain both somatic and reproductive conditions.