Growth trends during life stages in the Arabian Sea middle-sized form Sthenoteuthis oualaniensis (Cephalopoda: Ommastrephidae) from the Western Indian Ocean

Abstract

ABSTRACT The Arabian Sea middle-sized form (ASM) of the purpleback flying squid, Sthenoteuthis oualaniensis differs genetically from the other three morphotypes of the species from this region. Statolith microstructure analysis was used to investigate the age and growth of typical ASM squid. The number of increments in the statolith of the ASM form ranged from 38 to 156 which, assuming a daily periodicity of increment deposition, equates to a short lifespan. The growth rate varied between 0.12 and 2.1 mm of dorsal mantle length (DML) per day. Age-DML and age-body-weight data were best fitted with linear and power models respectively. The paralarval phase of S. oualaniensis in the Arabian Sea was about two months. Sthenoteuthis oualaniensis matured rapidly, some within 100 days. Median age at first maturity was 115 days at a size of 115 mm for males and 118 days at a size of 156 mm for females. The back-calculation of hatching dates of the ASM form indicated that spawning takes place throughout the year with a peak in November. The ASM form in the southern Arabian Sea may be an early maturing group, while squids in the Northwest Indian Ocean may be a late maturing group.