Life history of the steentjie Spondyliosoma emarginatum (Cuvier 1830) in Langebaan Lagoon, South Africa

Abstract

Morphometric measurements and fin spine and ray counts, external colouration, macroscopic gonad stage and diet were recorded for steentjie Spondyliosoma emarginatum (Pisces: Sparidae) collected from Langebaan Lagoon between August 2004 and September 2005. Sagittal otoliths were removed, and age estimates were obtained from whole and sectioned material to estimate growth and mortality parameters. In all, 369 steentjies (fork length, FL, 136–312mm) were sampled, of which 296 (80%) were female, 74 (20%) were male and 4 (>0.1%) were hermaphroditic. The absence of small males in the sample suggests that steentjies are protogynous hermaphrodites. Macroscopic examination of gonads and monthly gonadosomatic indices suggest spring spawning. Males develop an intense blue and yellow pattern on the head then, and the colouration is strongly correlated with gonad development. The length-at-50% maturity for females was 235mm FL. The size-at-50% sex change was estimated to be 249mm FL. Foregut contents showed steentjies to be opportunistic omnivores, changing from herbivory to carnivory as they grow. Age estimates from sectioned otoliths were used for fitting a two-stage growth model that allowed for accelerated growth after sex change. The species is short-lived compared with other sparids; the oldest one sampled was eight years old.