Spatiotemporal shape variation in sagittal otoliths of spotted grunter Pomadasys commersonnii in South African estuaries

The morphological structure of fish otoliths is under dual regulation by genetic and environmental factors, and has been successfully used to aid stock delineation. This study examined whether differences in sagittal otolith shape outlines could be used to delineate potential stocks of the spotted grunter Pomadasys commersonnii (family Haemulidae) in South Africa. We hypothesised that P. commersonnii from two biogeographically distinct estuaries exhibit differences in their otolith outlines, and that there will be differences in the otolith shape of P. commersonnii captured in the Breede Estuary pre-2002 versus post-2019, considering recent research that has revealed changes in their movement patterns. Significant differences were found in the outlines of P. commersonnii otoliths both spatially and temporally. These findings demonstrate that while the overall otolith shape is genetically constrained, finer details may vary under environmental influences.