Comparison of Otolith Outline and Landmark-based Geometric Morphometrics in Discriminating Six Sardine Species (Clupeiformes: Clupeidae)

Sardines are small pelagic fish of significant ecological and economic importance in the Philippines. However, they are prone to misidentification among closely resembling species, highlighting the need for reliable differentiation methods. Otolith shape analysis emerges as a cost-effective and promising tool in species identification. In this study, outline and landmark- based geometric morphometrics on sardine otoliths were employed to discriminate six species – namely Sardinella lemuru, Sardinella pacifica, Sardinella goni, Sardinella tawilis, Herklotsichthys quadrimaculatus, and Amblygaster sirm. The otolith contour and the 15 landmarks successfully detected interspecific variation. Ordination plots indicate congeneric species cluster together, whereas H. quadrimaculatus displayed the most distinctive otolith outline. Both methods exhibited high success rates in classifying species, with S. lemuru achieving the highest correct classification scores. Although outline-based analysis demonstrated superior correct classification rates (92–100%) than landmark-based analysis (65.4–97.5%), both yielded comparable results, emphasizing their combined significance for species discrimination. This study contributes to the characterization of the otolith shapes of sardines in the country and provides an alternative method for species discrimination.