Tuna fisheries are among the most valuable commercial fisheries worldwide, but their management is complicated by the highly migratory nature of tuna species. A major challenge is determining whether catches and biological data come from a single panmictic stock or multiple distinct populations. Various methods exist to infer population structure, but otolith shape analysis—a technique using the morphology of ear bones—has been underutilized for tuna.
This study aimed to evaluate the utility of otolith shape analysis for distinguishing between two important tuna species, Bigeye Tuna (T. obesus, BET) and Yellowfin Tuna (T. albacares, YFT), and to assess population structure across three regions: the Indian Ocean, Indonesian archipelago, and western Pacific Ocean. Additionally, the study compared otolith shape results with genetic, chemical, and parasitological data from related research.
A total of 1,307 BET and 2,274 YFT otoliths from young-of-the-year fish collected in 2013–2014 from Kendari (Indonesia), the Maldives, and the Solomon Islands were analyzed using digital imaging and Fourier shape analysis, with only intact otoliths included.
Results showed no significant differences in weight or shape between left and right otoliths, allowing random selection of left or right otolith for analysis. Otolith shape differed significantly between BET and YFT species (P=0.002). Among locations, BET otolith shape varied significantly (P=0.004), while YFT showed no regional variation (P=0.687).
These findings suggest otolith shape is a promising tool for species identification, especially for visually similar juveniles, and for detecting population structure in BET. The results align with other population discrimination methods from the related studies. Longer-term monitoring and integration with other techniques are necessary to validate whether these results are temporally stable in the longer-term, which is necessary for otolith shape to be a reliable method for tuna stock management.