Spatial structuring of the main demersal fish around Reunion Island (Western Indian Ocean) based on the external shape of their otoliths

- Knowledge of the spatial structuring of stocks is essential to study the dynamics of fish populations, and thus to manage fisheries. In this study, sagittal otolith shape was used to understand the stock structures of populations of the main commercial species caught around La Reunion Island. A total of 1091 individuals, belonging to nine species of bentho-pelagic bony fishes (Aphareus rutilans, Cephalopholis aurantia, Epinephelus fasciatus, Etelis carbunculus, Lutjanus kasmira, Lutjanus notatus, Pristipomoides argyrogrammicus, Pristipo-moides filamentosus, Variola albimarginata), were analyzed and compared between 10 areas around La Reun-ion. To describe the external shape of the otolith, normalized Fourier elliptical descriptors were extracted. For each species, the analysis of shape data was performed in two steps. The first step was investigating the potential effects of confounding factors such as fish size, symmetry between right and left otoliths, sexual dimorphism and spatial distribution. When location showed a significant effect on otolith shape, a second step coupling two complementary analyses was performed with hierarchical clustering (unsupervised machine learning) and linear discriminant analysis with jackknifed prediction (supervised machine learning), allowing characterization of the potential stock limits for each of the treated species. The results show that, for the nine species treated, only two species (Etelis carbunculus and Pristipomoides filamentosus) show spatial structuring around Reunion Island with, for each of them, two stocks potentially separated along a northwest/southeast axis. These results show that some species around La Reunion Island may have local subpopulations.