Otolith shape analysis of the austral sardine (Sprattus fuegensis) in the Patagonian inner sea of Chile.

The austral sardine has an extensive distribution within inner and outer waters along fiords, channels, and the continental shelf of the Chilean Patagonia, from Puerto Montt to Tierra del Fuego and extending to southern Argentina. With the aim of determining differences in morphology and shape of sagittal otoliths of the austral sardine, samples were obtained from inner waters of Chiloé (42ºS-43ºS), Aysén (44ºS-46ºS), Punta Arenas (54ºS), and from Argentinian waters. Traditional morphometry analysis considered length, width, area, perimeter, and size-based shape descriptors of otoliths. Instead, geometric morphometry was an outline otolith analysis on the basis of elliptic Fourier descriptors through multivariate statistical methods. Both approached showed intraspecific variability in otolith shape of austral sardine, with otoliths from inner waters of Chiloé statistically differenced from the Aysén Region, but with an important degree of mix between zones. Otoliths from Punta Arenas were excluded from the study because they were smaller, without the outline characteristic of the adult specimens. The sagittal otolith from inner waters of Chiloé exhibited an elliptical shape, defined rostrum, and concave antirostrum, while otoliths from the Aysén Región showed rounded shape along the dorsal and ventral borders, without defined postrostrum and antirostrum. The otolith rostrum of specimens from inner waters of Chiloé was very well defined, being this the main morphological trait generating differences with the rest of the zones.