Contribution à l'étude biologique de la sardine atlantique (Sardina pilchardus WALBAUM)

Scientists have always been interested in the biology of the sardine, but despite a large number of studies, it is still not very well understood. At the beginning of the century, sardines were considered as a great class migratory fish. Its periodic and successive appearances, from the north to the south of the Bay of Biscay, were considered as a unique formation invading, in spring, the west coast of Europe and swimming back to subtropical waters at the beginning of the "rough" season. Today's point of view, based on biometrical studies conducted over the last 25 years, does not validate these long-distance migrations. It's been demonstrated that the species can be divided into morphologically and biologically individualised groups (named "races"), evolving in a limited area with specific hydrological features, and migrating only to follow its habitat. One can no longer talk about migrations but more of restricted moves from off-shore and deep waters to coastal waters during spring and vice versa at the end of autumn; but never past the continental shelf. Such moves would be insignificant in areas where the continental shelf is narrow and where sardines stay next to the coast all year long. From this point of view, the biology of the sardine seems to be pretty simple and none of the numerous questions one could ask should stay unanswered. However, as studies on this topic become more and more numerous, the results of different analysis conducted over the years on the essential characteristics (growth, sexual evolution, morphology) of sardines from the same area prove to be divergent and cause to reconsider the whole group-making process, as well as the biological and morphological characteristics these groups (races) are based on. ... (unverified OCR)