Ontogenetic and seasonal changes in the feeding habits and trophic levels of two small pelagic fish species

Abstract

ABSTRACT: We investigated ontogenetic and seasonal changes in the feeding ecology of 2 smallpelagic fish species, the European anchovy Engraulis encrasicolus and the European pilchardSardina pilchardus in the Gulf of Lions (NW Mediterranean). By analysing the stable isotopes δ 13 Cand δ 15 N, we determined the seasonal variation in the food sources and in the trophic level ofthese species, and we examined dietary shifts during development. The results of these investiga-tions provided estimates of the diets of both species. We compared the values observed duringdifferent seasons (summer, autumn and winter) and at different developmental stages (late -larvae, juveniles and adults) for both species, together with the values of potential groups of prey(microplankton, cladocerans, copepods and appendicularians). Late-larvae preferred to feed onmicroplankton, although differences in the diet appeared after metamorphosis. Cladocerans wereusually the preferred prey when available (summer), and appendicularians were the preferredprey in autumn. During the winter, the diets seemed to be more heterogeneous. Different feedingbehaviours between the late-larvae of the 2 species were the most likely reason for the slightlydifferent trophic levels found in the present study. This research demonstrates that studies withstable isotopes can furnish an alternative and/or complementary method for determining the dietof small pelagic fishes over extended periods and provides comprehensive knowledge of the func-tioning of the pelagic ecosystem. KEY WORDS: