A PRELIMINARY STUDY ON THE TROFIC ECOLOGY OF Sardinella brasiliensis OFF SOUTHERN BRAZIL

Abstract

The feeding ecology of the brazilian sardine Sardinella brasiliensis was studied on the Brazilian continental shelf, from 22°S to 29°S. Based on the Index of Relative Importance (IRI) the diet S. brasiliensis was analysed qualitatively and quantitatively in autumn, winter and spring. An indirect volumetric analysis (called individual volume method) was also performed where food items were classified as geometric bodies and mean volumes were calculated for each food item. The length distribution of sardine in the bulk of the samples varied mainly between 170 and 200 mm. S. brasiliensis prey on a broad variety of phytoplankton and zooplankton organisms, including diatoms, dinoflagellates, tintinnids, copepods, decapods and amphipods. In the stomach contents of S. brasiliensis 27 different taxa were identified; 11 phytoplankton and 16 zooplankton taxa. The zooplankton fraction represented 74,2% of the total prey volume in the sardine stomachs in autumn, 36,8% in winter and 99,8% in spring. The diatom Coscinodiscus spp. and copepods were volumetrically the most important taxa in the diet. Among copepods, the cyclopoid Oncaea sp., the harpaticoid Microsetella norvegica, calanoids Centropages sp., Temora stylifera and Candacia curta were the most important species in the diet. Larvae of Brachyura and the amphipod Lestrigonus sp. constituted a large volume in the stomach contents. S. brasiliensis was found to be an omnivore species, which preys on zooplankton, but that is able to switch to filter-feeding on phytoplankton and microzooplankton.