Étude expérimentale de la prédation de la palourde japonaise, Ruditapes philippinarum, par la dorade royale, Sparus aurata, et le baliste, Balistes capriscus

Abstract

Since 1988, heavy mortality of reared Manila clam Ruditapes philippinarum have been observed in the basin of Arcachon. Clam predation by the gilthead bream Sparus aurata and the gray triggerfish Balistes capriscus has been suspected. Therefore, an experimental study of predation on this clam by these two fish has been carried out. Feeding rates were determined according to the size of clams, temperature and degree of protection. The amount of clams ingested varied with the size of predator and prey but both fish were serious clam predator. A daily ingestion of 500 seed and 350 spat has been recorded, 50 to 70% of the prey being eaten during the first 6 hours. Because clams were generally communited by these two fish and bottom marks quite similar, it was not possible to discrminate the intervention of both predators. When water temperature was below 16 °C, an important decrease in the feeding activity was observed. A net protection may be used to prevent this kind of predation. The Manila clam mortalities, recorded during the summer period in the basin of Arcachon, can be attributed, to a certain extend, to the intervention of these fish. Sparus aurata is a clam predator but the occurrence of the gray triggerfish Balistes capriscus in the basin of Arcachon is a serious concern because this is a vigorous species which is not commercialy fished and then out of control. © 1991 IFREMER-Gauthier-Villars.