FEEDING AND SCHOOLING BEHAVIOR OF BARRACOUTA (THYRSITES ATUN) OFF OTAGO, NEW-ZEALAND

To test the hypothesis that fish in schools forage more successfully t han individual fish, an analysis was made of the stomach contents of b arracouta (Thyrsites atun), a facultatively schooling species of fish, in a wild fish population. Schooling (n = 29) and non-schooling (n = 86) barracouta were captured during a side-scan sonar survey of pelagi c fish off the coast of Otago, New Zealand. The proportion of fish wit h empty stomachs was lower and the mean wet mass of gut contents was h igher in barracouta from schools. The increased feeding success of fis h in schools was due to increased consumption of krill, Nyctiphanes au stralis. In regions where the density of krill in net tows was high (> 1000 individuals km(-1) tow length) or moderate (100-1000 individuals km(-1)), the mean wet mass of krill in the stomachs of schooling barra couta was 2-4 times higher than in the stomachs of non-schooling barra couta. Few schools of barracouta were observed in areas with low densi ties of krill (<100 individuals km(-1)). Schooling by barracouta seems to be a feeding strategy to exploit surface swarms of krill.