Feeding and schooling behaviour of barracouta (Thyrsites atun) off Otago, New Zealand

Abstract

To test the hypothesis that fish in schools forage more successfully than individual fish, an analysis was made of the stomach contents of barracouta (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 pelagic fish off the coast of Otago, New Zealand. The proportion of fish with empty stomachs was lower and the mean wet mass of gut contents was higher in barracouta from schools. The increased feeding success of fish in schools was due to increased consumption of krill, Nyctiphanes australis. 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 barracouta was 2–4 times higher than in the stomachs of non-schooling barracouta. Few schools of barracouta were observed in areas with low densities of krill (<100 individuals km^-1). Schooling by barracouta seems to be a feeding strategy to exploit surface swarms of krill.