Abstract

The diet of Australasian gannets (Morus serrator) breeding in Port Phillip Bay was investigated before and after a mass mortality of pilchards (Sardinops sagax) in southern Australian waters in 1998. Gannets usually feed on inshore pelagic schooling fish, such as pilchards and barracouta (Thyrsites atun), and to a lesser extent on other species. Pilchards represented ~60% of the gannet diet examined before the spread of pilchard deaths into Victorian waters, but this component declined to 5% following the mortality event. This reduction was compensated by a substantial increase in the amount of barracouta taken, supporting the view that the gannet is a flexible forager. However, the 1998 mortality of pilchards is likely to have wider implications since pilchards are an important prey for other piscivorous fish, seabirds and marine mammals.