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.