The most recent abundance estimate for the inshore Bryde’s whale population is indicative of a decline in numbers since 1983 when the last estimate was made. This difference could be a result of differences in methods used and spatial coverage, but changes in prey availability over the past 25 years could also be a contributing factor. Estimates of anchovy and sardine biomass derived from annual acoustic surveys suggest an increase in prey availability in the area east of Cape Agulhas (within which our study area is located) over the past 10–15 years . These surveys do not, however, provide indices of prey abundance at a smaller temporal resolution and therefore make it impossible to link estimates of Bryde’s whale to forage fish abundance. Fluctuations in marine mammal abundance and distribution have been used as indicators of ecosystem change or as tools for ecosystem management. However, not all marine mammals are easy to monitor, so by understanding their relationship with other marine predators, such as Cape gannets in the case of Bryde’s whales in South Africa, inferences can be made regarding the availability of prey within the ecosystem.