Southern hemisphere humpback whales are high-fidelity krill predators relying on high Antarctic krill biomass to survive and undergo successful reproduction. During the austral summer, humpback whales consume large quantities of krill and build up their blubber reserves. The rest of the year is spent migrating to temperate waters and back while relying on accumulated energy reserves. This expected reliance on Antarctic krill underpins our understanding of Southern hemisphere humpback populations. Their Northern hemisphere counterparts are however known to be more flexible in their feeding habits, and recent work has shown that the Southern hemisphere populations are capable of a certain feeding plasticity, with multiple visual reports of supplementary feeding during the migration, and evidence of anomalous feeding observed in baleen plates. Due to the dependency of Antarctic krill on sea-ice duration and extent for its larval recruitment, the entire Antarctic sea-ice ecosystem is expected to destabilise in a changing climate. The resulting effects on high-fidelity krill predators, such as humpback whales, are unknown. Detailed, long-term information regarding current and past diet, migration and metabolism of humpback whales are needed to successfully assess possible trophodynamic variability, and to differentiate between the natural feeding plasticity of this species and population responses to climate driven environmental change. This thesis aims to evaluate whether Australian humpback whale populations display feeding plasticity in their prey choice and/ or feeding locations.