The metabolome of humpback whales (Megaptera novaeangliae) reveals clues as to their extreme fasting capabilities

Southern Hemisphere humpback whales are capital breeders, relying on energy reserves accumulated through summer feeding in the Southern Ocean to fuel reproduction and migration. Understanding the fasting physiology of these populations, which lose up to 50 % of their post-summer feeding body mass during seasonal migration, is of great importance, particularly in the context of a rapidly changing Antarctic sea-ice ecosystem. Additionally, fluctuations in lipid reserves are known to mobilise lipophilic contaminants, potentially rendering seasonal fasting a time of elevated toxicological risk. This study analysed blubber biopsies from humpback whales migrating along the east coast of Australia. Biopsies were collected at two timepoints on the migration, corresponding to ∼3 and 6 months fasted, respectively. Nuclear Magnetic Resonance spectroscopy identified 32 polar metabolites in blubber, mainly involved in fatty acid and amino acid metabolism. Eleven of these metabolites showed significant differences between the two fasting stages, indicating changes in fatty acid oxidation, body condition, protein catabolism and glucose conservation. This is the first study to investigate the polar metabolomic alterations associated with migration in humpback whales, providing insights into biochemical pathways related to their fasting physiology. Metabolomic analysis holds the potential to identify metabolite patterns linked to nutritional and environmental stress, critical for ongoing biomonitoring of the Antarctic ecosystem.