While humpback whales have occasionally been observed feeding during their seasonal migration along the east coast of Australia, a Griffith University research team has recently uncovered the first biochemical evidence of “snacking” during migration.
The research under Griffith’s Southern Ocean Persistent Organic Pollutants Program (SOPOPP), which formed the PhD topic for candidate Pascale Eisenmann, investigated the baleen plates of humpbacks that had stranded along Australia’s coastlines since 1940.
Baleen plates are composed of keratin and hang from the whales’ top jaw and are used to filter krill, other small fish and plankton from the water.
Findings published in PLOS ONE article Isotopic Evidence of a Wide Spectrum of Feeding Strategies in Southern Hemisphere Humpback Whale Baleen Records found that a high proportion of stranded whales had fed outside of the Antarctic in the years prior to death.
Migrational fasting examined
The current understanding of humpback ecology assumes exclusive feeding on krill in Antarctic waters during summer, followed by fasting during their annual migration to and from equatorial breeding grounds.
Pascale says some of the whales may have fed anywhere between Antarctica and the calving grounds around north Queensland.
The paper says diversity in the inter-annual feeding strategies of humpback whales demonstrates the feeding plasticity of the species, but it is unknown whether snacking behaviours are increasing and could therefore be indicative of changing dynamics within the Antarctic sea-ice ecosystem.
Pascale says less ice means that the krill numbers are impacted, resulting in less food for the whales. If there is less krill available, the whales may switch to other prey or different feeding grounds.
As the results were based on stranded animals, it remains unknown how much “anomalous” feeding the broader population undertakes, i.e. whether they only feed opportunistically, or whether they rely on substantial supplementation of their krill diet.
This distinction is important to ascertain whether there are sufficient food resources in the Antarctic for the expanding population.
This study presents the first investigation of trophodynamics in Southern hemisphere humpback whales derived from baleen plates, and further provides the first estimates of baleen plate elongation rates in the species.