New Insights into Pygmy Blue Whale Foraging
Endangered pygmy blue whales dive to depths in the ocean to forage and feed along their migratory path off the Western Australian coast, new research led by the Australian Institute of Marine Science (AIMS) and the Centre for Whale Research (WA) has documented.
In a new paper led by AIMS researchers Dr Michele Thums and Dr Luciana Ferreira , whale dives into the ocean’s depths were categorised into foraging, lunge feeding, travel and exploratory behaviours.
The diving behaviours were tracked during the whales’ northern migration along the coast of Western Australia en route to Indonesia using data from satellite tags and dive loggers attached to nine pygmy blue whales.
The researchers were focussed on the foraging dives and particularly those where the whales attempted to catch prey, known as lunge feeding dives. These were identified by the accelerometer (like a fitbit) on board the loggers.
Lunge feeding dives involve the whales swimming towards dense patches of their prey – often krill – at depth and at speed. Opening their mouths and engulfing the krill swarm, often hundreds of kilograms at a time, thousands of litres of water are filtered through their baleen plates and swallowed as a food bolus. And if their prey is plentiful, they will do it all over again.
This behaviour had previously been recorded for northern blue whales off California, however this is the first time it has been tracked along the northern migration of pygmy blue whales.
Study lead author Dr Michele Thums said previously, scientists’ understanding of where foraging occurred was based on areas where pygmy blue whales spent more time, gleaned from satellite tracking data.
“The combination of the satellite tags and the dive loggers has provided us with data that shows foraging and feeding is happening at depths of around 100 to 400 metres, is occurring every 1 to 10 days averaging four hours per day, and opportunistically while migrating between the north-west of Australia and Indonesia.
“Previously it was thought they only feed at specific places like Perth Canyon and off the North West Cape, with no feeding occurring between these places and their breeding grounds in Indonesia. But we show they feed and forage en route too. Feeding while migrating is thought to be essential for a streamlined species like the pygmy blue whale that has less capacity to store fat and needs to feed to fuel its migrations.
“Supplemental foraging during migration may be vital for pygmy blue whales with thousands of kilometres to travel between their main foraging grounds in the southern waters of Australia and Indonesian waters in the north. The study shows that tropical and temperate waters are both important for the health and recovery of the population.
“This is really significant information, as efforts are made to help this species recover from the impact of the whaling era. Correctly delineating their foraging areas is important to effectively manage potential threats to this species and protect critical habitats.”
The study also found that more concentrated foraging occurs off south-west Australia, and that foraging and feeding is occurring in Indonesia/Timor Leste waters, an area thought to be associated mainly with breeding.
The study was published in the journal Global Ecology and Conservation . It was co-authored by scientists from Curtin University, Flinders University and the Centre for Whale Research (WA).
The research was co-funded by Woodside Energy Ltd, with additional support provided for one of the field trips by the North West Shoals to Shore Research Program supported by Santos.
https://www.aims.gov.au/information-centre/news-and-stories/feeding-go-research-provides-new-insights-pygmy-blue-whale-foraging-behaviours