Recordings of humpback whales feeding off the Far South Coast have scientists suggesting that the whales' migratory behaviour is changing.
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Footage captured off Merimbula and Bermagui was aired in the ABC's Southern Ocean Live television event on Tuesday, June 21. The television event is also now available via iView.
Dr Vanessa Pirotta, postdoctoral researcher and wildlife scientist at Macquarie University, said it was the first photographically documented evidence of humpback whales bubble-net feeding in Australia's waters.
As Dr Pirotta explained in a paper that she co-authored and which was published in May 2021, scientists previously believed whales had a feast-and-famine regime. They feed intensively in the Antarctic waters during the summer, then fast while migrating north and spending the winter in warmer waters.
It is there that males sing the whale song to attract females and pregnant females give birth to their calves.
However, the Far South Coast recordings were taken as evidence that the whales were feeding outside their known foraging grounds.
Dr Pirotta and her fellow marine scientists have a few possible explanations for the apparent change in feeding regime.
In her May 2021 paper, Dr Pirotta wrote that their numbers have returned to pre-whaling levels.
Around 40,000 humpback whales were estimated to make the annual journey up Australia's east and west coasts from Antarctic waters.
In her May 2021 paper, Dr Pirotta suggested it was therefore possible the whales were reverting to behaviours that existed before their population was dramatically cut by whaling. The recovery in numbers may also make larger group sizes while feeding more common.
Dr Pirotta also explored the possibility that changes to the ocean, including ocean currents and distribution of prey, may be contributing to the change in feeding patterns.
Similarly, her May 2021 paper hypothesised that the formation of super groups of whales may be linked to changes in the type and density of prey available, either along the migratory route or in the feeding grounds of the previous summer.
However, a paper published in March 2022 suggests that rising sea surface temperatures may make the whales' breeding areas too warm.
Dr Pirotta said that humpback whales were removed from Australia's list of threatened species earlier this year.
If the feeding events recorded near Merimbula become annual events, it could mean southern New South Wales waters were becoming a significant area for humpback whales migrating from the Antarctic, said Dr Pirotta. Scientists are watching closely.