Video: Humpback whales spotted 'bubble-net feeding' for the first time in Australia

If you gaze at the ocean this winter, you might just be lucky enough to spot a whale migrating along Australia's coastline. This is the start of whale season, when the gentle giants breed in the warm northern waters off Australia after feeding in Antarctica.

This north-south migration happens every year, but the whales can still surprise us. Thanks to a citizen scientist and his drone, humpback whales were seen feeding in a mass super group and "bubble-net feeding" off the New South Wales coast last year.

As my new research paper confirms, this a big deal for two reasons: it's only the second time a super group of humpbacks has been observed in the southern hemisphere (a first for Australia) and the first time bubble-net feeding has been seen in Australia.

So what is bubble-net feeding, and why are these observations so important?

Blowing bubbles, catching krill

Bubble-net feeding is when whales deliberately blow bubbles from their noses to encircle their food—krill and fish—like a net, concentrating their prey into a tight ball. Then, the whale or group of whales swim together from beneath, rise to the surface opening their mouths, and gulp up their prey.

It remains a mystery as to why the whales feed in this way and how they learned to do it.

2020 was a year full of unprecedented events, and the humpback whales certainly didn't disappoint.

Humpback whales in this eastern Australian population are usually observed lunge feeding on their side, or feeding below the surface. Bubble-net feeding, on the other hand, is mostly documented in some Northern Hemisphere populations.

But we know there are individual whales in the eastern Australian humpback population who bubble-net feed in Antarctic waters. This means the unique behavior in Australian waters may have evolved independently, or through cultural transmission (learning new behaviors from different whales).

The drone footage and observations made in September from whale-watching boats was the first to document bubble-net feeding. To add to the excitement, citizen scientists also documented bubble-net feeding behavior further south of Tasmania a month later.

Using stills from the September drone footage, an estimated 33 humpback whales can be seen feeding at the same time. Unfortunately, it's not known exactly what the whales were feeding on.

Until then, humpback whale congregations this large had never been observed in Australian waters.

In fact, the only other time a mass humpback feeding event has been seen in the Southern Hemisphere was off South Africa in 2011 (this now occurs regularly there). This was the first time the term "super group" was used to describe a group of 20 or more whales feeding this way.

But why were they feeding in 'breeding waters' anyway?

The majority of the east Australian humpback whale population spends the summer months feeding in Antarctic waters. They then head north to warm breeding waters in the Great Barrier Reef during winter (June-August) to mate and give birth.

They forego feeding for love—humpbacks can go for months without eating, relying instead on energy reserves in order to reproduce. Animals that do this are called capital breeders.

From August to November, humpbacks migrate southward back to Antarctica. Along the way, they sometimes take a "pit-stop" on parts of Australia's east coast to feed.

It was originally thought this population never fed along the migratory route. However, we know they do now to possibly supplement their energy intake as they migrate.

This article is republished from The Conversation under a Creative Commons license. Read the original article.