Astonishing whale 'supergroups' a mystery for science

Scientists believe the clustering of whales is a relatively recent behaviour (Jean Tresfon / Supplied)
Scientists believe the clustering of whales is a relatively recent behaviour (Jean Tresfon / Supplied)

Just like Velvet Revolver or Audioslave, humpback whales have been forming their own supergroups - and no one knows why.

It is a relatively new phenomenon witnessed by a lucky few, and now documented and studied by scientists.

The groups can range from anywhere between 20 and 200 individuals, in close proximity to each other off the southwestern coast of South Africa.

Three research cruises in 2011, 2014 and 2015 spotted the groupings 22 times across a 220 nautical mile region of the south Benguela System, where they showed feeding behaviours.

At least seven occurrences were seen by complete fluke by the public, and four from aircraft.  

The supergroups are defined as 20 or more individuals estimated to be within five body lengths of each other - though researchers say they're much closer than that in real life.

The study, published in journal PLOS One, says the "reasons for this recent novel behaviour pattern remain speculative, but may relate to increasing summer humpback whale abundance in the region".

The main purpose appears to be related to feeding and could be a resurgence of a previously unobserved feeding strategy as their numbers increase.

The Southern Hemisphere humpbacks also seem to be welcoming, or at least tolerant, of other species with a fin whale and southern right whales seen amongst the supergroups on several occasions.

Estimating the size of the groups can be difficult, with photographs of whales on the surface not showing those below.

Many of the whales observed were small - around eight to 10 metres long - along with some larger, mature animals. However, only one calf was spotted in the more than 30 documented sightings.

For the most part, animals in the supergroups moved independently of each other, though on some occasions a sub-group of up to five would synchronise their diving and feeding.

Humpbacks typically stay in the polar regions of the Antarctic during the summer, where they feed build up fat stores before making the journey to warmer waters in winter.

Researchers believe the animals could be a confluence of young, non-breeding animals coming from Antarctic waters and a separate breeding group making their way south.

A previous study showed the area is used during spring and summer by a population of around 500 humpbacks thought to migrate and breed in the tropical waters off Gabon, central Africa.

However, there it is also thought the whales in the area may be breeding and calving in an area which is yet to be identified.