How do you get a super-group of whales to come together?

New research has shed light on the puzzling phenomenon of “super-groups” of humpback whales congregating off the coast of South Africa. (And, no, that’s not a technical term for a revival band comprising whales who have already had successful music careers.)

The study, a collaboration between Australian and South African researchers, suggests that climate change may be causing shifts in ocean currents and phytoplankton blooms that are driving changes in whale behaviour in the Southern Benguela Upwelling System (SBUS) near Cape Town.

Until 2011, humpback whales were typically only observed feeding in small groups of up to 20 individuals in this region. By contrast, the “super-groups” that appeared in the years 2011, 2014 and 2015 can comprise up to 200 whales. Whales in super-groups also appear to stay closer to one another while feeding.

“While humpback whales in the Southern Hemisphere are known for annual migrations between the summer high-latitude Southern Ocean feeding grounds and the winter mating and calving grounds in subtropical coastal waters, feeding in such dense packs is unprecedented,” said Dr Olaf Meynecke, a whale researcher and Manager of the Whales and Climate Program at Griffith University.

The study used records of chlorophyll levels in the water as a proxy for phytoplankton blooms in super-group years. Phytoplankton are tiny marine algae that, like plants, use chlorophyll to capture energy from sunlight and convert it into food. The phytoplankton are eaten by krill, which in turn are eaten by humpback whales.

The researchers found that phytoplankton blooms occurred about a month before the super-groups were seen. Changes in ocean circulation were also likely causing the blooms to hang around in the water for longer, turning the SBUS into an attractive buffet for the whales. 

By monitoring phytoplankton blooms via chlorophyll levels, scientists may be able to predict when and where a whale super-group will form.

“Understanding the causation leading to these events will allow researchers and the whale watching industry to prepare for the arrival of super-groups of humpback whales at least one month in advance, through the evaluation of chlorophyll from satellite data and ocean models,” explained Dr Subhra Prakash Dey from the University of Cape Town. 

Meynecke also suggested that the super-group trend could spread to Australia.

“Unlike in South Africa, the large whale pods that have started to show up in Australia only last for a short period of time, but super-groups of humpback whales off the coast of Australia are increasingly likely in the years to come,” he said.