Every winter, humpback whales off iSimangaliso form part of one of the great seasonal migrations of the western Indian Ocean
Some are travelling north towards breeding areas in Mozambique. Later in the season, whales return south, including mothers with calves beginning the first major journey of their lives.
Here are three remarkable facts about the humpbacks passing our coast.
1. iSimangaliso lies on a major migration corridor
Humpbacks using the southeast African migration corridor travel between Antarctic and sub-Antarctic feeding grounds and breeding areas in southern and central Mozambique.
During the northward winter migration, the orientation of the South African coastline and the south-flowing Agulhas Current funnel many whales relatively close to shore.
The migration is not one continuous line of whales moving together. Individuals are spread across the corridor and over an extended period.
This helps explain why whales may already be present in Mozambique while others are still moving north through KwaZulu-Natal.
2. Newborn humpbacks can look surprisingly pale
Very young humpbacks can look completely different from the dark whales most of us recognise. Newborn calves may be light grey or almost whitish.
They may also show visible foetal folds caused by their position before birth. The dorsal fin and other fins can initially appear softer or less fully formed.
These characteristics change as the calf develops. Scientists therefore use several clues together rather than relying on colour alone when identifying a neonate.
A very pale calf with visible foetal folds and incompletely straightened fins may be a very recent newborn.
Visible foetal folds can be consistent with a calf around a week old or younger. No single feature, however, provides an exact age.
3. Calves feed, grow and keep very close to their mothers
A young humpback has a lot of growing to do. During the first months of life, the calf depends entirely on its mother’s rich milk and may spend around a fifth of its time suckling.
Nursing can involve surprisingly subtle communication. Researchers have recorded very quiet grunts and tonal sounds between mothers and calves. These calls may travel less than 100 metres, allowing the pair to stay in contact without broadcasting their position over long distances.
Recent research has also identified low-frequency sounds associated with suckling. Calves produce sounds described as burps, barks and snorts before or during feeding, and scientists have suggested that some of these may function as begging calls.
Physical contact also appears to be important. Studies have recorded rubbing between mothers and calves during nursing, and calves usually remain within a few tens of metres of their mothers.
Keeping close may also reduce risk. Orcas are known to target humpback calves, and there has been several reported observations of orcas preying on a humpback calf off the iSimangaliso coast.
The video below shows that close association clearly, with the calf remaining immediately alongside its mother as the pair swims past our interns.
Research behind this article
Findlay, K.P., Best, P.B. & Meÿer, M.A. (2011). Migrations of humpback whales past Cape Vidal, South Africa, and an estimate of the population increase rate (1988–2002). African Journal of Marine Science 33(3): 375–392.
Pitman, R.L. et al. (2017). Humpback whales interfering when mammal-eating killer whales attack other species: mobbing behavior and interspecific altruism? Marine Mammal Science 33(1): 7–58.
AI assistance note: This article was developed by Sharklife Conservation Group with the assistance of AI-based drafting and editing tools. Final content, interpretation, and responsibility remain with Sharklife Conservation Group.