Source: The Conversation – Africa – By Matthew Germishuizen, Postdoctoral research fellow, Mammal Research Institute Whale Unit, Department of Zoology and Entomology, University of Pretoria
Most people are lucky to simply get a glimpse of some fragment of a whale. A subtle puff of mist over the horizon, the curve of a dark smooth back sliding beneath the surface, or for the fortunate, the flash of a tail or the explosive splash of 40 tons of flesh pounding the surface of the water when they breach. The immense satisfaction experienced during these brief appearances is a testimony to the whales’ elusiveness, and the immense difficulty of studying them.
For scientists, the challenge is even greater: whales spend most of their lives far offshore, hidden beneath the waves, or even well within the ice pack in some of the most remote and inhospitable oceans on Earth.
This difficulty has driven researchers to creative extremes – like using crossbows to gather skin samples, flying helicopters to count them, and sticking cameras with suction cups on their backs. I faced the challenge myself during my doctoral research at the University of Pretoria, which set out to unravel how southern right whales are responding to the combined pressures of climate change and shifting ocean ecosystems.
Southern rights are the species that draws thousands of visitors to Hermanus, a town on South Africa’s southern Cape coast, each spring when they reach peak numbers at their calving grounds. They generally start arriving here in June after feeding for a couple of years in the Antarctic, and generally all leave by November back into the Southern Ocean.
Southern right whales are one of the three species of right whales worldwide. All belong to the baleen whale group – the filter-feeding giants that include the blue, humpback and fin whales. Reaching up to 17 metres in length, they are among the larger whale species. The southern right is the only right whale found in the southern hemisphere, with populations off South America, South Africa, Australia and New Zealand.
My research shows that the South African population of southern right whales is being squeezed by climate change in the Southern Ocean. Their reproductive slowdown is a clear biological signal of environmental disruption: fewer calves in Hermanus most likely means there is less food under the ice thousands of kilometres away.
This has two important implications. First, it highlights the vulnerability of whale populations. These animals face an uncertain future in a warming ocean. Second, it demonstrates the remarkable role whales can play as sentinels. By monitoring their health and behaviour, we gain insight into vast, remote ecosystems that are otherwise costly and difficult to study.
Why southern right whales matter
Southern right whales were named by whalers who considered them the “right” whales to hunt: slow, predictable, and buoyant when killed. Those same traits almost drove them to extinction. Today, with international protection, many populations are recovering. But recovery is no guarantee of security. The very qualities that made them easy targets now make them excellent sentinels of environmental change.
These whales are what biologists call capital breeders. Mothers must accumulate enormous energy reserves during their foraging season in the Southern Ocean, then draw down on these stores through pregnancy, birth and nursing. If food is scarce, reproduction falters. This tight link between feeding and breeding makes them a living barometer of ocean health.
What I set out to investigate
For decades, South Africa has been at the forefront of southern right whale research. Since 1969, annual aerial surveys along the Cape coast have tracked mothers and calves, building one of the world’s most detailed datasets on any whale species.
In recent years, however, worrying trends have emerged. After 2009, calving intervals, the time between births, lengthened dramatically. Instead of a calf every three years, many mothers were only giving birth every four or five years. Female body condition declined, and stable isotope studies, which analyse molecules in the skin to indicate what whales have been feeding on, suggested whales were feeding further north than before. This indicates that mothers are potentially taking longer to meet the energy requirements of reproduction.
These red flags raised an urgent question: was climate change disrupting the whales’ food supply in their distant Southern Ocean feeding grounds?
Peering into the whales’ world
To answer this, I combined multiple approaches. I analysed 40 years of environmental data: sea ice cover, chlorophyll (a measure of ocean productivity), and historical whaling records. I deployed satellite tags on living whales to follow their migrations offshore. And I worked with international colleagues to use instruments attached directly to whales, tags that measure conductivity, temperature and depth, to understand the physical and biological features of their foraging habitats.
Read more: How microscopic ocean organisms and the earth’s temperature are linked
Together, these methods painted a clear picture. The traditional high-latitude feeding grounds, once rich in one of their preferred prey, Antarctic krill, have experienced dramatic environmental shifts driven by changes in the Earth’s climate. Sea ice, critical for krill survival and reproduction, has declined by 15%-30% in key regions. The marginal ice zone, once a reliable nursery for krill, has retreated southward. In parallel, whale mothers showed signs of poorer body condition, consistent with struggling to find sufficient food.
At mid-latitudes, meanwhile, whales were often found foraging near ocean fronts, dynamic boundaries where warm and cold waters meet, concentrating nutrients and prey. This suggests that when their polar larder fails, whales are forced to adapt by exploiting less predictable feeding zones further north.
Why it matters to all of us
Southern right whales are more than just a tourist attraction. They are indicators of the health of the Southern Ocean, a region that regulates Earth’s climate by absorbing heat and carbon dioxide. Changes in this system ripple far beyond Antarctica, shaping weather, fisheries, and biodiversity across the globe.
When fewer whale calves appear along South Africa’s coast, it is not only a local conservation concern. It is a message carried on the backs of these giants: our oceans are changing faster than they can adapt.
As we celebrate their return each spring, we should also reflect on the bigger story they tell. Protecting whales, and the oceans they depend on, is inseparable from protecting our own future.
– Southern right whales are having fewer calves: what this says about ocean health
– https://theconversation.com/southern-right-whales-are-having-fewer-calves-what-this-says-about-ocean-health-266375