Solving the mystery of the declining South African southern right whale population by discovering their blue corridors

© Peter Chadwick / WWF

The Whale Unit at the Mammal Research Institute at the University of Pretoria spent the last 50+ years researching southern right whales off the coast of South Africa. Right now, Research Manager Dr Els Vermeulen and her team are focused on solving a scientific mystery. Since 2009, very few southern right whales have been seen along the South African coastline. Their numbers, in coastal South Africa, have been fluctuating, and they don’t know why. The team also noticed that females are thinner and take longer to produce calves with 4-to-5-year calving intervals.

The Whale Unit is an African research, conservation and education facility that studies the ecology, population dynamics and behaviour of whales, dolphins and porpoises in the Southern African sub-region and surrounding oceans. Work on southern right whales started in the 1960s, and with 52 years of data, it is likely one of the longest-running research programs in the world.

© Whale Unit, University of Pretoria

The southern right whale is one of three species classified as right whales. Right whales are baleen whales, which means they have baleen plates instead of teeth through which they filter their food. These whales live in oceans south of the Equator. Right whales got their name because they were the “right whale to hunt.” They moved slowly and floated to the surface when they died. For these reasons, they were heavily hunted during the whaling era, and the global population plummeted to approximately 60 females by 1920. 

Fortunately, today, right whales are protected from commercial whaling, and their numbers have started to recover. But now, these whales face new threats, and the team is trying to figure out why these whales are thinner and calving at a slower rate.

Blue corridors is a term used to define migratory routes for whales. Migratory ocean species, such as whales, have no boundaries. Their range can often span state, national and international jurisdictions. Whales face threats across all oceans, including industrial fishing, ship strikes, pollution, habitat loss, and climate change. Protecting Blue corridors, a report from WWF and partners outlines a new approach to conserve whales.

Tracking whales to uncover their blue corridors and critical habitats

Solving a scientific mystery takes tools and time. The team uses tagging technology to track the whales to their feeding grounds. Tagging lets them investigate migration and feeding behaviour. They deployed a total of 11 tags in October 2022. 

Southern right whales are solitary creatures. They feed just below the surface of the water, consuming large amounts of zooplankton. Their primary source of zooplankton is Antarctic krill. 

© Whale Unit, University of Pretoria

Right whales are distinguishable by the callosities on their heads. Callosities refer to calcified skin patches. They appear white and form due to large colonies of tiny hitchhikers called cyamid amphipods or whale lice. Callosities produce a unique pattern on each right whale, making it easier to tell the whales apart.

By studying the deployed tags, the team made a few conclusions. Most of the tagged whales are going towards known foraging areas like Bouvet Island. They assume the green and purple tags are heading to Crozet Island. This area is historically documented as a foraging ground for southern right whales in this region. But, the other outliers, the pink and blue tags are heading in an unusual direction. The team predicts that they are possibly going to the Patagonian Shelf.

The Patagonian Shelf is not a known foraging destination for southern right whales from South Africa. Nonetheless, last year there were two whales that migrated in this direction and journeyed all the way to the South Georgia/South Sandwich Islands area, a well-known foraging ground for South American southern right whales. However, southern right whales from South Africa typically don’t travel this far west.

Since tagging technology is recent, Els and the team don’t know if this behaviour is due to a lack of food availability in areas where the whales usually find food or if southern right whales from South Africa have migrated to these areas for foraging in the past.

Using historical photographs and drone footage to determine body condition

To continue solving the mystery, the team used historical photographs to determine if the body condition of the whales had changed. To make the comparison, they used drones to take photos of the current population. Using this data, they concluded that there was a 23 per cent reduction in the body condition or the fatness of lactating females.

The team concluded that southern right whales, which calve in South Africa, are most likely experiencing a lack of food availability leading to altered migration patterns, lower calving rates and decreased body conditions.

How the climate crisis is impacting southern right whales

Southern right whales rely on a range of zooplankton, including Antarctic krill, to survive. Ocean temperatures in west Antarctica have risen by more than 2.7°C since the 1970s, about five times the global rate of warming. Melting sea ice poses a grave threat to krill, which feed on phytoplankton growing beneath the ice.

Like the southern right whale in South Africa, research shows that other top predators throughout the Southern Ocean also dependant on the Antarctic food web, including humpback whales, penguins and seals, are likewise experiencing changes in their demography and migration patterns.

“What specific climatic and oceanographic variabilities lie at the heart of this, we do not know for sure yet, but we intend to find out. The southern right whales are clearly acting as sentinels, bringing to coastal South Africa an important message about large-scale environmental changes in the vast Southern Ocean, which is undoubtedly affecting many other marine species,” says Dr Els Vermeulen. “Southern right whales need our attention and help to ensure that they can continue to thrive into the future in an ocean that is ever-changing.”

The Protecting Blue Corridors report calls for a new conservation approach to address these mounting threats and safeguard whales through enhanced cooperation from local to regional to international levels. WWF calls for governments to support the Americas Protection of the Oceans joint declaration to implement networks of MPAs, Marine Protected Areas, and OECMs, Other Effective Area-Based Conservation Measures, in the Eastern Pacific Ocean, with the goal of protecting or conserving at least 30 per cent of the ocean by 2030.

Learn more about Protecting Blue Corridors.