/ 7 November 2021

Satellite tags on whales to give reason for their decline

Southern Right Whale Juvenile Is Swimming Below The Surface
En route: Southern right whales’ migration, reproduction and body condition has changed. The adults nurse their young (above) in the Southern Ocean. Photo: Gerard Soury/Biosphoto/AFP

Satellite transmitters have been attached to four adult female southern right whales to track their migration and to understand how climate change is affecting their routes and feeding patterns.

This kind of research is of “paramount importance”, says the University of Pretoria’s whale unit at the Mammal Research Institute, considering the drastic changes that have been observed in southern right whale migration, reproduction and body condition in the past 10 years. These changes, it says, are probably caused by reduced food in the Southern Ocean caused by climate change.

The unit has, for the past 42 years, monitored the southern right whale population that breeds off the South African coast. 

Its most recent results show drastic changes in the population in the past decade, including significantly decreased reproductive success and body condition (or “fatness”), and a change in foraging and migration behaviour. 

All these factors have resulted in lower numbers of southern right whales being seen off South Africa’s shores. 

The unit’s 42nd annual aerial survey in October counted and photographed 382 females and calves (191 pairs) as well as 32 adult whales without a calf (“unaccompanied adults”), bringing the total to 414 southern right whales from Nature’s Valley to Muizenberg. 

The majority of female-calf pairs were observed between De Hoop Nature Reserve and Walker Bay. This number, the unit says, is higher than the numbers recorded in 2019 and 2020, but “still remains well below what we would expect under ‘normal conditions’. The number of unaccompanied adults (males, resting females and receptive females) continues to remain extremely low, as it has been since 2009, indicating that non-calving right whales are still not migrating to the South African coast as they used to.”

The main food source for hungry southern right whales is found thousands of kilometres away where they will nurse their young. As a result, southern right whales are called “capital breeders”, which means that their successful migration and calving is dependent on them eating enough during their feeding season in the Southern Ocean. 

The changes observed by the unit point strongly toward a decreased food availability for these whales in their Southern Ocean feeding grounds. “It is of utmost importance to identify these feeding grounds so that the whale unit can assess what climatological and/or oceanographic changes may lie at the root of this conservation problem.” 

The satellite transmitters will help find the answers. “These tags will provide us with information on the location of each individual for up to one year maximum, allowing the unit to investigate each animal’s migration and foraging behaviour in more detail.”

If all goes well, 30 more satellite transmitters will be used in the next two years.

This research is run in collaboration with the National Oceanic and Atmospheric Administration, University of Washington’s Cooperative Institute for Climate, Ocean and Ecosystem Studies and the Marine Ecology and Telemetry Research. The project is funded by the unit and Instituto Aqualie. 

Follow the whales in real time here.