• Southern Ocean: Where southern right whales feed and live. They migrate to warmer water to mate and give birth.
• 1969: The first aerial survey counting southern right whales along the South African coastline.
• Name: Its name came from the belief that it was the right whale to hunt, as they swim slowly and float when dead.
• De Hoop Nature Reserve: One of the best places in South Africa to spot southern right whales in season. Large numbers of whales congregate in this bay.
• 150 000: Estimated number hunted between the 17th and 19th centuries. Numbers are still recovering.
• June to October: The period when mating and calving takes place.
The University of Pretoria’s Mammal Research Institute (MRI) Whale Unit conducted an aerial survey of southern right whales between September 30 and October 5. This annual survey takes place between Muizenberg and Nature’s Valley not only to monitor population numbers, but to build a database of southern right whales.
This year the numbers were significantly lower, with only 190 females with calves (95 pairs) counted. The number of unaccompanied adults also plummeted and only 10 were counted. Adults usually mate in South Africa’s warmer waters, while pregnant females seek spots in calm bays to give birth.
Numbers of females with calves were very low from 2015–2017 and then peaked in 2018 when 536 cow-calf pairs were counted along the same stretch of coastline. Numbers have however been generally low for unaccompanied adults (males and females not calving that year) after 2009. In 2009, there were more than 300 unaccompanied adults.
“I am concerned over this,” says Dr Els Vermeulen, research manager and post-doctoral research fellow at the MRI Whale Unit. “We are seeing extreme fluctuations, with numbers of unaccompanied adults staying low,” she adds. Females could be failing to fall pregnant, migration routes could be altered or migration could have stopped.
From trends it seems that females now give birth every four to five years instead of every three years. There is also an apparent shift in the peak presence of cow-calf pairs from October to earlier in the year. This could mean females give birth earlier and leave South Africa earlier, or that female right whales leave the South African breeding ground quicker, possibly with a calf that is not ready to migrate.
According to Vermeulen, “They used to stay for about three months, but it seems they are leaving sooner. It may be that they are hungry and do not have the energy while nursing their calf.” Southern right whales feed on krill and copepods (crustaceans), a food source found in the Southern Ocean.
Vermeulen says that even if the whales are not migrating to South Africa, they can still mate and conceive. She is concerned, however, as calves learn migration routes from their mothers and they then return one day to where they were born. If the route is altered, calves will learn this route instead.
Whether these trends are temporary or not remains to be determined. “We are looking at the feeding grounds and took skin samples this year,” she says. Skin samples will reveal more about their diet.
Preliminary results indicate a correlation between climatic conditions in the Southern Ocean, fluctuations in food, and energy reserves. Future plans include satellite tagging the whales and looking at the hormonal profile of females.
Although similar trends are recorded in South America and Australia, the fluctuations are extreme in South Africa.
The long-term statistics and photo-identification records provide insight into the life of these whales and form part of an international project of the International Whaling Commission, co-led by the MRI Whale Unit. The total population estimate is 6 116 animals based on resighting history. Adult survival rate is high, and 85% of calves survive the first year. The current whale population is only at 20% of what it used to be
Fewer southern right whales can also affect the tourism industry. “It affected our sightings in Gansbaai and although we did have some, it was very slow. They seemed to have left a bit earlier in the season,” says Brenda du Toit, public relations for Dyer Island Cruises.
“Females with calves can’t be approached by boats as it puts extra pressure on females with already low energy levels,” Vermeulen explains.
Written by René de Klerk. Photos by Mammal Research Institute.
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