A Southern Right Whale (Eubalaena australis) is seen at Ribanceira Beach, Imbituba, Santa Catarina state, Brazil on July 09, 2019. (Photo: EDUARDO VALENTE/AFP via Getty Images)
A Southern right whale that was tagged along with her calf off South Africa’s coast nearly seven months ago has made an “unprecedented” 10 000km migration to Argentina, probably in search of sufficient food.
She was one of four adult female southern right whales fitted with satellite tags in Walker Bay in October last year. Since then she has crossed the South Atlantic and is now on the Patagonian Shelf, puzzling marine scientists.
The tag stopped transmitting on 14 December and came back online last week, “showing the incredible journey she and her calf have undertaken”, according to Els Vermeulen, the research manager of the Mammal Research Institute’s whale unit at the University of Pretoria.
The tags were used in a pilot study to investigate, in detail, the migration and feeding behaviour of these mammals.
“The southern right whale population of South Africa has shown quite remarkable changes in the last decade, including alteration in their foraging locations, which is the Southern Ocean, but this seems to have changed over time,” Vermeulen said.
“They have also shown decreased body condition, so the whales have got skinnier and there’s also a reduced reproduction rate meaning that the females take longer to reproduce a healthy calf.”
These changes are probably caused by reduced prey in the Southern Ocean as a result of climate change. “Now, in trying to understand everything, we need to understand where these whales are feeding in the Southern Ocean. Studying them in the Southern Ocean is obviously complicated so therefore we started a satellite tagging project.
“The fact that one of our whales has now pitched up in South America is unprecedented. So we know there is some genetic connectivity around the Atlantic — between the whales of South America and South Africa. However, in the genes you can also see that there’s quite some separation.”
South African whales tend to stay in local waters while South American whales tend to stay in that region. This is especially true for females with calves. “So we can see in the DNA that females are highly philopatric [the tendency of an animal to remain in or return to the area of its birth] and so they learn the migration from their mothers and then that is what they do,” said Vermeulen.
“We’ve always believed that maybe here and there, some males might randomly mate with the opposite stock. Now, seeing a female with a calf doing this kind of migration is unheard of.”
There is no certainty that her calf is still alive. “We’re talking about an adult female, which has now pitched up in South America. This is throwing everything out and we don’t know if this is more common than we think because we don’t usually satellite tag that often.”
The tagging project is only the second in South Africa. The first was in 2001 when six whales were fitted with satellite tags.
“This is the first time we can see this. There’s no indication in the DNA that this is a common behaviour. So, we’re trying to understand if this relates to this whale feeding there and coming back to the South African coast or if this whale is going to stay in that region now, which is hopefully what the tag will tell us as we go along in time.
“But, ja, in the entire scientific community this has really thrown us off — a lot of the stuff that we believed. It shows that these whales are more flexible than we might give them credit for. In other ways, that these whales have to migrate that far to find good food sources — because that’s what we believe has happened — is a worrying trend.”
Vermeulen said they hope to secure further funding to tag another 10 whales this year and 10 more next year. “We really need to understand how these whales are migrating and where they’re going to better understand what is happening.”
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