Critically endangered blue whales have returned to South Georgia for the first time since being hunted to the brink of extinction 50 years ago.

The return of Antarctic blue whales to seas off the British Overseas Territory in the southern Atlantic Ocean has been confirmed by an international research team led by UK scientists.

The new study follows recent research that humpback whales are also returning to the region.

Scientists say that the discovery, based on analysis of 30 years’ worth of sightings, photographs and underwater sound recordings, is “crucial” evidence in learning how the species is recovering following a ban on commercial whaling in the 1960s.

Blue whales were common off South Georgia before industrial-scale whaling between 1904 and 1971 killed 42,698 of them there. Most of the whales were killed before the mid-1930s.

The species all but vanished from the region with whale surveys from ships off South Georgia resulting in only a single blue whale sighting between 1998 and 2018.

Antarctic blue whales are currently classified as “critically endangered” under the International Union for Conservation of Nature (IUCN) Red List.

However, more recent surveys suggest blue whales are making a comeback.

A survey in February this year resulted in 58 blue whale sightings, and numerous acoustic detections, according to the new study published in the journal Endangered Species Research.

Lead author Susannah Calderan, of the Scottish Association for Marine Science (SAMS), said: “The continued absence of blue whales at South Georgia has been seen as an iconic example of a population that was locally exploited beyond the point where it could recover.

“But over the past few years we’ve been working at South Georgia, we have become quite optimistic about the numbers of blue whales seen and heard around the island, which hadn’t been happening until very recently.

“This year was particularly exciting, with more blue whale sightings than we ever could have hoped for.”

As well as looking for whales, the researchers used listening devices, which can detect the loud, low frequency calls of whales over long distances and can also work in rough weather.

The team also had records of whale sightings reported to the South Georgia Museum by sailors and tourist ship passengers, and photographs of blue whales, which enable individual animals to be identified.

In total, 41 blue whales have been photo-identified from South Georgia between 2011 and 2020, although none of them matched the 517 whales in the current Antarctic blue whale photographic catalogue.

Ms Calderan, an Honorary Research Fellow in Marine Mammal Ecology, added: “We don’t quite know why it has taken the blue whales so long to come back.

“It may be that so many of them were killed at South Georgia that there was a loss of cultural memory in the population that the area was a foraging ground, and that it is only now being rediscovered.”

She explained that there are limited opportunities for dedicated whale surveys in the region, known for its harsh weather and inaccessibility - but such surveys are “crucial” to the future management of South Georgia’s seas.

Co-author Dr Jennifer Jackson, of British Antarctic Survey and who led the 2020 whale expedition, said: “This is an exciting discovery and a really positive step forward for conservation of the Antarctic blue whale."