An international research team has welcomed the return of critically endangered Antarctic blue whales to the sub-Antarctic island of South Georgia – 50 years after industrial whaling had all but annihilated them.

The Scottish Association for Marine Science (SAMS) and the British Antarctic Survey (BAS) based their findings on photographs and underwater sound recordings along with records kept over the past 30 years.

Blue whales were abundant off South Georgia before whaling killed 42,700 animals between 1904 and 1971, mostly before the mid-1930s. Dedicated whale surveys over 20 years from 1998 revealed only a single sighting – but then a survey this February resulted in 58 sightings and numerous acoustic detections.

The preliminary findings from that survey, along with encouraging reports of a boost in humpback-whale numbers in the area, was reported at the time on Divernet. Opportunities for dedicated whale surveys in the region are limited by its harsh weather and inaccessibility.

“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,” said marine mammal ecologist Susannah Calderan of SAMS, lead author of the team’s  just-published report.

“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.”

The team combined its fieldwork with records of sightings reported to the South Georgia Museum by mariners and cruise-ship passengers, and photographs that enabled individuals to be identified. Forty-one blue whales have been photo-identified between 2011 and 2020, though none matched the 517 whales in the current Antarctic blue whale photographic catalogue.

“We don’t quite know why it has taken the blue whales so long to come back,” said Calderan. “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.”

“With South Georgia waters designated as a Marine Protected Area by the government of South Georgia and the South Sandwich Islands, we hope that these increased numbers of blue whales are a sign of things to come, and that our research can continue to contribute to effective management of the area,” said co-author and BAS whale ecologist Dr Jennifer Jackson, who led the 2020 whale expedition.

“This is an exciting discovery and a really positive step forward for conservation of the Antarctic blue whale.”

The report is published in the journal Endangered Species Research.