Blue Whales Return to South Georgia After Facing Near Extinction

They've been spotted again, 50 years after whaling almost erased them forever.

Antarctic blue whale
There are about 3,000 Antarctic blue whales in the world.

Paul Ensor/Oregon State University [CC BY-SA 2.0] / Flickr

Critically endangered Antarctic blue whales have been spotted again in the sub-Antarctic island of South Georgia. An international team of researchers discovered the animals five decades after whaling nearly erased them forever.

Researchers analyzed 30 years of data including whale sightings, photographs, and underwater acoustic recordings. They examined how the species eventually rebounded from near-extinction. Their findings were published in the journal Endangered Species Research.

“Blue whales at South Georgia were very heavily exploited during early 20th century industrial whaling,” Lead author Susannah Calderan, marine mammal ecologist with the Scottish Association for Marine Science (SAMS), tells Treehugger.

“The length of time taken for blue whale numbers to start to recover at South Georgia is indicative of that level of depletion, both of the local blue whale population at South Georgia and also that of surrounding areas.”

Antarctic blue whales (Balaenoptera musculus intermedia) were plentiful in the area until whaling began there in 1904, kicking off the beginning of industrial whaling in the Southern Ocean. While hunters originally focused on species that could be easily captured, like the humpback whale, the focus quickly moved to the blue whale.

Between 1904 and 1973, some 345,775 Antarctic blue whales were killed in the Southern Hemisphere and in the northern Indian Ocean. Around South Georgia, blue whale catches were reported year-round. Between 1904 and 1971, industrial whaling killed 42,698 blue whales.

“Blue whales around South Georgia and in the wider Southern Ocean were killed in such numbers that there was neither a remnant population which could recover, nor sufficient animals in adjacent areas which could recolonize,” Calderan says.

“There might also have been a loss of cultural memory of the area as a feeding habitat as so many of the whales which used South Georgia as a foraging ground had been killed.”

Antarctic blue whales are classified as critically endangered according to the International Union for the Conservation of Nature (IUCN) Red List. There are an estimated 3,000 adult animals alive today.

Analyzing the Return

For the study, researchers evaluated all Antarctic blue whale data from the last three decades. They analyzed sightings from scientific surveys collected by observers on ships, as well as opportunistic sightings reported by mariners and cruise ship passengers to the South Georgia Museum. They studied photographs of blue whales which specifically identified them as individuals.

They also examined acoustic recordings of blue whale vocalizations. Blue whales have several sounds: repeated songs believed to be made just by males and frequently modulated calls thought to be produced by both sexes. Researchers used these latter calls, associated with group and foraging behaviors, to estimate whale locations.

They found that dedicated whale surveys from ships off South Georgia resulted in just one blue whale sighting between 1998 and 2018. But more recent surveys suggest better news. A 2020 survey in February 2020 found nearly 60 blue whale sightings, and several acoustic detections.

A total of 41 blue whales have been identified through photos from South Georgia between 2011 and 2020. None of these whales, however, match the 517 whales that are in the current Antarctic blue whale photographic catalog.

“Their return is very significant, as it was widely thought that blue whales at South Georgia might have been exploited beyond a point where they could recover, and might never be seen again in significant numbers at South Georgia,” Calderan says.

South Georgia is an example of how vulnerable whales are to over-exploitation, she points out.

“There are other areas of the world where currently whales are being killed at higher rates than may be sustainable, either directly through whaling, or through human impacts such as ship strikes or fisheries bycatch,” she says.

“In those circumstances, there is a real risk of localized depletion, even if the populations as a whole seem quite large. However, our research also shows that populations can recover even from very low levels if they are given sufficient protection.”

View Article Sources
  1. https://www.int-res.com/articles/esr2020/43/n043p359.pdf

  2. https://www.iucnredlist.org/species/41713/50226962

  3. Lead author Susannah Calderan, marine mammal ecologist with the Scottish Association for Marine Science (SAMS)