After an almost complete absence for over half a century, Antarctic blue whales are returning in numbers to the waters surrounding South Georgia island in the south Atlantic. An international team led by Susannah Calderan of the Scottish Association for Marine Science (SAMS) has collected 58 sightings of the giant cetaceans as well as acoustic soundings of their presence.
One of the great tragedies of the 19th and 20th centuries was the near extinction of the blue whale population throughout the world's oceans. Once almost impossible to hunt, the invention of steam launches and the harpoon gun firing harpoons tipped with explosive heads resulted in the catch of an estimated 382,595 of the largest creature ever to inhabit the Earth, though this number may be higher due to unreliable counts by the USSR on its catch.
In 1967, the International Whaling Commission placed an outright ban on the hunting of blue whales. By that time, their numbers had dwindled to between 10,000 and 25,000. In the region around the British territory of South Georgia, the local blue whale population all but disappeared, with only a single sighting between 1998 and 2018.
Now, a survey conducted this year has shown that the blue whale is making a comeback. In addition to looking for whales directly, the research also used listening devices to detect the acoustic signal caused by the loud, low-frequency calls of the whales that they can send out over long distances. In addition, the team collected sighting reports from mariners and tourist ship passengers.
Photographs were also studied, resulting in the photo identification of 41 blue whales that had their pictures taken between 2011 and 2020, though none of these matched the 417 blue whales in the Antarctic blue whale photographic catalog.
"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," says Calderan. “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.
"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."
The research was published in Endangered Species Research. and the video below discusses the return of the blue whales to South Georgia island.
Source: British Antarctic Survey