Blue whales rediscover South Georgia | Polarjournal
Blue whales are still the largest whales on earth, despite extensive hunting. But before the hunt, the animals could reach up to 30 meters in size and weigh 140 tons, today still up to 27 meters. A total of four subspecies of blue whales are known, two of them in Antarctica. Picture: Michael Wenger

Blue whales are the largest animals that have ever lived on Earth. This size had also brought the animals to the brink of extinction when industrial whaling had gained traction. Especially around South Georgia, tens of thousands of the giants fell victim to the human exploitation from the beginning of the 20th century. Soon sightings became increasingly rare and blue whales seemed to have disappeared around the island. But now the giants are making a comeback, according to the results of an international research group.

A total of 41 new blue whales were identified around South Georgia by the researchers led by Susannah Calderan of the Scottish Society for Marine Research SAMS. Images of the animals’ backs were compared with 517 known blue whales from an international species catalogue, and the researchers also used whale sightings and images by tourist ships and sailors taken around South Georgia. In addition, acoustic underwater recordings were evaluated, which had recorded the loud but low-frequency sounds and calls of blue whales in the region. Data from the South Georgia Museum, which had collected sightings of whales around South Georgia over the past 30 years, was also included in the analysis. The total period of the investigations covered the time span between 1991 and 2020. The results of the study were published this week in the journal Endangered Species Research.

To identify blue whales, it is possible to use the pattern on the back of the animals and also the shape of the dorsaö fin, which, however, is one of the smallest of all known whales. The sightings, which were recorded in February 2020 alone between the Shag Rocks and South Georgia, show that the animals are returning more and more to the waters. Picture: Michael Wenger / Map: Calderan et al. (2020)

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

Dr Jennifer Jackson, British Antarctic Survey

For scientist Susannah Calderan, the results of the study are exciting. “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.” The investigations this February in particular were fruitful. A total of 58 blue whales could be observed over the course of the month on about 2,430 kilometres travelled around the island. But in addition to their own sightings, the researchers also collected data from other expeditions and trips. This included the first Swiss Antarctic expedition ACE, which had undertaken a research trip around Antarctica in 2016-17. The number of sightings of blue whales increased from 43 sightings between 1991 and 2020 (random sightings plus specific observation) to the 58 mentioned in February 2020 alone. The acoustic data used came from buoys that had been distributed around South Georgia since 2003. Here, the researchers recorded an increase in recorded sound hours from 46 in 2003 to 114 in 2020. “This is an exciting discovery and a really positive step forward for conservation of the Antarctic blue whale,” explains co-author Dr Jennifer Jackson of the British Antarctic Survey.

From 1904 on, permanent whaling stations were established on South Georgia so that the whales could be processed immediately. The Norwegian Carl Anton Larsen, who founded Grytviken in 1904 (pictured), was responsible for this. Here also, the largest whale ever was recorded with 33.6 metres. Picture: Michael Wenger

Blue whales had actually disappeared completely from the waters around South Georgia after the industrial whaling era. Since Carl Anton Larsen had founded the whalling station Grytviken in 1904, blue whales have been hunted. With the invention of harpoon cannons with explosive heads and fast whaling vessels, the animals could no longer escape the whalers. Between 1904 and 1971, 42,698 blue whales were killed around South Georgia compared to approximately 346,000 animals worldwide. In fact, it took just under 30 years for the animals to virtually disappear. Only a whalling stop at the end of the 60s, introduced to recover the numbers, ended the hunt for the whales. When asked why the animals are to be seen more often onl now, Susannah Calderan can only suspect and thinks that perhaps a loss of the “cultural memory” in the animals had taken place, because the population had disappeared and only now the region around South Georgia had been rediscovered.

Dr Michael Wenger, PolarJournal

Link to the study: Calderan SV, Black A, Branch TA, Collins MA et al. (2020) South Georgia blue whales five decades after the end of whaling. Endang Species Res 43:359-373. https://doi.org/10.3354/esr01077

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