Decades after they were wiped out by Soviet hunters, blue whales are making a return to the crystal clear waters of the Seychelles.
Researchers spent a year recording beneath the waves to detect the whales after filmmakers caught sight of them in 2021, and found they could be breeding in the area.
Blue whales are the largest animal to have ever lived on Earth, growing up to 30m in length and weighing up to 150 tons. Once prolific in the Indian Ocean and beyond, sustained hunting in the 20th century resulted in more than 340,000 being killed.
The species is now classified as endangered by the International Union for the Conservation of Nature.
However, numbers are increasing following a near worldwide ban on whaling, and their return to the Seychelles has been described as a ‘conservation win’ by the team, who published their findings in the journal Endangered Species Research.
‘It turns out if you stop killing animals on mass scales and you give them a chance to rebound, they can recover,’ said Dr Kate Stafford, one of the lead investigators.
Speaking to the BBC, she added: ‘We want to know where they are coming back, and knowing there’s a population around the Seychelles is incredibly exciting.’
Populations around the tropical islands were particularly targeted in the early decades of last century by Soviet whalers on their way to and from the Antarctic.
To determine whether the magnificent species had returned to the region, Dr Stafford and the team spent a month surveying the waters and listening to an underwater microphone for signs of them.
Unfortunately, there were none.
‘We heard remarkable things – the tapping of sperm whales thousands of feet down and dolphins echolocating and communicating, but sadly no blue whales,’ said wildlife sound recordist Chris Watson, speaking to BBC News.
However, the team had also planted a sound trap, which recorded every 15 minutes for a year. Within the masses of audio data were the loud and low sounds of blue whales, mainly during March and April.
‘This means the Seychelles could be really important for blue whales,’ said Dr Stafford. ‘They sing during the breeding season and we think it’s probably the males who are singing, based on what we know about other whales.
‘So there’s also potential that the Seychelles is a breeding area or a nursery area.’
However, the song of the blue whale, despite being the loudest in nature, is inaudible to humans.
Although reaching up to 188 decibels, equivalent to a jet engine, the frequency is so low it is beyond the range of human hearing.
What humans can hear are the whales’ ‘harmonics’, higher frequency sounds emitted when they sing.
‘It’s this really low, deep, consistent pulse,’ said Mr Watson.
‘When I recorded blue whales in Mexico, that was what was resonating in my headphones.’
The recordings even allowed the team to see which population was visiting the Seychelles, identifying them as a group normally found in the northern Indian Ocean.
The Seychelles is just one area in which blue whales are making a return. In recent years they have returned to the waters around South Georgia, and in 2021 they were spotted off Spain’s Atlantic coast for the first time in more than 40 years.
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