Rare population of blue whales found in Indian Ocean with help of nuclear bomb detectors

By Angela Heathcote 9 June 2021
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Heard but not seen: the discovery of a new population of blue whales in the Indian Ocean excites conservationists and scientists.

Blue whale populations have struggled to bounce back from the whaling era, which is said to have claimed over 300,000 individuals in the Southern Hemisphere alone. That a new population of these ocean giants has now been discovered in the middle of the Indian Ocean is of great excitement to scientists and conservationists. 

The new population of pygmy blue whale – the smallest species of blue whale – were recorded as far north as the Sri Lankan coastline and as far east in the Indian Ocean as the Kimberley coast in northern Western Australia. 

The discovery was made possible by using data from the Comprehensive Nuclear-Test-Ban Treaty Organization, which has been monitoring the sound of our oceans for evidence of nuclear bomb testing since 2002.

Marine biologists such as Tracey Rogers, a co-author on the paper describing this new population, have been using this data for over a decade to monitor whales. 

“I think it’s pretty cool that the same system that keeps the world safe from nuclear bombs allows us to find new whale populations, which long-term can help us study the health of the marine environment,” Tracey says. 

The data had previously been used to confirm the existence of a new population of blue whales in the north-western Indian Ocean in January of last year bringing the total number of blue whale populations to five. Because the song of the blue whale differs depending on the population it makes it easy to identify a possible new population, however, without seeing the whales in the wild, it can be difficult to confirm.

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According to Tracey, because blue whales don’t breach or slap their pectoral flippers, travel in small groups or alone and have a low profile in the water thanks to their sleek blue bodies, scientists rely heavily on audio recordings.  

Studying these whale songs is important as scientists believe they are changing.

“The blue whale song is very repetitive,” says lead author Emmanuelle Leroy. “The same song is repeated again and again with a regular interval during hours. It is also very stable over time, while the song of the humpback whales changes across years, the blue whales have the same song since they were recorded in the 1960s for some populations. However the pitch of their song is slightly but consistently decreasing over time, but we are not sure why.”

Big questions lie ahead, but for now, scientists are overjoyed with the new discovery. 

“Finding a new population of pygmy blue whales in the Southern Hemisphere is exciting,” Tracey says. “The conservation community has been concerned for Southern Hemisphere blue whales for some time because their populations have not recovered as well as other whale species since hunting stopped. This new population increases the global population that we did not realise was there before.”