Citizen journalist Rachel Kan interviews researcher Nikita Pinto on monitoring whale populations

CTBTO Science and Technology Conference coverage 2021

CYG Citizen Journalist Rachel Kan interviews researcher Nikita Pinto about her work using the CTBTO’s hydroacoustic monitoring systems to find new whale populations, following the Science and Technology Conference 2021.

Whales in the Indian Ocean tracked using nuclear explosion detectors

Researchers Nikita Pinto and Tracey Rogers spoke at the SnT 2021, the sixth CTBT: Science and Technology conference of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), about using sound recordings to study changes in whale behaviour. The data comes from underwater instruments called hydrophones, which form part of the International Monitoring System (IMS) for detecting nuclear explosions. Sound waves can travel long distances in water, so even faraway sources can be captured in the data. The recordings are then sent via satellite to a central data centre in Vienna, where it can be downloaded by authorized users. 

Both Pinto and Rogers have taken advantage of the recordings from hydrophones near Diego Garcia Island in the Chagos Archipelago, which is in the central Indian Ocean, to the south of India and east of Tanzania. There are two stations, one to the northwest of the island and one to the south, which ensures sounds coming from all directions are recorded without some being blocked by the island. The hydrophones are anchored around 1 km below the sea surface, and are connected to computers on Diego Garcia Island by underwater cables. They have been in service for nearly two decades and operate almost continuously, providing a unique, long-term dataset.

The blue whale is the largest known mammal, and because of its size, blue whale calls tend to be loud and of low frequency. This means that these calls are recorded more easily by the IMS hydrophones, and indeed blue whales appear frequently in the recordings made at Diego Garcia Island. Whales live together in groups known as ‘acoustic populations’, and are identified by songs – or repeated series of calls – that are unique to each population. Rogers and her colleagues have recently discovered a potential new population of blue whales in the Indian Ocean, which they called the Chagos blue whale. The hydrophone data shows that this population has been active in the central and north-eastern Indian Ocean for at least the past 16 years (see green area in the map), and can be tracked by the whale’s signature three-unit song. These results follow the finding in 2020 of another new population in the north-western Indian Ocean (see red area in the map).

The IMS data is not only useful for identifying whale populations and their movement, but also for studying changes in the whale songs themselves. Pinto and her research group recently found that the song of the Chagos whale has been showing a consistent pattern of change across 18 years

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. The importance of observing how animals change with time was highlighted by Rogers, who explained in her talk that shifts in animal behaviour can reflect climate change, which in turn impacts human activity. For example, disruption to predictable patterns of temperature change in the Indian Ocean causes blue whales to adjust the time when they migrate to particular parts of the ocean for feeding. The irregular temperatures can also lead to extreme weather, affecting farming and public safety, among other things. Therefore, studying the behaviour of marine animals has wide-ranging implications for both wildlife and human life.  

The fact that IMS data is available for free use is a gift to the scientists who rely on it, since they do not have to allocate funds or manpower to buy, deploy, and maintain the necessary equipment, particularly over long periods of time. ‘In biology, finding large term datasets on any animals let alone mammals, let alone the largest mammals that ever lived, is really difficult,’ said Rogers. In addition, the global coverage of the IMS hydrophones makes the system particularly suitable for observing moving animals and other phenomena in the vast seas that are otherwise difficult to locate and track. However, Pinto warned that findings from hydrophone data should be paired with visual confirmation. “Counting calls doesn’t always equate to number of whales,” she explained in an interview with the CTBTO Youth Group, although it provides an initial estimate of where an expedition might find the animals. As such, she calls the whales in her SnT 2021 presentation ‘unidentified’, meaning that population has not yet been confirmed with a sighting in scientific literature. As for Rogers, the discovery of the new population identified in the north-western Indian Ocean is supported by sightings at matching times and locations. 

Beyond whales, underwater sound can be used to study icebergs, underwater volcanoes, and shipping accidents. Together with other components of the CTBTO’s IMS, hydrophones have broad applications for civilian, scientific, and military use. For more information, visit

Video by Rachel Kan

Audio track credit: “The Cosmos” from Sirius Beat

The CTBTO Youth Group (CYG) is over 1000 members strong, and works to promote the entry into force of the CTBT, which would ban nuclear explosions everywhere.

During the Science and Technology conference, members of the Youth Group were able to meet virtually with scientists and diplomats from all over the world, listen to their expertise, and interview them as citizen journalists under the guidance of Atomic Reporters for the Citizen Journalism Academy.

To find out more, visit the Atomic Reporters website: