SYDNEY, June 9 (Xinhua) -- Australian scientists discovered a new population of pygmy blue whales in the Indian Ocean through recordings from hydrophones that were supposed to detect potential nuclear bomb tests.
The study, led by the University of New South Wales (UNSW), was published on Scientific Reports.
Dr. Emmanuelle Leroy, the lead author of the study and former postdoctoral researcher at UNSW Science, told Xinhua on Wednesday that pygmy blue whales are really hard to find since they are rare and spread out over wide areas. It is also the smallest subspecies of blue whales.
It was the whales' powerful singing, recorded by underwater bomb detectors, that gave them away.
Since 2002, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) has been using advanced underwater microphones to detect soundwaves from potential nuclear bomb tests. The recordings, which pick up many other detailed ocean sounds, are available to scientists to use for their marine science research.
The team were studying the data when they found an unusually strong signal: a whale song that had previously been identified in the recordings, but that scientists still knew little about.
After closely studying its composition (details like the song's structure, frequency and tempo), they realized that it belonged to a group of pygmy blue whales, but not any of the ones previously recorded in the area.
"At first, I noticed a lot of horizontal lines on the spectrogram," said Leroy. "These lines at particular frequencies reflect a strong signal, so there was a lot of energy there."
To find out if the signal was a random blip or something more, Leroy and the team scanned 18 years' worth of CTBTO data, the entire available dataset since the recording started, to look for any wider patterns.
They found the songs weren't just a random occurrence.
"Thousands of these songs were being produced every year," she said. "They formed a major part of the ocean's acoustic soundscape."
Leroy said blue whales are powerful singers and they sing very structured, simple songs compared to other whales' songs.
Leroy compared the acoustic features of the song with the three other blue whale song-types known in the Indian Ocean, as well as with four types of Omura's whale songs (another whale in the area) , but the evidence pointed towards this being an entirely new population of blue whales.
While the team are confident in their findings, Leroy said it is impossible to confirm the species without a visual observation, but visual sightings for such an elusive animal can be tricky and expensive to fund, so it's unlikely this will be verified anytime soon.
The finding is big news for marine conservation, as blue whales were brought to the edge of extinction after whaling in the 20th Century.
"Discovering a new population is the first step to protecting it," said Leroy. Enditem