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Nuclear bomb sensor exposes hidden population of blue whales

Monday, June 21st 2021, 4:19 pm - Researchers combing through acoustic data obtained by an underwater nuclear bomb detection array unexpectedly uncovered a new population of pygmy blue whales.

Blue whales are known for their massive size, but somehow a new population of pygmies went undetected in the Indian Ocean for nearly 20 years.

How were they discovered? Scientists combing through acoustic data obtained by an underwater nuclear bomb detection array, according to a study published earlier this year. The data collected also included sound recordings that revealed a never-before-heard song dating back almost two decades.

The new group of pygmy blue whales (Balaenoptera musculus brevicauda) is considered to be a smaller subspecies of blue whale that can grow to a maximum length of 79 feet (24 metres). They are known as the Chagos population, named after a chain of islands in the Indian Ocean near the group's home.

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Blue whale (YouTube/Todd Chandler, Oregon State University)

"We are still discovering missing populations of the largest animal that has ever lived," senior author Tracey Rogers, a marine ecologist at the University of New South Wales (UNSW) in Australia, told Live Science. "It's a testament to the difficulty of studying life in the ocean."

Because there are a finite number of scientific acoustic arrays established in the Indian Ocean, a group of scientists utilized underwater nuclear bomb detectors that belong to the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Researchers were then able to access a long-term database of noises encompassing the Indian Ocean.

"The CTBTO data is an important international asset," Rogers said. "I think it's cool that the same system that keeps the world safe from nuclear bombs is available to researchers, and allows a host of scientists, including us, to do marine science that would not be possible without such sophisticated hydroacoustic arrays."

EACH SUBSPECIES HAS UNIQUE SONG TYPE

Once the data was examined, scientists found a specific blue whale song that hadn't been heard before. Typically, blue whale songs are lengthy, consist of a low frequency, sometimes below the range that humans can hear (under 20 hertz), are of high intensity and replicated at regular intervals.

However, different groups of whales have calls that deviate in duration, structure and the quantity of defined sections.

"Blue whale songs are very simple in the way that they are the repetition of the same pattern," lead author Emmanuelle Leroy, a post-doctoral fellow at UNSW, told Live Science. "But each blue whale subspecies and population has a different song type."

The song that is from the new pygmy population contains three sections. The first is the most complex, with two basic parts that follow it.

"This new whale song has been a dominant part of the soundscape in the Central Equatorial Indian Ocean for the past nearly 18 years," Rogers said.

Due to the song's abundance, scientists are certain it belongs to an entirely new population and not just a few single individuals. But the precise size of the group is still unknown.

Visual identification is still needed to confirm their presence, but scientists believe it’s only a matter of time before it is.

According to the Center for Biological Diversity, there are approximately 5,000 to 10,000 blue whales currently in the Southern Hemisphere -- considerably lower than the pre-whaling population of about 350,000 there.

The study was published in April in the journal Scientific Reports.

Thumbnail courtesy of YouTube/Todd Chandler, Oregon State University.

Nathan Howes can be followed on Twitter: @HowesNathan.

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