Monday, 19 December 2016
Minke Whale Call May Be Mysterious Mariana Trench Noise
Scientists have picked up a "crazy," complex call from the depths of the Mariana Trench. Although the mysterious sounds haven't been attributed to an exact species just yet, marine researchers believe it's less the call of Cthulu and more a previously-unknown dialect of baleen whale song.
As the deepest known area of our planet's oceans, the Mariana Trench captures the imagination, especially when it produces sounds as eerie as these. That said, some of that other-worldliness is undermined by the name it was given – the "Western Pacific Biotwang" – by its discoverers, scientists from Oregon State University's Hatfield Marine Science Center. The calls were picked up by passive acoustic ocean gliders, instruments that can dive down to 1,000 m (3,281 ft) below the surface to record and study ocean sounds.
Made up of five distinct parts, the calls tend to last between 2.5 and 3.5 seconds. Frequency-wise, they're quite the roller coaster ride, with moans dropping as low as 38 Hz before jumping up to 8,000 Hz for a high-pitched finish the researchers describe as "metallic." That wide a range makes it hard for researchers to notice the calls, since studies often focus on narrow frequency bands.
"It's very distinct, with all these crazy parts," says Sharon Nieukirk, lead author of the study. "The low-frequency moaning part is typical of baleen whales, and it's that kind of twangy sound that makes it really unique. We don't find many new baleen whale calls."
Minke whales are the most likely culprits, according to the team. The closest match for the strangeness of the Western Pacific Biotwang are the calls emitted by dwarf minke whales around the Great Barrier Reef, northeast of Australia – sounds that scientists have dubbed "Star Wars" calls, since they apparently sound like blasters and lightsabers. And because minke whales have a wide variety of calls depending on their region, it stands to reason that the Western Pacific Biotwang is simply an as-yet-unheard dialect.
"We don't really know that much about minke whale distribution at low latitudes," says Nieukirk. "The species is the smallest of the baleen whales, doesn't spend much time at the surface, has an inconspicuous blow, and often lives in areas where high seas make sighting difficult. But they call frequently, making them good candidates for acoustic studies."
But in the case of the Western Pacific Biotwang, this frequent calling does raise further questions. Baleen whales tend to call more regularly in winter, during mating season, but this new sound wasn't limited to that time of year.
"If it's a mating call, why are we getting it year round? That's a mystery," says Nieukirk. "We need to determine how often the call occurs in summer versus winter, and how widely this call is really distributed."
Whether it is minke whales or not, confirming what's making all this racket is a priority for the researchers, and the team hopes that the sounds might turn up in existing recordings, where the wide frequency band may have led them to be previously missed.
"Now that we've published these data, we hope researchers can identify this call in past and future data, and ultimately we should be able to pin down the source of the sound," says Nieukirk. "More data are needed, including genetic, acoustic and visual identification of the source, to confirm the species and gain insight into how this sound is being used. Our hope is to mount an expedition to go out and do acoustic localization, find the animals, get biopsy samples and find out exactly what's making the sound. It really is an amazing, weird sound, and good science will explain it."
The research was published in The Journal of the Acoustical Society of America.
Source: Oregon State University