Baleen Whale May Be Behind Mysterious Mariana Trench Call

A previously unidentified call heard in the Mariana Trench could be a new baleen whale call as reported by the Oregon State University researchers who recorded and analyzed the sound. The scientists at Oregon State University's Marine Science Center have dubbed the sound the "Western Pacific Biotwang."

"It's very distinct, with all these crazy parts," shared Sharon Nieukirk, senior faculty research assistant in marine bioacoustics at Oregon State whose study was published in the Journal of the Acoustical Society of America. "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."

The sound was recorded by passive acoustic ocean gliders. These instruments could travel independently for months at a time with the ability to dive up to 1,000 meters. Researchers have observed that the Western Pacific Biotwang is very similar to the sound produced by dwarf minke whales on the Great Barrier Reef off the northeast coast of Australia. Minke whales produce a collection of regionally specific calls that include "boings" in the North Pacific and low-frequency pulse trains in the Atlantic.

"We don't really know that much about minke whale distribution at low latitudes," said 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."

Scientists, however, are not certain if the calls are indeed made by mating minke whales since baleen whale calls are mainly heard during the winter while the Western Pacific Biotwang was recorded throughout the year.

"If it's a mating call, why are we getting it year round? That's a mystery," said Nieukirk. Further research will be done by the team at the Cooperative Institute for Marine Resources Studies, along with Oregon State University and the NOAA Pacific Marine Environmental Laboratory. "We need to determine how often the call occurs in summer versus winter, and how widely this call is really distributed."

Due to its large frequency range, the Western Pacific Biotwang is difficult to detect. "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," said Nieukirk. "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."