Complex call recorded in Mariana Trench, probably from baleen whale

Researchers with Oregon State University (OSU) have recorded and analyzed a sound in the Mariana Trench notable for its complexity and wide frequency range, believing it represents the discovery of a new baleen whale call.

Recorded via passive acoustic ocean gliders, which are instruments that can travel autonomously for months at a time and dive up to 1,000 meters, the five-part call lasts between 2.5 and 3.5 seconds and includes deep moans at frequencies as low as 38 hertz and a metallic finale that pushes as high as 8,000 hertz.

It resembles the so-called "Star Wars" sound produced by dwarf minke whales on the Great Barrier Reef off the northeast coast of Australia, the researchers say.

Researchers at OSU's Hatfield Marine Science Center named it the "Western Pacific Biotwang."

"It's very distinct, with all these crazy parts," explained Sharon Nieukirk, senior faculty research assistant in marine bioacoustics at OSU. "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 Mariana Trench, located in the western Pacific Ocean, to the east of the Mariana Islands, is the deepest known part of the world's oceans with a maximum-known depth of nearly 11,000 meters. It is about 2,550 kilometers long with an average width of 69 kilometers.

Minke whales are baleen whales, meaning they feed by using baleen plates in their mouths to filter krill and small fish from seawater, and live in most oceans. They produce a collection of regionally specific calls.

"We don't really know that much about minke whale distribution at low latitudes," said Nieukirk, lead author on the study published in the Journal of the Acoustical Society of America. "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."

However, many questions remain. For example, baleen whale calls are often related to mating and heard mainly during the winter, yet 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," Nieukirk was quoted as saying in a news release from OSU. "We need to determine how often the call occurs in summer versus winter, and how widely this call is really distributed."

"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. 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." Endit