Baleen whale likely responsible for complex call recorded in Mariana Trench

CORVALLIS, Ore., Dec. 14 (UPI) -- Scientists believe a new, complex call recorded in the Mariana Trench was produced by a baleen whale. The call, dubbed the "Western Pacific Biotwang," was recorded and analyzed by researchers at the University of Oregon's Hatfield Marine Science Center.

The lengthy and varied call features a range of frequencies. It include five parts. The initial sections feature deep moans, as low as 38 hertz. The call crescendos with a high pitch of 8,000 hertz.

It was recorded by autonomous gliders off the east coast of Guam in the fall of 2014 and spring of 2015. Researchers described the call in the Journal of the Acoustical Society of America.

"It's very distinct, with all these crazy parts," Sharon Nieukirk, senior faculty research assistant in marine bioacoustics at Oregon State, said in a news release. "The low-frequency moaning part is typical of baleen whales, and it's that kind of twangy sound that makes it really unique.

Scientists say the call is most similar to the "Star Wars" call made by dwarf minke whales off the northeast coast of Australia near the Great Barrier Reef. Minke whales are a type of baleen whale. They've also been recorded making sounds called "boings" in the North Pacific, as well as low-frequency pulse trains in the North Atlantic.

The similarity between the Western Pacific Biotwang call and other minke whale calls suggest the baleen species is most likely responsible for the unique, five-part call. Still, questions remain.

"If it's a mating call, why are we getting it year round? That's a mystery," asked Nieukirk. "We need to determine how often the call occurs in summer versus winter, and how widely this call is really distributed."