A strange noise, sounding much like a duck, has been heard in waters surrounding Antarctica for decades. The sounds have also been recorded in the waters off Western Australia and the Eastern Weddell Sea off Antarctica. 

This "bio-duck" noise has been recorded in the Southern Ocean for more than 50 years. The unusual quack was first recorded by crews aboard submarines in the 1960's. The sound repeats in sets lasting 3.1 seconds each, and distinctive sounds accompany seasonal changes. 

At first, many people believed the sound was artificial, possibly created by other submarines. Later theories centered on fish as the sources of the sound, but no fish was large or powerful enough to create the sonic waves being recorded. Now, researchers believe they have found the source of the mysterious sounds. Antarctic minke whales (Balaenoptera bonaerensis) are the ones making the distinctive noises, according to a new study. 

Denise Risch from the Northeast Fisheries Science Center spent years studying the animals. The team was in Wilhelmina Bay, bordering the Western Antarctic Peninsula, in February 2013 when they found something unusual. 

Risch's team fitted a pair of the marine mammals with radio transmitters and microphones. These were attached to the whales with suction cups. The marine biologist intended to track the animals as they searched for food in the frigid waters. Researchers aboard inflatable rafts approached the whales, and applied the devices to the animals using hand-held rods. 

Microphones recorded sounds that match the bizarre bio-duck sounds. No other marine mammals were nearby when the sounds were recorded, lending further evidence that minke whales are the source of the bio-duck sounds. The research team does not know, however, if the sounds they recorded were from the tagged animals or other nearby Minke whales. 

"We analysed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species," researchers wrote in the journal article announcing their findings. 

Why whales create the sounds is a mystery, and they may be a form of communication with other whales. 

The investigator and her team believe their research will be able to provide a great deal of raw data on the lives, behavior and movement of the marine mammals. 

"These results have important implications for our understanding of this species. We don't know very much about this species, but now, using passive acoustic monitoring, we have an opportunity to change that, especially in remote areas of the Antarctic and Southern Ocean," Risch said. 

Study of B. bonaerensis and the source of the mysterious bio-duck sounds was detailed in the journal Biology Letters.