Scientists have conclusive¹ evidence that the source of a unique rhythmic² sound, recorded for decades in the Southern Ocean and called the "bio-duck," is the Antarctic minke whale（小须鲸） (Balaenoptera bonaerensis). First described and named by submarine personnel in the 1960s who thought it sounded like a duck, the bio-duck sound has been recorded at various locations in the Southern Ocean, but its source has remained a mystery, until now. In February 2013, an international team of researchers deployed⁴ acoustic⁵ tags on two Antarctic minke whales in Wilhelmina Bay off the western Antarctic Peninsula. These tags were the first acoustic tags successfully deployed on this species. The acoustic analysis of the data, which contained the bio-duck sound, was led by Denise Risch of NOAA's Northeast Fisheries Science Center (NEFSC) and was published April 23, 2014 in Biology Letters.

 

The bio-duck sound is heard mainly during the austral winter in the Southern Ocean around Antarctica and off Australia's west coast. Described as a series of pulses in a highly repetitive pattern, the bio-duck's presence in higher and lower latitudes⁶ during the winter season also contributed to its mystery. No one knew the minke whales were there. The identification of the Antarctic minke whale as the source of the sound now indicates that some minke whales stay in ice-covered Antarctic waters year-round, while others undertake seasonal⁷ migrations⁸ to lower latitudes.

 

"These results have important implications for our understanding of this species," said Risch, a member of the Passive Acoustics⁹ Group at the NEFSC's Woods Hole Laboratory. "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."

 

The acoustic tags, which also recorded water temperature and pressure, were placed on the animals using a hand-held carbon fiber¹⁰ pole by researchers working from a rigid-hulled inflatable boat（充气艇）. Animals were visually tracked from the boat during daylight hours to identify behavior and group composition. No other marine³ mammal species were observed in the area when calls were recorded, providing further evidence that the recorded sounds were produced by the tagged whale or other nearby Antarctic minke whales.

 

The mysterious sounds were thought to be made by submarines, by some oceanographic phenomenon, or even by fish. They were eventually identified as the bio-duck through comparisons with sounds in the published literature. They also matched recordings¹¹ on long-term, bottom-mounted recorders from several other locations in the Antarctic, including the Perennial¹² Acoustic Observatory¹³ in the Antarctic Ocean (PALAOA), and near Dumont D'Urville and Ross Island. Germany's PALAOA is an autonomous¹⁴ observatory with underwater hydrophones, or microphones, located on the Ekström Ice Shelf in western Antarctica. Dumont d'Urville on Petrel Island is the main French scientific research station in Eastern Antarctica.

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