Bio-duck: Mystery of Low-frequency Unique Sound Heard in Southern Ocean Revealed

In a new finding, scientists have unraveled the mystery of 'bio-duck' a unique rhythmic sound  heard in the Southern Ocean, which they say is produced by the Antarctic minke whale.

For decades, a mysterious low-frequency sound was heard in the Southern Ocean.  Initially described in the 1960s by submarine personnel, the sound was said to be similar to a duck and was named the bio-duck. This sound was recorded for years at several locations in the Southern Ocean but its source remained a big mystery, until recently when scientists concluded that the mysterious sound was made by a whale.

This  evidence was produced after a team of researchers led by Denise Risch of NOAA's Northeast Fisheries Science Center (NEFSC) deployed acoustic tags on two Antarctic minke whales in Wilhelmina Bay off the Western Antarctic Peninsula. The tags were deployed in February 2013. 

Minke whales are the second smallest baleen whales and the smallest of great whales or rorquals-the group that includes blue whales, humpback, fin and sei whales. Rorquals have pointed heads and small pointed fins.  

The researchers observed that the low frequency sound was mainly produced during the austral winter in the Southern Ocean around Antarctica and off Australia's west coast.  The sounds are a series of pulses produced in a highly repetitive pattern.  Apart from this, this sound was in higher and lower altitudes during the winter season. Till date it wasn't known that minke whales also existed on that region.

The presence of minke whales in the Southern Ocean around the Antarctic reveals that minke whales thrive in ice-covered Antarctic waters when other species migrate to lower latitudes.

"These results have important implications for our understanding of this species," said Risch, a member of the Passive Acoustics 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." 

Apart from this, the researchers also deployed tags on the specie that records water temperature and pressure.  The presence of animals was visually monitored from boats during the day in order to study the behavior and composition of the group.

When the calls were recorded, no other marine mammal species was present, clearly indicating that the recorded sounds came from the tagged whale or other untagged minke whale.

Initially these sounds were thought to be coming from a submarine or even a fish.  But after comparing the sounds with other sounds tracked in the published literature, they realized it was different and termed it the bio-duck.

This new finding will help researchers interpret several long-term, acoustic recordings and enhance the understanding of distribution and behavior of the species. 

"That ability to monitor minke whales is critical for a species that inhabits an environment that is difficult to access, has rapidly changing sea-ice conditions, and has been the subject of contentious lethal sampling efforts and international legal actions," the researchers conclude.

To Listen to the Bio-Duck Sounds 'CLICK HERE'.

The finding was documented in Biology Letters.