A new study led by Dr Denise Risch from NOAA’s Northeast Fisheries Science Center provides conclusive evidence that mysterious ocean sounds known as the bio-duck are produced by Antarctic minke whales (Balaenoptera bonaerensis).
Bio-duck, or quacker, is the name given to a quacking-like sound which was first described by submarine personnel in the 1960s.
The 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 latitudes during the winter season also contributed to its mystery.
The source of bio-duck sounds (thought to be UFOs, submarines, oceanographic phenomenon, or even fish) has remained a mystery, until now.
In February 2013, Dr Risch’s team deployed acoustic tags on two Antarctic minke whales in Wilhelmina Bay off the western Antarctic Peninsula.
The tags were placed on the whales using a hand-held carbon fiber pole by the scientists working from an inflatable boat. These tags were the first acoustic tags successfully deployed on this whale species (minke whales are the smallest of the great whales or rorquals, a group that includes the blue whale, Bryde’s whale, and humpback, fin, and sei whales).
The whales were visually tracked from the boat during daylight hours to identify behavior and group composition.
No other marine 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.
They were eventually identified as the bio-duck through comparisons with sounds in the published literature. They also matched recordings on long-term, bottom-mounted recorders from several other locations in the Antarctic, including the Perennial Acoustic Observatory in the Antarctic Ocean and near Dumont D’Urville and Ross Island.
“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,” explained Dr Risch, who is the first author of the paper describing the findings in the journal Biology Letters.
The findings will allow marine scientists to interpret numerous long-term, acoustic recordings, and improve understanding of the distribution, abundance, and behavior of Antarctic minke whales.
“Identifying the bio-duck sound will allow for broader studies of the presence of minke whales in other seasons and areas,” Dr Risch said.
“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.”
Denise Risch et al. 2014. Mysterious bio-duck sound attributed to the Antarctic minke whale (Balaenoptera bonaerensis). Biology Letters, vol. 10, no. 4; doi: 10.1098/rsbl.2014.0175