Since the 1960s, marine scientists have puzzled over the strange quacking sounds they often heard in the icy waters of Antarctica’s Southern Ocean. Submarine personnel first described the oddly repetitive call, which is one of the most common sounds in that ocean during the austral winter. They gave it the name “bio-duck.” The sound consists of a series of pulses with a 3.1-second interval between two series. The sound further stumped scientists when they discovered some years ago that it occurred each winter and spring simultaneously in the eastern Weddell Sea and off Western Australia. Now, cetacean researchers are declaring the mystery solved: Antarctic minke whales (Balaenoptera bonaerensis) produce the calls. The discovery is already providing new insights into the behaviors of this little-known cetacean species, which is the primary target for Japanese “scientific” whale hunts. The researchers made their discovery by attaching sensors that collect acoustic data to two of the whales in 2013. One tag recorded for 18 hours, the other for only eight. The tagged whales were traveling with their fellows in groups of five to 40 animals, and feeding almost nonstop. Although the tags registered only 32 clear calls, those were enough for the researchers to conclusively link the sound to the minke whales. The whales made 26 of these calls when close to the surface, sometimes just before diving to feed. The scientists compared their recordings to other bio-duck calls that have been collected over the years, some from recorders mounted at the bottom of the sea, making an unequivocal match, they report online today in Biology Letters. The researchers do not yet know the purpose of the whales’ calls, but say that they should help them unravel other mysteries, including the minke whales’ overall abundance and migration patterns.
(Audio credit: Ilse Van Opzeeland and Lars Kindermann/Alfred-Wegener-Institute [AWI], Germany)