With the help of an algorithm that took more than two years to be created, a new study describes for the first time that, like other baleen whale species, this cetacean produces songs.
The research, led by the Chilean researcher Diego Filun, was published in the prestigious journal Scientific Report of the Nature publishing group.
The story dates back to 2014, when a sound was first attributed to the Antarctic minke whale. It was called “bio-duck,” since it was similar to the noise a duck makes. At that time, for the scientific community, this species was considered a mystery; there was no further information about it: it was and —still is— very difficult to study, because it lives associated with ice and few ships can enter these marine ecosystems.
In the summer of 2008, when the sea ice opened up, a team of researchers from the Alfred Wegener Institute (AWI, Germany) installed 21 hydrophones in the Weddell Sea, east of the Antarctic Peninsula. These equipments are oceanographic instruments that allow the capture of underwater sounds and function as true underwater microphones. Since then and to date, they have managed to obtain thousands of data in real time that are stored in a library of marine acoustics.
With the objective of detecting and describing the “bio-duck,” the researcher of the AWI and the Center for Dynamic Research in High Latitude Marine Ecosystems (IDEAL) of the Austral University of Chile (UACh), Diego Filun, analyzed part of the database of that marine acoustics library. “We created a detection and classification algorithm that could automatically compare sounds in a robust and standardized way. The first thing that caught our attention was that in the summer the Antarctic minke whale does not vocalize. In winter, unlike all other species with similar characteristics, it does. This is opposite to what we know about whales,” he explains.
The results of the research led by Filun, which he carried out together with the researcher Ilse van Opzeeland, were recently published in the prestigious journal Scientific Report of the Nature publishing group. Thanks to the algorithm created, today it is possible to automatically compare different sound databases from different sites in the southern hemisphere in order to detect the acoustic presence of this whale. It is even possible to carry out monitoring between different places simultaneously.
The mystery of the songs
The Antarctic minke whale, whose scientific name is Balaenoptera bonaerensis, is the smallest of all. As an adult it can measure up to 11 meters and calves reach 2.7 meters. It lives in the southern hemisphere and its natural predators are killer whales. It feeds mainly on krill, is completely gray and, although it bears a strong physical resemblance to the common minke whale (Balaenoptera acutorostrata,) it differs from it in that the latter has a white patch on its fins.
The research describes, for the first time, that the Antarctic minke whale not only produces isolated sounds, but also songs that are repeated for hours. The scientists found three acoustically distinct population groups in the Weddell Sea. “It’s like they speak three different dialects. In addition, we found that this whale changes its language depending on the year,” says Filun, adding that “the question we are asking ourselves now is what do they use their song for?”
Melodies are usually associated with reproduction. For example, in the case of humpback whales, the males generally sing to find a mate. “It could be the only whale that breeds in Antarctica, however it is not yet possible to attribute that to acoustic behavior without visual confirmation.”
Minke whale, one of the most hunted
The Antarctic minke whale is solitary and has a unique ability: It can break through the ice with its head. It is not coastal and it is unknown where it has its calves. Given its size, when the whaling industry started, it showed no interest in it. However, as other species began to decline in population, whalers began to hunt it. Today it is not only estimated to be the most abundant whale, but also one of the most hunted by countries such as Japan, Iceland and Norway.
“In recent years, much of the information we know about this species of whale was generated from ‘scientific hunting’ by whalers. This type of research helps to study those animals in a non-invasive way. With the implementation of this methodology, we now hope to delve into the potential migration routes of these animals, comparing high and low latitude sites, their distribution, ecology and habitat use,” concludes Filun.